Umaine Semi IEA 15 MW- Static Equilibrium analysis -HEAVE issue

[JittuVinithaJose]

I am performing a hydrostatic (still-water) equilibrium check in OpenFAST for the IEA 15 MW turbine on the VolturnUS-S semi-submersible platform. Based on the literature, I expect steady-state offsets approximately equal to:

Surge ≈ +0.413 m
Heave ≈ −0.003 m
Pitch ≈ −1.457°

INITIAL CONDITIONS

OoPDefl: 0 m – Initial out-of-plane blade-tip displacement
IPDefl: 0 m – Initial in-plane blade-tip deflection
BlPitch(1): 1° – Blade 1 initial pitch
BlPitch(2): 1° – Blade 2 initial pitch
BlPitch(3): 1° – Blade 3 initial pitch (unused for 2-blade rotors)
TeetDefl: 0° – Initial/fixed teeter angle (unused for 3 blades)
Azimuth: 0° – Initial azimuth angle for Blade 1
RotSpeed: 0 rpm – Initial/fixed rotor speed
NacYaw: 0° – Initial/fixed nacelle yaw
TTDspFA: 0 m – Initial fore-aft tower-top displacement
TTDspSS: 0 m – Initial side-to-side tower-top displacement
PtfmSurge: 0 m – Initial/fixed platform surge displacement
PtfmSway: 0 m – Initial/fixed platform sway displacement
PtfmHeave: 0 m – Initial/fixed platform heave displacement
PtfmRoll: 0° – Initial/fixed platform roll angle
PtfmPitch: 0° – Initial/fixed platform pitch angle
PtfmYaw: 0° – Initial/fixed platform yaw angle

I am using the OpenFAST model of the IEA 15-MW reference wind turbine model directly from the GitHub repository ( IEA-15-240-RWT/OpenFAST/IEA-15-240-RWT-UMaineSemi at master · IEAWindSystems/IEA-15-240-RWT · GitHub ) and made some changes to the parameters for the test,

Changes made are :

Wind (InflowWind.dat)

WindType = 1
HWindSpeed = 0.001 # Effectively zero, to prevents code crash

Waves (HydroDyn.dat)

Wave Setting- Hydrodyn.dat, but seastste is enabled so- SeaState.dat
WaveMod = 0
TMax = 400
DT = 0.05

Elastodyn.dat

RotSpeed = 0.0
GenDOF = False
CompAero = 0
CompServo = 0
CompHydro = 1 # Hydro forces active
CompMooring = 3 # Keep mooring active

Turn OFF structural flexibility:

FlapDOF1 = False
FlapDOF2 = False
EdgeDOF = False
TwFADOF1 = False
TwFADOF2 = False
TwSSDOF1 = False
TwSSDOF2 = False

I obtained surge and pitch values that match the journal results closely (Surge ≈ 0.42 m and Pitch ≈ –1.45°).
However, the heave value is still off. I’m getting –0.35 m, whereas the expected value is approximately –0.003 m.
I am attaching the graph that I plotted. It would be very helpful for your valuable insights on what I am doing wrong.

[gbarter]

Hello,

I believe you posted a similar question in the OpenFAST forums. I have not done as careful a comparison analysis as you have, but there are multiple responses in other Issues on this repository where comparisons made to data in the original report are no longer valid. I suspect that might be the case here too. Some reasons for doubting the accuracy of the original report relative to the latest model version include:

• The floating tower was significantly redesigned in v1.1 and changed the overall mass, CoM, ballast, etc.
• The hydrodynamic model has seen a few upgrades and bug fixes since the report was published. See the git commit history here.
• The OpenFAST model itself has seen many releases since the original report.