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-   -   DFBI Embedded Translation&Rotation (http://www.cfd-online.com/Forums/star-ccm/87983-dfbi-embedded-translation-rotation.html)

naimishharpal May 4, 2011 13:51

DFBI Embedded Translation&Rotation
 
Hi STAR-CCM+ users,
Can anyone help me out at using 'DFBI Embedded Translation & Rotation' to model free-surface flow for marine application. I don't know how to create a body-fitted mesh on a preexisting volume mesh. Any suggestions? Does this approach requires interface?

Thanks,
NHarpal

abdul099 May 7, 2011 05:17

You will need two regions, one cylindrical or spherical where the 6DOF-body lies inside and one surrounding region where the cylinder or sphere is cut out. (When your preexisting volume mesh doesn't look like this, you need the remesh anyway)
The cylindrical or spherical (depends on the degrees of freedom) region will do the rotation of the 6DOF body while both regions together will do the translation of the 6DOF body.
As you need two regions, you can't do this without interfaces.

naimishharpal May 8, 2011 14:55

Thanks...! I didn't understood the '... while both regions together will do the translation of the 6DOF body.' Is there any way that only cut spherical domain shows 6 DOF, whereas outer domain remain stationary all the time?

abdul099 May 10, 2011 04:22

There is no way to do this with DFBI embedded rotation and translation. Just think about it. The spherical region can rotate in the surrounding region to do the rotational movement of the 6DOF body. But what should happen, when the 6DOF body should do a translation?
In this case, both regions will translate according to the movement of the 6DOF body. This shouldn't be a problem as long as there are no objects around your 6DOF body, like a ship on the sea.

When there are other objects around your 6DOF body and therefore the outer region HAS to stay stationary, you can try 6DOF morphing. With this model, there is only one region necessary as the mesh will be morphed according to the movement of the 6DOF body. Be aware, morphing needs a lot of time, so you will need an enormous quantity of computational time compared with other models.

naimishharpal May 10, 2011 21:47

I got you.

Another concern: Let's say I have rotating propeller attached to the boat, and boat is allowed for 2-DOF (Heave, and Pitch); and propeller is rotating and its 2-DOF has always to be synchronized with boat motion. How can I setup this problem?

Q: Can we use MRF (multiple reference frame) for unsteady simulation?
Q: How can I predict the incoming velocity for a given body geometry and propeller blade profile?, and say propeller is rotating at 'xyz' rpm.

Thanks.

abdul099 May 22, 2011 08:23

Don't know the exact name, but there is a motion option especially for propellers. I think, something like superposing rotation. Just have a look in the user guide.

Using MRF could make sense, because the time scale of the rotating propeller is much lower than the moving boat. But of course it will have an impact on the accuracy of the solution. It's up to you whether you want to use it or not.

What do you mean with "incoming velocity"? The flow velocity at the inlet of the domain? It should be the same as the velocity of the boat. But I thought, this would be a result of the calculation in the most cases where propeller rotation is involved...

saleh alsubari August 9, 2012 22:53

Dear Friends
I've a problem with the rotation of the blades in Wind turbine.
I want to know how I can rotate the blades when the wind is as the input? and find the rpm and torque associated with it using star-ccm...
can any one help


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