Abaqus接觸分析中出現(xiàn)收斂困難時的常用檢查方法(共4頁)

1、1、ABAQUS接觸分析的收斂問題常用檢查方法 來源 百度空間 接觸分析收斂不管怎么總還是一個很大的問題，而我們經(jīng)常在一個地方卡了很長的時間，怎么也找不到解決和提高的辦法。而aba_aba在abaqus常見問題匯總中給了我們模型改進(jìn)的方向和一些方法。在我分析的過程當(dāng)中，怎么找到模型中的影響收斂的關(guān)鍵問題所在也是一個很讓我迷茫了很長時間。下面談一下我個人的一些經(jīng)驗(yàn)和看法。如有錯誤還望大家指出，也希望大家給出自己更多的經(jīng)驗(yàn)分享。abaqus的隱式求解的就是求算出一個很大的剛度矩陣的解，這個方程能否通過一次一次的迭代到最后達(dá)到一個系統(tǒng)默認(rèn)的收斂準(zhǔn)則標(biāo)準(zhǔn)的范圍之內(nèi)，就決定了這一次計算能否收斂。因此要收

2、斂的話，系統(tǒng)與上一個分析步的邊界條件區(qū)別越小的話，系統(tǒng)就越容易找到收斂解。針對這一點(diǎn)，我們可以得到下面的幾種方法來盡可能的使系統(tǒng)的方程的解盡可能的接近上一步，以達(dá)到收斂。下面的方法的指導(dǎo)思想是：盡可能小的模型，前后兩個分析步的改變盡可能的少。1. 接觸分析真正加載之前，設(shè)置一個接觸步讓兩個面接觸上來，在這個步驟里面，接觸面的過盈小一點(diǎn)好，比如0.001.接下去再把作用與兩個接觸體的力及接觸方向的自由度放開。2. 如果系統(tǒng)的載荷很多的話，將系統(tǒng)的載荷分做多步進(jìn)行加載，一次性全上可能使系統(tǒng)無法在規(guī)定的迭代次數(shù)內(nèi)收斂。所以根據(jù)需要分開，讓abaqus的內(nèi)核慢慢消化去。少吃多餐在這邊好像也是成立的。3

3、. 系統(tǒng)有多個接觸的話，也最好如載荷一樣，分成幾個step讓他們接觸上。這樣的做法會讓你以后在模型的修改中更有方向性。4. 模型還是不收斂的話，你可以看一下是在哪一步或者那個inc不收斂。對于第一步直接不收斂的話，如果模型是像我上面把載荷和接觸分成很多步建立的話，可以把載荷加載的順序換一下。如果你把第二個加載的載荷換到第一步以后，計算收斂了，那影響收斂的主要問題應(yīng)該就是原來第一個加載或著接觸影響的。這種情況下面一般算到這個加載的時候還是不會收斂。這個時候可以考慮是否有什么其他辦法能夠使步驟的變化與上一步變動小一點(diǎn)，比如第一點(diǎn)里面提到，或者繼續(xù)把這個載荷細(xì)分呢？5. 對于接觸分析不收斂的情況，可

4、以自己看一下模型的接觸面。有時候是overclosure,這個時候在assemble里面將模型相對位置稍微移動下或者用接觸里面的那個adjust only to remove overclose,不過或一種方法會使你的網(wǎng)格扭曲變形。問題不大也是可以用的。有的時候是因?yàn)椋Ｐ椭械膬蓚€接觸面變成了一個點(diǎn)和一個面接觸，而點(diǎn)或者面中有一個位置并不是很穩(wěn)定。這個時候就會出現(xiàn)了dividing,有時候求解無法成功。這時候可以看一下是不是能夠?qū)⒛Ｐ驮撎幧晕⒏囊幌履兀炕蛘邔⒃撎幍木W(wǎng)格細(xì)化一下。6. 模型實(shí)在是比較大的話，可以修改solver的設(shè)定，將迭代次數(shù)改大一點(diǎn)。對于開始計算就不收斂的，而在迭代次數(shù)到了以

5、后時間增量還不是很小的話，可以將initial和minimum改小一點(diǎn)。模型越大的話這邊可以改的越小，特別是前后兩個step變化比較大的情況下。但對于模型不是很大的情況下，太小的時間增量是意義不大的，問題應(yīng)該從模型當(dāng)中是否有錯誤去考慮。7. 模型太大的話會導(dǎo)致求解的方程太大，不需要的不重要的接觸最好從模型當(dāng)中去除。這樣的話對結(jié)果影響也不會很大，而且可以是計算時間大大的減少。8. 對于收斂準(zhǔn)則的修改還是很不推薦的，應(yīng)作為下下策使用。不上一些這里面關(guān)系到的一些abaqus出錯信息，方便那些正在如自己當(dāng)初郁悶中的人更好的找到這篇文章。大家如果有什么不太清楚的也可以留言，有時間探討一下。*NOTE:

6、THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY.求解出現(xiàn)分歧，一般是狀態(tài)不穩(wěn)定，如你的某一個物體的自由度忘了約束或著分析到了一種極限狀態(tài)之類的，解決方案見上。*ERROR: TIME INCREMENT REQUIRED IS LESS THAN THE MINIMUM SPECIFIED步長比最小步長小，方案見上。*NOTE: SEVERE CONTACT OVERCLOSURES EXIST. CONVERGENCE IS JUDGED UNLIKELY.接觸出現(xiàn)問題，用visulazation的to

7、ol的job diagnostics查看，針對那個接觸進(jìn)行修改。把距離稍微改大一點(diǎn)點(diǎn)，應(yīng)該是很有幫助的。如果是計算中出現(xiàn)問題的話，應(yīng)該是你前后兩個step設(shè)置的有問題。 2、接觸分析中出現(xiàn)收斂困難時的常用檢查方法 來源Simwe仿真論壇Hint for obtaining a converged contact solution in Abaqus/Standard 2011/05/25/ q b1 F& G- Q9 oRequest detailed output of the contact state: Abaqus/CAE: Step Module: Output Diagnostic

8、 Print . Contact- o- U9 8 E, V E G& x& m+ e Contact state information will be written in the message (.msg) file. You should also write the necessary contact output variables to the data (.dat) and the output database (.odb) files frequently enough so that you can diagnose the problem.Consider the f

9、ollowing items:; D G% P: 1 d/ q5 x% F! M S% r 1. Check that the contact surfaces are properly defined, and correct any errors. The surfaces can be viewed in Abaqus/Viewer. If the surface has been created in the input file by automatically using the free surface of an element set, check whether the T

10、RIM parameter should have been used.0 R% f m7 A: v2 , E/ b H/ H4 j3 N) l2 x, r: l 2. Check the contact direction defined for each surface. The normals to a surface can be viewed in Abaqus/Viewer. If the normal directions are wrong, frequently you will get large overclosures that may lead to converge

11、nce difficulties.6 y3 j* H8 K6 d/ E5 ( s/ 1 f( F z8 q n2 t 3. Frictional contact problems are generally more difficult to solve than frictionless contact problems. Try solving the problem without friction to see if the difficulty is due to friction or if it is due to something else. If the difficult

12、y is indeed due to friction, consider the following:4 Z1 E1 o r2 ( X a.Reexamine the choice of the friction coefficientlarger coefficients of friction are generally more difficult to use.( i) d R7 q N$ b b.Examine the allowable elastic slip (low values can cause convergence problems, although too hi

13、gh a value can give physically incorrect solutions).& H$ e7 B* D- _/ C% j b4 L c.Refine the mesh so that more points come into contact at the same time. 8 / V U& B2 g9 f E0 M: K d.Use immediate onset of friction if only a few points are coming into in contact at the same time and slipping occurs. In

14、 Versions 6.1 and higher this is the default behavior. In earlier versions you can use*CONTACT CONTROLS, FRICTION ONSET=IMMEDIATE4. Rough friction with intermittent contact generally gives convergence problems. If appropriate for the analysis, do not allow the contacting surfaces to separate after c

15、ontact is established:$ V6 ( j$ ? x5 M& F* ?& p o Abaqus/CAE: Interaction Module: Interaction Property Create Contact Mechanical Normal Behavior deselect Allow separation after contact Y* * V2 R6 t. so Keyword: *SURFACE BEHAVIOR, NO SEPARATION # B $ I+ S8 b8 y- G+ Z! m, c x& X0 9 J1 z6 b5. Three-dim

16、ensional finite-sliding contact with highly curved faceted master surfaces generates a highly nonsymmetric tangent stiffness matrix. Use the unsymmetric solver even if the coefficient of friction is less than 0.2.) H$ 9 & l& y; h4 M( S2 S; # C2 V9 J2 6. If you have sharp corners on the contact surfa

17、ces, the comments in 5 apply. In addition, try the following: 7 R6 V4 G0 U$ o: j7 , A4 P F.Smooth the surface. Nodes on the slave surface can be caught in folds in the master surface, causing convergence difficulties when the surrounding elements deform to take this into account. The elements making

18、 up the slave surface should be small enough to be able to resolve the geometry. A rough guideline is to use 10 elements around a 90 corner; you must use your judgment to decide if this is adequate or too fine. 3 z8 u0 B S5 y; D) M/ F) I a. If the physical problem has a sharp concave fold, use two s

19、eparate surface definitions.$ A4 s2 n4 L1 A O3 q) Z( j1 A b.Sharp convex folds cannot be modeled with a reasonable finite element mesh. Smooth the fold with a radius larger than the element size on the slave surfaces. A rough guideline is to use 10 elements around a 90 degree corner; obviously, you

20、must use your judgment to decide if this is adequate or too fine.7. Contact chattering, which is indicated by the contact state for a group of slave nodes cyclically changing from open to closed until the maximum number of severe discontinuity iterations is reached. Abaqus/Standard can automatically

21、 compute an overclosure tolerance and a separation pressure tolerance to prevent chattering: : s C R( : K _+ ( L o Abaqus/CAE: Interaction Module: Interaction Contact Controls Create. Automatic overclosure tolerances2 K! D5 k4 8 J3 h6 s o Keyword: *CONTACT CONTROLS, AUTOMATIC TOLERANCES ( O, n- s! H

22、3 o/ u G, t4 V/ D- * ! I$ Z. N t4 v# v( I ?+ o/ j% 8. If you get an error message in the message (.msg) file that HCRIT should be increased, check that it makes sense to do so; if it does make sense, increase the value for the relevant contact pair. The current value of HCRIT is printed to the data

23、(.dat) fileFor more information see:, T, ) R0 v3 p! O ?4 I+ ! |( $ 3 j: Q3 7 N) _& O Contact pressure-overclosure relationships; N0 e) v. j6 d% J8 n. , u. $ P. F o Section 32.1.2 of the Abaqus 6.9 Analysis Users Manual; Q# L# I+ R8 E1 k; g5 r o Section 33.1.2 of the Abaqus 6.10 Analysis Users Manual# H1 v% w* F$ c7 g1 ( Z6 t. l3 x: d8 G& 6 , O Frictional behavior7 s5 O4 N3 F& h6 5 B, R o Section 32.1.5 of the Abaqus 6.9 Analysis Users Manual$ y7 d- M* s6 o Sect