harmonic force , displacement, in a caesar ii dynamic analysis

[somacast]

Hello and good day to you,

I have a question about the harmonic force or displacement being used in an analysis and sorry for this being so basic question, but how is it determined if really things are quite hazy about the real source of vibration in the pipe, i.e. 2 phase or slug flow maybe, flashing in the line due to control valve opening between 2 different pressure segments?

Thank you