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Old   January 12, 2006, 03:30
Default How to start modal analysis
  #1
Mvaz
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hello to all of u I have a question how to start modal analysis on ansys. can u light on that? pl.
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Old   January 12, 2006, 04:22
Default Re: How to start modal analysis
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Ahmed
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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

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Old   January 12, 2006, 04:51
Default Re: How to start modal analysis
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mvaz
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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
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Old   January 12, 2006, 04:56
Default Re: How to start modal analysis
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HVN
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You could apply the loads on nodes, surfaces
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Old   January 12, 2006, 05:54
Default Re: How to start modal analysis
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Alex Muthaiah
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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
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Old   January 12, 2006, 09:33
Default Re: How to start modal analysis
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Peter Attar
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It's a modal analysis..ie eigenvalue problem therefore you don't apply loads.
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Old   January 12, 2006, 11:58
Default Re: How to start modal analysis
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HVN
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What about fixed point or fixed surface?
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Old   January 12, 2006, 12:07
Default Re: How to start modal analysis
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Peter Attar
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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.
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Old   January 13, 2006, 04:17
Default Re: How to start modal analysis
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HVN
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OK thanks for the information
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Old   January 16, 2006, 05:07
Default Re: How to start modal analysis
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mvaz
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how do v decide the no of mode to extract and the method to extract? does there any theory regarding this?
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Old   January 16, 2006, 09:40
Default Re: How to start modal analysis
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Alex Muthaiah
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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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