Systematic Stochastic Reduction of Inertial Fluid-Structure Interactions subject to Thermal Fluctuations

We present analysis for the reduction of an inertial description of fluid-structure interactions subject to thermal fluctuations. We show how the viscous coupling between the immersed structures and the fluid can be simplified in the regime where this coupling becomes increasingly strong. Many descriptions in fluid mechanics and in the formulation of computational methods account for fluid-structure interactions through viscous drag terms to transfer momentum from the fluid to immersed structures. In the inertial regime, this coupling often introduces a prohibitively small time-scale into the temporal dynamics of the fluid-structure system. This is further exacerbated in the presence of thermal fluctuations. We discuss here a systematic reduction technique for the full inertial equations to obtain a simplified description where this coupling term is eliminated. This approach also accounts for the effective stochastic equations for the fluid-structure dynamics. The analysis is based on use of the Infinitesmal Generator of the SPDEs and a singular perturbation analysis of the Backward Kolomogorov PDEs. We also discuss the physical motivations and interpretation of the obtained reduced description of the fluid-structure system. Working paper currently under revision. Please report any comments or issues to tabak.gil@gmail.com.Comment: 19 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1009.564