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-   -   u,v,w in local Coordinate System (http://www.cfd-online.com/Forums/cfx/20203-u-v-w-local-coordinate-system.html)

martin weghaus March 1, 2004 06:09

u,v,w in local Coordinate System
 
hi

I need to have u,v,w in local coordinate System.

It should be easy to calculate it, but I do not get access to the coord-frame-values. Following will produce an error.

LIBRARY: CEL:

EXPRESSIONS:

zx1 = Coord 1.Axis 3 Point X Coord

END END END

Bye martin

Neale March 3, 2004 02:51

Re: u,v,w in local Coordinate System
 
Unfortunately the u,v,w velocity components are not automatically transformed by the flow solver into a local coordinate frame.

With knowledge of the orientation of your user defined coordinate frame with respect to the global coordinate frame (Coord 0), which the flow solver solves in, you can do this yourself using user fortran. Just pass u, v and w into your user fortran and multiply out by the transformation matrix.

Neale


martin weghaus March 3, 2004 03:17

Re: u,v,w in local Coordinate System
 
That is what I want, but For calculating the transformation matrix I need information about the coordinate frame like

"zx1=Flow.Coord 1.Axis 3 Point X Coord"

and on this I fail.

martin


Neale March 4, 2004 01:13

Re: u,v,w in local Coordinate System
 
If you managed to setup your local coordinate frame properly in CFX-Pre then you should be able to manually calculate the transformation. A velocity vector is non-variant under a translation so that part of the transform does not matter. You only need to calculate the direction cosine matrix and then multiply the flow solver u,v,w values by that to get velocity in your local frame.

Do you have a book with some documentation on coordinate transformations?

Neale

BAK_FLOW March 12, 2004 11:06

Re: u,v,w in local Coordinate System
 
Hi Neal,

what is your recommendation on the best simple but complete guide to transforms. I have seen many texts on vector and tensor analysis but few that explain things physically.

Any suggestions are useful.

Thanks.......BAK_FLOW


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