怎么会有两个0频率啊

ForCan2008

我现在学习，做了一个简单模型的模态分析，结果怎么会有两个0频率啊，我已经全约束了啊。求助，急啊！
代码：
/PREP7
!*************************数组定义
*DIM,FREQ,,5 !模态频率
!*************************进入前处理部分
WPSTYLE,,,,,,,,1  !显示工作坐标系
KEYW,PR_SET,1   
KEYW,PR_STRUC,1
!*************************参数定义
ET,1,solid45
MPTEMP,1,0
MPDATA,EX,1,,1.93e11
MPDATA,PRXY,1,,.31
MPDATA,DENS,1,,7750
!**************************建立模型
  
BLOCK,0,0.02,0,0.01,0,0.001,
BLOCK,0.005,0.007,0.006,0.008,0.001,0.002,
BLOCK,0.013,0.015,0.006,0.008,0.001,0.002,
BLOCK,0.005,0.007,0.002,0.004,0.001,0.002,
BLOCK,0.013,0.015,0.002,0.004,0.001,0.002,
/PNUM,VOLU,1
NUMCMP,ALL  
NUMMRG,ALL, , , ,LOW
ALLSEL,ALL

!约束
ALLSEL,ALL
ASEL,S,LOC,X,0
DA,ALL,ALL,
ALLSEL,ALL
!网格划分
ESIZE,0.001

vmesh,all
finish
/SOLU   !进入求解模块SOLUTION   
ANTYPE, MODAL   !申明求解类型是模态分析
MODOPT,LANB,5   !使用Block Lanczos方法求解前5阶振型和频率
SOLVE   !开始求解   
FINISH      !退出后模块
/POST1  !进入后处理模块POST1        
SET, 1, 1   !读入第一阶频率和振型
SET,LIST !读取模态频率
*get,FREQ(1),MODE,1,FREQ,imag,,
*get,FREQ(2),MODE,2,FREQ,imag,,
*get,FREQ(3),MODE,3,FREQ,imag,,
*get,FREQ(4),MODE,4,FREQ,imag,,
*get,FREQ(5),MODE,5,FREQ,imag,,
finish
/solu
*CFOPEN,result_model,xls
*VWRITE,FREQ(1)
(F8.4)
*CFCLOS
finish

daxiaguo

我来抛砖引玉
零频率可能是由于四个小体和下面大体相交的节点间缺少约束而引起的,在ForCan2008老兄的程序上多加以下几句就能算到非零频率了
ALLSEL,ALL
NSEL,S,LOC,Z,0.001
CPINTF,ALL
结果如下:
  *****  INDEX OF DATA SETS ON RESULTS FILE  *****

   SET   TIME/FREQ    LOAD STEP   SUBSTEP  CUMULATIVE
     1  2059.0             1         1         1
     2  9138.0             1         2         1
     3  12785.             1         3         1
     4  16938.             1         4         1
     5  29357.             1         5         1
不知对否,请各位大侠指正:@D