Increasing simulation time

Wind & Water General
1

Hello everybody
I use FAST v8.12.00a-bjj.Test12 and GPLLJ file for TurbSim v 1.06. When I run my simulation, it starts from 0 to 20 seconds but when I increase time to 60 seconds, it starts from 35 to 60 seconds. I would like to increase time which starts from 0 second.
Doese anyone know how can I increase simulation time?
Best regards,
Faeze

2

Dear Faeze,

FAST simulations always start at time = 0. Increasing the simulation length (input parameter TMax in the FAST primary input file) will not affect the start time. You can change when FAST begins to output time-series results to a file by changing input parameter TStart in the FAST primary input file (this will cause FAST to still simulate the first TStart seconds, but simply not write the results to a file e.g. to ignore potential start-up transients).

I’m not aware of any way to obtain the effects you are describing without changing the source code.

Best regards,

3

Dear Jason,

Thank you for your reply. I increased Tmax to 60 seconds in Test 12.fst file and I changed TStart in Test12.fst,Test12_ElastoDyn and Test12_ServoDyn from 5 to 0 but still I don’t have complete time and my simulation start from 35 to 60 seconds.
You can see my figures in the below picture.

Please, would you guide me?

  1. How can I correct start time in my simulation?
  2. Is it possible to increase my simulation time more than 60 seconds without changing wind file?(My turbsim wind file start from 0 to 59.85 seconds )

Yours sincerely,
Faeze

Start time.PNG
Start time.PNG558×502 26.3 KB

4

Dear Faeze,

Here are my answers to your questions

  1. My guess is the problem is not with FAST, but with how you are plotting the results. How did you generate those plots in MATLAB–could the 35-s start time be set within MATLAB?
  2. Your wind file should be at least as long as the simulation, unless you’ve generated periodic wind files (by setting the UseableTime to “ALL” in TurbSim v2), in which case the wind data will repeat itself. Normally, wind data is generated for at least 10 minutes to enable 10-minute long FAST simulations.

Best regards,

5

Dear Jason,
Thanks for your answers. I used scope to transfer each desire output variable from FAST to workspace in MATLAB, but in workspace every desire output variable data starts from 35.005 to 60 seconds (I mean e.g RotPwr.mat in workspace).
I wrote below commands in MATLAB.

Yours respectfully,
Capture.PNG

6

Dear Jason,

My problem with start time and increase length of simulation solved. I’ve just increased sampling time of scope in MATLAB from 0.005 to 0.025
but DT is 0.005 in primary input files in FAST. I don’t have any errors when I run simulation in MATLAB. I’m not sure whether it is correct or not.

Looking forward to receiving a reply.
Respectfully,

7

Dear Faeze,

Sorry, but I’m not familiar with the sampling time of the scope in MATLAB. You can directly change the sampling time of the FAST output (independent of the time step (DT) used by the FAST solver) by changing DT_Out in the FAST primary input file.

Best regards,

8

Dear Jason,

Thanks a lot for your replies.

Best regards,
Faeze