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Comparing Results from Dyn. Analysis

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f14-jbhoward

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Unread post Sat Dec 13, 2014 6:37 pm

Comparing Results from Dyn. Analysis

After working on the code for Project 2, I decided to test my simEngine with a simple model like doublePend from HW9. I am getting results that are very similar to the correct results but not exactly correct. It seems like the solution diverges at a point which causes the results after that point to be erroneous. I am not sure what to do about this problem, and my partner is equally as lost.

I have attached images for our results and the correct results for simplePend as verified by ADAMS and other sources.

If anyone has any ideas on how to fix this, let me know!

-James
Attachments
Results-wrong.png
Our INCORRECT Results
Results-wrong.png (4.78 KiB) Viewed 5942 times
Problem3.png
Correct Results
Problem3.png (51.54 KiB) Viewed 5942 times
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Dan Negrut

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Unread post Sun Dec 14, 2014 5:09 pm

Re: Comparing Results from Dyn. Analysis

This is hard.
Here's my suggestion, might not make sense.

take the simple pendulum example and prescribe a motion to the angle. Like phi1=2*pi*time.
Then you know how the pendulm moves: it's position and its velocity, right? The angular velocity is 2*pi, for instnace, from where you can get xdot and ydot. the same for x, y, phi.

then run your simEngine2D. You should step through your code in the debugger in MATLAB and see if you get after one time step the values that you expect.

I hope this helps.
dan
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f14-dfflaherty

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Unread post Mon Dec 15, 2014 6:13 pm

Re: Comparing Results from Dyn. Analysis

James and I have been able to resolve this issue. Our plots are now as follows:
Attachments
Howard_Flaherty_doublePend.png
Howard_Flaherty_doublePend.png (4.72 KiB) Viewed 5874 times
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f14-ghatch

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Unread post Tue Dec 16, 2014 11:03 am

Re: Comparing Results from Dyn. Analysis

Can you share what your issue was? My plots look like your originals. I'm suspecting that I may have the same issue.

Greg
Attachments
Matlab_9_Prob_3.PNG
Matlab_9_Prob_3.PNG (18.7 KiB) Viewed 5855 times
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f14-dfflaherty

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Unread post Tue Dec 16, 2014 1:16 pm

Re: Comparing Results from Dyn. Analysis

Hi Greg,

In our case, we needed to express a point force that is with respect to the LRF to an expression that is with respect to the GRF. In order to do this, we multiplied the force by the rotation matrix, and used the instantaneous angle of the body of interest to compute the rotation matrix. It is possible that you are calculating your rotation matrix based on the angle that is noted in the ADM file. Instead, try computing the rotation matrix based on the angle that you solve via the newmark equations. I hope this helps.

-Dan

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