Can you please help me clarify what should I take into account inside WAMIT? Should I consider as refernce point (pot file) the water’s free surface or the platform’s center of mass? Why does also seem that you took as center of mass (frc file) the same with the reference point?
The reference point for the potential flow solution is user-specified in HydroDyn via PtfmRefxt, PtfmRefyt, and PtfmRefzt. In most models, we place the reference point at the still water level (PtfmRefzt = 0), but you could place it somewhere else (such as the platform center of mass) if your potential-flow solution uses a different reference point.
I have another question, this time regarding the controller. I am using the 2.3.0 release of OpenFAST and when I execute a simulation, I use as initial rotor speed 12.1 rpm, combined with wind profiles having speed of 11/11.4/12 m/s at the turbine’s reference height. However, after few seconds of the simulation, the rotor speed drops around to 6 rpm and, thus, the generated power is of an order of magnitude of kW instead of MW. Since my main concern is the submerged platform, I am not familiar with the superstructure’s response under aerodynamic loads. Is this output rational or should I change something in the control files? Just to let you know, as soon as now I used the control files same as I downloaded them from the repository.
For your convenience, below I am sharing with you the content of the ServoDyn primary file. Can you please have a look and somehow guide me if I should do anything in a different way?
Which wind turbine model are you simulating? It looks like you are using the controller of the NREL 5-MW baseline wind turbine atop the OC3-Hywind spar; is this the OpenFAST model you are using?
Well, your ServoDyn file looks OK to me. I would guess there is a problem with a different setting in your OpenFAST model. It is difficult for me to guess what without more information.
Well, I would start by plotting basic response variables such time-series of hub-height wind speed, wave elevation, rotor speed, blade pitch, and blade and tower deflections, and floater displacements to check for reasonableness in the response.
Below I am attching several of the diagrams that you suggested me to. Blades seem not to have any deflection at all, so I did not attach the relevant diagrams.
The wave spectrum was of Hs=6 m, Tp=10 sec, while the wind spectrum was of wind speed 12 m/sec at hub height.
If you are sharing the correct files with me, I don’t see any reason for the rotor speed and power to be dropping.
As with any debugging issue, I would simplify the model to debug. Do you get the speed and power response you expect if you disable all structural DOFs in ElastoDyn except GenDOF?
I do share with you the actual files that I use during the simulations. I have also tried disabling all the DoF flags inside ElastoDyn, except for the GenDOF, as you suggested me. However, the problem persists.
I am also attaching the content of ElastoDyn primary file:
Are you using a precompiled executable of OpenFAST provided by NREL or did you change the source code in some way and recompile OpenFAST yourself?
How does the aerodynamic torque output from AeroDyn (RtAeroMxh) compare to RotTorq that you are outputting from ElastoDyn and GenTq you are outputting from ServoDyn?
I don’t remeber wether I downloaded directly the executable or just built it from the FAST.sln file supplied by NREL, but I am sure that I did not make any change to the code that I refer to. Below, I am attaching the time series of GenTq, RotTorq and RtAeroMxh, as you suggested. How do they look like in your opinion?
The generator torque and rotor torque start off where I’d expect them to be at rated conditions (around 4000 kN*m relative to the low-speed shaft). However, the aerodynamic torque seems much lower (400 Nm). I would guess the problem is in your aerodynamic model set up. You haven’t shared your AeroDyn blade input file, but I see in the AeroDyn primary file that you shared that you’ve introduced two extra airfoil data files (extra1.dat and extra2.dat). I’m not sure what these airfoils are and how they are used on the blade, but perhaps that is the problem.
