Barre de torsion

Résumé

vignette|En rouge, les barre de torsion avant d'une Alfa Romeo Alfetta. La barre de torsion est un des types de ressort les plus simples. En mettant à profit l'élasticité transverse des matériaux, il autorise de grandes déformations de structures, et permet la construction d'éléments d'une souplesse plus facile à contrôler. Il ne faut pas confondre ce phénomène avec celui des ressorts de torsion en spirale utilisés en horlogerie, qui eux travaillent en réalité en flexion. Pour la barre de torsion, si nous négligeons les extrémités, sa partie active est une barre pleine de diamètre d et de longueur L, ou bien un tube de diamètre intérieur di et de diamètre extérieur de. L'une des extrémités de la barre est bloquée et considérée comme fixe, l'autre, dite libre, est reliée aux éléments mobiles. L'application essentielle des barres de torsion est la suspension des véhicules, particulièrement de ceux dont les roues sont indépendantes. On les utilise non seulement sur des véhicules lége

Source officielle

https://fr.wikipedia.org/wiki/Barre_de_torsion

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Effect of trailing edge shape on hydrodynamic damping for a hydrofoil

Matthieu Dreyer, Mohamed Farhat, Zhifeng Yao

Flow induced vibration on a hydrofoil may be significantly reduced with a slight modification of the trailing edge without alteration of the hydrodynamic performance. Particularly, the so called Donaldson trailing edge shape gave remarkable results and is being used in a variety of industrial applications. Nevertheless, the physics behind vibration reduction is still not understood. In the present study, we have investigated the hydrodynamic damping of a 2D hydrofoil with Donaldson trailing edge shape. The results are compared with the same hydrofoil with blunt trailing edge. The tests are carried out in EPFL high speed cavitation tunnel and two piezoelectric patches are used for the hydrofoil excitation in non-intrusive way. It was found that the hydrodynamic damping is significantly increased with the Donaldson cut. Besides, as the flow velocity is increased, the hydrodynamic damping is found to remain almost constant up to the hydrofoil resonance and then increases linearly, for both tested trailing edge shapes and for both first bending and torsion modes.

Elsevier2014

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The influence of the boundary conditions on the added mass of a NACA0009 cantilever hydrofoil has been numerically and experimentally investigated. The study has been focused on the effects of a lateral solid wall close to the hydrofoil tip side and of a partially wetted vertical hydrofoil at different levels with the free surface parallel to the span. A detailed fluid–structure model has been built for both cases and a modal analysis has been carried out. The numerical three first natural frequencies have been used to calculate the added mass coefficients. These coefficients have been compared with the results of the analogous experiments carried out by means of an onboard excitation and response system based on piezoelectric patches. The btained results are in reasonable good agreement with experimental data. The proximity of a lateral solid wall provokes an increase of the added mass experienced by the hydrofoil which can be approximated by a 2nd order polynomial function for both bending and torsion modes. On the other hand, the increase of the added mass with the level of partial submergence is found to be dependent on the relative displacements of the hydrofoil submerged part and hence on the mode shape.

Pergamon-Elsevier Science Ltd2014

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