# Dambreak

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May 2, 2010, 03:56
Dambreak
#1
New Member

kate
Join Date: Jul 2009
Location: iran
Posts: 29
Rep Power: 10
Does anybody know how to model dam-break? i've attach the picture
there is no inlet or outlet and the volume of water is constant.
Attached Images
 dam break.JPG (65.9 KB, 46 views)

 May 2, 2010, 07:03 ??? #2 New Member   kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 10 it has a simple geometry but i don't know how to set boundary conditions ????????

 May 2, 2010, 07:19 #3 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,737 Rep Power: 106 This looks straight-forward. Have you done the tutorial example for free surface flow over a bump? That should give you the main idea of how to do it.

 May 2, 2010, 07:26 ? #4 New Member   kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 10 yea, i've done tutorials but this is special model, there is no inlet and outlet, i made my model in free surface with 2 fluids by volume fraction equation how do you think?

 May 2, 2010, 07:37 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,737 Rep Power: 106 No inlet and outlet makes it much easier. You will still probably need an air opening on the top to let air go in and out.

May 2, 2010, 07:42
#6
New Member

kate
Join Date: Jul 2009
Location: iran
Posts: 29
Rep Power: 10
honey i've already made a simple 2-D model, without inlet and outlet; just an opening above! i don't know why it doesn't run!
Attached Images
 dam.jpg (91.1 KB, 29 views)

 May 2, 2010, 07:52 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,737 Rep Power: 106 What is the error message? Post the output file. Honey? I have been called many things in CFD but never honey

 May 2, 2010, 07:56 #8 New Member   kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 10 ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Floating point exception: Overflow " you dont know how your help is valued to me!"

 May 2, 2010, 08:18 out file #9 New Member   kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 10 the out put file is not valid to upload

 May 2, 2010, 17:26 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,737 Rep Power: 106 Floating point exception means that the solver has diverged badly. You need to improve the numerical stability of the simulation. This can be caused by lots of things, but in rough order I would check: 1) That the physics is correct 2) That you time step is small enough 3) That the mesh quality is high enough 4) If using high order differencing switch to low order (but just for debugging, once things are working go back to high order differencing)

May 3, 2010, 02:28
#11
Member

Ali Torbaty
Join Date: Jul 2009
Location: Sydney, Australia
Posts: 72
Rep Power: 10
Quote:
 Originally Posted by katiyon ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Floating point exception: Overflow
This happens in free surface models with sharp vertical angles, with model has difficulties to start up, it needs some patience to resolve it. adding to items that Glen mentioned:
1- try to refine your mesh
2- In your intial conditons, instead of using automatic options try to provide information (e.g. velocity, hydrostatic pressure,...)

in cases other than dam break (e.g. flow over a spillway), I found, it is much easier to fill the domain with water and let model drain out extra water while converging toward steady condition.

 May 3, 2010, 06:21 this is the error message! #12 New Member   kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 10 to check anything!!! a 2-D model; no inlet or outlet; just an opening with air; initials: velocity components are zero; hydrostatic pressure is applied; homogeneous turbulent model, time step=.001s & total time=2s, turbulent eddy dissipation checked and this is the result: +--------------------------------------------------------------------+ | ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Floating point exception: Divide by zero | | i think the mesh size is small enough! now what? (((((

 May 3, 2010, 07:46 #13 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,737 Rep Power: 106 Divide by zero errors can come from many sources - you will have to find it. Try removing the hydrostatic pressure initial condition, removing gravity, running a laminar model as a few ideas to try to find the source of the error.

 September 19, 2011, 03:52 #14 Member     Omid Seyedashraf Join Date: May 2010 Posts: 49 Rep Power: 9 I would like to mention that the first two screen shots are showing the results from a smooth particle hydrodynamic ( SPH ) method not a VOF/FVM method

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