CEL Code for Sinusoidal Movement of Piston

ghorrocks · May 6, 2015, 20:14

For a 3D region you need to define it in your mesh. So you will need to set this up in the meshing software.

gbrajtm · May 22, 2015, 10:30

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.

ghorrocks · May 23, 2015, 07:18

FAQ: http://www.cfd-online.com/Wiki/Ansys..._went_wrong.3F

gbrajtm · July 4, 2015, 03:30

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

gbrajtm · July 10, 2015, 09:29

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.

ghorrocks · July 11, 2015, 07:06

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.

gbrajtm · July 13, 2015, 02:50

Sorry, its not diaphragm, its accumulator with certain pressure.
please find the image.

ghorrocks · July 13, 2015, 08:55

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.

gbrajtm · July 13, 2015, 09:01

yes, but the pressure acting on the accumulator opposite to piston, how can that be specified?

ghorrocks · July 13, 2015, 09:09

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.

gbrajtm · July 13, 2015, 10:45

i am sorry sir, I didn't understand, "piston location is an algebraic function of the fluid pressure"

ghorrocks · July 13, 2015, 19:53

It means the Piston location = f(known variables). It is not an ODE or PDE or implicit function.

gbrajtm · January 7, 2016, 06:23

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])

ghorrocks · January 7, 2016, 19:45

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.

gbrajtm · January 8, 2016, 02:05

ok sir,

http://www.cfd-online.com/Forums/new...=newthread&f=4

gbrajtm · January 8, 2016, 02:08

http://www.cfd-online.com/Forums/cfx...tml#post580052

Rubel Ahammed · November 1, 2019, 14:17

Dear Sir, Could you please share your mesh detail with me. I am in negative volume error problem.

ghorrocks · November 2, 2019, 05:52

It's an FAQ: https://www.cfd-online.com/Wiki/Ansy..._went_wrong.3F

gbrajtm · November 4, 2019, 02:37

Quote:

Originally Posted by Rubel Ahammed

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.

November 2, 2019, 05:52		#58
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	It's an FAQ: https://www.cfd-online.com/Wiki/Ansy..._went_wrong.3F __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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May 6, 2015, 20:14		#41
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	For a 3D region you need to define it in your mesh. So you will need to set this up in the meshing software.

May 23, 2015, 07:18		#43
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	FAQ: http://www.cfd-online.com/Wiki/Ansys..._went_wrong.3F

July 4, 2015, 03:30		#44
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	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

July 10, 2015, 09:29		#45
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	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.

July 11, 2015, 07:06		#46
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

July 13, 2015, 08:55		#48
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

July 13, 2015, 09:01		#49
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	yes, but the pressure acting on the accumulator opposite to piston, how can that be specified?

July 13, 2015, 09:09		#50
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

July 13, 2015, 10:45		#51
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	i am sorry sir, I didn't understand, "piston location is an algebraic function of the fluid pressure"

July 13, 2015, 19:53		#52
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	It means the Piston location = f(known variables). It is not an ODE or PDE or implicit function.

January 7, 2016, 19:45		#54
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

January 8, 2016, 02:05		#55
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	ok sir, http://www.cfd-online.com/Forums/new...=newthread&f=4

January 8, 2016, 02:08		#56
gbrajtm Member Dr Gurubasavaraju Join Date: Dec 2014 Location: Bengaluru India Posts: 78 Rep Power: 12	http://www.cfd-online.com/Forums/cfx...tml#post580052

November 1, 2019, 14:17		#57
Rubel Ahammed New Member Rubel Ahammed Join Date: May 2019 Posts: 13 Rep Power: 7	Dear Sir, Could you please share your mesh detail with me. I am in negative volume error problem.