HydroDyn with OpenFAST (v3.1.0) - Wave Seeds, Member Discretization & Hydrodynamic Coefficient Models

Wind & Water Computer-Aided Engineering Software Tools
1

Dear Jason,
Dear all,

I’m simulating the IEA 15-MW Offshore RWT with a jacket substructure (initially I started learning from the DEME Group implementation on GitHub by Maciej Mroczek)

While the simulation finally runs smoothly locally on Windows (OpenFAST v3.2.1 and HydroDyn v2.03.) I’m having problems with HydroDyn on our university cluster computer system (Unix/Slurm). Unfortunately, I cannot identify the HydroDyn version that is used (OpenFAST on the cluster is v3.1.0, so a slightly different version), but the error reports indicate that a different HydroDyn version number is probably being used.

  1. error: “FAST_InitializeAll:HydroDyn_Init:Waves_Init:VariousWaves_Init: The random number generator in use differs from the original code provided by NREL. This pRNG uses 8 seeds instead of the 2 in the HydroDyn input file.”
    –
    HydroDyn v2.03. only asks for WaveSeed(1) and WaveSeed(2). I also tried to give 8 random seeds (in one row or in 8 rows with one each) but this resulted in error messages as well. So what can I do here?

  2. error: “HydroDyn_Init:Morison_Init:SetupMembers:SetMemberProperties:The upper end-plate of a member must not cross the water plane. This is not true for Member ID 58
    SetupMembers:SetMemberProperties:The lower end-plate of a member must not cross the water plane. This is not true for Member ID 59
    SetupMembers:SetMemberProperties:The upper end-plate of a member must not cross the water plane. (…)”
    –
    First, I tried to adjust the member discretization ‘MDivSize’ - without an effect on the error message. In general, which parameter values would you recommend for (i) submerged members, (ii) semi-submerged members and (iii) members in air?
    –
    Second, I tried to switch the model from ‘simple hydrodynamic coefficients’ (model 1) to ‘depth-based hydrodynamic coefficients’ (model 2) for selected members (submerged, semi-submerged, in air). When simulating on Windows, I realized that I may not use model 2 for members that are semi-submerged (or in air) since I cannot define the depth above sea level. For the cluster simulation I could not achieve an improvement as well. Which model would you recommend for the hydrodynamic coefficients of different members?

I would be grateful for hints on how to debug and fix the error reports on Unix/Slurm and in general, which settings in HydroDyn lead to a robust simulation for scheduled thousands of simulation runs.

Many Thanks!

2

Dear @Andreas.Ehrmann,

  • OpenFAST should tell you what version is being run when you execute a simulation; what version does it say?
  • Documentation of the input file changes with each release of OpenFAST is available here: 4.1.2. API changes between versions — OpenFAST v4.0.2 documentation.
  • If you still can’t figure out the input file format issue, you could always enable the Echo option to debug issues with input file formatting.
  • The error about an “end-plate of a member must not cross the water plane” cannot be solved through adjustment to MDivSize; rather, this can only be solved by shifting joints up or down so that end plate of the members doesn’t cross through the free surface. FYI: More recent improvements to HydroDyn now permit this, so, I would encourage you to upgrade to OpenFAST v4 if you are not tied to an older version.
  • Wave stretching was introduced in HydroDyn in OpenFAST v4; in earlier versions, hydrodynamic calculations did not take place above the still water level.

Best regards,