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-   -   Error: Negative volume and Creating empty surface (https://www.cfd-online.com/Forums/fluent/102873-error-negative-volume-creating-empty-surface.html)

Faby February 14, 2013 03:45
Quote:
Originally Posted by sadjad.s (Post 386035)
hi mate,
actually with 6DOF option in dynamic mesh, fluent automatically considers buoyancy force between solid(ie. box) and fluid(water).
my problem was that i considered rather little mass for box (in the main problem it was sphere) so that it went up!
in this example(2d version), i made a structred grid around box and let it move with the same speed as box.(as you can see in picture).
and used remeshing method for unstructured grid.
i use fluent v14.0 64 bit, if you want, post me your email so i send you case & data and udf.
Attachment 16128
I did the same! :)

Faby February 14, 2013 03:53
Quote:
Originally Posted by subha_meter (Post 390688)
Hi Sadjad,

Although the dynamic mesh model worked for heavier particle (density > liquid). for lighter particle (particle density < liquid density), it seems there's some problem. The particle bounces off the interface instead of floating on the liquid. Any suggestion?

Regards,
Hi!
I was able to simulate a buoyant particle fully immersed in a fluid just setting the acceleration of gravity = 0 and the operating density ( in operating conditions) equals to the fluid density. It works.
For your case...have you seen the ansys tutorial about a 2D buoyant box? This is the video of simulation http://www.youtube.com/watch?v=UpFCF-ctMp0 , but you can find the tutorial on web http://www.scribd.com/doc/92954775/F...2d-Falling-Box.

samcfd February 28, 2013 23:59
2D airfoil O Grid- negative volume
 
Hi,

I'm carrying out a 2D pitching airfoil simulation using dynamic meshing with a "O" Grid.It is a structured mesh. The dynamic conditions i have given were
1) airfoil - rigid body with UDF with pitching over X=0.25
2)interior - deforming with the min and max length scale from zone scale info
3) fluid -deforming with the min and max length scale from zone scale info.

The spring constant i gave was 0.001 and
convergence tolerance 0.0001
No of iterations 150.

The time step tat i used is 0.001.

After running the iterations and after about 500 time steps i'm getting the following error

negative volume detected
dynamic mesh update failed.
i have worked around with the spring constant and also with the time step nothing worked.
could someone help me out rectify this issue..
thanks in advance,
sam

subha_meter March 1, 2013 00:39
negative volume - dynamic mesh failure
 
Hi Sam,

In dynamic mesh problems, the mesh around the solid body keeps deforming during each iteration. Now, when the mesh becomes too distorted that the centroid of the cell lies outside the cell boundary, a negative volume is detected triggering the solver failure.

In a structured mesh, cell distortion is always higher than the unstructured mesh. You may tighten the the remeshing criteria i.e. the minimum cell size, skewness ratio etc. however the best way to get rid of the problem is to use "unstructured" (tri/tetrahedral) mesh. This works.

engma May 8, 2017 02:55
hi

The message "Note: zone–surface: cannot create surface from sliding interface zone" simply means the boundaries of the non–conformal interfaces match exactly, such that there are no non–overlapping sections on either side of the interface.

chek this file for more details

https://events.prace-ri.eu/event/156...l/slides/5.pdf

engineer master May 8, 2017 05:02
Please any one help me ..how can L solve this problem which appears to me
( application error in CFD_post
error the doesn't exist or is not readable )
So what the reson and what solution? ???
Please. ..

Megan December 12, 2023 09:06
6-DOF buoyant wooden box
 
Quote:
Originally Posted by sadjad.s (Post 388159)
dear mate,
no need to specify volume, because fluent compute it by geometry.
you just need to enter mass of sphere via udf and density will be computed by "density=mass/volume".
a circle in 2d is actually a cylinder which has one meter depth so in order to compute volume just multiply section are by one.
to solve your problem just make sure that density of sphere is higher than fluid.
if there is still problem, send your email address to send you case&data&udf.
Thank you for your kind hints.
I have a similar project , but i have a floating box. actually this is a Wave Energy Converter which starts oscillating as a result of wave. I have tried both reducing the time step size and fine meshing but still face the same error as you. dynamic mesh failed. negative volume detected. would you please share your Dynamic mesh setting with us?
Thank you in advance.
Megan.


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