© 2021 SPIEThis paper discusses the vulnerability across Brazilian borders considering illicit trade. Smuggling affronts the public administration by bringing prohibited goods into the country. The typical characteristic of smuggling is the lack of collected taxes on goods transported across the border. Since the intelligence analysis estimates the events that are taking place for the movement of illicit goods, it can provide subsidies for agencies to make decisions to fight crime. The policy of the Brazilian State seeks to foster technologies that safeguard Brazil's immense land border with ten of the South American countries. The collection of satellite images is used for analyzes involving the recognition of paths that can be taken in the country. A technological trend is the periodic updating of the images to identify changes in the terrain. The analysis of the images allows monitoring of traffic routes known by the authorities, as well as identifying new routes. Because of their characteristics, satellite images allow, with good precision, the calculation of the distances traveled on each road segment, official or otherwise, and the estimation of the maximum speed that vehicles can travel according to the characteristics observed for the roughness and sinuosity of the road. It is considered unfeasible to observe the Brazilian borders with almost 17 thousand kilometers in length using only the military force. The authorities recognize the need to use equipment such as radios, antennas, radars, film cameras, X-ray sensors, UAVs, etc. to improve surveillance of these borders. Even so, the improvement of the information system speeds the planning of traffic control actions. The illicit drugs reaching at consumer center puts a flag in the information system. The combinations of these flags are triggered, and a control plan is mitigated. The more intelligence is used in this system, the greater the success of actions to combat illicit products.

© 2019 The Franklin InstituteThis paper deals with a non-ideal system with memory by possessing a fractional damping term. The system is characterized by additional cubic nonlinearity. Based on the time series form of the numerical simulations of this non-ideal model, the nonlinear dynamical response of the system is investigated. A DC electric motor with limited power supply driving by an unbalanced rotating mass provides the non-ideal excitation. To distinguish between periodic and non-periodic behaviors, they are used three different mathematical tools, which are the 0–1 test, scale index and wavelet technique. The response of the considered system is investigated with respect to the fractional damping derivative term and the voltage applied in the DC motor, which is considered as a control parameter. Numerical results showed that, the scale index, 0–1 test and the wavelet transform technique defined very accurately the periodic and non-periodic motions.

© 2019, Krishtel eMaging Solutions Private Limited.Objective: This paper presents a systematic approach to quantify the uncertainties that influences directly the design of a Piezoelectric Vibration Absorber applied to shell structures with arbitrary shape, normally employed in automotive body structures. Methodology: Sensitivity and spectral analyses are performed to study the impact of randomness in the optimal piezoelectric patch implementation in automotive structures. The randomness arising from the manufacturing process of the mechanical structure, such as stamping spring back effects, as well as in the boundary conditions, is considered in the analyses, likewise the effects of variability during the positioning process for piezoelectric patches. The effects of the inherent uncertainties in the dynamic behavior of the mechanical structure, the optimal electromechanical coupling coefficient and the piezoelectric vibration absorber attenuation are presented. Results: The present paper has the advantage of indicating the loss in the vibration attenuation when Piezoelectric Vibration Absorbers are used in arbitrary shape structures, such as automotive hoods, fenders and doors. The Dynamic Vibration Absorber deterministically optimized provides an attenuation of approximately 18 dB in the theoretical model. However, losses of 5 dB in the attenuation can be obtained when the uncertainties are taken into account, and can reach up to 10 dB when the temperature effects are involved, representing more than 50% loss in attenuation for real applications, such as automotive body structures.

© Springer Nature Switzerland AG 2020.The aim of the current work is to discuss the dynamic buckling of a sandwich plate, to identify the response signals, and to find the relevant frequencies and amplitudes. The analyses consider the thin face-sheets of the sandwich plate which are subject to in-plane compressive load lower than the estimated critical value for the local buckling, but the plate is also subject to vibration in specific frequency causing variation of the load amplitude. The dynamic variation of the inplane stress stiffening changes the natural frequencies representing the out-of-plane modes dynamically. The nonlinear variation of the response for the out-of-plane displacements is analyzed with the continuous wavelet transform (CWT) method for characterizing this behavior.

© 2019, Brazilian Association of Computational Mechanics. All rights reserved.This work presents an analysis of an ocean wave energy harvesting system. This system is composed of a direct current (DC) power generator attached at the middle-top of a floating platform. A pendulum is connected to the generator’s shaft. It is considered that the ocean waves motion swings the platform in the vertical direction, which transfers energy to the pendulum, making possible to convert mechanical energy, induced by the ocean wave, into a rotational motion due the pendulum and after in electric energy due the generator. With the objective to optimize the harvested power, several analyses of the pendulum parameters, ocean wave amplitude and frequency were carried out. This work was based on the Brazilian’s coast characteristics. Numerical and experimental results were performed which shows the efficiency of the conversion of mechanical energy provided by the pendulum into electric power.

© 2019, Brazilian Association of Computational Mechanics. All rights reserved.In this paper a mathematical model was found, and numerical results obtained for the pendulum behavior when coupled to a DC generator. A simple pendulum is vertically excited on its support and consequently exhibiting oscillations and rotations. The motion of the pendulum spins the axis of a DC generator and inducing a current. The dynamic model involving the generator and the pendulum dynamics is developed and analyzed in this article. Bifurcation diagrams demonstrate doubling-period and saddle-node bifurcations with the chaos. The presence of chaos is verified by the Lyapunov exponents applied on the time series of the pendulum speed and position. Nonideal interactions of a DC motor with a pendulum by a crank-shaft-slider mechanism is analyzed and compared with an ideal excitation of the pendulum.

© 2019 Praise Worthy Prize S.r.l.-All rights reserved.– The addition of an anti-roll bar for the dynamics of a full-car has improved the safety and comfort of the passengers along the years. For lorries and buses, the anti-roll bar is a standard configuration with active suspension, and it is heavily used when at high-speed on bumpy roads or tight bends. The adoption of the anti-roll bar corrects the undesired behavior and softens the suspension improving the comfort, and the active bar guarantees a safety operation. However, its adoption on cars depends on the category and the expected road. In this paper, the difference between front and rear anti-roll bars with a Magnetorheological (MR) damper to improve safety on regular cars is investigated. A square wave is used as a burst along ten seconds to compare and contrast the efficiency of the system with front and rear bar combined and separated. The MR damper was added with SDRE (State Dependent Riccati Equation) control to provide an extra safety level. The numerical results show that the impact of a nonlinear anti-roll bar on the rear affects the stability. The influence of lag angles led to a more active control.

© 2019, The Society for Experimental Mechanics, Inc.The influence of the aircraft boundary conditions when setting a Ground Vibration test is always an issue. As aircrafts designs are becoming bigger is size and weight, the challenge in developing test set-ups for a successful GVT also increases. These challenges include not only the mechanical design of test devices, but also the goal to have the test performed in a shorter time, and with limited budget. Embraer decided years ago to have reliable device, which could duplicate the aircraft boundary condition, allowing at the same time fast test set-up and fast dismount. Even though, that design was modified and some opportunities had to be evaluated. This paper shows the conclusions of some variations on actual aircraft GVT set-ups, as well as studies performed in a small aircraft- like structure.

© 2018 Elsevier LtdModern high-performance aircrafts operate in regular flight regimes, in which the nonlinearities of the system directly influence the dynamical response of the aircraft. This work studies the dynamics of a fighter aircraft operating at high angles of attack of the wing. A mathematical model was developed deriving a system of nonlinear dynamical differential equations representing the longitudinal flight of the aircraft, considering the effect of the variation of the wind speed due to the atmospheric turbulence in the dynamic response of the aircraft. The dynamics of the aircraft is modeled as a two-degrees-of-freedom system, and the variation of the wind gusts is considered as a single-degree-of-freedom system. The analysis of the behavior of the system is carried out through the 0–1 test method to determine if the system is chaotic or periodic, which is applied in relation to the speed and angle of attack of the aircraft. As an object of study, all the considerations and analyses regarding the F-8 aircraft “Crusader” were took into account. A control technique is proposed in a nonlinear way, at which the angle of tail deflection is considered as a control parameter and projected using the method of control of the State Dependent Riccati Equations (SDRE) in order to stabilize the wing angle oscillations, considering critical regions of the behavior of the aircraft. Numerical simulations demonstrated the efficiency of the SDRE control, taking into account the comparison of the dynamics of the system with and without control, by using phase planes and parametric uncertainties, where the controller showed to be able to respond quickly and reliably to recover the aircraft from a stall situation.

© 2018 Elsevier LtdThis paper concerns the probabilistic modeling of uncertainties in structural dynamics. For real complex structures, the accurate modeling and identification of uncertainties is challenging due to the large number of involved uncertain parameters. In this context, the nonparametric probabilistic approach which consists in modeling globally the uncertainties by replacing the mass, stiffness and damping reduced matrices by random matrices is attractive since it yields a stochastic modeling for which the level of uncertainties is controlled by a small number of dispersion parameters. In its classical version, these random matrices are assumed to be independent. This assumption is valid (and proven) in absence of information concerning the dependence structure of these random matrices. In some situation, such as the presence of geometry uncertainties, this assumption is not valid any more and may yield an overestimation of the output levels of fluctuation. In this context, the present paper presents an extension of the classical nonparametric probabilistic to take into account a dependence between the random mass and stiffness matrices. This new modeling is illustrated on a beam structure for which the diameter presents spatial random fluctuations along the longitudinal direction.

© 2018, Springer Science+Business Media B.V., part of Springer Nature.This paper was written in honor of Prof. Viktor Olimpanovich Kononenko from Ukraine and takes into account reports of recent progress about non-ideal vibrating systems (NIS) published in the period from 2004 to 2017. New and old studies of NIS, with limited power supply (small DC motors or electrodynamical shakers), are usually used in laboratory tests, and therefore, the investigation of mutual interactions of driven and driving sub-system is very important. In this paper, main properties of NIS have been reviewed, such as the Sommerfeld effect, i.e., jump phenomena and the increase in power supply that is required by an excitation source operating near resonance; the possibility of saturation phenomenon occurrence, i.e., the transference of energy from higher frequency and lower amplitude to lower frequency and higher amplitude mode; and the existence of regular (periodic motion) and irregular (chaotic motion) behaviors, depending on the value of control parameters (voltage of a DC motor). This paper is divided into two goals: on the one hand will be treated about NIS and on the other hand will be provided an overview of the main engineering applications, analyzing their physical phenomena involved and the adequate methodologies to deal with them.

© The Authors, published by EDP Sciences, 2018.The studies on the so-called smart materials have grown in the last years due to the diverse possibilities that these materials can provide. These types of materials have the ability to respond to an external excitation, altering its physical form, and being able to be considered as actuators. Among these materials are the Shape Memory Alloys (SMA), several metal alloys that are able to memorize a shape and recover it after a deformation through an increase of its thermal energy. In this paper, an actuator consisting of an SMA wire is used to attenuate the vibration and Sommerfeld effect of a non-ideal type oscillator. The temperature control of the actuator was carried out through the application of an electric current in the wire. Results are presented for different currents, with the objective of investigating the temperature variation for vibration control applications. The results showed that it is possible to apply SMA actuators to the attenuation of the Sommerfeld Effect as well as in the reduction of the total vibration of the system.

© CSP - Cambridge, UK; I & S - Florida, USA, 2018.The aeronautical industry is continuously investigating nonlinear phenomena that might happen as it evaluates. Every dynamic system is subject to nonlinear behavior, especially if it is very complex like an aircraft. The nonlinearity nature, for these cases, can be aerodynamic, such as dynamic stall or shock waves, or structural, for example, freeplay or large displacements and high flexibility. This work will investigate a very flexible wing with high aspect ratio subjected to unsteady flow with a slender body at the wing tip to induce flutter. A flutter analysis is proceeded in order to evaluate the error between the computational results and the experiment. Since the linear flutter theory considers small displacements, nonlinear phenomena are expected. So the experiment time series shall be analyzed and this nonlinearity studied. The evaluation if the system presents chaotic behavior will be performed through the 0-1 test.

© 2018 SPIE.This paper discusses the detection of borders vulnerability through remote sensing. Remote sensors enable government to collect rapidly synoptically data from areas where the access is restricted. Accordingly, we propose a preliminary survey of Brazil's borders and its structures by using remote sensing techniques. The extent of the area is a difficulty, as Brazilian borders measures more than 15,000 kilometers in total and marks the limit to 10 countries. The methodology used can be summarized in the following steps: (i) choosing twelve sample-areas along Brazil's frontier vis-à-vis each neighboring country, focusing on the existent infrastructure; (ii) defining classes of land-use and land-cover based on the elements of visual image interpretation; (iii) creating an image interpretation key; (iv) measuring spectral signature from different targets. Results allow creating a hierarchical model of bodies related to the visual image interpretation element and spectral curves. This model has been divided between natural and anthropogenic features, it is compared the infrastructure, land-cover and land-use from distinct parts along the Brazilian land border. It is concluded there are serious problems of frontier governance due to Brazil's border is very heterogeneous.

© Springer International Publishing AG, part of Springer Nature 2019.This work describes the nonlinear identification applied to an aeroelastic pitch-plunge system using polynomial NARMAX model and a stability analysis. The apparatus is available and consists of a wing typical section with pitch and plunge degrees of freedom. The identification procedure aims to obtain the parameters for the mathematical model including the torsional stiffness as a quadratic polynomial function. The candidate structure to the polynomial model is obtained from discretization of a continuous-time state-space model and the predictions are obtained via the identification procedure using simulated data. The simulation is performed considering the aerodynamics with free stream velocity increased within an established velocity range which includes the flutter phenomenon. In future work, a data acquisition from the experimental apparatus will be performed. The NAR-MAX model indicates a polynomial function of fourth order for the nonlinearity and a stability analysis, discussed in this work, mapping the nonlinear regions.

© Springer International Publishing AG, part of Springer Nature 2018.This work presents the modeling and simulation of a manipulator robot with three degrees of freedom and considering its structures with rigid behavior. The concepts of kinematics for the mathematical deduction and the Lagrangian mechanics were used to obtain the dynamic models of the manipulator and the DC actuators with permanent magnet. Due to nonlinearity and dynamics characteristics, both the states observer and the control used were based on State Dependet Ricatti Equation (SDRE). The simulations made for constant performance parameters demonstrated the effectiveness of the optimal control applied to the manipulator and to the chosen DC actuator models. The applications of trajectories to the manipulator enrich the applicability of the project and the results obtained with the techniques chosen show his efficiency.

© The Brazilian Society of Mechanical Sciences and Engineering 2018.This study analyzes a nonlinear system with a crank–shaft–slider mechanism linked to a pendulum. The crank is powered by a DC motor that moves horizontally the pendulum pivot. The speed of the motor is influenced by the pendulum dynamics, reason for calling the system as nonideal. In literature, the vibration of the pendulum support by a crank–shaft– slider is generally considered as harmonic what neglects the real complexity of the mechanism. It is also common, for the crank speed or the excitation frequency to be considered constant, so a unique degree-of-freedom can take place. The novelty in this research is the analysis of the feedback effect of the pendulum over the crank speed and the complexity of crank–slider mechanism without approaching to a harmonic motion. Different types of motion occur as oscillations, rotations, and chaos. Results with different initial conditions are worked out and basins of attractions plotted. Chaos was obtained when small variations of parameters are made. The methods of analysis include phase portraits, time histories, bifurcations diagrams, and basins of attraction. The verification of chaotic phenomena is performed through the 0–1 test. By the end, the feedback control is applied using the method of Tereshko by altering the energy of the chaotic system, leading the pendulum to a limit cycle.

© 2017 Alexandre de Castro Alves et al.Renewable energy sources for vehicles have been the motivation of many researches around the world. The reduction of fossil fuels deposits and increase of the pollution in cities bring the need of more efficient and cleaner energy sources. In this way, this work will present the application of a compressed air engine applied to a bicycle. The engine is composed of two pneumatic cylinders connected to the bicycle wheel through a crank-connecting-rod mechanism. In order to control the velocity of the bicycle, a strategy of control composed of two controls was implemented: a feedback and a feedforward control. For feedback control, the State-Dependent Riccati Equation (SDRE) control and also a proportional-derivative (PD) control are considered, considering three cases for velocity bicycle variation: 10 km/h, 20 km/h, and 30 km/h. The equations of motion of the system were obtained through the Lagrangian energy method. Numerical simulations were performed in order to analyze the dynamics of the system and the efficiency of the controllers.

© The Authors, published by EDP Sciences, 2016.Fractional damping is appearing in different contexts in any systems with memory and hysteresis. Such damping is defined by a fractional derivative term, in contrary to classical viscous damping which takes into account the first order derivative. In this work, we characterize the nonlinear dynamics of a non-ideal Duffing system, with fractional damping using nonlinear dynamical tools. The non-ideal excitation originates from a DC electric motor with limited power supply driving an unbalanced rotating mass. The response of the system is investigated with the voltage as a control parameter. Numerical simulations show the occurrence of regular and non-regular motions, which are investigated via bifurcation diagramoccurrence diagrams and phase plane portraits.

© The Authors, published by EDP Sciences, 2016.Piezoelectric energy harvesting from a vertical geometrically nonlinear cantilever beam with a tip mass subject to transverse harmonic base excitations is analyzed. One piezoelectric patch is placed on the slender beam to convert the tension and compression into electrical voltage. Applying the homotopy analysis method to the coupled electromechanical governing equations, we derive analytical solutions for the horizontal displacement of the tip mass and consequently the output voltage from the piezoelectric patch. Analytical approximation for the frequency response and phase of the geometrically forced nonlinear vibration system are also obtained. The research aims at a rigorous analytical perspective on a nonlinear problem which has previously been solely investigated by numerical and experimental methods.

This paper overviews recent developments on some problems related to elastic structures, such as portal frames, taking into account the full interactions of the vibrating systems, with an energy source of limited power supply (small motors, electro-mechanical shakers). We include a discussion on fractional (rational) damping and stiffness effects on the adopted modelling. This was a plenary lecture, delivered in the event titled: Mechanics of Slender Structures, organized in Northampton, England from 21-22, September 2015.

Copyright © 2016 by ASME.In this paper we consider the flight dynamics of fighter aircraft at high angles of attack with uncertain aerodynamic coefficients. Stochastic parametric uncertainty is dealt with by employing spectral decomposition of the random variables by means of the generalized polynomial chaos expansion. We propose an optimal linear feedback strategy for the automatic pilot system to recover the aircraft from stall and provide acceptable dynamic response. Optimality of the proposed control law is proved by solving the Hamilton-Jacobi-Bellman equation and asymptotically stability of the controlled nonlinear aircraft model is guaranteed in the Lyapunov sense. Numerical results are verified with Monte-Carlo simulations.

Copyright © 2016 by ASME.In literature, the classic parametrically excited pendulum is vastly studied. It consists of a pendulum vertically displaced with a harmonic motion in the support while it oscillates. The chaos in this mechanism may appear depending on the frequency and amplitude of excitation in superharmonic and subharmonic resonance. The double pendulum is also well analyzed in literature, but not under parametric excitation. Therefore, this is the novelty in the present paper. The present analysis considers a double pendulum under a harmonic excitation following the same idea performed previously for a single pendulum. The results are obtained based on methods, such as, phase portraits, Poincaré sections and bifurcation diagrams. The 0-1 tests analyze the presence of chaos while the parameters are varied. The dimensionless parameters take into account the excitation frequency and amplitude as mentioned for the classic parametric pendulum. In this case, we have the particular characteristic that the two pendulums have the same length, the same mass and the same friction coefficient in the joints. The types of motion observed include fixed points, oscillations, rotations and chaos. Results also demonstrated that there was a self-synchronization between these pendulums in ideal excitation.

This study investigates forced nonlinear vibrations of a simply supported Euler-Bernoulli beam on a nonlinear elastic foundation with quadratic and cubic nonlinearities. Applying the homotopy analysis method (HAM) to the spatially discretized governing equation, we derive novel analytical solutions and discuss their convergence to present nonlinear frequency responses with varying contributions of the nonlinearity coefficients. A comparison with numerical solutions is conducted and nonlinear time responses and phase planes are compared to the results from linear beam theory. The study demonstrates that apart from nonlinear problems of free vibrations, HAM is equally capable of solving strongly nonlinear problems of forced vibrations.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Nonlinear aeroelastic phenomena is continuously investigate in aeronautical researches. The nonlinearity nature, for these cases, could be aerodynamic, such as dynamic stall or shock waves or structural, for example, free play or large displacements due to high aspect ratio and high flexibility. This work will investigate a very flexible wing with high aspect ratio subjected to unsteady flow. A flutter analysis is proceeded in order to evaluate the error between the computational result and the experiment. Since the linear flutter theory consider small displacements, it is expected a nonlinear phenomena. In this case, the experiment time series is analyzed in order to understand this nonlinearity and a 0-1 test is performed to evaluate if the system has chaotic behavior.

© 2016, Brazilian Association of Computational Mechanics. All rights reserved.This study analyzes the fourth-order nonlinear free vibration of a Timoshenko beam. We discretize the governing differential equation by Galerkin’s procedure and then apply the homotopy analysis method (HAM) to the obtained ordinary differential equation of the generalized coordinate. We derive novel analytical solutions for the nonlinear natural frequency and displacement to investigate the effects of rotary inertia, shear deformation, pre-tensile loads and slenderness ratios on the beam. In comparison to results achieved by perturbation techniques, this study demonstrates that a first-order approximation of HAM leads to highly accurate solutions, valid for a wide range of amplitude vibrations, of a highorder strongly nonlinear problem.

Copyright © 2015 SAE International.The combustion engines evolution leads the engine manufacturers look for developments focused on downsizing, more powerful, lighter, with great fuel consumption and less noisy. With special attention to NVH, specifically to vibration issue, this work aims at studying the influence of mass balancer and inertia forces coming from engine components on internal combustion engine dynamics supported by vibration dampers. For mass balancer study several experimental analyses were performed in a dynamometer. The conclusions are obtained by comparison between measured engine displacements with and without mass balancer. In order to study the influence of inertia forces from engine internal components, a mathematical model was developed. In this model the inertia forces act on a rigid body, supported by four vibration dampers and six degrees of freedom. Some modifications are made on engine internal components such as mass and geometry, observing their influence on internal combustion engine dynamics. The mathematical model is validated by comparison against experimental analyses.

This paper presents the design process and measurement results of a shunted piezoelectric isolator, which can be a good compromise between a solely passive and an active isolator. The system will be used for the reduction of the vibration transmission between two idealized panels of a plane fuselage. During the design process, numerical models of both, the panel structure and the shunted isolator, are used in order to derive reduced state-space matrices. Based on modal superposition, the numerical models describe the dynamic behaviour of the components and are integrated into a simulation environment of the holistic system. The required modal data is derived from experimental and numerical modal analyses of the panel. By means of an analytical description, the geometry of the shunted piezoelectric isolator is automatically optimized to defined goal parameters. Applying an impedance-admittance simulation approach, both the isolator and the shunt circuit are modeled. Using this simulation environment, the configuration and the performance of the shunt can be investigated and adjusted. After hardware realization of the shunted isolator, it is examined in a test setup. The results from test measurements are compared to simulation results of the system. Finally, two shunted isolators are placed between a fuselage panel and an ideal mass. Measurement results show the vibration reduction potential of the semi-passive system in addition to the solely passive isolation effect. This paper indicates the feasibility of shunted piezoelectric elements in addition to the passive isolation system. Furthermore an effective preliminary design strategy for the layout of shunted piezoelectric isolators is presented and compared to measurement results.

The variations in the dynamic behavior of structures can be modeled by finite elements with the inclusion of uncertainties as parametric variations of the input data. Parametric models are not always feasible, mainly due to the high computational cost required for the numerical solution. In this work, uncertainties are applied directly to the global stiffness, mass and damping matrices of the finite element model using a nonparametric approach by means of the Random Matrix Theory. The definition of the randomness level for the problem requires a prior knowledge of the result dispersion generated by the uncertainties of the input parameters, what is often not available. The results dispersion is then estimated through a parametric analysis in the low frequency range, which is feasible due the coarser finite element mesh required to solve the lower order vibration modes. After the model calibration, the nonparametric model is used to predict the dynamic behavior of the structure throughout the frequency range of interest. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.

One of the existing challengers on the aircraft design is the cabin internal noise reduction. In this direction, this work emphasizes the transmission path problem taking into consideration vibration dampers for the structure-borne energy isolation between the fuselage and the aircraft interior. In general, simplified models are not able to predict the damper performance at mid and high frequencies, since they do not take into account the damper internal resonances. A finite element model is employed to assess a typical aeronautic damper dynamic behavior. Different approaches and complexity of the damper are modeled, resulting in distinct responses depending on the frequency of concern. In the high frequency range where the solid rubber modes are concentrated, the great number of plate modes causes difficulties in identifying the damper internal dynamic influence in whole system response. At high frequency it is difficult to apply the finite element method, due to its deterministic response, and since it points out the presence of local modes. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.

In the aircraft industry a great practical relevance is given to the extensive use of vibration dampers between fuselage and interior panels. The proper representation of these isolators in computer models is of vital importance for the accurate evaluation of the vibration transmission paths for interior noise prediction. In general, simplified models are not able to predict the component performance at mid and high frequencies, since they do not take into account the natural frequencies of the damper. Experimental tests are carried out to evaluate the dynamic stiffness and the identification of the material properties for a damper available in the market. Different approaches for its modeling are analyzed via FEA, resulting in distinct dynamic responses asfunction of frequency. The dynamic behavior, when the damper natural modes are considered jointly with the high modal density of the plate that represents the fuselage, required the averaging of results in the high frequency range. At this aim, the statistical energy analysis is then used to turn the comparison between models easier by considering the averaged energy parameters. From simulations, it is possible to conclude how the damper natural modes influence the dynamic response of aircraft interior panels for high frequencies.

This work presents the results of the modal analysis performed during the ground vibration testing of a testbed originally designed by the Group for Aeronautical Research and Technology in Europe (GARTEUR). The model testing brought challenges in determining modes with very close frequency values, which were detected independently of the excitation signal. A modal validation process was carried out in order to identify these close-spaced modes as well as their dynamic characteristics. The reliability of the experimental modal model was verified by modal assurance criterion calculations between the experimental data and validated by comparison with a finite element model. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

A three-layer finite element model for the vibration analysis of sandwich plates with laminated composite face sheets is evaluated. In the model the face sheets are represented as Reissner-Mindlin plates, and the core is modeled as a three-dimensional continuum. This representation allows accurate modeling for a wide range of core types. The three-dimensional problem is reduced to two dimensions by analytical through-thickness integration of the energy expressions for the evaluation of mass and stiffness matrices. The results from this model are compared to finite element results based on solid elements, classical sandwich analysis, and classical plate theory. The objective in the work is to compare natural frequency and mode shape predictions using these models for a broad range of core stiffness. When large differences between face sheet and core stiffness are present, it is illustrated that traditional laminate theories yield significant inaccuracy. Moreover, unlike plate models, the present theory is also capable of representing a variety of three-dimensional boundary conditions. Furthermore, compared to solid models, the present laminated model avoids numerical problems as a result of three-dimensional element aspect ratio. Therefore, the present model provides a powerful general tool for the analysis of natural modes and frequencies of sandwich plates.

The free vibration behavior of thin composite plates with surface bonded piezoelectric patches including stress stiffening effects is investigated. A finite element formulation is presented, based on the Reissner-Mindlin theory and including non-linear strain-displacement relations, to formulate a free vibration eigenvalue problem in the presence of a geometrical stiffness matrix. The case of symmetric laminates and ideal linear behavior is assumed for the piezoelectric actuation. Due to the absence of membrane-bending coupling, in-phase applied voltages produce only inplane-induced piezoelectric stress resultants, which are assumed proportional to the applied voltages. Examples with numerical results for unconstrained plates equipped with piezoelectric actuators show that inplane induced stresses may significantly affect the free vibration behavior. © 2000 Elsevier Science Ltd.