Coupling CFD code with FAST/OpenFAST

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Yingyi.Liu
Posts: 98
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Feb 13, 2020 10:47 am

Dear Jason,

Another question we want to ask is regarding the FAST Test 23 MIT-NREL-TLP. By setting WaveMod=6 and without specifying the input of WvKinFile in the HydroDyn setting file (which means there is no incident wave), FAST is still able to run and generate some result. Why it is able to? And what kind of incident wave has been used in the calculation? (The model can be downloaded from: https://share.iii.kyushu-u.ac.jp/public ... WV7dZbkEli)

Best regards,
Yingyi

Jason.Jonkman
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Feb 13, 2020 12:25 pm

Dear Yingyi.Liu,

Looking briefly at the source code, it appears that a fatal error should be triggered if the wave kinematics files don't exist. But perhaps there is an bug in error handling?

Looking briefly at your results, it appears that the wave elevation in this case is assumed to be zero

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Yingyi.Liu
Posts: 98
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Feb 13, 2020 7:27 pm

Dear Jason,

To make sure whether there is a bug in the source code, I then change the setting of WvKinFile to "TEST_004", and provide the wave kinematics files with a name of "TEST_004" in the same folder "/5MW_Baseline" (This model can be downloaded from https://archive.iii.kyushu-u.ac.jp/publ ... yWpjkN_QvC). However, the "Wave1Elev" output channel in Test23.out is still zero.

Since I do provide wave kinematics files to FAST with a proper setting, the "Wave1Elev" should no longer be zero any more. Therefore, could you check the source code? If there is such a bug in the code, could you please modify it and share the recompiled FAST_x64.exe file? We do need it in the calculations that we are doing now.

Many thanks.

Best regards,
Yingyi

Jason.Jonkman
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Location: Boulder, CO
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Fri Feb 14, 2020 7:06 am

Dear YingYi,

I ran your model and it appears that the wave kinematics data is not being processed correctly...likely due to formatting or naming problems with the files. I would expect FAST to throw a fatal error and abort, but it seems to be ignoring the data altogether instead. This sounds like a bug, but I have not had the opportunity to run the model through the debugger.

I would first try upgrading to OpenFAST v2.2: https://github.com/OpenFAST/openfast/releases. There was a bug involving WaveMod = 6 (https://github.com/OpenFAST/openfast/issues/118) that was fixed in a pull request (https://github.com/OpenFAST/openfast/pull/239), which has now been merged into the master branch and released in OpenFAST v2.2. If this doesn't fix the problem I suggest reopening issue #118 on OpenFAST and explaining your problem there.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Yingyi.Liu
Posts: 98
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Wed Feb 19, 2020 10:28 am

Dear Jason,

I substitute FAST_x64 with OpenFAST v2.2, it works. OpenFAST v2.2 will report error when an incorrect "WvKinFile" is given.

Thanks a lot.

Yingyi Liu

Yingyi.Liu
Posts: 98
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Wed Feb 19, 2020 10:33 am

Yingyi.Liu wrote:Dear Jason,

Following your instructions, we performed a calculation with the FAST Test24 CertTest. Note that in the legend, 'FAST-Morison' stands for calculation with the built-in functionality of FAST using the complete Morison model (PotMod=0 and PropPot=FALSE, WaveMod=1); 'FAST-Potential' stands for calculation with the built-in functionality of FAST using the hybrid Potential-Morison model (PotMod=1 and PropPot=TRUE, WaveMod=1); 'FOAM-Morison' stands for calculation with the OpenFOAM-generated 1st-order Stokes wave using the complete Morison model (PotMod=0 and PropPot=FALSE, WaveMod=6). The comparison of results for the Hywind spar platform motion is shown below.

To our disappointment, the agreement seems not good. Surprisingly, the results of 'FAST-Morison' and 'FAST-Potential' do not agree with each other, especially in surge and pitch. Do you know the reason? And is it reasonable and acceptable?

Thanks.

Best regards,
Yingyi


Dear Jason,

Could you check the above quoted my previous post on Fri Feb 14, 2020 3:37 am? I do not understand why the results of 'FAST-Morison' and 'FAST-Potential' do not agree with each other, because they are FAST built-in functionalities. Do you know why? Are the results reasonable and acceptable?

The calculation was done by FAST_v8.16.

Best regards,

Yingyi

Jason.Jonkman
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Wed Feb 19, 2020 12:43 pm

Dear Yingyi.Liu,

Sorry, I did not see your post on Feb 13, 2020 10:37 am, likely because you posted again right afterword.

I would expect that the strip-theory solution and potential-flow solution to give quite similar results for the OC3-Hywind floating wind system if the OpenFAST inputs are set properly.

For the strip-theory only solution, "FAST-Morison", what else did you change in the HydroDyn input file besides PotMod and PropPot? Did you specify the correct transverse added-mass coefficient (SimplCa = 0.969954), based on the OC3-Hywind specification document: https://www.nrel.gov/docs/fy10osti/47535.pdf? Did you add the correct hydrostatic restoring matrix (AddCLin), based on the HydroDyn documentation, section 6.8.3: https://wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf?

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Yingyi.Liu
Posts: 98
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Feb 20, 2020 3:03 am

Dear Jason,

Yes, you are correct, I have not changed other settings in the HydroDyn input file. Regarding the two settings you mentioned above, I have questions:

(1) Should SimplCa = 0.969954 be used only in Morison model? and in potential solution SimplCa should be 0 ?

(2) I notice that the HydroDyn manual suggests the users to calculate AddCLin by themselves. Can we use the hydro restoring matrix data in spar.hst which is calculated by WAMIT for AddCLin ? Since in this case we can avoid calculating it manually by ourselves.

Best regards,
Yingyi

Jason.Jonkman
Posts: 4539
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Feb 20, 2020 6:42 am

Dear Yingyi.Liu,

Here are my answers to your questions:

(1) For the potential-flow solution (PropPot = True), SimplCa is not used (because the fluid inertia and added mass terms are accounted for in the potential-flow solution rather than in the strip theory solution). So, it doesn't matter how SimplCa is set when PropPot = True.

(2) Yes, you can use the values from the *.hst file to set AddCLin. But please be aware that the values in the *.hst file are nondimensional, and so, have to be dimensionalized first (multiplying by WtrDens*Gravity*WAMITULEN^exp, where exp is 2, 3, or 4 depending on the term, but WAMITULEN is often set to 1 m, so, often doesn't matter).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


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