外文翻譯--有限元分析軟件的發(fā)展

1、<p><b>　　中文3240字 </b></p><p>　　Steps in Finite Element Analysis</p><p>　　Introduction</p><p>　　Recently there is a trend towards using it in the early stages of des

2、ign. A designer may use FEA just to validate the structural integrity of a design or she may use it for structural optimization along with the parametrized design techniques.This paper examines the requirements of a stru

3、ctural analysis agent and proposes an architecture to facilitate FEA in a concurrent design environment. The next section briefly describes how FEA is used in a typical industrial set up.Section 3 presents a sur</p>

4、;<p>　　Steps in Finite Element Analysis</p><p>　　The process of FEA starts with identification of the region of interest and the formulation of the physical problem。[1]. The region of interest might b

5、e an assembly, a component or a portion of a component (or an assembly). The interaction of the rest of the assembly and the environmental conditions with the region of interest is captured in two ways. One way to repres

6、ent this interaction is to idealize them as loads and displacement constraints on the region of interest. For example a spot weld</p><p>　　Analysts often draw a Free Body Diagram of the region of interest to

7、 clarify its interaction with the rest of the assembly and to gain more insight into its structural behavior.Required components and assemblies are then retrieved from the Solid Modeling system into the finite element pa

8、ckage.In recent years a number of commercial systems have started offering both: FEA and Solid Modeling capabilities.</p><p>　　In this case, the data exchange may occur between two modules of the same packag

9、e.The original design geometry is sometimes too complicated for the purpose of analysis. The analyst may choose to simplify it so that it is easier to mesh and incurs less computational cost.This task of simplifying the

10、design geometry is referred to as Global Idealization.Global Idealization may involve deletion/modification of some of the geometric features. The analyst may choose to take advantage of the symmetry </p><p>

11、;　　The next step in the modeling process is selection of type of elements and their material properties. Based on this decision, the user discretizes the idealized geometry into finite elements. This step is commonly ref

12、erred to as Mesh Generation.Traditionally the loads and boundary conditions are applied to the nodes and the element boundaries. In the proposed system they are applied to the geometry. Finally, he user has to select the

13、 type of analysis (static, modal,etc.) and the solution method </p><p>　　The raw answers computed by the finite element solver have to be processed further. This includes calculation of derived quantities (s

14、uch as stress and strain values), computing error estimates, creating創(chuàng)建 graphical displays showing deformed shapes , stress contour plots, etc. All these tasks are collectively referred to as post-processing. Based on th

15、e post-processing results the user may modify the model at any stage of idealization (including the original design itself)and start the loop once</p><p>　　An overview of the analysis process is shown in Fig

16、ure 1.</p><p>　　Figure 1 Steps in Finite Element Analysis</p><p>　　Development of Finite Element Tools</p><p>　　Due to the obvious pay-offs associated with speeding up of the analys

17、is process, there is almost an explosion of both research and commercial systems supporting FEA. The development of FEA tools has followed a path very similar to the development of Design Automation tools. The early soft

18、ware supporting FEA was primarily meant to automate tasks in the detailed analysis stage, namely Mesh Generation and Post-Processing. A survey of earlier work in automatic mesh generation methods can be found in</p>

19、;<p>　　The raw FE data is usually too difficult to interpret due to its large volume.Post-Processing tools aid visualization and facilitate easier interpretation of the data. Post-processing features provided by t

20、oday’s commercial packages include display of deformed shapes; calculation of useful engineering quantities such as Von Mises Stress, principal stresses, etc.; contour and shaded plotsshowing distributionf numerical para

21、meters over the analysis domain.</p><p>　　The emergence of Expert Systems technology saw the development of a new generation of FEA tools. The researchers became interested in applying Expert Systems techniq

22、ues to automate early stages of the finite element modeling process. These systems try to capture the experiential and often subjective knowledge used by expert analysts and act as “modeling assistant” to a novice user.

23、Fenves [8] suggested a framework for developing a knowledgebased system to assist FE analysis. Bennett et al. [9] d</p><p>　　Today’s commercial systems have incorporated most of the research in Mesh Generati

24、on and Post Processing. Also,the trend is towards developing integrated Computer Aided Engineering (CAE) packages which offer a range of facilities (solid modeling, drafting, analysis, etc.). This has greatly helped to e

25、ase the transition from a Solid Model of a design to its finite element model.</p><p>　　Issues in Developing a Finite Element Analysis Agent</p><p>　　An FEA agent must surely support all the FE

26、activities described in Section 2. But we prefer to use a commercial package for Mesh Generation and Post-Processing because today’s FE packages are fairly sophisticated in these areas and it seems pointless to duplicate

27、 this work. On the other hand, commercial codes are not suitable for合 the Model Preparation tasks in any specific domain and the proposed FEA agent is intended to fill this gap. As a result, the following discussion prim

28、arily focuses on</p><p>　　1Exchanging Finite Element Modeling Information</p><p>　　The FEA agent should facilitate exchange of an FE modeling problem at different levels of descriptions. A very

29、high level description would consist of the sketch of the part to be analyzed with a verbal description of the operating conditions and the analysis requirements. Another form of description may consist of a B-Rep of the

30、 part with a descriptionof the boundary conditions with reference to the B-rep entities of the part. An ontology for describing assemblies, components, boundary conditio</p><p>　　2Representation of a Finite

31、Element Model</p><p>　　A representation of an FE modeling problem would have to include the following information:</p><p>　　1. Geometry</p><p>　　2. Boundary Conditions</p>&l

32、t;p>　　3. Material Properties</p><p>　　4. Geometric Properties</p><p>　　5. Type of Analysis</p><p>　　6. Accuracy Desired</p><p>　　The geometry should be maintained at

33、 different levels of FE idealizations. This would require the use of a non-manifold geometric modeler since FE models are often composed of elements of different dimensionality (e.g. a model may consist of plates and bea

34、ms). The geometric description also needs to be maintained in the b-rep form since all of the mesh generators require it in this form.</p><p>　　Traditionally, the boundary conditions are applied to model aft

35、er it has been meshed even though the analyst knows what they are in the beginning and uses this knowledge in creating an appropriate FE mesh for the object. The Design Representation System (DRS) that we have developed

36、allows us to prescribe boundary conditions along with the geometry and attachthem to the b-rep of the FE model.</p><p>　　In practice, the FE problem seldom involves a single mechanical component, therefore i

37、t is desirable to maintain a symbolic representation of the assemblies and connections. The representation of connections can also be used to automatically derive the boundary conditions due to the interaction of mating

38、components.</p><p>　　3Geometry Editing</p><p>　　An analyst often wants to delete/modify certain geometric features of the model to simplify analysis procedure. This has been referred to as Globa

39、l Idealization.Therefore the FE agent should provide feature-editing facility and quickly compute the b-rep of the resulting object. Certain higher level commands that convert one FE model into another should be provided

40、 (E.g. building a 2-D model by extracting the radial cross section of an axi-symmetric model).Geometric properties such as feature vol</p><p>　　4 Interface with Commercial Finite Element Packages</p>

41、<p>　　The proposed agent would use a commercial code for Mesh Generation, Analysis and Post-Processing. </p><p>　　Therefore, the interface with this package may not be limited to just IGES or STEP files

42、. The FEA agent must incorporate the knowledge needed for the effective use of the chosen FE package. This knowledge can then be used to write “program files” that will direct the above mentionedactivities in the FE code

43、.</p><p>　　5Knowledge-based Assistance</p><p>　　The FE modeling decisions are primarily based on the two factors: shape of the components being analyzed and the boundary conditions. Since the ge

44、ometry is maintained in terms of it’s boundary representation, the b-rep informationcan be used to infer about the shape attributes of the component. DRS also allows the user to attach boundary conditions to the b-rep en

45、tities (vertex, edge, face) in the geometric model, therefore the system has an integrated representation of the geometry and the boun</p><p>　　Architecture of the Proposed FEA Agent</p><p>　　A

46、schematic of the proposed architecture is shown in Figure 2. The Central Representation Module will be implemented in CLIPS. It will maintain all the aspects of a FE model listed in Section 4.2. The Geometry Kernel will

47、be provided by the non-manifold geometric modeler called NOODLES. The graphics display programs will be written using TK/TCL interface builder. I-DEAS will be used for Mesh Generation, Analysis and Post-Processing. The K

48、nowledge-based Module will be written using CLIPS rules an</p><p>　　Figure 2 Schematic Diagram of the Proposed FEA Agent (Arrows indicate information flow.)</p><p>　　Concluding Remarks</p>

49、<p>　　The implementation of the proposed agent will be CLIPS/C/TK/TCL based.Some of the features described in the earlier section have been previously implemented in Lisp. </p><p>　　These are as follo

50、ws:</p><p>　　? Data structures for attaching boundary conditions to b-rep entities</p><p>　　? Simple shape recognition and b-rep updating</p><p>　　? Calculation of inertial properti

51、es such as volumes, centroids, moments of inertia, etc. from the solid b-reps</p><p>　　? Creation of I-DEAS program files for modal analysis of beam models</p><p>　　有限元分析軟件的發(fā)展</p><p&g

52、t;<b>　　介紹</b></p><p>　　最近有一種將有限元分析用在設(shè)計早期的趨勢。設(shè)計人員可以使用有限元分析軟件來設(shè)計和驗證結(jié)構(gòu)的完整性或者優(yōu)化參數(shù)設(shè)計技術(shù)。本文討論了對結(jié)構(gòu)分析媒介的要求，并且提供了一個在給定的設(shè)計環(huán)境下的有限單元分析的優(yōu)化體系結(jié)構(gòu)。下一節(jié)將簡要介紹有限單元是怎樣被用在典型工業(yè)的生產(chǎn)上的。第3節(jié)介紹了現(xiàn)有的有限元工具的調(diào)查。第4節(jié)討論了一些涉及到有限元分析的發(fā)展問

53、題。第4節(jié)發(fā)現(xiàn)的詳細(xì)問題是有限元分析的起因，筆者在第5節(jié)對其提出了一個結(jié)構(gòu)體系并在在第6節(jié)做出了總結(jié)。</p><p><b>　　有限元分析的發(fā)展</b></p><p>　　有限元是伴隨確認(rèn)重要部位和對物理學(xué)問題的構(gòu)想進(jìn)行的。[1] 重要的區(qū)域可能是一個配件、元件或者是元件的一部分。一個靜止配件的配合和重要部件的環(huán)境條件是捕獲的兩種途徑。一種代表配合的方法是用理想

54、化的負(fù)載和位移做為重要部位的系統(tǒng)規(guī)定參數(shù)。例如，把一個元件用焊接的方法固定在一個更大的部件上將導(dǎo)致這個點(diǎn)上所有的自由度受到約束。另一種常用的方法是使用彈簧或者間隙元素。</p><p>　　分析師們通常繪制一個重要部分的自由體受力圖來闡述它與靜止元件的配合并以此獲得更多的有關(guān)結(jié)構(gòu)性能的數(shù)據(jù)。然后從有限元程序的實體造型中檢索所需的部件和組件。近年來，一些商業(yè)系統(tǒng)開始提供兩種軟件：實體建模和有限元分析。</p&

55、gt;<p>　　在這種情況下，數(shù)據(jù)交換可能會出現(xiàn)兩個不相同的模塊。以前用于幾何分析的設(shè)計有時過于復(fù)雜。分析師們將其簡化后減少了設(shè)計的成本。這種簡化的幾何設(shè)計被稱為整體理想化。整體理想化可能涉及幾何特征的一些修改。分析師可能會選擇利用對稱度和分析模型的一部分。如果是軸對稱的，他們會將三維問題減少為二維問題來分析。如果分析師打算做一個幾何限制，首先他們可以選擇從草稿軟件包里導(dǎo)入一個幾何軟件包，然后再從軟件分析包里進(jìn)行修改。理

56、想化的特征元素是由整體理想化對象的有限元延伸產(chǎn)生的。原來的三維幾何結(jié)構(gòu)可轉(zhuǎn)化為一維的集合，二維和三維實體取決于對各種不同幾何部件的描述比如：梁，殼\板材，固體元素。理想化特征元素的確定是基于兩個因素：形狀對象和邊界條件。</p><p>　　下一步的建模過程，是選擇元素的類型和他們的物理屬性。根據(jù)這些，用戶就可以用有限元分析離散化那些理想化的幾何形狀。這一步通常稱為Mesh Generation。網(wǎng)格時代傳統(tǒng)上，

57、負(fù)載和邊界的條件，被用于節(jié)點(diǎn)和元素的界限。在所推薦的系統(tǒng)里他們被用于幾何圖形上。最后，他們選擇了分析的種類和解決辦法并為有限元模型做好了分析的準(zhǔn)備。</p><p>　　未經(jīng)處理的原始答案必須用有限元做進(jìn)一步的處理。類似于派生數(shù)量的計算（例如應(yīng)力和應(yīng)變），計算機(jī)運(yùn)算的錯誤估計，創(chuàng)建圖形顯示的外形形變，應(yīng)力、外形、平面圖等等。所有這些任務(wù)都統(tǒng)稱為后處理。基于后處理結(jié)果，用戶可以修改的任何理想化階段（包括原設(shè)計本身的

58、模型），并進(jìn)入下一個階段。分析過程的一個概述如圖1所示。</p><p>　　圖1.有限元分析步驟</p><p><b>　　有限元工具的發(fā)展</b></p><p>　　由于分析過程有顯著地提高，所以不管是科研領(lǐng)域或商業(yè)領(lǐng)域有限元分析軟件的誕生都是近乎于爆炸式的創(chuàng)新。有限元分析工具的發(fā)展遵循著與自動化設(shè)計工具發(fā)展類似的路徑。早期的軟件也支持

59、有限元分析，其主要目的是為了在詳細(xì)分析階段的進(jìn)行自動化任務(wù)，即Mesh Generation 和Post-Processing.一項有關(guān)于自動化網(wǎng)絡(luò)生產(chǎn)自動生成網(wǎng)格辦法的調(diào)查可以從參考資料[2]和[3]找到。此前網(wǎng)狀震蕩發(fā)生器可以在不考慮解決精確網(wǎng)格計算的情況下進(jìn)行對一束離散幾何模型的分析。自動適應(yīng)網(wǎng)格劃分方法提高了網(wǎng)狀震蕩發(fā)生器的可靠性。用在測試網(wǎng)上的方法使用了幾個離散化錯誤估計中的一個，并通過精簡確定區(qū)域或增加秩序元素來改善網(wǎng)格質(zhì)量

60、。</p><p>　　由于它的容量非常大，正常的原始數(shù)據(jù)是很難說明問題的。Post-Processing工具可以使其形象化，并讓解釋原始數(shù)據(jù)變的更容易。如今的商業(yè)軟件包提供的Post-processing的功能包括形變顯示，所需工程量計算，例如馮米塞斯應(yīng)力，主應(yīng)力，外形和輪廓在分析中都將由數(shù)字和參數(shù)來表示。</p><p>　　科技專用系統(tǒng)的出現(xiàn)使有限元分析工具得到發(fā)展。在自動化技術(shù)進(jìn)行

61、有限元模型分析的早期階段，研究人員開始對專用系統(tǒng)的應(yīng)用感興趣。對一個初學(xué)者來說系統(tǒng)將根據(jù)經(jīng)驗和主觀的知識來進(jìn)行模型分析。為了協(xié)助有限元分析的發(fā)展參考資料[8]里提出了一個知識系統(tǒng)框架。參考資料[9]中被稱為SACON的基礎(chǔ)規(guī)則系統(tǒng)的發(fā)展，推薦初學(xué)用戶使用MARC。</p><p>　　如今很多商業(yè)綜合系統(tǒng)被用在了網(wǎng)格生成和后期處理上。此外，分析軟件發(fā)展的趨勢是向著能提供一系列設(shè)施（例如 實體建模，制圖，分析等）的

62、整體計算機(jī)輔助工程的方向發(fā)展的。這非常有利于從實體建模到有限元建模的過度。</p><p><b>　　有限元發(fā)展的因素</b></p><p>　　第2節(jié)描述了，有限元軟件的發(fā)展必須能夠支持所有的有限元應(yīng)用。由于現(xiàn)在有限元軟件包相當(dāng)復(fù)雜，好多都是在重復(fù)沒有意義的工作，所以我們寧愿選擇使用商業(yè)化的軟件包如Mesh Generation and Post-Process

63、ing。從一方面來說，商業(yè)軟件卻不適合明確領(lǐng)域的模型制作任務(wù)，所以有限元發(fā)展的動力是為了填補(bǔ)軟件能力的不足空缺。因此，以下的討論主要集中在有限元分析軟件的模型制作工作上。</p><p>　　1有限元建模信息交流 </p><p>　　有限元軟件應(yīng)該對有限元建模與不同軟件之間的交流起到促進(jìn)作用。一個高水品的軟件應(yīng)該由草圖分析、操作環(huán)境的文字?jǐn)⑹龊头治鰲l件構(gòu)成。另一種是由臨界條件的邊界表示和

64、實體邊界表示組成。一個實體軟件的組成、部件和邊界條件等等，必須為數(shù)據(jù)交換提供正規(guī)的語言。軟件應(yīng)該具有生成和讀取IGES和STEP文件的能力。它們都具有處理和構(gòu)建幾何實體并且能夠表示邊界條件的能力。同時STEP還需要有實體交換的能力。</p><p><b>　　2有限單元的描述</b></p><p>　　有限單元的描述必須包括以下信息：</p><

65、;p><b>　　1?幾何形狀；</b></p><p><b>　　2?邊界條件；</b></p><p><b>　　3?材料性能；</b></p><p><b>　　4?幾何性質(zhì)；</b></p><p><b>　　5?類型分析；

66、</b></p><p><b>　　6?精度的期望。</b></p><p>　　幾何形狀應(yīng)該被保存在理想化的有限元中。這就要求非流形幾何模型時有限元要由不同維度的基礎(chǔ)組成。幾何描述總是被保存在網(wǎng)格線組成的邊界表示中。</p><p>　　傳統(tǒng)上，邊界條件被網(wǎng)狀化后就可以用于建模，分析師知道有限元分析的原始思想并將這些知識用在為物

67、體生成合適的有限元網(wǎng)格上。The Design Representation System (DRS)允許我們指定邊界環(huán)境和幾何形狀并注重有限元模型的邊界表示。</p><p>　　實踐中，有限元涉及的大都不是單一的機(jī)械元件，因此最好是使用裝配和連接符號來表示。由于連接部件之間互相作用，連接表示也能用在自動獲得邊界條件上。</p><p><b>　　3幾何圖形編輯</b&

68、gt;</p><p>　　分析師們通常會刪除或修改模型的某些已知幾何形狀來簡化分析過程。這被稱為整體理想化。因此有限元分析軟件應(yīng)該提供針對實體的專題編輯功能和快速計算邊界表示。確定的高級指令可以將一種有限元模型轉(zhuǎn)變?yōu)榱硪环N模型（比如二維模型和一維模型）。幾何性質(zhì)中的特征量和質(zhì)量中心等數(shù)據(jù)應(yīng)該自動計算。對有限元實體直接的添加和刪除例如梁和板材等，在結(jié)構(gòu)設(shè)計上應(yīng)該盡可能快的分析。</p><p&

69、gt;　　4商業(yè)有限元軟件的界面</p><p>　　建議對Mesh Generation，Analysis and Post-Processing 使用商業(yè)指令。這個軟件包的界面可能不僅僅局限于IGES或者STEP。有限元軟件用到到的軟件包里必須包括設(shè)計時所需的知識。這種知識必須能被寫入程序文件并能夠用來描述有限元軟件程序的指令。</p><p><b>　　5基礎(chǔ)知識幫助&l

70、t;/b></p><p>　　有限元的建模主要基于兩個因素：所分析的組成部件形狀和邊界條件。如果幾何圖形被保存在邊界表示項里，邊界表示信息就能被用于推斷元件的形狀屬性。DRS也允許用戶添加幾何模型的邊界條件（頂點(diǎn)，邊，面），此系統(tǒng)能夠繼承幾何條件和邊界條件的功能。這個功能至少能幫助用戶篩選選擇項目。舉例來說，如果沒有幾何軸對稱，軟件就不會顯示2維圖形。開發(fā)利用幾何圖形和邊界條件的具體資料可以進(jìn)一步發(fā)展知識

71、基礎(chǔ)。對新用戶來說這個功能可以提供專業(yè)的意見。</p><p>　　對有限元分析軟件結(jié)構(gòu)體系的建議</p><p>　　作者提出的結(jié)構(gòu)示意圖如圖2。中央模塊代表剪編輯命令。</p><p>　　這將保存在4.2節(jié)列出的有限元模塊中。被稱為NOODLES的非流形幾何模塊可以提供幾何圖形核心。圖形顯示程序?qū)⒈粚懭隩K/TCL界面。I - DEAS軟件將用于生成網(wǎng)格，分析

72、和后處理。知識基礎(chǔ)模塊將被寫入CLIPS的規(guī)則和標(biāo)準(zhǔn)中。 模塊界面可以讀寫IGES和STEP文件，寫I-DEAS程序文件并能夠用EIT軟件進(jìn)行軟件交流。</p><p>　　圖2 有限元分析軟件結(jié)構(gòu)示意圖 </p><p><b>　　結(jié)束語</b></p><p>　　以CLIPSC/TK/TCL為基礎(chǔ)的成就。早期發(fā)現(xiàn)的一些特征是不成熟的。&

73、lt;/p><p><b>　　具體如下：</b></p><p>　　?數(shù)據(jù)結(jié)構(gòu)的邊界條件附加到邊界表示上。</p><p>　　?簡單的形狀識別和邊界表示的更新。</p><p>　　?常用屬性的計算，如容量，質(zhì)量中心，轉(zhuǎn)動慣量等屬于邊界表示。</p><p>　　?為梁模型建模生成I-DEAS程