许多的汽车、机车、摩托车所用的弹簧阻尼器，在工作过程中受拉与受压时的阻尼值差别很大
，如何在动力学分析中考虑到振动过程中弹簧阻尼的变化？这一点非常重要。
以下以一简单的弹簧振子系统来说明：
/title,Analysis of Spring$Damper System
/prep7
multipro,'start',7
*cset,1,3,endtime,'enter endtime',.4
*cset,4,6,k1,'spring constant',14715
*cset,7,9,ylim,'posi of spring constant change',-.059
*cset,10,12,k2,'changed spring constant',26100
*cset,13,15,c1,'down damping coefficion',200
*cset,16,18,c2,'up damping coefficion',1000
*cset,19,21,vely,'initial speed of y-direction',-10
*cset,61,62,'input spring&damper coefficions'
multipro,'end'
et,1,14,,2
*if,vely,gt,0,then
r,1,k1,c2
*else
r,1,k1,c1
*endif
et,2,21
r,2,70,70,70
n,1
n,2
e,1,2
type,2
real,2
e,2
d,1,uy
acel,0,9.8
ic,2,uy,-0.0466,vely
fini
/solu
antype,trans
timint,on
kbc,1
time,0.004
nsubst,2
outres,all,all
solve
*get,uy,node,2,u,y
y2=uy
*do,i,.008,endtime,.008
time,i
nsubst,2
solve
*get,uy2,node,2,u,y
*if,uy2,gt,y2,then
*if,uy2,gt,ylim,then
r,1,k1,c2
*else
r,1,k2,c2
*endif
*else
*if,uy2,gt,ylim,then
r,1,k1,c1
*else
r,1,k2,c1
*endif
*endif
y2=uy2
*enddo
fini
/post26
/grid,1
/axlab,y,y-Direction Displacement
/gthk,axis,2
/gthk,curv,2
nsol,2,2,u,y
plvar,2