Entity

Time filter

Source Type

Saint-Leonard-de-Noblat, France

Assaf S.,Ecole Superieure des Techniques Aeronautiques et de Construction Automobile | Guerich M.,Ecole Superieure dIngenieurs Leonard de Vinci | Cuvelier P.,Ecole Superieure des Techniques Aeronautiques et de Construction Automobile
Acta Acustica united with Acustica | Year: 2011

The constrained-layer damping treatment is widely used to control the resonant response of vibrating structures, particularly in the automotive and aerospace industries. This technique requires design tools in order to select the best location, type and thickness of the damping and constraining-layer materials for optimum damping while minimizing the total weight of the damping treatments. In this study, a numerical tool is presented to analyze the vibration response of plates partially or fully covered with a constrained viscoelastic damping material. This tool is based on a finite element approach. The undamped plate structure is modeled using a discrete Kirchhoff theory (DKT) element. However, a sandwich plate element is specially derived to model the damped plate structure. This element is formulated in such a way that it is compatible with the DKT element. The natural frequencies and modal loss factors are derived from the modal strain energy method. The proposed approach is validated by comparing predictions with the results of various examples published in the literature. Hence, this approach is shown to predict accurately the damping characteristics of arbitrarily shaped sandwich plates, with different material properties and boundary conditions, fully or partially covered with constrained viscoelastic layers. The influence of the damping patch locations and the viscoelastic material's shear modulus on the vibration and damping characteristics is investigated. To damp the plate effectively using partial coverage, the damping patches must be distributed appropriately. To select the best damping patch locations, an indicator based on the energy dissipated through the viscoelastic layer is proposed. © S. Hirzel Verlag. Source


Adam C.,Ecole Polytechnique - Palaiseau | Adam C.,PSA Peugeot Citroen | Bouabdallah S.,Ecole Superieure dIngenieurs Leonard de Vinci | Zarroug M.,PSA Peugeot Citroen | Maitournam H.,ENSTA ParisTech
Computer Methods in Applied Mechanics and Engineering | Year: 2015

Automobile crashworthiness is a complex application for numerical methods in dynamics of structures which includes many high non-linearities. Explicit techniques are widely used for structural dynamics dealing with difficult and large problems that prevent the use of implicit methods. We propose, in this paper, a deep study of the stable time step, which guarantees the stability of the method, and its estimates, for one-dimensional and two-dimensional problems. Element and nodal time steps are presented and adapted to highly regular B-spline and NURBS functions, in the context of isogeometric analysis. The size of the proposed stable time estimates benefits from the properties of regularity and extended support of the basis. Their performance is assessed and compared in several examples, with an arbitrary mesh, uniform or non-uniform, and considering polynomial orders from one to five. The smoothness and order of the polynomials have a significant effect on the stable time step and its estimates. Several lumping schemes of the mass matrix are presented and their accuracy is assessed. © 2015 Elsevier B.V. Source


Adam C.,Ecole Polytechnique - Palaiseau | Adam C.,PSA Peugeot Citroen | Bouabdallah S.,Ecole Superieure dIngenieurs Leonard de Vinci | Zarroug M.,PSA Peugeot Citroen | Maitournam H.,Ecole Polytechnique - Palaiseau
Computer Methods in Applied Mechanics and Engineering | Year: 2015

B-spline reduced quadrature rules are proposed in the context of isogeometric analysis. When performing a full Gaussian integration, the high regularity provided by spline basis functions strengthens the locking phenomena and deteriorates the performance of Reissner-Mindlin elements. The uni-dimensional B-spline-based quadrature rules, given in a previous paper (part I), are extended to multi-dimensional problems such as plates and shells. The improved reduced integration schemes are constructed using a tensor product of the uni-dimensional schemes. A single numerical quadrature is performed for bending, transverse shear and membrane terms, without introducing Hourglass modes. The proposed isogeometric reduced elements are free from membrane and transverse shear locking. Convergence is first assessed in plate problems with several aspect ratios and then in the shell obstacle course problems. The resulting under-integrated elements exhibit better accuracy and computational efficiency. © 2014 Elsevier B.V. Source


Assaf S.,Ecole Superieure des Techniques Aeronautiques et de Construction Automobile | Guerich M.,Ecole Superieure dIngenieurs Leonard de Vinci | Cuvelier P.,Ecole Superieure des Techniques Aeronautiques et de Construction Automobile
Computers and Structures | Year: 2010

This paper presents a finite element formulation to analyze the vibro-acoustic response of plates with constrained-layer damping treatment. This formulation takes into account the effects of fluid loading. The governing coupled structural/acoustic equations of motion are solved using a modal approach combined with an interpolation technique of the reduced radiation impedance matrix components of the fluid. The numerical results show the accuracy of the proposed approach. In addition, a parametric study is carried out to highlight the influence of geometrical and material variables on the damping characteristics, which could be used as design parameters for the optimization problem. © 2010 Elsevier Ltd. All rights reserved. Source


Braouezec Y.,Ecole Superieure dIngenieurs Leonard de Vinci
Computational Economics | Year: 2010

We consider a repeated pricing decision problem of a monopolist (the decision-maker) who does not know the demand function of some new product, and hence the profit function. To decide, she is helped by a committee of N experts. Each expert has an estimation of the unknown demand function and use it to advise the decision-maker on how she should modify the current price. Decisions are taken with a weighted majority rule, where the weight of each expert, which may be interpreted as her decision power, evolves as a function of its accuracy. When a perfect exists, i.e., who always gives the correct advice, we show that she ends up with all the decision power in the long-run so that the decision-maker finds the optimal price. When such a perfect does not exist, the decision-maker is actually unable to consistently select an expert over time so that the sequences of prices and weights describe a limit cycle. Interestingly enough, if the decision-maker takes a large sample of the stationary behavior of prices, the empirical mean turns out to be arbitrarily close to the optimal price, independently of the "quality" of the experts, as long as there experts are "diverse" enough. This result gives thus support to the thesis developed in the books of Surowiecki (The wisdom of the crowd. Why the many are smarter than the few and how collective wisdom shapes business, economies, societies and nations, 2005) and Page (The difference: How the power of diversity creates better groups, firms, schools, and societies, 2007). © Springer Science+Business Media, LLC. 2009. Source

Discover hidden collaborations