How rotate a number as a vector in quiver plot?

Hi all, I am having a strange issue with rotating vector along the circle that I cannot seem to debug - I am hoping fresh eyes will help. The problem is best described if I explain it as follows:

I have 16 vectors, and I wonder to set them along the circumferential of the circle radially; like they are passing from the centre of my circle,

clc; clear ;close;

%% Geometry of accelerometer positions (in cm) - edit r and/or n if required

r=9; % radius of nodes in cm

n=16; % number of (equally spaced) nodes around the half-circumference

theta=-pi:2*pi/(n-1):pi;

% angular position from 12 o'clock

x=2*r*sin(theta)'; y=-r*cos(theta)';

%% Type in modal matrix (i.e. mode shapes are columns)

% Dummy data for you to replace

w=[6,1.74;6.06,0.212;2.67,+3.24;1.42,1.43; 3.22,0.983;3.96,0.66;6.37,0.829; 6.64,2.55;8.4,3.27;...

    6.07,1.74;6.06,0.212;2.67,3.24;1.42,1.43; 3.22,0.983;3.96,0.66;0.37,0.829];

% Type in the natural frequencies here

fn=[50,175];

%% Plot mode shapes as quiver plots - you should not need to edit this part

for ii=1:length(fn)

figure(ii)

quiver(x,y,x,w(:,ii))

hold on plot(x,y,'-r','Linewidth',3) % overlay geometry

title(['Mode shape of ', num2str(fn(ii)),' Hz mode'])

xlabel('x (cm)')

ylabel('y (cm)')

end

[Paul]

Any idea?

Answer 1

[Joe]

If I understand what you're going for, make these changes:

- Fix your x and y definition

 x = r*cos(theta)'; y= r*sin(theta)';

- Change the call to quiver so that you are plotting in the radial direction

 quiver(x,y,w(:, ii).*x, w(:, ii).*y)

- Put your circle plot on a new line from "hold on"

 hold on 
 plot(x,y,'-r','Linewidth',3) % overlay geometry

For me, this results in a plot with reasonable modeshapes, e.g.

[Paul]

Oh fantastic, thanks:)