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-   -   Beginners Guide Needed: Meshing. (http://www.cfd-online.com/Forums/star-ccm/67219-beginners-guide-needed-meshing.html)

charltonjames August 7, 2009 10:44

Beginners Guide Needed: Meshing.
 
Hi, i am very new to Star-CCM+ (3 days) and as i only have a 14 day license i dont have long to really teach myself too much. I was therefore hoping that some of you may be kind enough to help me out stage by stage. I am not looking for great accuracy, but just wish to check that Star-CCM+ is able to do what i wish before i purchase the software.

I am trying to model wind movement within city centre squares, in particular i am using a case study of Chamberlain Square in Birmingham. I have created a 3D model in sketchup, which i have managed to import into Star-CCM+ in a .stl format. However, i need to remesh this (i dont think thats the technical term). The only guidance i have is the first tutorial under the meshing tutorials in help guide. However, i have copy this correclty i end up with 20,000,000 + faces. If i leave the meshing values default it makes my model very angular.

Could anyone provide a relative solution to this.

Thank you for your time

James

vishyaroon August 7, 2009 12:36

You can play around with the minimum and maximum surface mesh sizes to get a coarser mesh. This can significantly reduces the surface mesh count

charltonjames August 7, 2009 17:10

Thanks vishyaroon, i have been doing that this afternoon and so far the results have been much better. Thanks for the help.

I do however, have one further problem, i am happy with the mesh generated by the Generate Surface Mesh button. However, when i then click the Generate Volume Mesh button i get an error stating surface not closed. Any idea how to resolve this?

Thanks

James

vishyaroon August 7, 2009 17:15

These are a result of having a region that is not closed or having free edges. Check for free edges in teh imported geometry and then you can either fill up loops of free edges or zip free edges to get rid of these.

If you have a lot of free edges that you feel might require zipping, go for Surface Wrapping, before the Surface Remeshing stage. This closes the gaps and you could have a closed surface.

f-w August 7, 2009 17:20

Select the wrapper as one of your mesh models. Also, you will need to enclose your city (in a box, for example) to define the fluid region. You can do this by going into Representations>Import>Create Surface>Block. Select the option to create separate boundaries for each side, which you later will have to assign conditions to ...

charltonjames August 8, 2009 07:40

Thanks vishyaroon and f-w that has been a great help!! Im slowly starting to get an understanding of this software thanks to your help. I'll give both of your suggestions a try this afternoon. One further question if you dont mind, do i create the box after i have generated the surface and volume mesh for my city? Also, do i have to generate a surface and volume mesh for the created box? or is it ok to leave it how it is?

Thanks again guys, you've been a great help.

James

vishyaroon August 8, 2009 22:08

You may want to generate the box with your city inside before you start generating the surface mesh. The region to be meshed will be inside the box but outside the buildings that you are considering, where you are interested in analyzing the flow.

f-w August 10, 2009 14:09

James,

You'll need to create the box BEFORE you mesh anything. Have all your boundaries in a single region, and then mesh.

To give you an idea of what happens when the wrapper goes to work: think of a balloon that's inflated inside the box you created, the balloon expands and wraps around everything it comes in contact with (boundaries of the box and buildings). The result is 3D space (stuff inside the balloon) defining where the air will be modeled.


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