Dear everyone，
I’m currently having some problems modeling with moordyn, I’m trying to model a mooring line consisting of ‘chain-synthetic fiber-chain’, where for the EA of the synthetic fiber I’m using data from the product in question, as follows
Here is my moordyn file
--------------------- MoorDyn Input File ------------------------------------
MoorDyn v2 sample input file
---------------------- LINE TYPES -----------------------------------
TypeName Diam Mass/m EA BA/-zeta EI Cd Ca CdAx CaAx
(name) (m) (kg/m) (N) (N-s/-) (N-m^2) (-) (-) (-) (-)
Chain 0.333 685.0 3.27E+09 -1 0 1.11 0.82 0.2 0.27
Polyester 0.266 46.5 'MoorLinePolyester.dat' -1 0 1.6 1.0 0.1 0.1
---------------------- POINTS ---------------------------------------
ID Attachment X Y Z Mass Volume CdA Ca
(#) (word/ID) (m) (m) (m) (kg) (m^3) (m^2) (-)
1 Vessel -58.000 0.000 -14.000 0 0 0 0
2 Connect 75.321 0.000 -24.000 0 0 0 0
3 Connect 231.205 0.000 -64.000 0 0 0 0
4 Fixed -837.600 0.000 -200.000 0 0 0 0
5 Vessel 29.000 50.229 -14.000 0 0 0 0
6 Connect 66.601 115.459 -24.000 0 0 0 0
7 Connect 144.603 250.458 -64.000 0 0 0 0
8 Fixed 418.800 725.383 -200.000 0 0 0 0
9 Vessel 29.000 -50.229 -14.000 0 0 0 0
10 Connect 66.601 -115.459 -24.000 0 0 0 0
11 Connect 144.603 -250.458 -64.000 0 0 0 0
12 Fixed 418.800 -725.383 -200.000 0 0 0 0
---------------------- LINES ----------------------------------------
ID LineType AttachA AttachB UnstrLen NumSegs LineOutputs
(#) (name) (ID) (ID) (m) (-) (-)
1 Chain 2 1 20.00 4 -
1 Polyester 3 2 80.00 16 -
1 Chain 4 3 750.00 150 -
2 Chain 6 5 20.00 4 -
2 Polyester 7 6 80.00 16 -
2 Chain 8 7 750.00 150 -
3 Chain 10 9 20.00 4 -
3 Polyester 11 10 80.00 16 -
3 Chain 12 11 750.00 150 -
---------------------- OPTIONS -----------------------------------------
0.001 dtM time step to use in mooring integration (s)
3000000 kbot bottom stiffness (Pa/m)
300000 cbot bottom damping (Pa-s/m)
0.1 dtIC time interval for analyzing convergence during IC gen (s)
60 TmaxIC max time for ic gen (s)
0.001 threshIC threshold for IC convergence (-)
0 MU_KT axial line friction coefficients
0 MU_KA transverse line friction coefficients
"wavedynamic.dat" WaterKin the wave elevations are provided in a grid (-)
---------------------- OUTPUTS -----------------------------------------
FAIRTEN1
FAIRTEN2
FAIRTEN3
ANCHTEN1
ANCHTEN2
ANCHTEN3
END
------------------------- need this line -------------------------------------
Here is my EA file
--------------------------- Polyester -------------------------------------
Strain Tension
(-) (N)
0.0 0.0
0.9 1079100
2.6 2158200
4.1 3237300
5.6 4316400
7 5395500
This is the error I am getting, I don’t think I should be making the same mistake as error, what is the problem?
Best regards，
Hello,
Upon verification from a colleague, Ryan Davies, we have determined that the EA file needs to be located in the same directory as the main OpenFAST executable. I would double check the location of your EA file in your OpenFAST run directory. Hopefully this solves the issue.
Stein
It’s glad to hear from you, so far I’ve been able to simulate it properly, but still have a little problem that I don’t know how to solve:
Here are some of the files I changed
--------------------- MoorDyn Input File ------------------------------------
MoorDyn v2 sample input file
---------------------- LINE TYPES -----------------------------------
TypeName Diam Mass/m EA BA/-zeta EI Cd Ca CdAx CaAx
(name) (m) (kg/m) (N) (N-s/-) (N-m^2) (-) (-) (-) (-)
Chain 0.333 685.0 3.27E+09 -1 0 1.11 0.82 0.2 0.27
Polyester 0.266 46.5 'MoorLinePolyester.dat' -1 0 1.6 1.0 0.1 0.1
---------------------- POINTS ---------------------------------------
ID Attachment X Y Z Mass Volume CdA Ca
(#) (word/ID) (m) (m) (m) (kg) (m^3) (m^2) (-)
1 Vessel -58.000 0.000 -14.000 0 0 0 0
2 Free -72.14 0.000 -28.14 0 0 0 0
3 Free -128.71 0.000 -84.71 0 0 0 0
4 Fixed -837.600 0.000 -200.000 0 0 0 0
5 Vessel 29.000 50.229 -14.000 0 0 0 0
6 Free 36.07 62.48 -28.14 0 0 0 0
7 Free 64.36 111.47 -84.71 0 0 0 0
8 Fixed 418.800 725.383 -200.000 0 0 0 0
9 Vessel 29.000 -50.229 -14.000 0 0 0 0
10 Free 36.07 -62.48 -28.14 0 0 0 0
11 Free 64.36 -111.47 -84.71 0 0 0 0
12 Fixed 418.800 -725.383 -200.000 0 0 0 0
---------------------- LINES ----------------------------------------
ID LineType AttachA AttachB UnstrLen NumSegs LineOutputs
(#) (name) (ID) (ID) (m) (-) (-)
1 Chain 2 1 20.00 2 p
2 Polyester 3 2 80.00 8 p
3 Chain 4 3 750.00 75 p
4 Chain 6 5 20.00 2 -
5 Polyester 7 6 80.00 8 -
6 Chain 8 7 750.00 75 -
7 Chain 10 9 20.00 2 -
8 Polyester 11 10 80.00 8 -
9 Chain 12 11 750.00 75 -
---------------------- OPTIONS -----------------------------------------
0.001 dtM time step to use in mooring integration (s)
3000000 kbot bottom stiffness (Pa/m)
300000 cbot bottom damping (Pa-s/m)
0.1 dtIC time interval for analyzing convergence during IC gen (s)
60 TmaxIC max time for ic gen (s)
0.001 threshIC threshold for IC convergence (-)
0 MU_KT axial line friction coefficients
0 MU_KA transverse line friction coefficients
"wavedynamic.dat" WaterKin the wave elevations are provided in a grid (-)
--------------------------- Polyester -------------------------------------
Strain Tension
(-) (N)
0.0 0.0
0.9 1079100
2.6 2158200
4.1 3237300
5.6 4316400
7 5395500
Here is a schematic of my 15MW model mooring lines with synthetic fibers 80m
-
I noticed that my synthetic fiber line segments here show that the dangling chain line solution fails to start with linearization, I would like to know what causes this and if it affects my final calculation results?
-
My calculations show a huge increase in the planar motion of the platform compared to a pure iron chain. I know this affects the motion of the platform, but is there something wrong with my settings that makes this big of a difference? How can I verify that my model is set up correctly?
-
Regarding the EA file where I applied the nonlinearity, I know that displacement-force curves are a good way to verify this. Can I also use this method to verify the second question I mentioned above for this mooring line where chains and synthetic fibers are fused together?
Hello,
In regards to your first question, Matt Hall had a previous reply related to this, which was very well stated. From my understanding, this is simply a warning with the initial mooring line setup. The program is still able to solve the mooring line dynamics, but the initialization was irregular. So, it should not affect your final results. Refer back to Matt Hall’s previous response on this for further explanation.
The most noticeable difference I can find is the magnitude of your strain in the MoorLinePolyester.dat file. A strain of 1 refers to a stretch of the unstretched line length (strain = \Delta L / L ). So, it seems like your polyester line is stretching 7*80 = 560 m to reach a tension of 5.39 MN. Maybe check your values in the EA file.
Stein
Hi,
I can answer question 1, and I will defer to Stein’s answer for 2 and 3. The “Catenary solve unsuccessful” warnings from MoorDyn simply mean that an analytical solution could not be found for the catenary line shape. MoorDyn then tries to solve for equilibrium by holding all coupled points static and letting the line ‘fall’ into place. In your case, after 19.75 sections the fairlead tensions converged for each line indicating that the line had reached an equilibrium position. This will not affect your results and means the simulation is starting with the line in the correct position.
This initial condition solver is controlled by the flags TmaxIC, dtIC, CdScaleIC, and threshIC in the options section of the MoorDyn input file. You can read more here: Input Files — MoorDyn 2.1.0 documentation
Ryan
