DC motor modelling to drive a ship propeller

[ameenbassam]

Hi There,

I want to mathematically model a DC motor connected to a ship propeller through shaft but i am very confused because of the load torque.

I am using the following block diagram to model my motor. Is the load torque is the propeller torque ?? or the motor torque should be equal to the required propeller torque and the load torque in the block diagram should be zero ??

Many Thanks in advance

 

[iop95]

Tl is load torque and is propeller torque. J and B are values of motor (rotor) itself.
Model of load (propeller), to obtain Tl at any speed (from allowed range) it's another task, maybe much difficult.

 

[ameenbassam]

Thank you for your kind reply.
I can calculate load torque (propeller torque) but how will we take moment of inertia (J) of the propeller and the shaft into consideration ??

 

[Skogsgurra]

??? It is in the denominator of the last block (the FIO that calculates w from net T). That is how the total moment of inertia is taken care of.

Or are you asking us how many kgm2 that moment of inertia is? We cannot know. You've got the dimensions and the specific gravity of those parts.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[ameenbassam]

So @ Skogsgurra J and B in the last block are not only for the motor but for the load as well. am i right ?
J total = J motor + propeller + shaft ???

 

[iop95]

Yes, J and B are total values reported to motor shaft. Sorry for my mistake in previous post.