Dear Dr. Jonkman,

I’m currently use Openfast V2.5. We carried out many measurements on a platform designed in-house. The objective is to study the hydrodynamic behavior of the floater and to compare it with the outputs of the OpenFAST code. For the integration of the 1:64 scale model, we had to modify the mooringsystem to adapt to the constraints of the tank. The mooring is done not like the catenary line model but like stretched lines whose stiffness we can modify. Which anchor models should I use? Can the MAP++ or MoorDyn model take into account stiffness modifications?

Best regards,

Dear @salic.tom,

I’m not sure I understand what you mean be “stiffness modifications”, but we have used both MAP++ and MoorDyn to model the as-built configuration of a mooring system in wave tank tests. I’d probably have to understand more about the test set up to provide more specific recommendations.

Best regards,

Dear Dr Jonkman,

I am attaching a photo of the model in the tank testing. The photo is not of good quality I admit it but you could see the way in which the mooring was carried out (black arrows). So my question is this. How to adapt the Moordyn or MAP code to be able to compare the forces in the lines?

Best Regards,

Dear @salic.tom,

It looks like you should define both the fairlead and anchor location above the water. And it looks like the lines are taut. This should be fairly straightforward to define in either MAP++ or MoorDyn. You could probably tune the elastic stiffness to match the measured force-displacement relationships.

Best regards,

Dear Dr. jonkman,

Thank you for your response. How can I change elastic stiffness in Moordyn? From what I understand, Moordyn’s input file allows changing density, young’s modulus and diameter. How to integrate this parameter in moordyn?

Best regards,

Dear @salic.tom,

Are you asking about specifying a simple linear spring constant (k)? You can specify the Young’s modules (E) in MAP++ or MoorDyn, from which the equivalent linear spring constant (neglecting geometric nonlinearities) is k = E*A/L, where A is the cross-sectional area and L is the unstretched length of the mooring line.

Best regards,

Dear Dr Jonkman,

Thank you for your answer, I will try on my side.

Best Regards

Dear Dr Jonkman,

To simplify the contribution of the mooring on the model. is it possible to add, knowing the stiffness matrix of the mooring, in Hydrodyn in the AddClin part?

Best Regards

Dear @salic.tom,

Yes, you can use `AddCLin`

to specify a stiffness matrix directly in HydroDyn instead of enabling a mooring module, if that is what you prefer.

Best regards,