dxxdt.m

FEM tools for caculation of nonlinear problems

function xd = dxxdt(t,x)


global dof h CH CH2 C K zdd delta_t  CH_1 CH_2  Mi 

ku = max(1,floor(t/delta_t));                    
zddnow = zdd(ku) + (zdd(ku+1)-zdd(ku))*(t/delta_t - ku);

displ = x(1:dof);                                
veloc = x(dof+1:2*dof);                          
accel = -CH\(CH2\(C*veloc + K*displ)) - h*zddnow;   
xd = [ veloc; accel ];