愿与大家分享，共同进步。当然也欢迎大家把自己的想法与我交流。
  考虑预应力影响的模态分析的方法如下：
1。先进行静力分析，注意分析时打开预应力开关(PSTRES,ON)。
2。改变分析类型，获取模态解。(再用一次PSTRES,ON)
3。特别注意：a.静力分析中和随后的模态分析中的集中质量选项(LUMPM)必须一致。
            b.进行模态分析时，应保证静力分析的保存的.emat和.esav文件存在。
            c.步骤1也可以是瞬态分析，但应当在需要的时间保存.emat和.esave文件。
下面是自己做的一个小例子。
两端固结
 
的梁，长10m，截面为0.1m*0.1m,材质为钢材。对比降温90度前后的模态分析解。

!考虑温度预应力的模态分析
FINI
/CLEAR,NOSTART
/prep7
k,1,0,0,0
k,2,10,0,0
l,1,2
et,1,beam4
MP,EX,1,200e9
MP,NUXY,1,0.3
mp,alpx,1,0.000012
MP,dens,1,7800
R,1,0.01,8.3E-6,8.3E-6,0.1,0.1, ,
LESIZE,ALL, , ,10, , , , ,1
LMESH,ALL

/SOLU
ANTYPE,STATIC
PSTRES,ON
lumpm,off
NSEL,S,LOC,X,0
D,all,all
ALLSEL,ALL
NSEL,S,LOC,X,10
D,ALL,UY
D,all,all
esel,all
acel,,-9.8,
BFE,all,TEMP,1,-90, , ,
ALLSEL,ALL
SOLVE
SAVE
FINI

/SOLU
ANTYPE,MODAL
MODOPT,LANB,10
EQSLV,SPAR
MXPAND,0, , ,0
lumpm,off
PSTRES,1
MODOPT,LANB,10,0,500, ,OFF
NSEL,S,LOC,X,0
D, all,all
ALLSEL,ALL
NSEL,S,LOC,X,10
D, all,all
ALLSEL,ALL
SOLVE
SAVE

/POST1
SET,LIST

!不考虑温度预应力
FINI
/CLEAR,NOSTART
/prep7
k,1,0,0,0
k,2,10,0,0
l,1,2
et,1,beam4
MP,EX,1,200e9
MP,NUXY,1,0.3
mp,alpx,1,0.000012
MP,dens,1,7800
R,1,0.01,8.3E-6,8.3E-6,0.1,0.1, ,
LESIZE,ALL, , ,10, , , , ,1
LMESH,ALL

/SOLU
ANTYPE,STATIC
PSTRES,ON
lumpm,off
NSEL,S,LOC,X,0
D,all,all
ALLSEL,ALL
NSEL,S,LOC,X,10
D,ALL,UY
D,all,all
esel,all
acel,,-9.8,
!BFE,all,TEMP,1,-90, , ,
ALLSEL,ALL
SOLVE
SAVE
FINI

/SOLU
ANTYPE,MODAL
MODOPT,LANB,10
EQSLV,SPAR
MXPAND,0, , ,0
lumpm,off
PSTRES,1
MODOPT,LANB,10,0,500, ,OFF
NSEL,S,LOC,X,0
D, all,all
ALLSEL,ALL
NSEL,S,LOC,X,10
D, all,all
ALLSEL,ALL
SOLVE
SAVE

/POST1
SET,LIST

不考虑预应力的结果    考虑预应力的结果      
   SET   TIME/FREQ   SET   TIME/FREQ 
     1  5.1946         1  10.446     
     2  5.1946         2  10.446     
     3  14.320         3  22.833     
     4  14.320         4  22.833     
     5  28.088         5  38.449     
     6  28.088         6  38.449     
     7  46.493         7  57.983     
     8  46.493         8  57.983     
     9  69.639         9  81.852     
    10  69.639        10  81.852