Dear jason

In the latest OpenFAST v3.0, I rebuild the model mentioned above. The main ElastoDyn and HydroDyn parameters are attached below, .hst file which calculated from WAMIT is also included.

- ElastoDyn

In ElastoDyn, PtfmCMxt=-42.97 (More offset than Point A to account for the mass of the RNA and tower, same reason for the PtfmPIner).

- HydroDyn

In HydroDyn, PtfmRefxt=-40.414(Point A),PtfmVol0 is the same as the WAMIT output, PtfmCOBxt also =-40.414. No strip theory member accounted because the damping are set up according to the model test.

- WAMIT output

In WAMIT output used here, the WAMIT model was built with the orgin at Point A, and the C44 and C55 in .hst file proved that,these values are same because the WAMIT model was built up with the symmtery geometry, and the Vertical center of mass was zero in WAMIT model.

4.MoorDyn

In moordyn, the mooring parameters are basically set up and the static pull-up test shows good agreement between the FAST and the model test.

Based on the setup above, I can get the static equilibrium position and acceptable Surge and Heave Decay result, however, the Roll and Pitch Decay show different natural periods between these two modes while the model test shows the same(see figure attached). In my assumption, the rotational inertia of the intire system (RNA ,tower, platform)was close between Roll and Pitch mode. The hydrostatic restoring matrix in the hst file also show that C44 and C55 is the same. So the roll and pitch decay test should agree well.

Would you please give my question a look?

Best regards,

ElastoDyn

```
-42.97 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters) //to be decided
0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters) ////to be decided
-7.59 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters) //14-6.41
0 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters) //to be decided
---------------------- MASS AND INERTIA ----------------------------------------
0 TipMass(1) - Tip-brake mass, blade 1 (kg)
0 TipMass(2) - Tip-brake mass, blade 2 (kg)
0 TipMass(3) - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
44501 HubMass - Hub mass (kg)
76465 HubIner - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
534.116 GenIner - Generator inertia about HSS (kg m^2) //LY4MW Undefined
140000 NacMass - Nacelle mass (kg)
2.05E+06 NacYIner - Nacelle inertia about yaw axis (kg m^2)
0 YawBrMass - Yaw bearing mass (kg)
8.578E+06 PtfmMass - Platform mass (kg)
8.08E+09 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
6.78E+09 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
1.37E+10 PtfmYIner - Platform inertia for yaw rotation about the platform CM (kg m^2)
type or paste code here
```

HydroDyn

```
1 PotMod - Potential-flow model {0: none=no potential flow, 1: frequency-to-time-domain transforms based on WAMIT output, 2: fluid-impulse theory (FIT)} (switch)
1 ExctnMod - Wave-excitation model {0: no wave-excitation calculation, 1: DFT, 2: state-space} (switch) [only used when PotMod=1; STATE-SPACE REQUIRES *.ssexctn INPUT FILE]
1 RdtnMod - Radiation memory-effect model {0: no memory-effect calculation, 1: convolution, 2: state-space} (switch) [only used when PotMod=1; STATE-SPACE REQUIRES *.ss INPUT FILE]
60 RdtnTMax - Analysis time for wave radiation kernel calculations (sec) [only used when PotMod=1 and RdtnMod=1; determines RdtnDOmega=Pi/RdtnTMax in the cosine transform; MAKE SURE THIS IS LONG ENOUGH FOR THE RADIATION IMPULSE RESPONSE FUNCTIONS TO DECAY TO NEAR-ZERO FOR THE GIVEN PLATFORM!]
Default RdtnDT - Time step for wave radiation kernel calculations (sec) [only used when PotMod=1 and ExctnMod>1 or RdtnMod>0; DT<=RdtnDT<=0.1 recommended; determines RdtnOmegaMax=Pi/RdtnDT in the cosine transform]
1 NBody - Number of WAMIT bodies to be used (-) [>=1; only used when PotMod=1. If NBodyMod=1, the WAMIT data contains a vector of size 6*NBody x 1 and matrices of size 6*NBody x 6*NBody; if NBodyMod>1, there are NBody sets of WAMIT data each with a vector of size 6 x 1 and matrices of size 6 x 6]
1 NBodyMod - Body coupling model {1: include coupling terms between each body and NBody in HydroDyn equals NBODY in WAMIT, 2: neglect coupling terms between each body and NBODY=1 with XBODY=0 in WAMIT, 3: Neglect coupling terms between each body and NBODY=1 with XBODY=/0 in WAMIT} (switch) [only used when PotMod=1]
"HydroData/Middle" PotFile - Root name of potential-flow model data; WAMIT output files containing the linear, nondimensionalized, hydrostatic restoring matrix (.hst), frequency-dependent hydrodynamic added mass matrix and damping matrix (.1), and frequency- and direction-dependent wave excitation force vector per unit wave amplitude (.3) (quoted string) [MAKE SURE THE FREQUENCIES INHERENT IN THESE WAMIT FILES SPAN THE PHYSICALLY-SIGNIFICANT RANGE OF FREQUENCIES FOR THE GIVEN PLATFORM; THEY MUST CONTAIN THE ZERO- AND INFINITE-FREQUENCY LIMITS!]
1 WAMITULEN - Characteristic body length scale used to redimensionalize WAMIT output (meters) [only used when PotMod=1]
-40.414 PtfmRefxt - The xt offset of the body reference point(s) from (0,0,0) (meters) [1 to NBody] [only used when PotMod=1]
0.0 PtfmRefyt - The yt offset of the body reference point(s) from (0,0,0) (meters) [1 to NBody] [only used when PotMod=1]
0.0 PtfmRefzt - The zt offset of the body reference point(s) from (0,0,0) (meters) [1 to NBody] [only used when PotMod=1. If NBodyMod=2,PtfmRefzt=0.0]
0.0 PtfmRefztRot - The rotation about zt of the body reference frame(s) from xt/yt (degrees) [1 to NBody] [only used when PotMod=1]
9130.78 PtfmVol0 - Displaced volume of water when the platform is in its undisplaced position (m^3) [only used when PotMod=1; USE THE SAME VALUE COMPUTED BY WAMIT AS OUTPUT IN THE .OUT FILE!]
-40.414 PtfmCOBxt - The xt offset of the center of buoyancy (COB) from the platform reference point (meters) [only used when PotMod=1]
0 PtfmCOByt - The yt offset of the center of buoyancy (COB) from the platform reference point (meters) [only used when PotMod=1]
```

.hst

```
3 3 3.580E+02
3 4 -8.514E-02
3 5 -1.265E-01
3 6 0.000000E+00
4 1 0.000000E+00
4 2 0.000000E+00
4 3 0.000000E+00
4 4 2.257E+05
4 5 1.377E+00
4 6 8.61E+02
5 1 0.000000E+00
5 2 0.000000E+00
5 3 -1.533109E-02
5 4 0.000000E+00
5 5 2.257E+05
5 6 3.186E+02
6 1 0.000000E+00
6 2 0.000000E+00
6 3 0.000000E+00
6 4 0.000000E+00
6 5 0.000000E+00
6 6 0.000000E+00
```