弹性地基梁模态振动分析

弹性地基梁模态振动分析，为什么自振频率与理论计算结果差别很大呢，请大侠指教下面命令流有什么错误
!参数定义
E0=3.0e10!模量
u=0.15!泊松比
p=25000!密度
B=0.2 !梁宽
h=0.2 !梁高
L=1 !梁长
k=3e8 !弹性地基系数
/PREP7
ET,1,BEAM54 ! UNSYMMETRICAL BEAM ELEMENT
R,1,0.04,1.333e-4,B/2,h/2 ! AREA, IZ, H/2, H/2
RMODIF,1,16,k ! ELASTIC FOUNDATION STIFFNESS
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,EX,1,,E0
MPDATA,PRXY,1,,u
MPDATA,DENS,1,,p
K,1
K,2,1
L,1,2
LESIZE,ALL,,,20
LMESH,1
D,1,UX, ! FIX MOTION OF END ALONG X-DIRECTION
/solu
ANTYPE,MODAL
MODOPT,SUBSP,10
NSEL,ALL
OUTPR,ALL,1
MXPAND,10
SOLVE
*GET,FREQ,MODE,1,FREQ
FINISH