Modelling of a single point mooring system

Provide feedback, request enhancements, and get help with wind-turbine computer-aided engineering tools.

Moderators: Bonnie.Jonkman, Jason.Jonkman

Shuijin.Li
Posts: 8
Joined: Tue Nov 20, 2018 8:35 am
Organization: University of Dundee
Location: UK

Modelling of a single point mooring system

Postby Shuijin.Li » Sat Jan 11, 2020 4:33 pm

Dear Dr. Jonkman,

I'm modelling a single point mooring system by MoorDyn. I use the "Connect" type to connect the taught lines and the catenary lines. The program is crashed when I run it. The messages are shown below:

Running MoorDyn (v1.01.02F, 8-Apr-2016).
Creating mooring system. 3 fairleads, 3 anchors, 3 connects.
Finalizing ICs using dynamic relaxation.

t=2 FairTen 1: 9.08057E+06, 0, 0
t=3.9999 FairTen 1: 6.42890E+06, 9.08057E+06, 0
t=5.9997 FairTen 1: 5.66854E+06, 6.42890E+06, 9.08057E+06
t=7.9996 FairTen 1: 5.66904E+06, 5.66854E+06, 6.42890E+06
t=10 FairTen 1: 5.91223E+06, 5.66904E+06, 5.66854E+06
t=12.001 FairTen 1: 5.71609E+06, 5.91223E+06, 5.66904E+06
t=14.002 FairTen 1: 5.76915E+06, 5.71609E+06, 5.91223E+06
t=16.003 FairTen 1: 5.66611E+06, 5.76915E+06, 5.71609E+06
t=18.002 FairTen 1: 5.82703E+06, 5.66611E+06, 5.76915E+06
t=20.001 FairTen 1: 5.70953E+06, 5.82703E+06, 5.66611E+06
t=22 FairTen 1: 5.66990E+06, 5.70953E+06, 5.82703E+06
t=23.998 FairTen 1: 5.70613E+06, 5.66990E+06, 5.70953E+06
t=25.997 FairTen 1: 5.66090E+06, 5.70613E+06, 5.66990E+06
t=27.996 FairTen 1: 5.67416E+06, 5.66090E+06, 5.70613E+06
t=29.995 FairTen 1: 6.32161E+06, 5.67416E+06, 5.66090E+06
t=31.994 FairTen 1: 5.66489E+06, 6.32161E+06, 5.67416E+06
t=33.993 FairTen 1: 6.09927E+06, 5.66489E+06, 6.32161E+06
t=35.992 FairTen 1: 5.67193E+06, 6.09927E+06, 5.66489E+06
t=37.991 FairTen 1: 5.75716E+06, 5.67193E+06, 6.09927E+06
t=39.99 FairTen 1: 5.66598E+06, 5.75716E+06, 5.67193E+06
t=41.989 FairTen 1: 5.75036E+06, 5.66598E+06, 5.75716E+06
t=43.987 FairTen 1: 5.66603E+06, 5.75036E+06, 5.66598E+06
t=45.986 FairTen 1: 5.66959E+06, 5.66603E+06, 5.75036E+06
t=47.985 FairTen 1: 5.70357E+06, 5.66959E+06, 5.66603E+06
Fairlead tensions converged to 1% after 47.985 seconds.

FAST_InitializeAll:InitModuleMappings:ED_L_2_AD_L_T:MeshMapCreate:CreateMotionMap_L2_to_L2:CreateM
apping_ProjectToLine2:Node 1 does not project onto any line2 element.

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

Aborting FAST.


The schematic of the mooring lines is shown in the attachment.

The MoorDyn file is shown below:

--------------------- MoorDyn Input File ------------------------------------
Mooring system for OC4-DeepCwind Semi
TRUE Echo - echo the input file data (flag)
----------------------- LINE TYPES ------------------------------------------
2 NTypes - number of LineTypes
Name Diam MassDen EA BA/-zeta Can Cat Cdn Cdt
(-) (m) (kg/m) (N) (N-s/-) (-) (-) (-) (-)
catenary 0.0766 113.35 7.536E8 -1.0 0.8 0.25 2.0 0.4
tensioned 0.09 77.7066 3.84E8 -0.8 1.0 0.0 1.6 0.1
---------------------- CONNECTION PROPERTIES --------------------------------
9 NConnects - number of connections including anchors and fairleads
Node Type X Y Z M V FX FY FZ CdA CA
(-) (-) (m) (m) (m) (kg) (m^3) (kN) (kN) (kN) (m^2) (-)
1 Fixed -311.8067 512.6174 -200 0 0 0 0 0 0 0
2 Fixed -288.0364 -803.5412 -200 0 0 0 0 0 0 0
3 Fixed 839.9053 -124.8762 -200 0 0 0 0 0 0 0
4 Connect 80.0207 -138.6 -66 0 0 0 0 0 0 0
5 Connect 80.0207 -138.6 -66 0 0 0 0 0 0 0
6 Connect 80.0207 -138.6 -66 0 0 0 0 0 0 0
7 Vessel 0 0 -4.2 0 0 0 0 0 0 0
8 Vessel 0 -277.2 -4.2 0 0 0 0 0 0 0
9 Vessel 240.0605 -138.524 -4.2 0 0 0 0 0 0 0
---------------------- LINE PROPERTIES --------------------------------------
6 NLines - number of line objects
Line LineType UnstrLen NumSegs NodeAnch NodeFair Flags/Outputs
(-) (-) (m) (-) (-) (-) (-)
1 tensioned 200 20 4 7 -
2 tensioned 200 20 5 8 -
3 tensioned 200 20 6 9 -
4 catenary 835.35 40 1 4 -
5 catenary 835.35 40 2 5 -
6 catenary 835.35 40 3 6 -
---------------------- SOLVER OPTIONS ---------------------------------------
0.001 dtM - time step to use in mooring integration (s)
3.0e6 kbot - bottom stiffness (Pa/m)
3.0e5 cbot - bottom damping (Pa-s/m)
2.0 dtIC - time interval for analyzing convergence during IC gen (s)
60.0 TmaxIC - max time for ic gen (s)
4.0 CdScaleIC - factor by which to scale drag coefficients during dynamic relaxation (-)
0.01 threshIC - threshold for IC convergence (-)
------------------------ OUTPUTS --------------------------------------------
FairTen1
FairTen2
FairTen3
FairTen4
FairTen5
FairTen6
AnchTen1
AnchTen2
AnchTen3
AnchTen4
AnchTen5
AnchTen6
END
------------------------- need this line --------------------------------------


Could you please help me solve the problem? Please let me know if you need more information.

Besides, I was wondering is it possible to input the mooring line stiffness matrix into FAST? Or is it possible to constrain the degree of freedom of a point in MoorDyn, MAP++ or FEAMooring?

Thank you very much for your help in advance!

Sincerely,

Shuijin
Attachments
schematic.png
schematic.png (11.68 KiB) Viewed 429 times

Jason.Jonkman
Posts: 4539
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Modelling of a single point mooring system

Postby Jason.Jonkman » Sun Jan 12, 2020 12:29 pm

Dear Shujin,

The error you receiving doesn't seem related to MooDyn. Instead, the error that is causing FAST to abort is relating to the mesh-mapping search for ED_L_2_AD_L_T, which is the mesh-mapping search between the ElastoDyn Line2 tower motion output mesh and the AeroDyn Line2 tower motion input mesh. I'm not sure why this error is triggered in your case, but my guess is that you have an incompatibilty between how the tower discretization is defined in ElastoDyn and AeroDyn. FAST / OpenFAST will trigger this error e.g. if the tower in AeroDyn starts lower than the tower in ElastoDyn or if the tower in AeroDyn ends higher than the tower in ElastoDyn.

I'm not sure what you mean when you refer to a "mooring line stiffness matrix" and "constraining the DOF of a point". Please clarify your questions.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Shuijin.Li
Posts: 8
Joined: Tue Nov 20, 2018 8:35 am
Organization: University of Dundee
Location: UK

Re: Modelling of a single point mooring system

Postby Shuijin.Li » Mon Jan 13, 2020 9:52 am

Jason.Jonkman wrote:Dear Shujin,

The error you receiving doesn't seem related to MooDyn. Instead, the error that is causing FAST to abort is relating to the mesh-mapping search for ED_L_2_AD_L_T, which is the mesh-mapping search between the ElastoDyn Line2 tower motion output mesh and the AeroDyn Line2 tower motion input mesh. I'm not sure why this error is triggered in your case, but my guess is that you have an incompatibilty between how the tower discretization is defined in ElastoDyn and AeroDyn. FAST / OpenFAST will trigger this error e.g. if the tower in AeroDyn starts lower than the tower in ElastoDyn or if the tower in AeroDyn ends higher than the tower in ElastoDyn.

I'm not sure what you mean when you refer to a "mooring line stiffness matrix" and "constraining the DOF of a point". Please clarify your questions.

Best regards,


Dear Dr. Jonkman,

Thank you very much for your reply!

Yes, you are right. It works after I change the configuration of the tower in ElastoDyn and AeroDyn!

To clarify the questions I asked, I am trying to model a single-point mooring system for a floating offshore wind turbine. The mooring system is modelled in another finite element analysis tool, and now I have its 6x6 global stiffness matrix.

I wonder, to model the same mooring system in FAST, is it possible just to input the stiffness matrix that I have computed with another tool? Or if this is not possible in FAST, I would like to model the single point mooring(SPM) system in FAST. The SPM has a turret bearing in the merging point as showing in the picture as I attached before. I want to constraint the degrees of freedom of this merging point such that it can only have translational motion in the x-y plane. I was wondering whether it is possible to do this in FAST. If so, in which module, namely MoorDyn, MAP++ or FEAMooring, is this possible?

Thank you very much!

Best,

Shuijin

Jason.Jonkman
Posts: 4539
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Modelling of a single point mooring system

Postby Jason.Jonkman » Mon Jan 13, 2020 10:25 am

Dear Shuijin,

You can choose to enter a stiffness matrix in FAST / OpenFAST rather than to enable a mooring module. The 6x6 stiffness matrix can be specified as AddClin in HydroDyn. Presumably you also have a 6x1 vector of preloads, which you can enter as AddF0 in HydroDyn.

I'm not aware of any capabilities in the mooring modules of FAST / OpenFAST to constrain a subset of DOFs. Of course, you can enable or disable a subset of the floating platform DOFs in the ElastoDyn module.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Shuijin.Li
Posts: 8
Joined: Tue Nov 20, 2018 8:35 am
Organization: University of Dundee
Location: UK

Re: Modelling of a single point mooring system

Postby Shuijin.Li » Mon Jan 13, 2020 10:35 am

Jason.Jonkman wrote:Dear Shuijin,

You can choose to enter a stiffness matrix in FAST / OpenFAST rather than to enable a mooring module. The 6x6 stiffness matrix can be specified as AddClin in HydroDyn. Presumably you also have a 6x1 vector of preloads, which you can enter as AddF0 in HydroDyn.

I'm not aware of any capabilities in the mooring modules of FAST / OpenFAST to constrain a subset of DOFs. Of course, you can enable or disable a subset of the floating platform DOFs in the ElastoDyn module.

Best regards,


Dear Dr. Jonkman,

Thank you very much for your reply! This really helps me a lot!

Best,

Shuijin


Return to “Computer-Aided Engineering Software Tools”

Who is online

Users browsing this forum: No registered users and 1 guest