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Modal Superposition in Transient Analysis

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Posts: 4
Topic starter
(@sandon101)
Barista
Joined: 5 years ago

I been tinkering with transient analysis, I am currently having some trouble with modal superposition method.  I am having trouble understanding how to correctly implement the Control_implicit_modal_dynamics keyword.  In the direct transient analysis method I can just utilize the implicit solver to directly find the response of my model using the load_node or load_node_set keywords.

The current errors I get are:

1. Error 21122 (STR+1122) The file C:\LSDYNA\Dyna_examp does not exist

2.Error 60319 (IMP+319) Binary modal database C:\LSDYNA\Dyna_examp is not compatible with this execution. Use a double precision version of LS-DYNA when creating the database along with IBINARY=0 on *DATABASE_FORMAT. Then use a double precision version of LS-DYNA for the modal simulation. Double precision is recommended for ALL modal jobs.

I am already using the double precision solver in LS-Dyna.  

Control keywords I am currently using are:

1. Control_implicit_general
2. Control_implicit_eigenvalue
3. Control_implicit_modal_dynamics
4. Control_termination

I am also currently using load_node_set which might not be correct for this case.

Any help on implementing Control_implicit_modal_dynamics would be of great help. 

4 Replies




Negative Volume
Posts: 639
Admin
(@negativevolume)
CEO
Joined: 5 years ago

@sandon101

Unfortunately, I am not nearly as familiar with the implicit side of LS-Dyna as I am with the explicit. 

Those errors are strange and seem like something that may be going on with your license. I'll look into both of these and get back to you. 

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Posts: 4
Topic starter
(@sandon101)
Barista
Joined: 5 years ago

I was able to get transient analysis working using implicit_dynamics setting analysis type to modal superposition, however the results were very noisy.  I have compared the LS-Dyna results with other solvers such as the Optistruct modal superposition solver and the direct integration method in LS-Dyna and Optistruct.  The modal superposition method in LS-Dyna is highly effected by the modes of the model, which makes the results noisy.

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2 Replies
Negative Volume
Admin
(@negativevolume)
Joined: 5 years ago

CEO
Posts: 639

@sandon101

You may have seen this already, but these examples may help fine-tune your simulation to remove the noise:

https://www.dynaexamples.com/implicit

What results are noisy and what method are you using to obtain them?

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(@sandon101)
Joined: 5 years ago

Barista
Posts: 4

@negativevolume

Only LS-Dyna results calculated from modal super position is noisy.  Results from LS Dyna direct integration results correlates well with results obtained from Optistruct using the modal superposition and direction integration methods.  The modal superposition solver in LS-Dyna is effected by higher level modes.

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