How to use MoorDyn V2

Dear everyone,
I now want to carry out a combination of synthetic fibers and anchor chains for mooring, as synthetic fibers are very nonlinear, but MoorDyn can only compute linear chains, and I learned that MoorDynv2 can compute nonlinearities and Wave kinematics, and Bending stiffness. so I would like to upgrade my MooeDyn to the V2 version.
Normally I modify MoorDyn’s inputfile to modify the mooring parameters, but I looked at https://moordyn.readthedocs.io/en/latest/theory.html and it’s not too clear how MoorDynv2 is coupled to openfast, is it still necessary to MoorDynDriver? , and at the same time is it required to be coupled with Python to work?
I hope to get help from everyone, thank you very much!
Best regards,

Dear @Yushun.Fu,

As of OpenFAST v3.3 and newer, OpenFAST is coupled to MoorDyn v2 rather than older versions of MoorDyn.

Best regards,

Dear Jason,


Thank you for your reply, as stated above, if I want to use synthetic fibers as my mooring lines, in order to account for nonlinearities, please is there an example of the file content for the alternative number, I’d like to see what the content and format of the file looks like.
I didn’t understand why there is also a column about time, do Stiffness, Internal damping, and Bent stiffness change over time, and is nonlinearity expressed through time changes?
Best regards,

Dear @Matthew.Hall
I want to try to simulate IEA15MW using the moordynv2 version in openfast, and I’m currently experiencing three problems.

The first one is the problem that I want synthetic fibers as my mooring lines, so I need to take into account its nonlinearity, which is new in v2. But I’m not quite sure what a time column and a data column stand for, is there a relevant example for me to learn from?
image

The second question is I see that v2 supports Wave Kinematics and The seabed friction[Input Files — MoorDyn 2.1.0 documentation]), why does it show as uninterpretable in the initialization in fast, is there a problem with my formatting?

The third question is I see that v2 version can consider Water Kinematics, in this input file waveelev.dat here can I use the Wave1Elev output in hydrodyn?

By the way, what is MoorDynDriver_x64 used for, I’m a little bit confused
Looking forward to your reply!

Best regards,

Dear @Matthew.Hall,
I’m working on a floating offshore wind turbine with semisubmersible platform using OpenFAST (namely, test 25, “5MW_OC4Semi_WSt_WavesWN”). I’m trying to model the mooring dynamics nonlinearly by using MoorDyn model (Fortran). As far as I know, MoorDyn model is based on a linear relationship between the tension and strains of mooring lines, represented by module of elasticity (E). However, I read that MoorDyn v2 can handle a nonlinear relationship between the tension and the strains of mooring lines. This paper : https://www.nrel.gov/docs/fy23osti/83342.pdf, discusses how to extend the capabilities of MoorDyn to handle this nonlinear relationship by looking into a user-defined lookup table.

My concern is about whether there’s a regression test in OpenFAST that incorporates MoorDyn v2, particularly considering its capability to handle the nonlinear relationship of mooring lines in MoorDyn.

Any help is appreciated.

Regards,

@Asma.Omar there is not a regression test that incorporates the non-linear look-up table in MoorDyn, however all the regression tests are up-to-date with MoorDyn v2. The paper you reference does document how MoorDyn incorporate non-linear line behavior. For the specifics of how to implement that in an input file, check out this section of the docs: Input Files — MoorDyn 2.2.2 documentation.

In general if you want example MoorDyn input files, the testing directory of the MD-C repo has a lot of good examples with v2 features (none have non-linear EA): MoorDyn/tests/Mooring at dev · FloatingArrayDesign/MoorDyn · GitHub

Heres an example of a v2 input file using non-linear stress-strain relationship:

MD input:

MoorDyn Input File                                        
----------------------- LINE TYPES ------------------------------------------        
Name  Diam  MassDen  EA       BA/-zeta   EI    Cd    Ca   CdAx   CaAx 
(-)   (m)   (kg/m)   (N)      (N-s/-)   (-)   (-)   (-)   (-)   (-)      
main  0.333  685.00  strain.txt  -1        0     1    0.27  1      0.20 
---------------------- ROD TYPES ------------------------------------
TypeName      Diam     Mass/m    Cd     Ca      CdEnd    CaEnd
(name)        (m)      (kg/m)    (-)    (-)     (-)      (-)
main           0.333   3.27E+09   1      0.27   1         0.20
---------------------- RODS ----------------------------------------
ID   RodType  Attachment  Xa    Ya    Za    Xb      Yb     Zb    NumSegs  RodOutputs
(#)  (name)    (#/key)    (m)   (m)   (m)   (m)     (m)    (m)   (-)       (-)
1     main      Fixed       0     0     -15   0       0     -10   3         p
---------------------- POINTS --------------------------------                                       
Node Type      X     Y      Z     M    V   CdA   CA
(-)  (-)      (m)   (m)    (m)   (kg) (m^3)  (m^2) (-)
1   Fixed  -800.0   0.0  -215.0    0    0    0    0
2   Fixed  800.0   0.0  -215.0    0    0    0    0
---------------------- LINES --------------------------------------       
Line  LineType NodeAnch  NodeFair UnstrLen  NumSegs    Flags/Outputs                   
(-)   (-)      (-)       (-)      (m)       (-)        (-)                 
1     main      1         R1a       850.00    40          p  
2     main      2         R1a       850.00    40          p                   
---------------------- SOLVER OPTIONS ---------------------------------------    
2        writeLog 
215      WtrDpth                                       
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)
1.0      dtIC      - time interval for analyzing convergence during IC gen (s)
200.0     TmaxIC    - max time for ic gen (s)
4.0      CdScaleIC - factor by which to scale drag coefficients during dynamic relaxation (-)
0.001    threshIC  - threshold for IC convergence (-)   
0.1             dtOut                                       
-------------------------- OUTPUTS --------------------------------
FAIRTEN1   
Line1N20Ten                               
------------------------- need this line --------------------------------------                                                                                     

strain.txt:

----Polyester----
  Strain    Tension
  (-)       (N)
  0.0       0.0
  100       1e8

Dear @Ryan.Davies,
Thank you for your response. I have a few questions.
1- Based on my understanding, I can not use the example of MoorDyn v2 with non-linear look-up table that you have included in your response as my MoorDyn input file for test “5MW_OC4Semi_WSt_WavesWN”, because the MoorDyn input file has to be compatible with the specifications of the test I am using, is this correct?
2- Those examples of MoorDyn v2 you were referring to, can they be used with any of OpenFAST’s regression tests?
3- Based on your response: “all the regression tests are up-to-date with MoorDyn v2”, the MoorDyn input file I’m using with test “5MW_OC4Semi_WSt_WavesWN” is then v2?

Your help is appreciated, Ryan.

Regards,

Hi @Asma.Omar,

  1. Correct, if you wanted to use a non-linear look-up table in the 5MW_OC4Semi_WSt_WavesWN case you mentioned then you would format the look-up table it like the one I shared above and then replace the value of EA in the MoorDyn input file with the file name (like it is done in the example). The look-up table text file needs to be in the same directory as the executable calling MoorDyn, or you can provide the file path as the EA value. The example I provided would work with the MoorDyn driver, using a standard driver file. The driver allows MoorDyn to be run on it’s own, separate from OpenFAST. You can find more info about it in the MoorDyn documentation I linked above.
  1. No, the examples I mentioned are just examples of what MoorDyn input files looks like. The regression tests are each a unique configuration, and so the mooring systems described in the MoorDyn input file wont necessarily swap between them.

  2. Yes. MoorDyn v1 is deprecated and not used in any of the most recent versions of OpenFAST, WECSim, or other codes. MoorDyn v1 still is available as a C++ code, but all users should use v2 unless they have a specific reason not to.

Hi @Ryan.Davies,
Thank you for your clear responses. I appreciate your assistance.

Regards,