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-   -   How to start modal analysis (http://www.cfd-online.com/Forums/fluent/39207-how-start-modal-analysis.html)

Mvaz January 12, 2006 03:30

How to start modal analysis
 
hello to all of u I have a question how to start modal analysis on ansys. can u light on that? pl.

Ahmed January 12, 2006 04:22

Re: How to start modal analysis
 
This is not the right forum to answer your question! But if you read the tutorials of Ansys you will get the answer, good luck and cheers


mvaz January 12, 2006 04:51

Re: How to start modal analysis
 
i have gone through the tutorial that given in ansys help but i have a problem how to decide load and how to apply it? thxs

HVN January 12, 2006 04:56

Re: How to start modal analysis
 
You could apply the loads on nodes, surfaces

Alex Muthaiah January 12, 2006 05:54

Re: How to start modal analysis
 
Hi, Eventhough my specialisation is in CFD I can help u Modal analysis is a type of Dynamic analysis where in u r going to extarct natural frequencies of a structure.Required parameters for this is density of the structure and proper boundary conditions. Define number of modes u need extarct(generally first5),method of extraction its better to go for Lanczos method . which gives first 5 modal frequency values after solution the interpretaionis if anyone of the above frequency matches with ur operating one resonance will occur.Pls go through the tutorial of MODAL ANALYSIS OF A CANTILVER BEAM.

regards

Alex

Peter Attar January 12, 2006 09:33

Re: How to start modal analysis
 
It's a modal analysis..ie eigenvalue problem therefore you don't apply loads.

HVN January 12, 2006 11:58

Re: How to start modal analysis
 
What about fixed point or fixed surface?

Peter Attar January 12, 2006 12:07

Re: How to start modal analysis
 
Well if you apply a static load in a nonlinear analysis you can then use the subsequent tangent stiffness matrix generated via the displacement due to this applied load in a modal analysis...but I don't think that is what the original poster was looking for.

HVN January 13, 2006 04:17

Re: How to start modal analysis
 
OK thanks for the information

mvaz January 16, 2006 05:07

Re: How to start modal analysis
 
how do v decide the no of mode to extract and the method to extract? does there any theory regarding this?

Alex Muthaiah January 16, 2006 09:40

Re: How to start modal analysis
 
Hi I think I have already told u 1)The number of modes depends upon the number of DOF of the systems. So Usually it depends on Client request or generally we got first 6 modes (because we know 6 Dof 3 translate 3 rotary at a particular node).

2)Methods I.Tracking Method. II.Transormation Method. III.Lanczos Method But in Industry we always go for 3rd method.

Refer 3rd method (Lanczos) in detail always good and stable. Also apply proper boundary conditon to extract eigen values, because it also depends on u r Bc's

Alex


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