Code covered by the BSD License

# Co-Blade: Software for Analysis and Design of Composite Blades

### Danny Sale (view profile)

18 Sep 2012 (Updated )

Analysis and design of composite blades for wind and hydrokinetic turbines

polygeom2(x, y)
```function [Geom, Iner] = polygeom2(x, y)
%
% This is a modified version of the original polygeom.m code published by
% H.J. Sommers: http://www.mathworks.com/matlabcentral/fileexchange/319-polygeom-m
%
%   Changes by D.Sale include:
%   -added a check to see if inputs are empty and to return empty values
%   -changed the outputs to structure data class
%   -removed some error checking on the inputs
%   -removed computation of polar moment
%   -removed computation of principal inertias and principal axes
%   -removed calls to shiftdim()
%   -removed calls to mean()

% check if inputs are empty
if isempty(x) || isempty(y)
Geom.A     = [];
Geom.x_c   = [];
Geom.y_c   = [];
Geom.P     = [];
Iner.Ix    = [];
Iner.Iy    = [];
Iner.Ixy   = [];
Iner.Iu    = [];
Iner.Iv    = [];
Iner.Iuv   = [];
return;
end

% make sure that x and y are column vectors
x = x(:);
y = y(:);

% number of vertices
n = numel(x);

% temporarily shift data to mean of vertices for improved accuracy
xm  = sum(x) / n;
ym  = sum(y) / n;
ons = ones(n,1);
x   = x - xm*ons;
y   = y - ym*ons;

% delta x and delta y
dx = x( [ 2:n 1 ] ) - x;
dy = y( [ 2:n 1 ] ) - y;

% summations for CW boundary integrals
A   = sum( y.*dx - x.*dy )/2;
Axc = sum( 6*x.*y.*dx -3*x.*x.*dy +3*y.*dx.*dx +dx.*dx.*dy )/12;
Ayc = sum( 3*y.*y.*dx -6*x.*y.*dy -3*x.*dy.*dy -dx.*dy.*dy )/12;
Ixx = sum( 2*y.*y.*y.*dx -6*x.*y.*y.*dy -6*x.*y.*dy.*dy ...
-2*x.*dy.*dy.*dy -2*y.*dx.*dy.*dy -dx.*dy.*dy.*dy )/12;
Iyy = sum( 6*x.*x.*y.*dx -2*x.*x.*x.*dy +6*x.*y.*dx.*dx ...
+2*y.*dx.*dx.*dx +2*x.*dx.*dx.*dy +dx.*dx.*dx.*dy )/12;
Ixy = sum( 6*x.*y.*y.*dx -6*x.*x.*y.*dy +3*y.*y.*dx.*dx ...
-3*x.*x.*dy.*dy +2*y.*dx.*dx.*dy -2*x.*dx.*dy.*dy )/24;
P   = sum( sqrt( dx.*dx +dy.*dy ) );

% check for CCW versus CW boundary
if A < 0,
A   = -A;
Axc = -Axc;
Ayc = -Ayc;
Ixx = -Ixx;
Iyy = -Iyy;
Ixy = -Ixy;
end

% centroidal moments
xc  = Axc / A;
yc  = Ayc / A;
Iuu = Ixx - A*yc*yc;
Ivv = Iyy - A*xc*xc;
Iuv = Ixy - A*xc*yc;

% replace mean of vertices
x_cen = xc + xm;
y_cen = yc + ym;
Ixx   = Iuu + A*y_cen*y_cen;
Iyy   = Ivv + A*x_cen*x_cen;
Ixy   = Iuv + A*x_cen*y_cen;

%% Collect output
Geom.A     = A;
Geom.x_c   = x_cen;
Geom.y_c   = y_cen;
Geom.P     = P;
Iner.Ix    = Ixx;
Iner.Iy    = Iyy;
Iner.Ixy   = Ixy;
Iner.Iu    = Iuu;
Iner.Iv    = Ivv;
Iner.Iuv   = Iuv;

end % function polygeom2

```