reading velocity vectors from figure 1 at ly = 0.5 and lx = 0.5 and plotting the graph

Hi everyone,

This code below creates figure 1,

      if floor(25*k/nt)>floor(25*(k-1)/nt), fprintf('.'), end
      if k==1|floor(nsteps*k/nt)>floor(nsteps*(k-1)/nt)
          % stream function
          rhs = reshape(diff(U')'/hy-diff(V)/hx,[],1);
          q(perq) = Rq\(Rqt\rhs(perq));
          Q = zeros(nx+1,ny+1);
          Q(2:end-1,2:end-1) = reshape(q,nx-1,ny-1);
          clf, contourf(avg(x),avg(y),P',20,'w-'), hold on
          contour(x,y,Q',20,'k-');colormap;
          Ue = [uS' avg([uW;U;uE]')' uN'];
          Ve = [vW;avg([vS' V vN']);vE];
          Len = sqrt(Ue.^2+Ve.^2+eps);
          unode = (Ue./Len);
          vnode = (Ve./Len);
          quiver(x,y,unode',vnode',.4,'k-')
          hold off, axis equal, axis([0 lx 0 ly])
          p = sort(p); caxis(p([8 end-7]))
          title(sprintf('Re = %0.1g t = %0.2g',Re,k*dt))
  drawnow
      end

end

Figure 1 can be found at,

http://imageshack.us/photo/my-images/830/figure1.jpg/ ____________________________________________________________

What i am trying to do now is to to plot a graph called figure 2 by taking the velocity values from figure 1 at, (lx=0.5) vertical center line (u-component) and the (ly=0.5) horizontal center line (v-component).

Figure 2 should look like, refer to the link below,

http://imageshack.us/photo/my-images/443/correctplotoutput.jpg/

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So can anyone guide me on how to achieve figure 2 ?

_____________________________________________________________

I tried creating figure 2 using the code below but it was incorrect.

    for ly = 0.5 
       lyloc = find(abs(y - 0.5) < 100*eps(0.5), 1);
       thisv = vnode(:, lyloc);
       fid = fopen('ly=0.5.txt','w');
       fprintf(fid,' %5.3f \n' ,thisv)
       status = fclose(fid);
    end

   for lx = 0.5 
       lxloc = find(abs(x - 0.5) < 100*eps(0.5), 1);
       thisu = unode(:, lxloc);
       fid = fopen('lx=0.5.txt','w');
       fprintf(fid,' %5.3f \n' ,thisu)
       status = fclose(fid);
       figure (2) , plot(thisu,thisv), axis([-1 1 -1 2])
    end

[Walter Roberson]

That is not my code. The code I gave indexes vnode and unode with the same index (and thus in the same loop). I would not give code that continually overwrote a variable needed after the loop, and I would not give code that keep overwriting the same file. Yes, I do see that the loops only go one iteration, but I would not have provided code that looked like that.

[iceuday]

I am sorry Mr Walter.

You said,

"If y = 0.5 is exactly in the list of y, then

yloc = find(abs(y - 0.5) < 100*eps(0.5), 1);

thisu = unode(:, yloc);

thisv = vnode(:, yloc);

That is, thisu and thisv would give the vector field values all along the line y = 0.5 ."

I did as you said and tried other ways but i still cannot get my output to look like figure 2 in the link above.

[Walter Roberson]

I was not able to see the vector field arrows in your figure 1. I do see black lines, but those look to be lines from the contour() call.

[iceuday]

The velocity vector field arrows are there, it is hard to see them as they are small and the blue color makes it difficult to view it.

I have uploaded another link for figure 1, refer to the link below,

http://imageshack.us/photo/my-images/406/figure1withvisibleveloc.jpg/