Code covered by the BSD License

# Mastering Mechanics 1: Using MATLAB 5

### Doug Hull (view profile)

20 Aug 2002 (Updated )

Companion Software

[result]=halfcircle(r,orient,req)
function [result]=halfcircle(r,orient,req)
%HALFCIRCLE Semicircle shape routine.
%
%   Shape described: A semi-circle.
%
%   Datum location: Center of circle.
%
%   Input arguments:
%     ORIENTATION: Either 'n','e','s', or 'w'.
%
%   Requests: (Must be in single quotes)
%     'area':  Area of the shape.
%     'circ':  Circumference of shape.
%     'Ix':    Area moment of inertia about the neutral x axis.
%     'Iy':    Area moment of inertia about the neutral y axis.
%     'centX': Distance from datum to centroid in the x direction.
%     'centY': Distance from datum to centroid in the y direction.
%     'comp':  All of the above in a 1x6 matrix.
%
%      OBEAM, QUARTERCIRCLE, RECTANGL, RECTUBE, TBEAM, VERTRAP, VERTRIA.

%   Details are to be found in Mastering Mechanics I, Douglas W. Hull,
%   Prentice Hall, 1998

%   Douglas W. Hull, 1998
%   Copyright (c) 1998-99 by Prentice Hall
%   Version 1.00

req=lower(req);
orient=lower(orient);

if     strcmp(req,'area')  result=(pi*r^2)/2;
elseif strcmp(req,'circ')  result=(2*pi*r)/2+2*r;
elseif strcmp(req,'ix')    result=r^4*pi/8;
elseif strcmp(req,'iy')    result=r^4*pi/8;
elseif strcmp(req,'centx')
if strcmp(orient,'w') result=-4*r/(3*pi);
elseif strcmp(orient,'n') | strcmp(orient,'s')
result=0;
else
result=4*r/(3*pi);
end
elseif strcmp(req,'centy')
if strcmp(orient,'s') result=-4*r/(3*pi);
elseif strcmp(orient,'e') | strcmp(orient,'w')
result=0;
else
result=4*r/(3*pi);
end
elseif strcmp(req,'comp')
result(1,1)=halfcircle(r,orient,'area');
result(1,2)=halfcircle(r,orient,'circ');
result(1,3)=halfcircle(r,orient,'centx');
result(1,4)=halfcircle(r,orient,'centy');
result(1,5)=halfcircle(r,orient,'ix');
result(1,6)=halfcircle(r,orient,'iy');
elseif strcmp(req,'draw')
if strcmp(orient,'n')
angle =[0: DR(1): DR(180)];
elseif strcmp(orient,'e')
angle =[DR(-90): DR(1): DR(90)];
elseif strcmp(orient,'s')
angle =[DR(180): DR(1): DR(360)];
else strcmp(orient,'w')
angle =[DR(90): DR(1): DR(270)];
end
xcentroid=halfcircle(r,orient,'centx');
ycentroid=halfcircle(r,orient,'centy');
X=r*cos(angle);
Y=r*sin(angle);
fill(X,Y,'r');
hold on
ColA=strvcat('Area','Circumference','Centroid X','Centroid Y','Ix','Iy');
ColB=makecol(halfcircle(r,orient,'comp')');
plot (xcentroid,ycentroid,'ko',0,0,'g*')
hold off;
axis ('equal')
titleblock(ColA,ColB)
expandaxis(5,5,5,0)
else
disp ('That is not a valid request, try area, circ, Ix, Iy, centX,')
disp ('centY, comp.')
disp ('You must use single quotes')
end