Free decay tests

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Florence.Haudin
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Location: France

Free decay tests

Postby Florence.Haudin » Tue Nov 05, 2019 4:00 am

Good morning,
I would like to know if there is among the examples provided for openfast, an example of free decay tests for a semi submersible or another platform?
I guess that the user has to implement himself the AddCLin matrix taken into account the mooring configuration/parameters?

Thanks in advance.
Best regards.
Florence Haudin.

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Free decay tests

Postby Jason.Jonkman » Thu Nov 07, 2019 10:52 am

Dear Florence,

No, none of the example simulations provided with FAST are for a free-decay test, but such a simulation is quite simple to set up. Normally free-decay tests are performed without wind or wave excitation (CompInflow=0 and most likely CompAero=0 in the FAST primary input file, and WaveMod=0 in the HydroDyn input file). Enable whichever degrees of freedom you want (most certainly the platform DOFs) and set a nonzero initial platform displacement. You shouldn't need to set AddCLin for the mooring system; instead you can enable one of the mooring modules.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Florence.Haudin
Posts: 10
Joined: Fri Feb 08, 2019 3:11 am
Organization: Vulcain
Location: France

Re: Free decay tests

Postby Florence.Haudin » Thu Nov 28, 2019 9:31 am

Dear Jason,
Thanks for your answer.
Is it possible with Openfast to run a simulation with Hydrodyn, Moordyn and Elastodyn with nothing on the floater or only a rigid tower for instance but no turbine. I don't understand how to "remove" the tower or the blades in Elastodyn.
Thanks in advance.
Best regards.
Florence.

Jason.Jonkman
Posts: 4394
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Free decay tests

Postby Jason.Jonkman » Fri Nov 29, 2019 9:00 am

Dear Florence,

To "remove" the rotor, nacelle, and tower from an ElastoDyn model, disable the relevant degrees of freedom (blades, drivetrain/generator, nacelle, tower) and set the relevant geometry and mass properties to zero (or epsilon for the variables that do not permit a value of exactly zero).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Florence.Haudin
Posts: 10
Joined: Fri Feb 08, 2019 3:11 am
Organization: Vulcain
Location: France

Re: Free decay tests

Postby Florence.Haudin » Fri Dec 06, 2019 7:05 am

Dear Jason,
Thanks for your answer. In fact that was what I thought I had to do and started to do : freeze unrelevant degrees of freedom, and set to zero mass and inertia.
Nervertheless, I still don't really understand what I have to do with the geometric data of the section Turbine Configuration (copied hereunder). It seems that there are some strong relationships between some of them like and can't be set to zero :

FAST_InitializeAll:ED_Init:ED_ValidateInput:ValidatePrimaryData:TowerHt must be greater than zero.
ValidatePrimaryData:TowerBsHt must be less than TowerHt.
ValidatePrimaryData:HubRad must be less than TipRad.
ValidatePrimaryData:TowerHt + Twr2Shft + OverHang*SIN(ShftTilt) must be greater than TipRad.


Also, I am wondering about the number of nodes for the blades and tower that can't be put to 0 or 1, in a case where there is no structure on the floater (so no turbine).


Naively for me, I would set all dimensions to zero and set nodes to zero for unexistant structures.

Many thanks for any help.
Best regards.
Florence.


---------------------- TURBINE CONFIGURATION -----------------------------------
3 NumBl - Number of blades (-)
63 TipRad - The distance from the rotor apex to the blade tip (meters)
1.5 HubRad - The distance from the rotor apex to the blade root (meters)
-2.5 PreCone(1) - Blade 1 cone angle (degrees)
-2.5 PreCone(2) - Blade 2 cone angle (degrees)
-2.5 PreCone(3) - Blade 3 cone angle (degrees) [unused for 2 blades]
0 HubCM - Distance from rotor apex to hub mass [positive downwind] (meters)
0 UndSling - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
0 Delta3 - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
0 AzimB1Up - Azimuth value to use for I/O when blade 1 points up (degrees)
-5.0191 OverHang - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters)
1.912 ShftGagL - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
-5 ShftTilt - Rotor shaft tilt angle (degrees)
1.9 NacCMxn - Downwind distance from the tower-top to the nacelle CM (meters)
0 NacCMyn - Lateral distance from the tower-top to the nacelle CM (meters)
1.75 NacCMzn - Vertical distance from the tower-top to the nacelle CM (meters)
-3.09528 NcIMUxn - Downwind distance from the tower-top to the nacelle IMU (meters)
0 NcIMUyn - Lateral distance from the tower-top to the nacelle IMU (meters)
2.23336 NcIMUzn - Vertical distance from the tower-top to the nacelle IMU (meters)
1.96256 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
87.6 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
10 TowerBsHt - Height of tower base above ground level [onshore] or MSL [offshore] (meters)
0 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
-8.6588 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)
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Jason.Jonkman
Posts: 4394
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Free decay tests

Postby Jason.Jonkman » Fri Dec 06, 2019 12:46 pm

Dear Florence,

There are a few checks within ElastoDyn to check for physical correctness of the input settings. I would recommend setting input parameters TipRad through TowerBsHt to zero in the "Turbine Configuration" section, then make a few small adjustments (by setting values slightly nonzero) based on the errors received when trying to run the simulation. When doing so, make sure to disable all structural degrees of freedom (DOFs) in ElastoDyn except the platform DOFs.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


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