【正文】 and solids can be created by connecting, rotating or translating the existing surfaces. Points, lines and curves, surfaces and solids can be translated, rotated or reflected to form new ones.Graphic interfaces are often used to help in the creation and manipulation of the geometrical objects. There are numerous Computer Aided Design (CAD) software packages used for engineering design which can produce files containing the geometry of the designed engineering system. These files can usually be read in by modelling software packages, which can significantly save time when creating the geometry of the models. However, in many cases, plex objects read directly from a CAD file may need to be modified and simplified before performing meshing or discretization. It may be worth mentioning that there are CAD packages which incorporate modelling and simulation packages, and these are useful for the rapid prototyping of new products.Knowledge, experience and engineering judgment are very important in modelling the geometry of a system. In many cases, finely detailed geometrical features play only an aesthetic role, and have negligible effects on the performance of the engineering system. These features can be deleted, ignored or simplified, though this may not be true in some cases, where a fine geometrical change can give rise to a significant difference in the simulation results.An example of having sufficient knowledge and engineering judgment is in the simplification required by the mathematical modelling. For example, a plate has three dimensions geometrically. The plate in the plate theory of mechanics is represented mathematically only in two dimensions (the reason for this will be elaborated in Chapter 2). Therefore, the geometry of a ‘mechanics’ plate is a twodimensional flat surface. Plate elements will be used in meshing these surfaces. A similar situation can be found in shells. A physical beam has also three dimensions. The beam in the beam theory of mechanics is represented mathematically only in one dimension, therefore the geometry of a ‘mechanics’ beam is a onedimensional straight line. Beam elements have to be used to mesh the lines in models. This is also true for truss structures. MeshingMeshing is performed to discretize the geometry created into small pieces called elements or cells. Why do we discretize? The rational behind this can be explained in a very straightforward and logical manner. We can expect the solution for an engineering problem to be very plex, and varies in a way that is very unpredictable using functions across the whole domain of the problem. If the problem domain can be divided (meshed) into small elements or cells using a set of grids or nodes, the solution within an element can be approximated very easily using simple functions such as polynomials. The solutions for all of the elements thus form the solution for the whole problem domain.How does it work? Proper theories are needed for discretizing the governing differential equations based on the discretized domains. The theories used are different from problem to problem, and will be covered in detail later in this book for various types of problems. But before that, we need to generate a mesh for the problem domain.Mesh generation is a very important task of the preprocess. It can be a very time consuming task to the analyst, and usually an experienced analyst will produce a more credible mesh for a plex problem. The domain has to be meshed properly into elements of specific shapes such as triangles and quadrilaterals. Information, such as element connectivity, must be created during the meshing for use later in the formation of the FEM equations. It is ideal to have an entirely automated mesh generator, but unfortunately this is currently not available in the market. A semiautomatic preprocessor is available for most mercial application software packages. There are also packages designed mainly for meshing. Such packages can generate files of a mesh, which can be read by other modelling and simulation packages.Triangulation is the most flexible and wellestablished way in which to create meshes with triangular elements. It can be made almost fully automated for twodimensional (2D) planes, and even threedimensional (3D) spaces. Therefore, it is monly available in most of the preprocessors. The additional advantage of using triangles is the flexibility of modelling plex geometry and its boundaries. The disadvantage is that the accuracy of the simulation results based on triangular elements is often lower than that obtained using quadrilateral elements. Quadrilateral element meshes, however, are more difficulty to generate in an automated manner. Some examples of meshes are given in Figures –. Property of Material or MediumMany engineering systems consist of more than one material. Property of materials can be defined either for a group of elements or each individual element, if needed. For different phenomena to be simulated, different sets of material properties are required. For example, Young’s modulus and shear modulus are required for the stress analysis of solids and structures, whereas the thermal conductivity coefficient will be required for a thermal analysis. Inputting of a material’s properties into a preprocessor is usually straightforward。 YING Fuqiang Design of 60 MN main hydraulic cylinder of squeezing casting based on finite element analysis[J]. Journal of Mechanical amp。感謝陳志浩老師和幫助我的同學(xué)們。正是因?yàn)橛辛四銈兊闹С趾凸膭?lì)。致 謝本文是在導(dǎo)師陳志浩老師的悉心指導(dǎo)下完成的，在整個(gè)設(shè)計(jì)過程中，陳老師非常認(rèn)真負(fù)責(zé)、專業(yè)經(jīng)驗(yàn)豐富，正確解答同學(xué)的提問，使我受益匪淺，在此表示謝意！經(jīng)過半年的忙碌和工作，本次畢業(yè)設(shè)計(jì)已經(jīng)接近尾聲，由于經(jīng)驗(yàn)的匱乏，難免有許多考慮不周全的地方，如果沒有指導(dǎo)老師的督促指導(dǎo)，以及一起工作的同學(xué)們的支持，想要完成這個(gè)設(shè)計(jì)是難以想象的。而且CAE技術(shù)也在向著集成化、網(wǎng)絡(luò)化、標(biāo)準(zhǔn)化、專業(yè)化、開放化、虛擬化和智能化發(fā)展。CAE在當(dāng)前已經(jīng)在各個(gè)運(yùn)用得非常廣泛，隨著計(jì)算機(jī)技術(shù)的不斷完善，CAE技術(shù)已經(jīng)變得勢(shì)不可擋。我們可以通過改變澆注位置、增加冷鐵氣孔等方式，對(duì)工藝進(jìn)行改善。可鍛鑄鐵件的冒口通常采用側(cè)冒口，如圖42圖42 冒口D=(3～5)TH=(～)D結(jié)論和展望本次設(shè)計(jì)是對(duì)大學(xué)四年學(xué)習(xí)的總結(jié)和運(yùn)用，本次對(duì)管狀三通件鑄造