Corrosive effects using openFast

[Krishnaraj18]

how can we account for corrosion in OC4 jacket in openFast?

[jjonkman]

Dear @Krishnaraj18,

Can you clarify what specifically about corrosion you want to account for in OpenFAST? Are you referring to changes in mass or stiffness?

Best regards,

[jjonkman]

Dear @Krishnaraj18,

I'm not really familiar with incremental dynamic analysis.

General post-processing tools such as MCrunch can calculate probability of exceedance of a given time series or set of time series.

Please note that your questions imply that you want to consider some sort of nonlinear push-over analysis, but you also mention that you are modeling the OC4 jacket in OpenFAST, so, presumably you are making use of the SubDyn module. However, SubDyn is limited to linear elasticity.

Best regards,

[Krishnaraj18]

sir, I have one doubt regarding the natural frquency.How can I calculate natural frequency of the entire OC4 jacket wind turbine?

[jjonkman]

Dear @Krishnaraj18,

You can use the full-system linearization functionality of OpenFAST, followed by Eigenanalysis, to determine the natural frequencies of land-based, fixed-bottom offshore, and floating offshore wind turbines. This topic has been discussed many times in other posts.

Best regards,

[Krishnaraj18]

sir, I am doing dynamic analysis corresponding to indian ocean ,so instead of JONSWAP i have to give PM spectrum.But in OpenFast JONSWAP/PM is coming as an combined option in waveMod ( WaveMod - Incident wave kinematics model {0: none=still water, 1: regular (periodic), 1P#: regular with user-specified phase, 2: JONSWAP/Pierson-Moskowitz spectrum (irregular)).So if I am giving PM what are the other input parameter I have to change. Because its coming as same option 2.If i give WaveMod 2 means which spectrum it will read?

[jjonkman]

Dear @Krishnaraj18,

The JONSWAP spectrum is a simple modification of the Pierson-Moskowitz spectrum, making the spectrum more "peaky" for storm conditions. To use the Pierson-Moskowitz spectrum, set WaveMod = 2 with WavePkShp = 1.0 in HydroDyn.

Best regards

[Krishnaraj18]

Dear Jason,
Is it possible to edit the member properties (thickness) of the members in OC4 jacket model using subdyn and will it cause any change in response of the structure. Also can we reduce the thickness of OC3 monpile in subdyn. I've tried to do the above mentioned tasks but the results are not changing. Do I only need to change the code in subdyn.dat file or should i do anything else?

[jjonkman]

Dear @Krishnaraj18,

Yes, you can modify the member properties (including thickness) within the SubDyn input file and I would expect this to change the results (loads, motions, though, the change in results may be minor for minor changes in member thickness).

Best regards,

[Krishnaraj18]

Dear Jason,
In OPenFAST I had edited the member properties (thickness) in the "subdyn.dat" file of the OC3 monopile supported OWT, but the corresponding reflections are shown in the subdyn summary file. So the loads and deflections are not changing, but instead I am getting the exact same value.( I reduced the member thickness from 6cm to 5cm).

[jjonkman]

Dear @Krishnaraj18,

I'm sorry, but I don't know what you mean when you say that, "the corresponding reflections are shown in the subdyn summary file." Are you saying that the thickness changes are seen in the SubDyn summary file in terms of changes to the masses, eigenfrequencies, etc., but are not seen in the SubDyn output file in terms of loads and deflections?

Best regards,

[Krishnaraj18]

Dear Jason,
I am extremely sorry for the typing error. What I really meant was the "the corresponding reflections are not shown in summary file".

[jjonkman]

Dear @Krishnaraj18,

So, you are not seeing any change to any SubDyn output when you change the member thickness? I would not expect this. Are you saving the file after making the input file change? Are you actually using the cross-sectional properties in a member for the PropSetID you are changing?

Best regards,

[Krishnaraj18]

Dear Jason,
Now when I checked the summary file is not generating even after giving "True" for SumPrint. I am attaching my sundyn.dat file along with this .Please say what to do.

5MW_OC3Mnpl_DLL_WTurb_WavesIrr.txt

[jjonkman]

Dear @Krishnaraj18,

Can you confirm that SumPrint is being interpreted correctly by reviewing the echo (.ech) file?

Does changing SumPrint from 1 to True solve the issue?

Best regards,

[Krishnaraj18]

Dear Jason,
I am currently working on the 5MW NREL offshore wind turbine supported over OC3 monopile. I've been trying to change the thickness of the monopile from 6cm up to 10cm and planning to conduct fatigue analysis. For that I edited the thickness in "subdyn.dat" file to 10cm, but unfortunately the results are showing the same as for 6cm thickness. Can you explain me the reason for this paradox. I am attaching the corresponding files with this reply, can you please look into it.
Output_file_6cm_thickness.txt
Output_file_10cm_thickness.txt
SubDyn.dat _For_6cm_thickness.txt
SubDyn.dat _For_10cm_thickness.txt
SubDyn.sum _For_6cm_thickness.txt
SubDyn.sum _For_10cm_thickness.txt

[jjonkman]

Dear @Krishnaraj18,

I'm not sure I understand your question. I see a lot of differences when I compare the SubDyn summary files and OpenFAST output files for your two SubDyn input files.

Please note that I see you changed more than just the thickness between these two SubDyn input files. In the 6cm file, you've selected MPropSetID1 = MPropSetID2 = 1 for all members, whereas in the 10cm file, you've selected MPropSetID1 = MPropSetID2 = 3 for all members.

Best regards,