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by Jason.Jonkman
Mon May 17, 2021 10:10 am
Forum: Structural Analysis
Topic: OC3-Hywind eigenanalysis
Replies: 1
Views: 12

Re: OC3-Hywind eigenanalysis

Dear Hao Nguyen, I would think you'd need to include the off-diagonal coupling terms to predict the correct natural frequencies of the NREL 5-MW turbine atop the OC3-Hywind spar buoy. The full-system mass, center of mass, and inertia of the OC3-Hywind system, from which the 6x6 mass matrix can be fo...
by Jason.Jonkman
Mon May 17, 2021 8:20 am
Forum: Structural Analysis
Topic: Processing OpenFast linearization output
Replies: 58
Views: 9210

Re: Processing OpenFast linearization output

Dear Younes,

I would guess there is some excitation happening at the period of the response, which I estimate at about 3.6 s or 0.278 Hz, e.g., wave excitation or a harmonic of the rotor speed. What incident waves (WaveTp) have you defined? What is the rotor speed you are simulating?

Best regards,
by Jason.Jonkman
Mon May 17, 2021 8:05 am
Forum: Airfoils
Topic: Inlet Velocity for DU 35 and DU 40 Airfoils
Replies: 7
Views: 88

Re: Inlet Velocity for DU 35 and DU 40 Airfoils

Dear Victor, Yes, those are the correct airfoil coordinates. These coordinate files are also available along with the airfoil data in the FAST v8 archive and OpenFAST r-test. I'm not sure what differences you are seeing, but please be aware that the airfoil data NREL has provided includes 3D correct...
by Jason.Jonkman
Fri May 14, 2021 4:08 pm
Forum: Computer-Aided Engineering Software Tools
Topic: Heydrodynamic coefficients HELP!
Replies: 7
Views: 48

Re: Heydrodynamic coefficients HELP!

Dear Bartosz, OK, thanks for clarifying. The natural frequencies of the platform modes will be dictated by the full system mass / inertia (including added mass) and stiffness (including hydrostatic and mooring), and will thus be based on the system configuration (geometry, material properties). If t...
by Jason.Jonkman
Fri May 14, 2021 11:47 am
Forum: Computer-Aided Engineering Software Tools
Topic: Heydrodynamic coefficients HELP!
Replies: 7
Views: 48

Re: Heydrodynamic coefficients HELP!

Dear Bartosz, I'm not sure I understand the problem you are describing. What are the various results you are plotting (I don't understand the labels: ORE Catapult and OpenFAST, N-S, E-W, etc.)? What is the difference between HWS.png and SurgeSawySparInput.png ? I see some basic differences in your f...
by Jason.Jonkman
Fri May 14, 2021 9:20 am
Forum: Structural Analysis
Topic: Retrieve information about wind turbine model
Replies: 4
Views: 117

Re: Retrieve information about wind turbine model

Dear Junius, Most of the models in the OpenFAST r-test came from the original CertTest in FAST v8, which are documented in Table 6 of the FAST v8 ReadMe file: https://drive.google.com/file/d/17LDwMnCVmLfbRWSaVFxxqphVrtawMwlj/view?usp=sharing. What type of wind turbine model do you want to use? Best ...
by Jason.Jonkman
Fri May 14, 2021 6:56 am
Forum: Computer-Aided Engineering Software Tools
Topic: FF wind array boundaries violated
Replies: 3
Views: 29

Re: FF wind array boundaries violated

Hi Atinuke, I'm not sure I know what is the underlying problem based on the information provided, but just a few comments: ⋅ The Y-direction error is much more sensible in that the aerodynamic analysis node lies just outside the wind domain, such that increasing the width of the domain may...
by Jason.Jonkman
Thu May 13, 2021 5:25 pm
Forum: Computer-Aided Engineering Software Tools
Topic: FF wind array boundaries violated
Replies: 3
Views: 29

Re: FF wind array boundaries violated

Dear Atinuke, The error is being triggered because the position of an aerodynamic analysis node is NaN (Not a Number). This suggests that your model has gone numerically unstable, resulting in unrealistically large motions. It looks like the simulation failed about 50 s in; I would guess you are see...
by Jason.Jonkman
Thu May 13, 2021 3:55 pm
Forum: Computer-Aided Engineering Software Tools
Topic: The frequency component of flapwise
Replies: 15
Views: 3088

Re: The frequency component of flapwise

Dear Feng, The hydrostatic stiffness matrix (CH in your example) includes the effects of waterplane area and center of buoyancy, but it does not include the effects of full system body mass and center of mass. The full system mass matrix linked in the forum topic linked above (M in your example) inc...
by Jason.Jonkman
Thu May 13, 2021 2:56 pm
Forum: Computer-Aided Engineering Software Tools
Topic: The frequency component of flapwise
Replies: 15
Views: 3088

Re: The frequency component of flapwise

Dear Feng,

I see the problem. I don't see that you've included the restoring in roll and pitch associated with the influence of the full system body weight / center of mass. Effectively, you must add to KT(4,4) the contribution of gravity*M(2,4); likewise for KT(5,5).

Best regards,
by Jason.Jonkman
Thu May 13, 2021 6:30 am
Forum: Rotor Aerodynamics
Topic: Local angle of attack computation
Replies: 5
Views: 121

Re: Local angle of attack computation

Sounds reasonable.

Best regards,
by Jason.Jonkman
Thu May 13, 2021 6:28 am
Forum: General
Topic: FAST.Farm
Replies: 205
Views: 25122

Re: FAST.Farm

Dear Younes, Sometimes the debugger has problems viewing variables that are part of complex data types such as u%. I see that the local variables CosTerm and dp are computed correctly even though u%xhat_plane and u%p_plane are not viewable by the debugger (all of the inputs to AWAE, u%, are set to 0...
by Jason.Jonkman
Wed May 12, 2021 4:09 pm
Forum: Computer-Aided Engineering Software Tools
Topic: The frequency component of flapwise
Replies: 15
Views: 3088

Re: The frequency component of flapwise

Dear Feng, Your equation for the natural frequencies above applied to mass and stiffness values written as scalars (or only consider separate terms uncoupled). How are you calculating the natural frequencies with 6x6 matrices? Are you forming the first-order state-space matrix (A) and computing its ...
by Jason.Jonkman
Wed May 12, 2021 3:17 pm
Forum: Computer-Aided Engineering Software Tools
Topic: The frequency component of flapwise
Replies: 15
Views: 3088

Re: The frequency component of flapwise

Dear Feng, Yes, that is the correct full-system mass matrix. Have you now included the coupling between platform DOFs (off-diagonal terms in the matrices, including surge-pitch and sway-roll)--not just for the mass matrix, but also for the added mass matrix and mooring stiffness matrix? Best regards,
by Jason.Jonkman
Wed May 12, 2021 1:52 pm
Forum: Computer-Aided Engineering Software Tools
Topic: The frequency component of flapwise
Replies: 15
Views: 3088

Re: The frequency component of flapwise

Dear Feng, I agree with your numbers, but you seem to be missing three important effects: ⋅ The influence of the platform center of mass (from (0,0,0) on the roll and pitch inertia of platform; ⋅ The influence of the supported wind turbine mass, center of mass, and inertia; and &...

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