Errors encountered in muti-segment mooring line simulation

Teng.Long · August 17, 2023, 5:04pm

Dear all

I am currently using OpenFAST to simulate a multi-segment mooring line. However, I’ve encountered errors during the process. I’ve attached my MoorDyn file and the error message below for reference. The mooring line has two segments, with one being 270m long and the other being 320m.

Running MoorDyn (v2.0.0, 2022-12-08).
   This is MoorDyn v2, with significant input file changes from v1.
   Copyright: (C) 2022 National Renewable Energy Laboratory, (C) 2019 Matt Hall
   Parsing MoorDyn input file: .\5MW_WN_MoorDyn_mutiseg.dat
   Created mooring system:  18 lines, 27 points, 0 rods, 0 bodies.
   Finalizing initial conditions using dynamic relaxation.

 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 NaN detected at time   0.450000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.450000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.450000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.450000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.450000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.450000000000000       in Line           18  in MoorDyn
 .
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
   t=0.5  FairTen 1: 1.36096E+46, 1, 2
 NaN detected at time   0.500000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.500000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.500000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.500000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.500000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.500000000000000       in Line           18  in MoorDyn
 .
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
 NaN detected at time   0.550000000000000       in Line           10  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           11  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           12  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.550000000000000       in Line           18  in MoorDyn
 .
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
   t=0.6  FairTen 1: Infinity, 1.36096E+46, 1
 NaN detected at time   0.600000000000000       in Line           10  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           11  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           12  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.600000000000000       in Line           18  in MoorDyn
 .
NaN detected at time 0.6 in Point 19 in MoorDyn.
NaN detected at time 0.6 in Point 20 in MoorDyn.
NaN detected at time 0.6 in Point 21 in MoorDyn.
NaN detected at time 0.6 in Point 22 in MoorDyn.
NaN detected at time 0.6 in Point 23 in MoorDyn.
NaN detected at time 0.6 in Point 24 in MoorDyn.
NaN detected at time 0.6 in Point 25 in MoorDyn.
NaN detected at time 0.6 in Point 26 in MoorDyn.
NaN detected at time 0.6 in Point 27 in MoorDyn.
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
 NaN detected at time   0.650000000000000       in Line            1  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            2  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            3  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            4  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            5  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            6  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            7  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            8  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line            9  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           10  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           11  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           12  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.650000000000000       in Line           18  in MoorDyn
 .
NaN detected at time 0.65 in Point 19 in MoorDyn.
NaN detected at time 0.65 in Point 20 in MoorDyn.
NaN detected at time 0.65 in Point 21 in MoorDyn.
NaN detected at time 0.65 in Point 22 in MoorDyn.
NaN detected at time 0.65 in Point 23 in MoorDyn.
NaN detected at time 0.65 in Point 24 in MoorDyn.
NaN detected at time 0.65 in Point 25 in MoorDyn.
NaN detected at time 0.65 in Point 26 in MoorDyn.
NaN detected at time 0.65 in Point 27 in MoorDyn.
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
   t=0.7  FairTen 1: NaN, Infinity, 1.36096E+46
 NaN detected at time   0.700000000000000       in Line            1  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            2  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            3  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            4  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            5  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            6  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            7  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            8  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line            9  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           10  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           11  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           12  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time   0.700000000000000       in Line           18  in MoorDyn
 .
NaN detected at time 0.7 in Point 19 in MoorDyn.
NaN detected at time 0.7 in Point 20 in MoorDyn.
NaN detected at time 0.7 in Point 21 in MoorDyn.
NaN detected at time 0.7 in Point 22 in MoorDyn.
NaN detected at time 0.7 in Point 23 in MoorDyn.
NaN detected at time 0.7 in Point 24 in MoorDyn.
NaN detected at time 0.7 in Point 25 in MoorDyn.
NaN detected at time 0.7 in Point 26 in MoorDyn.
NaN detected at time 0.7 in Point 27 in MoorDyn.
 Warning: extreme pitch moment from body-attached Point            1
 Warning: extreme pitch moment from body-attached Point            2
 Warning: extreme pitch moment from body-attached Point            3
 Warning: extreme pitch moment from body-attached Point            4
 Warning: extreme pitch moment from body-attached Point            5
 Warning: extreme pitch moment from body-attached Point            6
 Warning: extreme pitch moment from body-attached Point            7
 Warning: extreme pitch moment from body-attached Point            8
 Warning: extreme pitch moment from body-attached Point            9
 ......
 NaN detected at time    1.45000000000000       in Line            1  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            2  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            3  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            4  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            5  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            6  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            7  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            8  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line            9  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           10  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           11  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           12  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           13  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           14  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           15  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           16  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           17  in MoorDyn
 .
 NaN detected at time    1.45000000000000       in Line           18  in MoorDyn
 .
NaN detected at time 1.45 in Point 19 in MoorDyn.
NaN detected at time 1.45 in Point 20 in MoorDyn.
NaN detected at time 1.45 in Point 21 in MoorDyn.
NaN detected at time 1.45 in Point 22 in MoorDyn.
NaN detected at time 1.45 in Point 23 in MoorDyn.
NaN detected at time 1.45 in Point 24 in MoorDyn.
NaN detected at time 1.45 in Point 25 in MoorDyn.
NaN detected at time 1.45 in Point 26 in MoorDyn.
NaN detected at time 1.45 in Point 27 in MoorDyn.
   t=1.5  FairTen 1: NaN, NaN, NaN
   Fairlead tensions converged to 1% after 1.5 seconds.
   MoorDyn initialization completed.

FAST_InitializeAll: NaN state detected.

 OpenFAST encountered an error during module initialization.
 Simulation error level: FATAL ERROR

 Aborting OpenFAST.

I am uncertain whether these errors are related to the initial coordinates I’ve set for the Connection points. Despite multiple attempts at adjustments, I have been unable to resolve the issue. Therefore, I am seeking suggestions to address this matter.

Thank you in advance for any guidance you can provide!

Long Teng

Jason.Jonkman · August 17, 2023, 6:45pm

Dear @Teng.Long,

Given the NaNs that are showing up in the solve, I assume that this model has gone numerically unstable. Can you share the full input file, including Solver Options.

Best regards,

Teng.Long · August 18, 2023, 2:33am

Dear @Jason.Jonkman

Thanks for prompt response.

I didn’t reply in a timely manner due to the time zone difference. Below is the full input file.

Furthermore, I am uncertain about the cause of the extreme pitch moment. The mooring line stiffness is not significant, and the distance between connection points has not exceeded the line length (the line has not been excessively tensioned).

Best Regards
Long Teng

Jason.Jonkman · August 18, 2023, 12:23pm

Dear @Teng.Long,

@Matthew.Hall can likely provide better guidance, but I would guess that your dtM is set far too large for this highly-discretized model; does dropping dtM by several orders of magnitude solve the issue?

Best regards,

Teng.Long · August 18, 2023, 2:35pm

Dear @Jason.Jonkman

I found that setting dMt to 0.001 can solve the issue.

Thanks a lot!

Best regards,

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