Publications of Ghislain Raze
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See detailH∞ optimization of multiple tuned mass dampers for multimodal vibration control
Raze, Ghislain ULiege; Kerschen, Gaëtan ULiege

in Computers and Structures (2021), 248

In this paper, a new computational method for the purpose of multimodal vibration mitigation using multiple tuned mass dampers is proposed. Classically, the minimization of the maximum amplitude is ... [more ▼]

In this paper, a new computational method for the purpose of multimodal vibration mitigation using multiple tuned mass dampers is proposed. Classically, the minimization of the maximum amplitude is carried out using direct H∞ optimization. However, as shall be shown in the paper, this approach is prone to being trapped in local minima, in view of the nonsmooth character of the problem at hand. This is why this paper presents an original alternative to this approach through norm-homotopy optimization. This approach, combined with an efficient technique to compute the structural response, is shown to outperform direct H∞ optimization in terms of speed and performance. Essentially, the outcome of the algorithm leads to the concept of all-equal-peak design for which all the controlled peaks are equal in amplitude. This unique design is new with respect to the existing body of knowledge. [less ▲]

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See detailPiezoelectric Digital Vibration Absorbers for Multimodal Vibration Mitigation of Complex Mechanical Structures
Raze, Ghislain ULiege

Doctoral thesis (2021)

Engineering structures are becoming lighter and more complex to accommodate the ever-increasing demand for performance and to comply with stringent environmental regulations. This trend comes with several ... [more ▼]

Engineering structures are becoming lighter and more complex to accommodate the ever-increasing demand for performance and to comply with stringent environmental regulations. This trend comes with several challenges, one of which is the increased susceptibility to high-amplitude vibrations. These vibrations can be detrimental to structural performance and lifetime, and may sometimes even threaten safety. Passive and active vibration reduction techniques can provide a solution to this issue. Among the possibilities, piezoelectric damping is an attractive option, due to its compact and lightweight character, its reduced cost and its tunability. This technique uses the ability of a piezoelectric transducer to transform part of its mechanical energy into electrical energy. The converted energy can then be dissipated by connecting a shunt circuit to the transducer. However, the difficulty of realizing such circuits limits the broad applicability of piezoelectric shunting. This doctoral thesis investigates the potential of replacing the electrical circuit comprising classical components such as resistors and inductors by a digital unit and a current source, thereby creating a digital vibration absorber (DVA). Virtually any circuit can be emulated with a digital controller, providing this approach with an extreme versatility for vibration mitigation of complex mechanical structures. In this regard, the DVA is first analyzed in terms of power consumption and stability of the controlled system. Then, effective and easy-to-use tuning approaches for the control of multiple structural modes either with passive electrical circuits or a DVA are proposed, namely a passivity-based tuning of shunt circuits, a modal-based synthesis of electrical networks interconnecting multiple piezoelectric transducers, and a numerical norm-homotopy optimization resulting in an all-equal-peak design. These techniques are eventually applied and adapted to real-life structures with potentially complex dynamics. Specifically, effective vibration mitigation is demonstrated on structures exhibiting nonlinear behaviors and high modal density. [less ▲]

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See detailMultimodal vibration damping of nonlinear structures using multiple nonlinear absorbers
Raze, Ghislain ULiege; Kerschen, Gaëtan ULiege

in International Journal of Non-Linear Mechanics (2020), 119

This paper presents a tuning methodology for multiple nonlinear vibration absorbers that mitigate several nonlinear resonances simultaneously. Specifically, the objective is to maintain equal peaks in the ... [more ▼]

This paper presents a tuning methodology for multiple nonlinear vibration absorbers that mitigate several nonlinear resonances simultaneously. Specifically, the objective is to maintain equal peaks in the frequency response for all controlled resonances in an as large as possible range of forcing amplitudes. Relying on an all-equal-peak design for linear regimes of motion and adopting a principle of similarity for nonlinear regimes, a semi-analytical expression of the absorber coefficients is derived using first-order harmonic balance and a series expansion of the harmonic coefficients. The proposed methodology is demonstrated numerically using two spring-mass systems. [less ▲]

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See detailA digital nonlinear piezoelectric tuned vibration absorber
Raze, Ghislain ULiege; Jadoul, Andy; Guichaux, Sylvain et al

in Smart Materials and Structures (2020), 29(1), 015007

This study presents the practical realization of a digital vibration absorber that, owing to the flexibility provided by the digital unit, synthesizes linear and nonlinear shunt circuits. The absorber ... [more ▼]

This study presents the practical realization of a digital vibration absorber that, owing to the flexibility provided by the digital unit, synthesizes linear and nonlinear shunt circuits. The absorber, composed of a microprocessor and a current source, is connected to the host structure with piezoelectric patches. The performance of both circuits is compared experimentally for a nonlinear host structure. The superiority of a properly-tuned nonlinear absorber over its linear counterpart is validated, but the limits of the nonlinear absorber are also explored. Moreover, the accuracy of the tuning procedure and formulas is assessed through experimental parametric studies. [less ▲]

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See detailA Multimodal Nonlinear Tuned Vibration Absorber
Raze, Ghislain ULiege; Kerschen, Gaëtan ULiege

in Kovacic, Ivana; Lenci, Stefano (Eds.) IUTAM Symposium on Exploiting Nonlinear Dynamics for Engineering Systems (2019, July 25)

This paper presents a tuning methodology to design a vibration absorber able to mitigate the vibratory amplitude of multiple resonances of a nonlinear structure. The linear characteristics of the absorber ... [more ▼]

This paper presents a tuning methodology to design a vibration absorber able to mitigate the vibratory amplitude of multiple resonances of a nonlinear structure. The linear characteristics of the absorber are first tuned to obtain the equal-peak design on every mode to be controlled when the structure is behaving linearly. Nonlinearities are then introduced intentionally in the absorber to counteract the effect of the nonlinearities inside the host structure. Their functional formis chosen according to a principle of similarity, and their coefficients are determined to enforce equal peaks in the nonlinear regime. [less ▲]

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See detailSuppression of Delay-induced Instabilities of Digital Piezoelectric Vibration Absorbers
Raze, Ghislain ULiege; Paknejad, Ahmad; Zhao, Guoying et al

in Benjeddou, Ayech; Mechbal, Nazih; Deü, Jean-François (Eds.) Proceedings of the 9th ECCOMAS Thematic Conference on Smart Structures and Materials - SMART 2019 (2019, July)

Digital piezoelectric vibration absorbers synthesizing passive shunt circuits may be subject to instabilities. This work investigates the cause for these instabilities, and highlights the role of sampling ... [more ▼]

Digital piezoelectric vibration absorbers synthesizing passive shunt circuits may be subject to instabilities. This work investigates the cause for these instabilities, and highlights the role of sampling delays in their onset. If for practical reasons the sampling frequency cannot be increased, a stabilization procedure which anticipates the sampling delays is proposed. The theoretical developments in this work are experimentally validated on a piezoelectric beam. [less ▲]

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See detailOptimisation Topologique sans Maillage - Vers la reconnaissance d'éléments structuraux
Raze, Ghislain ULiege; Charlotte, Miguel; Morlier, Joseph

Conference (2017, May)

Cet article présente des résultats d’une étude d’optimisation topologique utilisant une nouvelle approche par ajout de variables de localisation des nœuds. Dans cette approche, la discrétisation spatiale ... [more ▼]

Cet article présente des résultats d’une étude d’optimisation topologique utilisant une nouvelle approche par ajout de variables de localisation des nœuds. Dans cette approche, la discrétisation spatiale est découplée de la distribution matérielle. Les effets de la méthode de discrétisation, de l’optimiseur et de la fraction de volume sont étudiés. Les résultats de l’approche par ajout de variables de localisation des nœuds sont prometteurs et suggèrent que cette approche pourrait constituer une alternative aux méthodes actuellement utilisées en optimisation topologique. [less ▲]

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