6dof

Birkov · August 27, 2010, 04:04

Hi to all,

I have little problem with 6DOF moving. I have cube in cube model and I followed star-ccm+ tutorial to set up my problem but there is one problem. As 6DOF object I choosed inner cube and set all needed properties.
When I run solver,region starts falling, not just cube which is selected as 6DOF.
Could you give me any suggestions?

Thank you very much.

B.

Edit: SOLVED

Henry Arrigo · September 1, 2010, 04:12

Hi Brikov,
I suggest you to check out your rigid body 's property for solving this problem. may be the weight and buoyancy don t match.

Birkov · September 1, 2010, 04:17

Hi,
I already solved this problem. I used filed function instead Flatvofwave. But thanks for reply.

B.

Henry Arrigo · September 1, 2010, 04:39

Good luck.

Henry Arrigo · September 1, 2010, 04:52

I v a problem with solving a DFBI case too, do you have any idea plz? I want too run a boat with thrust force in a domain. is that possible? I mean instead of setting a velocity inlet i want to move the boat using a force acting on it. this case is very helpful to study maneuvering. I v already solved a simple case, but the results are not reliable for example free surface deformation is unreasonable and drag force plot is strange too, but as i expected the whole domain moves in the direction of applied force, and also boat motions seems to be rational. do you have any idea how to come up with this case?
thank you

tobe · September 8, 2010, 03:09

You can add forces and moments to a hull in 6DOF but stil lock the motion in the required axis. This will give better solutions instead of moving the model as time steps are very critical.

Henry Arrigo · September 8, 2010, 15:39

Hi tobe,
Thanks for your reply. I still confused about your suggestion:
Why should I lock the motion in required direction? I want to see the boat raising up and moving down but if I lock the motions I won t see how does the boat respond to the fluid incidence.
Also I don t know what kind of B.Cs I have to use for the domain? for the case which I mentioned above I used mass flow inlet with flow rate equal to zero for all six faces of the cubic domain, but seems it has not worked out correctly.

tobe · September 8, 2010, 20:54

You can choose which motions to lock and which ones to have free, so you can lock logitudanal motion but have it free to trim and sink.
As to boundary conditions the roof we usually have as a non-slip wall, we usually only model 1/2 the boat so the there is a sym plane and the rest are velocity inlets.

What motions are you trying to model ?

Henry Arrigo · September 9, 2010, 07:51

Although I had in mind to study heave and pitch motions but preferably I would like to let the boat be free in six directions. I think for some cases like turning tests it is mandatory to do so. Does n 't it need to move forward when a force acts behind it? I cant make a sense about that!
For the velocity inlets, what magnitude of velocity should I assign to them? for mass flow inlet I used zero. Can I use zero for this case too?

tobe · September 9, 2010, 21:10

You can certianly have zero for your velocity inlets, if you are using VOF waves then they need to be set to VOF waves. What sort of time steps and cell sizes are you trying to use?

The boat can have a force applied with it fixed in that identical axis.

Henry Arrigo · September 10, 2010, 06:33

Implicit unsteady with 0.01s timestep size.
About the gird, here is the report of volume range: Volume range: [3.9930201368e-009, 9.4388723373e-002] m^3.

August 27, 2010, 04:04	6dof	#1
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	Hi to all, I have little problem with 6DOF moving. I have cube in cube model and I followed star-ccm+ tutorial to set up my problem but there is one problem. As 6DOF object I choosed inner cube and set all needed properties. When I run solver,region starts falling, not just cube which is selected as 6DOF. Could you give me any suggestions? Thank you very much. B. Edit: SOLVED Last edited by Birkov; August 30, 2010 at 07:44.

September 10, 2010, 06:33		#11
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	Implicit unsteady with 0.01s timestep size. About the gird, here is the report of volume range: Volume range: [3.9930201368e-009, 9.4388723373e-002] m^3. Last edited by Henry Arrigo; September 11, 2010 at 09:03.

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September 1, 2010, 04:12		#2
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	Hi Brikov, I suggest you to check out your rigid body 's property for solving this problem. may be the weight and buoyancy don t match.

September 1, 2010, 04:17		#3
Birkov New Member Join Date: Jul 2009 Location: Prague Posts: 28 Rep Power: 0	Hi, I already solved this problem. I used filed function instead Flatvofwave. But thanks for reply. B.

September 1, 2010, 04:39		#4
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	Good luck.

September 1, 2010, 04:52		#5
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	I v a problem with solving a DFBI case too, do you have any idea plz? I want too run a boat with thrust force in a domain. is that possible? I mean instead of setting a velocity inlet i want to move the boat using a force acting on it. this case is very helpful to study maneuvering. I v already solved a simple case, but the results are not reliable for example free surface deformation is unreasonable and drag force plot is strange too, but as i expected the whole domain moves in the direction of applied force, and also boat motions seems to be rational. do you have any idea how to come up with this case? thank you

September 8, 2010, 03:09		#6
tobe New Member toby Join Date: Aug 2010 Posts: 14 Rep Power: 16	You can add forces and moments to a hull in 6DOF but stil lock the motion in the required axis. This will give better solutions instead of moving the model as time steps are very critical.

September 8, 2010, 15:39		#7
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	Hi tobe, Thanks for your reply. I still confused about your suggestion: Why should I lock the motion in required direction? I want to see the boat raising up and moving down but if I lock the motions I won t see how does the boat respond to the fluid incidence. Also I don t know what kind of B.Cs I have to use for the domain? for the case which I mentioned above I used mass flow inlet with flow rate equal to zero for all six faces of the cubic domain, but seems it has not worked out correctly.

September 8, 2010, 20:54		#8
tobe New Member toby Join Date: Aug 2010 Posts: 14 Rep Power: 16	You can choose which motions to lock and which ones to have free, so you can lock logitudanal motion but have it free to trim and sink. As to boundary conditions the roof we usually have as a non-slip wall, we usually only model 1/2 the boat so the there is a sym plane and the rest are velocity inlets. What motions are you trying to model ?

September 9, 2010, 07:51		#9
Henry Arrigo Senior Member Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 16	Although I had in mind to study heave and pitch motions but preferably I would like to let the boat be free in six directions. I think for some cases like turning tests it is mandatory to do so. Does n 't it need to move forward when a force acts behind it? I cant make a sense about that! For the velocity inlets, what magnitude of velocity should I assign to them? for mass flow inlet I used zero. Can I use zero for this case too?

September 9, 2010, 21:10		#10
tobe New Member toby Join Date: Aug 2010 Posts: 14 Rep Power: 16	You can certianly have zero for your velocity inlets, if you are using VOF waves then they need to be set to VOF waves. What sort of time steps and cell sizes are you trying to use? The boat can have a force applied with it fixed in that identical axis.