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-   -   a simulation with rotation and vibration (http://www.cfd-online.com/Forums/cfx/122867-simulation-rotation-vibration.html)

liuzexiang August 30, 2013 01:15

a simulation with rotation and vibration
 
description of the problem: the fluent flow to the hole with the pressure 0.8MPa along the tool which is the capillary. this is 1/4 the geometry model in the figure. the tool rotate and vibrate with high frequency.
i do the simulation about rotation and vibration respectively. when the rotation simulation is done ,the tool model is set the immersed solid and when the vibration simulation is done, i just use the fluid model and set the mesh deformation. all the simulation ara sucessful to compute. the fluctuation of pressure and velocity appear.
questions:
1. Are these simulation right?
2.when i want add the voltage to the tool and the workpiece and do the simulation about rotation and vibration of tool simultaneously ,how to do? the immersed solid do not support the electric field model. when i set the tool as solid demain, and the tool set the rotation, the error appear.
3. when add the vibration to the tool, how to do? add the mesh deformation to the tool and fluid or and the mesh deformation to the fluid and set the solid motion equation to the tool. when the solid motion is set, the electric field model is not used.

liuzexiang August 30, 2013 01:22

1 Attachment(s)
Attachment 24939
there is the geometry model.

ghorrocks August 30, 2013 07:02

1) I have no idea if your simulation is right. I do not understand what you are modelling.
2) What does the voltage do? Why do you want to model it?
3) If the vibration is known in advance then use moving mesh to implement it. Do not use rigid bodies for this.

liuzexiang August 30, 2013 07:33

Thank you for your reply.
The fluid is brine which contain water, NaCl and gas. when there is voltage on the tool and workpiece, there is current along the workpiece ,brine to the tool. I want to simulate the change of the characteristic of the brine when the tool rotate and vibrate, such as conductivity , temperature , gas volume fraction distribution ,pressure and velocity and so on. i don't know is the model right. Maybe just need the fluid model to simulate this problem, set the rotation and vibration on the interface of the tool and brine, set the voltage on the interfaces of the tool and brine , interface of workpiece and brine.
the vibration equation is known, i can try the moving mesh. thank you very much for your advice.

liuzexiang August 31, 2013 22:40

Quote:

Originally Posted by ghorrocks (Post 448888)
1) I have no idea if your simulation is right. I do not understand what you are modelling.
2) What does the voltage do? Why do you want to model it?
3) If the vibration is known in advance then use moving mesh to implement it. Do not use rigid bodies for this.

I do the simulation about rotation and vibration respectively.
About the rotation simulation
one way setting the tool domain as solid domain and another way setting the tool domain as immersed solid,which one is right?
About the vibration simulation
one way setting the tool domain as immersed solid and the motion as specified displacement,give the Z direction a displacement quation. the result show the fluctuation of pressure but too small. Another way just using the fluid domain. setting the fluid domain as mesh deformation,and gaining the mesh displacement: areaAve( Mesh Displacement Z)@wall and the velocity: areaAve( Mesh Displacement Z)@wall. the result show the fluctuation of pressure and it is bigger.i want to konw which way is right?

ghorrocks September 1, 2013 05:54

I do not understand your question, but you describe a number of methods to model the motion (immersed solid, moving mesh) and they are all useful for some cases. But whether it is appropriate for this simulation I cannot say as I have no idea what you are modelling.

liuzexiang September 1, 2013 11:20

Quote:

Originally Posted by ghorrocks (Post 449153)
I do not understand your question, but you describe a number of methods to model the motion (immersed solid, moving mesh) and they are all useful for some cases. But whether it is appropriate for this simulation I cannot say as I have no idea what you are modelling.

the case of the simulation is that :
the tool is made of stainless steel, which connected the negative of the power supply. the motion of the tool is rotation and vibration.it is capillary tube. the work is made of stainless steel,which connect the anode of the power supply. it is stationary. the brine which is conductive electrolyte flow along the capillary to the work. the current flow from the work , brine to the tool .so is the simulation.
i have done the rotation and vibration respectively. but there is no voltage in the simulation. for this time, the voltage is added to the simulation. is it of coupling problem. if it is the coupling problem, it is not estabished on the ANSYS WORKBENCH. the electric uint and cfx uint can not be coupled.
the simulation is done by the ANSYS WORKBENCH using the coupling method and by CFX using the electromagntic model, but both are failure. i have no idea how to simulate? maybe the fluent ?

ghorrocks September 1, 2013 18:36

What type of vibration? In which direction? Is it coupled to the flow or imposed?

liuzexiang September 1, 2013 21:16

Quote:

Originally Posted by ghorrocks (Post 449259)
What type of vibration? In which direction? Is it coupled to the flow or imposed?

the displacement equation of the vibration is sine function along the axial direction of the capillary tube named Z direction. it is imposed to the flow by ultrasonic vibration.

ghorrocks September 2, 2013 07:50

How is the electric component coupled to the flow? If the fluid is a constant resistivity then the current flow will just be related to the tube position and there is no need for CFD.

liuzexiang September 2, 2013 09:19

Quote:

Originally Posted by ghorrocks (Post 449347)
How is the electric component coupled to the flow? If the fluid is a constant resistivity then the current flow will just be related to the tube position and there is no need for CFD.

if there is gas in the fluid, the resistivity is different . and the temperature effect the ion activity,so the resistivity of the brine is not the constant.
such as caviation ,if the pressure is lower, the gas is produce from the fliud. when the tool is ultrasonic vibration, the low pressure will appear. i think it worth to simulate.

ghorrocks September 2, 2013 18:24

This is looking like a very complex model. Have you done simulations where you simulate these effects by themselves - that is a cavitation only model, a moving mesh only model, and an electric field only model? Do not attempt the model with everything before you can successfully simulate the physics in isolation.

liuzexiang September 3, 2013 00:22

Quote:

Originally Posted by ghorrocks (Post 449445)
This is looking like a very complex model. Have you done simulations where you simulate these effects by themselves - that is a cavitation only model, a moving mesh only model, and an electric field only model? Do not attempt the model with everything before you can successfully simulate the physics in isolation.

i have done the rotation simulation with cavitation model and moving mesh with cavitation. but the rotation simulation and moving mesh simulation can not support the electromagnetic model.so the electri field can not be simulated . i am doing this now .i have try a lot ,but failure. so i need some idea !

ghorrocks September 3, 2013 19:01

Is the electric field model just to get the current flowing from anode to cathode? In other words, there is just a variable resistance in the fluid section, and you only care about the current flow? Or does the electric field do more than that?

liuzexiang September 4, 2013 01:59

yes. i need just the current. the gas volume fraction effect the conductive.

ghorrocks September 4, 2013 03:06

So if it does not want to do this using the maxwell equation solver, can't you put a simple diffusive additional variable on to represent electric potential with the diffusivity set as the conductivity of the material? You will just have to transfer the units to diffusion.

liuzexiang September 4, 2013 04:12

Quote:

Originally Posted by ghorrocks (Post 449731)
So if it does not want to do this using the maxwell equation solver, can't you put a simple diffusive additional variable on to represent electric potential with the diffusivity set as the conductivity of the material? You will just have to transfer the units to diffusion.

Thank you for your reply. i have done a simulation with the voltage in the vibration simulation.I set two solid domain and a fluid domain. the voltage is added to the tool and workpiece respecitively. Does the cfx support the maxwell equation solver.

liuzexiang September 4, 2013 04:15

1 Attachment(s)
there is the electri field of a point in the fluid in every time. But i can not gain the current or current density. why

ghorrocks September 4, 2013 06:04

I have never used the maxwell solver in CFX so cannot help you with details. If the variable you are looking for does not appear to exist then create it as a user variable.

Your time step size looks horribly coarse judging by the facets on your time history. You are going to need MUCH finer time steps than that.

liuzexiang September 4, 2013 08:11

Quote:

Originally Posted by ghorrocks (Post 449781)
I have never used the maxwell solver in CFX so cannot help you with details. If the variable you are looking for does not appear to exist then create it as a user variable.

Your time step size looks horribly coarse judging by the facets on your time history. You are going to need MUCH finer time steps than that.

Thank you for your advice. in the simulation,when the mesh quality is fine, the error appear ,so the mesh is coarse. i will define small time step.

hi,ghorrocks. as the immersed solid can not used in the multiphase flow, so the rotation simulation is not correct in my simulation. i want to set the rotation simulation. but as the tool is set the solid domain and the fluid is set the fluid domain. as you konw the tool rotates in the simulation, i set the tool as rotation in the domain motion,but how to set the wall function. when i set the fluid domain as rotation, the wall volecity of the interface of the tool and the fliud is set counter rotating wall . but two kinds of simulation are not correct.
can you give me how to set the rotation just using the solid domain and fluid domain . a example is ok


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