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CEL Code for Sinusoidal Movement of Piston

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Old   May 6, 2015, 19:14
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For a 3D region you need to define it in your mesh. So you will need to set this up in the meshing software.
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Old   May 22, 2015, 09:30
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Hi sir,

I considered 3D region, But i am getting an negative volume element. I tried by changing the mesh size, but i am not able to get rid of the error(attached). Can you please suggest some remedy.
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Old   May 23, 2015, 06:18
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FAQ: http://www.cfd-online.com/Wiki/Ansys..._went_wrong.3F
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Old   July 4, 2015, 02:30
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Hello sir,

Greetings, Hope your are doing great.

After trying many iteration to resolve negative element implementing CEL, now i am getting some results (force vs displacement) need to verify them with experimental results after the completion of test. Hope it will have agreement.
Thank you very much for your kind help.
I will contact you if i get any trouble forth.

Kind Regard's
Guru
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Old   July 10, 2015, 08:29
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Hello sir,

i wanted to give a boundary condition for bottom of the piston, which is diaphragm with certain elastic constants. Presently i have given wall boundary condition. I searched for elastic boundary condition.

Could you please suggest some remedy, if there is any possibility of modelling it.
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Old   July 11, 2015, 06:06
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Elastic constants? You mean the piston has a diaphragm which deforms? Then this is an FSI simulation, or possibly a moving mesh with the motion prescribed by the force on the diaphragm.
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Old   July 13, 2015, 01:50
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Sorry, its not diaphragm, its accumulator with certain pressure.
please find the image.
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Old   July 13, 2015, 07:55
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If the accumulator piston has no inertia then you can model its motion using CEL expressions in CFX. If the accumulator has inertia you will need to use a rigid body solver.
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Old   July 13, 2015, 08:01
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yes, but the pressure acting on the accumulator opposite to piston, how can that be specified?
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Old   July 13, 2015, 08:09
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If there is no interia then the piston will move such that the fluid force equals the accumulator pressure force. So the piston location is an algebraic function of the fluid pressure, and you do not need to model the piston or accumulator directly at all.
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Old   July 13, 2015, 09:45
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i am sorry sir, I didn't understand, "piston location is an algebraic function of the fluid pressure"
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Old   July 13, 2015, 18:53
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It means the Piston location = f(known variables). It is not an ODE or PDE or implicit function.
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Old   January 7, 2016, 05:23
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CFD.PNGDear sir,

As in attached, I have used solid body as the rigid body. Here i need to specify the two region in an if condition to distinguish Newtonian and Non Newtonian.

Since there are two non newtonian region i am not able to specify it in one if condition. How to specify it?
Previously i used this for one Non Newtonian region.
if(inside@piston == 1,a, 0.11 [kg m^-1 s^-1])
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Old   January 7, 2016, 18:45
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In future please start a new thread for a new question.

The easiest way of doing this is as you have done, by making the material properties a function as you have done. Note that this is quite likely to lead to convergence problems as you might get a step change in material properties.

If you are modelling a fluid where it has non-Newtonian behaviour near the piston and Newtonian behaviour away from the piston as the fluid is shear dependant (or something like that) - then I would not use any special model for this at all. Model the entire fluid region with the same non-Newtonian model and it will naturally revert to Newtonian behaviour away from the piston as the shear rate is low.
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Old   January 8, 2016, 01:05
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ok sir,


http://www.cfd-online.com/Forums/new...=newthread&f=4
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Old   January 8, 2016, 01:08
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http://www.cfd-online.com/Forums/cfx...tml#post580052
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Old   November 1, 2019, 13:17
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Dear Sir, Could you please share your mesh detail with me. I am in negative volume error problem.
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Old   November 2, 2019, 04:52
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It's an FAQ: https://www.cfd-online.com/Wiki/Ansy..._went_wrong.3F
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Old   November 4, 2019, 01:37
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Quote:
Originally Posted by Rubel Ahammed View Post
Dear Sir, Could you please share your mesh detail with me. I am in negative volume error problem.
Mesh size dependent on the geometry of the model. I have used the mesh sensitivity check method to choose the mesh size. Also, try to reduce the time step size.
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