Curl, Divergence calculation from velocity data

Hi,

I have calculate the Curl, Divergence from the velocity data file available in 4650 x 4 array. Here 1, 2, 3, and 4 columns reprsents x, y, u, v. I have tried with below script, but I am getting some error. Please help..

X = data (:,1);

Y = data (:,2);

UU = data (:,3);

VV = data (:,4);

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

[UU, VV] = meshgrid(UU,VV);

f = curl(UU,VV);

[Sudheer Bhimireddy]

"some error" doesn't help much. Post your error so that we can help.

[Turbulence Analysis]

Hi, The error msg is as below

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Answer 1

[Bruno Luong]

Your data is already gridded, no need to gridded on top of it

load('matlab.mat')

UU=reshape(data(:,3),[75 62]);
VV=reshape(data(:,4),[75 62]);
X=reshape(data(:,1),[75 62]);
Y=reshape(data(:,2),[75 62]);

close all
figure
quiver(X,Y,UU,VV);
f = curl(UU,VV);
figure
imagesc(f');

[Turbulence Analysis]

Hi, Bruno,

Many thanks for your quick reply..

Actually, I am getting only vector plot. Stiil, getting below error while exceuting 'curl'

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Answer 2

[Turbulence Analysis]

Hi, Bruno,

Now, I am able to execute curl function. However, it seems, some mistake in curl computtaion. Actually, the calculated vorticity should look something similar to the attached fig.

Furthermore, I would like to get the vector plot and vorticty plot on the same fig, I tried with 'hold on', but I am not gettting correct figure..

I would be great if you could help me with this...

[Bruno Luong]

load('matlab.mat')
sz = [75 62];
UU=reshape(data(:,3),sz);
VV=reshape(data(:,4),sz);
X=reshape(data(:,1),sz);
Y=reshape(data(:,2),sz);
x=X(:,1);
y=Y(1,:);
f = curl(x,y,UU',VV');

close all
figure

imagesc(x,y,f);
hold on
V = sqrt(UU.^2+VV.^2);
quiver(X,Y,UU./V,VV./V,'k');
colormap(jet)
set(gca,'ydir','normal')

[Turbulence Analysis]

Thanks a lot Bruno.

Furthermore, If I have to calculte divergence, for e.g. dVx/dy or dVx/dx.. Do i hve to just use 'divergence' ??

[Bruno Luong]

yes

[Turbulence Analysis]

Thnaks..

For instnace if I need to get only dVx/dy , how to implement this ..

[Bruno Luong]

doc gradient

Answer 3

[Turbulence Analysis]

Hi,

Many thanks for your support..

For gradieant I have used as follows

[dx, dy]= gradient (UU');

I am getting good results

I am getting good results...