workbench与APDL如何match?

一个简单的问题，圆形薄板（直径800mm，厚度0.4mm），边缘施加固定载荷（fixed support），进行模态分析。材料采用silicon（密度2330,杨氏模量1.6e11，泊松比0.22）。
我用workbench求解出的六阶模态分别为：
1. 6344.5
2. 13211
3. 13211
4. 21680
5. 21686
6. 24734
但在APDL中用SHELL181单元求解出的六阶模态完全不同:
1. 0
2. 0
3. 0
4. 4802.54
5. 13772.5
6. 13772.6
求高手帮忙解答！
------------------------------------------------------------------------------------
FINISH
/CLEAR,NOSTART
/FILNAME,test,1
/TITLE,test modal
/REPLOT
/PREP7
!*
ET,1,SHELL181
SECTYPE,1,SHELL
SECDATA,4E-7,1,0,3
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,EX,1,,1.6e11
MPDATA,PRXY,1,,0.22
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,DENS,1,,2.23e3
CYL4,0,0,4E-4
FLST,5,4,4,ORDE,2
FITEM,5,1
FITEM,5,-4
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1,1e-5, , , , , , ,1
!*
MSHAPE,0,2D
MSHKEY,0
!*
CM,_Y,AREA
ASEL, , , , 1
CM,_Y1,AREA
CHKMSH,'AREA'
CMSEL,S,_Y
!*
AMESH,_Y1
!*
CMDELE,_Y
CMDELE,_Y1
CMDELE,_Y2
/SOLU
ANTYPE,MODAL
MODOPT,LANB,6
DL,ALL,,UZ,0
SOLVE
*GET,F,MODE,1,FREQ