使用ANSYS建立模型經(jīng)驗和技巧

1、使用 Ansys軟件建模的經(jīng)驗與技巧1.始終注意保持使用一致的單位制；2 求解前運(yùn)行 allsel 命令求解前運(yùn)行 allsel 能會沒有傳到 nodes or elements 上去；3 網(wǎng)格劃分問題牢記建模與分網(wǎng)指南上有關(guān)建模的忠告。網(wǎng)格劃分影響模型是否可用，網(wǎng)格劃分影響計算結(jié)果的可接受程度；自適應(yīng)網(wǎng)格劃分(ADAPT)前必須查自適應(yīng)網(wǎng)格劃分可用單元，在 ansys 中能夠自適應(yīng)網(wǎng)格劃分的單元是有限的。網(wǎng)格劃分完成后，必須檢查網(wǎng)格質(zhì)量！權(quán)衡計算時間和計算精度的可接受程度，必要時應(yīng)該 refine網(wǎng)格4 實體建模布爾運(yùn)算應(yīng)用實體建模以及布爾運(yùn)算（加、減、貼、交）的優(yōu)勢解決建立復(fù)雜模型時的困難

2、；但是，沒有把握時布爾運(yùn)算將難以保證成功！5 計算結(jié)果的可信度一般來說，復(fù)雜有限元計算必須通過多人，多次，多種通用有限元軟件計算核對，互相檢驗，相互一致時有限元分析不是搞什么英雄主義，而需要多方面的質(zhì)量保證措施。6 了解最終所需要的成果建立模型之前，應(yīng)該充分了解最終要求提交什么樣式的成果，這樣能形成良好的網(wǎng)格，早期良好的建模規(guī)劃對于后期成果整理有很大的幫助；7 撰寫分析文檔文檔與分析過程力求保持同步，有利于小組成員之間的溝通和模型的檢驗和查證；8 熟悉命令對沒有把握的命令應(yīng)該先用簡單模型熟悉之，千萬不能抱有撞大運(yùn)的想法；9 多種單元共節(jié)點不同單元使用共同節(jié)點時注意不同單元節(jié)點自由度匹配問題導(dǎo)致

3、計算結(jié)果的正確與否(建模與分網(wǎng)指南P 8 ) 殼單元的轉(zhuǎn)動自由度的含義不一樣。殼的ROTZ不是真實的自由度,它與平面內(nèi)旋轉(zhuǎn)剛度相聯(lián)系，在局部坐標(biāo)中殼的單元剛度矩陣 ROTZ對應(yīng)的項為零，對此不能將梁與殼單元僅僅有一個節(jié)點相連，例外的是當(dāng) shell43 or shell63(兩者都有 keyopt(3)=2)的 Allman旋轉(zhuǎn)剛度被激活時。Solid65 單元和 shell63 shell63 單元的轉(zhuǎn)動自由度的節(jié)點唯一則不會傳到相連的 solid65 單元上。10 查找文獻(xiàn)資料確定混凝土的材料參數(shù)輸入（ Tb, concr, , , ）11 預(yù)測內(nèi)存和磁盤空間大型復(fù)雜模型（例如 10 萬個

4、節(jié)點，非線性問題，多工況問題，1000 步以上的瞬態(tài)分析等等）求解之前預(yù)測求解所需要的求解時間、內(nèi)存和磁盤空間，使分析盡在掌握之中；12 收斂問題題的建議；對于以下參數(shù)，可以試一試這些參數(shù)對收斂速度以及結(jié)果精度的影響neqit = 625?加載荷載步大小 = ？接觸單元的實常數(shù) = ？ 例如接觸剛度的大小取值必須權(quán)衡計算結(jié)果精度（穿透大小）和收斂問題（ 收斂時間 ）兩者的可接受程度，需要經(jīng)驗值或者試算；13 啟動重分析14 兩個相貫的薄壁圓筒建模，殼單元沒有公共節(jié)點Element Connectivity Error, 8-Node Curved Shell ElementsIn this i

5、mage, the red stiffener was intended to be welded to the purple pipe. Note that the elements of the redstiffener do not match up with those on the pipe. There is no connection, and the meshing was done independently.This is due to a geometric modeling error by the user (me). There are superimposed c

6、urved lines where theinterface is located. There should have been a shared line for the connection to have worked. I found this onlybecause of careful examination of the model - I had already run a stress analysis.What to do about these error concerns? Read and think. Share and listen to ideas and c

7、oncerns with others. Reviewyour own work, and the work of your co-workers. (Recently an experienced co-worker who does not even do FEAwork asked me if I had eliminated the added mass of water in pipes when evaluating shipping loads on a product. Ihadnt. Eliminating the added mass got rid of a high-s

8、tress problem. These errors are very easy to make.) Befriendly. Communicate with other departments. Have a check list and design reviews. Never use FEA blindly, orbelieve the results of an analysis without some critical review. Accept a critical review without taking it personally.Develop a good und

9、erstanding of the intent of the design codes that regulate your work. Consult an expert when itis appropriate. Pay attention to the ethics and standards of your professional association. Choose your employerwisely. (Some of these things you were supposed to have learned in Kindergarten, but life isn

10、t always that simple.)解決方法：通過 volumn 建模形成相貫線，該方法建模使面相交處共線，xmesh后有公共 nodes15 選擇集的應(yīng)用為了利用選擇集 cm / xsel 的強(qiáng)大功能，可以合理定義線，面的實常數(shù) real 屬性，為了選擇操作方便而賦予更多的單元實常數(shù)號，材料號18 UPGEOM 和 MPCHG 的應(yīng)用! UPGEOM更新幾何形狀!a.rst為計算結(jié)果文件名，最后一個為目錄這兩個參數(shù)應(yīng)根據(jù)你的計算情況定UPGEOM,1,LAST,LAST,NEW,rst,F:729! MPCHG彈性模量恢復(fù)為真值esel,s,mat,3mpchg,4,allYou m

11、ight be tempted to try to deactivate or reactivate elements by changing their material properties MPCHG ( Main MenuPreprocessorMaterial PropsChange Mat Num ).However, you must proceed cautiously if you attempt such a procedure. The safeguards and restrictions that affectkilled elements will not appl

12、y to elements that have their material properties changed in SOLUTION. (Elementforces will not be automatically zeroed out;nor will strains, mass, specific heat, etc.) Many problems could resultfrom careless use of MPCHG . For instance, if you reduce an elements stiffness to almost zero, but retain

13、its mass,it could result in a singularity if subjected to acceleration or inertial effects.One application of MPCHG would be in modeling construction sequences in which the strain history of a bornelement is maintained. Using MPCHG in such cases will enable you to capture the initial strain experien

14、ced byelements as they are fitted into the displaced nodal configuration19 Ansys 中的坐標(biāo)系統(tǒng)，使用各種坐標(biāo)系時應(yīng)該明白在各處理器中輸入輸出會受到那些坐標(biāo)系的影響整體和局部坐標(biāo)系 CSYS-用于定位幾何形狀參數(shù)的空間位置顯示坐標(biāo)系 DSYS-用于幾何形狀參數(shù)的列表和顯示節(jié)點坐標(biāo)系-定義節(jié)點自由度方向和節(jié)點結(jié)果數(shù)據(jù)的方法。輸入數(shù)據(jù)時受到節(jié)點坐標(biāo)系影響的有：約束自(從)自由度；在/POST26 中在節(jié)點坐標(biāo)系下輸出文件和顯示的數(shù)據(jù)結(jié)果有：自由度解，節(jié)點荷載，反作用荷載；Forces are defined in the

15、 nodal coordinate system. The positive directions of structural forces and moments arealong and about the positive nodal axis directions. The node and the degree of freedom label corresponding to theforce must be selected NSEL , DOFSEL .單元坐標(biāo)系-每個單元都有自己的坐標(biāo)系，單元坐標(biāo)系用于確定材料特性主軸，加面壓力和和單元結(jié)果數(shù)據(jù)（如應(yīng)力和應(yīng)變）的輸出方向；AN

16、SYS規(guī)定了單元坐標(biāo)系的缺省方向；許多單元都有 keyopts 可用于修改單元坐標(biāo)系的缺省方向；對于面和體單元而言，可以用 ESYS 命令將單元坐標(biāo)系的方向調(diào)整到已定義的局部坐標(biāo)系；結(jié)果坐標(biāo)系 RSYS-/POST1 /POST1中結(jié)果數(shù)據(jù)換算到結(jié)果坐標(biāo)系(RSYS)*GET, ACTSYS, ACTIVE,CSYS$ RSYS, ACTSYS使結(jié)果坐標(biāo)系與激活的坐標(biāo)系（用于定義路徑）相匹配求解坐標(biāo)系-PSD,CQC,SRSS RSYS,SOLU命令來避免在結(jié)果坐標(biāo)系中發(fā)生變換，使結(jié)果數(shù)據(jù)保持在求解坐標(biāo)系中。20 Ansys 5.7通過函數(shù)定義邊界條件 5.6中介紹的表格化邊界條件的擴(kuò)展功能。

17、用戶可以創(chuàng)建大量函數(shù)并存儲起來，以便于將來使用。5.6 的表格化邊界條件(Tabular boundary conditions)Tabular boundary conditions ( VALUE = % tabname %) are available only for structural (UX, UY , UZ, ROTX, ROTZ) and temperature degree of freedom (TEMP) labels and are valid only in static ( ANTYPE ,STATIC)and full transient ( ANTYPE ,TRANS) analyses.滯回曲線位移加載*DIM,dis,TABLE,9,1,TIME, ,DIS(1,0) = 0,1,2,3,4,5,6,7,8DIS(1,1) = 0,3,0,-3,0,4,0,-4,0D,22, , %DIS% , , , ,UZ, , , , ,ansys 5.6 help files- 2.6.3. Applying Loads Using TABLE Type Array Parame