Problemes with the difference of FASTv7 and FASTV8

Dear Jason,
I am a new user of Aerodyn V15.04, and FAST v8 also. I am a graduated student, I used the Oc3-monpile model of TEST19 in FASTV8. I have encountered some problems, and I think you can share your experience in this field.

1.I used the model was conducted in a typical working conditions, the typical working condition is steady wind v = 8 m/s , regular wave T = 10 s, H = 6 m, other primary input file I didn’t change, when using a FAST simulation of wave height of Airy wave curve is not a regular wave, it is like a stream function, the picture is the wave height. Then I disable the WvDiffQTF and WvSumQTF in HydynDyn files, I found my output wave high schedule rules is airy wave, I want to ask is that disable and enable both what effect will the wave height schedules, and have an effect on other parameters.

2.Under the same conditions,I set the RotorSpeed=8rpm, In addition, the results were simulated , and the results were compared with the simulation of FASTv7, and the difference was found to be large. This is the input file and comparison diagram of my ElstonDyn.
NRELOffshrBsline5MW_OC3Monopile_ElastoDyn.zip (4.24 KB)

3.I also set up three different types of rotor speed, respectively is rotorSpeed = 8, rotorSpeed = 10, rotorSpeed = 11.4, and has carried on the simulation in FAST18, I found that the output RotorSpeed will eventually tend to 8.9, which I don’t really understand this situation.

Best regards,
Zhou Lin

Dear Zhou.Lin,

I’m not sure I fully understand your questions, but here are my attempts to answer them:

  1. Input parameters WvDiffQTF and WvSumQTF in HydroDyn can be used to enable/disable difference-frequency and sum-frequency second-order wave kinematics. Disabling both will result in linear Airy waves. See the draft HydroDyn User’s Guide and Theory Manual for more information: wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf.

  2. I would not expect large differences between FAST v7 and FAST v8 simulations under equivalent conditions. I would guess that there are some differences in the simulation set-up between your FAST v7 and FAST v8 models. But it is difficult for me to guess as to what these differences would be.

Please note that when briefly perusing your ElastoDyn input file, I noticed that you eliminated the initial PtfmHeave of -0.0009 m from the setting used in Test19. However, this was set to eliminate ringing in the vertical direction as a result of a small compression of the monopile structure modeled in SubDyn. See section 5.4 of the draft SubDyn User’s Guide and Theory Manual for more information: wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf.

  1. If you are not changing the wind speed between the various simulations, I would expect the active control system to regulate the rotor speed to the same equilibrium condition regardless of the initial rotor speed set.

Best regards,

Dear Jason,
Thank you for your quick reply.I’m sorry that I can’t clearly describe my problem.
For the first question I have a general idea of what these two parameters(WvDiffQTF and WvSumQTF) mean.Thank you for your advice on HydronDyn Files.

For your second question, I want to say is that using FASTv7 simulation time step is the interval step 0.0123 s and 0.0122 s, and I in FASTv8 simulation time step is 0.005 s, at the same time I will ElstoDyn module will Integration time step (s) from the Default changed to 0.0025 s,The difference between FASTv7 and FASTv8 is due to the difference in time step, of course, the most likely is due to the model is different between the two.
Below is my main input file.
input files.zip (2.19 MB)

Third question, I think I should understand what you mean. Thank you for your advice.

Best regards,
Zhou Lin

Dear Zhou,

I’m not sure I understand what you are saying regarding the second question. Are you asking me a new question or did you solve the problem yourself?

Best regards,

Dear Jason,
Thank you very much for your help. I have benefited a lot from this.

I am sorry for what I said, but I have understood the second question.

Also, I have a little problem.I have a little doubt about the output of the SubDyn files. If I want to output the bending moment on the MSL, I have to specify the Joints and the member. but, for M2N1MKxe, M2N1MKye. The explanation for these two parameters is that the local side-to-side and fore-aft bending moments at node 1 of member 3 (located at 0 m, i.e. MSL). ,Why is M2N1 interpreted as node 1 of member 3 ? So, M2N1Mkxe is the shear force on the MSL or the half way between MSL and mudline ?),

Best regards,
Zhou Lin

Dear Zhou Lin,

From Appendix C of the draft SubDyn User’s Guide and Theory Manual: wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf:

In this case, M2N1 is associated with row 2, which reads:

   3          1          1

, which refers to node 1 of member 3.

I hope that helps.

Best regards,

Dear Jason,
Thank you for your quick reply,I have already understood the related nodes parameters of the output in SubDyn . Thank you very much for your help. This is very useful for me.

I have another problem in the post-processing Mcrunch, I hope you can share your experience.I have already install the MatLab Component Runtime (MCR) and read the Mcrunch manual,

but,I can’t find the McRunch.exe and McRunch.ctf files,So I can’t copy, and how to run MCrunch is also a question, I hope you can help me to solve my doubt, thank you for your kindness! :slight_smile:

Best regards,
Zhou Lin

Dear Zhou.Lin,

The MCrunch.exe and MCrunch.ctf files are contained in the “Compiled” directory of the MCrunch archive: nwtc.nrel.gov/MCrunch.

To run these, copy MCrunch.exe and MCrunch.ctf to the folder that that contains the MCrunch input file you want to use. In a Windows Command Prompt, cd to that folder and type in

MCrunch FileName.mcru

, where FileName is the filename of the MCrunch input file.

Best regards,

Dear Jason,
Thank for you quick reply,
I have copied all the files in the “Compiled” in accordance with your steps,

and put them in the folder I specified. and I installed the MatLab Component Runtime (MCR). But I still can’t run, This is my folder


and the running window is as follows, I don’t quite understand this meaning.1526995478.png
Thank you for your kindness. Thank you very much.

Best regards,
Zhou.Lin

Dear Zhou.Lin,

It looks the executable you are using is named MCrunch_win64.exe or MCrunch_win32.exe rather than MCrunch.exe. Which version of MCrunch are you using?

Best regards,

Dear Jason,
Thank you for you quick reply.
I used the compiled version of MCrunch,And it’s downloaded from your website.https://nwtc.nrel.gov/MCrunch,

.
In the “Compiled” directory of the MCrunch archive nwtc.nrel.gov/MCrunch., I can only find MCrunch_win64. exe or MCrunch_win32. exe rather than MCrunch.exe, I’m confused. I hope you can solve my doubts.
Thank you for your kindness and thanks again.
Best regards,
Zhou Lin

Dear Zhou.Lin,

Can you run the software by opening up a Windows Command Prompt to the folder where your files and executables are stored and type in:

MCrunch_win32.exe Test_01.mcru

?

Best regards,

Dear Jason,
Thank you for your quick reply,I have solved this problem. Thank you again
Best regards,
Zhou Lin