Jean-Mathieu Mencik

On the Acoustic Radiation of Axisymmetric Fluid-Filled Pipes Using the Wave Finite Element (WFE) Method

This paper investigates the efficiency of the wave finite element (WFE) method to assess the vibroacoustic behavior of finite baffled axisymmetric elastic pipes interacting with internal and external acoustic fluids. The pipes, of either homogeneous or multi-layered cross-sections, are surrounded by an external fluid of infinite extent, which can be light or heavy. The Sommerfeld radiation condition is taken into account by considering a perfectly matched layer (PML) around the external fluid. The method involves the computation of waves traveling along an axisymmetric multi-physics waveguide that incorporates a pipe, internal and external fluids, as well as a PML. Numerical experiments are carried out which highlight the relevance of the WFE method in terms of accuracy and CPU time savings, in comparison with the conventional finite element analysis.

Roller Bearing Monitoring by New Subspace-Based Damage Indicator

A frequency-band subspace-based damage identification method for fault diagnosis in roller bearings is presented. Subspace-based damage indicators are obtained by filtering the vibration data in the frequency range where damage is likely to occur, that is, around the bearing characteristic frequencies. The proposed method is validated by considering simulated data of a damaged bearing. Also, an experimental case is considered which focuses on collecting the vibration data issued from a run-to-failure test. It is shown that the proposed method can detect bearing defects and, as such, it appears to be an efficient tool for diagnosis purpose.

Wave and Vibration Analysis of Rotating Periodic Structures by Wave-Based Methods

The vibration of flexible rotating structures has been extensively investigated by the rotordynamics community. The analysis is usually performed via the finite element method using normal mode superposition. However, some interesting features of these structures may be hidden using a modal approach. In this paper, a wave-based approach is used to study the dynamic behavior of flexible rotating structures. Using a wave description, it is straightforward to show that the gyroscopic effect inherent to flexible rotating structures breaks the time-reversal symmetry. This corresponds to an asymmetric wave propagation, i.e., a forward-going wave and its corresponding backward-going pair travel with different wave speeds. In this paper, we show that this feature of flexible rotating structures makes them a natural mechanical circulator. On the other hand, we show that in the case of inhomogeneous flexible rotating structures designed as spectral gap elastic materials, i.e., phononic crystals or locally resonant metamaterials, the rotational speed has a strong influence in the location and width of the band gaps. The mathematical formulation of these problems have been presented by the authors elsewhere. Here, the conceptual aspects of these investigations are discussed under the light of original numerical simulation results.

A WAVE FINITE ELEMENT STRATEGY TO COMPUTE THE DYNAMIC FLEXIBILITY MODES OF STRUCTURES WITH CYCLIC SYMMETRY AND ITS APPLICATION TO DOMAIN DECOMPOSITION

A wave-based numerical approach is proposed for modeling periodic structures with cyclic symmetry. Wave modes which travel around the circumferential direction of those structures are calculated with the wave finite element method. Emphasis is placed on building the matrices of dynamic flexibility modes of the periodic structures by considering unit forces which are successively applied to the degrees of freedom of their boundaries. As it turns out, the matrices of dynamic flexibility modes may be quickly computed, leading the way to efficient domain decomposition techniques to analyze assemblies made up of several periodic structures. 484 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 484-499

A wave-based reduction technique for the dynamic behavior of periodic structures

The wave finite element (WFE) method is investigated to describe the dynamic behavior of periodic structures like those composed of arbitrary-shaped substructures along a certain straight direction. A generalized eigenproblem based on the so-called S + S −1 transformation is proposed for accurately computing the wave modes which travel in right and left directions along those periodic structures. Besides, a model reduction technique is proposed which involves partitioning a whole periodic structure into one central structure surrounded by two extra substructures. In doing so, a few wave modes are only required for modeling the central periodic structure. A comprehensive validation of the technique is performed on a 2D periodic structure. Also, its efficiency in terms of CPU time savings is highlighted regarding a 3D periodic structure that exhibits substructures with large-sized FE models.

A 2D WAVE FINITE ELEMENT-BASED SUPERELEMENT FORMULATION FOR ACOUSTIC ANALYSIS OF CAVITIES OF ARBITRARY SHAPES

A substructuring technique is proposed which enables fast computation of the acoustic response of arbitrary-shaped 2D cavities subject to different kinds of excitations. It combines rectangular superelements which are modeled by means of the wave finite element (WFE) method, and arbitrary-shaped superelements modeled using component mode synthesis (CMS). Within the WFE framework, the so-called receptance matrices of rectangular superelements — which link the pressure vectors to the acoustic force vectors over the boundaries — can be derived in an efficient way in terms of wave modes, without the need of explicitly condensing the internal degrees of freedom of the systems. A model reduction strategy is proposed which aims at expressing the receptance matrices with a few wave modes only. The proposed strategy involves enclosing each rectangular superelement in a finite element (FE) layer with a small width. In this way, smoothed pressure fields are likely to occur over the WFE superelements, hence enabling these superelements to be described with a few wave modes only. By considering those WFE-based rectangular superelements surrounded by FE layers, this yields the so-called hybrid WFE/FE superelements whose dynamic stiffness matrices can be computed in a very fast way. Modeling a whole arbitrary-shaped acoustic cavity follows from conventional assembly procedure between hybrid WFE/FE superelements, CMS superelements and other FE components. Numerical experiments are carried out to highlight the relevance of the proposed substructuring technique.

On the dynamics of fuzzy structures

In this presentation, one proposes a prediction at low‐ and mid‐frequencies of the dynamics of fuzzy structures. As introduced by Soize, the term ‘‘fuzzy structure’’ designates a master structure, whose geometrical, material characteristics, boundary conditions, and excitations are known, coupled with complex systems, called the structural fuzzy or fuzzy, whose characteristics are imprecisely known. Previous works done on this subject analyze the concept of a master structure coupled with a locally homogeneous fuzzy, composed of a large number of linear oscillators excited by their supports. In the present work, the concept of a homogeneous fuzzy is extended to an elastic continuum medium. One theoretically formulates the action of the elastic fuzzy on the master structure: it is shown that the proposed formulation is different from the solution proposed by Soize, derived from the model of a linear oscillator excited by its support. The proposed theory is successfully applied to the case of a homogeneous ...