Dear All,
I’m trying to see the response of the system under periodic wave (only wave, without wind) conditions. I am executing Test23.fst file from the FAST directory with the default AeroDYn, HydroDyn and other module files.
I provide the “no wind” condition with these adjustments in Test23.fst file: CompInflow =0 & CompAero=0 & CompServo=0
For the periodic wave, I simply adjust WaveMod=1 (WaveHs=6m & WaveTp=10 sec)
Under these conditions FAST terminates normally.
But, I see that there is a problem.
1- Surge response: All I see is the oscillation in the natural surge frequency with an amplitude of few millimeters. Other degrees of freedom are also oscillating with the corresponding natural frequency values.
2- Wave1Elev is constantly zero.
3- I have also tried another analysis with WaveTp = 60 sec to be close to the resonance but I’ve got the same response.
4- At the end I am convinced that I am making a mistake with setting WaveMod=0 but getting the same response.
I have checked the HydroDyn manual. For periodic wave simulations, WaveHs & WaveTp adjustments are advised.
Regarding on the “no wind” conditions, I have also checked this topic “Simulating the parked turbine”: Simulating the parked turbine
I’ve tried analysis with default .fst file and the settings mentioned in the topic.
Same results…
Do you have any idea?
Sincerely,
Mustafa
Dear Mustafa,
It sounds like you’ve set WaveMod = 0 in HydroDyn, which is the model for still water (no incident waves). Use WaveMod = 1 for regular waves, 2 for irregular waves, etc. (see the HydroDyn documentation for more information: wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf).
Best regards,
Dear Jason,
Thanks for your help and suggestions.
I have checked all the settings in the input files and the fst file (Test23). Since I’m using the default settings, everything looks ok. I’ve also checked the HyrdoDyn Manual regarding on regular wave analysis. Unfortunately, I’m getting a zero response (free decay response) under regular waves without wind.
Also, I notice that Wave1Elev response is constantly zero.
On the other hand,
- I have also tried the TLP under irregular waves (JONSWAP/Pierson-Moskowitz spectrum, WaveMod=2), without wind. Works fine.
- Spar Buoy simulations under regular waves, without wind. Works fine.
I will try to simulate the regular wave conditions with WaveMod=5 (Externally generated wave-elevation time series)
Is it possible that a default setting is preventing wave generation for TLP? Have any idea?
Sincerely,
Mustafa
Dear Mustafa,
Have you applied low- or high-frequency cut-offs (WvLowCOff, WvHiCOff) that would zero out the wave spectrum at the regular wave frequency you are simulating?
Test23 originally applied directional spreading (WaveDirMod=1) to the irregular sea state (WaveMod=2); have you tried disabling directional spreading (WaveDirMod=0) for the regular sea state (WaveMod=1)?
Best regards,
Dear Jason,
Thanks for sharing your time.
The problem is solved after switching WaveDirMod from 1 to 0. It is stated that WaveDirMod is only used when WaveMod=2,3, or 4. I didn’t switch it off, continued with the default switch, while changing WaveMod from “2” to “1”. And didn’t expect that it would change the results since it is unused.
I have an another question about debugging.
I execute the FAST code by using Matlab. When I execute the code, I see that some information flows in the MATLAB command window. When I get an error, I easily get the regarding information. In the case when FAST terminates normally, I see huge amount of result matrices in the command window so the initial information feedback coming from the modules such as AeroDyn, HydroDyn is not available anymore.
In my case above, maybe FAST printed out a warning about WaveDirMod but I didn’t notice.
I’ve already turned on “ECHO” switch to TRUE in all modules and also in the main fst file for debugging purposes.
Is there a way to get the initial module feedback or another way of debugging?
Thanks again for sharing your time, help and suggestions.
Sincerely,
Mustafa
Dear Mustafa,
Regarding WaveDirMod, it looks like there is a small bug in HydroDyn. I’ve just reported this issue in OpenFAST: github.com/OpenFAST/openfast/issues/246.
I’m not sure I understand your question regarding running FAST in MATLAB. I would not expect to see a “huge amount of result matrices in the command window”. Please clarify how you are running FAST from MATLAB i.e. what commands in MATLAB you are calling.
Best regards,
Dear Jason,
Thanks for your help.
I execute the FAST code in MATLAB by simply running:
command_3=(‘FAST_x64 Test23.fst’)
[status,cmdout] = system(command_3)
Once the FAST terminates normally, I immediately call the ReadFASTbinary function:
r=ReadFASTbinary(‘Test23.outb’)
Sorry for taking your time. I’ve got my mistake, which is directly calling the ReadFASTbinary function that prints out all the result matrix.
Sincerely,
Mustafa
