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henderh
Posts: 649
Registered: ‎06-07-2007
Message 11 of 11 (57 Views)

Re: Engine Dynamic Simulation

02-08-2013 04:33 PM in reply to: willgysi

HI willgysi,

 

  I was able to adjust the assembly model slightly to remove the redundant DOF's (attached).

 

  I removed the Design Accelerator sub-assembly gearset as a quick and dirty way to accomplish this, but still using those same components.  Now DS will be able to calculate unique reaction forces.

 

To answer your questions:

 

<<I increased the run time to 10s as that is what I set the full rpm range to be.  When viewing the simulation, you can see that the gears slow down and change directions.  It looks as if the cam and crank turn as they should to each other though.

 

Is this a screen refresh issue or something like that?  I don't think it is as the cam and crank look to be blazing by.>>

 

  Yes, it was an optical illusion, much like the classic wagon wheel in old-time western movies appearing to rotate backwards, due to the frame rate of image captures.

 

<<The revolution joint between the spur gear and camshaft (7th order polynomial) are where I start to worry.  There is no change in position, velocity, or acceleration as expected but there is this noisy graph for force of about a .5 lb.  Where could this force be coming from?  There shouldn't be anything acting here dynamically

 

Also, the two cylindrical joints give strange results I think as well..>>

 

  This may be from the redunancies in the previous version of the simulation.  It was a statically indeterminite solution, so the forces may not been unique (i.e. false).   Now these two components are in a welded group, so they are considered as one body / mass without any type of internal loads, with respect from one component to another.

  

  I noticed the student banner opening the model, and thought you might be interested in viewing the crank-piston DS model for verification if you haven't done so already:  Theoretical cases for validation

 

  As always, please let us know if you have any additional questions, comments or suggestions.

 

Best regards, -Hugh

 

DS_NG_No_DAcc.png



Hugh Henderson
Simulation QA Engineer
DLS

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