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Simple piston movement simulation

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Old   February 15, 2015, 11:37
Default Simple piston movement simulation
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Nam Nguyen
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Hello everyone,

I'm doing a simple simulation of a moving piston with constant speed.

Here's the general idea:


As a beginner in both ansys and fluent, I decided to use layering dynamic mesh to control the motion of the piston.
Here's the content of my UDF:

#include "udf.h"
DEFINE_CG_MOTION(piston_head, dt, cg_vel, cg_omega, time, dtime)
{
cg_vel[0] = 0.001;
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;
NV_S(cg_omega, = , 0.0); /* no angular motion */
}


* The fluid is air (ideal gas) and I start with a steady time calculation.

* The boundary condition for the inlet is set to "mass-flow inlet = 0.02 kg/s" and "gauge pressure = 0" for the outlet.

* I ran the steady solution with 200 timesteps, but the solution seemed not to be converged.


Then I continue with the transient time calculation.
* I compiled and loaded my UDF succesfully.

* In the dynamic mesh settings, I set the "piston zone" to rigid body, choose the piston_head::libudf, retain CG (0,0), cell height is 0.001m.

* That's it for dynamic mesh settings.

* Then I run the calculation again, the solution is converged but the piston didn't move at all. I don't know what I'm missing.

Can anyone please help?? My truly appreciation!
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Old   February 20, 2015, 08:28
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Quote:
Originally Posted by ReVl27 View Post
Hello everyone,

I'm doing a simple simulation of a moving piston with constant speed.

Here's the general idea:


As a beginner in both ansys and fluent, I decided to use layering dynamic mesh to control the motion of the piston.
Here's the content of my UDF:

#include "udf.h"
DEFINE_CG_MOTION(piston_head, dt, cg_vel, cg_omega, time, dtime)
{
cg_vel[0] = 0.001;
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;
NV_S(cg_omega, = , 0.0); /* no angular motion */
}


* The fluid is air (ideal gas) and I start with a steady time calculation.

* The boundary condition for the inlet is set to "mass-flow inlet = 0.02 kg/s" and "gauge pressure = 0" for the outlet.

* I ran the steady solution with 200 timesteps, but the solution seemed not to be converged.


Then I continue with the transient time calculation.
* I compiled and loaded my UDF succesfully.

* In the dynamic mesh settings, I set the "piston zone" to rigid body, choose the piston_head::libudf, retain CG (0,0), cell height is 0.001m.

* That's it for dynamic mesh settings.

* Then I run the calculation again, the solution is converged but the piston didn't move at all. I don't know what I'm missing.

Can anyone please help?? My truly appreciation!
Please contact via mail. May be I can help.
sankarram90(a)gmail.com
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