Abstract: A numerical vibroacoustic model that can manage multilayered plates locally covered with damping patches is presented. All the layers can have an on-axis orthotropic viscoelastic behavior. Continuity of displacements and transverse shear stresses at each interface is enforced, which permits to write the entire displacement field in function of the displacements of the-common-first layer, leading to a two-dimensional plate model. The problem is then discretized by Rayleigh-Ritz's method using a trigonometric basis that includes both sine and cosine functions in order to treat various boundary conditions. The excitation can be of mechanical kind (concentrated or distributed forces) or of acoustic kind (plane wave of any incidence, diffuse field, etc.). The model permits to compute different vibroacoustic indicators: the mean square velocity of the plate, the radiation efficiency, and the transmission loss. Comparisons between the present model and numerical results from literature or finite element computations show that the model gives good results in both mechanical and acoustical aspects. Then, a comparison of the effects of different distributions of patches is presented. The role of the surface covering rate is first discussed, followed by a study involving different geometries for the same surface covering rate. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3546096]
Abstract: In this paper, the sensitivity analysis methodology is applied to numerical welding simulation in order to rank the importance of input variables on the outputs of the code like distorsions or residual stresses. The numerical welding simulation uses the finite element method, with a thermal computation followed by a mechanical one. Classically, a local sensitivity analysis is performed, hence the validity of the results is limited to the neighbourhood of a nominal point, and cross effects cannot be detected.
This study implements a global sensitivity analysis which allows to screen the whole material space of the steel family mechanical properties. A set of inputs of the mechanical modelâmaterial properties that are temperature-dependentâis generated with the help of latin hypercube sampling. The same welding simulation is performed with each sampling element as input data. Then, output statistical processing allows us to classify the relative input influences by means of different sensitivity indices estimates.
Two different welding configurations are studied. Considering their major differences, they give a different ranking of inputs, but both of them show that only a few parameters are responsible for the variability of the outputs. To illustrate the pertinence of the overall process, for the first of the two configurations, two series of computations are performed: one for a complete sample and one for its reduced versionâwhere all the secondary parameters are set to mean values. They match perfectly, showing a substantial economy can be done by giving mean values to the rest of the inputs.
Sensitivity analysis has then provided answers to what we consider one of the probable frequently asked questions regarding welding simulation: for a given welding configuration, which properties must be measured with a good accuracy and which ones can be simply extrapolated or taken from a similar material? That leads us to propose a comprehensive methodology for welding simulations including four sequential steps: a problem characterization, a sensitivity analysis, an experimental campaign, simulations.
Abstract: In some studies requiring predictive and CPU-time consuming numerical models, the sampling design of the model input variables has to be chosen with caution. For this purpose, Latin hypercube sampling has a long history and has shown its robustness capabilities. In this paper we propose and discuss a new algorithm to build a Latin hypercube sample (LHS) taking into account inequality constraints between the sampled variables. This technique, called constrained Latin hypercube sampling (cLHS), consists in doing permutations on an initial LHS to honor the desired monotonic constraints. The relevance of this approach is shown on a real example concerning the numerical welding simulation, where the inequality constraints are caused by the physical decreasing of some material properties in function of the temperature.
Abstract: This study is composed of three essential parts. The first part describes an indirect semi-experimental method which is used to reconstruct the excitation force of an operating diesel engine from the acceleration data measured at the mounting points. These internal forces can not be directly measured with force sensors; they have to be derived from the dynamic deformation of the engine support, so a theoretical analysis is carried out to derive the equations for the force re-construction. The second part deals with prevention of low frequency vibration of the powertrain from spreading to the rest of the vehicle. Three uncoupling techniques are used to minimize these vibrations. The first technique reduces the non-diagonal elements of stiffness matrix. The second technique uses the elastic axes decoupling criterion. The third technique uncouple the torque roll axis (IRA) by using the previously determined excitation efforts. In the third part, numerical and experimental results are discussed. The solicitations deducted and the positions of mounts allowing decoupling of the powertrain are presented. (C) 2010 Elsevier Ltd. All rights reserved.
Abstract: Noise generated by a turbulent grazing flow over a cavity at low Mach number: an application to car door cavities. Noise produced by turbulent grazing flow over a generic cavity representing car door cavities was measured in a semi-anechoic wind tunnel. Two cavities were studied: one 50 mm large (dimension perpendicular to the airflow), functioning as a Helmholtz resonator, reaching sound pressure levels of 136 dB at 1776 Hz, for a downstream velocity of 54 m/s. The other, of scale 250 mm could not be regarded as a Helmholtz resonator although resonance occurred at 1902 Hz, at a level of 125 dB, for the same velocity. In both cases, noise was caused by Kelvin-Helmholtz instabilities in the mixing layer. To cite this article: A. Da Silva et al., C. R. Mecanique 337 (2009). (c) 2009 Academie des sciences. Publie par Elsevier Masson SAS.
Abstract: This paper presents a direct method for the static reanalysis of structures. We use the concept of the reflexive inverse in the sense of Moore-Penrose generalized inverse to express a general solution of discrete systems without any boundary condition. We use a simple decomposition of the stiffness matrix to avoid its inversion. We give a comparison of the processing time of this method with the duration of a complete analysis with finite elements. The reanalysis of the stiffness is based on the mixed conditions linking displacements and related efforts. In the second part we concentrate on this reanalysis and we give as an application the reanalysis of the geometry and the reanalysis for mesh refining. This method is general, enabling the reanalysis of structures with variation of the boundary conditions in loading and displacement. It also enables reanalysis of the structural stiffness and makes it possible to add or remove structural elements. it can easily be applied to the study of nonlinear behavior (case of damaging, plasticity, nonlinear elasticity...). (C) 2002 Published by Elsevier Science Inc.
Abstract: In this paper we present a technique based on the finite element method, formulated in displacement, that enables stress conditions to be imposed. We use the method to impose the equilibrium condition at the interface of two bonded joints. We also show how the method reduces the times for repetitive calculations of structures such as bonded assemblies. We show that a calculation by standard FEM can have errors in the case of heterogeneous structures. We give the example of the calculation of a single lap joint and compare this with the mixed finite element method. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: The purpose of this paper is to show how reanalysis the equilibrium system of structures without inversion of the stiffness matrix. We use the Moore-Penrose partial inverse to obtain a simple decomposed reanalysis system.
Abstract: II is shown how to compute the generalized inverse of a non-negative definite symmetric matrix, from the knowledge of its eigenvectors associated to the null eigenvalue. Two methods, respectively inspired by Gauss and Cholesky algorithms, are presented. These direct methods rake advantage of a possible band-form of the matrix.
Abstract: This paper presents a new method to solve the thermal equilibrium with, in a first step, the formulation of the general solution of the linear equations and, in a second step, the particular solution of the study by introducing the boundary conditions which specialize the system of equations. This method enables to reanalyze easily the problem for various modified boundary conditions and applied thermal loads.
