© 2022, Krishtel eMaging Solutions Private Limited.This paper is devoted to the reliability analysis of rotor-bearing systems, based on the combination of Kriging metamodels and the First-Order Reliability Method (FORM). The main motivation arises from the fact that high-fidelity structural models generally lead to high computation costs, which can be strongly alleviated using surrogate models. Since applications to rotating machines have not been sufficiently explored so far, the contribution of the present paper consists in the evaluation of the performance, both in terms of accuracy and computational effort, of a numerical strategy based on the combination of Kriging metamodels and FORM to this type of machines, accounting for their typical frequency domain responses and applicable limit-states. Such an evaluation is made by confronting four different strategies, combining: (i) full finite element models and Monte Carlo simulations; (ii) full finite element models and FORM; (iii) Kriging metamodels and Monte Carlo simulations; (iv) Kriging metamodels and FORM. Results show that the Kriging/FORM strategy provides substantial decrease of computation effort, while keeping satisfactory accuracy of reliability estimations. In addition, a procedure is proposed for improvement of the accuracy of Kriging/FORM reliability estimates, by enriching the Kriging design of experiments in the vicinity of the Most Probable Failure Point.

© 2022 Elsevier Masson SASConsidering that flutter represents a potential catastrophic event in the context of aerospace structures, numerous studies have evaluated a number of strategies to avoid and/or control this kind of aeroelastic phenomenon. Currently, both active and passive control have been investigated to prevent instabilities induced by the interaction between aerodynamic and structural forces. It is also important to highlight the successful cases in which passive control techniques using viscoelastic materials have been useful to mitigate several types of vibration problems. However, there are still opportunities to explore the potential of control using viscoelastic material in the scope of aeroelasticity, especially when involving its combination with other control techniques. Therefore, this work presents a strategy involving a hybrid approach to aeroelastic control of a simplified unswept and untapered wing, using a combination of passive and active techniques. Passive control is achieved by the use of viscoelastic materials inserted as resilient elements in the aeroelastic model, while active control is performed by means of the deflections of a flap-like aerodynamic control surface, governed by a proportional-derivative control law. The results show that the application of the passive control alone causes an increase of up to 25.4% in critical flutter speed. In addition, the association of passive and active controls lead to higher control performance and the critical speed is increased by a further 6.8%, thus providing a broader safe flight speed range. Hence, the investigation indicates that the hybrid control approach exploring viscoelastic materials can be advantageous in practical applications.

© 2021 IAAThe present study addresses the problem of automatic path planning of a manipulator-like spacecraft in orbit. Based on the concept of optimal control and off-line establishment of optimal trajectories, the study proposes a formulation of multiobjective optimization that accounts for multiple aspects of motion. The effect of manipulator mass is analyzed. Then, the effect of multiple objectives on the optimal path, such as the satellite displacement, arm manipulability and maximum torque, are evaluated. In addition, the end-effector positioning, avoidance of collision between the arm and the spacecraft, and minimization of torque requirements are considered as objectives to be minimized, subject to uncertainty inside the berthing box. The numerical procedure includes a machine learning strategy that is able to learn from both training data and mission tasks. It is used during inverse kinematics analysis, when the Cartesian position is the input parameter and the joint angle estimate is the output. This information improves the convergence rate of the optimization procedure, which leads to the precise value of the angle of the joint. The learning strategy is effective for estimating the solution when five or more samples are available, and the result is improved as new data is added to the analysis. The diversity of scenarios, metrics and parameters considered in the numerical experiments confirms the viability and robustness of the proposed methodology.

© 2021, Brazilian Society for Automatics--SBA.A comparative analysis of machine learning techniques for fault diagnosis of rotating machines based on images of vibration spectra is presented. The feature extraction of different types of faults, including unbalance, misalignment, shaft crack, rotor–stator rubbing, and hydrodynamic instability, is performed by processing spectral images of vibration orbits acquired during the machine run-up. The classifiers are trained with simulated data and tested with both simulated and experimental data. The latter are obtained from laboratory measurements performed on an rotor-disc system supported on hydrodynamic bearings. To generate the simulated data, a numerical model is developed using the finite element method. Deep learning, ensemble and traditional classification methods are evaluated. The ability of the methods to generalize the image classification is evaluated based on their performance in classifying experimental test patterns that were not used during training. The results of this research indicate that, despite considerable computational cost, the method based on convolutional neural networks presents the best performance.

© (2022) by International Council of Aeronautical Sciences (ICAS) All rights reserved.The objective of the present work is to discuss the effects of model enhancements on the capability of performing static aeroelastic analyses of aeronautical configurations. The model improvements addressed in this effort concern the use of finer aerodynamic grids, different turbulence models and the size of the modal base for the representation of the structural deflection solution. The study considers the NASA Common Research Model (CRM), from the 6th AIAA CFD Drag Prediction Workshop, and the High Reynolds Number Aerostructural Dynamics (HIRENASD) configuration, from the 1st AIAA Aeroelastic Prediction Workshop. A clear improvement in the aerodynamic prediction of drag, pitching moment and pressure coefficient distributions is observed for the NASA CRM case. For the HIRENASD test case, aerodynamic grid refinement has yielded results that demonstrate the robustness of the developed fluid-structure interaction process.

© 2020 Elsevier LtdThe emergence of automated manufacturing techniques has allowed the realization of the so-called tow-steered composite laminates, in which the fibers are deposited following continuous curvilinear paths. This enables to broaden the design space to satisfy a variety of design objectives. Previous studies have shown that conventional composites can be designed to maximize the modal frequencies and modal damping factors. However, similar investigations have not been devoted to tow-steered composites so far. In this context, the objective of this paper is to investigate the use of multi-objective optimization aiming at simultaneously maximizing the fundamental modal frequency and corresponding specific damping capacity of tow-steered composite laminates. The fiber trajectories are parameterized using two different schemes, and the parameters are taken as design variables. The equations of motion are derived from the combination of the Classical Lamination Theory with the Rayleigh–Ritz method. Damping is modeled by using the Strain Energy Method. Numerical optimization is performed using the evolutionary Direct Multisearch method, which provides optimal solutions forming Pareto fronts. Results obtained from various scenarios, including fully and partially steered laminates, and different boundary conditions, show that fiber steering can indeed improve substantially the dynamic characteristics, including damping, of composite laminates.

© 2020 Elsevier LtdMany studies previously reported in the literature have demonstrated, both theoretically and experimentally, the influence of thermally-induced stresses on the static and dynamic behavior of structures, due to the so-called stress-stiffening effect. In most cases of practical interest, temperature variations associated to environmental and operational conditions are governed by rather complex combinations of conduction, convection and radiation mechanisms. As a result, the temperature values at different points of a structure are very difficult to control and can rationally be considered as random quantities. In this context, the present paper addresses the stochastic modeling and characterization of the influence of thermal stresses on the natural frequencies of thin rectangular plates, assuming space-dependent temperature fluctuations modeled as stationary two-dimensional Gaussian random fields. For this purpose, based on the hypotheses of the classical Kirchhoff plate theory, a Rayleigh-Ritz-based dynamic model is first derived for the bending vibrations of plates, accounting for the presence of thermal stresses. This model is combined with the Karhunen-Loève expansion (KL), which is used to discretize the temperature random field, after which the statistics of the random natural frequencies are estimated by Monte Carlo sampling. Numerical simulations are performed for plates under free boundary conditions. Simulation results, which encompass sampling-based statistics for the thermal stresses and the first six natural frequencies of the plate, are presented and discussed. In addition, since thermal stresses can induce buckling, reliability has also been estimated considering this type of failure. Results enable to conclude that space-dependent temperature uncertainty can be significant upon the vibration and buckling behavior of plates, which justifies its consideration.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, aerostructural deflections of the aircraft structures, mainly in the wings. In this work, the in-house Computational Fluid Dynamics (CFD) code, BRU3D, and previously developed fluid-structure interaction (FSI) tools are tested for different loading conditions using the High Reynolds Number Aero-Structural Dynamics (HIRENASD) model. The work also investigates the effects of grid refinement on the improvement of the correlation obtained with the results of the present simulations and the experimental and computational data available from the AIAA Aeroelastic Prediction Workshop (AePW). Comparisons are made in terms of aerodynamic coefficients and wing structural deflections.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.The present work has the objective of presenting recent developments of a static aeroelastic computational process for the analysis of typical aircraft configurations in transonic flows. The analysis procedure is assessed through the study of static aeroelastic characteristics of the HIRENASD model, which is a test cases with extensive experimental database for validation of computational results. The in-house BRU3D computational fluid dynamics (CFD) solver, which uses the fully turbulent compressible Reynolds-averaged Navier-Stokes (RANS) equations, is combined with a finite element method (FEM) modal basis code through the uses of radial basis functions (RBF) for smooth volume grid movements. Results in terms of structural displacements have shown good agreement with experimental data, although indicating that further grid refinement for the fluid domain is still necessary in order to improve the correlation of the aerodynamic coefficients.

© "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. All rights reserved.Over the last decades, the development of novel permanent magnets, especially those having rare earth metals in their composition, has led to a great improvement in their performance, as compared to conventional ferrite permanent magnets. Therefore, there has been an increasing demand for these magnets in many (including new) application fields. In particular, the strong magnetic forces exerted between magnets can be explored as a means of promoting contactless mechanical coupling between separate parts and structural components. In this context, this paper investigates the dynamic behavior of a multiphysics system composed of two parallel cantilever beams at the extremity of which cubic permanent magnets are attached. Given the nonlinear nature of the magnetic forces, the main interest is to characterize the dynamic phenomena induced by the magnetic coupling. The study also encompasses analyses of the influence of the gaps between the two magnets and the relative orientation of their polarization axes. For this purpose, an elasto-magnetic structural model is developed, accounting for the flexibility and mass distributions of the beams and also the magnetic interactions. Upon resolution of the equations of motion, this model is used to perform a number of numerical simulations, the results of which are presented and discussed.

© Springer Nature Switzerland AG 2021.Previous studies have demonstrated the influence of thermal stresses on the static and dynamic behavior of structures. In most cases of practical interest, temperature variations are governed by complex combinations of heat transfer mechanisms. As a result, the temperature values at different points of a structure can be considered as random variables. The present paper addresses the stochastic modeling of the influence of space-dependent temperature variations on the natural frequencies of beams. For this purpose, based on the hypotheses of the classical Euler-Bernoulli beam theory, a finite element model is constructed for the bending vibrations of beams, accounting for thermal influences. A particular scenario is considered in which the beam is subjected to random linearly-varying temperature fields, parameterized by two random variables. A probabilistic model is derived, which provides the PDF of the thermally-induced axial force from the PDFs of the random variables. Numerical simulations are performed for a clamped aluminum beam. Sampling-based statistics for the thermal axial load and the first six natural frequencies of the beam are presented. In addition, since thermal stresses can induce buckling, the probability of failure by this mechanism is also computed. Results enable to conclude that temperature uncertainty can be significant upon the vibration and buckling behavior of beams, which justifies its consideration in structural analyses.

© 2020 Elsevier LtdThis present paper is devoted to the numerical and experimental investigation of the modal characteristics of composite laminates, with emphasis on damping. Complementing previous studies dedicated to conventional laminates, one considers variable-angle tow laminates, in which the fibers are deposited following curvilinear trajectories. The main objective is to characterize the influence of fiber steering on the damping levels, and evaluate the possibility of achieving increased damping. A dynamic model is derived by combining the semi-analytical Rayleigh-Ritz approach, the Classical Lamination Theory, and the Strain Energy Method. This later enables to estimate the specific damping capacity of each vibration mode. Based on this model, analytical developments are performed aiming at putting in evidence the contribution of each strain component in each layer of the laminate to the specific damping capacities. The results of numerical simulations are presented, enabling to compare the values of specific damping capacities and vibration natural frequencies obtained for variable-angle tow and conventional laminates in a variety of simulation scenarios. Some of the numerical results are validated by comparisons with experimental counterparts. The results confirm the effectiveness of design strategies intended to regulate and possibly increase the damping levels of composite laminates by exploring fiber steering.

© 2020, The Brazilian Society of Mechanical Sciences and Engineering.This article presents a novel morphing unit cell concept which relies on the combination of shape memory alloy wires for actuation and permanent magnets to enable multistability. Two distinct applications are investigated experimentally, consisting in a morphing beam metastructure made with three unit cells and a variable camber airfoil metastructure having six unit cells in the chord-wise direction. Tests are performed to assess the influence of the permanent magnets on the morphing behavior of the two referred metastructures. It is verified that the permanent magnets are able to provide new stable equilibrium configurations to the metastructure and to reduce the time necessary for morphing. Another interesting feature, which enables the reduction in energy consumption, is that, due to the magnetic interactions, the thermal activation of the SMA wires can be ceased once an equilibrium configuration is achieved. The paper describes the design premises, evaluates its limitations and devises future improvements.

© 2020 Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. All rights reserved.Electrodynamic loudspeakers can be used to absorb sound energy in a narrow frequency band around the loudspeaker resonance. To increase the operational bandwidth, active and passive impedance control techniques have been described in the literature. In this work, we propose a passive technique that makes use of a periodic array of small loudspeakers mounted as side branches along a straight duct. A larger loudspeaker is mounted at one end of the duct, which acts as a conventional narrow-band absorber. This system aims at absorbing the sound energy flowing inside the duct, leading to a small reflection coefficient at the entry of the periodic waveguide. We investigate the sound absorption of such a device through numerical simulations based on the transfer matrix method. The unit cell is made up of a one-dimensional acoustic waveguide with a side-branch loudspeaker. It is shown that the proposed approach might increase the absorption bandwidth, even with 1-inch loudspeakers and a number of cells as small as five in the periodic structure.

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, aerostructural deflections of the aircraft. Computational Fluid Dynamics (CFD) tools have been widely integrated with Computational Solid Mechanics (CSM) solvers, based on finite element discretization, in order to improve predictions of the aerodynamic performance and aircraft structural loads. The main objective of the paper is to describe the methodology and the numerical effort to integrate an in-house CFD code with a CSM solver for static aeroelastic applications in a high fidelity approach. The cases used for process validation are the static aeroelastic results from the High Reynolds Aerostructural Dynamics project (HIRENASD) and NASA’s Common Research Model (CRM) from the 6th AIAA CFD Drag Prediction Workshop. All fluid-structure interaction (FSI) procedures have been implemented in FORTRAN and integrated via shell script. Results demonstrating converged wing surface pressures and deflections are compared to available experimental data. For the HIRENASD model, FSI aerodynamic results indicated considerable degradation in both pitching and rolling moment curves when compared with ideal rigid CFD simulations. Moreover, NASA CRM FSI simulations are performed for two different sets of modal shapes, showing wing tip deformation sensitivity.

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Panel flutter is a real design issue for supersonic flying aerospace vehicles caused by flexible panels subject to unsteady supersonic aerodynamics loading that can lead to critical fatigue damages and catastrophic failures. Many efforts earlier were devoted to this problem, considering the numerical evaluation of a single panel solution typically. Rather than this approach, it is proposed in this paper the nonlinear aeroelastic analysis of adjacent panels, the so-called multibay panels, within the context of variable stiffness composites laminates (VSCL). The aeroelastic model is based on coupling the first-order piston theory with the VSCL structural model developed in accordance with the Classical Lamination Theory (CLT) using the von Kármán’s assumptions to account for geometrical structural nonlinearities. Moreover, the Newmark numerical time-integration is used, aiming to improve computational efficiency. The results of numerical solutions considering four different scenarios are presented, enabling the aeroelastic performance comparison with a conventional laminate, taking into account different fiber trajectories with and without ply contiguity between panels.

© 2020 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The numerical investigation of the stochastic aeroelastic characteristics of conventional and tow-steered composite laminates subjected to random uncertainties affecting the laminate fiber volume is addressed in the present paper. A computationally efficient stochastic model is constructed combining the semi-analytical Rayleigh-Ritz approach with the Karhunen-Loève discretization of the two-dimensional random field representing the fiber volume. In addition, polynomial chaos expansions are used as stochastic metamodels of the output random variables characterizing the onset of aeroelastic instability and the mass of the laminate. Such a metamodeling approach enables to alleviate the computational cost involved in the estimation of the statistics of the output variables of interest based on Monte Carlo simulations. In addition, the study encompasses both subsonic and supersonic flow conditions, for which two appropriate aerodynamic models are used. The numerical results provide effective uncertainty quantification in a variety of simulation scenarios, which are found to be useful for the incorporation of uncertainty quantification in the design of aircraft and spacecraft structures when uncertainties induced by the manufacturing process must be dealt with.

© 2019 Elsevier Masson SASAmong the aeroelastic phenomena most commonly affecting flexible and very flexible aircraft, those caused by gusts deserve special attention due to their potential either in degrading flying qualities and ride comfort or in increasing structural loads. It is then of interest to structural loads and flight controls engineers that solutions be developed to attenuate the effects of gusts on aircraft. Particularly, the use of piezoelectric transducers arises as one of the potential solutions in the design of gust load alleviation and structural mode suppression systems. In this paper, the gust load alleviation on a flexible smart idealized wing using only piezoelectric transducers is analyzed and experimentally tested. The numerical model includes a finite-element model of the wing, employing two-node, seven-degree-of-freedom smart beam elements, assuming small deformations and neglecting transverse shear. A quasi-steady, strip-theory-based aerodynamic model is used. Two control laws are evaluated: one based on output feedback, and the other based on feedback of observed states of a truncated system. Using a gust generator, wind-tunnel tests were performed at different flow speeds and gust frequencies to validate the computational model and to verify the performance of piezoelectric transducers. The results show a considerable attenuation of the wing root bending moment, especially using two piezoelectric actuators. Important performance improvements were overall verified with feedback of observed states when compared with static output feedback, specially to decrease the participation of the elastic modes in the gust response.

© 2018 Elsevier LtdIn this work, viscoelastic materials are adopted for handling aeroelastic features of typical section models with three degrees-of-freedom, which present non-smooth, free-play type nonlinearities in their control surface. A rotational viscoelastic damper is added to the resilient element associated to the control surface motion of the typical section. Equations of motion are derived accounting for the viscoelastic damper dependence on frequency and temperature. For this, a fractional derivatives-based viscoelasticity constitutive law is considered. Aerodynamic forces are introduced based on linear potential unsteady aerodynamics accounting for arbitrary airfoil motions. The aeroelastic behavior is investigated through time domain simulations, from which bifurcation diagrams are constructed. Numerical results show that the addition of viscoelastic damping can increase the flutter speed noticeably and reduce the amplitudes of limit cycle oscillations for the system under consideration. Another observed benefit provided by the viscoelastic damper is that undesirable subcritical behavior for the bifurcation onset can be eliminated or modified to have a supercritical character. The influence of temperature on the aeroviscoelastic behavior is also investigated. Using the proposed strategy, nonlinear instabilities can be controlled, improving the safety margins of aeroelastic systems.

© 2019 ASMEIt has been amply demonstrated that the development of SMA actuators has a great potential of application in several branches of industry. Obviously, the efficiency of the actuators depends both on the inherent features of the materials they are made of and the geometric characteristics of the devices. This work considers a particular type of actuator first conceived by [1], consisting in the association of two cantilever beams, the first presenting the shape memory effect and the second presenting the superelastic effect, coupled mechanically so as to guarantee two equilibrium positions and thus a stand-alone cyclic actuator, in which the superelastic beam provides the bias action. Numerical simulations of the behavior of the actuator are performed using the commercial finite element software COMSOL, which implements the Boyd-Lagoudas thermomechanical model. The goal of the simulations is to characterize the actuation range of the actuator, in terms of maximum displacement obtained at the tip. The effect of the dimensions of the beams on the tip displacement under some load scenarios is investigated. The results provide guidelines for the design of the actuator to fulfill specific requirements, also suggesting the use of numerical optimization for the optimal design of the actuator accounting for constraints.

© 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The uncertainty propagation of a stochastic random spatial field in the fiber volume applied to steered carbon reinforced composite plates designed for aeroelastic purposes is assessed. Based on the Karhunen-Loève expansion (KLE), considering fixed covariance functions, the lamina material properties are estimated using the mixture rule affected by the fiber volume spacing variation. The structural model is based on the Classical Lamination Theory considering symmetric stacking sequence and fiber trajectories described by Lagrange polynomials. Two distinct aeroelastic models are evaluated: i) modeled according to the quasi-steady aerodynamic model with the inclusion of the term of unsteadiness in pitch velocity; (ii) based on the piston theory for high Mach number approximation. The uncertainty propagation is done using the generalized polynomial Chaos (gpC) expansion to evaluate the flutter onset, flutter frequency and plate mass variabilities with computational efficiency.

Copyright © 2019 ASMEIn order to enhance competitiveness of rigid risers for the Brazilian pre-salt, great effort has been devoted to study the feasibility of Steel Catenary Risers (SCR) directly connected to Floating Production Storage and Offloading (FPSO) units, where cost savings are expected from the reduction of pipe buoyance modules and overall piping length. A recent paper presented the technical feasibility of Damped SCR, which is a new SCR concept. In that study, some non-field-proven fatigue performance improvements were required, such as girth welds for mechanically lined pipe (MLP) with increased fatigue strength and/or upset end pipes. During the development of this technology, a fracture mechanics approach became essential for the assessment of fatigue and fracture limit state in order to guarantee that the risks associated with fabrication and inspection are within acceptable safety levels. This paper presents the main issues related to fabrication and inspection activities with a particular focus on the smallest critical flaw size. A semi-deterministic Engineering Critical Assessment (ECA) was performed as part of the conceptual design. The uncertainties about input data are discussed and a simplified procedure is proposed. Results are compared with relevant nondestructive testing reliability statistics. This study indicates that the benefits obtained from the use of materials with superior fatigue resistance are limited to the non-destructive testing reliability at some degree. As the proposed methodology deals with uncertainty in input data, a roadmap for the development of a full probabilistic risk assessment of fabrication and inspection feasibility at early design stages is devised.

© 2019, Springer Nature Switzerland AG.This chapter is devoted to the use of viscoelastic materials as a strategy intended for passive vibration control in mechanical systems. It provides a review of the theoretical foundations underlying the constitutive modeling of the viscoelastic behavior, and the association of constitutive models with modern numerical resolution procedures, especially the finite element method. This currently enables the accurate prediction of the dynamic behavior of rather complex structural systems featuring viscoelastic dampers, duly accounting for the particular characteristics of the viscoelastic behavior, namely the memory effect and the dependence of stiffness and damping properties on frequency and temperature. Other relevant aspects considered are: (i) model condensation techniques, intended to reduce the computation cost involved in the evaluation of the response of viscoelastic structures using finite element models with large numbers of degrees-of-freedom; (ii) the identification of viscoelastic constitutive models from experimental data. In addition, some applications of viscoelastic materials to structures of engineering interest are presented to illustrate the use of some techniques discussed.

© 2018 by the American Institute of Aeronautics and Astronautics, Inc.The supersonic aeroelastic stability of tow-steered carbon reinforced composite panels, in each layer of which the fibers follow curvilinear paths, is assessed.Astructural model based on the Rayleigh-Ritz method, combined with the aerodynamic piston theory, is derived to represent the aeroelastic behavior of rectangular plates under different boundary conditions. In this model, the classical lamination theory, considering a symmetric stacking sequence and fiber trajectories described by Lagrange polynomials of different orders, is used. In addition, manufacturing constraints, which impose limitations to the feasible fiber trajectories, and the effect of in-plane loads are considered in the model. Using a multicriteria differential evolution algorithm, numerical optimization is performed for a variety of scenarios and aimed at increasing the flutter and linear buckling stability margins of tow-steered plates, considering the geometrical parameters defining the fiber trajectories on the layers as design variables. The results obtained for the different optimization scenarios are compared, having a composite plate with unidirectional fibers as the baseline and aimed at evaluating the benefits achieved by the optimum tow-steered plates. The results enable quantification of the stability improvements by exploring fiber steering, which has been shown to be beneficial, even in situations in which manufacturing constraints are accounted for.

© 2019, Springer Nature Switzerland AG.The present paper is devoted to the modeling of systems comprising a flexible rotor mounted onto an elastic base, undergoing arbitrary rotations. By using a Lagrangian approach, the equations of motion are derived for the coupled rotor-base system, considering finite element discretization for both the base and the rotor. Numerical simulations are performed for a specific configuration of the rotor-bearing system and attitude motion. Results are interpreted to evaluate, both qualitatively and quantitatively, the influence of the base motion and flexibility on the dynamic behavior of the rotor, in terms of unbalance responses. Based on the results, conclusions are drawn, especially in terms of the conditions under which the flexibility of the base is indispensable for accurate prediction of the rotor behavior.

© 2018 Elsevier LtdCylindrical bodies subjected to external flow can vibrate due to the fluctuations of the forces induced by vortex shedding. The way these coherent fluid flow structures are formed and how they excite the structure depends on parameters, such as the Reynolds number, the reduced velocity, and the geometry e.g., the proximity of the structure to other bodies. These vibrations change the drag and lift forces by means of a nonlinear interaction. In addition, vibrations can cause crack nucleation and propagation in the structure. This is especially important when oil or natural gas is being transported in pipe-like structures, subjected to waves and sea currents. The present paper aims to characterize the influence of the proximity of the seabed on the fluid–structure interaction, considering horizontal pipes anchored by dunes. The simulations were undertaken for a nominally horizontal, elastic pipeline, 42 m in length and 0.273 m in diameter, with a mid–span static sag of 1.06 m due to self-weight. Seven different distances between the pipeline and the seabed were tested. The structural and fluid-dynamic models were coupled numerically, which allows the simulation and analysis of the flow using a single computational tool. The equations modeling the flow were solved in an Eulerian domain, while the surface of the immersed body was represented by a set of Lagrangian points. The immersed boundary method was used to impose a Dirichlet boundary condition on the Eulerian domain at the boundary between the structure and the fluid. It was also used to determine the fluid dynamic forces acting on the structure. An in-house three-dimensional computational framework was developed to simulate the turbulent incompressible flow subjected to fluid–structure interaction in conjunction with a beam modeled according to Timoshenko's theory. The obtained results are consistent, as expected for this problem.

© 2018 Elsevier LtdAmong various strategies developed for the attenuation of noise and vibration in mechanical structures, piezoelectric shunt damping, which consists in connecting piezoelectric transducers integrated in a structure to electric or electronic circuits, is a promising alternative for use in small- and mid-scale structural components. Despite the fact that the shunt damping technology has been investigated for quite a long time, it is recognized that its application to real-world structures still requires developments aiming at improving its effectiveness and range of application under unavoidable practical constraints. As a result, research on improved solutions related to piezoelectric shunt damping is still very active. Due to the very nature of the piezoelectric shunt damping, it becomes clear that further improvements must consider both mechanical and electrical/electronic aspects. Based on the current state-of-the-art, this paper provides a systematic literature review of different piezoelectric shunt damping strategies developed for the attenuation of vibration and noise in mechanical systems, including an assessment of the basic principles underlying the electromechanical behavior, as well as design procedures and numerical modeling of piezoelectric shunt damping devices applied to elastic vibrating systems. Emphasis is placed on the various types of shunt circuits, including the traditional passive resonant circuits, multimode resonant circuits, adaptive tuning circuits, switching circuits, and negative capacitance. The strategies for location and shape of the piezoelectric transducers is also discussed. A variety of applications recently reported in the scientific literature and in patents are presented. An assessment is made about more significant recent achievements and technological issues to be faced in further developments.

© 2018 IEEE.Shape memory alloy (SMA) wires have extensive use in many areas of the industry nowadays and its development continues reaching new applications as studies progress. This paper proposes a SMA measurement device that uses affordable components, such as the Arduino micro-controller and a LabVIEW programming language interface. With an antagonistic mechanism design, data on temperature, strain and stress is acquired to confirm the measuring capabilities of the full equipped instrument, rendering visualizations of phase transformations and opening way for further development in control and detailed acquisition of shape memory alloy wire properties.

© 2018 Elsevier LtdNonlinear aeroelastic systems are prone to the appearance of limit cycle oscillations, bifurcations, and chaos. Such problems are of increasing concern in aircraft design since there is the need to control nonlinear instabilities and improve safety margins, at the same time as aircraft are subjected to increasingly critical operational conditions. On the other hand, in spite of the fact that viscoelastic materials have already been successfully used for the attenuation of undesired vibrations in several types of mechanical systems, a small number of research works have addressed the feasibility of exploring the viscoelastic effect to improve the behavior of nonlinear aeroelastic systems. In this context, the objective of this work is to assess the influence of viscoelastic materials on the aeroelastic features of a three-degrees-of-freedom typical section with hardening structural nonlinearities. The equations of motion are derived accounting for the presence of viscoelastic materials introduced in the resilient elements associated to each degree-of-freedom. A constitutive law based on fractional derivatives is adopted, which allows the modeling of temperature-dependent viscoelastic behavior in time and frequency domains. The unsteady aerodynamic loading is calculated based on the classical linear potential theory for arbitrary airfoil motion. The aeroelastic behavior is investigated through time domain simulations, and subsequent frequency transformations, from which bifurcations are identified from diagrams of limit cycle oscillations amplitudes versus airspeed. The influence of the viscoelastic effect on the aeroelastic behavior, for different values of temperature, is also investigated. The numerical simulations show that viscoelastic damping can increase the flutter speed and reduce the amplitudes of limit cycle oscillations. These results prove the potential that viscoelastic materials have to increase aircraft components safety margins regarding aeroelastic stability.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The active control of aeroelastic flutter panel and optimization of the best placement location of the piezoelectric patch is evaluated in composite tow steered laminates. The aerodynamic model is based on potential supersonic flow piston theory. The structural model based on Ritz method is used to represent the tow steered composite laminate and the PZT transducers. Classical lamination plate theory and symmetric stacking sequence are used and the fiber trajectories are defined by Lagrange interpolation functions. The control system is designed using the proportional-derivative feedback approach, resulting in active damping and stiffness effects. The flutter stability boundaries for optimal tow steered composite laminates layups and optimal active steered laminate (using piezoelectric patch) are numerically compared to quantify the benefits of active control system. The instability analysis varying the proportional feedback gains is also investigated. The position and size of the patch and tow steered paths are optimized using a differential evolution algorithm to increase the aeroelastic instability margin.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The continuous search for aircraft flight performance to obtain lower fuel consumption leads to the optimization of wings shape and structure focused in the longer flight phase of its mission, the cruise phase. However, this leads to a loss of efficiency for other flight phases such as take-off and landing, resulting in the need for high-lift surfaces, that are basically triggered by electro-mechanical or hydro-mechanical actuators, adding a considerable amount of weight, complexity and cost to the design project. New concepts of aircraft have wing solutions that are optimized for every flight phase and, consequently, are capable of adjusting their structures in order to achieve the best performance on each flight situation. One of the main ideas on how to get this result is the implement of morphing wings by using smart actuators. Shape memory alloys are classified as smart materials and they can be used in order to develop light, simple and cheap solutions to obtain controlled modifications on aircraft aerodynamic surfaces. This paper focuses on evaluating the airfoil thickness effects on morphing wings composed by memory alloy actuators capable of camber adjustment. In order to achieve this goal, the morphing NACA 0020 designed for the present project is compared to a morphing NACA 0012 wing prototype. The fact that previously mentioned prototypes have different airfoil thickness promotes the ideal environment to investigate this effect on the performance of morphing wings capable of camber adjustment. In addition, each previously mentioned morphing wing prototype was compared to its traditional flap configuration to investigate the aerodynamic pros and cons related to this morphing mechanism. The comparison shows that despite the morphing wing as studied resulting in a lower performance, it’s design simplicity and weight reduction brings advantages to the whole aircraft in certain conditions.

© 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018. All rights reserved.This paper presents a numerical investigation of the effects of parametric uncertainties propagated through Polynomial Chaos Expansion on the design of a Receptance-based active controller for aeroelastic systems. The test-case is representative of an experimental rig featuring a subsonic flexible wing with multiple control surfaces. The uncertainty is introduced in the Young's modulus of the main spar. Such uncertainty is firstly propagated to assess the open loop behavior of the aeroelastic system in terms of flutter velocity and frequency responses. A Receptance-based controller is then designed deterministically with the goal of increasing the flutter boundary and its performance is tested against the uncertain aeroelastic system. Finally, the PDFs of the receptance control gains are evaluated and discussed.

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved.In composite materials, previous studies show that carbon-fiber reinforced polymers (CFRP) can be designed in terms of damping characteristics by acting on its physical and geometric features. In recent years, the development of automatic fiber placement (AFP) allows the realization of variable stiffness composite laminates (VSCL), among which tow steered composites are considered very promising. Therefore, the objective of this paper is to present a numerical assessment of the influence of fiber steering on the modal damping of CFRP plates for different fiber trajectories. The dynamic model is derived by using a semi-analytical approach based on the combination of the Classical Lamination Theory with the Rayleigh-Ritz (Assumed-Modes) approach. The modal damping factors are calculated using the Strain Energy Method, which is based on the ratio between the stored and the dissipated energies, giving the specific damping capacity (SDC) for each vibration mode.

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved.It has been shown in the literature that temperature variations can induce modifications of the static and dynamic characteristics of beam-like and plate-like structures, due to the so-called stress-stiffening effect. In most cases of practical interest, temperature variations associated to environmental and operational conditions are very difficult to control and can be rationally considered as random quantities. In this context, the present paper addresses the propagation of uncertainties affecting the temperature on the natural frequencies of thin rectangular plates. A Rayleigh-Ritz-based dynamic model is first derived for the bending vibrations of plates, accounting for the presence of thermal stresses. This model is combined with a Karhunen-Loève expansion (KL), used to discretize the temperature distribution, which is modeled as a Gaussian random field. The results enable to quantify the influence of temperature randomness on the thermal stresses, and evaluate the sensitivities of the natural frequencies with respect to such randomness.

© Springer International Publishing AG, part of Springer Nature 2019.In the last years, many techniques and procedures have been employed to optimize traditional composite laminates, which can be classified as constantstiffness composite laminates (CSCL), since the local stiffness is independent on the position over the laminate. On the other hand, recent advances in manufacturing processes now enable to explore non conventional designs. In particular, the development of automatic fiber placement allows the realization of variable stiffness composite laminates (VSCL), in which the local stiffness varies over the laminated as intended by the designer. In practice, VSCL can be achieved by making the fibers follow curvilinear trajectories over the plies (tow steering), or varying the matrix/fiber fraction over the laminate. Some authors have explored the benefits of VSCL to improve the performance of composite laminates in terms of stress distributions, static deformations, buckling, dynamic behavior and aeroelastic stability. In this context, this work proposes a strategy to optimize tow steered rectangular plates by controlling the angles that define the fiber trajectories. These latter are described by Lagrange polynomials of different orders, and two different sets of boundary conditions are considered. A structural model based on the Ritz method, combined with the classical lamination theory to model the composite laminate are used. The plate is considered thin, being modeled based on Kirchhoffs hypotheses. The equations of motion are obtained from Lagrange equations. The proposed model is validated by comparing natural frequencies and mode shapes with the counterparts obtained by using Nastran finite element software. The model is also validated by using experimental results obtained from a tow steered plate manufactured by the automatic fiber placement. A convergence analysis is carried-out to determine the number of functions in the Ritz basis necessary to ensure convergence of the semi-analytical model. A differential evolution (DE) algorithm is used to maximize the first natural.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Optimization of wing shapes has been a constant struggle throughout the years of aircraft and aerodynamic development. Innovations have flourished in all scientific fields that influence wing design, such as materials, structural, manufacturing and aeronautical engineering, in order to improve performance and consequently reduce fuel consumption of aircraft, which translates in a light wing with an airfoil shape that assures the best lift coefficients required for a specific mission. On the other hand, this penalizes other maneuver possibilities for the same aircraft, hindering its capabilities and demanding development of different solutions, impacting on costs and draining resources. An “one fits all” concept solves this hurdle, since one design could accomplish a variety of missions, with adequate values for lift coefficient for each different flight phase. This concept can be achieved by wings capable of morphing, adjusting their structures on demand. One widely investigated field of research is morphing wings that uses smart materials, such as shape memory alloys, for actuation. Shape memory alloys are lightweight, simple and cheap materials that, combined with a morphing compliant rib, can achieve controlled displacements on aerodynamic surfaces. This paper analyses different rib concepts modifying chordwise positions for actuation by making use of shape memory alloy wires built-in a NACA 0012 reference wing. A comparison is made between different percentages of chordwise morphing capability and a simple NACA 0012 wing with a 25 percent chord plain flap, as usually seen on many simple aircraft designs. The results show an increase on lift coefficient values and a delay of stall angle for some chordwise actuation locations. The comparison parameter was a 15 degree of trailing-edge tip displacement related to the airfoil leading-edge. By reducing external surface gaps and steps, a simple and lightweight smart morphing wing can overcome a common flap design and still achieve a variety of different missions by adjusting itself in flight.

© 2017 IAAThe primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions different from zero for both attitude and elastic vibrations. Additionally, the control efforts for the three cases are compared. Results indicate that the attitude control is able to excite the solar panels' vibration modes and vice-versa. The piezoelectric vibration control shows significant performance improvement when compared to contributions of the attitude control to the vibration damping.

© 2016 Elsevier LtdViscoelastic materials have been widely used for the purpose of passive vibration mitigation in various types of mechanical systems, including, industrial machinery, civil structures and vehicles. In this paper, the use of those materials in aeroelastic systems is investigated, with emphasis placed on the influence of the viscoelastic behavior on the flutter speeds of two-degree-of-freedom typical section models, in which viscoelastic elements are introduced in addition to elastic elements associated to heave and pitch motions. The equations of motion of the aeroelastic system are modified to account for the dependence of the viscoelastic behavior on frequency and temperature, by using the concepts of complex modulus and shift factor. The aerodynamic forces and moments in subsonic regime are modeled according to Theodorsen's method. Numerical simulations are conducted to evaluate the influence of the addition of viscoelastic elements on the flutter speed and elucidate the separated influences of stiffness and damping additions. An experimental wind tunnel setup consisting of a rigid wing supported by flexible elements in pitch and plunge motions has been modified to enable the introduction of viscoelastic elements in parallel to those flexible elements. For various configurations of viscoelastic additions, the flutter instability is characterized from vibration measurements performed for increasing flow speeds in the vicinity of the stability boundary. The experimental results are used to validate the numerical model derived for the aeroviscoelastic system and confirm both qualitatively and quantitatively the predictions of the simulations, especially the possibility of increasing the flutter speed by the inclusion of viscoelastic materials.

Copyright © (2017) by International Astronautical Federation. All rights reserved.The main purpose of this paper is to implement a technique of passive elastic vibration control for a low Earth orbit satellite comprising two symmetric flexible solar arrays. While the solar arrays flexible vibration is passively controlled by using piezoelectric materials, the spacecraft attitude control is implemented by using the proportional integral derivative control technique. The idea is to compare the control effort when implementing the passive control with the control effort when using the piezoelectric for the same spacecraft. The solar panels are assumed to be in a sun synchronous rotation mode so its solar cells can continuously be illuminated by the Sun. The panels contain surface-bonded piezoelectric patches to implement the passive control of the solar panel elastic vibration. The gravitygradient torque as well as the torque due to the interaction of the Earth magnetic field with the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control. Computer simulations are performed using the MATLAB® software package. For analysis, one considers a station-keeping correction maneuver performed by a thruster actuator. Resulting elastic vibrations are investigated while considering the cases in which i) only the attitude control subsystem is considered; and ii) passive vibration control is adopted through piezoelectric shunt damping. As expected, the use of the considered passive control strategy is able to mitigate elastic vibrations effectively, and also help in reducing control efforts performed by the attitude reaction wheel controllers.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The utter behavior of tow steered composite panels, in which the fiber placement follow curvilinear trajectory, is evaluated. A simple structural model based on Ritz method combined with supersonic aerodynamic piston theory is used to analyze the aeroelastic behavior. Classical lamination plate theory and symmetric stacking sequence are used and the fiber trajectories are defined by Lagrange interpolation functions. The utter stability boundaries for optimal conventional (constant stiffness laminates) layups and non- conventional (variable stiffness laminates) steered panels are numerically compared. The effect of in-plane loads is also accounted for in the aeroelastic analyses.

© 2017, Brazilian Association of Computational Mechanics. All rights reserved.A broad class of engineering systems can be satisfactory modeled under the assumptions of small deformations and linear material properties. However, many mechanical systems used in modern applications, like structural elements typical of aerospace and petroleum industries, have been characterized by increased slenderness and high static and dynamic loads. In such situations, it becomes indispensable to consider the nonlinear geometric effects and/or material nonlinear behavior. At the same time, in many cases involving dynamic loads, there comes the need for attenuation of vibration levels. In this context, this paper describes the development and validation of numerical models of viscoelastic slender beam-like structures undergoing large displacements. The numerical approach is based on the combination of the nonlinear Cosserat beam theory and a viscoelastic model based on Fractional Derivatives. Such combination enables to derive nonlinear equations of motion that, upon finite element discretization, can be used for predicting the dynamic behavior of the structure in the time domain, accounting for geometric nonlinearity and viscoelastic damping. The modeling methodology is illustrated and validated by numerical simulations, the results of which are compared to others available in the literature.

© 2016 Elsevier Ltd.Flutter in aeronautical panels is a type of self-excited oscillation which can occur during supersonic flights. At the flutter point the vibrations of the panel become unstable and increase significantly in time. This manuscript presents a semi-analytical model taking into account the stiffener's base effects, in order to predict the aeroelastic response of laminated composite stiffened panels under supersonic flow. Krumhaar's modified supersonic piston theory, which considers the radius effect, is adopted to model the aerodynamic loading. The proposed model has been validated against results available in the literature for various configurations. A parametric study considering different panels and stiffener configurations is also presented. The numerical results indicate that the stiffener base significantly affects the panel aeroelastic behavior. Preliminary studies also indicate that redistributing the laminate plies from the stiffener's flange to its base significantly increases the torsion stiffness of the panel locally, opening new design possibilities that may lead to higher critical flutter speeds and therefore to better designs. The results also indicate that designs with plies distributed on the base may lead to a better flutter performance when the airflow is transverse to the longitudinal stiffener direction.

© 2016 Elsevier LtdThis paper describes the development and experimental evaluation of a particular type of piezoelectric energy harvester, composed of four aluminum cantilever blades to which piezoelectric patches are bonded, in such way that electric energy is generated when the blades undergo bending vibrations. Concentrated masses, whose values can be varied, are attached to the tips of the blades. Due to the geometric shape of the harvester, in which the four blades are oriented forming right angles, the harvester is named cruciform. As opposed to the large majority of previous works on the subject, in which harvesters are excited at their bases by prescribed acceleration, herein the harvester is connected to a vibrating structure excited by an imbalance force. Hence, the amount of harvested energy depends upon the dynamic interaction between the harvester and the host structure. Laboratory experiments were carried-out on a prototype connected to a tridimensional truss. The experimental setup includes a force generator consisting of an imbalanced disc driven by an electrical motor whose rotation is controlled electronically, a voltage rectifier circuit, and a battery charged with the harvested energy. After characterization of the dynamic behavior of the harvester and the host structure, both numerically and experimentally, the results of experiments are presented and discussed in terms of the voltage output of the piezoelectric transducers as function of the excitation frequency and the values of the tip masses. Also, the capacity of the harvester to charge a Lithium battery is evaluated.

© Springer International Publishing Switzerland 2016. All rights are reserved.Structural Health Monitoring-SHM-is known as the nondestructive process of online, in service, allowing the systems and structures to monitor their own integrity all along their useful lives. The most important goals in this context are to prevent failures, to increase security, and to reduce maintenance costs. One of the most important available techniques is the so-called impedance-based structural health monitoring, which is the focus of the present chapter. Practical implementations of the technique are described for illustration purposes.

© Springer International Publishing Switzerland 2016. All rights are reserved.This chapter first introduces the basic definitions and concepts related to smart materials and structures. Then, the underlying physical principles and main operational features of some of the smart materials most widely used in engineering applications are described. The potential of the technology of smart materials and structures for innovative solutions of practical problems is put in evidence by the description of some relevant research studies and engineering applications, with the support of relevant bibliographic references. The concepts introduced in this chapter are further developed in the other chapters of the book.

Smart and periodic structures have received the attention of researchers by virtue of their great potential. These structures have powerful properties like adaptiveness and the ability to operate as mechanical filters. Although, the presence of uncertainties must be taken into account to guarantee robustness. Thus, a finite element model is proposed to elucidate the importance of stochastic aspects and to present the concept of robust frequency bandgap. The smart part consists of piezoelectric actuators connected to resonant circuits in a tridimensional truss unit cell. The periodic part is the replication of this cell to assemble the final structure. Floquet/Bloch conditions are used to model the infinite representation. Then, a Monte Carlo Simulation is carried out and the bandgaps' bounds are analyzed considering frequency responses and dispersion diagrams. The goal being to evaluate the influence of uncertainties affecting the prediction of the attenuation zones. Likewise, the consequences of increasing the uncertainty level are evaluated.

This paper deals with attitude and vibration control of a satellite containing flexible solar arrays. The vibration motion is controlled by using piezoelectric transducers as sensors and as actuators. A lab test is conducted with a piezoelectric element bonded on a thin plate for two specific applications, the piezoelectric acting as a sensor and as an actuator. The attitude motion is controlled by using reaction wheels and thruster. For this purpose a mathematical model is developed for a rigid-flexible satellite comprising reactions wheels, thrusters, and piezoelectric transducers to act as sensors and actuators aiming the solar panels vibration control. The Finite Elements method is used to model the piezoelectric elements and the solar arrays. The method is combined with the Lagrangian formulation to obtain the complete mathematical model of the spacecraft taking into account the attitude and the vibration coupled motions. The sensor mathematical model involves the electric potential in addition to the conservative potential energy associated with the elastic properties of the piezoelectric element. The Linear Quadratic Regulator controller is designed for the attitude and vibration control. The MatLab software is used to simulate the dynamics of the system. The interaction between the attitude and the vibration motion is analyzed as well as the performance of the piezoelectric actuator to damp the vibration motion of the solar arrays.

© 2014 Elsevier Ltd.It has been demonstrated by many authors that the internal damping mechanism of the viscoelastic materials offers many possibilities for practical engineering applications. However, in traditional procedures of analysis and design of viscoelastic dampers subjected to cyclic loadings, uniform, constant temperature is generally assumed and do not take into account the self-heating phenomenon. Moreover, for viscoelastic materials subjected to dynamic loadings superimposed on static preloads, such as engine mounts, these procedures can lead to poor designs or even severe failures since the energy dissipated within the volume of the material leads to temperature rises. In this paper, a hybrid numerical-experimental investigation of effects of the static preloads on the self-heating phenomenon in viscoelastic dampers subjected to harmonic loadings is reported. After presenting the theoretical foundations, the numerical and experimental results obtained in terms of the temperature evolutions at different points within the volume of the viscoelastic material for various static preloads are compared, and the main features of the methodology are discussed.

It is widely known that traditional damping materials such as elastomers present a number of interesting characteristics when applied for vibration mitigation, such as inherent stability and good damping performance in relatively broad frequency bands, besides cost effectiveness. However, the behavior of those materials is highly dependent upon environmental and operational parameters such as excitation frequency and temperature. Another typical drawback is the added weight entailed by viscoelastic treatments. Especially regarding environmental influences, uncontrolled temperature variations and moisture can jeopardize the damping capacity and endurance of viscoelastic dampers. On the other hand, shape memory alloys present potential advantages in vibration damping due to their large pseudoelastic hysteresis loop in stress-strain relationship and can be used both as a damping material and structural elements in various engineering applications. Thus, it becomes apparent the convenience of combining both types of materials in such a way to explore the advantageous features of each of them. In this paper, a time-domain modeling procedure of structures containing both viscoelastic materials and shape memory alloys is addressed. The main goal is the development of a finite-element-based methodology intended to perform the analysis of engineering structures treated by passive constraining layer damping and pseudoelastic shape memory alloy wires for vibration mitigation. The viscoelastic behavior is modeled by using a four parameter fractional derivative model. To model the hysteresis response of the shape memory alloy, a phenomenological simplified model suitable for performing the parametric study of such dynamic system is used. After the discussion of various theoretical aspects, the time-domain responses are calculated for a three-layer sandwich beam containing viscoelastic materials and shape memory alloy wires and the main features of the modeling methodology are highlighted. © 2014 Elsevier Ltd.

This paper is devoted to the investigation of the possibility of increasing fatigue life of engineering structures subjected to multiaxial random loads by applying constrained viscoelastic layers. The rationale for such study is the fact that as the addition of viscoelastic materials provide decreased vibration amplitudes, it becomes important to quantify the increase of reliability that can be obtained. Moreover, despite the fact that many multiaxial fatigue damage criteria applicable to undamped structures exist in the literature, none of them is adapted to deal with the problem of estimation the fatigue damage in structures incorporating viscoelastic damping, since they must conveniently account for the frequency- and temperature-dependent behavior of the viscoelastic material. Due to the nature of the stress state of the considered problem, the fatigue damage is assessed by using Sine's global criterion. After presenting the theoretical aspects, the numerical fatigue damage analyses of a three-layer sandwich plate treated by passive constrained damping layer are addressed, and the main features of the methodology are discussed.© 2012 Published by Elsevier Ltd. All rights reserved.

© 2015 Brazilian Association of Computational Mechanics. All rights reserved.Many authors have shown that the effective design of viscoelastic systems can be conveniently carried out by using modern mathematical models to represent the frequency- and temperature-dependent behavior of viscoelastic materials. However, in the quest for design procedures of real-word engineering structures, the large number of exact evaluations of the dynamic responses during iterative procedures, combined with the typically high dimensions of large finite element models, makes the numerical analysis very costly, sometimes unfeasible. It is especially true when the viscoelastic materials are used to reduce vibrations of nonlinear systems. As a matter of fact, which the resolution of the resulting nonlinear equations of motion with frequency- and temperature-dependent viscoelastic damping forces is an interesting, but hard-to-solve problem. Those difficulties motivate the present study, in which a time-domain condensation strategy of viscoelastic systems is addressed, where the viscoelastic behavior is modeled by using a four parameter fractional derivative model. After the discussion of various theoretical aspects, the exact and reduced time responses are calculated for a three-layer sandwich plate by considering nonlinear boundary conditions.

Among the passive techniques of vibration control, the use of piezoelectric transducers connected to electric circuits has been intensively investigated lately. However, as is the case of any engineering system, uncertainties affecting the physical and geometrical characteristics of the control device are unavoidable and prone to jeopardize the control performance. In this context, this paper is devoted to the numerical procedures intended for the evaluation of the reliability of structures containing shunted piezoelectric transducers. Reliability here is meant as the probability of complying with pre-defined control goals, given the probability distributions ascribed to the uncertain variables, which are modeled as continuous random variables. The performance goals are accounted for by the proper choice of the so-called limit state functions (LSF), which are computed from the structural responses. The reliability indices are computed by using First Order Reliability Method (FORM) and the results are compared to Monte Carlo Simulation (MCS) associated to Latin Hypercube Sampling (LHS). Numerical simulations are presented for a truss structure modeled by finite elements, containing a piezoelectric stack transducer connected to a resistive-inductive (resonant) shunt circuit. The comparison between FORM and MCS results enables to evaluate the accuracy and computational effort involved in the use of both methods.

This paper is devoted to the attitude and vibration control of spacecraft containing flexible appendages. It entails an investigation of a passive control strategy which consists in connecting piezoelectric transducers bonded to the flexible elements to electric circuits in such a way that the vibration energy, once converted into electrical energy, is transferred and partially dissipated into the electric circuit. This strategy enables to circumvent some difficulties involved in active control such as instability and the necessity of a large amount of hardware, which can be critical in space applications. One considers an artificial satellite model composed of a hub, a reaction wheel used for angular position control and two identical flexible panels, which contain piezoelectric patches symmetrically bonded to their surfaces. The equations of motion are derived based on the Assumed Modes approach, accounting for the electromechanical coupling and the presence of two types of circuits (resistive, and resistive-inductive). The effectiveness of the control strategy suggested is assessed by means of numerical simulations of a satellite undergoing an angular position correction commanded by proportional-derivative torque applied by the reaction wheel. The results demonstrate that the panel vibrations levels and coupling between flexible and rigid-body motions are significantly reduced for both types of circuits considered, such effectiveness being greater for resistive-inductive shunt circuits. © 2013 Elsevier Masson SAS. All rights reserved.

Vibratory feeders or vibratory conveyors have been widely used for the transport and orientation of individual parts and bulk materials in many branches of industrial activity. From the designer's standpoint, the current endeavor is to conceive efficient vibratory feeders, satisfying constraints of power consumption, vibration transmission and noise emission. Moreover, the interest in the reduction of maintenance cost is always present. In this context, this paper investigates experimentally the concept of vibratory conveying based on the use of piezoelectric materials for motion generation. A small-size prototype of a linear conveyor, in which lead-zirconate-titanate (PZT) patches are bonded to the resilient elements, is described. One of the main design goals is that the prototype is intended to be fed directly from the electric network, aiming at avoiding the use of electronic equipment for driving. To comply with this feature and, at the same time, enable to adjust the transport velocity, a mechanical device has been conceived in such a way that the first natural frequency of the conveyor can be changed. It is shown that the transport velocity is determined by the proximity between the excitation frequency and the first natural frequency of the conveyor. The experimental tests performed to characterize the dynamic behavior of the prototype are described and the range of transport velocities is determined.

This work concerns the optimisation of linear two-dimensional planar metallic structures subjected to stationary Gaussian random loads. A strategy intended to improve the design of this category of structures is proposed according to the multiaxial high-cycle fatigue, by varying the thicknesses of the zones where the structure is assumed to be divided. To achieve this goal, a computationally efficient framework for the determination of the fatigue life is firstly proposed. It is based on a frequency formulation of the Sines' fatigue criterion, adapted according to Pitoiset and Preumont works [1]. Two examples are presented to demonstrate the ability of the methodology to provide better structural topologies. © 2012 Elsevier Ltd. All rights reserved.

It is widely known that the mechanical characteristics of viscoelastic materials are highly dependent upon temperature. In traditional procedures of analysis and design of viscoelastic dampers, uniform, constant temperature is generally assumed. However, this procedure can lead to poor designs or even severe failures since the energy dissipated within the volume of the material leads to temperature rises, which depend on a number of factors such as material properties, load conditions and the geometry of the damping device. This phenomenon, which has been frequently disregarded in the literature, is known as self-heating. In this paper, a hybrid numericalexperimental investigation on the self-heating phenomenon in viscoelastic materials subjected to harmonic loadings is reported. The main goal is the development of a finite-element-based methodology intended to perform the thermoviscoelastic analysis of discrete damping devices such as translational and rotational mounts. Since direct coupling between thermal and structural fields would result in prohibitive computational costs, the problem is solved by assuming weak coupling between both fields and the nonlinear coupled thermal and structural analyses are performed in a sequential iterative scheme, implemented in ANSYS™ finite element software. In order to put in evidence the self-heating phenomenon and evaluate the accuracy of the modeling procedure, laboratory experiments are carried-out using a translational viscoelastic mount, subjected to shear harmonic loading with various frequency and amplitude values. The numerical and experimental results obtained in terms of the temperature evolutions at different points within the volume of the viscoelastic material are compared. Additionally, an optimization-based procedure is used to identify some unknown thermal parameters intervening in the model. The obtained results confirm that accounting for self-heating can be of capital importance in the design and performance analysis of viscoelastic dampers. © 2011 Elsevier Ltd. All rights reserved.

Piezoelectric actuators are widely used in smart structural systems to actively control vibration and noise, and to enhance performance. Because of the highly capacitive nature of these actuators, special power amplifiers, capable of delivering high currents, are required to drive these systems. In this paper, a study to reduce the reactive energy that is necessary in such systems is carried out. This is accomplished by associating the actuator with its capacitive characteristic circuit. Also, non-idealities of the circuit performance are addressed, along with theoretical limits regarding possible power savings and practical difficulties in achieving them. The proposed converter introduces energy to correct the difference of phase between current and voltage that is supplied to the piezoelectric transducer (PZT) actuator. This process is optimized by the introduction of reactive power to the characteristic process of the PZT's actuator circuit. Therefore the system is supposed to present an electric characteristic that is close to resistive, and is not capacitive any more. © The Author(s) 2011 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

The Structural Health Monitoring - SHM method based on electrical impedance has been developed as a promising tool for structure failure identification in real time and is considered a novel non-destructive evaluation method. The piezoelectric - PZT impedance can be directly associated to the structure's mechanical impedance where de PZT is bonded. Assuming that the mechanical PZT properties do not change over the monitoring time, the electrical PZT impedance can be used for monitoring structural health. The use of each PZT as both sensor and actuator reduces the total number of sensor and wires connecting them to the switching circuit. The technique consists in obtaining Frequency Response Functions - FRF, with the related signal modification, periodically. Modifications in the FRF of each PZT would indicate structural changes and, therefore, a possible failure. The required number of PZTs will be determined by the dimensions of the monitored structure and the precision required for locating a possible failure. To obtain the FRF of the entire monitored structure it is used a switching and signal conditioning system that continuously activate and deactivate each PZT. This paper proposes a solid state, low power, small sized and low signal distortion switching system. The system is quite modular and each module can manage 16 PZTs. It is possible to expand the sensing net by interconnecting a non limited number of modules. Descriptions of the working principles, circuits used and experimental results are presented. © 2011 IEEE.

The essence of structural health monitoring (SHM) is to develop systems based on nondestructive inspection (NDI) technologies for continuous monitoring, inspection and detection of structural damages. The electromechanical impedance (EMI) method has been regarded as a promising tool for SHM. In this article, a new architecture of a remote SHM system based on electromechanical impedance measures is described. The proposed environment is employed to automatically monitor the structural integrity of aircrafts and is composed by sensor networks, signal conditioning and acquisition hardware, and a data processing system.

The Structural Health Monitoring - SHM method based on electrical impedance has been developed as a promising tool for structure failure identification in real time and is considered a novel non-destructive evaluation method. The piezoelectric - PZT impedance can be directly associated to the structure's mechanical impedance where de PZT is bonded. Assuming that the mechanical PZT properties do not change over the monitoring time, the electrical PZT impedance can be used for monitoring structural health. The use of each PZT as both sensor and actuator reduces the total number of sensor and wires connecting them to the switching circuit. The technique consists in obtaining Frequency Response Functions - FRF, with the related signal modification, periodically. Modifications in the FRF of each PZT would indicate structural changes and, therefore, a possible failure. The required number of PZTs will be determined by the dimensions of the monitored structure and the precision required for locating a possible failure. To obtain the FRF of the entire monitored structure it is used a switching and signal conditioning system that continuously activate and deactivate each PZT. This paper proposes a solid state, low power, small sized and low signal distortion switching system. The system is quite modular and each module can manage 16 PZTs. It is possible to expand the sensing net by interconnecting a non limited number of modules. Descriptions of the working principles, circuits used and experimental results are presented. © 2011 IEEE.

The electromechanical impedance (EMI) method has been regarded as a promising tool for structural health monitoring (SHM) in real time. Usually, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent, EMI functions, from which features related to the presence, position, and extent of damage can be extracted. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively so as to increase the probability of successful detection of damage in an early phase. In this context, a miniaturized, low-cost, highly expandable SHM architecture for monitoring an array of multiplexed piezoelectric transducers is proposed. Each logical block of the proposed architecture is presented in detail. The proposed architecture does not use costly fast Fourier transform analyzers/algorithms nor requires a digital computer for processing. A personal computer is only necessary for user interfacing. It has been verified that the system can work for frequencies ranging from 0 to 400 kHz with high accuracy and stability. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer; however, a WiFi® connection is also available. © The Author(s) 2010.

This paper proposes an active vibration control technique, which is based on linear matrix inequalities, that is numerically applied to a piezoelectric actuator bonded to a composite structure forming a so-called Smart Composite Structure. Serendipity-type finite element based on First-Order Shear Deformation Theory with rectangular shape, eight nodes, five mechanical degrees of freedom (DOF) per node and eight electrical DOF per piezoelectric layer is established for the composite structural model. Additionally, a mixed theory that uses a single equivalent layer for the discretization of the mechanical displacement field and a layerwise representation of the electrical field is adopted. Temperature effects are neglected. Simulation results illustrate the effectiveness of the proposed vibration control methodology for composite structures.

In this paper, numerical simulations of incompressible flows around rotating circular cylinders have been performed. The two-dimensional Navier-Stokes equations are solved by using a Cartesian non-uniform grid. The Immersed Boundary Method (IBM) with the Virtual Physical Model (VPM) was used in order to model the presence of the circular cylinder in the flow. The fractional time step method was used to coupling the pressure and velocity fields. The simulations were carried out for Reynolds numbers equals to 60, 100 and 200 for different specific rotations. The effects of rotation on flow characteristics and fluctuating forces were investigated. The Strouhal number, obtained by performing the Fast Fourier Transform (FFT) of the temporal distribution of the lift coefficient, and the pressure coefficients, were also been calculated. Vorticity contours are presented considering different values of the Reynolds number and specific rotation. The numerical results obtained are compared to those obtained by other authors and the usefulness of the numerical methodology composed by the combination of the IBM with the VPM to simulate flows in the presence of mobile bodies is highlighted. Copyright © 2011 by ABCM.

The mechanical properties obtained from mechanical tests, such as tensile, buckling, impact and fatigue tests, are largely applied to several materials and are used today for preliminary studies for the investigation of a desired element in a structure and prediction of its behavior in use. This contribution focus on two widely used different tests: tensile and fatigue tests. Small PZT (Lead Titanate Zirconate) patches are bonded on the surface of test samples for impedance-based health monitoring purposes. Together with these two tests, the electromechanical impedance technique was performed by using aluminum test samples similar to those used in the aeronautical industry. The results obtained both from tensile and fatigue tests were compared with the impedance signatures. Finally, statistical meta-models were built to investigate the possibility of determining the state of the structure from the impedance signatures.

Purpose The purpose of this paper is to present a deterministic, stochastic and reliability analysis through numerical simulations in 2D and 3D dynamic fluidstructure interaction problems. Design/methodology/approach The perturbation methods allied to reliability analysis are applied to fluidstructure finite element models. Reliability analysis couples finite element analysis with first and second order reliability methods and ant colony optimization in a modified first order reliability method. Findings Results obtained show the potentialities of the proposed methodology and encourage improvement of this procedure for use in complex coupled fluidstructure systems. Originality/value The understanding of the mechanical interaction between a fluid and an elastic solid has a capital importance in several industrial applications. In order to couple the behaviour of two different media, deterministic models have been proposed. However, stochastic analysis has been developed to deal with the statistical nature of fluidstructure interaction parameters. Moreover, probabilisticbased reliability analysis intends to find safe and costeffective projects. © 2010, Emerald Group Publishing Limited

The effective design of viscoelastic dampers as applied to real-world complex engineering structures can be conveniently carried out by using modern numerical optimization and/or model updating techniques. However, the large number of exact evaluations of the cost functions, combined with the typically high dimensions of large finite element models of industrial structures incorporating viscoelastic materials, makes the numerical processes very costly, sometimes unfeasible. Those difficulties motivate the study reported herein, in which a general strategy to improve the standard condensation methods by taking into account a priori information of the modifications into the viscoelastic zones is introduced. The proposed method can be used with any condensation procedure, including direct reductions and component mode synthesis. © 2010 Elsevier Ltd.

The effective design of viscoelastic dampers as applied to real-world complex engineering structures can be conveniently carried out by using modern multiobjective numerical optimization techniques. The large number of evaluations of the cost functions normally combined with the typically high dimensions of finite element models of industrial structures makes multiobjective optimization very costly, sometimes unfeasible. Those difficulties motivate the study reported in this paper, in which a strategy is proposed consisting in the use of evolutionary algorithms specially adapted to multiobjective optimization of viscoelastic systems, combined with robust condensation and metamodeling. After the discussion of various theoretical aspects, a numerical application is presented to illustrate the use and demonstrate the effectiveness of the methodology proposed for the optimal design of viscoelastic constrained layers. Copyright © 2010 by ABCM.

Engineering structures incorporating viscoelastic materials are characterized by inherent uncertainties affecting the arameters that control the efficiency of the viscoelastic dampers. In this context, the handling of variability in viscoelastic systems is a natural and necessary extension of the modeling capability of the present techniques of deterministic analysis. Among the various methods devised for uncertainty modeling, the stochastic finite element method has received major attention, as it is well adapted for applications to complex engineering systems. In this paper, the stochastic finite element method applied to a structural three-layer sandwich plate finite element containing a viscoelastic layer, with random parameters modelled as random fields, is presented. Accounting for the dependence of the behaviour of the viscoelastic materials with respect to frequency and temperature, using the concepts of complex modulus and shift factor, the uncertainties are modelled as homogeneous Gaussian stochastic fields and are discretized according to the spectral method, using Karhunen-Loève expansions. The modeling procedure is confined to the frequency domain, and the dynamic responses are characterized by frequency response functions (FRF's). Monte Carlo Simulation (MCS) combined with Latin Hypercube Sampling is used as the stochastic solver. The typically high dimensions of finite element models of viscoelastic systems combined with the large number of Monte Carlo samples to be computed make the evaluation of the FRF's variability computer intensive. Those difficulties motivate the use of condensation methods specially adapted for viscoelastic systems, in order to alleviate the computational cost. After the presentation of the underlying formulation, numerical applications of moderate complexity are presented and discussed aiming at demonstrating the main features and, particularly, the computation cost savings provided by the association of MCS with the suggested condensation procedure. © 2010 - IOS Press and the authors.

In the scope of structural dynamics, sensitivity analysis is a very useful tool in a number of numerical procedures such as parameter identification, model updating, optimal design and uncertainty propagation. In this paper the formulation of first-order sensitivity analysis of complex frequency response functions (FRFs) is developed for composite sandwich plates composed by a combination of fiber-reinforced and elastomeric viscoelastic layers, in arrangements that are frequently used for the purpose of noise and vibration attenuation. Although sensitivity analysis is a well known numerical technique, the main contribution intended for this study is its extension to viscoelastic structures, which are characterized by frequency- and temperature-dependent material properties and, thus, require particularly adapted analytical and numerical procedures. Due to the fact that finite element discretization has become the most used method for dynamic analysis of complex structures, the sensitivity analysis addressed herein is based on such models, being computed from the analytical derivatives of the FRFs with respect to a set of design parameters, such as fiber orientations and layer thicknesses. Also, a procedure for evaluating the sensitivity of the FRFs with respect to temperature of the viscoelastic material is suggested. After discussion of various theoretical aspects, including a parameterization scheme of the structural matrices with respect to the design variables, first-order response derivatives are calculated for a composite plate with inherent structural damping, and for a composite sandwich plate with a viscoelastic core. The results are compared to those obtained from first-order finite-difference approximations. © 2009 Elsevier Ltd. All rights reserved.

In this paper, a methodology of uncertainty propagation is investigated as related to constrained viscoelastic layers in the context of passive vibration damping. The uncertainties are introduced on multilayer beam and plate finite elements by means of an original strategy, which consists in introducing the perturbations after an adequate parameterisation of the mass and complex stiffness matrices. Such parameterisation scheme enables to perform iterative model updating, sensitivity analyses and uncertainty propagation analyses at a moderate computational cost since re-actualisation of the nominal global finite element matrices is not required. The design space is composed by both the parameters characterising the viscoelastic treatment and those of the base structure. The theoretical foundations related to the modelling of viscoelastic systems and stochastic finite element models are first reviewed, followed by a description of the parameterisation technique. Finally, numerical applications are presented to demonstrate the effectiveness of the proposed strategy for the robust design of structures incorporating viscoelastic materials. Crown Copyright © 2009.

The mechanical properties obtained from the strength tests like tensile, buckling, impact and fatigue tests are largely applied to several materials and are used today for previous studies for investigation of a desired element in a structure and its behavior in use. This contribution focus on two different tests: tensile and fatigue tests. Small PZT (Lead Titanate Zirconate) patches are bonded on the surface of the coupons for the impedance-based health monitoring purposes. Together with these two tests, the electromechanical impedance technique was performed by using Aluminium coupons similar to those used n the aeronautical industry. The results obtained both from tensile and fatigue testes were compared with the impedance signatures. Finally, statistical meta-models were built aiming at investigating the possibility of determining the state of the structure from the impedance signatures. © 2009 Society for Experimental Mechanics Inc.

In the context of computational fluid dynamics a numerical investigation of incompressible flow around fixed pairs of rigid circular cylinders was carried out. The two-dimensional filtered Navier-Stokes equations with the Smagorinsky sub-grid scale model were solved using a Cartesian non-uniform grid. The immersed Boundary Method with the Virtual Physical Model was used in order to model the presence of two circular cylinders embedded in the flow. The fractional time step method was used to couple pressure and velocity fields. The simulations were carried out for Reynolds number equal to 72,000 for pitch ratio equal to 2 and different arrangements regarding the relative positions of the cylinders. The flow interference between the two cylinders, the vortex shedding process and the behavior of the dynamic coefficients were investigated. The results of the present study were compared with experimental data from the literature. The Immersed Boundary Method has showed to be efficient in the simulation of flows, taking into account the presence of multi-body compositions. © 2009 Tech Science Press.

In this paper it is suggested a modeling methodology of structural systems supported by translational and rotational viscoelastic mounts or joints based on a frequency response function coupling technique. Such strategy enables to predict the dynamic behaviour of the composite systems given a set of frequency response functions of the main structure and a driving point frequency response function of the viscoelastic support. These frequency response functions can be obtained either experimentally or by finite element modeling. Both cases are considered in the study. After presenting the underlying theoretical aspects, the results of numerical simulations of two-dimensional structures are presented, emphasizing the procedure conceived to compute the frequency response functions of the viscoelastic mounts or joints from a detailed finite element model using commercial packages and material properties provided by manufacturers. The dependency of the viscoelastic behaviour on frequency and temperature is accounted for by using the complex modulus approach and the concepts of reduced frequency and shift factor. An investigation using experimentally acquired frequency response functions of a frame structure with a translational viscoelastic damper is presented. Based on the obtained results, the main features of the modeling methodology are highlighted. © 2008 Elsevier Ltd. All rights reserved.

The aim of this paper is to evaluate the use of the Structural Health Monitoring (SHM) technique based on the concept of electromechanical impedance for the assessment of low-energy impact damage in laminated carbon-fiber composite plates. The experiments were carried-out by using an especially designed pendulum, and were planned in such a way to accommodate a range of test conditions, such as impact energy and dimension of the impacting piece. Also, it was investigated the influence of the frequency band in which the impedance functions are measured. Additionally, statistical metamodels were built aiming at establishing functional relations between the values of the damage metric and impact energy for single and multiple impacts. The obtained results demonstrate the capability of the monitoring method to identify various damage levels corresponding to different impact conditions. Copyright © 2008 by ASME.

The present contribution deals with the optimal tuning of two different types of dynamic vibration absorbers (DVA) by using ant colony optimization, namely the vibrating blade DVA and the multi-mode DVA. Dynamic vibration absorbers are mechanical appendages constituted by mass, spring and damping elements, which are coupled to a mechanical system to provide vibration attenuation. The tuning of the dynamic vibration absorber is the procedure that sets the anti-resonance frequency to a given value by adjusting the parameters of the dynamic vibration absorber. Based on this methodology, the optimization problem is defined as the minimization of the objective function that describes the vibration amplitude of the primary structure. To solve the optimization problem, ant colony optimization was used. In the early nineties, when the Ant Colony algorithm was first proposed, it was used as an alternative approach for the solution of combinatorial optimization problems, such as the traveling salesman problem. However, the extension for operating with continuous variables is recent and this feature is still under development. In the present formulation, the optimization technique was extended to handle continuous design variables. Numerical results are reported, aiming at illustrating the success of using the proposed methodology, as applied to mechanical system design. © 2007 Elsevier Ltd. All rights reserved.

In this paper, a methodology of uncertainty propagation is investigated as related to constrained viscoelastic layers in the context of passive vibration damping. The uncertainties are introduced on multilayer plate finite elements by means of an original strategy which consists in introducing the perturbations after an adequate parameterisation of the mass and complex stiffness matrices. Such parameterisation scheme enables to perform iterative model updating, sensitivity analyses and uncertainty propagation analyses at a moderate computational cost since re-actualisation of the nominal global finite element matrices is not required. The design space is composed by both the parameters characterising the viscoelastic treatment and those of the base structure. The theoretical foundations related to the modelling of viscoelastic systems and stochastic finite element models are first reviewed, followed by a description of the parameterisation technique. Finally, numerical applications are presented to demonstrate the effectiveness of the proposed strategy for the robust design of structures incorporating viscoelastic materials.

It is widely known that welding processes induce the generation of residual stresses, which, through the so-named stress stiffening effect, can influence the static and dynamic behavior of the welded components. Thus, accounting for this influence becomes important for the understanding of experimental observations and accurate modeling of the dynamic behavior. In this study, the numerical and experimental characterization of the influence of welding residual stresses on the flexural dynamic characteristics of rectangular plates is addressed. It is suggested a general modeling methodology based on finite elements comprising three subsequent analyses, namely: a thermal analysis to compute the transient temperature history due to welding thermal loading; a structural analysis accounting for plastic strains to obtain the welding residual stress fields and geometric distortions, and a dynamic analysis to compute the dynamic characteristics taking into account the stress-stiffening effect and geometric distortions. The results demonstrate the importance of considering the influence of welding residual stresses in the prediction of the flexural dynamic behavior of plates and the feasibility and efficiency of the simplified modeling approach, which can readily be extended to more complex situations, for characterizing this influence.

Aiming at eliminating the dependency on a mesh of the classical modeling methods, meshless methods have been developed in recent years. Additionally, research in meshless methods allied to probabilistic analysis needs much attention. In this context, this paper presents a reliability procedure that couples first and second order reliability methods and heuristic-based optimization method with an element-free Galerkin method. Numerical applications in statics problems are used to illustrate the applicability and effectiveness of proposed methodology. These examples consist in a bar and a beam whose load, material and geometrical parameters are considered as random variables. The results show that the predicted reliability levels are accurate in comparison with similar approach that uses analytical and finite element analysis to evaluate the limit state functions. © 2007 Civil-Comp Press.

The understanding of the mechanical interaction between a fluid and an elastic solid has a capital importance in several industrial applications. In order to couple the behaviour of two different media, deterministic models have been proposed. However, stochastic analysis has been developed to deal with the statistical nature of fluid-structure interaction parameters. Moreover, probabilistic-based reliability analysis intends to find safe and cost-effective projects. In this work, it is presented a deterministic, stochastic and reliability analyses through numerical simulations in 2- D and 3-D dynamic fluid-structure interaction problems. The perturbation methods allied to reliability analysis are applied to fluid-structure finite element models. Reliability analysis couples finite element analysis with first and second order reliability methods and Ant Colony Optimization. The results tend to confirm the potential of this methodology. © 2007 Civil-Comp Press.

The use of viscoelastic materials has been regarded as an interesting means of achieving effective vibration mitigation in various types of vehicles, machines and structures at a relatively low cost. More recently, considerable effort has been devoted to the development of modelling procedures of structures containing viscoelastic elements taking into account the typical dependence of the mechanical characteristics of viscoelastic materials with respect to frequency and temperature. As a result, to date, it is possible to perform numerical predictions of complicated viscoelastic structural systems. Such high-fidelity models can thus be used in the early phases of design (especially for optimization) of viscoelastic dampers as applied to structures of industrial interest. In this paper, the performance of passive constrained viscoelastic layers, as applied to vibration attenuation of plate-like structures with potential application to refrigeration systems is evaluated both numerically and experimentally to demonstrate the utility of proposed methodology to reduce vibration amplitudes. © IMechE 2007.

This paper presents an optimization-based inverse procedure for the determination of external loads applied to a given mechanical structure, by using information concerning the dynamic behavior of the system and its corresponding finite element model. The influence of the stress-stiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamic responses and the applied external forces. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their finite element counterparts. The loading parameters (magnitude, position and direction) assumed as being unknown, are considered as design variables. The identification procedure is illustrated by means of numerical simulations and experimental tests, in which a heuristic technique known as LifeCycle model was used. © 2007 Elsevier Ltd. All rights reserved.

The present contribution deals with the optimal tuning of a vibrating blade dynamic vibration absorber by using Ant Colony Optimization (ACO). Dynamic vibration absorbers (DVAs) are systems constituted by mass, spring and damping elements, which are coupled to a mechanical system to provide vibration attenuation. The main idea behind the DVAs is the generation of a force that has the same intensity as the excitation force but in the opposite phase. This phenomenon is known as anti-resonance. The tuning of the DVA is the procedure that sets the anti-resonance frequency to a given value by adjusting the DVA parameters. Based on this theory, the optimization problem is described as the minimization of the objective function that relates the difference between the resonance frequencies of the primary system and those of the DVA. To solve the optimization problem, ACO techniques were used. In the early nineties, when the Ant Colony algorithm was first proposed, it was used as an approach for the solution of combinatorial optimization problems, such as the traveling salesman problem. However, the extension for operating with continuous variables is recent and is still being developed. In this context, this paper presents an engineering application for a continuous domain problem. Numerical results are reported, illustrating the success of using the methodology presented, as applied to mechanical systems. ©2006 IEEE.

A novel hybrid numerical/experimental identification procedure for the assessment of welding-induced residual stresses in rectangular plates is proposed and evaluated. This procedure explores the influence of the stress state on the dynamic responses of structural components, according to the so-named stress-stiffening effect. The technique consists in using a set of experimental natural frequencies of the welded plate and a mathematical model relating the residual stresses to the natural frequencies to formulate an optimization problem. The cost function represents the differences between the experimental and model-predicted dynamic responses and the design variables are interpreted as parameters of the mathematical model describing the stress distribution over the plate. A parameterized stress model suitable to the case of welding residual stresses is presented in terms of a differential equation that relates an Airy's stress function to the plastic strains resulting from the welding process. From this stress function, the stress components s x , s y and t xy (assuming plane stress state) are computed. Genetic Algorithms are used to solve the numerical optimization problem. To demonstrate the feasibility of the method, it is used for the assessment of residual stresses generated by TIG (GTAW) welding of a thin rectangular steel plate, for which experimentally measured natural frequencies and numerically computed residual stress distributions are available in the literature.

The use of viscoelastic materials has been regarded as an interesting means of achieving effective vibration mitigation in various types of mechanical systems at a relatively low cost. To enable efficient analysis and design of viscoelastic dampers as applied to complex structures such as vehicles, machines and structures to reduce the vibration levels, the optimization procedures based on multi-objective evolutionary algorithms (MOEAs) is an important step to be investigated. In such applications, including optimal and/or robust design and model updating, the MOEAs combining meta-models and robust condensation is a very useful tool. In this paper, the interest is the use of the so called non sorting dominated genetic algorithms (NSGA), combining robust condensation and meta-models for the viscoelastic damped systems. This approach enables us to avoid the updating of the exact analysis during the optimization leading to a significant time-reduction cost in the design process. © 2006 Civil-Comp Press.

In the context of control of sound and vibration of mechanical systems, the use of viscoelastic materials has been regarded as a convenient strategy in many types of industrial applications. Numerical models based on finite element discretization have been frequently used in the analysis and design of complex structural systems incorporating viscoelastic materials. Such models must account for the typical dependence of the viscoelastic characteristics on operational and environmental parameters, such as frequency and temperature. In many applications, including optimal design and model updating, sensitivity analysis based on numerical models is a very usefull tool. In this paper, the formulation of first-order sensitivity analysis of complex frequency response functions is developed for plates treated with passive constraining damping layers, considering geometrical characteristics, such as the thicknesses of the multi-layer components, as design variables. Also, the sensitivity of the frequency response functions with respect to temperature is introduced. As an example, response derivatives are calculated for a three-layer sandwich plate and the results obtained are compared with first-order finite-difference approximations. © 2006 - IOS Press and the authors. All rights reserved.

The use of viscoelastic materials has been regarded as an interesting means of achieving effective vibration mitigation in various types of vehicles, machines and structures at a relatively low cost. More recently, considerable effort has been devoted to the development of modeling procedures of structures containing viscoelastic elements taking into account the typical dependence of the mechanical characteristics of viscoelastic materials with respect to frequency and temperature. In this paper, it is suggested a modeling strategy of structural systems supported by viscoelastic mounts, based on a FRF coupling technique. Such strategy enables to predict the dynamic behavior of the complete system (main structure+viscoelastic mount) a set of FRFs of the main structure and the driving point frequency response function of the viscoelastic mount, which can be obtained either experimentally or by finite element modeling. This second alternate is considered in the paper. After presenting the underlying theoretical aspects, the results of numerical simulations of two-dimensional civil structures are presented, emphasizing the procedure conceived for computing the FRF of the viscoelastic mount from a detailed finite element model using a commercial package and the FRF coupling procedure. In these numerical simulations, the influence of temperature on vibration attenuation is investigated.

Temperature variations can significantly change the dynamic characteristics of structures. Active and passive control systems which do not account for these temperature variations and their effect on the dynamics of the structure may cause problems even more severe than those they were designed to solve. In this paper it is shown how the performance of an actively controlled beam deteriorates as temperature varies, by simulating its step response. Then, two distinct designs of adaptive controllers are proposed: one in which temperature is measured and used to update the controller gains, based on an analytical model of the structure which includes temperature effects; and a second design based on an adaptive control technique known as Model Reference Adaptive Control (MRAC), in which the controller gains are updated so as to minimize the error defined as the difference between the response of the actual system and an ideal, preconceived response given by the Reference Model. Numerical simulations are carried out for a simply supported beam modeled as a Single Degree of Freedom system. Results are discussed in terms of the performance of the controlled system and the control effort required. These simulations are meant to provide the necessary knowledge basis which precedes the experimental tests to be carried out in the future.

In the present paper, the finite element modeling of vibrating structures combined with piezoelectric materials and passive electric circuits (shunt circuits) is addressed, with emphasis placed on the analysis of two circuit topologies: resistive shunts and resistive-inductive shunts. The underlying formulation is first presented and then some numerical simulations using commercial finite element software are performed considering a free-free square plate and a complex piezoelectric vibrating beam accelerometer cell for which some target vibration modes must be attenuated. Results are presented and evaluated in terms of the vibration attenuation attained in each case analyzed.

Piezoelectric elements connected to shunt circuits and bonded to a mechanical structure form a dissipation device that can be designed to add damping to the mechanical system. Due to the piezoelectric effect, part of the vibration energy can be transformed into electrical energy that is conveniently dissipated. Therefore, by using appropriate electrical circuits, it is possible to dissipate strain energy and, as a consequence, vibration is attenuated. The dissipation mechanism can be tuned to attenuate vibration either of a single mode, or multiple modes, according to the design of the shunt circuit and the frequency band of interest. The present contribution discusses the modeling of piezoelectric patches coupled to shunt circuits, where the basic parallel resonant shunt circuit is presented. The modeling of multi-degree-of-freedom mechanical systems, including the effects of the shunt circuit is briefly reviewed. A design methodology for the multi-modal case is discussed. Finally, experimental results are reported, illustrating the success of using the methodology presented, as applied to mechanical and mechatronic systems.

Due to problems caused by noise and vibration in industrial environment and in human daily life, techniques of active noise and vibration control have received increasing attention lately. More recently, the use of piezoelectric elements in noise and vibration control systems has been investigated. The present paper addresses techniques of active control by employing multiple piezoelectric patches bonded to the surface of thin plate with relatively small dimensions suitable for laboratory tests. A fuzzy control is used in the active control. The paper brings the development of a finite element model of the system and presents some numerical simulations. Experimental implementation is realized aiming at attenuating the vibration modal amplitudes of the plate.

This paper presents an inverse procedure for the determination of external loads, given the dynamic responses of the loaded structure and its corresponding finite element model. The influence of the stress-stiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamical responses and the applied external loading. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their FE counterparts. The loading parameters (magnitude, position and direction), assumed as being unknown, are considered as design variables. The identification procedure is illustrated by means of numerical simulations, in which the identification problem is solved by using the heuristic named Particle Swarm Optmization together with the Lagrange-Newton SQP (Sequential Quadratic Programming) method.

This paper presents an inverse procedure for the determination of external loads, given the dynamic responses of the loaded structure and its corresponding finite element model. The influence of the stressstiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamical responses and the applied external loading. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their FE counterparts. The loading parameters, assumed as being unknown, are considered as the design variables. The identification procedure is illustrated by means of numerical simulations. In which the identification problem is solved by using the heuristic named LifeCycle model together with the Lagrange-Newton SQP (Sequential Quadratic Programming) method.

This paper presents an inverse procedure for the determination of external loads, given the dynamic responses of the loaded structure and its corresponding finite element model. The influence of the stress-stiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamic responses and the applied external loading. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their finite element counterparts. The loading parameters (magnitude, position and direction) assumed as being unknown, are considered as design variables. The identification procedure is illustrated by means of numerical simulations, in which the identification problem is solved by using heuristic techniques coupled with classical optimization methods. Two heuristic techniques are considered, namely the LifeCycle Model and Particle Swarm Optimization. The classical optimization strategy is the Lagrange-Newton SQP (Sequential Quadratic Programming) method.

The present paper addresses the attenuation of mechanical vibrations using Active Dynamic Vibration Absorbers (DVAs). These devices possess an actuator placed between the primary system and the absorber mass, which applies a control force computed according to an appropriate control law. By adjusting some parameters (gains) of this control law, the DVA can be tuned to absorb vibrations at any given value of the excitation frequency in a relatively large frequency band. Thus, tuning can be achieved without any change in the values of the passive parameters. Here, a particular configuration of active DVA is investigated, based on a control law according to which the control force is expressed as a linear combination of the relative displacement, velocity and acceleration responses of the DVA mass with respect to the primary system. The basic formulation is first presented, including stability analysis, tuning of the DVA by frequency response zero placement and optimization of the control gains. Then, some of the theoretical findings are verified through numerical simulations and laboratory tests, considering a beam as the primary system and using an active DVA constructed with a piezoelectric actuator.

This paper presents orthogonal function techniques for the identification of mechanical systems. For this purpose, mechanical systems are represented by state-space equations and the input and output signals are developed in series of orthogonal functions. The equation of motion can be integrated using numerical techniques together with integration properties specific for orthogonal functions. This procedure permits to obtain a simple algebraic equation, which leads to the determination of the unknown parameters. Different orthogonal functions were tested in numerical and experimental applications, including gyroscopic systems.

The present paper addresses the attenuation of mechanical vibrations using active dynamic vibration absorbers (DVAs). Besides the typical parameters of passive DVAs (inertia, stiffness and damping), active DVAs possess an actuator placed between the primary mass and the absorber mass, which applies a control force according to an appropriate control law. This way, active DVAs can be tuned to any value of the excitation frequency within a relatively large frequency band by modifying the control force, without any change in the values of the passive parameters. A particular configuration of active DVA is proposed, based on a control law in which the control force is expressed as a linear combination of the relative displacement, velocity and acceleration responses of the DVA mass with respect to the primary system. The basic formulation is first presented, including stability analysis, DVA tuning by frequency response zero placement and optimal frequency response shaping. Finally, the main features and performance of the active DVA are assessed through numerical simulations.

This paper examines two passive techniques for vibration reduction in mechanical systems: the first one is based on dynamic vibration absorbers (DVAs) and the second uses resonant circuit shunted (RCS) piezoceramics. Genetic algorithms are used to determine the optimal design parameters with respect to performance indexes, which are associated with the dynamical behavior of the system over selected frequency bands. The calculation of the frequency response functions (FRFs) of the composite structure (primary system + DVAs) is performed through a substructure coupling technique. A modal technique is used to determine the frequency response function of the structure containing shunted piezoceramics which are bonded to the primary structure. The use of both techniques simultaneously on the same structure is investigated. The methodology developed is illustrated by numerical applications in which the primary structure is represented by simple Euler-Bemoulli beams. However, the design aspects of vibration control devices presented in this paper can be extended to more complex structures.

The objective of this work is to perform an assessment of the identification of mount parameters of vibratory systems using genetic algorithms. Two methodologies are used: in the first one, linear and non-linear support parameters are identified from the time-domain responses. In the second one, the parameters are identified considering a sub-structure coupling technique using frequency response functions. Applications to numerically simulated structures are performed. Based on numerical simulation examples, the identification method is appraised in terms of the accuracy of the obtained solutions and robustness to random noise present in the used data.

This paper is focused on the reduction of vibration levels of mechanical systems using dynamic vibration absorbers (DVAs). A general methodology is proposed for the optimum selection of DVA parameters so as to guarantee the efficiency of those devices over a previously selected frequency band. The presented methodology utilizes a substructure coupling technique exploring frequency response functions (FRFs), which enables one to calculate the FRFs of the composite structure (primary system+DVAs), from the FRFs of the primary structure and the theoretical expressions of the FRFs of the DVAs. The FRFs of the composite structure, which are expressed as functions of the DVA parameters, are then used to define scalar performance indexes related to the vibration levels of the composite structure over the selected frequency band. These performance indexes are optimized with respect to the DVA parameters by solving a general non-linear constrained optimization problem. The first part of the paper is devoted to the formulation of the substructure coupling method and the optimization procedures. Numerical applications using experimentally acquired FRFs are then presented to illustrate the main features of the proposed methodology.

A methodology for the optimum design of single and multiple dynamic vibration absorbers, applicable to multi-degree-of-freedom damped primary systems, is proposed. The method is based on a substructure coupling technique that can be used to explore analytical or experimental frequency response functions. The problem is formulated as a general nonlinear optimization problem for which different types of design constraints can be considered. Since only a small number of coordinate points are concerned in the substructure coupling method, only small matrices have to be manipulated. Consequently, the method is very computationally efficient.

This paper examines two passive techniques for vibration reduction in mechanical systems: the first one is based on dynamic vibration absorbers (DVAs) and the second uses resonant circuit shunted (RCS) piezoceramics. Genetic algorithms are used to determine the optimal design parameters with respect to performance indexes, which are associated with the dynamical behavior of the system over selected frequency bands. The calculation of the frequency response functions (FRFs) of the composite structure (primary system + DVAs) is performed through a substructure coupling technique. A modal technique is used to determine the frequency response function of the structure containing shunted piezoceramics which are bonded to the primary structure. The use of both techniques simultaneously on the same structure is investigated. The methodology developed is illustrated by numerical applications in which the primary structure is represented by simple Euler-Bernoulli beams. However, the design aspects of vibration control devices presented in this paper can be extended to more complex structures.

In this paper a study focusing the zeros of frequency response functions (FRFs) of linear mechanical systems is presented. Two major aspects are focused: the underlying theory, including a physical interpretation of the zeros of both transfer and driving point FRFs in terms of structural modifications, and the possibility of practical exploration of the FRF in some structural dynamics applications, namely: finite element updating, structural damage identification and vibration attenuation using dynamic vibration absorbers. After presentation of the theory, some results of applications performed on both numerically simulated and experimental mechanical systems are presented o illustrate the practical use of the zeros.

This paper is focused on the reduction of vibration levels of mechanical systems using dynamic vibration absorbers (DVAs). A general methodology is proposed for the optimum selection of DVA parameters so as to guarantee the efficiency of those devices over a previously selected frequency band. The presented methodology utilizes a substructure coupling technique exploring frequency response functions (FRFs), which enables to calculate the FRFs of the composite structure (primary system+DVAs), from the FRFs of the primary structure and the theoretical expressions of the FRFs of the DVAs. The FRFs of the composite structure, which are expressed as functions of the DVA parameters, are then used to define scalar performance indexes related to the vibration levels of the composite structure over the selected frequency band. These performance indexes are optimized, with respect to the DVA parameters, by solving a general nonlinear constrained optimization problem. The first part of the paper is devoted to the formulation of the substructure coupling method and the optimization procedures. Numerical applications using experimentally acquired FRFs are then presented to illustrate the main features of the proposed methodology.

This paper addresses the problem of identifying the mechanical characteristics - inertia, stiffness and damping - of supporting elements of vibrating structures using dynamic responses. A feasibility study is presented on a method operating in the time domain, whose implementation comprises two basic steps: in the first step, the effect of the supports is represented as external forces applied to the dismounted configuration. These forces are identified by inversion of the time domain multi-input-multi-output transfer relation. The force identification method requires, as experimental data, the acceleration time responses measured at a given set of coordinates of the mounted configuration, including the support locations, and a set of impulse response functions relating measurement and excitation coordinates. In the second step, the equations of motion of the supports, which are modeled as SDOF systems, are used for estimating the values of the unknown physical parameters. The paper is organized as follows: the basic formulation related to the two steps mentioned above is first presented. Then, ill-conditioning of the force identification computations is discussed and the conjugate gradient algorithm, which is used for obtaining stable force estimates, is described. Finally, an application to a simple numerically simulated structure is presented to illustrate the main features of the method.

A strategy for the enrichment of experimental data is examined in connection with the problem of finite element model updating. The strategy is based on the simultaneous exploitation of the dynamic responses of various structural configurations, obtained by deliberate changes of the original boundary conditions, by grounding of one or several degrees of freedom. The main theoretical aspects of the methodology are first introduced, including the formulation of an updating method based on the inverse eigensensitivity of non-self-adjoint systems and also the basic formulation of a technique enabling the eigensolutions of more constrained structural configurations to be calculated from the frequency response functions of a less constrained configuration, so that additional tests can be avoided. Some numerical examples illustrating several key points of the methodology are presented. Through these examples, regarding the problem of localisation and correction of FE modeling errors, it is demonstrated that the proposed strategy enables an effective enlargement of the knowledge space of the structure, and can lead to improved results. © 1998 Academic Press Limited.

This paper addresses the problem of input force reconstruction from the dynamic responses of the structure. A feasibility study is performed on a method operating in the time domain, which is based on the modal equilibrium equations. It requires, as experimental data, the acceleration time responses of the structure when acted upon by the forces to be identified as well as a set of eigensolutions (natural frequencies, mode shapes, modal damping factors and generalized masses). After the basic formulation of the method is presented, numerical applications to a simple numerically simulated test structure are shown aiming at demonstrating the main characteristics and the effectiveness of the method. Some key points are also examined, such as the effects of incompleteness of the experimental data and measurement noise upon the performance of the method. The numerical results reveal that the method can be quite accurate and well adapted to real-world applications.

This paper addresses the Analysis of Modified Structures by using experimental data. In particular, modifications of the boundary conditions of the structure by grounding of one or several of its degrees of freedom are considered. Three methods are proposed, which are conceived to obtain the eigenvalues and eigenvectors of more constrained configurations, given the experimental Frequency Response Functions measured on a less constrained configuration. The formulations of the three methods are first presented and their performances are then evaluated through applications to an automotive structure tested in laboratory.

A time domain method of identification based on the Fourier series is presented. The formulation is derived for general second order linear time - invariant systems. Some simple applications are given to show the potential of the method for solving mechanical vibration problems.

In this paper a time domain method of identification based on the Fourier series is presented. The method is applied for linear-time-invariant mechanical systems with N degrees of freedom. Some simple applications show the potentiality of the method.