Making fault

Discuss acquisition, use, and manipulation of airfoil data.

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Yichau.Liu
Posts: 18
Joined: Sun Nov 27, 2016 6:07 pm
Organization: Tsinghua University
Location: China

Re: Making fault

Postby Yichau.Liu » Sat Feb 16, 2019 6:03 am

Dear Jason,

It's very kind of you. Thank you for helping check the results. In my case, the OWT starts to generate wind power only after 50s since the rotor speed and generator speed have a set-up process and increase from 0 at the beginning (0s) and reach rated value at around 50s. I think this is the reason that the tower side-to-side don't deflect until ~50s. Anyway, good to know that such a steady tower top acceleration seems reasonable and I will try to include some turbulence if large tower acceleration is expected. Thanks again.

Best

Yichau.Liu
Posts: 18
Joined: Sun Nov 27, 2016 6:07 pm
Organization: Tsinghua University
Location: China

Re: Making fault

Postby Yichau.Liu » Wed Mar 13, 2019 4:36 pm

Dear Matt.Hall,

Thank you for your help last time and I also hope to realize the same mooring line failure (fairlead and anchor failures) in the MoorDyn C, namely the C lib. that I downloaded on your website (http://www.matt-hall.ca/moordyn.html). It also would be connect to the MATLAB in my case. The fairlead failure is zeroing the tension at the fairlead while the anchor failure is realized by a large length of the line segment attached to the seabed, as you suggested. But it seems that the source code in MoorDyn C is a much different with the MoorDyn in FASY v8 that I asked before. I have no idea which source code (Connection.cpp, Line.cpp, NoorDyn.cpp), which variable and which sub-function I can revise. Can you give me some clues? Many thanks to you and look forward to hearing from you.

Best

Matt.Hall wrote:Hi Yichau.Liu,

Simulating mooring line failures would be an interesting capability. I've thought of the idea itself, but never how to go about realizing it in MoorDyn. Here are a few initial thoughts in case they are of help.

Most of MoorDyn's information about the mooring system is stored in "m" (the MiscVar structure), so you would probably want to add variables within it to specify the details of the failure, unless you chose to hardcode in the specifics of each failure.

I can think of two general approaches for implementing the failure:
(1) Modifying the data in m once the failure occurs to represent the disconnection without changing MoorDyn's calculation process, or
(2) Modifying the calculations within MD_CalcContStateDeriv (specifically within DoLineRHS) to get the same effect as a failed line.

Your ideas are in the second category, which is I think a good place to start. For the fairlead failure, I agree that zeroing the tension seems reasonable. You could simply set FairFtot to zero in DoLineRHS for the failed line. For the anchor failure, you could change the anchor node position (Line%r(J,0) in DoLineRHS), but abrupt position changes might cause some problematic damping forces. An option that I think would be just as effective and potentially simpler would be to set the length of the line segment that attaches to the anchor to be very large (i.e. set Line%l(1) in DoLinesRHS to a large number).

Hope that helps, and I look forward to hearing how it goes!

Best,
Matt


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