Fluid-Structure Interaction (FSI)

What is Fluid-Structure Interaction (FSI)

CFD Model of the MSIV (left) and MSCV (right)
CFD Model of the MSIV (left) and MSCV (right)

Fluid-structure interaction (FSI) analyses are those in which flowing fluid has an influence on the structural displacements/deformations. As the structure deforms or is displaced, the shape of the fluid domain changes, and hence flow behavior is affected. The interaction between the fluid and structure is complicated via the flow-induced forces acting on the structure and the structural dynamic response. Typically, an FSI analysis is highly complex in nature and needs to be solved using a transient solver. In addition to the coupling of the fluid forces with the structural response, material and geometric non-linearities can add complexity. The complexity and size of the numerical grid required to accurately predict an FSI problem requires much more computational resources than the structural and fluid problems require by themselves. Kalsi Engineering, Inc. has both the expertise required to model the complex fluid structure interaction problems as well as the computational resources to solve these problems effectively.

Case Study: Valve Closure/Piping Transient Prediction

Kalsi Engineering recently performed a coupled fluid transient and dynamic structural prediction of a Main Steam Isolation Valve (MSIV) and a Main Steam Check Valve (MSCV) for a US nuclear power plant. The purpose of the analyses was to predict the closing time and speed for the MSIV and MSCV under various conditions including a high energy pipe break. The results of the FSI problem were used as an initial condition for a transient dynamic FEA prediction.

The FSI prediction was performed by developing a dynamic/kinematic model of the MSIV valve and actuator (or valve for the MSCV). The dynamic model was then coupled to transient fluid results in RELAP (a software package used to calculate fluid transients in piping systems).

The dynamic model utilized hydrodynamic torque coefficients that were developed by performing CFD predictions on the disc of the MSIV/MSCV at various positions.