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by Jason.Jonkman
Fri Jan 22, 2021 4:16 pm
Forum: General
Topic: Irregular Waves and Pitch Momentum in MATLAB
Replies: 1
Views: 15

Re: Irregular Waves and Pitch Momentum in MATLAB

Dear Leonardo, I haven't reviewed your MATLAB code in detail, and I don't see any results attached to review. Regardless, in the FFT method, the frequency step is related to the simulation length and the time step is related to maximum frequency, i.e.: domega = 2*pi/t_max omega_max = pi/dt (The freq...
by Jason.Jonkman
Fri Jan 22, 2021 7:06 am
Forum: Computer-Aided Engineering Software Tools
Topic: Question about using TMD in nacelle
Replies: 18
Views: 1572

Re: Question about using TMD in nacelle

Dear Akheel, I'm not an expert at setting up the nacelle-TMD inputs to minimize the motion of the floating wind turbine. So, I can't really readily comment regarding (1) without digging into it myself. Have you reviewed related papers and set up the inputs appropriately for the system you are simula...
by Jason.Jonkman
Fri Jan 22, 2021 6:55 am
Forum: Computer-Aided Engineering Software Tools
Topic: problems while building the codes using Intel Visual FORTRAN
Replies: 1
Views: 10

Re: problems while building the codes using Intel Visual FORTRAN

Dear Mohamed, Given that YawDyn is quite an old software, you need an old version of AeroDyn to compile with it, specifically AeroDyn v12.57 (the version on https://github.com/old-NWTC is much newer). I've placed the old AeroDyn v12.57 archive on my Google drive: https://drive.google.com/file/d/1Oe0...
by Jason.Jonkman
Fri Jan 22, 2021 6:43 am
Forum: Testing
Topic: Error running HydroDyn file
Replies: 23
Views: 6337

Re: Error running HydroDyn file

Dear Yicheng, I don't really see anything unexpected with this response. The system appears to be initialized with zero initial conditions. And the initial platform velocities are zero. During the start-up transient, the system will want to pitch (due to the overhanging weight of the rotor), which i...
by Jason.Jonkman
Thu Jan 21, 2021 8:30 am
Forum: Computer-Aided Engineering Software Tools
Topic: Error: FF wind array was exhausted
Replies: 8
Views: 3456

Re: Error: FF wind array was exhausted

Dear Younes, Just a few comments: ⋅ The wind data is shifted when read by InflowWind. As such the FAST.Farm documentation recommends generating the full-field wind data files periodically so that the wind domain in InflowWind effectively extends forever along the wind propagation direction...
by Jason.Jonkman
Wed Jan 20, 2021 11:22 am
Forum: Computer-Aided Engineering Software Tools
Topic: TurbSim wind direction change
Replies: 7
Views: 1059

Re: TurbSim wind direction change

Dear Younes.

A similar question was asked and answered on our forum before--see: viewtopic.php?f=13&t=2483&p=14631.

Best regards,
by Jason.Jonkman
Wed Jan 20, 2021 11:19 am
Forum: Airfoils
Topic: Updating Airfoil files for Conversion to OpenFAST from v8
Replies: 1
Views: 19

Re: Updating Airfoil files for Conversion to OpenFAST from v8

Hi Bridget, NREL has not developed a fully automated script to upgrade airfoil data input files from AeroDyn v14 format to AeroDyn v15 format. That said, there are scripts to aid in the process, e.g., see: https://github.com/OpenFAST/matlab-toolbox/blob/master/Utilities/WritePolarAD15.m. The pitchin...
by Jason.Jonkman
Wed Jan 20, 2021 8:02 am
Forum: Rotor Aerodynamics
Topic: Simulation error while simulating extreme yaw case
Replies: 5
Views: 43

Re: Simulation error while simulating extreme yaw case

Dear Vishal, I'm glad you solved the main problem. Really high wind speeds result in large pitch angles, which can result in abnormal blade deflection, e.g., deflection upwind. But I'd have to understand more about the cases that fail to really understand why some still result in an instability. Bes...
by Jason.Jonkman
Tue Jan 19, 2021 1:21 pm
Forum: AeroDyn Development
Topic: Blade-Element/Momentum Theory and Implementation
Replies: 33
Views: 39344

Re: Blade-Element/Momentum Theory and Implementation

Dear Ricardo,

In AeroDyn v15, the BEM formulation does not distinguish between the wind velocity and structural velocity. The relative velocity (wind minus structure) is used in all blade-element and momentum equations.

Best regards,
by Jason.Jonkman
Tue Jan 19, 2021 6:54 am
Forum: Controls
Topic: FAST8 Linearization
Replies: 103
Views: 39158

Re: FAST8 Linearization

Dear Martin, Just a couple comments: ⋅ I would not expect the floating platform modes to be rigid-body modes with zero frequency unless you don't have proper hydrostatic or mooring restoring set. ⋅ I would expect the complex conjugate pair to be between a DOF and its first deriva...
by Jason.Jonkman
Tue Jan 19, 2021 6:44 am
Forum: Structural Analysis
Topic: Tower top tilt moment and Tower bottom side-side moment looking strange
Replies: 11
Views: 342

Re: Tower top tilt moment and Tower bottom side-side moment looking strange

Dear Vishal,

I would guess the key difference is between the mean wind speed profile between your simulations with steady wind and turbulent wind. How does the mean wind speed profile (shear, perhaps veer) compare across the rotor disk?

Best regards,
by Jason.Jonkman
Tue Jan 19, 2021 6:37 am
Forum: Rotor Aerodynamics
Topic: Simulation error while simulating extreme yaw case
Replies: 5
Views: 43

Re: Simulation error while simulating extreme yaw case

Dear Vishal, It looks like the wind turbine controller has gone unstable, as evident by the large oscillation in blade-pitch angle and lack of rotor-speed regulation. I would guess that this could be caused by incorrect initial conditions in the controller. Because you are simulating with large yaw ...
by Jason.Jonkman
Tue Jan 19, 2021 6:29 am
Forum: Computer-Aided Engineering Software Tools
Topic: FAST - Warning: tower model/possible tower strike
Replies: 16
Views: 3739

Re: FAST - Warning: tower model/possible tower strike

Dear Rui.Hao, You shouldn't need to change the time step to be smaller than 0.0125 s for the OC3-Hywind model , unless you change the structural properties (mass, stiffness, or geometry). If PCMode = VSContrl = 5 works well while PCMode = VSContrl = 4 does not, this sounds like a problem in how you'...
by Jason.Jonkman
Tue Jan 19, 2021 6:23 am
Forum: Computer-Aided Engineering Software Tools
Topic: OC6 Phase I in AQWA
Replies: 3
Views: 30

Re: OC6 Phase I in AQWA

Dear Pengzhi,

I would suggest using the mooring line properties in Tables 4 and 5 as stated, not considering how the lines curve around a pulley and attached to a spring.

Best regards,
by Jason.Jonkman
Mon Jan 18, 2021 8:28 am
Forum: Computer-Aided Engineering Software Tools
Topic: FAST - Warning: tower model/possible tower strike
Replies: 16
Views: 3739

Re: FAST - Warning: tower model/possible tower strike

Dear Rui.Hao, We'll, it sounds like your model has gone numerically unstable, but you haven't provided enough information for me to know why. A few clarifying questions: ⋅ Are you running one of the sample models provided by NREL (in the CertTest or r-test) or something else? If you are ru...

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