Coupled interaction between HydroDyn and SubDyn

OpenFAST / openfast

Main repository for the NREL-supported OpenFAST whole-turbine and FAST.Farm wind farm simulation codes.

http://openfast.readthedocs.io

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Coupled interaction between HydroDyn and SubDyn #948

Open DaraeShin opened 2 years ago

DaraeShin commented 2 years ago

Dear all,

The analysis conditions are as follows.

NREL 5MW Windturbine
Sub-structure : Monopile (rigid foundation) Dia = 6.0m, Thickness = 0.06m
Load case summary

Water depth : 20m

Analysis Results

Both wind turbine(tower, nacelle, blade) and sub-structure(monopile) conditions are rigid. Therefore, HydroFxi(Total integrated hydrodynamic load along the global x-direction) and ReactFXss(Total base reaction forces) results should be the same. However, as shown in the figure above, there are many differences.

Is there a difference in the analysis results due to the coupled interaction between HydroDyn and SubDyn? I would appreciate it if you could think about the cause.

If you need more analysis input information, please contact me.

Best regards,

jjonkman commented 2 years ago

Dear @DaraeShin,

When you say that both the wind turbine and substructure conditions are rigid, can you clarify how you defined the following inputs:

Are the platform DOFs in ElastoDyn (PtfmSgDOF ...PtfmYDOF) enabled or disabled?
Is the static improvement method (SIM) enabled in SubDyn (SttcSolve = True)?
What are CBMod and NModes set to in SubDyn?

Best regards,

DaraeShin commented 2 years ago

Dear @jjonkman

Are the platform DOFs in ElastoDyn (PtfmSgDOF ...PtfmYDOF) enabled or disabled? : All DOF False
Is the static improvement method (SIM) enabled in SubDyn (SttcSolve = True)? : SttcSlve = False
What are CBMod and NModes set to in SubDyn? : CBMod = Ture / NModes = 0

jjonkman commented 2 years ago

Dear @DaraeShin,

The loads cannot be calculated from SubDyn properly when the substructure is modeled rigidly. This is because SubDyn can model statically indeterminate structures from which the loads can only be calculated properly if structural flexibility is enabled. To capture accurate loads from SubDyn, you should enable the platform DOFs in ElastoDyn (which control the DOFs of the Guyan modes in SubDyn), you should enable the SIM (SttcSolve = True), and enable as many Craig-Bampton modes as necessary (typically the lowest modes that can be excited by the applied loading, with Nmodes > 0).

Best regards,

3sdb commented 5 months ago

Dear： I have a question: can I enter layer data in subdyn to help me implement pile-soil coupling?

jjonkman commented 5 months ago

Dear @3sdb,

What do you mean by "layer data"? Are you referring to different soil layers?

Regardless, SubDyn currently only supports the modeling of a coupled springs foundation with user-specified soil stiffness matrix.

Best regards,