搜索ANSYS中PSTRES和SSTIF區(qū)別
2016-09-16 by:CAE仿真在線 來(lái)源:互聯(lián)網(wǎng)
從預(yù)應(yīng)力大變形模態(tài)分析到 PSTRES 和 SSTIF 的辨異
一,前言:
在ANSYS中有兩個(gè)命令可以將預(yù)應(yīng)力效應(yīng)激活并考慮在求解方程計(jì)算中,但是他們是有區(qū)別,最近在論壇上出現(xiàn)很多的帖子討論預(yù)應(yīng)力大變形模態(tài)分析,但是好象大家對(duì)以上兩個(gè)命令出現(xiàn)一定程度的混淆,本文結(jié)合例子對(duì)以上兩個(gè)命令及相關(guān)問(wèn)題做以闡釋。不妥之處,歡迎高手批評(píng)指正
二,例子簡(jiǎn)單介紹:
借用網(wǎng)友的例子進(jìn)行說(shuō)明,下面簡(jiǎn)單介紹以下我們分析的問(wèn)題。
實(shí)際的問(wèn)題是兩根拉索,通過(guò)圓鋼管聯(lián)系在一起成以下平面形狀,拉索中通過(guò)施加應(yīng)變yingbian=3.51e-3考慮索中的預(yù)應(yīng)力。本文將對(duì)以下結(jié)構(gòu)進(jìn)行靜力求解和模態(tài)求解。
三,靜力求解結(jié)果分析:
本文采用以下四種不同的求解方式進(jìn)行求解,并對(duì)結(jié)果進(jìn)行分析:
SOLUTION 1 小變形求解,不激活以上兩個(gè)命令,使用以下命令流:
Nlgeom,off
Sstif,off
Pstres,off
Solv
SOLUTION 2-1 小變形求解,激活Pstres命令,使用以下命令流:
Nlgeom,off
Pstres,on
solv
SOLUTION 2-2 大變形求解,激活Pstres命令,使用以下命令流:
Nlgeom,on
Pstres,on
solv
SOLUTION 2-2 大變形求解,激活SSTIF,on命令,使用以下命令流:
Nlgeom,on
Sstif,on
solv
經(jīng)過(guò)求解分別得到以下計(jì)算結(jié)果:以UX變形為例
結(jié)論:通過(guò)以上結(jié)果可見(jiàn),PSTRES,ON 是不適合用于大變形分析,因?yàn)樵撁畈粫?huì)激活△U的附加剛度矩陣。
四,命令辨析:
為從根本上闡明以上問(wèn)題,我們先從兩個(gè)命令的說(shuō)明上進(jìn)行對(duì)比,區(qū)分其中的不同之處。
4-1PSTRES 命令
PSTRES, Key
Specifies whether *1pstress effects are calculated or included.
注1,Pstres主要為激活預(yù)應(yīng)力效應(yīng),注意和SSTIF使用目的的區(qū)別
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*2within the first load step.
注2,Pstres只在第一個(gè)荷載步中有效,注意命令的生存時(shí)間
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 (*3rather than a PSTRES,ON command) in the static analysis.
注3:如果在靜力分析和瞬態(tài)分析(用于預(yù)應(yīng)力大變形模態(tài)分析)中計(jì)算預(yù)應(yīng)力效應(yīng),則應(yīng)該指定ssitf命令而不是pstres命令
4-2 SSTIF 命令
SSTIF, Key
Activates*1 stress stiffness effects in a nonlinear analysis.
注1,Ssfif主要為非線性分析中激活應(yīng)力剛度效應(yīng),注意和SSTIF使用目的的區(qū)別
Notes
Activates stress stiffness effects in a nonlinear analysis (ANTYPE,STATIC or
TRANS). (*2The PSTRES command also controls the generation of the stress stiffness matrix and therefore should not be used in conjunction with SSTIF.)
注2,Pstres命令同樣控制應(yīng)力剛度矩陣,因此不能和sstif連用。
If used in SOLUTION, *3this command is valid only within the first load step.
注3,該命令同樣僅在第一荷載步內(nèi)有效。
When SOLCONTROL and NLGEOM are ON, SSTIF defaults to ON. *4 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,當(dāng)激活SOLCONTROL或NLGEOM,ON時(shí),sstif默認(rèn)被激活,一般來(lái)講會(huì)形成一致切線剛度矩陣,然而對(duì)于一些特殊的非線性情況,會(huì)因?yàn)橐恍﹩卧?特別是18X系列以外的單元)不能提供一致切線剛度矩陣而導(dǎo)致不收斂。此時(shí)ANSYS要求SSTIF,off以獲得收斂
*5The 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,該命令默認(rèn)激活SOLCONTROL,ON,命令
附注:SOLCONTROL,為是否選擇默認(rèn)的非線性求解設(shè)定值和內(nèi)部的增強(qiáng)收斂的解法
SOLCONTROL, Key1, Key2, Key3, Vtol
Key1à為是否激活一系列默認(rèn)的非線性求解的命令
SSTIF Key ON for geometrically nonlinear analysis (NLGEOM, ON). OFF
其關(guān)于SSTIF的默認(rèn)是在執(zhí)行大變形非線性分析的時(shí)候起用sstif,on
4-3 簡(jiǎn)單對(duì)比
從4-1~2可見(jiàn):
1 SSTIF,on在大變形非線性分析中同樣具備激活預(yù)應(yīng)力效應(yīng)的功能,
2 PSTRES,不能應(yīng)用于大變形非線性分析(僅僅是開(kāi)關(guān)功能的不同)
3如果先后激活以上兩個(gè)命令,結(jié)果是后一個(gè)命令直接取代前一個(gè)命令
五,大變形模態(tài)分析:
對(duì)于大變形模態(tài)分析推薦使用以下標(biāo)準(zhǔn)命令流進(jìn)行求解,本命令流較其他命令流對(duì)于大變形模態(tài)分析具有廣泛的適用性。
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!大變形非線性求解
finish
/solu
antype,static
nlgeom,on !打開(kāi)大變形求解器
sstif,on !激活應(yīng)力剛度效應(yīng)
time,1
kbc,0
nsubst,1,1,1
ematwrite,yes
solve
!!!!!!!!!!!! Modal Solution
finish
/solu
antype,modal
upcoord,1,on !對(duì)變形后的結(jié)構(gòu)重新計(jì)算
pstres,on !激活預(yù)應(yīng)力對(duì)模態(tài)求解的效應(yīng),模態(tài)求解為線性求解
modopt,lanb,50,0,0, !采用LANB求50個(gè)特征值,有四種方法可以選用
mxpand,50,,,yes, !擴(kuò)展50個(gè)模態(tài)
psolve,triang !切線剛度求解
psolve,eiglanb !注意方法和的modopt,lanb,對(duì)應(yīng)性
finish
/solu
expass,on !!擴(kuò)展模態(tài)求解答
psolve,eigexp
二,例子簡(jiǎn)單介紹:
借用網(wǎng)友的例子進(jìn)行說(shuō)明,下面簡(jiǎn)單介紹以下我們分析的問(wèn)題。
實(shí)際的問(wèn)題是兩根拉索,通過(guò)圓鋼管聯(lián)系在一起成以下平面形狀,拉索中通過(guò)施加應(yīng)變yingbian=3.51e-3考慮索中的預(yù)應(yīng)力。本文將對(duì)以下結(jié)構(gòu)進(jìn)行靜力求解和模態(tài)求解。
三,靜力求解結(jié)果分析:
本文采用以下四種不同的求解方式進(jìn)行求解,并對(duì)結(jié)果進(jìn)行分析:
SOLUTION 1 小變形求解,不激活以上兩個(gè)命令,使用以下命令流:
Nlgeom,off
Sstif,off
Pstres,off
Solv
SOLUTION 2-1 小變形求解,激活Pstres命令,使用以下命令流:
Nlgeom,off
Pstres,on
solv
SOLUTION 2-2 大變形求解,激活Pstres命令,使用以下命令流:
Nlgeom,on
Pstres,on
solv
SOLUTION 2-2 大變形求解,激活SSTIF,on命令,使用以下命令流:
Nlgeom,on
Sstif,on
solv
經(jīng)過(guò)求解分別得到以下計(jì)算結(jié)果:以UX變形為例
結(jié)論:通過(guò)以上結(jié)果可見(jiàn),PSTRES,ON 是不適合用于大變形分析,因?yàn)樵撁畈粫?huì)激活△U的附加剛度矩陣。
四,命令辨析:
為從根本上闡明以上問(wèn)題,我們先從兩個(gè)命令的說(shuō)明上進(jìn)行對(duì)比,區(qū)分其中的不同之處。
4-1PSTRES 命令
PSTRES, Key
Specifies whether *1pstress effects are calculated or included.
注1,Pstres主要為激活預(yù)應(yīng)力效應(yīng),注意和SSTIF使用目的的區(qū)別
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*2within the first load step.
注2,Pstres只在第一個(gè)荷載步中有效,注意命令的生存時(shí)間
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 (*3rather than a PSTRES,ON command) in the static analysis.
注3:如果在靜力分析和瞬態(tài)分析(用于預(yù)應(yīng)力大變形模態(tài)分析)中計(jì)算預(yù)應(yīng)力效應(yīng),則應(yīng)該指定ssitf命令而不是pstres命令
4-2 SSTIF 命令
SSTIF, Key
Activates*1 stress stiffness effects in a nonlinear analysis.
注1,Ssfif主要為非線性分析中激活應(yīng)力剛度效應(yīng),注意和SSTIF使用目的的區(qū)別
Notes
Activates stress stiffness effects in a nonlinear analysis (ANTYPE,STATIC or
TRANS). (*2The PSTRES command also controls the generation of the stress stiffness matrix and therefore should not be used in conjunction with SSTIF.)
注2,Pstres命令同樣控制應(yīng)力剛度矩陣,因此不能和sstif連用。
If used in SOLUTION, *3this command is valid only within the first load step.
注3,該命令同樣僅在第一荷載步內(nèi)有效。
When SOLCONTROL and NLGEOM are ON, SSTIF defaults to ON. *4 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,當(dāng)激活SOLCONTROL或NLGEOM,ON時(shí),sstif默認(rèn)被激活,一般來(lái)講會(huì)形成一致切線剛度矩陣,然而對(duì)于一些特殊的非線性情況,會(huì)因?yàn)橐恍﹩卧?特別是18X系列以外的單元)不能提供一致切線剛度矩陣而導(dǎo)致不收斂。此時(shí)ANSYS要求SSTIF,off以獲得收斂
*5The 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,該命令默認(rèn)激活SOLCONTROL,ON,命令
附注:SOLCONTROL,為是否選擇默認(rèn)的非線性求解設(shè)定值和內(nèi)部的增強(qiáng)收斂的解法
SOLCONTROL, Key1, Key2, Key3, Vtol
Key1à為是否激活一系列默認(rèn)的非線性求解的命令
SSTIF Key ON for geometrically nonlinear analysis (NLGEOM, ON). OFF
其關(guān)于SSTIF的默認(rèn)是在執(zhí)行大變形非線性分析的時(shí)候起用sstif,on
4-3 簡(jiǎn)單對(duì)比
從4-1~2可見(jiàn):
1 SSTIF,on在大變形非線性分析中同樣具備激活預(yù)應(yīng)力效應(yīng)的功能,
2 PSTRES,不能應(yīng)用于大變形非線性分析(僅僅是開(kāi)關(guān)功能的不同)
3如果先后激活以上兩個(gè)命令,結(jié)果是后一個(gè)命令直接取代前一個(gè)命令
五,大變形模態(tài)分析:
對(duì)于大變形模態(tài)分析推薦使用以下標(biāo)準(zhǔn)命令流進(jìn)行求解,本命令流較其他命令流對(duì)于大變形模態(tài)分析具有廣泛的適用性。
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!大變形非線性求解
finish
/solu
antype,static
nlgeom,on !打開(kāi)大變形求解器
sstif,on !激活應(yīng)力剛度效應(yīng)
time,1
kbc,0
nsubst,1,1,1
ematwrite,yes
solve
!!!!!!!!!!!! Modal Solution
finish
/solu
antype,modal
upcoord,1,on !對(duì)變形后的結(jié)構(gòu)重新計(jì)算
pstres,on !激活預(yù)應(yīng)力對(duì)模態(tài)求解的效應(yīng),模態(tài)求解為線性求解
modopt,lanb,50,0,0, !采用LANB求50個(gè)特征值,有四種方法可以選用
mxpand,50,,,yes, !擴(kuò)展50個(gè)模態(tài)
psolve,triang !切線剛度求解
psolve,eiglanb !注意方法和的modopt,lanb,對(duì)應(yīng)性
finish
/solu
expass,on !!擴(kuò)展模態(tài)求解答
psolve,eigexp
finish
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