February 25, 2021 at 8:38 am

1shan

Ansys Employee

Hello Array,nOnce you have the transient response of the structure(displacement of any node vs time) you need to convert it in the frequency domain by taking the fast fourier transform. You could do this in other mathematical softwares(like MATLAB). The peaks in the resulting graph (amplitude vs frequency) would correspond to the natural frequencies. Also, you need to do this for different nodal locations to extract all possible natural frequencies. Since FSI would result in a non linear system, you cant couple it directly to the modal analysis. However if you are only interested in understanding the effect of liquids added mass on the natural frequency and not of the surrounding fluid viscous damping you could skip doing a 2 way FSI and model it using acoustic elements instead and do a modal analysis. Please refer this thesis https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/76519/eth-7837-02.pdf?sequence=2(page 19).nRegards,nIshan.n