More updates to the Morison module

[luwang00]

r-tests will not pass. Need to update HydroDyn input files with the new buoyancy coefficient, $C_b$, entries and the hydrostatic load model switch, MHstLMod. (See PR #100 to r-test)

• Hydrostatic load calculation is skipped with MHstLMod=0.
• The existing hydrostatic load calculation is used with MHstLMod=1.
• The new alternative hydrostatic load calculation is used with MHstLMod=2.

Feature or improvement description

• Added buoyancy coefficient $C_b$ entries to the member-based hydrodynamic coefficients (Models 1, 2, and 3). When computing the hydrostatic load along a member and on the end plates, the scaled member radius (scaled by $\sqrt{C_b}$ ) is used. (Setting $C_b=0$ zeros the hydrostatic load on the member.)
• Implemented an alternative approach for hydrostatic load calculation (MHstLMod=2) based on numerical integration along the length of the member. This approach should support arbitrary intersection between the instantaneous free surface (or still water level if no wave stretching) and the strip-theory member, including partially wetted end plates.
  • The original hydrostatic load calculation (MHstLMod=1) is more suitable for (nearly) vertical surface-piercing columns with the bottom end plate fully submerged and the top end plate dry at all times. Preferably the normal of the waterplane area is mostly aligned with the member axial direction. This method also works with fully submerged members.
  • The new alternative approach (MHstLMod=2) is more general but might be computationally more expensive.
• Improved the robustness of the strip-theory hydrodynamic load calculation. The updated implementation should no longer assume the end node of a member is at the same level as or above the start node of the same member or that each member centerline crosses the free surface at most once. Neither assumption is guaranteed when WaveStMod>0 and WaveDisp=1.

Related issue, if one exists

• Merge this after Additional features for the new SeaState module and HydroDyn #1008
• Requires PR #100 to r-test

Impacted areas of the software
HydroDyn => The modifications are confined to the Morison submodule of HydroDyn.

Release checklist:

• add regressions tests from private @luwang00 repository (new feature tests) this will be a separate PR for 4.0.0 (https://github.com/orgs/OpenFAST/projects/2?pane=issue&itemId=30000600)
• Update the versions in docs/source/user/api_change.rst
• Update input files for regression tests (See PR #100 to r-test)