Modeling a compliant/shared anchor in MoorDyn (not fixed): recommended approach

[skvibimigger]

Hi OpenFAST community.

I’m trying to model a shared anchor that is not rigidly fixed to the seabed. The goal is to capture finite compliance in the anchor/foundation (e.g., soil–structure flexibility) while multiple mooring lines attach to the same anchor point.

Questions

• What’s the recommended strategy in MoorDyn to represent this?
• Is there a way to assign translational (and possibly rotational) stiffness/damping directly at an anchor/point so the “anchor” behaves like a spring–damper to ground?
• If not, would you recommend approximating the anchor compliance by adding short line segments in horizontal and vertical directions and specifying stiffness per unit length, effectively creating equivalent springs? Any guidance on avoiding spurious added mass/hydrodynamics from those short segments would be helpful.
• If a 6-DOF stiffness is appropriate, is there a clean way to represent coupling between directions, or is the expectation to stick to uncoupled linear springs?
• Are there existing examples or best practices for modeling compliant foundations/anchors in MoorDyn that you’d recommend?

My aim is to avoid treating the anchor as a fixed constraint while keeping the model numerically stable and physically reasonable for shared-anchor loading.

Thanks in advance for any pointers.

Best regards,
Nikolaj