Learning Forum

[CrisWu]

Hi,

I am trying to assign dielectric constant for a body in ANSYS. I would like to calculate how voltage distribute in air with a charged plate using Electric in ANSYS workbench. It is a 3D model.

The small body is charged plate with 1 Voltage, and the enclosure body is full with air. I would like assign dielectric constant for air body and metal body. I have tried the APDL command, but some errors occured. And the results are not as well as expected. My APDL code:

"mpdele,rsvx,matid,

mp,perx,matid,1

et,matid,232"

So is there any other way to assign dielectric constant for a body? Or is there any wrong with my code? 

Thanks for reading and I would appreciated it if you can give me any advice. 

[Sheldon Imaoka]

Hi CrisWu,

What may be a little confusing is that there are two types of 'electric' analysis that can be performed in Mechanical APDL - current conduction analysis and electrostatic analysis.  You can find more details in the Mechanical APDL Help documentation, under "Low-Frequency Electromagnetic Analysis Guide", Chapter 12 "Electric Field Analysis" and Chapter 13 "Electrostatic Field Analysis".

In Workbench Mechanical, only the former (electric current conduction) is presently natively supported as the "Electric" system.  Mechanical uses SOLID232, but you probably want to use SOLID122 instead, if you want to perform an electrostatic analysis.  Try changing "et,matid,232" to "et,matid,122" as a starting point. (Electrostatic analyses have 'infinite' elements and other features that may require additional "Commands (APDL)" objects.)

Regards,
Sheldon

[CrisWu]

Hi Sheldon:

Thanks for your answer! Now I edit my APDL code with "

et,matid,122

mpdele,rsvx,matid,

mp,perx,matid,1

Now problem solved! Thanks a lot!

Moreover, I try to add a new plate in this system. Under the electric feild from the charged plate, there must be voltage on the new plate and I want to detect it. So I left the new plate with no voltage assigned. However, when I run the model, an error occured: 

I was wondering if you can give me some advice in solving this error. I did not think I have set some temperature-related conditions in my model. Thank you!

 

Best,

Cris

 

[Sheldon Imaoka]

Hi Cris,

If you only have a charge specified in an electrostatic analysis without any other boundary condition, you cannot solve for voltage (no unique solution in such a case).  You need to have somewhere grounded or add 'infinite' elements (where infinity=zero voltage).

Also, if you added a part, ensure that topology is shared (shared nodes) to ensure that the model is connected.

Regards,
Sheldon

 

[CrisWu]

Hi Sheldon:

Thanks for your reply! So is it impossible to detect voltage on the new plate without assigning condition? I think there should be some voltage because of the electric field. I tried to construct a 2D model and I successfully get the voltage from a plate without boundary conditions. Why there is different between 2D and 3D model?

Moreover, I was wondering if a certain amount of charge could be set for a plate in this analysis system? I would like to see the charge distribution for this system. 

Best,

Cris 

[Sheldon Imaoka]

Hi Cris,

There isn't any difference between 2D and 3D models for electrostatic simulations.  Did you have 2D 'infinite' elements present in your successful 2D analysis?  Infinite elements provide a far-field boundary condition.

The setup of 2D vs. 3D is very similar (just different element type), so if you were able to solve a 2D electrostatic problem, the same process can be used for 3D.  In terms of applying a charge for a plate, you need the "CP" command to couple the voltage and then use "F" command to apply charge (CHRG).

Because Mechanical doesn't natively support electrostatic field simulations, it can be a bit tricky to try to do this with "Commands (APDL)" objects if you are not familiar with APDL.  How did you solve the 2D model - was it done in Workbench Mechanical or Mechanical APDL?

Regards,
Sheldon

 

[CrisWu]

Hi Sheldon:

Sorry for the late reply, I was in a trip last week.

I checked my model and find some connection problems. When I fixed them, the 3D model could work. Thanks for your help!

I solved the 2D model in Workbench Mechanical, I think. For assigning the charge, I will try to use the "CP" command in my model.

Thank you very much!

Best,

Cris