FAST8 Linearization

Dear Jason,

I need to calculate the fatigue damage for the blade and the tower, so Could you please suggest me a matlab script to calculate the random vector A from the time simulation to be used for rainflow analysis.

the random vector A comes from calculating the peaks and valleys. It is the first time for me to deal with this issue. I was going to use LIFE 2 that has been supported by FAST, but I have used my own turbulence model that differs from FAST turbulence.

Regards,
Taha

Dear Taha,

I’m sorry, but I don’t really understand your question. I don’t know what you mean by the “random vector A” or by “LIFE 2”.

Best regards,

Dear jason,

I want to calculate the fatigue damage for the blade and the tower using rain flow analysis, I have the time response for the blade and tower moments.

I have read about the rainflow analysis but I don’t know actually which steps should I follow? could you please help me for this?

Regards
Taha

Dear Taha,

NREL has provided the MLife post-processor for calculating fatigue damage from time series based on rainflow counting and Miner’s rule: nwtc.nrel.gov/MLife.

Best regards,

Dear Jason,

I would like really to thank you for your great support, I have done my work but I have faced the problem of the unstable pole caused by the generator azimuth state caused after MBC transformation which I didn’t solve. I would like to find a reference or scientific paper for this issue.

Thanks so much Mr. Jason

Best Regards,
Taha Fouda

Dear Taha,

MBC and azimuth-averaging should eliminate the influence of the generator-azimuth state, which should then be removed from the linear model before use. This is discussed e.g. in the following forum topic: http://forums.nrel.gov/t/fast-linearization-v7/1680/17.

Best regards,

Dear Jason,

I have read it before and when Yanhua delete the column that represent the generator azimuth state, the repose doesn’t not linearly increased. I have also eliminate this state and the response doesn’t linearly increase but I have to include it in my model.

I have done the azimuth average ( 36 Linearization times i.e every 10 degree azimuth ) and I have done mbc but the response again linearly increased.

it is written that :- rigid-body modes (i.e. modes without stiffness) show up in MBC3 as a pair of zero-valued (or near-zero-valued) frequencies with +/- inf damping (i.e., eigenvalues with real values only). That is, each rigid-body mode will introduce an additional mode beyond the number of enabled DOFs and the damping is unphysical.
This is really what happen with me, I have one positive eigenvalue. If I want to neglect it, I have to neglect the generator azimuth state which I have to include in my model.

Best Regards
Taha

Dear Taha,

I’m not sure I understand what you are saying. Why do you have to include the generator-azimuth state in your linear model?

Best regards,

Dear Jason,

I have done my work two times, one with the generator azimuth state and one without. but what I am confused about why MBC makes the system unstable? I am not mechanical background to understand the reason of the rigid bodies, I would like to find a scientific paper explains this in details

Regards
Taha

Dear Taha,

A rigid body mode is a mode with zero stiffness, such that a perturbation will not result in the body returning back to its equilibrium point.

You should not include rigid-body modes in a linear model because linear models are limited to small motion and rigid-body modes tend to undergo large motion (e.g. the generator-azimuth state continually increases as it rotates).

Best regards,

Dear Jason,

I hope that you are doing great.

I am working on designing and implementing a control system for 1.5 MW premanent magnet wind turbine with full power conveter. I want to develop a linear model for control design using FAST 8. I have Chosen the test for 1.5 MW WP Baseline turbine but it is induction generator turbine. So What I have to do is to make my user defined routine for servoDync (servoDync.f90) or modiy in the exsit one and then recompile FAST.
Am I right?

as it is my fist time to deal with servoDync.f90 code. I see that it is too long and I don’t know How can I modify it ? Could you please Suggest me an idea or give me any help?

Best Regards

Taha

Dear Taha,

If one of the the built-in generator torque or torque control options (simple variable-speed controller, simple induction generator, or Thevenin-Equivalent Circuit) is not applicable to your technology, then, yes, you can implement your own torque logic. There are several methods available to do this e.g. as summarized in my Mar 01, 2016 post in the following forum topic: http://forums.nrel.gov/t/active-drive-train-damping-in-fast/1293/2. The exact process will depend on which method you select.

Best regards,

Dear Jason,

I have found the pitch and torque Controller for my turbine written in fortrain code (DISCON.f90) and compiled to(DISCON.Dll). I think this Controller was used by Bladded and FAST 7 before.
what should I do to use this Controller with FAST 8? which files I need to Change or replace or edit in order to use it? Do I Need to recompile FAST?

Dear Taha,

Assuming your DISCON.dll file is compatible with the FAST/ServoDyn interface to Bladed-style DLL controllers, you shouldn’t need to change the FAST source code or recompile. Instead, all you should need to do is to enable the ServoDyn module (CompServo=1 in the FAST primary input file) and in the ServoDyn input file set PCMode=5, VSContrl=5, and the values appropriately in the BLADED INTERFACE section.

Best regards,

Dear Jason,

Could you please give me an Explanation for what does those Parameter meant:-

      Ptch_SetPnt  - Record  5: Below-rated pitch angle set-point (deg) [used only with Bladed Interface]
      Gain_OM      - Record 16: Optimal mode gain (Nm/(rad/s)^2) [used only with Bladed Interface]
      GenSpd_MinOM - Record 17: Minimum generator speed (rpm) [used only with Bladed Interface]
      GenSpd_MaxOM - Record 18: Optimal mode maximum speed (rpm) [used only with Bladed Interface]
      GenSpd_Dem   - Record 19: Demanded generator speed above rated (rpm) [used only with Bladed Interface]
      GenTrq_Dem   - Record 22: Demanded generator torque above rated (Nm) [used only with Bladed Interface]
      GenPwr_Dem   - Record 13: Demanded power (W) [used only with Bladed Interface]

Dear Taha,

I don’t have a detailed description of those inputs, which are inputs in Bladed that we simply mimic in FAST in case the Bladed-style DLL needs them. My guess is you’d know what they are and how to set them if your DLL needed them. Otherwise, the only things you’ll likely need to set in the BLADED INTERFACE section of the ServoDyn input file is DLL_FileName, DLL_InFile, DLL_ProcName, DLL_DT, and BPCutOff.

Best regards,

Dear Jason,

Thank you. I have found them. the dll Controller which I have is working with FAST8. I have changed the trubine configuration and the Primary Input files according to the configuration of the turbine which I use.

the Simulation is runing well without activating the Aerodynamic module ( setting CompAero to 0 ) but when I activate it, I got this error

Running ElastoDyn (v1.04.00a-bjj, 26-Jul-2016).

FAST_InitializeAll:ED_Init:ED_ReadInput:ReadBladeInputs:ReadBladeMeshFileAD:Invalid numerical
input for file “D:\FAST1\FAST8\CertTest\WP_Baseline/WP_Baseline_AeroDyn15_Dynin.dat” occurred
while trying to read NumFoil.

FAST encountered an error during module initialization.
Simulation error level: FATAL ERROR

I don’t know from where this error come but I figured that the airfoil data which I used was developed for FAST 7 which is not the same like in FAST8
I have attched here my Airfoil file, and the AeroDyn Primary Input files. Could you please adjust my Airfoil to be compatable with FAST 8 and check the AeroDyn Input files and let me know from where this error Comes.

Best Regards
Taha

Dear Taha,

Are you attempting to use AeroDyn v14 or AeroDyn v15 within FAST v8? Your first attachment is an AeroDyn v14 input file whereas the third attachment is an AeroDyn v15 input file. Your second attachment is an airfoil data file formatted for AeroDyn v14.

The error you are receiving would be triggered by using an AeroDyn input file formatted for v15, but identified as v14 in the FAST primary input file (CompAero=1 selects v14 and CompAero=2 selects v15).

Best regards,

Dear Jason,

yes, Thank you. I have solved this error but now when I use Aerodyn v15, I recieve this error

Running AeroDyn (v15.03.00, 27-Jul-2016).

FAST_InitializeAll:AD_Init:ReadInputFiles:ReadPrimaryFile:Invalid numerical input for file
“D:\FAST1\FAST8\CertTest\WP_Baseline/WP_Baseline_AeroDyn15_Dynin.dat” occurred while trying to
read TwrNds.
ReadPrimaryFile:Invalid numerical input for file
“D:\FAST1\FAST8\CertTest\WP_Baseline/WP_Baseline_AeroDyn15_Dynin.dat” occurred while trying to
read TwrNds.
FAST encountered an error during module initialization.
Simulation error level: FATAL ERROR

Aborting FAST.

Best Regards,
Taha

Dear Taha,

I did notice that the first line in your tower nodes table has a TwrElev of 60 whereas the second node is 1.30. This will cause a problem because TwrElev must be specified in monotonically increasing order–from the lowest (tower-base) to the highest (tower-top) elevation. You can also enable the Echo flag in AeroDyn v15 to debug problems in your input file.

Best regards,