FAST

Hi my friends!
I am trying to simulate the “NRELOffshrBsline_Monopile_RF” model that I downloaded from Jason Jonkman’s NRELOffshrBsline5MW public directory. To create a wind file I used the TurbSim turbulent wind simulator. I used the TurbSim.inp file that is provided when downloading TurbSim sw. I made some changes in that input file. These are the changes: NumGrid_Z = 31, NumGrid_Y = 31, AnalysisTime = 630, UsableTime = 630, HubHt = 90, GridHeight = 160, GridWidth = 200, refHt = 90, URef = 12 and CTEventFile = “C:\TSM_structures\EventData (Downloaded from NREL’s turbsim directory). The TimeStep is 0.05 and RandSeed1 = 2318573 and RandSeed2 = RANLUX. I renamed this input file “90m_12mps”. I executed TurbSim. It took almost one hour to create de .wnd .cts and .sum files. So I have copied these files into the Aerodata directory of FAST and I have executed FAST. The following error message has been shown: “An ADAMS control file for a LINEAR analysis can’t be built when using incident wave kinematics. Set WaveMod to 0 or MakeLINacf to False”. So I have set MakeLINacf to False in the “NRELOffshrBsline5MW_ADAMSSpecific” file. I have executed again FAST and the following error has been shown: GBRatio must be set to 1.0 when using Kink Pierce’s UserUSCont() routine. So I have set GBRatio to 1.0 in the “NRELOffshrBsline5MW_Monopile_RF” file. I have executed again FAST. This error appears: “Error: FF wind boundaries violated. Grid too small in Z direction (height (Z=-181.06m) is below the grid and no tower points are defined). Error getting velocity in Aerodyn/AD_WindVelocityWith disturbance(). And I am blocked because of this error; I don’t know how to solve it. Can anybody help me? Thanks in advance. Have a good day!

Dear Jose Manuel Ezquerra,

I suspect your model is going numerically unstable. The error regarding FF wind boundaries is simply the first error that the program found.

The likely reason your model is going unstable is because you are not using the appropriate controller. The NREL 5-MW turbines do not use Kirk Pierce’s sample variable-speed controller, UserVSCont_KP.f90, nor do they use Craig Hansen’s sample pitch controller, PitchCntrl_ACH.f90. Instead, the NREL 5-MW turbine uses a torque and pitch controller implemented in GH Bladed-style DLL format. The DLL (i.e., DISCON.dll) is supplied with the NREL 5-MW models. These controllers require FAST’s interface to GH Bladed-style DLLs, which is not a default option in FAST v7.00.01. You can find a version of FAST with this interface here: wind.nrel.gov/public/jjonkman/FA … erface.exe. Or if you’re adventurous, you can recompile FAST yourself using the guidance found in the FAST User’s Guide.

I hope that helps.

Bet regards,

Dear Jason!
Thank you very much for your fast answer! I did what you suggested me, this is, I dowloaded the Fast version of FAST, which is the one that interfaces to GH Bladed-style DLLs and it run perfectly. Thank you again! Have a nice daY!
Jose Manuel

Sir ,
As FAST don’t have a theory manual i want to know on which scheme it works example CFD, FEM ,BEM .and wether it will take the effect of tower aerodynamics or not .

Dear Anuj Gupta,

For information on the FAST theory basis, see the forum topic found here, especially my post from December 15, 2010: http://forums.nrel.gov/t/coupled-blade-modes-in-fast/314/1. To answer your direct questions:

*FAST is based on combined modal and multi-body dynamics formulation with nonlinear beam elements.
*FAST’s aerodynamics module (AeroDyn) is based on a blade-element/momentum (BEM) or generalized dynamic wake (BEM) wake model, together with a Beddoes-Leishman dynamic stall model.
*The direct wind load on the tower is not currently included, but it is something we are working to add.

Best regards,

Dear Janson,
Thanks for the reply . i want to know that how can we get the mode shapes plot .I am attaching a fig of tower mode shape .
Capture.PNG

Dear Anuj,

If you already know the coefficients c_i for i = 2, 3, … 6 for the mode shapes you want to plot, the mode shape can be plotted as y versus x of the following polynomial:

y(x) = SUM( c_i*x^i, i = 2, 3, …6) for x <= 0 <= 1

Please note:
y(0) = 0 (the mode shape is always for a cantivered beam)
y(1) = 1 = SUM( c_i, i = 2, 3, …6) (the mode shape is normalized by the tip displacement)

I hope that helps.

Best regards,

Sir,
I want to know that FAST will give these mode shapes in output or we are giving as a input to FAST , as i see in Baselinetower.dat and Baselineblade.dat ,there is something written at the last about mode shapes and coefficient.

Dear Anuj,

The blade and tower mode shapes are input to FAST (as specified by the polynomial coefficients in the FAST blade and tower input files). These can be derived from BModes: wind.nrel.gov/designcodes/preprocessors/bmodes/. More information can be found from: http://forums.nrel.gov/t/tower-and-blades-mode-shapes-bmodes-vs-fast/121/1.

Best regards,

Dear Jonkman,
I have a question that suppose we are running a simulation for 500 sec and we want to change some data in between simulation then how can we do that, suppose we have to change the blade mass properties at 100 sec .then how can we do that?

Dear Anuj,

It is not possible in FAST to change the blade mass in the middle of a simulation. I’m not sure why one would want to anyway.

Best regards,

I am asking this because i read one paper of Kim and Yae in that paper they are doing the analysis for a partially broken blades and they are doing like that i.e after 100 sec of simulation they are changing the blade properties .

Dear Anuj,

Kim and Bae have also made their own customizations to FAST. It is not possible in the standard version of FAST to change the blade mass in the middle of a simulation.

Best regards,

Dear sir,
I am trying to simulate the “NRELOffshrBsline5MW_OC3_Hywind” model that I downloaded from Jason Jonkman’s NRELOffshrBsline5MW public directory.First of all the wind file is not given in the directory for 5MW so I have taken 1.5MW wind file and did appropriate changes such that hub height =90m, wind speed =11 m/s,AnalysisTime =600, GridHeight=155 , GridWidth=155 and then i have simulate windfile in cmd prompt as “turbsim windfile.inp”.Then it is terminating normally and generating wnd file which is further used in AERODYN while simulating the FAST fst file.

but when i start simulating the fst file it is giving error as:
[b]small angle assumption violated in SUBROUTINE smllRotTrans<> due to large blade deflection

Blade element #1 is supersonic

Grid in y direction is small

error getting velocity in aerodyn[/b]
I have made changes in grid width and grid height several times but it is not terminating. Please guide me if am doing anything wrong or there is another way to complie this 5MW Files instead of compiling in cmd prompt.How we can remove this “grid error and error getting velocity in aerodyn”.

kindly suggest me

with regards
Neeraj.Kumar

Dear Neeraj,

We purposely left out the wind files from the NREL 5-MW model archives because adequately sized wind files for the NREL 5-MW are typically very large. See the last four posts on the forum topic linked here for an explanation and for a link to where you can download a TurbSim input file for this turbine: http://forums.nrel.gov/t/updated-nwtc-design-codes-available-on-our-web-site/237/1.

Warnings regarding a “small angle approximation violation,” warnings regarding “supersonic blades,” a simulation crash, or very large deflections that occur in the time series near the start of a simulation are good signs of a numerical instability. Without knowing more about your simulation settings, it’s hard to know that what the problem is. But the NREL 5-MW turbine models should not have these problems, unless you’ve customized the model in some unphysical way. See the following forum topic for more information: http://forums.nrel.gov/t/nrel-5mw-controls-dll-interface/183/1.

I don’t understand your question about compiling. Input files don’t need compiling and you don’t need to recompile FAST unless you need to make changes to the source code.

Best regards,

dear sir
Thanks for your reply
actually i was trying to simulate .fst file in command prompt and i havn’t made any changes in source code, I just used sample file for wind with the following changes only :

511347 RandSeed1
RanLux RandSeed2

7 NumGrid_Z
7 NumGrid_Y
0.05 TimeStep
600.0 AnalysisTime
600.0 UsableTime
90.2876 HubHt
165.0 GridHeight
165.0 GridWidth
0 VFlowAng
0 HFlowAng

  1.            RefHt      
    

8.0 URef
then turbsim terminated normally but when running .fst file with all the other inputs (aerodyn,tower,blade,platform,spd_trq,pith control)
then also it is giving error like “Rzero = 1.0423 must be smaller than 1” and “blade deflection large”.
sorry to ask you for the basics but i am a new user to FAST, so suggest me sir.

Dear Neeraj,

I don’t think the problem is with turbulent wind data file.

In your e-mail you refer to “spd_trq”, which is only used by Kirk Pierce’s sample variable-speed controller, UserVSCont_KP.f90. However, as explained in my Apr 06, 2011 post in this forum topic (above), the NREL 5-MW turbine models do not use this controller. To use Kirk Pierce’s controller, you must set GBRatio to unity. I suspect you made these changes, which are causing the model to go numerically unstable. Change GBRatio back to 97.0 and use the executable of FAST provided with the OC3-Hywind model and your simulation should run fine.

Best regards,

Dear sir
Thanks for your suggestion but again when i run the simulation with GBratio 97 it is giving error as :
stack trace terminated abnormally .
Induction factor calculation did not converge.

Dear Neeraj,

I don’t know what is causing your problem. Please download the original OC3-Hywind model files (include FAST input files, DLL controller, and FAST executable) from my website and run it without modification using the TurbSim wind data file that you’ve generated.

Best regards,

Dear Jonkman,

Thank you very much for your constant help in the forum.

I have run FAST 8 for offshore NREL 5MW Jackets and monopiles. I need to validate my results with verified responses (Displacements and forces in top of tower and transition piece or forces in mudline) in time history. I read NREL reports of this turbine and also this forum, but I was not able to find this kind of responses . I just found electricity power plots vs wind speed and they are very electrical. Could you please introduce a reference that has this kind of responses (Time history of structural responses for NREL 5MW Offshore jackets and monopile).

Thank you in advance for your reply.

Best Regard,

Arash,