『求助』应力集中问题？

分析一个圆柱的约束应力集中问题：半径为0.1m，高度为0.3m的圆柱，下表面固定，上表面受均布载荷900000Pa，求应力
得到下表面的应力随着网格的加密不断增大！
它实际的应力应该是多大，应该如何处理这类问题？
fini
/clear

/filname,cylind,1
/prep7
r=0.001
r1=100*r
h=300*r

cylind,r1,,,h,
wprota,,90
vsbw,all
wprota,,,90
vsbw,all

et,1,solid45
mp,ex,1,200e9
mp,dens,1,7871
mp,prxy,1,0.3

et,2,mesh200
keyopt,2,1,6
keyopt,2,2,0

nr=10
nh=nr*3

lesize,22,,,nr,,,,0
lesize,20,,,nr,,,,0
lesize,15,,,nr,,,,0
lesize,16,,,nr,,,,0
lesize,9,,,nh,,,,0
mshape,0,2d
mshkey,1
amesh,14,22,4
amesh,2
vsweep,all

/solu
alls
csys,0
asel,s,loc,z,h
sfa,all,,pres,9000000

alls
!csys,1
asel,s,loc,z,0
nsla,s,1
!da,all,uz,0

da,all,all

csys,0
alls

eqslv,pcg,1e-8
solve

/post1
plnsol,s,eqv,0,1.0

alls
nsort,s,eqv
*get,vms_max,sort,,max !最大的应力
*status

*dim,a,,3
nsort,u,z
*get,a(1),sort,,max
*get,a(2),sort,,min
nsort,s,eqv
*get,a(3),sort,,max
/output,pp,dat
*status,a,1 !显示数组的值
/output


得到的应力云图如下所示：