I am trying to model a semi-submersible platform with small freeboard, such that the columns are submerged with small tilt angles, and low waves pass over the columns.
The potential flow model does not take these phenomena into account, so I understand that perhaps a model based on Strip Theory elements is more appropriate. But it is not clear to me that the Strip Theory member based model takes this into account.
My question is, does the Strip Theory member based model calculate dynamic pressure and added mass on each element, taking into account whether the element is submerged or not (given the wave profile and the position of the platform)?
Thank you in advance
Such a “green water” problem is not really solvable with the HydoDyn module of OpenFAST.
As of OpenFAST v2.6 and newer, the strip theory solution solves the hydrostatic problem nonlinearly for large motion, but the solution will not permit a joint that was previously above the waterline to pass below the waterline, and vice-versa, will not permit a joint that was previously below the waterline to pass above the waterline.
We at NREL are also working on updates to HydroDyn that permit the wave-excitation loads in the strip-theory solution to be based on wave stretching to the actual free surface, but again, this functionality wont allow joints to enter or exit the water. We are also working on updates to HydroDyn that permit the wave-excitation loads in the strip-theory solution to depend on the displaced position of the hydrodynamic nodes, but only in the horizontal direction (not vertically). This new functionality is forthcoming, but will not solve the “green water” problem.