How I can get mooring line tension!

Wind & Water Computer-Aided Engineering Software Tools
1

Hello everyone,
I am facing some problems while doing mooring line analysis. Problems are:

  1. In MoorDyn dat file (input file) I want the tension load for 20 segment of mooring line. For example, in the output channel i want the tension load for 20 segments of mooring line. (I don’t want FairTen1, FairTen2, FairTen3, AnchTen1, AnchTen2, and AnchTen3).
  2. I have generated a Inflow wind speed of 15 m/s using TurbSim. I want to run the .fst file for 20 min, but it cannot be executed. It shows errors. How can I solve this?
    Could you please give me the answers of these two questions?
    For details please see the attached image.
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2

Dear @JMRaisulIslam.Shohag,

Regarding (1), MoorDyn can output the tension at each node along the line by setting LineOutputs = t; see the MoorDyn v2 documentation here for more information: Input Files — MoorDyn 2.2.2 documentation.

Regarding (2), you should generate wind data from TurbSim for as long as you want to simulate in OpenFAST. It doesn’t appear that you’ve run TurbSim long enough.

Best regards,

3

Dear Dr. Jonkman,
I have generated wind speed (15m/s) by TurbSim. Then I have modified MoorDyn output as I need 20 segment mooring line tension load.

Please have a look at the MoorDyn output section whether it is right or wrong?

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:

I do simulation for 1200 s and time step 0.0125 s. After simulation I have got the tension loads for each node (63 nodes for 3 mooring line). I am calculating the number of cycles.

Now the question is: Will the number of cycles be different for each node tension loads?
N.B: I have got different different number of cycles for each node.

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Dear @JMRaisulIslam.Shohag,

Your input file looks fine. And “yes”, different nodes could have different numbers of tension cycles, depending on the system and conditions simulated.

Best regards,

5

Hi Dr. Jonkman,
I am facing some issues. Could you please help me to solve the issues?
Issues are followings:

  1. When I am setting Recommended module time step (0.5 s) in .fst file then it shows error. please look at the attached file.
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6

Dear @JMRaisulIslam.Shohag,

My guess is that you’ve set the time step of your model too large compared to the system dynamics, resulting in a numerically unstable simulation. Guidance for choosing an appropriate DT can be found in other forum topics.

Best regards,

7

Hi Dr. Jonkman,
As I told you, I am working on fatigue of mooring line of FOWTs. At first thank you for your kind and proper guidelines. Now I have one question that I am facing:

  1. I have plotted number of cycles and remained fatigue life. I have considered three mooring line and each consists of 21 nodes (20 segments). Total nodes are 63. I have found different tension for each node and afterwards my predicted number of cycles and remaining fatigue life for 63 nodes are different from each other. My question is for which nodes I should consider to go for further research. Could you please suggest me to solve this problem?

Thank you

8

Dear @JMRaisulIslam.Shohag,

I would expect the highest mooring loads to be at or near the fairleads, but I suppose that could depend on the line configuration and associated vibration characteristics.

Best regards,

9

Dear Dr. Jonkman,
Thank you.
From where I can get the line configuration and associated vibration characteristics information? Could you please tell me the specific modules or documents link?

10

Dear @JMRaisulIslam.Shohag,

I meant that you define the mooring system configuration within MoorDyn. And the full-system mode shapes (including the mooring system) can be found through an OpenFAST linearization analysis.

Regardless, if you are not certain where the “hot spots” in the mooring loads are, you can post-process the results from many nodes and identify that via post-processing.

Best regards

11

Dear Jason,

Where can I download the FAST v7 of the floating offshore wind turbine model?
Thanks in advance!

Best regards,
Kevin

12

Dear @Kevin.Chang,

The various offshore versions of the FAST v7 models of the NREL 5-MW baseline wind turbine are available from my Google Drive: NRELOffshrBsline5MW - Google Drive.

Best regards,