When trying to simulate a 15 MW spar turbine in MD, I noticed a fairly large difference in the hydrostatic equilibrium positions calculated by MD-C and other tools (MD-F, MoorPy). My set-up is the turbine+spar mass and moments of inertia are defined as a body located at the systems center of gravity. From there a massless rod is attached defined relative to the body to capture the hydrodynamics and statics of the spar. This is the same system as https://www.nrel.gov/docs/fy24osti/87475.pdf. This system should initialize in equilibrium, with 15m of the rod above the surface and 85m below. However what we see is this (TmaxIC = 0):
I'm not sure how tests and other things never caught this. Here is my input file:
MoorDyn v2 Input File. 200m depth. Spar based on Spar15.yaml RAFT model.
Viscoelastic terms dropped from rope becasue not supported by MDC (dynamic or spring 2 terms)
Body is located at the CG of the FOWT, inertia and mass for FOWT from RAFT. Spar is 0 mass,
becasue mass is accounted for in FOWT. It's just for the hydro coefficients.
---------------------- 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 0.2791 480.93 2.058e+09 -1.000e+00 0.000e+00 1.200 1.000 0.20 0.00
rope 0.1438 22.42 1.424e+08 -1.000e+00 0.000e+00 1.200 1.000 0.20 0.00
cable 0.1410 35.78 2.030e+08 -1.000e+00 8.410e+03 1.200 1.000 0.20 0.00
buoy 0.2886 60.68 2.030e+08 -1.000e+00 8.410e+03 1.200 1.000 0.20 0.00
--------------------- ROD TYPES -----------------------------------------------------
TypeName Diam Mass/m Cd Ca CdEnd CaEnd
(name) (m) (kg/m) (-) (-) (-) (-)
Spar 19 0 0.8 1.0 0.6 0.6
----------------------- BODIES ------------------------------------------------------
ID Attachment X0 Y0 Z0 r0 p0 y0 Mass CG* I* Volume CdA* Ca*
(#) (-) (m) (m) (m) (deg) (deg) (deg) (kg) (m) (kg-m^2) (m^3) (m^2) (-)
1 Free 0 0 -56.366 0 0 0 24268136.698 0 71380282163.669|71380282163.669|1117249149.315 0 0 0
---------------------- RODS ---------------------------------------------------------
ID RodType Attachment Xa Ya Za Xb Yb Zb NumSegs RodOutputs
(#) (name) (#/key) (m) (m) (m) (m) (m) (m) (-) (-)
1 Spar Body1 0 0 71.366 0 0 -28.634 100 p
---------------------- POINTS -------------------------------------------------------
ID Attachment X Y Z Mass Volume CdA Ca
(#) (-) (m) (m) (m) (kg) (m�3) (m^2) (-)
1 Fixed 350.00 606.22 -200.00 0.00 0.00 0.00 0.00
2 Free 108.24 187.48 -138.42 0.00 0.00 0.00 0.00
3 Body1 5.00 8.66 26.366 0.00 0.00 0.00 0.00
4 Fixed -700.00 0.00 -200.00 0.00 0.00 0.00 0.00
5 Free -216.49 0.00 -138.42 0.00 0.00 0.00 0.00
6 Body1 -10.00 0.00 26.366 0.00 0.00 0.00 0.00
7 Fixed 350.00 -606.22 -200.00 0.00 0.00 0.00 0.00
8 Free 108.24 -187.48 -138.42 0.00 0.00 0.00 0.00
9 Body1 5.00 -8.66 26.366 0.00 0.00 0.00 0.00
10 fixed 305.00 0.00 -200.00 0.00 0.00 0.00 0.00
11 free 133.75 0.00 -179.35 0.00 0.00 0.00 0.00
12 free 47.93 0.00 -128.83 0.00 0.00 0.00 0.00
13 Body1 9.00 0.00 -21.366 0.00 0.00 0.00 0.00
---------------------- LINES --------------------------------------------------------
ID LineType AttachA AttachB UnstrLen NumSegs LineOutputs
(#) (name) (#) (#) (m) (-) (-)
1 chain 1 2 500.0 20 pv
2 rope 2 3 230.0 6 pv
3 chain 4 5 500.0 20 pv
4 rope 5 6 230.0 6 pv
5 chain 7 8 500.0 20 pv
6 rope 8 9 230.0 6 pv
7 cable 10 11 160.0 18 pv
8 buoy 11 12 124.0 18 pv
9 cable 12 13 140.0 18 pv
---------------------- OPTIONS ------------------------------------------------------
0.001 dtM
3000000.0 kb
300000.0 cb
0 TmaxIC
9.81 g
200 WtrDpth
1025 WtrDnsty
1 ICgenDynamic
4 CdScaleIC
2 dtIC
0.001 ThreshIC
0 Currents
----------------------- OUTPUTS -----------------------------------------------------
Rod1NAPZ
Body1PZ
Line2NBPZ
Line4NBPZ
Line6NBPZ
--------------------- need this line ------------------------------------------------
When trying to simulate a 15 MW spar turbine in MD, I noticed a fairly large difference in the hydrostatic equilibrium positions calculated by MD-C and other tools (MD-F, MoorPy). My set-up is the turbine+spar mass and moments of inertia are defined as a body located at the systems center of gravity. From there a massless rod is attached defined relative to the body to capture the hydrodynamics and statics of the spar. This is the same system as https://www.nrel.gov/docs/fy24osti/87475.pdf. This system should initialize in equilibrium, with 15m of the rod above the surface and 85m below. However what we see is this (TmaxIC = 0):
I'm not sure how tests and other things never caught this. Here is my input file:
Spar15_200m_cable.txt