RyanDavies19
commented
8 months ago Hi @MikeFengK, the reason you are seeing issues is because you have three points listed as vessel, which is equivalent to having three coupled points. This means that you would need to provide MoorDyn a state vector and derivative of size 9 (3 coupled points x 3 dof per point). Additionally your input file defines the points at non-zero positions, but the state vector you provide tells MoorDyn the points are at 0,0,0. If you change to a size 9 vector with positions of the line attachments you should get the results you are looking for in terms of the forces at each fairlead. Your x vector in that case would look something like: [p4x, p4y, p4z, p5x, p5y, p5z, p6x, p6y, p6z] with dx in the same order.
If you wanted to get a 6 DOF response on your model, you should use a coupled body object and attach your fairleads to the body: Bodies. In this case, MoorDyn will take the 6 dof location of the coupled body as input and return the forces and moments at the bodies location.
I'll also note that MoorDyn has a Matlab wrapper if you compile the code from the source. Your method will work fine as well, but if you want you can read more about it here: https://moordyn.readthedocs.io/en/latest/drivers.html#matlab
MikeFengK
Hello!
I established the model of OC4-5MW semi-submersible wind turbine in Matlab, and the wind turbine platform was connected with three mooring lines. It is hoped that the tension of the three mooring lines on the three connection points of the platform can be obtained through MoorDynV2. Or obtain the resultant force of the three lines at the center of gravity of the platform and the resultant moment at the center of gravity of the platform, please note that it is not the moment at the intersection point of the horizontal plane and the tower (the origin of the reference frame).
However, I have encountered a problem that cannot be solved. I will explain my research process and hope to get your help. Thank you.
1 Download and install: Open “ moordyn-2.2.2-win64.exe” , get “moordyn-2.2” , find “moordyn.dll” in “moordyn-2.2 \bin”, and find ”MoorDyn2.h“ in “moordyn-2.2 \include\moordyn”.
2Code： I will first try the stationary state of the platform. The resultant force generated by the three mooring lines should be [0;0;1839000] in the xyz direction, and the resultant torque should be [0;0;0].
I used the following code in matlab.
mooring_load_ptr = zeros(1,6);
mooring_load_ptr = libpointer('doublePtr',mooring_load_ptr);
[notfound,warnings] = loadlibrary('moordyn.dll','MoorDyn2.h'); system = calllib('moordyn','MoorDyn_Create','lines.txt');
x = zeros(6,1); dx= zeros(6,1);
calllib('moordyn','MoorDyn_Init',system, x, dx);
t = 0.0; dt = 0.001; calllib('moordyn', 'MoorDyn_Step', system, x, dx, mooring_load_ptr, t, dt); mooring_load = mooring_load_ptr.value;
lines.txt contains the following --------------------- MoorDyn Input File ------------------------------------ Mooring system for OC4-DeepCwind Semi ----------------------- LINE TYPES ------------------------------------------ Name Diam MassDen EA BA/-zeta EI Cd Ca CdAx CaAx (-) (m) (kg/m) (N) (N-s/-) (-) (-) (-) (-) (-) main 0.0766 113.35 7.536E8 -1.0 0 2.0 0.8 0.4 0.25 ---------------------- POINTS --------------------------------
ID Attachment X Y Z M V CdA CA (-) (-) (m) (m) (m) (kg) (m^3) (m^2) (-) 1 Fixed 418.8 725.383 -200.0 0 0 0 0 2 Fixed -837.6 0.0 -200.0 0 0 0 0 3 Fixed 418.8 -725.383 -200.0 0 0 0 0 4 Vessel 20.434 35.393 -14.0 0 0 0 0 5 Vessel -40.868 0.0 -14.0 0 0 0 0 6 Vessel 20.434 -35.393 -14.0 0 0 0 0 ---------------------- LINES --------------------------------------
ID LineType AttachA AttachB UnstrLen NumSegs Outputs (-) (-) (-) (-) (m) (-) (-)
1 main 1 4 835.35 20 - 2 main 2 5 835.35 20 - 3 main 3 6 835.35 20 - ---------------------- SOLVER OPTIONS --------------------------------------- 0 writeLog - 0.001 dtM - time step to use in mooring integration (s) RK2 tScheme
9.81 g - The gravity acceleration (m/s^2) 1025 rho - The water density (kg/m^3) 200 WtrDpth - The water depth (m) 1.0 dtIC - time interval for analyzing convergence during IC gen (s) 120.0 TmaxIC - max time for ic gen (s) 5.0 CdScaleIC - factor by which to scale drag coefficients during dynamic relaxation (-) 0.001 threshIC - threshold for IC convergence (-) 0 WaveKin - 0.25 dtWave - The time step to evaluate the waves, only for wave grid (WaveKin = 3) (s) 0 Currents - The currents model to use ------------------------- need this line --------------------------------------
When I run it once mooring_load=[1.13e+07,1.96e+07,-5.86e+06,-2.26e+07,0,-5.86e+06]， What went wrong, please