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 shiva ram February 7, 2002 15:50

Helix

Hi all,

Can anybody tell me if theres a way i can draw helix in Gambit.i am trying to model a 3D geometry which has a helix..so if anybody knows how to do it,please let me know.

Thanks

Shiva Ram

 Erwin February 7, 2002 16:55

Re: Helix

Yeah.

First create a number of vertices in a circle, eq. by copying a vertex 12 x by rotation around origin.

Then translate every vertex in the direction normal to the circle plane. If you have 12 vertices then the 1st one stays put, the second one is translated by helix lead /12, the second one by 2 leads/12, until the last one is copied to the place where one helix lead ends.

Now connect all vertices (I think by NURBS, not entirely sure) to obtain a spiral.

Now you can place a circle at the beginnning of the spiral and 'sweep' it along the spiral to get a helix.

You can optimize certain steps to get better results, just make sure you don't get slivers when you connect multiple helices.

 shiva ram February 7, 2002 17:21

Re: Helix

Hi Erwin,

Thank you very much for your suggestion... but i am unable to interpret what exactly you mean by--SECOND VERTEX IS TRANSLATED BY HELIX LEAD/12......i would appreciate if you could clarify this.

Thanks

Shiva Ram

 Erwin February 7, 2002 17:57

Re: Helix

Suppose your helix is 12 units in diameter and 36 units long.

Let's say your circle consists of 12 vertices (or more, maybe needs some experimentation) in the xy plane.

Now, vertex.1 must stay in place, vertex.2 must be moved to z=3, vertex.3 must be moved to z=6, vertex.4 must be moved to z=9, etc etc vertex.11 must be moved to z=33, and finally vertex.1 must be copied to z=36. Now the 13 vertices form a spiral.

 Scott Whitney February 12, 2002 17:53

Re: Helix

Sorry for not responding earlier. I was quite busy. Here is the method I use to make a scroll. There are other methods. I will make an example scroll in the 'z' direction. Of course you can change it to a helical line or helical rope pretty easily with a few minor changes to this technique.

1) Create two points: (.5,0,0) and (1,0,0). 2) Connect these points into a line. 3) Create a face by sweeping this edge: 3a) Select the edge you created. 3b) Define a vector path with the length of one rotation. In this example my vector will be created from two points - (0,0,0) and (0,0,2) - for a length of 2 in the 'z' direction. 3c) Select perpendicular, twist, 360. 4) Copy this face in the 'z' direction to give the scroll a finite thickness. Face copy, translate, (0,0,.1). You now have two sides of this scroll volume and you need four more. 5) Create four additional edges connecting the vertices on the screen. In this example these four edges are in the 'z' direction with a length of 0.1. 6) Create four faces - two end faces and two curved side faces. This is done with the create face from wireframe button. 7) Finish by creating a volume. This is done by stitching the 6 faces together. 8) If you need more than one revolution, copy this volume in the 'z' direction. Repeat as needed. 9) If you copied these volumes, then there will be duplicate faces where the volumes meet. Duplicate faces are bad. Go to the face menu and use the connect face button. This should be done on all Gambit models to avoid problems, not just this scroll. 10) To make these separate scroll volumes into one volume, use the merge volume button.

 Scott Whitney February 12, 2002 17:57

Re: Helix

If you want a sample file, use this journal:

vertex create coordinates 0.5 0 0

vertex create coordinates 1 0 0

edge create straight "vertex.1" "vertex.2"

face create rotate "edge.1" vector 0 0 2 origin 0 0 0 twist 360

face copy "face.1" to "face.2"

face move "face.2" offset 0 0 0.1

edge create straight "vertex.1" "vertex.7"

edge create straight "vertex.2" "vertex.8"

edge create straight "vertex.3" "vertex.6"

edge create straight "vertex.4" "vertex.5"

face create wireframe "edge.1" "edge.9" "edge.7" "edge.10" real

face create wireframe "edge.4" "edge.12" "edge.5" "edge.11" real

face create wireframe "edge.12" "edge.8" "edge.3" "edge.10" real

face create wireframe "edge.11" "edge.6" "edge.2" "edge.9" real

volume create stitch "face.1" "face.2" "face.3" "face.4" "face.5" "face.6" real

volume copy "volume.1" to "volume.2"

volume move "volume.2" offset 0 0 2

face connect "face.1" "face.2" "face.3" "face.4" "face.5" "face.6" "face.7" "face.8" "face.9" "face.10" "face.11" "face.12" real

volume merge "volume.1" "volume.2" real

 stefan February 13, 2002 08:58

Re: Helix

(nearly) the same a little bit shorter:

face create width 0.1 height 0.5 offset 0.25 0 0.05 zxplane rectangle
face move "face.1" offset 0.5 0 0
volume create rotate "face.1" vector 1e-08 1e-08 2 origin 0 0 0 twist 360
volume cmove "volume.1" multiple 1 offset 0 0 2
volume unite volumes "volume.1" "volume.2"

 shiva ram February 13, 2002 12:54

Re: Helix

Thank you very much for your suggestions.i shall try them out and let you know how they work out.

Thanks

shiva ram

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