The prebent blade and aerodyn15

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Jason.Jonkman
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Wed Sep 16, 2020 6:38 am

Der Abhinay,

All you've attached is the list of natural frequencies. Are these in Hz or rad/s? You'll need to examine the eigenvectors (and/or visualize the mode shape) to properly interpret the result. The runCampbell.m script can be used to generate an XLS or CSV file to aid in interpretation.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Thu Sep 17, 2020 2:36 am

Dear Jason,

The attached natural frequencies are in Hz. With your suggestion, using the runCampbell script I did linearization for 4 operating points. (LinearizationPoints_Servo file considered from example directory) The Campbell plot script is running but not producing any results. Here in the following attaching the csv files for Operating point 1,2 and Mode number table. Any insights to figure out the high frequencies, thereby to reduce the time step for simulation would be very much appreciated.

Thanks and kind reagards
Abhinay Goga
Attachments
Campbell_Point01.csv
(2.61 MiB) Downloaded 42 times
Campbell_ModesID.csv
(975 Bytes) Downloaded 42 times
Campbell_Point02.csv
(4.78 MiB) Downloaded 44 times

Jason.Jonkman
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Fri Sep 18, 2020 10:55 am

Dear Abhinay,

A natural frequency of 128 Hz would imply a time step requirement of DT = 1/(10*128) = 0.00078 s. However you likely have many modes of higher frequency than that, which are not showing up in your CSV file because they are above critical damping. Regardless, these modes may be requiring a smaller time step.

Regardless, your results don't really make sense to me given how you described your BeamDyn model. You said you were using order_elem = 4, which would imply 5 finite-element nodes (the root being fixed to the hub), which means the CSV file should show BeamDyn modes associated with finite element nodes 2-6. However, your CSV shows that the highest finite element node is 17. Are you sure you are not using order_elem = 16? Or perhaps you are using multiple finite elements / members (member_total > 1)? Reducing the number of finite elements / members and/or reducing order_element will result in a lower range of natural frequencies, which should allow for the use of a small time step.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Mon Sep 21, 2020 12:05 am

Dear Jason,

As you mentioned, I used member_total 4 in the previous simulations with 34 key points (kp_total). After your comment, I tired with member_total 1, and the simulation runs with 0.0003s (previously it was 0.0001).

What could be the possible reason for such very high frequencies? Blade structural properties in BeamDyn_Blade? Or any other input parameters in FAST setup?

I am not entirely sure, if my understanding is correct. For a simulation (BeamDyn included), does FAST calls for blade inputs from both ElastoDyn blade file and BeamDyn_Blade file, then compare or perform something for convergence between ElastoDyn and BeamDyn? If so, then the inputs for the both files need to be similar right?

Thanks and kind regards
Abhinay Goga

Jason.Jonkman
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Mon Sep 21, 2020 7:06 am

Dear Abhinay,

In general, I recommend running BeamDyn with one member (one finite element) and with a sufficiently high element order (order_elem = 5-8) to obtain convergence ("p" refinement instead of "h" refinement). A lower order_elem will allow for lower time steps. Higher order_elem will introduce higher frequency modes that require a smaller time step. The blade structural properties (mass and stiffness) also plays a large role in the natural frequencies and time-step requirement.

When BeamDyn is enabled (CompElast = 2), the blade-related inputs in ElastoDyn (DOFs, initial conditions, tip radius , tip masses, blade nodes, blade files, blade outputs) are not used; instead, these come from the BeamDyn-related inputs.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Mon Sep 21, 2020 8:14 am

Dear Jason,

Thanks for the informative insights. I kept total number of members to 1 with 34 key points. (Hoping that the number of key points doesn't effect the simulation time-step. I made sure that the curve is smoother) Order_elem as 4 initially.

In the OpenFAST guide section 4.5.3.4, there is clear description for how to calculate the stiffness and sectional mass matrices. Previously used values are calculated using BLADED. Now I self calculated using excel and implemented the new matrices. The solutions does not coverges even for 0.00001s
And I can't even perform linearization to calculate natural frequencies cause the solution is not converging. Any guidance on this situation?

Thanks and kind regards
Abhinay Goga

Jason.Jonkman
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Mon Sep 21, 2020 8:27 am

Dear Abhinay,

Well, it now sounds like there may be an issue with your sectional mass and stiffness matrices. To make sure the blade is responding as expected, I would recommend running standalone BeamDyn with the BeamDyn driver (uncoupled from OpenFAST) and make sure simple responses, e.g. applied tip loads, give the expected deflection.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Tue Sep 22, 2020 2:52 am

Dear Jason and Bonnie,

The following question is off-topic from this thread. But I haven't found any relevant threads for standalone BeamDyn driver. From the github repository (https://github.com/old-NWTC/BeamDyn) downloaded the data. It doesn't contain any BeamDyn driver binaries directly to use. I tried recompiling with visual studio. Faced with the following errors.

''Error Error running FAST Registry for BeamDyn. T:\Software archive\BeamDyn-master\source\Registry_BeamDyn.txt 1
Error error PRJ0019: A tool returned an error code from "Running Registry for BeamDyn" Project ''

Using notepad++ I verified that both registry.bat and .txt files are with windows line endings(CR LF). In a different thread (https://github.com/OpenFAST/openfast/issues/152) there was discussion about a similar error. I have understood that the error can be cleared out by relocating the following lines somehow.

':BeamDyn
SET CURR_LOC=%BD_Loc%
%REGISTRY% "%CURR_LOC%\Registry_BeamDyn.txt" -I "%NWTC_Lib_Loc%" -O "%CURR_LOC%"
GOTO checkError'

After many trail and errors, its still not a success. Any assistance in this regard much appreciated.

Thanks and kind regards

Jason.Jonkman
Posts: 5733
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Tue Sep 22, 2020 6:28 am

Dear Abhinay,

BeamDyn has been extensively updated in the OpenFAST repository, so, I wouldn't take BeamDyn files form the old-NWTC archive. I would recommend posting compiling-related questions on the OpenFAST github issues page: https://github.com/OpenFAST/openfast/issues.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Tue Sep 22, 2020 7:10 am

Dear Jason,

Outside the old NWTC library, is there any repository for BeamDyn standalone direct binaries or source code for recompilation? Myself, I wasn't able to find any other sources.

Thanks and kind regards

Jason.Jonkman
Posts: 5733
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Tue Sep 22, 2020 7:14 am

Dear Abhinay,

No, NREL has not been releasing compiled Windows binaries of the standalone module-level drivers in OpenFAST.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Tue Sep 22, 2020 7:29 am

Dear Jason,

Thanks for the info. I have shared the issue on github. I will recompile the driver myself. As you mentioned old NWTC library is really old (last updated 4 years ago)
When recompiling can I use BeamDyn source file and directories from OpenFAST library, instead of old NWTC ones? What I meant to ask is, will the OpenFAST dependencies source code can be used for standalone model!?

Thanks and kind regards

Jason.Jonkman
Posts: 5733
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Tue Sep 22, 2020 8:37 am

Dear Abhinay,

Yes, all of the source code and compile scripts for compiling the standalone module-level drivers for BeamDyn and other modules is available in the OpenFAST repository. It is only the compiled Windows executables of the standalone drivers that are not released.

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

Abhinay.Goga
Posts: 40
Joined: Tue Oct 25, 2016 8:12 am
Organization: SETEC elektronische Antriebsregelung GmbH
Location: Germany

Re: The prebent blade and aerodyn15

Postby Abhinay.Goga » Wed Sep 23, 2020 2:24 am

Dear Jason,

Once again thanks for the informative insights. I am able to compile the standalone BeamDyn driver. The balde structure with lesser order_elem say 4, the solution converges even for a time step of 0.01s. As you explained, with the increase in mesh elements (through iterations I verified upto 30) the convergence required a considerably larger time step of 0.002s. So, I can't understand the reason for extremely larger time step when coupled with FAST even for very less order_elem. Could you please guide me through, how can I verify the possible reasons for such requirements?

Thanks and kind regards

Jason.Jonkman
Posts: 5733
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: The prebent blade and aerodyn15

Postby Jason.Jonkman » Wed Sep 23, 2020 5:52 am

Dear Abhinay,

Are you saying that you can run your simulation with order_elem = 4 with a time step of 0.01 s in BeamDyn standalone and 0.002 s when BeamDyn is coupled to OpenFAST? This difference generally makes sense to me. The BeamDyn module itself uses a stiff integrator (generalized alpha), which allows time steps larger than what is dictated by the natural frequencies inherent in the model (effectively, the high frequencies are numerically damped out by the integrator). While BeamDyn still uses this integrator when coupled to OpenFAST, the time step required by OpenFAST glue code is dictated by the frequencies inherent in the module-level inputs and outputs passed through the glue code. When BeamDyn is coupled to OpenFAST, high frequencies are introduced in the coupling between BeamDyn and other modules (especially ElastoDyn), which dictate a smaller time step requirement.

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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