abaqusexplicit接觸問(wèn)題

1、1. Abaqus/Explicit中的接觸形式雙擊Interactions,出現(xiàn)接觸形式定義。分為通用接觸(General contact )、面面接觸(Surface-to-Surface contact )和自接觸(Self-contact )。1 .通用接觸 General contact通用接觸用于為多組件，并具有復(fù)雜拓?fù)潢P(guān)系的模型建模。General contact algorithm? The contact domain spans multiple bodies (both rigid and deformable)? Default domain is defined el

2、ement-based surfaceautomatically via an all-inclusive? The method is geared toward models with multiple components and complex topology 。? Greater ease in defining contact model2. Surface-to-Surface contactContact pair algorithm? Requires user-specified pairing of individual surfaces? Often results

3、in more efficient analyses since contact surfaces are limited in scope3. 自接觸(Self-contact )自接觸應(yīng)用于當(dāng)部件發(fā)生變形時(shí)，可能導(dǎo)致自己的某兩個(gè)或多個(gè)面發(fā)生接觸 的情況。如彈簧的壓縮變形，橡膠條的壓縮。?容易使用？ “自動(dòng)接觸”？節(jié)省生成模型的時(shí)間？通用接觸算法一般 比雙面接觸算法快機(jī)械約束形式?運(yùn)動(dòng)依從 Kinematic contact method（只有接觸對(duì)形式可用,General contact 不可用）默認(rèn)的運(yùn)動(dòng)接觸公式達(dá)到的計(jì)算精度與接觸條件相一致。在多數(shù)情況下，它 工作得很好。但是在某些情況

4、下，如抖動(dòng)接觸，使用罰函數(shù)接觸會(huì)更容易得到收斂的解。不能為剛體-剛體接觸建模。? 罰函數(shù)（通用接觸和接觸對(duì)均可使用）Penalty contact method罰函數(shù)接觸算法中接觸約束的嚴(yán)格性低于運(yùn)動(dòng)學(xué)算法。罰函數(shù)算法可以處理更一般類(lèi)型的接觸；比如，剛體之間的接觸。因?yàn)榱P函數(shù)算法在模型中引入附加剛度，該附加剛度將影響穩(wěn)定時(shí)間增量。Abaqus/Explicit自動(dòng)計(jì)算由與接觸力相關(guān)的侵徹距離引入的“彈簧”剛度 或“罰”剛度。但是必須考慮相關(guān)的影響：應(yīng)該盡量減少對(duì)穩(wěn)定時(shí)間增量的影響。 在所有的分析中，允許的侵徹不可以太大。?對(duì)于接觸對(duì)算法：通過(guò)在*CONTACT CONTR砒S指定SCALE P

5、ENAL修數(shù)，用戶(hù)可以縮放默 認(rèn)的罰剛度。?對(duì)于通用接觸算法：可以使用 *CONTACT CONTROLS ASSIGNMENT, TYPE=SCALE PEJNALTB 罰剛度。綜上，多數(shù)情況下，運(yùn)動(dòng)依從算法和罰函數(shù)算法將得到幾乎一致的結(jié)果。然而，在某些情況下，一種方法可能比另一種方法更可取。如果需要知道 kinematic algorithms 和 penalty algorithms 之間的 區(qū)別，那就需要啃理論教材了 （當(dāng)然看abaqus幫助文件也可以）.簡(jiǎn)略的說(shuō)：1） penalty algorithms（罰函數(shù)法）在被abaqus檢測(cè)到接觸距離以?xún)?nèi)的節(jié)點(diǎn)之間定義罰剛度，進(jìn)而來(lái)迭代出

6、接 觸力。在每一個(gè)時(shí)間步先檢查各從節(jié)點(diǎn)是否穿透主面。如沒(méi)有穿透則進(jìn)入下一個(gè)時(shí) 間步；如果穿透，則在該從節(jié)點(diǎn)與被穿透主面問(wèn)定義罰剛度， 引入一個(gè)較大的界 面接觸力，其大小與穿透深度、主面的剛度成正比。2） kinematic algorithms先在一定時(shí)間內(nèi)檢查所有未與主面（master surface） 接觸的從節(jié)點(diǎn)（slavenode）,看是否在此時(shí)間內(nèi)穿透了主面。如果存在穿透則縮小時(shí)間步，使那些穿 透主面的從節(jié)點(diǎn)都不貫穿主面，而使其正好到達(dá)主面。在計(jì)算下一時(shí)間步之前， 對(duì)所有已經(jīng)與主面接觸的從節(jié)點(diǎn)都施加約束條件，以保持從節(jié)點(diǎn)與主面接觸而不 貫穿。此外還應(yīng)檢查那些和主面接觸的從節(jié)點(diǎn)所屬單元

7、是否受到拉應(yīng)力作用。如受到拉應(yīng)力，則施加釋放條件，使從節(jié)點(diǎn)脫離主面。就abaqus接觸計(jì)算的初級(jí)使用來(lái)說(shuō)，如果接觸對(duì)中有剛體，一般用penalty algorithms ;如果接觸對(duì)是彈性體，有限選 Kinematic algorithms. 無(wú)剛體的 接觸，建議直接用Kinematic algorithms 試算?？偨Y(jié):1）接觸面存在剛體，用penalty算法2）接觸面之間的相對(duì)運(yùn)動(dòng)方向平行于接觸面，用 penalty算法3）彈性碰撞分析不可用 hard-kinematic 算法。碰撞之中塑性變形控制的 接觸分析4） penalty算法一般會(huì)減小穩(wěn)定時(shí)間增量5）接觸計(jì)算與以下情況耦合時(shí)推薦

8、penalty算法：constraint equation, multi-point constraint, tie constraint, embeddedelement constraint, or kinematic constraint6) breakable bond model 模擬， 必須用 hard kinematic contact碰撞應(yīng)該用罰函數(shù)法吧，要是用運(yùn)動(dòng)學(xué)算法時(shí)需要?jiǎng)澐州^細(xì)的網(wǎng)格以避免能 量的丟失。kinematic contact要求更嚴(yán)格，不允許出現(xiàn)穿透，而 penalty contact 允許。默認(rèn)的Penalty stiffness 為彈性剛度的10%所以如

9、果是解決塑性變形問(wèn) 題的話，二者算出來(lái)的結(jié)果相差不大。penalty對(duì)切向的相對(duì)位移的接觸比較有效。3.初始運(yùn)動(dòng)學(xué)依從關(guān)系A(chǔ)baqus/Explicit不允許接觸表面的初始過(guò)盈。?接觸表面的節(jié)點(diǎn)將被調(diào)整，刪除分析之前的初始過(guò)盈：?只移動(dòng)接觸表面的節(jié)點(diǎn)。?對(duì)于分析過(guò)程第一個(gè)分析步定義的接觸對(duì)，由于調(diào)整表面引起的位移不 產(chǎn)生初始應(yīng)變或應(yīng)力。?在隨后的分析步中：?對(duì)于接觸對(duì)算法，調(diào)整將產(chǎn)生應(yīng)變。?對(duì)于通用接觸算法，忽略初始過(guò)盈。Contact Formulations接觸程式，包括1. Contact discretization 接觸離散化Where is the constraint appli

10、ed 接觸約束應(yīng)用在哪? Node-to-surface? Surface-to-surface2. Constraint enforcement執(zhí)行接觸How is the constraint enforced接觸約束怎么執(zhí)行? Default (Explicit )? Direct (Lagrange multipliers) Standard? Penalty method Standard? Augmented Lagrange (Lagrange multipliers combined with penalty method) Standard3. Contact trackin

11、g (relative sliding)跟蹤接觸How does the constraint evolve接觸約束怎么發(fā)展? Finite sliding? Small slidingContact DiscretizationNode-to-surface technique:節(jié)點(diǎn)和面接觸? Default method for contact pairs 。接觸對(duì)的默認(rèn)接觸定義方法。? Not available for general contact 。不適用于 General contact 。? Nodes on one surface (the slave surface) co

12、ntact the segments on the other surface(the master surface).從面上的節(jié)點(diǎn)接觸主面的面。? Contact is enforced at discrete points (slave nodes)。在從面節(jié)點(diǎn)處執(zhí)行接觸。從面需要?jiǎng)澐州^細(xì)的單元來(lái)提高精度和消除應(yīng)力振動(dòng)即消除應(yīng)力噪聲。Useof a“matched mesh" across the contact interface will eliminate thissolution noise 。Surface-to-surface technique :面面接觸? Onl

13、y method for general contact , Alternative method for contact pairs? The method considers the shape of both the master and slave surfaces.? Contact is enforced in an average sense over the slave surface.當(dāng)面面接觸用于接觸對(duì)時(shí)，contact pairs 和 general contact 和性能表現(xiàn)erformance。Node-to-SurfaceSlave surfaceMaster su

14、rface區(qū)別不大，主要的區(qū)別在于使用方便性Surface-to-SurfaceSlave surfaceMaster surface可以看出Node-to-Surface參與接觸節(jié)點(diǎn)個(gè)數(shù)較少。而 S-to-S較多The contact pressure contours are much smoother and the peak contact stress is in very close agreement with the analytical solution using the surface-to-surface approach.Analytical CPRESS - 3.0

15、1 e+05Node-to-surfaceSurface-to-surfaceFinite-Sliding Contact FormulationsFeaturesSurface-To-SurfaceNode-To-SurfaceGnntact stresses接觸應(yīng)力More accurate if surface re pres eolation is adequateLess accurate with mismatched meshesShell find membrane 由ickn的總殼和膜的犀度ConsjderedConsidered only for small sliding

16、internal "smoothing" of the master surface主面的內(nèi)部干荒Not requiredRequired for finite sliding Smoothing is aho performed for the anctior point calculation in small sliding.Exlens ion zore for master surface1玉面.延伸Nat requiredRequired 1or finite slidingSome penetration may be observed at individu

17、al nodes; however. largeH undotectod penetralions of masier nodes into 由日 slave surface do rot occur對(duì)于面面接觸，個(gè)別點(diǎn)小的穿透可能會(huì)出現(xiàn)，但是不會(huì)發(fā)生漏檢測(cè)到的主面Finite-Sliding Contact FormulationsFeaturesSurface-ToSu rfaceN ode-To *Su rfaceMemory requirement and solver cost內(nèi)存消耗和求解獨(dú)享GeneraHy requires increased memory and soluti

18、on time (particularly if the master surface is more refined than the slave).Default constraint enkrcement默認(rèn)機(jī)行”P(pán)enalty method束Direct methodRobustness 穩(wěn)定畦iU嶼r Minimizes snagging anti adds stability at the fudges and corners.Contact EnforcementEdi十 Cont act Propertyffame： contactMechanical Them alHarm

19、al or"H打C antaeConstr-aint enforcement method： Defaultv Alltw s七par'tion wEtet fontsDefaultAufmtntad La.口 m晤* 6 tlmdurd)Penalty Standard)Direc tHard contact:In Abaqus/Standard, the default contact behavior is “hard” contact .The behavior is described by a contact property known as the press

20、ure-penetration curve (alternative behavior can be specified; discussed later).h<0No pressure.p. contact pressureAny pi1白ssuro> possible when IncontactNa penetration;m constraint requiredConstraint enforcedpositive contact pressureht ponctrationPhysically "hard0 pressure vs. penetration b

21、ehaviorThe desired behavior (no penetration) is achieved using an enforcement method.理想的沒(méi)有穿透的接觸行為可以用三種強(qiáng)化方法來(lái)獲得。Three numerical methods are available in Abaqus/Standard to achieve or approximate “hard” contact conditions:Direct enforcement method:Strict enforcement of pressure-penetration relationship

22、 using theLagrange multiplier method.嚴(yán)格壓力-穿透關(guān)系，用拉格朗日乘法算法。Pros and cons of direct enforcement : 優(yōu)缺點(diǎn)Advantages: Accuracy constraint is satisfied exactly.Disadvantages:Adds to equation solver cost.求解代價(jià)高Additional variable per contact constraint, which enlarges the system of equations to be solved.Restr

23、icts elimination order for sparse solver, which can degrade performance.Potential convergence difficulties.潛在的收斂問(wèn)題。Abrupt change from zero contact stiffness (while contact is inactive) to infinite contact stiffness (while contact is active).從 0 岡U度至U無(wú)窮剛度變化的劇烈。Difficulties with overconstraints.Overla

24、p between contact constraints and MPC ' s, etc.用罰剛度近似Penalty method:Approximate enforcement using penalty stiffness.The penalty method is a stiff approximation of hard contactNo pressureh. penetrationSiricdy-enforced hard contactl contact pressureAr>y pressure” possible when in contactPenalty

25、 method approximation of hard conlacl罰剛度可以是:Linear (default):線性Easier convergence.容易收斂? Better suited for problemsinvolving firm contact.較適用于硬面接觸。? Difficult to choose stiffness appropriate for all regimes.難以選擇剛度值適用于所有情況。Nonlinear:非線性? The lower initial stiffness makes it better suited for problems

26、involving chattering.初始的小剛度值適合于解決包括顫振的接觸。? The higher final stiffness helps reduce penetrations.高的最終剛度降低穿透? Convergence overall can be more difficult.收斂較困難。Default penalty stiffness :默認(rèn)的剛度值? Abaqus折中選擇剛度：剛度小，過(guò)度穿透。剛度大， 收斂速度；Lagrange multiplier DOF are needed to avoid ill-conditioning.? The default pe

27、nalty stiffness is based on a representative stiffness of the underlying elements.A scale factor is applied to this representative stiffness to set thedefault penalty stiffness; its magnitude is higher in Abaqus/Standard than in Abaqus/Explicit.默認(rèn)剛度不合適，可以設(shè)置比例系數(shù)調(diào)節(jié)。? Order-of-magnitude changes are rec

28、ommended. 推薦? If the scale factor > 100, Abaqus will automatically invoke avariant of the method that uses Lagrange multipliers to avoid ill-conditioning issues. 如果 比例系 數(shù)大于100,自動(dòng)采用Lagrange multipliers 來(lái)避免病態(tài)。罰剛度值：? Stiff or blocky problems :硬的或短而結(jié)實(shí)的接觸。默認(rèn)剛度值產(chǎn)生結(jié)果：比的上 direct method的精確度。Requires lessm

29、emory and CPU time。? Bending-dominated problems :彎曲占主導(dǎo)地位的接觸：默認(rèn)剛度值會(huì)被縮減但是不顯著影響精確度。Scale back two orders of magnitude without any significant loss of accuracy.Scaling back the penalty stiffness for bending-dominated problemsO縮減剛度值還或sometimes dramatically increases the convergence rate許會(huì)提高收斂率。 Example:

30、Hertz contact1.5% differenceHertz conUct resultsPenetrationStressDirect Lagrange:Penalty (default:4.482E-6Penalty (Sf = 0.01):2492 EY1.201 E6.334E4 J47% difference可以看出對(duì)于Hertz接觸，默認(rèn)的罰剛度值和Direct Lagrange結(jié)果最接近。Advantages:Significantly improved convergence ratesBetter equation solver performance. NoLagra

31、nge multiplier DOFunless contact stiffness is very high.Good treatment of overlapping constraints.Disadvantages:Small amount of penetration. Typically insignificantMay need to adjust the penalty stiffness in some casesUsed by default for each of the following: General contact、Contactpairs with the f

32、inite-sliding, surface-to-surface formulation 。Automatic contact pair detection capability in Abaqus/CAE。Augmented Lagrange method:Approximate enforcement using penalty method with augmentation iterations; not discussed further here.Used by default for: 3D self contact with node-to-surface discretiz

33、ationDirect enforcement (Lagrange (multiplier method)Penalty methodAdvantagesDisadvantagesAdvantagedDisadvantages-Exact constraint enforcemenl (no penetration) l.agrange multipliers add to equation soever cos'* Sensitive to chatl麗ng (convergencfi problems Difficult to treat Improved convergence

34、due tn numerical softening No Lagrange multipl鼎 decjrefls of freedorri* Avoid a nvefconstrHint iscuvs Some penetratiewn exists (smAll) Need to adjust penalty stiffness in some casespt contact pressureDirect enforcemenlNo pressureSome numerical “softening" with penalty or augmented Lagrange enfo

35、rcement h、penetrationContact tracking (relative sliding)Finite slidingKinematically, finite sliding of deformable bodies against each other allows the most general relative motion between the bodies:? Arbitrarily large sliding is allowed.? Arbitrarily large rotations and deformations of the surfaces areallowed.?任意大的滑動(dòng)和轉(zhuǎn)動(dòng)都允許。接觸對(duì)和通用接觸中均可以使用Small slidingSmall sliding assumesthat the relative motion per