Natural frequency of a pipe with fluid 2

[elogesh]

Hai,

I was asked to estimate the modal parameters of the pipe along with the flowing liquid.

They carried out the FRF analysis(Experimental) like this,

1) FRF analysis of the pipe is carried out without the liquid

2)FRF analysis of the pipe with static liquid

3)FRF analysis of the pipe with certain fluid velocity.The velocity is adjusted to maintain the laminar flow.

Can I estimate the modal parameters using the FEM technique?

1) I have no issues for the empty pipe.

2) For the second case, pipe with static fluid, I planned to carryout the analysis by adding extra mass in pipe based on the gravitiational direction.The understanding I have is liquid adds only distributed mass.

3) For the third case with the flowing fluid,I planned to estimate the fluid forces(Normal and tangential).Apply these forces on the pipe and solve for linear static analysis.Then carrying out modal analysis based on the pre-stressing of the fluid force.

Can I have you feedbacks/suggestions in this regard.

Regards,
Logesh.E

 

[hacksaw]

You are going in the right direction.

Depending on the L/D of your pipe and at very high flow rates coriolis forces can become important. If you are dealing with normal pipe flows this is not usually an issue.

The fluid mass affects the modal parameters even in zero gravity.

Gravity is just an external force. That will give you a static deflection.

The is a some recent work being done, but a good starting point is Blevin's "Flow-induced Vibration".

 

[electricpete]

Some good technical articles on piping vibration available free on-line here (see #17, 20, 27, 37, 57,72)

http://www.engdyn.com/papers_table.htm

 

[pja]

Look for articles and books by the author Paidoussis.