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ispartof: pages:2203-2217 ispartof: Proceedings of ISMA2020 pages:2203-2217 ispartof: ISMA-USD Noise and Vibration Engineering Conference 2020 location:Leuven date:7 Sep - 9 Sep 2020 status: Published online

Most companies do not take assembly aspects of a product into account during the early design process. This often results in designs that are optimal from a performance point of view, but are hard or impossible to assemble. This leads to numerous design changes late in the product development process, causing significant extra costs. To solve this issue, a co-optimization framework is developed that takes into account the assemblability as a constraint during the performance optimization. The presented framework is applied to minimize the mass of a gearbox with constraints on the axle stiffness and the first resonance frequency of the housing, while also respecting a set of assembly rules. The assembly rules take into account the complexity of the assembly, for instance the number of unique standard parts used and geometric properties like weight and dimensions.In each iteration, the performance of the design is evaluated with a parametrized finite element model, while a numerical assemblability score of the current design is estimated based on the assembly STP file. The obtained performance and assemblability metrics and their combination serves as a constraints and objective function for the design optimization. ispartof: pages:2753-2762 ispartof: Proceeding of ISMA2020 including USD2020 pages:2753-2762 ispartof: ISMA-USD Noise and Vibration Engineering Conference 2020 location:Leuven, Belgium (Virtual event) date:7 Sep - 9 Sep 2020 status: published

Double panel partitions with a foam core suffer from a poor sound transmission loss at the mass-spring-mass resonance frequency. This paper investigates the use of vibro-acoustic resonant metamaterials as a solution to improve the acoustic insulation performance for this vibro-acoustic problem while adding only 8% of mass to the complete double panel. To design the metamaterial, unit cell analysis is applied to calculate dispersion curves and predict the stop band behaviour, while the sound transmission loss is predicted with Heckl’s model extended with the equivalent dynamic mass of the metamaterial. The dynamic mass is obtained from the dispersion curves analysis, which allows to take into account complex and realizable resonator geometries. The designed metamaterial double panel is realized and its experimentally measured insertion loss shows a strong improvement around the mass-spring-mass resonance of the original double panel. The predicted insulation performance agrees well with the measured performance, validating the proposed method. ispartof: pages:3111-3123 ispartof: Proceedings of ISMA 2018 pages:3111-3123 ispartof: International Conference on Noise and Vibration Engineering - ISMA 2018 location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. A transfer admittance relation is commonly used in frequency domain linear acoustics to represent elements, characterized by a geometrical length scale which is much smaller than the acoustic wavelength, in an efficient way. However, the equivalent time domain formulation involves costly convolution integrals. This paper presents an efficient time domain formulation: using a rational approximation of the transfer admittance coefficients, formulated in frequency domain, a recursive formulation is obtained with significantly reduced memory and CPU requirements. This formulation has been implemented in a time domain solver for the linearized Euler equations, using a discontinuous Galerkin spatial discretization and a Runge-Kutta time integration scheme. The methodology is successfully validated on two benchmark cases: a lined duct with a grazing flow and a simplified automotive muffler with a perforated duct. ispartof: pages:571-584 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA 2018) pages:571-584 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

This paper presents a dispersion-based method for identifying visco-elastic material properties by minimizing the residue between data of virtual experiments and data based on a viscoelastic model through the use of surrogate modeling. The dispersion data retrieved from a virtual experiment of a finite beam with constrained layer damping (the real and imaginary part of the wavenumber) is fitted with numerical dispersion data through an optimization scheme, which can be computationally expensive. In order to alleviate this issue, attention has been focused on the construction of a surrogate model that makes the optimization scheme cheaper without loosing much accuracy in the prediction. This paper uses an interpolation method based on radial basis functions. Once the surrogate model is constructed, the viscoelastic parameters can then beidentified and results are compared to the reference parameters. no ISSN ispartof: pages:4691-4705 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) pages:4691-4705 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven. Belgium date:17 Sep - 19 Sep 2018 status: Published online

In many mechanical applications, a design optimization is performed on the frequency response functions of the mechanical system. In this work, a novel model reduction technique is explored for the parametric analysis of the frequency response functions of dynamical mechanical systems. This approach entails two novel aspects. First, a super-local reduced order basis is introduced which allows models of much lower order compared to models obtained with single, frequency independent reduced order basis approaches. Secondly, a novel hyper-reduction scheme is introduced which selects a subset of the considered, discrete frequency domain and computes the corresponding interpolation matrix. During the online phase, the full frequency domain response is reconstructed by interpolating between these sampled frequency lines. The proposed approach is validated numerically on an academic mass-spring-damper system and shows promising results. ispartof: pages:2461-2468 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA2018) and the International Conference on Uncertainty in Structural Dynamics (USD2018) pages:2461-2468 ispartof: ISMA 2018 International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

In order to fully exploit available computer aided engineering (CAE) models for modern mechatronic systems they need to be merged with measurement data in order to obtain reliable Digital Twins. These Digital Twins are evolving to become instrumental assets that accompany the product throughout its lifetime, enabling virtual quality assurance, virtual sensing and model-based control. However, in mechatronics, the typical CAE design models are relatively expensive physics based models which cannot be directly used throughout the entire lifecycle as Digital Twins. Model order reduction approaches for these nonlinear dynamic applications allow to reduce the computational cost sufficiently for use in a Digital Twin setting. This work gives an overview of nonlinear dynamics engineering applications in modern mechatronics products design, and demonstrates the role of (novel) MOR techniques in the design engineering process. ispartof: pages:2415-2429 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA2018) and the International Conference on Uncertainty in Structural Dynamics (USD2018) pages:2415-2429 ispartof: ISMA 2018 International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

This paper investigates the broadband vibro-acoustic and dynamic behavior of different structures, such as flat and curved panels and cylindrical shells. The aim of this work is to investigate propagation and dispersion features through the analysis of the wavenumber domain. The technique used to investigate the vibro-acoustic behavior is a wave propagation based technique, implemented to obtain the propagative and evanescent waves using a harmonic force excitation. The employed techniques are used to obtain the harmonic displacement field, given as primary input for the wavenumber domain analysis. To deeply investigate the dispersion features, a Discrete Fast Fourier Transform (DFFT) technique is used. The whole displacement field could be obtained by experimental tests or by numerical simulations; in our case, it is calculated using a classical Finite Element Analysis (FEA), by a commercial Finite Element package, or by an in-home algorithm, developed in a commercial numerical computing software. no ISSN ispartof: pages:4627-4636 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) pages:4627-4636 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: Published online

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. The vibration and noise amplitude levels at resonance frequency depends on the amount of damping present in the component. In this work, damping enhancement is achieved through a cold working process like shot peening. The residual stress measurements-using X-ray diffraction technique-and vibro-acoustic property measurements of a sheet metal plate is carried out in the original condition. The residual stress measurements are repeated on the plate after subjecting it to shot peening and found considerable increase in the stress levels in both longitudinal and transverse directions. The experimental modal testing of the plate confirmed the increase in the damping values of the system. The sound pressure levels of the shot-peened plate have reduced significantly. A brief simulation study of shot peening using ABAQUS is carried out to establish a transfer function between residual stress and shot peening process parameters. Further, attempts will be made to understand the relationship between residual stresses and damping in the system. ispartof: pages:4559-4569 ispartof: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics pages:4559-4569 ispartof: International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) location:BELGIUM, Leuven date:17 Sep - 19 Sep 2018 status: published

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. This paper presents an experimental study of the aeroacoustic characteristics of Helmholtz resonators. The two-port characterization technique is applied to compute the scattering properties of the resonators from measured pressure spectra. The onset of aeroacoustic instabilities is investigated using an acoustic power balance based on the linear scattering matrix formulation. The influence of the grazing flow velocity on the aeroacoustic instability onset is discussed. Additionally, the effect of the orifice dimensions is analyzed with two different configurations. The results offer a valuable database for the validation of computational techniques for the prediction of whistling onset in duct systems. ispartof: pages:601-611 ispartof: https://www.isma-isaac.be/ pages:601-611 ispartof: ISMA2018 location:Leuven date:17 Sep - 19 Sep 2018 status: Published online

Developing an accurate product model is a crucial task for the numerical simulation of the dynamic behavior of mechanical components. In this setting, this work considers the specific case of components manufactured through a deep drawing process. Because of the large deformations involved, a thickness variation is obtained in the final manufactured component with respect to the initial blank thickness, which has to be accounted for in order to have an adequate model for numerical analysis. Furthermore, the intrinsic variability of the process and local variations of the stiffness, due to plastic hardening and residuals stresses, give rise to nominally identical components with different dynamic properties, especially at high frequencies. Two simulation frameworks are considered in this study for the product model development: the first one is based on a purely numerical approach, where the dynamic simulation is performed on a model obtained from a finite element simulation of the forming process. The second one considers a reverse engineering framework, where the product model is computed by a surface reconstruction procedure starting from laser scan measurements on the manufactured component; this reverse engineering procedure can be realized either by (i) a triangular surface reconstruction that forms the starting point to obtain a finite element mesh of the component or by (ii) fitting a smooth B-spline surface on the point cloud data that can be used directly for the analysis employing the paradigm of isogeometric analysis (IGA). The different approaches are applied to predict the dynamic behaviour of an axis-symmetric deep drawn steel cup and are validated with experimental measurements. Finally, it is shown how a model updating procedure of the stiffness can be easily implemented in the framework of IGA, which can further improve the accuracy of the product model. no ISSN ispartof: pages:3605-3615 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) pages:3605-3615 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: Published online

Non-deterministic methods such as the random field approach suffer from the curse of dimensionality from computational burden of industrially sized models. The computational complexity increases at high dimensions due to increased time complexity of eigenvalue computations, leading to the Karhunen-Loéve series expansion becoming intractable. This makes the corresponding propagation routines to become inviable. A novel methodology is proposed for efficient propagation of a random field by tackling this problem from the discretization perspective. The method uses a twin-model that efficiently discretizes a random field on a coarse mesh grid using a KL expansion, which is then propagated on a high-dimensional grid of the Finite Element model. A two-dimensional model of moderate-dimensionality with 10000 elements is used to illustrate the numerical efficiency of this approach through a convergence study focusing on the resolution of the twin-model when applied in a dynamic analysis. The method is also well suited for higher dimensions. ispartof: pages:5111-5123 ispartof: Proceedings of International Conference on Uncertainty in Structural Dynamics pages:5111-5123 ispartof: International Conference on Uncertainty in Structural Dynamics location:Leuven, Belgium date:17 Sep - 18 Sep 2018 status: Published online

ISMA 2018, 28th Conference on Noise and Vibration Engineering, Leuven, BELGIQUE, 17-/09/2018 - 19/09/2018; International audience; Modal validation is an integral part of any modal analysis scheme. Recent advances in efficient variance computation of modal parameter estimates from the output-only subspace-based identification algorithms made the computation of variance feasible for the modal parameters, such as natural frequencies, damping ratios and mode shapes. One of the other practical modal indicators is Modal Assurance Criterion (MAC), for which uncertainty computation scheme is missing. This paper builds on the previous results using the propagation of the measurement uncertainties to estimates of MAC. The sensitivity of the MAC with respect to output covariances is derived using a first order perturbations and the uncertainties are propagated using the Delta method. The influence of the underlying mode shape scaling on both the uncertainty of mode shapes and MAC is investigated. The results are presented in context of operational modal analysis (OMA) of a spring mass system.

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. This paper proposes a method for the indirect measurement of wheel center loads which makes use of a suspension flexible multibody model and strain measurements on the suspension components. Wheel center loads are the loads acting at the center of the vehicle wheels and due to the interaction with the road. Those loads are the principal cause of damage to the vehicle structural integrity and hence are very important for durability analyses, but their direct measurement requires the use of expensive and intrusive dedicated measurement devices. By reusing available design simulation models and common sensors, the proposed method thus represents an appealing alternative to the direct measurement approach. After the presentation of the method, which is based on an augmented extended Kalman filter to perform the information fusion, validation results on a McPherson suspension test rig are reported. ispartof: pages:325-339 ispartof: Proceedings of ISMA2018 pages:325-339 ispartof: International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: Published online

© 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 this work, harmonic and temporal responses of structures composed of 1D periodic waveguides are computed using the wave finite element method framework (WFEM) in conjunction with model order reduction (MOR) methods. First, a model order reduction strategy at the unit cell level is introduced and extended to parametric model order reduction (PMOR) when the mesh does not depend of the interfaces. The method relies on a mode based MOR of the inner degrees of freedom of the unit cell combined with a wave based model order reduction of the interfaces' degrees of freedom by projecting them on a collection of wave shapes obtained through the inverse approach. A first example analyses the merits of the proposed PMOR. A second example exploits the MOR method to analyze guided-waves interactions with a 3D defect in the mid-frequency domain. The proposed methodology enables the computation of highly complex and detailed models while providing substantial time reduction when computations were already possible. no ISSN ispartof: pages:4663-4677 ispartof: Proceedings of the International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) pages:4663-4677 ispartof: International Conference on Noise and Vibration Engineering (ISMA 2018) location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: Published online

© Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. All rights reserved. Component-based TPA is a relatively new TPA approach that allows to characterize a structureborne source component independently from the receiver structure (as opposed to classical TPA) and to predict its behavior when coupled to different receivers. This approach would allow to frontload the development process and considerably increase the flexibility during the design process. However, there are a number of challenges affecting its applicability, such as a proper modelling of the coupling degrees of freedom at the interface, the difficulty to access the interface connection points and the conditioning of the equations. A number of innovative methods were developed to address these issues, that will be investigated by means of measurements on a laboratory test bench. A systematic analysis will be performed through which the accuracy and applicability of the component-based TPA will be analyzed and assessed. ispartof: pages:4131-4145 ispartof: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics pages:4131-4145 ispartof: ISMA 2018 - International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:17 Sep - 19 Sep 2018 status: published

In the traditional design of passive anti-roll tanks (ART), the energy associated with the tank fluid motion is dissipated. The work reported in this paper explores the possibility that this energy is instead harvested. It is analytically determined in the paper how the natural frequency and the damping ratio of a U-tube ART should be tuned to maximise the power absorbed by the tank assuming a perfectly flat spectrum of the moment representing the excitation of the ship by waves. It is found that this tuning also minimises the average kinetic energy of the ship roll. This is a result of the fact that the power input of the wave excitation moment into the ship plus tank system does not depend on how the ART is tuned. The power input into the ship plus tank system is found to be proportional only to the natural frequency of the ship roll to the power of four multiplied by the moment of inertia of the ship. Therefore, different tunings of the ART natural frequency and damping ratio only affect the distribution of the power dissipated by the ship roll damping and the power absorbed by the ART.

A methodology for evaluating the acoustic behaviour of two-port inhomogeneous media in experimentally unavailable thermal conditions is proposed. The method consists of an inverse estimation of the geometrical and material properties of the object at room temperature followed by a forced thermal input. The properties of interest for the inverse estimation are the spatially-varying cross-section and/or bulk properties. The underlying model relies on a transfer matrix approach, allowing for a representation of spatially inhomogeneous objects as piece-wise equivalent homogeneous fluids, while ensuring continuity conditions between successive elements. A model of non-stationary thermal conduction is used as a first approximation, where an integral formulation accounts for the cumulative effect of multiple homogeneous elements. In order to evaluate the validity of the extrapolation, a validation against a fully numerical simulation is presented in two cases, namely a simple expansion chamber and a complex muffler. QC 20190403

This paper presents a regularized nonlinear least-squares-based identification method for linear parametervarying (LPV) systems. The objective of the method is, on one hand, to obtain an LPV model the response of which as accurately as possible fits the measured response generated by the system to be identified. On the other hand, by introducing ℓ2,1-norm regularization of the model matrices the method prefers models with a dependency on the scheduling parameter that is as simple as possible. The optimal model is therefore one that satisfies both criteria. The experimental validation on a mechatronic XY-motion system shows that through ℓ2,1-norm regularization, a sparse model is obtained with a smoother evolution of its poles and zeros, compared to the model obtained without regularization. This is at the cost of only very limited loss of model accuracy. ispartof: pages:2797-2807 ispartof: Proceedings of ISMA 2016 pages:2797-2807 ispartof: International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:19 Sep - 21 Sep 2016 status: published

Recent years have seen a huge increase in the development and use of small unmanned aircraft, otherwise known as drones or Unmanned Aerial Vehicle (UAV). A lot of published research work focusses on new applications, control optimization and flight range maximization. However, there is very little published work that deals with a thorough structural vibration analysis of a typical UAV chassis. This paper discusses the experimental and numerical vibration analysis of a multirotor chassis. The paper provides an analysis of the main vibration sources affecting this UAV and an experimental modal analysis of the main structural components of the multirotor chassis. The resulting data is applied to a numerical modal analysis of the UAV chassis and allows, for instance, locating low-vibration regions where sensitive electronics should best be mounted. ispartof: pages:2329-2337 ispartof: Proceedings of ISMA 2016 International Conference on Noise and Vibration Engineering pages:2329-2337 ispartof: ISMA - International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:19 Sep - 21 Sep 2016 status: published

The aim of this paper is to investigate the possibility to detect defects in pipes based on wave-scattering in the audible frequency range. Therefore, the influence of a 1cm long defect extending in axial direction and a defect extending over a 12° angle in circumferential direction on the wave scattering in a DN80 steel pipe is investigated. At first the reflection and transmission of different incident wavemodes at these defects is studied using a hybrid wave and finite element/finite element formulation. To investigate the effect of finite dimensions, in a next step, FE calculations are performed on finite pipes, which are harmonically excited with a 0-order wavemode with dominant radial or longitudinal displacement, respectively. It is found that the wave scattering at the defect happens according to the scattering matrix prediction based on the hybrid WFEM/FEM method. Furthermore, the wave scattering can be magnified due to the resonance behavior of a finite structure, so that it gives a dominant contribution to the overall displacement, even though the scattering coefficient might be small. ispartof: pages:1147-1161 ispartof: PROCEEDINGS OF ISMA2016 INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING AND USD2016 INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS pages:1147-1161 ispartof: ISMA2016 location:Leuven date:19 Sep - 21 Sep 2016 status: published

For broadband active noise control applications with rapidly changing transfer paths, it is desirable to find algorithms with rapid convergence, fast tracking performance, and low computational cost. Recently, a numerically stable algorithm has been presented: a convex mixing fast-array RLS filter. The algorithm exhibits the fast convergence, tracking properties and the linear calculation complexity of the fast-array RLS sliding window filter with numerical stability. The algorithm assumes that deviations of the secondary path from the nominal value are small. If these deviations become significant then the model of the secondary path has to be updated in accordance with the real physical situation. In this paper we present results of a version of the algorithm with on-line adjustment of the secondary path model, using two mixing fast-array RLS filters, in which the first mixing filter minimizes a modified error signal while the second mixing filter minimizes the modeling error of the secondary path. ispartof: pages:105-112 ispartof: PROCEEDINGS OF ISMA2016 INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING AND USD2016 INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS pages:105-112 ispartof: International Conference on Noise and Vibration Engineering (ISMA) / International Conference on Uncertainty in Structural Dynamics (USD) location:Leuven, BELGIUM date:19 Sep - 21 Sep 2016 status: published

The knowledge of loads acting on machines and components is crucial in many application fields. Input estimation though is a very challenging inverse problem with which researchers have struggled over the last decades. Several issues related to ill-conditioning and ill-posedness are not sufficiently understood nor solved. This paper proposes an in-depth numerical study covering some of the aspects that can make the difference between a reliable and an unreliable force estimation. A states-input estimation algorithm for multiple force estimation is implemented as a linear augmented Kalman filter/smoother coupled with a reduced order model of a complex ill-posed mechanical structure, namely a twistbeam rear suspension. The influence of different noise levels, measurements scaling and time horizon used for the estimation is thoroughly analyzed. Finally, an observability-based optimal sensors placement strategy is implemented showing robustness improved accuracy of the estimated quantities. ispartof: pages:1741-1756 ispartof: In International Conference on Noise and Vibration Engineering (ISMA2016), pages:1741-1756 ispartof: ISMA location:Leuven date:19 Sep - 21 Sep 2016 status: published

This paper describes a synthetic turbulence reconstruction method based on filtering of the white noise field and convection of the particles by means of the Random Particle Mesh method (RPM) in three dimensions. For that purpose a Gaussian filter is derived from the Gaussian energy spectrum. The method is applied to simple threedimensional geometry. The parametric study is performed in order to analyse the sensitivity of the method to several computational parameters. The retrieved statistics of the flow is then compared to the analytical solution. The results of the research suggest an optimal choice of these parameters to obtain the accurate numerical solution. The parallel performance of the hybrid MPI-OpenMP implementation of the method is shown. ispartof: pages:363-372 ispartof: PROCEEDINGS OF ISMA2016 INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING AND USD2016 INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS pages:363-372 ispartof: ISMA-USD location:Leuven, BE date:19 Sep - 27 Sep 2016 status: published

Finite element analyses of vibro-acoustic systems are usually performed in the frequency domain, meaning that the obtained results cannot straightforwardly handle time-varying input signals. These limitations can be overcome by performing a time domain analysis of the finite element model. To reduce the calculation complexity needed for time integration a model order reduction technique is proposed. A time stable Krylov subspace reduction technique is derived for the coupled exterior vibro-acoustic problem case. The Sommerfeld radiation condition is taken into account by applying infinite elements on the boundary of the mesh. The application of time stable infinite elements leads to a potentially singular mass matrix. A method is developed that circumvents mass matrix inversion, which is based on a singular value decomposition. Combined with a special formulation of the system matrices, the proposed method is shown to preserve the stability of the full model. The resulting model order reduction procedure is applied on a numerical model of a loudspeaker. ispartof: pages:1277-1290 ispartof: Proceedings of ISMA 2016 pages:1277-1290 ispartof: ISMA 2016 location:Leuven date:19 Sep - 21 Sep 2016 status: published

In CAA the computation of the sound sources is typically the most time-consuming step. It is frequently based on unsteady CFD simulations, which can be expensive for large Reynolds number flows. In this context, the Random Particle-Mesh (RPM) method which is a stochastic approach to reconstruct the sources in time domain from a solution to the Reynolds-Averaged Navier-Stokes (RANS) equations is discussed with an aim to predict airfoil trailing edge noise. In this work the RPM method is used for generating synthetic turbulence in the wake of an airfoil and the statistics of the reconstructed fluctuations are compared with model statistics. Further some guidelines for determining the parameters used in the stochastic turbulence generation process are presented in addition to the guidelines presented in previous works. ispartof: pages:347-362 ispartof: PROCEEDINGS OF ISMA2016 INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING AND USD2016 INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS pages:347-362 ispartof: ISMA-USD location:Leuven, Belgium date:19 Sep - 27 Sep 2016 status: published

This paper quantifies the system damping of a offshore meteorological mast supported by a Mono Bucket foundation based on a long-term experimental campaign. The structure is located at Dogger Bank west, North Sea, and equipped with a measurement system monitoring acceleration, strain, inclination and sea surface elevation. Natural frequencies and corresponding damping ratios are assessed using different operational modal analysis techniques, enhanced frequency domain decomposition and stochastic subspace identification. Application and results from both methods are compared and discussed. Research shows that the total damping ratio of the lowest eigenmode is normally distributed with mean value of 1.11% of critical damping. Linear correlation between the damping ratio and the significant wave height is observed.

Precision engineering tasks require active isolation systems that are efficient especially at low frequencies. The limitations of such control systems include the resolution of the sensor used and the magnetic coupling between the sensor and the actuator. In order to bypass these limitations, inertial sensors using Michelson interferometer are being developed. A first prototype has been built and tested. It has been shown that it has a sub-nanometer resolution over a large frequency range, extending from 0.1 Hz to 100 Hz. To further improve the resolution, a new optical design will be presented in this paper. The elements of the setup are chosen to lower the noise of the whole system. Actually, two main sources of noise can be reduced. The first one is due to the optical components, inducing a phase shift which is converted into a displacement error. The second is a consequence of the pendulum movement of the piece/spring holding the moving mass. It couples the vertical translation and the rotation. By choosing correctly the optical components, the first source can be diminished. The resolution reached is compared with that predicted by the optical model implemented on MATLAB. With the best optical resolution of the setup achieved, the interferometer had been integrated into a STS1 seismometer to reduce the pendulum movement. The optical sensor replaces the conventional capacitive sensor of the device without disturbing the mechanical parts. The resulting modified STS1 has a spectral resolution below 10^(-13) m/rtHz, while at the same time is insensitive to magnetic field. The final objective of this research consists in introducing the inertial sensor into a single-axis isolation system equipped with a voice coil actuator. In feedback configuration, the setup will allow to reach an unprecedented high level of isolation, opening a new window in gravimetry and gravitational wave detection.

The knowledge of external loads acting on a vehicle is necessary in order to perform design analysis. While performing durability analysis for instance, the encountered loads due to the interaction with the road have to be known. Specific physical devices are normally used by test engineers in order to measure those quantities, but these devices have the disadvantage of being intrusive, expensive and time consuming to install. An appealing alternative is represented by the use of more general purpose sensors in combination with a structural model of the component on which the loads are applied. State estimation theory can be used in order to combine the experimental information coming from the sensors with simulation data coming from the model. This so-called virtual sensing approach for the estimation of loads is investigated in this paper. Numerical experiments in which a suspension multibody model generates virtual measurements are performed in order to assess the feasibility of the technique. ispartof: pages:1711-1724 ispartof: PROCEEDINGS OF ISMA2016 INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING AND USD2016 INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS pages:1711-1724 ispartof: In International Conference on Noise and Vibration Engineering (ISMA2016) location:Leuven date:19 Sep - 21 Sep 2016 status: published

Over the years, concept models have found increased use in the design of mechanical systems, such as automotive applications. However, these models can also be exploited as low-cost counterparts of high-fidelity models for use in online applications such as virtual sensors and control. In this work the use of structural models for input force estimation is discussed. Two different approaches are compared to model a twistbeam rear-suspension for estimating the vertical input forces. the first model is an equivalent trailing arm description and the second is a modal reduced model. An experimental setup in which the forces are measured through a Kistler cell is used to estimate the vertical input force from an optical tracking system. The equivalent trailing arm model is shown to be incapable to produce accurate results due to the strong coupling of the vertical motion with the non-vertical loads, whereas the modal reduced model accurately reproduces the vertical forces. ispartof: pages:1639-1651 ispartof: ISMA proceedings pages:1639-1651 ispartof: . International Conference on Noise and Vibration Engineering location:Leuven, Belgium date:15 Sep - 17 Sep 2014 status: published

Realistic descriptions of a carbon-epoxy 2/2 twill woven composite are generated by a stochastic multi-scale modelling approach. First, experimental data are collected on the short- and long-range variations in the reinforcement structure. Statistical information of each tow path parameter is computed in terms of mean, standard deviation and correlation information. Next, virtual reinforcements are constructed as a combination of average trends with zero-mean deviations. Depending on the presence of cross-correlation, either the Monte Carlo Markov Chain algorithm or a cross-correlated Series Expansion is applied to generate the random tow path deviations. The stochastic tow path instances are subsequently used to construct virtual composite specimens in the WiseTex format. Each specimen possesses the statistical data of the experimental samples on average. ispartof: pages:4741-4750 ispartof: Proceedings of the International Conference on Uncertainty in Structural Dynamics pages:4741-4750 ispartof: USD location:Leuven date:15 Sep - 17 Sep 2014 status: published

Trim materials are designed to minimize sound transmission and maximize sound absorption. Often, a balance between those two quantities is desired with an emphasis on one or another depending on the application in hand. Porous material are typically used as they allow for both sound absorption and transmission loss while minimizing the added mass. In this paper, the performance of a melamine foam panel is assessed. The considered sample is glued on the A2-size opening of a heavy concrete cabin designed for material testing in absorption (Alpha-cabin-like) and transmission (from the cabin to surrounding environment). The material is excited through a random sound field within the cabin. The proposed work concerns the comparison and validation of several measurement techniques in order to evaluate i) the acoustic pressure and intensity maps at the test sample outer surface (radiating area), ii) the Sound Power Reduction (SPR) - assessed as the acoustic power difference on both sides of the sample, and iii) the Acoustic Radiation Ratio (ARR) - defined as the ratio of acoustic power radiated from the A2 opening with and without the sample. Amongst the selected techniques, the classical per-point sound intensity scanning (ISO9614-1) is compared to a bi-layer array of microphones and acoustic holography. ispartof: pages:1521-1529 ispartof: Proceedings of the ISMA2014 pages:1521-1529 ispartof: ISMA2014 location:Leuven date:15 Sep - 17 Sep 2014 status: published

A new type of suspension component with dry friction damping has been developed. It consist of an Omega-shaped spring wire which ends can slip in their mountings. By positioning these components under 90 degrees around the suspended object, the suspension functions in all six degrees of freedom. The suspension component will be modeled as a series connection of a spring with a coulomb damper, which in turn is in parallel with a second spring. This model will be analyzed using Hamilton’s equations of motion to deal with the non-linear phenomena. An experimental setup has been realized whereupon the suspension components are validated using hammer impulses. The observed response is an efficiently damped sinusoidal motion which turns into an undamped sinusoid with small amplitude. In the spectrum, the resonance has been limited in magnitude to 10 dB and the isolation characteristic remains −40 dB/decade equivalent to the undamped spring. ispartof: pages:537-545 ispartof: Proceedings of ISMA2014 including USD2014 pages:537-545 ispartof: ISMA2014 location:BELGIUM, Leuven date:15 Sep - 17 Sep 2014 status: published

Accurate prediction of the lifetime of rolling element bearings is a crucial step towards a reliable design of many rotating machines. Recent research emphasises an important influence of external dynamic loads on the lifetime of bearings. The loads can result from structural resonances, gear meshing, etc. Lifetime calculations of bearings are based on the classical ISO 281 standard, neglecting their influence. Inaccurate estimations of the lifetime lead to excessive safety factors during design and unexpected failures during operation. This paper analyses the influence of external dynamic loads using a novel bearing test rig. The test rig allows applying static and dynamic loads on the test bearing in both the radial and axial direction. The effect of radial, axial and combined radial and axial dynamic loads is separately investigated. Microscope images reveal the effect of dynamic loads on wear of the raceway surfaces. ispartof: pages:405-414 ispartof: Proceedings of International Conference on Noise and Vibration Engineering pages:405-414 ispartof: International Conference on Noise and Vibration Engineering location:Leuven date:15 Sep - 17 Sep 2014 status: published

This paper describes an extensive measurement campaign in order to characterize gearbox vibro-acoustic behavior. The measurements have been performed at ZF Wind Power on a 13.2MW test rig facility. Accelerations have been measured at more than 250 locations on the test rig and for different load levels and operating conditions. It is important to extract from the test rig measurements those parameters which are representative for the gearbox dynamic behavior. Several techniques, such as Operational Modal Analysis (OMA) and Order Based Modal Analysis (OBMA), have been applied to the acceleration data in order to extract the modal parameters in the test rig configuration. While the first technique shows some limitations, such as the so-called "end-of-order" effect, the second technique combining advanced Order Tracking with Operational Modal Analysis, does not suffer from "end-of-order" related peaks in the spectrum and identifies only the physical poles of the system. ispartof: pages:4349-4362 ispartof: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2014) AND INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2014) pages:4349-4362 ispartof: ISMA 2014 location:Leuven, Belgium date:Sep - Sep 2014 status: published

Vibration-based damage detection techniques use the change in modal data as an indicator to assess damages in the structure. Knowing the structural dynamic characteristics of the healthy and damaged structure, the estimation of the damage location and severity is possible by solving an inverse problem. This paper presents a mathematical expression relating damage location and depth to the frequency shifts of the bending vibration modes. This expression permits the extraction of a series of coefficients that characterize each damage location and are independent of the damage severity. The vector aggregating these coefficients for a given location constitutes a Damage Location Indicator (DLI) that unambiguously characterizes the position of a geometrical discontinuity in the beam. A set of vectors typifying all locations along the beam may be used as patters opposable to the damage signature found by measurements. The similarity between the signature and one of the patterns indicates the location of damage.

In this paper an experimental-numerical approach is presented to tackle the vibro-acoustic characterization of composite sandwich structures. A novel experimental setup allows for fast and comprehensive understanding of the NVH behaviour of composite sandwich panels. This information can then be further exploited in numerical model updating and design tools for optimized solutions. Experimental modal analysis and acoustic insertion loss tests are carried out in order to verify the structural and acoustic numerical models of a given sandwich panel. The symmetric motion coincidence frequency is used to retrieve the compression modulus of the core foam material. Later on a second design, derived from the first, is considered. The predicted improvements in NVH behaviour are experimentally verified with good accuracy. The vibro-acoustic test rig is shown to be a valuable support for the design of composite structures when NVH performance is a key indicator attribute. ispartof: pages:1921-1932 ispartof: PROCEEDINGS OF ISMA2012-USD2012 vol:3 pages:1921-1932 ispartof: ISMA2012 location:Leuven date:17 Sep - 19 Sep 2012 status: published

The wind turbine industry is continuously trying to reduce the cost of wind energy. A trend in this regard is the upscaling trend which tries to increase the power output of wind parks by increasing the power produced by each individual turbine. However bigger wind turbines impose higher loads on the wind turbine drive train. Good design of the drive train is indispensable for the reliable and optimal operation of the turbine. This paper discusses some of the trends related to the drive train design for these upscaled machines. ispartof: pages:4345-4359 ispartof: Proceedings of ISMA International Conference On Noise And Vibration 2012 vol:6 pages:4345-4359 ispartof: ISMA International Conference On Noise And Vibration location:BELGIUM, KU Leuven, Dept Mech Engn, Leuven 2012 status: published

A stochastic multi-scale modelling approach is discussed using the textile preprocessor software WiseTex. Random unit cell structures are acquired by generating variable tow reinforcement consisting of systematic trends, determined from experimental data, added with stochastic deviations, produced by a recently proposed Markov Chain algorithm. The input statistical information is collected from a prior experimental campaign quantifying the tow path using X-ray micro-computed tomography. The tow information is transformed in the WiseTex format that is compatible with the micromechanical analysis tool TexComp to evaluate the stiffness properties corresponding to each virtual sample. This stochastic model is tested using statistical data of a seven ply polymer textile composite, with each ply consisting of a twill 2/2 woven carbon fabric in an epoxy matrix. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved. ispartof: pages:5053-5064 ispartof: Proceedings of the International Conference on Uncertainty in Structural Dynamics (USD2012) vol:6 pages:5053-5064 ispartof: International conference on Uncertainty in Structural Dynamics (USD) location:Leuven, Belgium date:17 Sep - 19 Sep 2012 status: published

The experimental estimation of frequency response functions characterizing SISO linear systems is a well established topic. Several estimators are defined in the literature, each estimator being optimal depending upon the assumptions with respect to the balance of noise between the input and output of the system. H1 and H2 have to be used in case of presence of noise on output and input, respectively. The HV or Hs estimator is chosen if input and output are assumed to have equivalent SNR. These estimators are also established for MIMO linear systems, with additional difficulties due to the necessity of inversing cross spectral matrices. A transmissibility function is generally defined as a linear relationship between two outputs of a linear system. For SIMO systems, transmissibility functions are uniquely defined. The Hs estimator is thus advised if both outputs are of equivalent SNR. In the case of MIMO systems, transmissibility functions are no more defined by the system only, it also depends on the input quantities. It is however possible to define a transmissibility matrix between two sets of outputs that is, under some assumptions, uniquely defined. This approach is especially the base of Operational Transfer Path analysis, an engineering method benefiting of a strong research effort in the last few years. This paper deals with the use of the application of MIMO system estimators to the experimental assessment of transmissibility matrices. Transmissibility matrices are generally estimated using a H1 like approach in the literature. The possibility of using H2 and Hs is presented in this work, from the theoretical point of view and with a numerical illustration. ispartof: pages:3563-3569 ispartof: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2012) / INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2012) vol:5 pages:3563-3569 ispartof: ISMA2012 location:Leuven date:17 Sep - 19 Sep 2012 status: published

Rotors exposed to lateral vibration can become unstable at a certain speed due to rotor internal damping. This stability threshold speed is unique and it is impossible to rotate above the threshold. In this paper, a rotor is treated as a linear speed dependent system and inertia, stiffness, gyroscopic and damping forces are included. In order to find the stability threshold, the multiple degree of freedom equations of motion are decoupled into a set of scalar equations. Therefore, the quadratic eigenvalue problem has to be solved. Consequently, the stability threshold speed can be calculated as the lowest speed by which one of the roots has a positive real part. The parameters that influence this stability threshold are discussed and verified by numerical results.

Keynote Lecture; International audience; The paper deals with the robustness of uncertain computational elastoacoustic models in low- and medium-frequency ranges. The elastoacoustic system is made up of a heterogeneous viscoelastic structure coupled with an internal acoustic cavity filled with a dissipative acoustic fluid. A reduced mean elastoacoustic model is deduced from the mean finite element model by using the modal approach with the structural modes of the structure and the acoustic modes of the acoustic cavity. Both data uncertainties and model uncertainties are taken into account by using a nonparametric probabilistic approach for the structure, for the acoustic cavity and for the vibroacoustic coupling interface. The main objectives of this paper are (1) to present an experimental validation of the nonparametric probabilistic approach of model uncertainties for computational elastoacoustics of complex systems in the low- and medium-frequency ranges and (2) to propose a method to perform the experimental identification of the probabilistic model parameters. The experimental configuration which is analyzed with the stochastic computational elastoacoustic model is a car made up of a complex heterogeneous structure coupled with a complex acoustic cavity.

The Finite Element Method is the most commonly used prediction technique for dynamic simulations of mechanical structures. Given the increasing model sizes and subsequent increasing computational load for increasing frequency, the use of the Finite Element Method (FEM) is limited to low-frequency applications. The Wave Based Method (WBM) is a novel Trefftz-based deterministic prediction technique that is capable of relaxing the existing frequency limit. This paper gives an overview of the principles of the WBM for the steady-state dynamic analysis of structures. First the flat plate bending and membrane behaviour are described. Subsequently, the theory for these two problems is united to handle non-coplanar flat plate assemblies. Finally, a hybrid FE-WBM is shown, which combines the strengths of the FEM and the WBM. Throughout the paper the performance of the WBM is compared with that of the FEM, which demonstrates the enhanced computational efficiency of the WBM. ispartof: pages:433-459 ispartof: Proceedings of the 5th International Workshop on Trefftz Methods pages:433-459 uri: www.mech.kuleuven.be/slame08/ ispartof: 5th International Workshop on Trefftz Methods location:Leuven, Belgium date:31 Mar - 2 Apr 2008 status: published

International audience; The focus of this investigation is on the formulation and validation of a novel approach for the inclusion of uncertainty in the modeling of the boundary conditions of linear structures and of the coupling between linear substructures. First, a mean structural dynamic model that includes boundary condition/coupling flexibility is obtained using classical substructuring concepts. The application of the nonparametric stochastic modeling approach to this mean model is next described and thus permits the consideration of both model and parameter uncertainty. Finally, a dedicated identification procedure is proposed to estimate the two parameters of this stochastic model, i.e. the mean boundary condition/coupling flexibility and the overall level of uncertainty.

Most of the tools used in the analysis of vibro-acoustic systems are based on the manipulation of frequency response function (FRF) matrices. The different procedures foresee the use of complete matrices where both translational and rotational degrees of freedom (TDOF and RDOF) information are contained. Unfortunately the second group of data is very often neglected with substantial errors in the final results. In order to overcome this problem, known since the early sixties, many solutions have been tried using existing sensors, developing new ones, defining different methodologies and approximations. This article will give a short review of the different techniques used to measure and excite accurately the RDOF data. Following a historical path, the different procedures will be presented, the finite difference methods, the t-block approaches, the multi-point approximations, the single beam LDV, the multiple laser systems, the scanning laser procedure, the magnetostrictive moment shaker, the pure moment exciter and so on. This work will hopefully help the researchers involved in dynamic modelling to select the most appropriate tools and procedures.

International audience; In order to obtain good estimates of the mechanical system of the parameters, an original identification method will be presented in this paper. A standard modal analysis is performed by using an autoregressive model. Our main contribution is to link the prediction error approach of standard system identification (based on an autoregressive data model) to a subspace based realization algorithm. By merging these two different approaches, a method which uses the advantages of both is obtained. The key idea is to use the non-iterative realization algorithm to obtain an order estimate of a state-space model. The state-space model order so obtained defines a subspace which is used to reduce the set of modal parameters. An evaluation of the method is presented in the experimental case of a free-end beam, showing satisfactory results.

In many structural dynamic tools, mobility matrices manipulations are foreseen. It’s understood that the full matrices, containing translational and rotational degree of freedom data are requested in order to obtain meaningful and correct results. Unfortunately the latter data that comprehend mobility function either with rotational responses or angular excitations are neglected due to the difficulties related to their measurements. In this article a method to derive RDOF data will be presented. The proposed technique relay on response data obtained with standard force excitation and on numerical matrix expansion techniques. The approach is based on the assumption that, in the surrounding of the point of interest, within the frequency range of interest, the structure behaves as a rigid body. Under this condition, if reciprocity holds, some relations between linear and rotational motions can be established and the RDOF functions due to angular excitation can be derived.

In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. for the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals. In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. for the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.

Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SSI) algorithm. These are compared to other methods such as traditional Modal Analysis. Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SSI) algorithm. These are compared to other methods such as traditional Modal Analysis.