# Connectivity problem in Gambit

 Register Blogs Members List Search Today's Posts Mark Forums Read

 March 31, 2009, 19:35 Connectivity problem in Gambit #1 New Member   Gabriel Lozano Join Date: Mar 2009 Location: Monterrey, México Posts: 4 Rep Power: 9 I am doing some simulations in FLUENT of heat transfer in electrical transformer windings. I have the mesh in Gambit of the sole winding, and I have done forced convection simulations. The winding consists in solid regions (paper and conductor) with several ducts through it. The connectivity problem occurs when I want to make the natural convection case simulation, in wich the winding will be submerged in oil, I need to connect the volumes of the ducts with the volume of the oil surrounding the winding, and substract the conductor an paper volumes of the winding. If i substract the volumes of paper and conductor from the tank´s oil volume, the resultant oil volume of the oil isn´t connected with the winding. I tried to extrude the upper faces of the winding volume, and then, define them as fluid regions, and then, creating another volume that represents the remaining oil inside the tank (the tank is rectangular), but when I try to mesh the oil that surrounds the winding, I can´t do it with any mesh type. I attach some pictures of the problem I´m trying to analyze. I hope you can understand it and give me some tips to mesh it. The first one is the top view of the winding, i made the 2D geometry, and then extrude it to have the 3D volume. I have that mesh correctly made, the problem is to connect it with the tank´s oil. This winding will be submerged inside a rectangular tank full of oil. The second one is the scheme of the winding and the core around it. That would be submerged in oil. ¿Is there an easy way to substract the winding volume from the tank´s oil volume mantaining the ducts of the winding (fluid entities) and having a good connectivity in the mesh? I hope i made myself clear with the whole problem. http://img256.imageshack.us/img256/715/winding.jpg http://img14.imageshack.us/img14/373/transformador.gif Thanks a lot.

 April 1, 2009, 02:09 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,145 Rep Power: 32 can you provide the dbs file?

 April 1, 2009, 11:33 #3 New Member   Gabriel Lozano Join Date: Mar 2009 Location: Monterrey, México Posts: 4 Rep Power: 9 Hi Max, thanks for the interest in my problem. I do have the dbs file but it´s quite large (>300 Mb). Right now, I solved the connectivity problems with my model, but the problem is that i can not mesh it properly. I made the mesh for the winding, using a Hex/Wedge Cooper scheme (i first made the mesh for the upper faces). But when I try to mesh the surrounding volume of fluid, Gambit shows an error. I tried to mesh it with a TGrid Mesh and it doesn´t work. Gambit shows the following message: "Initialization failed to mesh 8 nodes. ERROR: TG_Mesh_Domain failed with error code 1. ERROR: Tetrahedral meshing has failed for volume volume.1294 This is usually caused by problems in the face meshes. Check the skewnesses of your face meshes and make sure the face mesh sizes are not too large in areas of small gaps" How can I solve this problem?, do I have to change the mesh of the winding to make sure the mesh of the surrounding fluid can be done with the required element size? I made a mesh using the Staristep Scheme, but it creates faceted volumes which are not connected with the rest of the model. Thanks for the help.

 April 1, 2009, 11:51 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,145 Rep Power: 32 complex geometries can't be meshed with hexa so simply. You have to divide your domain into simply volumes, which can be easily meshed in hexa. The message regarding skewness means that you have small edges or small angle in your domain. The dbs is 300MB with ou without the mesh?

 April 1, 2009, 12:18 #5 New Member   Gabriel Lozano Join Date: Mar 2009 Location: Monterrey, México Posts: 4 Rep Power: 9 Ok, I am working now in separating the main volume in simplified volumes. Thanks for the tip. The dbs file is 17 mb without the mesh.

 April 2, 2009, 01:40 #6 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,145 Rep Power: 32 ok, I think your winding is wrong constructed. Thus, if I isolate alle the volumes included in this big "elbow", and if I try to unite all the volumes, gambit fused all the volumes and generates a big "elbow" without any crack. But I assume there should be crack where fluid may flows (between conductor layers). In other words you should modelled just the fluid domain, and substract the solid one. I think you have both in your model. Return and sketch your 2d profile with substracting the solid section (enable shade for checking the substract operation), then extrude, etc... Maybe I didn't understand the geometry

 April 2, 2009, 19:18 #7 New Member   Gabriel Lozano Join Date: Mar 2009 Location: Monterrey, México Posts: 4 Rep Power: 9 Hi Max. Thanks a lot for the tips. About the elbow you are talking about, that´s the core of the transformer, which won´t be meshed for this analysis. I am working on simplifying the volume of the tank, extruding faces that I already meshed until I can form the total volume. I don´t know if that´s the fastest or best method, but I am ensuring the connectivity in the whole mesh. Thanks for the help!

 April 3, 2009, 00:42 #8 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,145 Rep Power: 32 OK if you don't need to mesh it, then your model is quite simple to mesh.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post cestrin FLUENT 3 July 4, 2012 02:33 Rachid BANNARI (Bannari) OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 25 September 11, 2011 07:58 Panos FLUENT 4 March 5, 2009 23:44 Adrian FLUENT 8 October 7, 2008 08:39 Win Win Maw FLUENT 3 January 25, 2006 12:09

All times are GMT -4. The time now is 01:40.