# RotorTorque, FAST interfaced with simulink

**URL:** <https://forums.nlr.gov/t/rotortorque-fast-interfaced-with-simulink/625>\
**Category:** Computer-Aided Engineering Software Tools\
**Created:** [January 12, 2013, 3:21pm UTC](https://forums.nlr.gov/t/rotortorque-fast-interfaced-with-simulink/625 "2013-01-12T15:21:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![George.Georgiadis](https://avatars.discourse-cdn.com/v4/letter/g/a88e57/32.png) [@George.Georgiadis](https://forums.nlr.gov/u/George.Georgiadis)\
**Post date:** [January 12, 2013, 3:21pm UTC](https://forums.nlr.gov/t/rotortorque-fast-interfaced-with-simulink/625/1 "2013-01-12T15:21:25Z")

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Hello,

I’d like to know how does FAST compute the torque of the rotor.  
I also have a problem when FAST is interfaced with simulink.I am working on my master thesis as an electrical engineer on wind energy. I made the model of the yaw control and variable speed control in simulink and it worked fine, but when I insert FAST in order to simulate the wind turbine the simulation is very slow. For example a simulation of 20s may take up to 45 minutes! In the beginning I thought that maybe it has to do with the sample time. I use in my simulink model a sample time of 10^-5 and in FAST a DT of 0.004. I put a rate transition block before and after the FAST block, but nothing changed. Have you any idea, of the cause of this problem?

Thank you in advance,

George

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**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [January 15, 2013, 2:31pm UTC](https://forums.nlr.gov/t/rotortorque-fast-interfaced-with-simulink/625/2 "2013-01-15T14:31:54Z")

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Dear George,

For information on how the rotor torque is computed in FAST, please see the forum post found here: [Resistant moment of the rotor and of the electric generator](http://forums.nlr.gov/t/resistant-moment-of-the-rotor-and-of-the-electric-generator/408/1).

Regarding your long run times, I’m not sure I understand what you mean when you say, “I use in my simulink model a sample time of 10^-5.” Regardless, have you chosen time steps that are appropriate to your model? There are many good topics on this forum explaining how to choose a proper time step (DT) for FAST. But basically, the highest natural frequency in your model determines the required DT. Algebraic loops in a Simulink model are also known to cause long run times. More information and suggetions on how to resolve a problem regarding algebraic loops are availalable in the Simulink documentation and in the forum post found here: [Error Running Test01\_SIG](http://forums.nlr.gov/t/error-running-test01-sig/493/1).

Best regards,