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-   -   simulation of free falling sphere into calm water? (http://www.cfd-online.com/Forums/cfx/79704-simulation-free-falling-sphere-into-calm-water.html)

pedyspider September 1, 2010 00:05

simulation of free falling sphere into calm water?
 
hi there,
i'm somehow new to cfx and want to model a free falling sphere into calm water.
can anyone help me how to start?
previously i've done a 2D simulation of flow around airfoil, using FLUENT.

ghorrocks September 1, 2010 20:02

A sphere of what? A fluid or is it rigid? What do you want to get out of the simulation?

Nevel September 2, 2010 00:56

If the sphere is rigid you can easely use Immersed Body Method (new CFX v12 feature).

bionic September 2, 2010 05:51

Hi pedram
I have a paper that's exactly what you want.
Also u can speak to me more easier;)
I'm saeed

pedyspider September 3, 2010 13:36

it's a rigid sphere, with density less than water, i want to calculate the time it take for maximum penetrate, and the penetration depth.

ghorrocks September 4, 2010 06:41

The immersed solid feature would be the easiest way to get this going. 6DOF is a beta option for V12 but fully supported in V13 - talk to your CFX support person to get the preview version (it is on the ANSYS Customer web page).

pedyspider September 5, 2010 07:09

i've read a tutorial here wich told this about immersed solid
"transient runs should be incompressible and single phase."

but my question was a solid sphere that will fall from air into a calm water which is a multiphase problem.
can i use re-meshing or moving mesh?

ghorrocks September 5, 2010 20:16

There are examples of floating objects with a free surface model available from CFX support. Talk to CFX support to get them.

I was not aware of the single phase limitation - are you sure this is correct? Has CFX V13 overcome this limitation?

belgacem May 25, 2012 06:17

Hi Friends
I am also studying immersed boundary method and and try to simulate a block falling in the water. I am using "immersed solid" then rigid body 6DOF and I let it fall freely but it can't stoped in the bottom where the velocity must be zero. I give a density to the block and i let it fall freely under gravity. Noted that the rigid body is defined as an immersed solid. i have specified a stationary coordinate frame that has its origin at the center of mass of the physical rigid body. Another fixed coordinate frame was specified related to the water at rest.
What can I do to stopped the rigid body in the bottom where the potentiel energy must be zero?

thank you!

pedyspider May 25, 2012 15:34

as the 2.5D simulation i've done, i hadn't used immersed body, as i told it's for single phase fluid. they may improved it in cfx 13, which i'm not aware.

i've used motion specified option for the solid wedge boundries, and applied free falling equation motion to it:
d2=ft^2/m-gt^2+vt+d1

i hope this help!

vinu2907 December 24, 2012 03:40

Quote:

Originally Posted by bionic (Post 273734)
Hi pedram
I have a paper that's exactly what you want.
Also u can speak to me more easier;)
I'm saeed

Hai bionic/ saeed,

Can you please post the paper that you are talking about?

vinu2907 December 24, 2012 03:45

Quote:

Originally Posted by pedyspider (Post 363164)
as the 2.5D simulation i've done, i hadn't used immersed body, as i told it's for single phase fluid. they may improved it in cfx 13, which i'm not aware.

i've used motion specified option for the solid wedge boundries, and applied free falling equation motion to it:
d2=ft^2/m-gt^2+vt+d1

i hope this help!

Hai pedram,

Have you solved the problem of the sphere falling into calm water?. I'm also trying to simulate similar problem. Its also a sphere falling into water. I'm also trying to get the maximum penetration depth etc. If you have solved, can you please help me in this regard. I'm new to CFX command language.

pedyspider January 1, 2013 13:44

yes, i've solved it with CFX
look for "motion specified" option for sphere wall boundaries, and specify the displacement or position by CEL
this may help:
https://www.sharcnet.ca/Software/Flu.../i1304009.html

http://img141.imageshack.us/img141/9880/wedge.png

Mondi September 3, 2013 09:49

Hi Pedram
Would you modify your suggested link I can not open it?
and any body know about floating object or immersed solids tutorial (buoy) tutorial? where i can find it?


Centurion2011 September 25, 2013 03:22

Did you try tutorial "Falling box" first? Using 6DOF solver and remeshing is your best bet

you can download tutorial here

Mondi September 25, 2013 10:16

Quote:

Originally Posted by Centurion2011 (Post 453458)
Did you try tutorial "Falling box" first? Using 6DOF solver and remeshing is your best bet

you can download tutorial here


dear sir
i can not download it would you send it to my mail?
Saiiid1001@yahoo.com

Centurion2011 September 25, 2013 14:32

OK I'll send it to you tomorrow

amanjain058 June 25, 2015 11:03

I am trying the free falling box 2D . I am following the exact steps in tutorial . Except I am interpreting the UDF ,which I think is fine ? . I am getting negative mesh . Does the result depend on the size of time step ?. When I give other time steps the box goes out of the boundaries . Please can you help me ?
Thanks .


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