moving wall setting
 

hi I try to simulate a flow pattern in a tube. there are some baffles in this tube to enhance mixing efficiency. On one side of thid tube, the wall moves in "sin" function like a piston. I set the other side to be an "opening" and give an expression of wall movement in "V:Umax*sin(3.14*t/1[s]; Umax:2 [mm s^-1]). And the rest boundaries are set to "wall" and no slip. After simulation, I can not find any movement in this moving wall but there is no error message given. Do I need to set the wall with "slip" and how can I identify the static part and moving part in this tube? I actually can not figure out what is wrong. Could anyone give me some advices, please?

Re: moving wall setting
 

There are different aspects u can check in here.first plot the displacement using the output control and monitor options in CFX pre.setting it to free slip has no effect on the wall movement.free slip will not retard the velocity of the fluid near the side walls.using the post processor plot a plane across the model with mesh elements on it and use he time step editor to view the movement of the elements in various time steps.

What iam not sure if you could detail me abt the expression then i can give you more information.

Is the movement of the wall based on the force of the fluid if not there are lots of ways to move this wall.

Thanks Rajit

Re: moving wall setting
 

Thanks, Rajit . This tube can be seen as a syringe or piston. This wall can move itself without any applied force from fluid. The model is: the geometry is cylinder; length is 200mm, diameter is 10mm; there are some baffles inside it(non-axissym); left side of this cylinder can move 100 mm in axis direction and back to origin in SIN function; right side of this cylinder is opening; This is very simple but bother me for a long time. It's a real bottle-neck to me! If you can, could I send my file to you and please give me your suggestion ?

Re: moving wall setting
 

By the way, Rajit, I try to simulate a flow pattern in a cubic container (top is open, not a box). There is water inside it about 1/3 in height and some baffles at the bottom of this container. This container can rock +/- 10 degree based on x-axis. I set the whole domain in moving (rotation) and give body force as a function of (degree ,time). But I do not know how to set the pressure on the other boundaries. Could you give me advices?

Re: moving wall setting
 

Alright since you know the distance it has to move try this.

create a function.there should be one by symbol fx.use this to createa function.

lets say your function name is Left.

the form opens then there should be 2 blanks at the top it is augment units and resultant units.

your augment units will be the distance in mm(define your own units) and the resultant units will be the time in sec(define youe own units).

this is nothing but you are moving the left wall with respect to time.other conditions remaining the same.then while creating the wall movement for the left side say specified direction and insert the function just created like left(t)

make sure you move it by very small distance.with a small time step.the smaller the movement the more robust it is.

as i said in my earlier mail plot the movement using the output control.

the most important cache is you have to declare the side walls of the cylinder as unspecified while declaring the wall movement.

try declaring unspecified for the equation u hav defined using a sin function.it might be the reason it did not move.

you have asked the left side of the cylinder to move but the side walls are restricting it from moving.

hope these are helpful.

thanks Rajit

Re: moving wall setting
 

Bioman it would be great if you could send me a word document of the model with the axis definitions and boundary conditions we can discuss further.

But i think i see what you mean.since you are moving the entire domain.you must have declared them as wall.is it true?.if yes in this case you have to set the pressure in the appropriate boundaries and overide the command in the MS Dos prompt to unspecified movement.

Thanks Rajit

Re: moving wall setting
 

Hi Rajit, Very appreciate for your help !! If I want to send my files including **.gtm & **.cfx to you, how can I do? Could you tell me your mail address? My mail address is " q111111a@yahoo.com.tw " I really want to de-bottlenecking what I meet in the road of CFX !

Re: moving wall setting
 

~ sorry, I put it in wrong place ~ Hi Rajit, Very appreciate for your help !! If I want to send my files including **.gtm & **.cfx to you, how can I do? Could you tell me your mail address? My mail address is " q111111a@yahoo.com.tw " I really want to de-bottlenecking what I meet in the road of CFX !

Re: moving wall setting
 

No mate i dont use CFX any more.iam using fluent at the moment.so it is better for you to giv it a shot and report the errors to me.i will do my best to help you out.

Thanks Rajit

Re: moving wall setting
 

Ok, I will run it again and send the record to you. I also want to use fluent to solve my ploblem. But while knowing fluent needs udf to describe the moving region, I give up. Anyway, could cfx slove the problem with larger mesh deformation? If it could not, I think I need to look for another cfd software like adina. Actually, I seem to catch the points to solve moving boundary. In my question, piston moves along y-axis and I set 1. wall velocity in x=0; y=4 mm/s; z=0; relative to mesh motion. And mesh motion is displacement: x=0; y=4*t; z=0. 2. side-wall: all velocity =0; relative to boundary. And mesh motion is unspecified. From the result, those results sould be correct. But I do not understand that what is different between "displacement" and "location" in mesh motion setting? And If I want to use "SIN" function to simulate periodic movement, whether I only need to change y=4*t to y=4*sin(w*t)*t ?

Re: moving wall setting
 

alrgiht now.the name of your function should be put in the specified motion blank.

function name-Distance in the function as i told you earlier move it with distance and time.

your time will be the time step you are using.

then use this function in the moving wall settings tab as specified below.

Distance(t)

and for the side walls unspecified.

if possible move it by 2mm rather than 4mm.

it is very simple just follow the step u should get through it.

i hav lost memory of the difference between location and displacement.but dont bother about displacement for the time being.

yup thts right if u have defined all the variables in the function just put y in the specified motions tab.

Thanks Rajit

moving wall
 

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to write a c programe for the motion of a wall
 

dear Sir/madam

I want to ask about how to writy my c programe for the moving wall in Fluent.i want to move my mesh and i want to move each node.i am not very expert in C.can some one help me.