Fluid-Structure Interaction (FSI) analysis is an example of a multiphysics problem where the interaction between two different physics phenomena, done in separate analyses, is taken into account. From the perspective of Mechanical, an FSI analysis consists of performing a structural or thermal analysis in the application, with some of the loads (forces or temperatures, for example) coming from a corresponding fluid analysis or previous CFD analysis. In turn, the results of the Mechanical analysis may be used as loads in a fluids analysis. The interaction between the two analyses typically takes place at the boundaries that the Mechanical model shares with the fluids model. These boundaries of interaction are collectively called the fluid-structure interface. It is at this interface where the results of one analysis are passed to the other analysis as loads.
A general way of tying two otherwise independent analyses together is described in System Coupling. The specific use of System Coupling as one way to perform certain FSI analyses is mentioned where applicable in the following sections.
For one specific multiphysics problem, the structural thermal-stress analysis, an FSI analysis is not always required. If the thermal capabilities of the Mechanical application are sufficient to determine a proper thermal solution, an FSI approach (using separate applications for separate analyses) is not required and the thermal-stress analysis can be done entirely within Mechanical. In the case where the thermal solution requires the specialized capabilities of a CFD analysis, the structural thermal-stress analysis is done using the FSI approach. The CFD analysis is done first, then the calculated temperatures at the fluid-structure interface are applied as loads in the subsequent Mechanical analysis.
Typical applications of FSI include:
Biomedical: drug delivery pumps, intravenous catheters, elastic artery modeling for stent design.
Aerospace: airfoil flutter and turbine engines.
Automotive: under-the-hood cooling, HVAC heating/cooling, and heat exchangers.
Fluid handling: valves, fuel injection components, and pressure regulators.
Civil engineering: wind and fluid loading of structures.
Electronics: component cooling.
The Mechanical application supports two types of Fluid-Structure Interaction: one-way transfer and two-way transfer. In one-way FSI, CFD results are applied as loads in the Mechanical analysis, but the results of the Mechanical analysis are not passed back to a fluids analysis. In two-way FSI, the results of the Mechanical analysis are passed back as loads to the fluids model. Two-way FSI is important when the Mechanical analysis could produce results that, when applied as loads in the fluids analysis, would significantly affect the fluids analysis.