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-   -   6DOF with floating body bounce back. (http://www.cfd-online.com/Forums/fluent/76983-6dof-floating-body-bounce-back.html)

 paka June 10, 2010 00:50

6DOF with floating body bounce back.

Good day everyone,

I'm trying to model a floating body (similar to the one in 6DOF Fluent tutorial), however at some point the floating body is suppose to "bounce off" or rather stay in rest position on the floor.

I'm not interested in fluid-structure interaction analysis, my aim is to first drop a body on the floor then induce its movement with water blow. Rigid body description is fine enough.

My trouble occurs when body is suppose to hit the floor. Instead of staying at rest the body contour is crossing the floor line with mesh cells around the body intersecting the domain and going off the domain, which results with Fluent error of "negative volume cells".

Does anyone had similar problem or can help me tackle the problem?

Thanks a lot.

 ekakavand August 29, 2010 06:34

floating body

Hi Paka
I'm modeling a floating body on the water with fluent in 2D. I use a udf to limit the movement of body in Y coordinate. it just can heave(up and down). But when it run, pressure in domain increase very much. I solve this problem with 6dof, too but i can not get result from it.
You solve this problem before, could you help me?

elahe

 paka August 29, 2010 19:55

Well, you don't provide enough information. It is hard for me to say anything or give you any tip.

I would advise, go through tutorial carefully and make sure you understand EVERYTHING about the model/case.

Check boundary condition, that's usually what people tend to make mistakes. Also make sure about the center of gravity of your body. Mesh might play also an important role. There are plenty of variables.

Read carefully 6DOF documentation, carefully search documentation, not always all the information is included in particular section. Make sure there no limitations to the 6DOF model which possibly you might be violating.

At this moment this is all I can advise to you.

Best!
Krystian

 ekakavand August 30, 2010 06:52

Hi There,

I really get happy if you have time and help me.
Do you publish a paper from your work? I do not know your name and couldn't search your papers...

I should model a floating body in a wave tank in two status in 2D.
1. floating body can only oscillate in vertical direction
2. floating body can move in any direction(3dof equation is needed)

Now I have a question about 6dof equations. about moment of inertia.
I use these formula for calculating them. But there are a example in fluent tutorial that is not like mine.
Ixx=(mass/3)*(x^2)
Iyy=(mass/3)*(y^2)
Izz=(mass/12)*(x^2+y^2)