symmetry for rigid body

ghoroobeaakhar · May 11, 2014, 15:22

Hi
I need to define symmetry for the yellow and blue edge to decrease time simulation. I can do it for the yellow parts (fluid) but I dont know how I can do it for the blue edge (my rigid body).
thanks.

ghorrocks · May 11, 2014, 18:20

I am not sure what restrictions there are in symmetry for rigid bodies - you would have to look that up.

But you can impose symmetry by constraining the motion. If you constrain the motion to only be vertical and stop the relevant rotations then you have imposed symmetry.

ghoroobeaakhar · May 12, 2014, 08:33

thanks ghorrocks
I did my simulation in two ways. for the first time I simulated my model completely without using symmetry for the right side of my domain (yellow and blue parts) and for the second time I did it and put symmetry only on the yellow part that has shown in the picture. I did not change the center of mass and weight of my wedge in both of them.
there is a little difference between results.
what is your opinion? I do my simulation completely (without symmetry) or use symmetry and ignore the difference between results?
thanks

ghorrocks · May 12, 2014, 18:32

As always, that depends.....

How big is the difference between the results? Is it big enough to be significant? Numerical simulations never give exactly the same answer.

Assuming the difference is significant - then is the model in both cases correct? Was the symmetry correctly applied? Is the simulations accurate for what they tried to model?

Assuming it was correctly modelled - then is it showing that the flow is in fact not symmetric? For instance, like a vortex street coming off a cylinder.

May 11, 2014, 18:20		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,816 Rep Power: 144	I am not sure what restrictions there are in symmetry for rigid bodies - you would have to look that up. But you can impose symmetry by constraining the motion. If you constrain the motion to only be vertical and stop the relevant rotations then you have imposed symmetry. ghoroobeaakhar likes this.

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May 12, 2014, 08:33		#3
ghoroobeaakhar Member aliali Join Date: Apr 2014 Posts: 35 Rep Power: 12	thanks ghorrocks I did my simulation in two ways. for the first time I simulated my model completely without using symmetry for the right side of my domain (yellow and blue parts) and for the second time I did it and put symmetry only on the yellow part that has shown in the picture. I did not change the center of mass and weight of my wedge in both of them. there is a little difference between results. what is your opinion? I do my simulation completely (without symmetry) or use symmetry and ignore the difference between results? thanks

May 12, 2014, 18:32		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,816 Rep Power: 144	As always, that depends..... How big is the difference between the results? Is it big enough to be significant? Numerical simulations never give exactly the same answer. Assuming the difference is significant - then is the model in both cases correct? Was the symmetry correctly applied? Is the simulations accurate for what they tried to model? Assuming it was correctly modelled - then is it showing that the flow is in fact not symmetric? For instance, like a vortex street coming off a cylinder.