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Fluid Structure Interaction (FSI)

Fluid structure interaction is one of most complex engineering analyses, coupling CFD and finite element structural and/or thermal analysis. In an FSI calculation, the solid surfaces act as interfaces between the fluid and solid domains to provide transfer of loads- mechanical or thermal. The CFD solution provides unsteady flowfield solutions for pressure or heat fluxes on solid surfaces, then the FEA solver calculates solid deformations or temperatures based on the CFD results. The deformed solid surfaces will in turn constitute a new boundary for CFD calculation, which leads to a different pressure or thermal loading. Thus, the FSI analysis requires a two-way interactions and a fully coupled iterative solution at each time level. Understanding the physics for both solid and fluid parts is critical to an FSI analysis. Representative FSI applications include airfoil (or blade) flutter analysis, pressure controlled valve opening and closing, blood flow in arteries, and squeeze film dampers in gas turbine engines.

Inferior Vena Cava Filter- Solid Deformation
 


The figures above demonstrate an FSI analysis applied to the ‘Inferior Vena Cava Filter’, a medical device inserted into blood vessels to prevent the passage of large life-threatening emboli to the lungs. There are complex physics involved in this FSI analysis. In the fluids part, it involves an unsteady pressure pulse, moving mesh/boundary due to solid surface deformation, recirculations, etc. On the FEA side, material strength and properties, deformation, and dynamic response to pressure loads need to be considered. Without fully coupled FSI analysis, the interactions between the two domains are one- directional, without the simultaneous feedback from the other part, potentially producing misleading results. Precise numerical prediction of FSI phenomena leads to overall understanding of the filter characteristics, ultimately contributing to a better product design.