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In Simscape Rankine Cycle example the Turbine does not rotate

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I tried to see how the rankine example worked but could not get my head around.
I have seen that elements like motor convert electrical energy to torque and you can measure it using an Ideal Rotational Motion Sensor:
In the "Rankine Cycle" example you can see a turbine connected to a flow energy:
If you replace the Load by a "Rotational Motion Sensor" it will never change from 0, no matter how much flow passes into the turbine through the ports A and B:
So, my question is why? I saw in the "load" block there is a speed source forcing the turbine to rotate at nominal speed, and summing the linear torque to it but why?

Accepted Answer

Yifeng Tang
Yifeng Tang on 21 Aug 2020
Hi Marlon,
I tried to modify the example the way you showed in the screenshot. The model had difficulty initializing and won't run. Did you need to do anything else to simulate the model and get zero speed?
I am actually not surprised to see an error with just a speed sensor connected to the shaft. Now the turbine has no external load or resistance, AND no inertia! If you add a rotational damper into the model, parallel to the sensor, you will see some shaft rotation again.
Now back to why the "load" subsystem is set up the way it is. I believe it's representing a dynamometer setup. Some dyno can maintain a constant speed (through its internal feedback system I suppose) and measure the resulting torque output from the system, which in its idealized form is modeled by a velocity source and a torque sensor. You can defintely replace that with a more realistic mechanical load.
Hope this helps.
  1 Comment
Marlon Trujillo
Marlon Trujillo on 24 Aug 2020
Nice answer @Yifeng. I guess my mistake was no adding any payload to the torque... Thanks!

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