Openfast-Adjust the configuration of floating platforms

[tyq-123-111]

Could anyone tell me where to modify the draft of a floating platform in OpenFAST?

Besides adjusting the node coordinates in Member-Joints, are there any other parameters I need to change if I want to modify the platform dimensions?

Any advice would be greatly appreciated. Thank you!

[jjonkman]

Dear @tyq-123-111,

I guess this depends on how you are modeling the floater in OpenFAST. It sounds like you are using the strip-theory solution in HydroDyn, which would require modification of the joints and members as you state. If you are also considering potential flow, that solution (from WAMIT or equivalent) would also be affected by a change in draft. If you are using SubDyn to model floater elasticity, you'd have to change the members and joints there as well. And perhaps other items change, such as the fairlead locations in the mooring module, or the platform center of mass in ElastoDyn (if the floater is treated rigidly without SubDyn). And, of course, when changing draft, you'll still want to ensure that the unloaded model is in heave equilibrium, by changing system masses or ballasting.

Best regards,

[tyq-123-111]

Dear Thank you very much for your detailed explanation. Currently, I am encountering some difficulties while modeling a floating platform in OpenFAST. I am trying to modify several key dimensions of the OC4 floating platform, such as increasing the spacing between the columns and the diameter of the columns. I have adjusted the nodal coordinates mainly in the Member-Joints section of HydroDyn, but the simulated 6-DOF motion results show almost no difference compared with the original model, which is clearly unreasonable. Therefore, I would like to ask: if I want to adjust the column spacing of the OC4 floating platform, which other modules do I need to modify accordingly? Thank you again for your help. I look forward to your reply. Best regards At 2026-03-13 03:49:31, "jjonkman" ***@***.***> wrote: Dear @tyq-123-111, I guess this depends on how you are modeling the floater in OpenFAST. It sounds like you are using the strip-theory solution in HydroDyn, which would require modification of the joints and members as you state. If you are also considering potential flow, that solution (from WAMIT or equivalent) would also be affected by a change in draft. If you are using SubDyn to model floater elasticity, you'd have to change the members and joints there as well. And perhaps other items change, such as the fairlead locations in the mooring module, or the platform center of mass in ElastoDyn (if the floater is treated rigidly without SubDyn). And, of course, when changing draft, you'll still want to ensure that the unloaded model is in heave equilibrium, by changing system masses or ballasting. Best regards, — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

[jjonkman]

Dear @tyq-123-111,

The OpenFAST model of the OC4-DeepCwind semisumbmersible as provided in the OpenFAST r-test (which is what I assume you are using) uses a hybrid hydrodynamic formulation, employing both a potential flow and strip-theory solution. By moving the joint locations, you would only change the strip-theory solution. You'd also have to generate the potential-flow solution from a frequency domain wave-body solver, e.g., WAMIT or equivalent.

Best regards,