优化算例(材力上册P200_5.5)

yujb025

问题：20a工字钢梁的支承及受力情况如图所示,若许用应力[σ]=160MPa,试求许可载荷P。

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!求解过程
/prep7
*set,Nforce,1000
et,1,3  
r,1,355780,2370e4,200   !查表可得
mp,ex,,2e5  
mp,nuxy,,0.3
n,1
n,61,6000   
fill
type,1  
real,1  
e,1,2   
egen,60,1,1,61,1
FINISH
/solu   
d,1,ux,0,0,,,uy
d,61,uy,0  
fcum,repl,

*do,i,0,100000,10
*set,Nforce,1000+i
/solu
f,21,fy,-Nforce  
f,41,fy,Nforce
solve   
FINISH  
/post1   
etable,mises,nmisc,1
esort,etab,mises,0,1,
*get,smax,sort,,max,

*if,abs(smax-160),le,0.1,then  !若应力在许用应力附近，则（精度为0.1）
save,opt,db,,all   !存储最优(结果)数据库
*endif  
*enddo

!方法二：(解：56.850KN)
/prep7
*set,Nforce,1000
et,1,3  
r,1,355780,2370e4,200   
mp,ex,,2e5  
mp,nuxy,,0.3
n,1
n,61,6000   
fill
type,1  
real,1  
e,1,2   
egen,60,1,1,61,1
FINISH
/solu   
d,1,ux,0,0,,,uy
d,61,uy,0  
fcum,repl,

*do,i,0,100000,10
*set,Nforce,1000+i
/solu
f,21,fy,-Nforce  
f,41,fy,Nforce
solve   
FINISH  
/post1   
etable,mises,nmisc,1
esort,etab,mises,0,1,
*get,smax,sort,,max,

*if,abs(smax-160),le,0.1,:b  !合乎条件，跳转到b
*enddo
:b
finish

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方法三：采用优化方法求解(解：56.847KN)
!p200_5.lgw文件
/prep7  
*set,Nforce,1000
et,1,3  
r,1,355780,2370e4,200   
mp,ex,,2e5  
mp,nuxy,,0.3
n,1
n,61,6000   
fill
type,1  
real,1  
e,1,2   
egen,60,1,1,61,1
FINISH  
/solu   
d,1,ux,0,0,,,uy
d,61,uy,0   
f,21,fy,-Nforce  
f,41,fy,Nforce
solve   
FINISH  
/post1   
etable,mises,nmisc,1
esort,etab,mises,0,1,
*get,smax,sort,,max,
*set,var_obj,abs(smax-160)

!opt.db
/input,p200_5,lgw   
FINISH  
/opt
opanl,p200_5,lgw
opvar,Nforce,dv,0,100000,1  
opvar,smax,sv,159.9,160.1,0.01  
opvar,var_obj,obj   
optype,subp
opexe   
oplist,all,,1   
save