Platform yaw in farm with shared mooring lines

Wind & Water Wind Farm Modeling
1

Hi everyone,

I am using OpenFAST-v4.0.0 in a farm modeling of two wind turbines with semi-submersible platform. The two wind turbines are aligned in streamwise direction. The front turbine is T1 and the downstream one is T2. To set up a shared mooring line case, the front platform is rotated by 180 in yaw to a position that one column is downstream and two columns are in the front (see the Figure).

In MoorDyn_shared.dat, the turbines points are specified in local coordinates, while the fixed anchor points are given in global coordinates. To achieve the platform orientation of T1, set: ElastoDyn_T1: PtfmYaw = 180 deg, PtfmYDOF=True, NacYaw=180, HydroDyn_T1: PtfmRefY = 180 deg. Both rotors are facing upstream.

The problem is:

1, If Turbine1 fairlead coordinates remain local and unmirrored, after initialization, the mooring line L1, L2 and L5 are connected to the original fairlead before 180 platform yaw (dotted lines in linex_reference.vtp), and the simulation crashes in a few steps.

Error message: T2:FARM_UpdateStates:NearWakeCorrection:Wake model is not valid in the propeller-brake region, i.e., Ct > 2.0 Aborting FAST.Farm

2, If Turbine1 fairlead coordinates remain local and mirrored, after initialization, the mooring line L1, L2 and L5 are connected to the right column in the linex_reference.vtp, but shifted to the unmirrored location (dotted line) in linex_00000.vtp, the simulation crashes in one step

Error message: T1:FARM_UpdateStates:WD_UpdateStates:The time-filtered nacelle-yaw error has reached +/- pi/2.

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I am wondering which is the correct way to input the fairlead coordinates of the turbine with a given platform yaw while keeping the rotor fixed, or anything that I have missed in the setting. I have tested the case with two independent turbines without any platform yaw, it runs fine. Any suggestions and comments are greatly appreciated.

Best regards,

Xiaoqin

2

Dear @Xiaoqin.Zhang,

I’m not sure I fully understand the two model setups you are describing (sharing input files would help). That said, I would suggest that the model set-up would be less ambiguous if you define T1 with the floater properties mirrored about its local Y axis, rather than by trying to orient the system through 180-degree yaw rotations. Do you have any issue if you set up the FAST.Farm model with shared mooring lines this way, with all yaw angles zeroed?

Best regards,

3

Dear @Jason.Jonkman

I manually switched the position of the platform T1 substructures, the mooring lines are connected properly and it runs fine. Thank you for your suggestions.

Best regards,

Xiaoqin

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