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Noel O.,University of Maine, France | Mazeran P.-E.,CNRS Roberval Laboratory (Mechanical Research Unit) | Nasrallah H.,University of Maine, France
Physical Review Letters | Year: 2012

The influence of sliding velocity on the adhesion force in a nanometer-sized contact was investigated with a novel atomic force microscope experimental setup that allows measuring adhesion forces while the probe is sliding at continuous and constant velocities. For hydrophobic surfaces, the adhesion forces (mainly van der Waals forces) remain constant, whereas for hydrophilic surfaces, adhesion forces (mainly capillary forces) decrease linearly with a logarithmic increase of the sliding velocity. The experimental data are well explained by a model based on a thermally activated growth process of a capillary meniscus. © 2012 American Physical Society. Source

Simard P.,CNRS Roberval Laboratory (Mechanical Research Unit) | Antoni J.,INSA Lyon
Applied Acoustics | Year: 2013

This work experiments and investigates the problem of acoustic sources identification from a limited number of measurements delivered by a microphone array as a Basis Pursuit problem. The basic idea beyond Basis Pursuit is to search for a solution that minimizes the ℓ1 norm of the solution rather than the usual sum of squares (ℓ2 norm) of the residual error. Basis Pursuit has been developed in the context of Compressed Sensing (CS), and has already proved to be efficient in a great number of applications. However, the quality of the obtained results is subdued to restricted conditions whose fulfillment in acoustics are investigated in this paper depending on geometrical parameters such as the source/array distance or the array aperture. This leads to the proposition of several practical guidelines for the experimenter as how to select a microphone array and how to optimaly position it w.r.t the radiating source of interest. Simulations and experimental data are used to demonstrate the relevance and limitations of this approach. The results proved to be better than those obtained by conventional Beamforming (BF), even in its near-field focusing version based on spherical waves. © 2013 Elsevier Ltd. All rights reserved. Source

Jourani A.,CNRS Roberval Laboratory (Mechanical Research Unit)
International Journal of Surface Science and Engineering | Year: 2015

This study focuses on the belt finishing process to understand the effect of the local geometry of each abrasive grain via the curvature radius and the attack angle on the local contact temperature. In order to reach this last parameter, a three-dimensional numerical model is established and presented in order to determine the temperature distribution at the interface abrasive papers/workpiece. The established model considers that the local geometry of each abrasive grain is conical with a hemispherical tip. The numerical results show that at a small depth of penetration, both sphere and cone have an influence on temperatures distribution. For larger depths, this distribution depends only on the conical geometry of the abrasive grains. It is also shown that the effect of the interaction of asperities on the temperature during belt finishing cannot be neglected, especially at higher load. Copyright © 2015 Inderscience Enterprises Ltd. Source

Jourani A.,CNRS Roberval Laboratory (Mechanical Research Unit)
International Journal of Materials and Product Technology | Year: 2015

In this work, we study the influence of roughness geometries on the contact force, contact area and pressure distribution during a static contact between a rough surface and a smooth rigid plane by using two elastic geometrical models. The first one is spherical where each asperity can be characterised by the height and the radius of curvature. The second approach is a conical where the rough contact is modelled by cones. In order to discuss the validity of these two geometrical models, they are compared with a numerical solution of the Boussinesq equation which does not take into account the local geometry of the asperities. The results show clearly that the conical model allows having more realistic values of the contact parameters and model correctly the elastic rough contact. However, the spherical approach of the asperities overestimates the pressures undergone by the asperities. Copyright © 2015 Inderscience Enterprises Ltd. Source

Chazot J.-D.,CNRS Roberval Laboratory (Mechanical Research Unit) | Nennig B.,Laboratoire dIngenierie des Systemes Mecaniques et des Materiaux | Perrey-Debain E.,CNRS Roberval Laboratory (Mechanical Research Unit)
Journal of Sound and Vibration | Year: 2013

The paper deals with the numerical simulation of the acoustic field in two-dimensional cavities in which absorbing materials are present. Though Finite Element Method (FEM) could be employed for this purpose, the discretization level required for achieving reasonable accuracy renders the method impractical in the mid-frequency range. To alleviate this limitation, the Partition of Unity Finite Element Method (PUFEM) using plane wave functions has been shown to be very effective for solving short wave Helmholtz problems. In the present work, the method is extended to the computation of the pressure wave field within the absorbing media which is modeled as a bulk-reacting material characterized by a complex-valued and frequency dependent mean density and dynamic compressibility. Lagrange multipliers are used to enforce the transmission conditions at the air-material interface. Performances of the PUFEM are compared with a standard FEM in several examples of practical interests. It is shown that the technique is a good candidate for solving noise control problems at high frequency. © 2012 Elsevier Ltd. All rights reserved. Source

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