Simulating the structrual response and platform motion based on the specified wind load series

[QB-Lin]

I have a number of wind load series. The wind load consist of the aerodynamic lift, drag, and torque on each mass point of blade and tower. The wind load varied with time, and the wind load series are stored in a csv file.
Could OpenFAST read the wind load series from a specified csv file, and calculated the structural response (blade tip displacement and root force, tower top displacement) and platform motion of floating offshore wind turbine using beamdyn and hydrodyn modules? Is it easy to realize? I am a primary programer.
Based on the introduction book, I found that modifying the fortran code might work. Is that true?
"
https://openfast.readthedocs.io/en/main/source/user/beamdyn/input_files.html

BeamDyn is capable of handling more complex loading cases, e.g., time-dependent loads, through customization of the source code (requiring a recompile of stand-alone BeamDyn). The user can define such loads in the BD_InputSolve subroutine in the Driver_Beam.f90 file, which is called every time step. The following section can be modified to define the concentrated load at each FE node:

u%PointLoad%Force(1:3,u%PointLoad%NNodes) = u%PointLoad%Force(1:3,u%PointLoad%NNodes) + DvrData%TipLoad(1:3)
u%PointLoad%Moment(1:3,u%PointLoad%NNodes) = u%PointLoad%Moment(1:3,u%PointLoad%NNodes) + DvrData%TipLoad(4:6)
where the first index in each array ranges from 1 to 3 for load vector components along three global directions and the second index of each array ranges from 1 to u%PointLoad%NNodes, where the latter is the total number of FE nodes. Note that u%PointLoad%Force(1:3,:) and u%PointLoad%Moment(1:3,:) have been populated with the point-load loads read from the BeamDyn driver input file using the call to Transfer_Point_to_Point earlier in the subroutine.

For example, a time-dependent sinusoidal force acting along the X
direction applied at the 2nd
FE node can be defined as

u%PointLoad%Force(:,:) = 0.0D0
u%PointLoad%Force(1,2) = 1.0D+03SIN((2.0pi)*t/6.0 )
u%PointLoad%Moment(:,:) = 0.0D0
with 1.0D+03 being the amplitude and 6.0 being the period. Note that this particular implementation overrides the tip-load and point-loads defined in the driver input file.

Similar to the concentrated load, the distributed loads can be defined in the same subroutine

DO i=1,u%DistrLoad%NNodes
u%DistrLoad%Force(1:3,i) = DvrData%DistrLoad(1:3)
u%DistrLoad%Moment(1:3,i)= DvrData%DistrLoad(4:6)
ENDDO
where u%DistrLoad%NNodes is the number of nodes input to BeamDyn (on the quadrature points), and DvrData%DistrLoad(:) is the constant uniformly distributed load BeamDyn reads from the driver input file. The user can modify DvrData%DistrLoad(:) to define the loads based on need.

We note that the distributed loads are defined at the quadrature points for numerical integrations. For example, if Gauss quadrature is chosen, then the distributed loads are defined at Gauss points plus the two end points of the beam (root and tip). For trapezoidal quadrature, p%ngp stores the number of trapezoidal quadrature points.
"

[jjonkman]

Dear @QB-Lin,

If you have predefined force and moment point load time series, you could use the StC_DOF_MODE = 4 option of the Structural Control (StC) submodel of ServoDyn to apply these point loads to the blades, nacelle, tower, or substructure of a full OpenFAST model. You'll need to define one instance of StC for each point load you want to apply. StC cannot read .csv files, but but you could convert these to simple text files that StC could read. This approach would not require a source code change. More information on using StC is available on readthedocs: https://openfast.readthedocs.io/en/main/source/user/servodyn-stc/StC_input.html#prescribed-time-series.

You could also change the source code, but this would potentially be more work.

FYI: By applying precomputed aerodynamic loads to a structural model, these loads will naturally not depend on the structural motion, and so, aero-elastic interaction would be lost in the process. This may not be the best approach, depending on what you want you are after.

Best regards,

[QB-Lin]

Thank you very much, and I would try it as soon as possible @jjonkman
Actually, my wind load series are from the output of OpenFAST AERODYN15 MODULE
For example,
"
AB1N002Fxi
AB1N002Fyi
AB1N002Fzi
AB1N002Mxi
AB1N002Myi
AB1N002Mzi
"
I noticed that the StC model requires the wind load in the global coordinate.
Do the wind load series above available for the STC module?

[QB-Lin]

I found that OpenFAST 3.5.0 could not output these variables

"
AB1N002Fxi
AB1N002Fyi
AB1N002Fzi
AB1N002Mxi
AB1N002Myi
AB1N002Mzi
"

My setting about output in Aerodyn15.dat is:

"
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
====== Outputs for all blade stations (same ending as above for B1N1.... =========================== [optional section]
3 BldNd_BladesOut - Number of blades to output all node information at. Up to number of blades on turbine. (-)
"All" BldNd_BlOutNd - Future feature will allow selecting a portion of the nodes to output. Not implemented yet. (-)
OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
Vrel
Alpha
Phi
Vindx
Vindy
Fxi
Fyi
Fzi
Mxi
Myi
Mzi
Fn
Ft
Mm
Fl
Fd
Cn
Ct
Cm
Cl
Cd
"

The log is:

BldNdOuts_SetOutParam:Fyi is not an available output channel.
BldNdOuts_SetOutParam:Fzi is not an available output channel.
BldNdOuts_SetOutParam:Negative channels not allowed for nodal outputs. Resetting channel name.
BldNdOuts_SetOutParam:xi is not an available output channel.
BldNdOuts_SetOutParam:Negative channels not allowed for nodal outputs. Resetting channel name.
BldNdOuts_SetOutParam:yi is not an available output channel.
BldNdOuts_SetOutParam:Negative channels not allowed for nodal outputs. Resetting channel name.
BldNdOuts_SetOutParam:zi is not an available output channel.

[QB-Lin]

I found that the STC control for each blade is identical, which is unsuitable when the turbine is under the parked condition. The wind load on different blades might have significant variation in the parked condition.
Are there any method?

Actually, I just hope to calculate the blade deformation without the full consideration of aeroelasticity using OpenFAST. Are there any tricks?

[jjonkman]

Dear @QB-Lin,

You can always check the change logs to figure out which release include AeroDyn nodal outputs Fxi, Fyi, ...., Mzi; I don't recall. Alternatively, you could upgrade to the newest release of OpenFAST (now v4.1.0), which does include these outputs.

But good point regarding StC. You'd have to specify the same applied forces to each blade, which is not ideal. To apply your own load time series without this limitation will require a source-code change.

Or you could certainly change tactics and consider aero-elasticity, using AeroDyn coupled within OpenFAST. I'm actually not sure why you'd want to precompute aerodynamic loads from AeroDyn and then apply these loads to a separate OpenFAST model.

Best regards,

[andrew-platt]

Dear @QB-Lin,

I'm not positive that we always list all the output channel changes in the release notes for each OpenFAST release. If you want a list of the currently available output channels and their descriptions, take a look at the OutListParameters.xlsx file corresponding to the release you are using (for 4.1.0: https://github.com/OpenFAST/openfast/blob/v4.1.0/docs/OtherSupporting/OutListParameters.xlsx)

As you noted, the StC for the blade time series load application is applied identically to all blades. This is something we will likely change in a future release, but that may be a year or more away. If you do make code modifications, feel free to start a discussion about it.

Regards,

[QB-Lin]

Thank you! @jjonkman @andrew-platt
Is the induction in BEMT calculations (induced velocity) the key for the aero-elasto interaction of OpenFAST module?
Could I close some setting as false in OpenFAST to ignore the aero-elasto interaction? For example, TanInd and WakeMod in Aerodyn module.

[jjonkman]

Dear @QB-Lin,

The key to aero-elastic interaction in OpenFAST is that the aerodynamic loads computed by AeroDyn depend on the structural motions (position, orientation, velocity) computed by the structural solver (ElastoDyn and/or BeamDyn). This is true even when the wake / induction is disabled in AeroDyn with WakeMod = 0.

Best regards,

[jjonkman]

This conversation continues in the following issue: #2893.