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Fraunhofer-Institut für Algorithmen und Wissenschaftliches Rechnen SCAI

Fluid-Structure Interaction Calculations Using a Linear Perturbation Method

Antti Timperi - VTT Technical Research Centre of Finland

at 20th International Conference on Structural Mechanics in Reactor Technology (SMiRT 20)

Two-way coupled Fluid-Structure Interaction (FSI) calculations become numerically unstable in certain cases. If the structural displacements are relatively small, it may be sufficient to use only one-way mapping of fluid pressure to the structure. However, often the fluid still affects frequency of the structural motion considerably through the added mass effect.

This work presents FSI calculations with a linear perturbation method where only one-way coupling is used and the added mass effect is accounted for. Commercial Computational Fluid Dynamics (CFD), structural analysis and coupling codes are used. Modeling of condensation pools of boiling water reactors during injection of gas into the pool water is considered as a specific application.

Basis of the method and its validity for modeling condensation pools are first examined mathematically with an order of magnitude analysis. The method is then validated against numerical data by using a simplified model of a condensation pool. Finally, validation is carried out against scaled-down condensation pool experiments where air was blown into the pool. Results obtained with the method are reasonably close to the experiments whereas in one-way coupled calculations absence of the added mass effect is clearly seen.