Selecting modes with mode number higher than 100 for steady state deterministic wave analysis

Good day,

I am trying to determine the steady state response of a large model loaded by waves and current.

Due to the size of the structure and the number of dofs to be considered for dynamic analysis, the number of structural eigenmodes is far larger than 100.

The exiciting loads all have periods of around 5 seconds - and this happens to coincide with the period of mode 150; with modes 100 having a period of 6.3 seconds and 199 at around 3.3s.

Due to the nature of the wave response module, it can't handle more than 100 modes to be passed to it. By selecting modes 100-199 to be considered, this should be fine.

However, the wave response module can't handle dynmod. files containing more than 100 modes - regardless if they are all used. 

Recognizing the limitations of the wave response module, I would like to modify the dynmod. file to only contain only modes 100-199.

They are, however, encrypted.

This leads me to my question; is it possible to decrypt and modify these files? Or is there some editor for these files I haven't found?

I hope to hear from you.

Parents
  • Try using the MODSEL line your wave response input file to select the modes that you want to analyze. Enter the number of modes you want to analyze on the WROPT line (100) and then enter modes (100-199) on the MODSEL line. You can use multiple MODSEL lines since you want to analyze more than 20 modes.

    You can also try modifying the retained degrees of freedom in your SACS input file to isolate the particular modes that you are interested in. Typically the higher order modes will have a significantly reduced mass participation which means that the response should still be quite low. If you are interested in the response of a particular part of the structure, you may want to consider only using retained degrees of freedom for those joints.

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  • Try using the MODSEL line your wave response input file to select the modes that you want to analyze. Enter the number of modes you want to analyze on the WROPT line (100) and then enter modes (100-199) on the MODSEL line. You can use multiple MODSEL lines since you want to analyze more than 20 modes.

    You can also try modifying the retained degrees of freedom in your SACS input file to isolate the particular modes that you are interested in. Typically the higher order modes will have a significantly reduced mass participation which means that the response should still be quite low. If you are interested in the response of a particular part of the structure, you may want to consider only using retained degrees of freedom for those joints.

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