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.

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

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

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

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.

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).

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?

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?

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!

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 bionic/ saeed,

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

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.

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

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?

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

OK I'll send it to you tomorrow

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 .