How to plot streamlines ?

Lets say I have channel of length x = 200 and height y = 200. I have my velocity (u and v) distributed throughout the channel of size 200X200 for u and v each. How can I plot streamlines for this ? I have gone through the matlab documentation and am not clear about 'startx' and 'starty'. How should I define this ?

Answer 1

[Chad Greene]

One way is to define a bunch of random seed locations within the domain like this:

N = 75; % number of seed locations
xstart = max(x)*rand(N,1); 
ystart = max(y)*rand(N,1);

For example, try this:

x = 1:200; 
y = 1:200; 

[X,Y] = meshgrid(x,y); 

vx = 30 + 30*cos((Y-100)*pi/100); 
vy = 5*cos(X/10).*cos((Y-100)*pi/100); 

figure
pcolor(X,Y,hypot(vx,vy))
shading interp

N = 75; 
xstart = max(x)*rand(N,1); 
ystart = max(y)*rand(N,1); 

h=streamline(X,Y,vx,vy,xstart,ystart);
set(h,'color','red')

[Chad Greene]

I'm not sure what your application is, but you may alternatively consider quiver. Just downsample the field, perhaps with imresize like this:

x = 1:200; 
y = 1:200; 

[X,Y] = meshgrid(x,y); 

vx = 30 + 30*cos((Y-100)*pi/100); 
vy = 15*cos(X/10).*cos((Y-100)*pi/100); 

figure
pcolor(X,Y,hypot(vx,vy))
shading interp

sc = 1/10; 
hold on
quiver(imresize(X,sc),imresize(Y,sc),imresize(vx,sc),imresize(vy,sc),'r')

Above I used sc = 1/10 to downsample by a factor of 10.

[RAJA RAMA KRISHNAA B.U]

I have a situation like, I have U and V values of velocity for 1023 frames. Now I need to load it and find a proper streamline plot for all frames at any desirable point.

[Eseosa Ekanem]

Hi Raja, did you find a solution to your problem? I have similar challenge but I want to plot the streamlines for just one frame.