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muhsin May 26, 2012 22:19

DFBI for very high rotation?
Hi All
I have some difficulties in simulating rolling motion of a small barge in wave flume...
-- I am using fine mesh near free surface and body but since DFBI rotation and translation treats whole volume mesh as rigid body, after some time the free surface moves to coarse mesh region and gets distorted and looks like the free surface submerges the body.
-- I am able to get comparable results for angles > 10 degrees. but for higher angles like 25 or 30 degrees I am facing the above problem.
-- Can anyone suggest what other DFBI models can be used to accommodate for larger DFBI rotation angles for better results.
boundary conditions are same as for Boat in head sea tutorial.

thank you

abdul099 May 27, 2012 03:58

DFBI morphing should be capable of doing it, but morphing usually needs a lot of power and resources. Of course, depending on the mesh size, but the same mesh size needs more resources than the rotation and translation model. And further, you have to make sure, cells don't get too distorted, otherwise you need to remesh, adding additional overhead.

When you're using 7.02, you can use overset meshes, that would be my first choice. But you will need a fine mesh in the whole overlapping area, due to compatibility in cell sizes when the boat rolls, so most likely your mesh will not be smaller due to use of overset meshes.

ryancoe May 28, 2012 14:12

Not sure if it's been published in a paper, but this looks like a similar study that might be useful

muhsin May 29, 2012 05:05

Thank you Abdul and Ryan. im trying to use morphing it seems to be working.
also the residuals seem to much better than DFBI rot n trans. lets see for larger roll hw it behaves.
Ryan i will also have a look into the link sent.

arun7328 March 7, 2014 06:51

Dear Munshin,

Can you please re-post the link? It is not working now. I am having a problem with DFBI+morphing.


Lingfeng Su November 10, 2015 08:00

DFBI Morphing with Roll motion
Dear Munshin and abdul099

I also use DFBI Morphing to simulate the roll motion and heave motion in the same time, however, when I chose free motion → roll motion and heave motion and monitor them, I found that there was only heave motion, but no any roll motion (no rotation angle was detected).

What was wrong with my case?



muhsin November 10, 2015 09:53

Dear Su,
Please check if you are monitoring properly. If the roll angle is zero all the the time,then do this >>>>>>
The roll what you have set is about what axis? X-axis probably... so in your monitors please check that axis correctly. I hope this would help.

Lingfeng Su November 10, 2015 10:15

3 Attachment(s)
Dear Muhsin

I checked nearly everything that I know and everything I can control, and there was no error with my settings.

As you can see from the images attached.

The zero degree of rotation angle still confuse me.

Best wishes


muhsin November 10, 2015 10:42

Dear Su,
I mean this axis in reports...
hope you understand.
see the image below:

Lingfeng Su November 10, 2015 13:00

Dear Muhsin

Can you upload your picture again?

And there is no need to define the axis in the report, cus I can use 6Dof rotation angle report directly from REPORT Tree, and generate the plot.


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