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A novel approach is presented for the time-domain system identification of structural dynamic components exploiting the high spatial density of vision-based measurements. By using spatially dense measurements, the number of spatial measurement points is much larger than the dimensionality of the underlying dominant dynamics (i.e., the number of measurement points needed to meet observability of the targeted dynamics). This opens up the potential to develop new experimental identification methods that use this spatial overdetermination which were out of reach with conventional discrete sensors. The new approach presented in this paper directly extracts a relatively noise-free, low-order set of dynamic states by projecting the spatially dense time-domain measurements on a low-order dominant deformation motion basis. The basis is constructed by applying an over-complete singular value decomposition on the measurements. These dynamic states together with their numerically calculated first and second order time-derivatives are then used in a two-step identification of the structural dynamic parameters. Here, the structure of the model to identify is based on a-priori physical knowledge of the underlying set of partial differential equations, unlike a purely data-driven method. This approach has the benefits of providing a mathematical formulation that is straightforward to understand and implement and is time-efficient to solve. The presented approach is experimentally validated on a clamped plate as well as on a flexibly suspended plate which requires a correction of the rigid body motion. The identified models have shown to provide an accuracy up to 1 × 10-5 m with respect to the dominant measured motion components in both validation cases. ispartof: Mechanical Systems And Signal Processing vol:182 status: Published online

ispartof: Journal Of Sound And Vibration vol:535 status: published

Experimental Modal Analysis (EMA) allows to assess the dynamical properties of a mechanical component or structure by estimating the modal parameters. Whereas EMA is usually based on local accelerometers or laser vibrometer data, in this paper we focus on camera-based EMA as cameras offer full field and contact-less data. However, besides few very specific controlled cases, camera-based EMA is limited by the low frame rate of the camera in comparison to accelerometers and vibrometers. In this paper we propose a novel acquisition scheme that allows to estimate modal parameters above the Nyquist-Shannon limit (i.e., half of the camera frame rate) by employing a random sampling scheme in time in combination with one accelerometer. With this information we reconstruct the Impulse Response Function (IRF) modal model through a nonlinear optimization problem, where the accelerometer ensures a global solution by providing an initial guess of the eigenfrequencies. We investigate numerically the accuracy of the methodology by simulating multiple damped sine waves. Furthermore, we present an experimental validation on a clamped-clamped beam excited by an impact hammer. Thereby, the displacement information is captured by a single camera triggered by random pulses, and computed by Lucas-Kanade (LK) optical flow. The complexity and modal assurance criterion (MAC) of the modes show that all modes whose amplitudes are higher than the noise level are measured successfully with only one excitation hit, where the highest mode, at 218 Hz, is measured with a random sampling scheme comparable to 50 fps (to reach 218 Hz, a regular sampling with 436 fps would be required). ispartof: Mechanical Systems And Signal Processing vol:170 status: published

This paper investigates the influence of the boundary conditions on the stop band effect in finite locally resonant metamaterial beams. In a first step, a Timoshenko beam with tuned vibration absorbers is used to describe a metamaterial beam. The influence of different boundary conditions for beams with different lengths as well as of tuned vibration absorbers with different amounts of added mass or different tuned frequencies is assessed numerically. It is found that edge modes are present inside the stop band frequency region predicted by the unit cell analysis and these edge modes reduce the level of vibration attenuation achieved. Three solutions are analysed to reduce the effect of the edge modes: (i) varying the tuned frequency, (ii) the number or (iii) the positions of the individual tuned vibration absorbers added to the host structure. In a second step, the results of the numerical investigation are experimentally validated: the experimental results are in good agreement with the numerical results.

This study presents the performance and the potential use of an isogeometric indirect variational boundary element method (IGiBEM) for industrial acoustics applications. The method is validated against semi-analytical frequency response solutions for a basic problem. After being validated, the performance of the IGiBEM is tested and benchmarked against the conventional indirect boundary element method (iBEM) for geometrically complex industrial applications. A vibrating car hood and a loudspeaker model with a vibrating woofer are used as industrial numerical tests. A non-isoparametric iBEM is included in the benchmarks to distinguish the contribution of the discretization versus the geometrical errors to overall error. The tests indicate that the geometrical errors play a more important role in problems involving complex geometries and high-frequency excitations. The study also demonstrates the advantages of IGiBEM over the conventional iBEM regarding the accuracy and computational effciency for geometrically complex problems. ispartof: Engineering Analysis With Boundary Elements vol:110 issue:Jan 2020 pages:124-136 status: Published online

This paper discusses the design and validation of a thermoformed locally resonant metamaterial panel tuned to attenuate the excitation of the first acoustic mode of a cavity. Moreover, it brings resonant metamaterials closer to industrial realisations by exploiting a cheap and widely used production process. The concept is explained, and it is shown how the stop band can be tuned to a targeted frequency. Additionally, multiple stop bands are achieved by combining two differently tuned locally resonant parts in the same metamaterial panel. The proposed thermoformed metamaterial panels have similar weight as the original panel and superior experimentally evaluated insertion loss performance in the frequency range of the stop band. ispartof: APPLIED ACOUSTICS vol:156 pages:78-82 status: published

Vibro-acoustic locally resonant metamaterials with structural stop band behaviour can lead to a strongly increased sound transmission loss in a targeted frequency range. This work assesses the impact of damping in the constituents of metamaterial plates on their acoustic insulation performance by means of infinite periodic and finite structure modelling. Besides applying the hybrid Wave Based - Finite Element unit cell method for infinite plates and the Finite Element Method for finite plates, qualitative dispersion curve based predictions are extended to quantitative sound transmission loss approximations by introducing a dispersion curve based equivalent plate method. Both an idealised and a realisable locally resonant metamaterial plate are analysed. Damping in the resonators in particular is found to have an important impact in and around the stop band, reducing the sound transmission loss peak, but improving the subsequent dip and reducing resonant transmission in a broadening frequency range around the stop band. The damping influenced sound transmission loss predictions for the realisable locally resonant metamaterial plate are experimentally validated by means of insertion loss measurements. It is shown that, by including damping in the infinite periodic structure modelling, acoustic insulation performance predictions with improved accuracy are obtained. ispartof: JOURNAL OF SOUND AND VIBRATION vol:461 status: Published online

A parametric model order reduction scheme is presented for second order systems that does not require a-priori sampling of the parameter space. The proposed scheme \revi{transfers} the parameter dependence to the throughput matrix of the dynamic system by using an auxiliary input matrix. The resulting model can thus be reduced with non-parametric model reduction techniques. Furthermore, it allows for independent low rank changes in the stiffness, damping and mass matrix of the system. It is shown that in combination with the tangential iterative rational Krylov algorithm, a high number of low rank changes can be parametrized, while keeping the reduced model accurate and of moderate size. Also, a scheme is proposed to further reduce the model size, by a frequency limited post-processing step. The methodology is illustrated with two numerical examples: A purely structural example that simulates an unknown defect by locally reducing the stiffness and damping, and a fully coupled vibro-acoustic example that demonstrates how the method can be used to simulate added mass loading, due to for instance the placement of sensors/actuators. ispartof: MECHANICAL SYSTEMS AND SIGNAL PROCESSING vol:130 pages:597-609 status: published

In this work a method for the virtual sensing of the acoustic intensity is derived for exterior vibro-acoustic radiation of a complex deepdrawn structure. The proposed method estimates the acoustic intensity and acoustic pressure resulting from structural excitation in the full acoustic domain, by utilizing a model-based state estimator in the form of a Kalman filter. The used model is a high fidelity, fully coupled vibro-acoustic finite element model with infinite elements to model the acoustic radiation to infinity. The model is reduced to about 0.1% of the original size by a Krylov based model order reduction technique that preserves the stability of the full model. This allows for the usage of the model in a Kalman filter. The effectiveness of the Kalman filter is demonstrated with several numerical experiments, in which both the measured pressure and the measured sound intensity are compared with the estimations from the filter at several locations. Furthermore, the robustness of the filter to changing acoustic environments is assessed. ispartof: MECHANICAL SYSTEMS AND SIGNAL PROCESSING vol:134 status: Published online

In this work, a fully predictive high-fidelity numerical approach for the simulation of a car tire rolling with a constant angular velocity over a coarse road surface is presented. A fully nonlinear vibro-acoustic finite element tire model is combined with an Arbitrary Lagrangian Eulerian formulation to describe both the rolling dynamics as well as the interaction between the tire and coarse road surface. A geometrical constraint approach is used to describe the tire/road interaction rather than a constitutive approach in order to keep the proposed method fully predictive, i.e. to not rely on measurement data. As both the use of a nonlinear finite element tire model, as well as the use of the geometrical constraint approach result in large computational costs and simulation times, the nonlinear Multi-Expansion Modal Reduction hyper-reduction method is applied. Numerical costs and corresponding simulation times are reduced by a factor of order of magnitude 100 (from several months to hours), therefore making the proposed approach feasible to use in an industrial design and development process. Two alternative linearized approaches, based on the proposed nonlinear approach, are considered as well. While the proposed nonlinear approach shows a good, consistent qualitative and quantitative correspondence between experimental and numerical simulation results for the entire 0–400 Hz frequency range of interest, with normalized Power Spectral Density differences between 0.1 and 0.2 dB (ref. 1 N/Hz), the linearized approaches are limited to lower frequency ranges of 0–85 Hz and 0–200 Hz and are therefore not suitable for the intended application. The overall performance of the proposed nonlinear approach confirms its use as a possible alternative to standard time-consuming experimental approaches. ispartof: Journal of Sound and Vibration vol:452 pages:147-168 status: published

[EN] Accurate prediction of Flow Induced Vibration phenomena is currently a field of major interest due to the use of lightweight materials in the automotive and aerospace industry. This article studies the turbulent flow around a wall-mounted obstacle, and the induced deformations produced by the pressure fluctuations on a plate located downstream the obstacle. The methodology used is a combination of experimental tests and numerical simulations. On one side, experiments were carried out in a wind tunnel test facility equipped with Particle Image Velocimetry to characterize the fluid velocity field, and laser vibro-meter to measure the vibrations of the plate. On the other side, Fluid-Structure Interaction (FSI-one-way) has been calculated by considering different turbulence modeling approximations (RANS and LES). Finally, numerical results have been analyzed and validated against the experiments in terms of main flow structures and the vibroacoustic response of the plate., This work has been partially supported by Universitat Politecnica de Valencia through the grant Programa de apoyo a la Carrera Academica del Profesorado 2018/03/14 and by the Spanish Ministerio de Economia y Competitividad through Grant No. DPI2015-70464-R. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders and the Flemish Government department EWI. The Research Fund KU Leuven and the Flanders Innovation and Entrepreneurship Agency, within the SILENCEVENT project, are gratefully acknowledged for their support.

To enhance the sound insulation performance of double panel partitions at their mass-air-mass resonance frequency, novel compact and low-mass solutions are sought. This paper investigates the use of the locally resonant vibro-acoustic metamaterial concept as a possible solution. The metamaterial solution is applied to one panel of a double panel partition in order to enhance the sound transmission loss at the mass-air-mass resonance. To design the metamaterial solution and predict its sound transmission loss performance, an extension of the multiple reflection theory is proposed, incorporating the dynamic mass of a metamaterial panel. The latter is obtained from the metamaterial plate dispersion curves, calculated using finite element based unit cell modeling. The designed metamaterial solution is manufactured and its insertion loss is measured. The novel design outperforms the original double panel and an equivalent total mass double panel configuration in the targeted mass-air-mass resonance frequency region. The predictions obtained with the proposed method are in good agreement with the experimentally obtained results. This demonstrates the potential of the metamaterial solution to enhance the acoustic insulation at the mass-air-mass resonance and indicates that the proposed method allows a fast, simple and representative indication of their acoustic insulation performance. ispartof: Journal of Sound and Vibration vol:442 pages:28-44 status: published

To further improve the sound absorption enhancement of flexible micro-perforated panels (FMPPs), a new sort of perforated sound absorbers – metamaterial-based micro-perforated panels (MMPPs) – is proposed by combining a micro-perforated host panel and local resonators (LRs) attached on a sub-wavelength scale, targeting the flexural waves. Theoretical and numerical models show that MMPPs are able to further enhance sound absorption in a wide frequency range. The theoretical model is developed based on the effective medium method as the structural wavelength in the host panel is much larger than the distance between the LRs, and the full simulation model, including visco-thermal effects, is conducted by utilizing multi-physical coupling integrated in COMSOL. Besides, a structural finite element unit cell method is used to evaluate the stop band behavior of the MMPP. Good agreement is achieved between the theoretically predicted acoustical properties and the simulation results for both conventional FMPPs and the proposed MMPPs, validating the numerical and theoretical models. Both models reveal that the sound absorption enhancement of the MMPP stems from the resulting acoustic surface impedance improvement, caused by the sub-wavelength attached local resonances. The effect of key properties of the LRs (i.e. mass, damping and multiple resonances) on the sound absorption performance of MMPPs is then analyzed by applying the theoretical model and effective frequency-adjustability of the absorption enhancement performance is found. The proposed MMPP shows great potential for the noise reduction industry. ispartof: Mechanical Systems And Signal Processing vol:117 pages:138-156 status: published

After recalling the first Brillouin zone (BZ) and the first irreducible Brillouin zone (IBZ) of a lattice in terms of its plane crystallographic group, we investigate the danger of restricting a band-gap detection to the contour of the IBZ, instead of its full IBZ. Based on hundreds of porous phononic crystal simulations, we provide for the 17 plane crystallographic groups (i) statistics of the band-gap localizations, (ii) probabilities to get non-full band-gaps, and (iii) averages of the bandwidth error made when only the IBZ contour is considered. It is found that for phononic crystals, the IBZ contour provides accurate results only for highly symmetric lattices. ispartof: International Journal of Solids and Structures vol:135 pages:26-36 status: Published online

© 2016 Elsevier Ltd This paper explores the simulation of small deformation contact problems with a coupled isogeometric-meshless formulation, based on local maximum-entropy (LME) approximants. The framework of isogeometric analysis (IGA) is employed on a thin region close to the boundary of the domain and the meshless formulation in its interior. The method maintains the advantages of IGA in the simulation of contact and introduces a higher flexibility in the discretization of complex shapes. In addition, a new integration strategy is presented for the IGA-LME blending and its advantages respect to the original approach are discussed. publisher: Elsevier articletitle: Contact mechanics with maximum-entropy meshfree approximants blended with isogeometric analysis on the boundary journaltitle: Computers & Structures articlelink: http://dx.doi.org/10.1016/j.compstruc.2016.11.008 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved. ispartof: Computers & Structures vol:182 pages:165-175 status: published