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Christian Soize - One of the best experts on this subject based on the ideXlab platform.

  • Stochastic reduced-order model for dynamical structures with high Modal Density in the low-frequency range
    2017
    Co-Authors: Anas Batou, Christian Soize
    Abstract:

    The problem considered here concerns the construction of a stochastic reduced-order model for dynamical structures having a high Modal Density in the low frequency range. The classical methods used for the low-frequency range to construct a reduced-order model are not adapted in this case. We then use a recently proposed method which consists in constructing a basis of the global displacements and a basis of the local displacements by solving two separate eigenvalue problems. We then construct a stochastic reduced-order model using the basis of the global displacements and the contribution of the local displacements is taken into account using a probabilistic approach. The theory is presented and is applied to tube bundles structures which is are quasi-periodic structures for which the dynamical response is characterized by ensemble (global) displacements and more local displacements.

  • Stochastic reduced-order model for dynamical structures having a high Modal Density in the low frequency range
    2017
    Co-Authors: Adrien Arnoux, Anas Batou, Christian Soize, Laurent Gagliardini
    Abstract:

    This paper is devoted to the construction of stochastic reduced-order model for dynamical structures having a high Modal Density in the low-frequency range. We are particularly interested in automotive vehicles which are made up of stiff parts and flexible components. This type of structure is characterized by the fact that it exhibits, in the low-frequency range, not only the classical global elastic modes but also numerous local elastic modes which cannot easily be separated from the global elastic modes. To solve this difficult problem, a new approach is proposed for constructing a reduced-order computational dynamical model adapted to the low-frequency range. Model uncertainties induced by modeling errors in the computational model are taken into account using the nonparametric probabilistic approach which is implemented in the reduced-order model. The methodology is applied on a complex computational model of an automotive vehicle.

  • Stochastic reduced-order model for the dynamical analysis of complex structures with a high Modal Density
    2017
    Co-Authors: O. Ezvan, Anas Batou, Christian Soize
    Abstract:

    In this research, we are interested in predicting the dynamical response of complex structures characterized by the presence of numerous local elastic modes that appear immediatly in the low-frequency range. Where the Modal analysis method would classically provide a small-dimension basis constituted of global displacements for the construction of a robust and accurate reduced-order model adapted to the case of a low Modal Density, it is not the case considered here. Unlike global displacements, the local displacements are very sensitive to both parameters uncertainties and model uncertainties induced by modeling errors. This paper presents an original methodology which allows us to separate the admissible displacements space into the two algebraically independent subspaces of global and local displacements. This global/local separation allows a separated nonparametric probabilistic model of uncertainties to be implemented and thus allows the variabilities of the global displacements and of the local displacements to be controlled separately.

  • Uncertainty quantification in low-frequency dynamics of complex beam-like structures having a high-Modal Density
    International Journal for Uncertainty Quantification, 2017
    Co-Authors: Anas Batou, Christian Soize
    Abstract:

    The paper deals with the construction of a stochastic reduced-order model for beam-like dynamical structures having a high Modal Density in the low-frequency range for which the classical methods used to construct a reduced-order model are not adapted. We then use a method recently proposed which consists in constructing a basis of the global displacements and a basis of the local displacements by solving two unusual eigenvalue problems. The stochastic reduced-order model is then construct using the basis of the global displacements. The contribution of the local displacements is taken into account in the reduced-order model using a statistical approach. The theory is presented and is applied to a computational model of fuel assemblies for which the dynamical response must be characterized in terms of global displacements.

  • Reduced-order model for the dynamical analysis of complex structures with a high Modal Density
    2014
    Co-Authors: O. Ezvan, Anas Batou, Christian Soize
    Abstract:

    The low-frequency (LF) band is classically characterized by the presence of relatively well separated resonances associated with global elastic modes (non local elastic modes). In this work, we are interested in predicting the dynamical response of complex structures presenting several structural scales (for instance, the presence of flexible panels connected to a stiff master structure). For such structures, a high Modal Density can be observed in the low- and in the medium-frequency bands. This high Modal Density for the low-frequency band is not the usual case considered by the Modal analysis which would require a large number of elastic modes to represent the response with a good accuracy. In this context, a new methodology is introduced for constructing a small-size reduced-order basis adapted to span the global displacements space.

Rui Zhao - One of the best experts on this subject based on the ideXlab platform.

  • Modal Density and mode counts of sandwich panels in thermal environments
    Composite Structures, 2016
    Co-Authors: Jingyong Han, Rui Zhao
    Abstract:

    Abstract A theoretical model for calculating the Modal Density and mode counts of sandwich panels with composite face sheets in thermal environments is presented. Governing equations are derived by applying the Hamilton’s principle based on an improved ordinary sandwich panel theory. Modal Density and mode counts are calculated using the wavenumber space integration with simply supported and clamped boundary conditions taken into consideration. The accuracy of the proposed model is verified by the finite element model. Thermal effects of both thermal stresses and temperature-dependent material properties on Modal Density and mode counts are investigated for an aluminum honeycomb sandwich panel with simply supported and clamped boundary conditions. Results indicate that the Modal Density and mode counts increase with the increment of the temperature. Both of the two effects should be considered in the calculation of the Modal Density and mode counts of sandwich panels in thermal environments. The proposed model has a wider application scope and can contribute to the prediction of vibration response of sandwich panels in the high frequency range.

  • Modal Density of sandwich panels based on an improved ordinary sandwich panel theory
    Composite Structures, 2015
    Co-Authors: Jingyong Han, Rui Zhao
    Abstract:

    Abstract Modal Density of sandwich panels with composite face sheets and orthotropic core is presented based on an improved ordinary sandwich panel theory. The governing equations are derived by applying the Hamilton’s principle, where in-plane rigidity of the core is considered and the material and reference axes are not limited to be identical to each other. Modal Density is obtained using wavenumber space integration, and the effects of boundary conditions on both Modal Density and mode counts are also studied. The accuracy of the proposed models is validated by comparing with the existing Modal Density expressions, piecewise shear deformation theory and finite element models. Parametric studies are performed in order to investigate the influence of the ply angle of face sheets and the core, in-plane rigidity of the core, transverse shear rigidity and boundary conditions on Modal Density. The proposed Modal Density formula has a wider application scope and will be beneficial to the predication of sound transmission and radiation of sandwich panels.

K. Renji - One of the best experts on this subject based on the ideXlab platform.

  • Modal Density and critical frequency of composite panels considering transverse shear deformation and rotary inertia
    Journal of Vibration and Control, 2020
    Co-Authors: K. Renji
    Abstract:

    In this work, expressions for estimating the Modal Density, speed of the bending wave, critical frequency and coincidence frequency of panels are derived considering orthotropic properties of the f...

  • Modal Density of thin composite cylindrical shells
    Journal of Sound and Vibration, 2016
    Co-Authors: S. Josephine Kelvina Florence, K. Renji
    Abstract:

    Abstract Modal Density is an important parameter in Statistical Energy Analysis (SEA) based response estimation. Many space structures use composite cylinders. Modal densities of such structural elements are not reported. In this work an expression for Modal Density of composite cylindrical shells is derived. Its characteristics and sensitivity to various parameters are discussed. The frequency at which the Modal Density has a maximum is derived. Modal densities of typical composite cylinders are obtained. It is shown that computing Modal Density considering an equivalent isotropic cylinder can lead to significant errors.

  • EXPERIMENTAL Modal DENSITIES OF HONEYCOMB SANDWICH PANELS AT HIGH FREQUENCIES
    Journal of Sound and Vibration, 2000
    Co-Authors: K. Renji
    Abstract:

    The model Density of a structure can be experimentally determined from the real part of its driving point admittance. Due to the impedance of the impedance head and the attachment elements, the measured admittance values can be different from the actual driving point admittance, especially at higher frequencies. A correction factor is usually applied to take into account this effect. It is seen that beyond certain frequency, the Modal Density of honeycomb sandwich panels obtained experimentally using this technique reduces with frequency though the theoretical estimates increase with frequency. This anomaly is investigated in this study. It is found that though the parameter of interest is the real part of the admittance, correction has to be applied considering both real and imaginary parts of the measured admittance. By doing so, it is seen that the experimental Modal Density values match well with the theoretical results.

  • Modal Density OF COMPOSITE HONEYCOMB SANDWICH PANELS
    Journal of Sound and Vibration, 1996
    Co-Authors: K. Renji, P.s. Nair, S. Narayanan
    Abstract:

    Honeycomb sandwich panels with composite face sheets are widely used in spacecraft applications. It is necessary to obtain the Modal Density of such panels to study their behaviour under acoustic excitation. The governing differential equation, with consideration of the shear flexibility of the core, is derived. From this equation the expression for the Modal Density is derived. Experimental results for a typical panel are also presented. These results match well with those obtained from theory.

Jan Swevers - One of the best experts on this subject based on the ideXlab platform.

  • A novel design strategy for iterative learning and repetitive controllers of systems with a high Modal Density: Theoretical background
    Mechanical Systems and Signal Processing, 2010
    Co-Authors: Gregory Pinte, Bert Stallaert, Paul Sas, Wim Desmet, Jan Swevers
    Abstract:

    This paper discusses the design and application of iterative learning control (ILC) and repetitive control (RC) for high Modal Density systems. Typical examples of these systems are structural and acoustical systems considered in active structural acoustic control (ASAC) and active noise control (ANC) applications. The application of traditional ILC and RC design techniques, which are based on a parametric system model, on systems with a high Modal Density has several important drawbacks: the design procedure is complex, the controllers require much computational power and the robustness of the controllers is low. This paper describes a novel strategy to design noncausal ILC and RC filters, which is especially suited for high Modal Density systems. Since it does not require a parametric system model, the novel strategy avoids several drawbacks of the traditional techniques: no cumbersome parametric model estimation is required; the ILC and RC controllers are robust to small changes of the poles and zeros of the controlled system; and the complexity of the ILC and RC control filters is restricted. A crucial element in the proposed strategy is the noncausal filtering in the ILC and RC controllers, which requires the availability of a trigger signal to announce a new ILC trial or RC period in advance. A numerical validation on a simulation model proves the potential of the developed strategy.

  • A novel design strategy for iterative learning and repetitive controllers of systems with a high Modal Density: Application to active noise control
    Mechanical Systems and Signal Processing, 2010
    Co-Authors: Bert Stallaert, Gregory Pinte, Paul Sas, Wim Desmet, Jan Swevers
    Abstract:

    This paper describes the application of a novel design strategy for iterative learning and repetitive controllers for systems with a high Modal Density, presented in the companion paper, on two experimental case studies. Both case studies are examples of active structural acoustic control, where the goal is to reduce the radiated noise using structural actuators. In the first case study, ILC is used to control punching noise. An electrodynamic actuator on the frame of the punching machine is driven by the ILC algorithm which takes advantage of the repetitiveness of the consecutive impacts to reduce noise radiation. In the second case study, an RC algorithm is used to control the noise radiated by rotating machinery, which is often mainly periodic. A piezoelectric actuator incorporated in the bearing is driven by the RC algorithm which is capable of reducing harmonics of the rotational frequency of the shaft. Both applications show the practical usefulness of the novel design strategy.

Robin S. Langley - One of the best experts on this subject based on the ideXlab platform.

  • A transient hybrid FE-SEA method
    2018
    Co-Authors: David Hawes, Robin S. Langley, T. Butlin, Y Ishii
    Abstract:

    © INTER-NOISE 2018 - 47th International Congress and Exposition on Noise Control Engineering: Impact of Noise Control Engineering. All rights reserved. The hybrid approach coupling Statistical Energy Analysis (SEA) and the finite element method has become a prominent technique for analysing structures under steady-state loads in the ‘mid-frequency’ range where some components behave in a deterministic manner with low Modal Density and others in a statistical manner with high Modal Density. In this paper, the method is extended from its current steady-state capability to provide calculation of a structural response under impulsive and time-varying loads. Similar to the steady-state method, a system is split into components with low Modal Density that are modelled using the finite element approach and statistical components with high Modal Density that are modelled as SEA subsystems. An evolutionary spectrum approach based on the Priestley description of random processes is applied to model the response of both the SEA and deterministic components which are coupled by considering a power balance between the subsystems and using an amended form of the diffuse field reciprocity relationship that accounts for the build-up of a reverberant field following an impulse. Results from the method are compared against finite element simulations for systems involving coupled plates and provide strong validation.

  • Impact dynamics in cylindrical shells
    2013
    Co-Authors: Mauro Caresta, Robin S. Langley, Jim Woodhouse
    Abstract:

    This work presents an asymptotic approach to predict the response of random structures to an impact in the time domain. The theory is based on the calculation of an asymptotic impulse response function by knowledge of the Modal Density of the structures involved in the impact. The approach presented predicts a mean response on an ensemble of structures with uncertainty on properties and boundary conditions. Both numerical and experimental results are presented. The theory has been successfully applied to thin and thick cylinders; in the latter case a Modal Density has been developed that differs from the classical case available for thin cylinders.

  • Comparison of two nonparametric models of uncertainty in structural dynamics
    2012
    Co-Authors: Julien Legault, Jim Woodhouse, Robin S. Langley
    Abstract:

    This study compares the nonparametric model of random uncertainty introduced by Soize [Prob. Eng. Mech. (2000), vol. 15] with a randomization using randomly placed point masses for a thin plate in bending. It is shown that, contrary to the randomization using point masses, the nonparametric approach can alter the average Modal Density and the underlying dispersion relation of the system. This suggests that the nonparametric approach can in some sense account for the unknown presence of terms of higher or lower order in the governing differential equation, but that its predictions may conflict with certain prior expectations about the system such as its average Modal Density.

  • Response probability distribution of built-up vibro-acoustic systems.
    The Journal of the Acoustical Society of America, 2012
    Co-Authors: Edwin Reynders, Robin S. Langley
    Abstract:

    The vibro-acoustic response of built-up structures, consisting of stiff components with low Modal Density and flexible components with high Modal Density, is sensitive to small imperfections in the flexible components. In this paper, the uncertainty of the response is considered by modeling the low Modal Density master system as deterministic and the high Modal Density subsystems in a nonparametric stochastic way, i.e., carrying a diffuse wave field, and by subsequently computing the response probability Density function. The master system’s mean squared response amplitude follows a singular noncentral complex Wishart distribution conditional on the subsystem energies. For a single degree of freedom, this is equivalent to a chi-square or an exponential distribution, depending on the loading conditions. The subsystem energies follow approximately a chi-square distribution when their relative variance is smaller than unity. The results are validated by application to plate structures, and good agreement with Monte Carlo simulations is found.

  • On the response distribution of nonparametric probabilistic models for mid- and high-frequency analysis
    2012
    Co-Authors: Edwin Reynders, Julien Legault, Robin S. Langley
    Abstract:

    The local response of built-up structural and acoustic systems, consisting of stiff components with low Modal Density and flexible components with high Modal Density, may be very sensitive to uncertainty in spatial variations in the geometry, material properties, and boundary conditions of the flexible components. In this work, this uncertainty is considered by modeling the low Modal Density master system as deterministic and the high Modal Density subsystems in a nonparametric stochastic way, and by subsequently computing the response probability Density function. The probability distribution of the master system's displacement degrees of freedom and the total subsystem energies is numerically computed by assuming that the distribution of the eigenvalues and eigenvectors of a decoupled subsystem correspond to those of a Gaussian Orthogonal Ensemble matrix. This approach is extensively validated by application to structures, consisting of thin plates attached to stiff structural components. Good agreement between the predicted probability distributions and the results of detailed Monte Carlo simulations is found. The validation examples also illustrate that the numerical procedure agrees better with the Monte Carlo simulations than a closed-form evaluation of the response probability Density, which requires additional assumptions. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.