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-   -   Simple question about defining a volume in Gambit (http://www.cfd-online.com/Forums/fluent/43436-simple-question-about-defining-volume-gambit.html)

Amit January 22, 2007 13:59

Simple question about defining a volume in Gambit
 
Hi all,

I would like to use Gambit to create a 3-D volume which is kind of like a cylinder, except that the two sides are different. I would like for one side to be a circle of radius r1, and the other side to be an ellipse of major axis r1, and a different minor axis, r2. The centers of the circle and ellipse would be on the axis of the final shape. In essence, I would like to make a 3-D shape where one circular axis maintains constant and the other one varies.

How would I do this? I know there are options in Gambit for stitching faces and protrusions, but I am having trouble locating how to make a shape from one circle and one ellipse.

Sincerely, Amit

Jason January 23, 2007 08:51

Re: Simple question about defining a volume in Gam
 
Create the circle and split it in half. Create the ellipse and split it in half. Delete the extra portions and merge the two faces together. Then extrude the merged face to create your volume.

Hope this helps, and good luck, Jason

Amit January 23, 2007 10:42

Re: Simple question about defining a volume in Gam
 
Ahh, I think I have not clearly explained my shape. I do not want the shape to be a simple extrusion. I want it to have the properties of a frustom-- in which the two bases are slightly different shapes. Perhaps the word cylinder was not quite right.

If I wanted to make a frustom, let's call it, with base 1 = circle, and base 2 = ellipse, how would I do that?

Thanks again, Amit

Jason January 23, 2007 15:41

Re: Simple question about defining a volume in Gam
 
Sorry, I misunderstood what you were trying to do. That's a little more complex, and I would recommend using a different solid modeling package like Pro/E or SolidWorks and then importing the geometry into Gambit as a step or iges file.

If you don't have a choice, or you'd rather do it all in Gambit then here's one way of doing it (this is just a quick example... I just tried this in Gambit 2.3.16 and it works).

Face Tools->Create Face->Circle to create the circular base. Using the Create Face saves a step instead of creating the edge and then using the edges to create the face. When you're done you'll have Face.1 Edge.1 and Vertex.1 that form a circular face.

Face Tools->Create Face->Ellipse to create the elliptical base (Face.2 Edge.2 and Vertex.2). Move Face.2 to the correct position (Face Tools->Move).

Edge Tools->Split Edge and split Edge.1 (the circle) using the "point" option and "U Value" of 0.5. Do the same for Edge.2 (the ellipse). This splits the arcs in half.

Edge Tools->Create Edge to create a straight line from the vertex on the circular face to the corresponding vertex on the ellipse face.

Face Tools->Net Surface to create the vertical sides of the frustrum. You'll have to do one half of the frustrum at a time. For the U Dir Edges, pick one arc on the circle and the corresponding arc on the ellipse (make sure the arrows are pointing the same direction). For the V Dir Edges, pick the vertical edges (making sure the arrows are pointing in the same direction). Repeat this for the opposite half of the frustrum.

Once you have all the faces (click the "Shade Geometry" icon to be sure) then you can stitch them together to create a volume (Volume Tools->Stitch Volume).

This is just a simple example. You can make it more complex by adding more control lines for the net surface. And you're not forced to use straight lines connecting the two bases. They can be complex, but the more complex you make it, the more you're setting yourself up for something to go wrong.

Hope this helps, and good luck, Jason


Amit January 24, 2007 17:10

Re: Simple question about defining a volume in Gam
 
Hey Jason,

I tried your method and it works fine- my thanks. Also, I realized that using Gambit to perform this object creation is rather time-consuming and I may consider switching to SolidWorks (thanks for that advice also).

Sincerely, Amit


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