Modelling of a single point mooring system

Wind & Water Computer-Aided Engineering Software Tools
1

Dear Dr. Jonkman,

I’m modelling a single point mooring system by MoorDyn. I use the “Connect” type to connect the taught lines and the catenary lines. The program is crashed when I run it. The messages are shown below:

The schematic of the mooring lines is shown in the attachment.

The MoorDyn file is shown below:

Could you please help me solve the problem? Please let me know if you need more information.

Besides, I was wondering is it possible to input the mooring line stiffness matrix into FAST? Or is it possible to constrain the degree of freedom of a point in MoorDyn, MAP++ or FEAMooring?

Thank you very much for your help in advance!

Sincerely,

Shuijin

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2

Dear Shujin,

The error you receiving doesn’t seem related to MooDyn. Instead, the error that is causing FAST to abort is relating to the mesh-mapping search for ED_L_2_AD_L_T, which is the mesh-mapping search between the ElastoDyn Line2 tower motion output mesh and the AeroDyn Line2 tower motion input mesh. I’m not sure why this error is triggered in your case, but my guess is that you have an incompatibilty between how the tower discretization is defined in ElastoDyn and AeroDyn. FAST / OpenFAST will trigger this error e.g. if the tower in AeroDyn starts lower than the tower in ElastoDyn or if the tower in AeroDyn ends higher than the tower in ElastoDyn.

I’m not sure what you mean when you refer to a “mooring line stiffness matrix” and “constraining the DOF of a point”. Please clarify your questions.

Best regards,

3

Dear Dr. Jonkman,

Thank you very much for your reply!

Yes, you are right. It works after I change the configuration of the tower in ElastoDyn and AeroDyn!

To clarify the questions I asked, I am trying to model a single-point mooring system for a floating offshore wind turbine. The mooring system is modelled in another finite element analysis tool, and now I have its 6x6 global stiffness matrix.

I wonder, to model the same mooring system in FAST, is it possible just to input the stiffness matrix that I have computed with another tool? Or if this is not possible in FAST, I would like to model the single point mooring(SPM) system in FAST. The SPM has a turret bearing in the merging point as showing in the picture as I attached before. I want to constraint the degrees of freedom of this merging point such that it can only have translational motion in the x-y plane. I was wondering whether it is possible to do this in FAST. If so, in which module, namely MoorDyn, MAP++ or FEAMooring, is this possible?

Thank you very much!

Best,

Shuijin

4

Dear Shuijin,

You can choose to enter a stiffness matrix in FAST / OpenFAST rather than to enable a mooring module. The 6x6 stiffness matrix can be specified as AddClin in HydroDyn. Presumably you also have a 6x1 vector of preloads, which you can enter as AddF0 in HydroDyn.

I’m not aware of any capabilities in the mooring modules of FAST / OpenFAST to constrain a subset of DOFs. Of course, you can enable or disable a subset of the floating platform DOFs in the ElastoDyn module.

Best regards,

5

Dear Dr. Jonkman,

Thank you very much for your reply! This really helps me a lot!

Best,

Shuijin