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July 10, 2009, 01:09 |
Streamline plotting logic
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#1 |
New Member
Join Date: Jun 2009
Posts: 10
Rep Power: 16 |
hello,
I was wondering if anyone could explain the logic of how streamlines are plotted. I have a stream function of a Karman vortex street defined wrt a fixed co-ordinate system. Now, i need to plot the streamlines, I can evaluate the value of the stream function all over the domain. How do I go about plotting the stream lines from there. Also, I would need to plot the same stream function with different frame of reference - i.e. wrt an observer moving with the stream, wrt an observer moving with the vortices. How would I incorporate a change of reference frame in the stream function? Thanks in Advance |
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July 10, 2009, 02:22 |
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#2 |
New Member
sanjay kumar shukla
Join Date: Jul 2009
Posts: 4
Rep Power: 16 |
If you have a stream function and you can evaluate stream function at any point in the domain than what is the problem with plotting. I mean, if you have stream function as function of space coordinates than your problem is solved.
make a bit clear about your difficulity that you are facing. |
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July 10, 2009, 04:09 |
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#3 |
Super Moderator
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Level curves of the stream-function will give you the instantaneous streamlines. See
http://en.wikipedia.org/wiki/Stream_function |
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July 10, 2009, 04:19 |
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#4 |
New Member
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^Ah yes, but what logic do I use to code in a level curve plotting function- is it like
Search through the domain for a certian value of the function and store all such points and then connect them by a curve Or search in the neighborhood of a point and keep joining the points of equal values |
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July 10, 2009, 04:43 |
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#6 |
New Member
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^Thats too easy . I was looking for the logic for plotting the stream lines from scratch - i prefer working with code I personally wrote so that I can mangle it in any way I see fit. Or do you think its really not worth it?
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July 10, 2009, 05:07 |
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#7 |
Super Moderator
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Unless you have some special needs which existing softwares cannot deal with, it is not worth doing it yourself.
If you still want to do it yourself, then the procedure would be close what you described. But first you would need to generate a grid. Choose a set of discrete values for the stream-function. Locate these values in each grid cell and then try to join all points having same value. I think its easier to do this if you use triangular grids. |
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July 10, 2009, 05:35 |
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#8 |
New Member
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Ok, will sleep on it then, thanks for all the help
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July 10, 2009, 08:14 |
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#9 |
Member
M. Nabi
Join Date: Jun 2009
Posts: 44
Rep Power: 16 |
If you ask about the logic of streamlines:
in 2D, the stream function is u=ds/dy , v=-ds/dx and the vorticity is vort=dv/dx-dudy subsitute d^2s/dx^2+d^s/dy^2=-vort you need to solve a poisson equation in each time step to see the moving stream lines. If you are only interested in steady state solution, you can solve this poisson equation once , at the end of simulation. |
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