k0=4.5;
hc=3.5;

d=[3.15 3.23];
a1=tan(pi*(d)./(2*hc));
a2=cot(pi*(d)./(2*hc));
% plot(d,a1)
y=(a1+a2)*2*k0*hc*1e-3./pi
y=y./9.8*8

% 
var=1+(tan(pi*(d+0.25)./(2*hc))).^2;
k=2*k0*hc/pi*( var*pi./(2*hc)+var*pi./(2*hc)./(var-1))
% % hold on
% % plot(d,y)
% k2=k0.*(var+var./var-1)
% plot(d,k2)
% figure
% plot(d,y)