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validating methodology to solve rolling of half filled tank problem

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Old   November 23, 2016, 02:00
Question validating methodology to solve rolling of half filled tank problem
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Hi...
I am working on a problem which involves a half filled tank and which is under rolling motion. I had set a VOF model for 2 phases ( Water and air).
For applying rolling motion I wrote a udf as follows:
************************************************** ***************
#include "udf.h"
#include "dynamesh_tools.h"
DEFINE_ZONE_MOTION (oscillation, omega, axis, origin, velocity, time, dtime)
{
*omega=(0.3323*cos(3.81*time)); //here 3.81 is frequency of rotation
return;
}
************************************************** **************
After that this i interpreted this udf in ansys fluent
Then I choosed for cell zone condition on fluent window and surface body under zone selection box. then to this "surface body" zone i ticked on mesh motion and hooked the above udf.
but the results are not satisfactory...
PLEASE TELL ME WHETHER MY APPROACH IS RIGHT?
OR IF WRONG THE HOW CAN I GIVE ROLLING MOTION TO TANK..
I AM A NEW USER SO HAVING A BIT OF KNOWLEDGE.


Thanks in advance



edit : I am verifying the result with pressure measurement at a point and comparing with available literature. For measuring pressure I had used 'point' under 'surface'
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Old   November 23, 2016, 02:07
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Hallo,

just an idea, why just not to change the direction of the gravity vector, it should be much easier than moving mesh?

There is also VOF UDF tutorial in FLUENT about splashing tank where the acceleration changes in time.

Regards, Maksim.
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Old   November 24, 2016, 04:06
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hi kirmaks ... can you please elaborate . I am not getting what you want to say.
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Old   November 24, 2016, 04:12
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It's a matter of perspective: instead of moving the entire tank/mesh, you could instead change the direction of gravity. Have a read of this post on applying a gravity force to the momentum source terms: http://www.cfd-online.com/Forums/flu...tml#post356732

Note: you'll need to apply similar source terms in the x and y directions with sine and cosine functions to mimic the rolling motion.
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Old   December 6, 2016, 05:13
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Hi 'e' I tried to figure out what you mean but I could not. Can this momentum source method be used for sloshing under roll motion of tank?
I am new member and know a bit of fluent.
Thanks for your reply.
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Old   December 6, 2016, 05:18
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Hi 'e' rather I made a udf as follow:
.................................................. ..
#include "udf.h"
#include "dynamesh_tools.h"
DEFINE_ZONE_MOTION (oscillation, omega, axis, origin, velocity, time, dtime)
{
*omega=(5*3.14/180*3.81*cos(3.81*time));
return;
}
.................................................. ........................

and in fluent I interpreted it. Then I hooked it to frame motion menu under cell boundary condition.
I want to know whether my approach is correct ?

Thanks in advance....
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