Nonlinear dynamical analysis for coupled fluid-structure systems

International audienceThe present research concerns the numerical dynamical analysis in elasto-acoustics, taking into account the geometrical non-linearities induced by the large displacements/deformations of the structure and assuming the internal acoustic fluid occupying an internal cavity coupled to the structure to remain in a linear range of vibration. More particularly, the modeling includes sloshing and capillarity effects on the free surface. A numerical application is presented

Nonlinear geometric analysis of a mistuned bladed disk

This paper deals with the dynamical analysis and uncertainty quantification of a mistuned industrial rotating integrally bladed disk, for which the operating regime under consideration takes into account the nonlinear geometric effects induced by large displacements and deformations. First, a dedicated mean nonlinear reduced-order model of the tuned structure is explicitly constructed using three-dimensional solid finite elements. The random nature of the mistuning is then modeled by using the onparametric probabilistic approach extended to the nonlinear geometric context. Such a computational strategy provides an efficient tool, which is applied to a computational model of an industrial centrifugal compressor with a large number of degrees of freedom. This allows for putting in evidence some new complex dynamical behaviors

Analyse d'une expérimentation exhibant une instabilité dans un liquide avec un modèle réduit non linéaire fluide-structure

National audienceCet article propose de revisiter et d’expliquer, au travers d’un modèle réduit numérique fluide-structure, une observation expérimentale d’un phénomène de résonance de la surface libre d’un liquide dans un réservoir cylindrique. Le système expérimental a été simulé par un modèle numérique du cylindre élastique en présence de non-linéarités géométriques, partiellement rempli d’un liquide acoustique prenant en compte les effets de ballottement. Les résultats obtenus montrent qu’une excitation inattendue de grande amplitude des modes de ballottement a lieu lorsque la structure est excitée sur certaines de ses résonances

Properties of water confined in hydroxyapatite nanopores as derived from molecular dynamics simulations

Bone tissue is characterized by nanopores inside the collagen-apatite matrix where fluid can exist and flow. The description of the fluid flow within the bone has however mostly relied on a macroscopic continuum mechanical treatment of the system, and, for this reason, the role of these nanopores has been largely overlooked. However, neglecting the nanoscopic behaviour of fluid within the bone volume could result in large errors in the overall description of the dynamics of fluid. In this work, we have investigated the nanoscopic origin of fluid motion by conducting atomistic molecular dynamics simulations of water confined between two parallel surfaces of hydroxyapatite (HAP), which is the main mineral phase of mammalian bone. The polarizable core–shell interatomic potential model used in this work to simulate the HAP–water system has been extensively assessed with respect to ab initio calculations and experimental data. The structural (pair distribution functions), dynamical (self-diffusion coefficients) and transport (shear viscosity coefficients) properties of confined water have been computed as a function of the size of the nanopore and the temperature of the system. Analysis of the results shows that the dynamical and transport properties of water are significantly affected by the confinement, which is explained in terms of the layering of water on the surface of HAP as a consequence of the molecular interactions between the water molecules and the calcium and phosphate ions at the surface. Using molecular dynamics simulations, we have also computed the slip length of water on the surface of HAP, the value of which has never been reported before

Application au désaccordage des roues aubagées.Dynamique des structures tournantes à symétrie cyclique en présence d'incertitudes aléatoires

The objective of this research is to propose new probabilistic methodologies for the dynamic analysis of themistuning of rotating structures with cyclic symmetry in the low frequency range. The structure under consideration is a bladeddisk. Firstly, a recent nonparametric probabilistic model is used for constructing a direct probabilistic approach, allowingthe dynamic amplification of the forced response on blades induced by mistuning to be analyzed. Particularly, such aprobabilistic approach allows the blade-eigenfrequencies mistuning and the blade-modal-shape mistuning to be modeled withcoherence. Secondly, an inverse probabilistic approach, based on an identification method of the dispersion parameterscontrolling the nonparametric probability model, is constructed in order to define the blade tolerances yielding a givenprobability level of the dynamic amplification of the forced response. Finally, both methodologies are numerically applied on asimple case and on a complex structure. The mistuned forced response obtained with the nonparametric probabilistic model andwith the parametric probabilistic approach traditionally used in the mistuning context are compared. In addition, the inverseprobabilistic approach allows the blade tolerances to be optimized in order to reduce the amplifications of the forcedresponse. The analysis of these results validate the relevance of the proposed methodologies.L'objet de ce travail de recherche est de proposer de nouvelles méthodologies probabilistes pour l'analysedynamique basses fréquences du désaccordage des structures tournantes à symétrie cyclique. La classe de structure étudiée estla roue aubagée. Tout d'abord, un modèle probabiliste non paramétrique récent est utilisé pour construire une approcheprobabiliste directe, permettant d'analyser l'amplification dynamique de la réponse forcée des aubes, induite par ledésaccordage. En particulier, une telle approche permet de modéliser de manière cohérente le désaccordage en fréquences desaubes et le désaccordage en modes des aubes. Ensuite, une approche probabiliste inverse, reposant sur une méthoded'identification des paramètres de dispersion du modèle probabiliste non paramétrique, est construite afin de déterminer lestolérances des aubes, conduisant à une probabilité donnée du facteur d'amplification dynamique de la réponse forcée. Enfin, cesméthodologies sont mises en oeuvre numériquement sur un exemple numérique simple et sur un modèle complexe de roue aubagée.Les réponses forcées désaccordées obtenues par le modèle probabiliste non paramétrique et par le modèle probabilisteparamétrique classiquement utilisé pour la problématique du désaccordage sont comparées. Par ailleurs, la méthodologie duproblème inverse permet d'optimiser les tolérances de l'aube pour réduire l'amplification de la réponse forcée. L'analyse desrésultats valide la pertinence des méthodologies proposées

Désaccordage des roues aubagées - concepts technologiques et modélisation.

Université d'été de l'inspection générale de mathématiques, Internat d'excellence de Sourdan, 24 août 2011