Dear @Marwa.Mohamed ,
I’m not familiar with the papers you are citing, and as I said, you’d have to dig into the details to fully understand the results you are showing. I can’t comment more on that.
Regarding (1), the natural frequency will depend on the mass and stiffness and boundary conditions. Depending on the nonlinearities of the model, these may change with magnitude of applied loads, which can vary between DLCs.
Regarding (3), I would not expect DLC 6.3 to have yaw errors larger than 20 degrees. This is certainly possible in DLC 6.2 and in the yaw error range of 20-60 degrees, I expect that you are running into the known blade edgewise / tower side-side instability that happens under parked/idling conditions under high winds and sizeable yaw error, which has been discussed in other topics on our forum:
[Yaw errors.png] Hello,
I am trying to design monopiles for the NREL baseline 5MW turbine using site specific hurricane hazard according to IEC 61400-3 load case 6.2a, which requires the consideration of all yaw errors from -180 to +180 degrees. I have read some literature mentioning that there is an “instability” that occurs for the NREL baseline turbine at around +35 degrees. This is described as an “aero-elastic interaction causing negative damping in a mode that couples rotor azimuth with…
Hi, I am trying to recreate the following study for a turbine at SWiFT:
“Assessment of Wind Parameter Sensitivity on Ultimate and Fatigue Wind Turbine Loads: Robertson, Sethuraman, Jonkman, Quick (2018)”.
I will be using TurbSim → OpenFAST and examining different parameters than those in the above study, but I did want to examine veer (β in the paper). I grepped all the input files and found nothing. I also didn’t find anything in the TurbSim Manual. How can I change the veer for these simulat…
Hello,
I am currently working on a thesis’ project which includes the computation of campbell diagram, mode shapes and modal dampings of the blades of a 5MW NREL reference wind turbine. I would like to do so using the full model of the machine on OpenFAST.
I have already managed to compute the power curve and the Cp-TSR curves of the rotor but I don’t know how to compute the natural frequencies, mode shapes and modal dampings at different wind speeds. Can you please show me how to do it if it’…
Hi forum,
I am have been working with OpenFAST and the IEA 15MW RWT on the UMaine semisubmersible platform since May 2021, and this week, when I tried to update my software and model to v3.1 of OpenFAST and v1.1 of the turbine, my initial test simulations ended almost immediately with tower strikes. I wanted to report this issue and hear any advice others may have.
For OpenFAST v3.1, I downloaded the Windows 64-bit executable from the OpenFAST GitHub releases page , and for the IEA 15MW model, …
Hi, everyone
I’m performing 10-min simulation with NREL 5MW turbine based on 5MW_Land_DLL_WTurb.fst with NTM condition in the wind speed range of 3m/s-25m/s. When the simulation is performed in large wind speed (e.g. 25m/s), I got the following warnings:
FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:RotCalcOutput:BEMT_CalcOut
put(node 5, blade 1):UA_CalcOutput:UA_BlendSteady:Temporarily turning off UA due to high angle of
attack or low relative velocity. This warnin…
opened 02:42PM - 13 Mar 24 UTC
closed 12:59PM - 26 Mar 24 UTC
Type: Question
hello everyone，
I am simulating the idle shutdown state with normal turbul… ent wind files with wind speeds of 40m/s and 45m/s, grid size (X=284, Y=284), which can be calculated when PropagationDir=0° and PropagationDir=270°. However, when the wind field is deflected counterclockwise by 30° (PropagationDir=330°), it warns of "violation of the small angle assumption" and then reports the error "GF wind array boundary violated: grid is too small, Y direction." Y=142.03;Y boundary=[-142,142]. When the wind field is deflected 60° counterclockwise (PropagationDir=300°), an error is reported that”TwrInfl:Tower strike“. Is there any solution? Thank you very much！
Dear @jjonkman , I'm trying to study the tower stability problem recently. As mentioned in your Ph.D dissertation "Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine", Tower ...
opened 02:40AM - 14 Oct 24 UTC
closed 02:12PM - 27 Nov 24 UTC
Type: Question
Hi all,
I am currently comparing results between OpenFAST and Bladed for FOWT… through the IEA 15MW wind turbine atop UMaine platform. But I found some differences existed in the platform pitch and roll movements under some specified condition like parked with an azimuth angle of 50 degree.
In the following picture, the results were obtained under still water, steady wind with no wind sheer and the wind direction is -30°. The turbine was parked and the azimuth angle is 50°. The unsteady aerodynamic or dynamic stall were both closed in Bladed and OpenFAST
It seems like Bladed and OpenFAST show different damping effects.
Do you have any ideas or experiences about this kind of problem? Is this related to aerodynamics or hydrodynamics?
Thanks!
Chao Li
Best regards,