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 arun7328 February 26, 2013 08:39

Oscillating body

Hi all,

I am trying to study some simple problems while training myself on STAR CCM.I have successfully done some study on flow past cylinder. Now I am trying to calculate the hydrodynamic pressure on a 2D oscillating cylinder. Its a problem with free surface.

Can anyone please give me some advice? I have gone through some relevant tutorials and got a rough idea.
Should i define the motion as morphing or define it as user defined vertex and specify a simple harmonic function in the field functions and specify that in regions motion?

I just need a start and i will try to find my way.

thanks
Regards
Arun

 SB123 March 25, 2013 14:38

I'm doing a similar problem. would be interested to find out what's the best way to do that oscillation: through the fluid velocity (field function) or with body motion and how best to define it so its easily manipulated

 arun7328 March 25, 2013 16:30

hey i have managed to solve the prob in 2 different ways..so please shoot if you have any query. I could use overset, morphing and trying rigid body now.

Getting good agreement with experiements. I am in the process of making my solutions better and doing sensitivity analysis and stuff.

Thanks
Arun

 nitman118 June 4, 2013 10:16

so arun..... which do you think is the best method to impart oscillations to the body?.... could u give a bit stepwise explanation...... thanks

 arun7328 June 4, 2013 10:25

Dear Nitish,

Working with all 3 methods I think morphing is surely one the better ones. I am not sure what problem you are looking into. I had worked on a problem of swaying and heaving a cylinder on the free surface.

I used tables (time, Vel_X,Vel_Y,Vel_Z are the columns.In my case X longitudinal, Y vertical and Z was 3rd dimension. For swaying velocity for X column was Awsinwt and other 2 columns 0) to define SHM velocity and create a field function to interpolate this table of velocity vector. This can be found in the help file.

Apply morphing to your region and assign grid velocity to the body you want SHM. In grid velocity define the velocity field function you defined.

Hope I have given you an idea of how to go about.

Thanks
Regards
Arun

 nitman118 June 4, 2013 10:44

hi arun,

i am doing an analysis in which a cylindrical workpeice is oscillating radially with some specific frequency while a viscous flow passes through it....... i am unable to write a udf for this.... all i have managed to do is impart it a translational velocity for a specific time..... morphing sure sounds a better way.... could u provide some link for its tutorial..... thanx a lot btw...!!

 arun7328 June 4, 2013 10:53

hey..

I did not get any tutorial. The way to interpolate a table using a field function is given in the manual.

First try to impart oscillations to cylinder with out any flows. You can do that by following the method i mentioned. Create a table with time of interval of approximately your time step and the final time to be the maximum physical time you want your simulation to run or more. In my case I made a time interval of 0.005 and for 20 secs in excel. velocity in the direction of interest can be given using awsinwt where w is the frequency and a is amplitude of oscillation. The other velocities will be 0..

save this as .csv file. Import table into your sim file and write a field function to interpolate this table.

Then follow steps of assigning a motion to region, you will be fine. Hope you have got the idea.

Regards
Arun

 nitman118 June 4, 2013 11:12

thanks a ton........... i will try as such.... hope i succeed... :)

 SB123 November 13, 2014 10:22

arun,

how are you defining motion in 2D, is it translational or rotational (or both) ?
do you have to run dfbi . i ask because i'd like to allow a cylinder(or finned body) to freely rotate in a steady flow and measure rotation and find equlibrium in flow, if there is one

- my understanding is you have a cylinder that you're oscillating both within the mesh and in a steady flow, can you include pictures to show what you're actually doing? because i think that a superimposed velocity in the flow would be the most efficient, maybe i'm not understanding

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