为什么有涂层的和没涂层的频率差别那么大？

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/TITLE, coating structure
/PREP7
MP,EX,1,1.1032e11
MP,PRXY,1,0.31
MP,DENS,1,4500
ET,1, Solid95
MP,EX,2,10e9 !
MP,PRXY,2,0.3
MP,DENS,2,3300
ET,2, Shell63
r,1
r,2,60/1e6
Lb=110/1000
Wb=110/1000
Tb=3/1000
K,1,0,0,0.5*wb
K,2,Lb,0,0.5*wb
K,3,Lb,0,-0.5*wb
K,4,0,0,-0.5*wb
K,5,0,Tb,0.5*wb
K,6,Lb,Tb,0.5*wb
K,7,Lb,Tb,-0.5*wb
K,8,0,Tb,-0.5*wb
V,1,2,3,4,5,6,7,8
K,9,0,Tb,0.5*wb
K,10,Lb,Tb,0.5*wb
K,11,Lb,Tb,-0.5*wb
K,12,0,Tb,-0.5*wb
A,9,10,11,12
NL=20
NW=20
Type,1
Mat,1
Real,1
LESIZE,1,,,NL
LESIZE,6,,,NL
LESIZE,3,,,NL
LESIZE,10,,,NL
LESIZE,2,,,NW
LESIZE,8,,,NW
LESIZE,12,,,NW
LESIZE,4,,,NW

VMESH,1
Type,2
Mat,2
Real,2
LESIZE,13,,,NL
LESIZE,15,,,NL
LESIZE,14,,,NL
LESIZE,16,,,NL
AMESH,7
NSEL,S, LOC, x
D,all,all
ALLSEL,ALL
nummrg,all !
numcmp,all
/SOLU
ANTYPE,MODAL
MODOPT,LANB,10
MXPAND, 10,,,YES ！
SOLVE
所求结果为：
SET TIME/FREQ LOAD STEP SUBSTEP CUMULATIVE
1 205.28 1 1 1
2 496.68 1 2 2
3 1251.4 1 3 3
4 1591.9 1 4 4
5 1801.3 1 5 5
6 1937.4 1 6 6
7 1939.6 1 7 7
8 1948.6 1 8 8
9 1952.3 1 9 9
10 1955.0 1 10 10

/TITLE, coating structure
/PREP7
MP,EX,1,1.1032e11
MP,PRXY,1,0.31
MP,DENS,1,4500
ET,1, Solid95
Lb=114.3/1000
Wb=114.3/1000
Tb=3.175/1000
K,1,0,0,0.5*wb
K,2,Lb,0,0.5*wb
K,3,Lb,0,-0.5*wb
K,4,0,0,-0.5*wb
K,5,0,Tb,0.5*wb
K,6,Lb,Tb,0.5*wb
K,7,Lb,Tb,-0.5*wb
K,8,0,Tb,-0.5*wb
V,1,2,3,4,5,6,7,8
NL=20
!划分单元
NW=20
Type,1
Mat,1
LESIZE,1,,,NL
LESIZE,6,,,NL
LESIZE,3,,,NL
LESIZE,10,,,NL
LESIZE,2,,,NW
LESIZE,8,,,NW
LESIZE,12,,,NW
LESIZE,4,,,NW

VMESH,1
NSEL,S, LOC, x
D,all,all
ALLSEL,ALL
/SOLU
ANTYPE,MODAL
MODOPT,LANB,10
EXPAND, 10,,,YES
SOLVE
所求结果为：
SET TIME/FREQ LOAD STEP SUBSTEP CUMULATIVE
1 202.14 1 1 1
2 489.01 1 2 2
3 1232.6 1 3 3
4 1569.2 1 4 4
5 1777.7 1 5 5
6 3094.2 1 6 6
7 3537.8 1 7 7
8 3682.0 1 8 8
9 4075.0 1 9 9
10 4539.9 1 10 10