Dear all, Does anybody know what the difference beween SPLIT VOLUME and SUBSTACT VOLUME usage in Gambit? If I want to mesh one box, inside which the cylinder locates in the center, which option I should use? I want to define the cylinder is a source flow. But Gambit and Fluent could not allow me to define the cylinder as INTERIOR. The error is Error: Cannot change sta to interior because there is only one adjacent cell thread. Error Object: #f I tied the above two options SPLIT and STRACT. Both of them don't work. Does anybody help me? Is something wrong with my operation of these two options? Thanks a lot. Zwdi

I think more detail is needed to describe the domain. Does the cylinder originate from outside the box or is it wholy contained within the box?

"Split volume" will produce two seperate volumes but you usually need to create a face from scratch (split edge -> then connect nodes to create edges -> then connect edges to create a face). If you use "subtract volume" then "nothing" will be left behind, and you would have to rebuild your volume from nodes, edges and faces. In your situation is sounds like the subtract volume is the function to use. Make sure you select "retain" when subtracting, therefore the lower geometry (nodes) will be left behind so you can rebuild the volume you just subtracted - BUT make sure that when you rebuild that the nodes, edges and faces aren't being used/referenced for use in the other volume (this will save you a lot of headaches during meshing and in FLUENT). When you do any of this make sure that you delete all of your meshes as Gambit sometimes won't allow some operations if items are being used for other purposes.

I don't have too much experience with INTERIOR BC (boundary condition), I mainly use the INTERFACE BC, for connecting two volumes together. Each volume will need to have an INTERFACE BC designated along the area where the fluid will be passing through. Then you have to set the interface zone in FLUENT using the two interfaces you designated in Gambit.

From your error message it almost sounds like you did use the subtract volume tool and it is telling you that you cannot perform that function because "nothing" is there.

I hope this was somewhat helpful.

Cheers, Tim.

Thanks, Tim.

In my case, the cylinder is wholy contained within the box. There are some exhausts from the cylinder, which will mix with the fluid outside the cylinder. It is difficult for me to define top of cylinder as velocity inlet, and the other part of cylinder as wall. Fluent does not recognize the top of cylinder as velocity inlet. That is the reason I change my mind and define the whole cylinder as an another fluid domain with source term in Fluent. After I splited the box using cylinder, I did find there left two volumes: one is box splited with cylinder(like one cylinder hole inside the original box), the other is the cylinder. For substact option, after I substacted the box with the cylinder(NO retain), and then defined the top of cylinder as velocity inlet and other parts of cyliner as wall separately in Gambit, Fluent will again define the whole cylinder as another wall.So no fluid inside can exhaust out. I could do nothing to change this situation in Fluent. Hope my english is clear. Thanks for your time.

Best regards,

Zwdi