命令 SSTIF 和 PSTRES 之区别辨析

ql84604253

有坛友问道 命令 SSTIF 和 PSTRES的区别，正好手上有这方面的研究资料。基本都帮助文件，如有纰漏请指正。

从两个命令的说明上进行对比，区分其中的不同之处。

PSTRES, Key
Specifies whether pstress effects are calculated or included.
注1，Pstres主要为激活预应力效应，注意和SSTIF使用目的的区别
Notes
Specifies whether or not prestress effects are to be calculated or included. Prestress effects are calculated in a static or transient analysis for inclusion in a buckling, modal, harmonic (Method = FULL or REDUC), transient (Method = REDUC), or substructure generation analysis. If used in SOLUTION, this command is valid only within the first load step.
注2，Pstres只在第一个荷载步中有效，注意命令的生存时间
If the prestress effects are to be calculated in a nonlinear static or transient analysis (for a prestressed modal analysis of a large-deflection solution), you can issue a SSTIF,ON command (rather than a PSTRES,ON command) in the static analysis.
注3：如果在静力分析和瞬态分析（用于预应力大变形模态分析）中计算预应力效应，则应该指定ssitf命令而不是pstres命令
PS:SSTIF 命令 PSTRES，ON 是不适合用于大变形分析，因为该命令不会激活△U的附加刚度矩阵。

SSTIF, Key
Activates stress stiffness effects in a nonlinear analysis.
注1，Ssfif主要为非线性分析中激活应力刚度效应，注意和SSTIF使用目的的区别
Notes
Activates stress stiffness effects in a nonlinear analysis (ANTYPE,STATIC or  
TRANS). (The PSTRES command also controls the generation of the stress stiffness matrix and therefore should not be used in conjunction with SSTIF.)  
注2，Pstres命令同样控制应力刚度矩阵，因此不能和sstif连用。
If used in SOLUTION, this command is valid only within the first load step.
注3，该命令同样仅在第一荷载步内有效。
When SOLCONTROL and NLGEOM are ON, SSTIF defaults to ON. This normally forms all of the consistent tangent matrix. However, for some special nonlinear cases, this can lead to divergence caused by some elements which do not provide a complete consistent tangent (notably, elements outside the 18x family). In such a case, ANSYS recommends issuing an SSTIF,OFF command to achieve convergence. For the 18x family of elements, setting SSTIF,OFF when NLGEOM is ON has no effect (because stress stiffness effects are always included).
注4，当激活SOLCONTROL或NLGEOM，ON时，sstif默认被激活，一般来讲会形成一致切线刚度矩阵，然而对于一些特殊的非线性情况，会因为一些单元（特别是18X系列以外的单元）不能提供一致切线刚度矩阵而导致不收敛。此时ANSYS要求SSTIF,off以获得收敛
The default values given for this command assume SOLCONTROL,ON (the default). See the description of SOLCONTROL for a complete listing of the defaults set by SOLCONTROL,ON and SOLCONTROL,OFF.
注5，该命令默认激活SOLCONTROL,ON,命令
附注:SOLCONTROL，为是否选择默认的非线性求解设定值和内部的增强收敛的解法
SOLCONTROL, Key1, Key2, Key3, Vtol
Key1为是否激活一系列默认的非线性求解的命令
SSTIF  Key  ON for geometrically nonlinear analysis (NLGEOM, ON).  OFF
其关于SSTIF的默认是在执行大变形非线性分析的时候起用sstif,on

总结：命令 SSTIF 和 PSTRES 本质上是一样的，都是考虑应力刚度的影响。但是用在不同的情况，PSTRES 主要用于线性分析，而 SSTIF 主要用于非线性分析。

犀利糊涂

太经典了，正在学习这方面，真是雪中送炭，建议加技术分

midasgalaxy

总结得不错

ql84604253

midasgalaxy版，过奖了

kevin210099

謝謝分享!學習了

523402750

经典讲解，值得收藏！！！