Simulate vibration pipe stress.

Hi,

I would like to simulate the vibration pipe stress with frequency response (FRA).

The source of vibration came from motor in compressor that we know frequency input that simulate from 20 Hz to 100 Hz 

Load Set

- Internal pipe pressure 3 bar

- gravity load

- torque from compressor

The steps 

1. Static analysis with pressure and gravity

2. Prestress Modal analysis using the above static analysis for prestress.

3. Run Frequency response dynamics analysis with torque varies on frequency.

Are these steps correct? However, on FRA I don't know the amplitude. How can I find this amplitude?
Also, There are 2 loading load functions and base excitation. My understanding this simulate should do the base excitation due to there are vibration from the base that pipe connected. Is this correct?

Also, the what is the value in base excitation and how can I find the amplitude. And in the calculate that relative to Ground and Supports. What are different of this 2? 

Thank you.

Chokchai