Potential Flow - Strip Theory hybrid model

Dear all,

I am trying to make a hybrid Potential Flow and Strip Theory model for a semisub platform in OpenFAST. To this end, I am adding Strip Theory elements to the original Potential Flow model (WAMIT output files) in Hydrodyn, to model viscous effects on the platform. All Strip Theory element coefficients, except the drag coefficients, are set to 0.

I have substracted the submerged volume of the Strip Theory members to the submerged volume of the Potential Flow model (PtfmVol0). This way, the equilibrium position of the platform remains the same. However, I don’t know if I also have to correct the hydrostatic stiffness coefficients of the Potential Flow model in the hybrid version.

I have made some FreeDecays to compare the hybrid model and the Potential Flow model (setting the drag coefficients of the Strip Theory elements in the hybrid model to 0), and the results suggest that I don’t have to correct any hydrostatic coefficients in the hybrid model. However, logic tells me that this is what should be done.

Many thanks in advance.

Best regards,

Nicolás Deza

Dear Nicolás Deza,

HydroDyn will calculate buoyancy, etc. for any strip-theory member marked with PropPot = False. You should update the additional linear stiffness matrix with the hydrostatic restoring associated with these strip-theory members. More information is provided in the draft HydroDyn User’s Guide and Theory Manual.

Best regards,