SD: Comment out the geometric stiffness terms associated with cable pretension to prevent unphysical results #2363
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…retension to prevent unphysical results
andrew-platt
approved these changes
Aug 12, 2024
jjonkman
approved these changes
Aug 12, 2024
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Feature or improvement description
Currently, the geometric stiffness due to preloading in the SubDyn structure is not consistently accounted for. Only the contribution from cable pretension is included in the stiffness matrix, not the contribution from the preload in other members that arises from cable pretension. This results in unphysical stiffness for the Guyan modes. For a floating structure, this error causes the Guyan modes to deviate from rigid-body modes when cables with pretension are present.
As a temporary fix, the geometric stiffness terms associated with cable pretension are commented out in SubDyn. This prevents unphysical Guyan mode stiffness but also led to the geometric stiffness being neglected. A more permanent solution would require the preload and the resulting geometric stiffness from all members to be consistently accounted for, not just those from pre-tensioned cables.
Related issue, if one exists
See Issue #1956
Impacted areas of the software
SubDyn
Test results, if applicable
TBD