Sonlu Eleman Deplasman Yönteminin (şasi-karoseri Hesapları Üzerine) Bilgisayar Uygulaması

Abstract

Bu çalışmada sonlu elemanlar yönteminin(Fe-Metodu) şasi-karoseri hesaplarında kullanılmasını incelemiştir. Bu amaçla sınırlı kapasitede çalışan bir bilgisayar programı ele alınmış ve kapasitesi arttırılarak yeniden yazılmıştır. Böylelikle program gerçeğe uygun modeller çözebilir hale getirilmiştir. Yeni programımızda çözülebilecek yapıları ifade ve veri hazırlama şeklini göstermek amacıyla bir midibüs karoseri modeli ve bir kamyon şasi modeli çözdürülmüştür. Yeni program Visual Basic programlama dilinde yazılmıştır. Verileri ve sonuçlar Excel ortamı kullanılarak değerlendirilmiştir. Böylece veri girişindeki hatalar azaltılmış, sonuçları görmek ve değerlendirmek ve gerekirse değişiklikler yapmak ve bunları tablo veya grafik halinde kolayca ifade etmek mümkün hale gelmiştir.

In real design cases, generally structural systems are composed of a large assemblage of various structural elements such as beams, plates, and shells or a combination of the three. Their overall geometry becomes extremely complex and cannot be represented by a single mathematical expression. In addition, these built-up structures are intrinsically characterised as having material and structural discontinuities such as cutout, thickness variations of members etc., well as discontinuities in loading and support conditions. Given these factors, relative to the structure geometry and discontinuities, it becomes apparent that the classical methods can no longer be used, particularly those whose prerequisites are the formulation and the solution of governing differential equations. Thus, for complex structures, the analyst has to resort to more general methods of analysis where the above factors place no difficulty in their application. These methods are the finite element stiffness method and the finite element flexibility method. With the advent of high speed, large-storage-capacity digital computers, the finite element matrix methods have become one of the most widely used tools in formulations of a simultaneous set of linear algebraic equations relating forces to corresponding displacements (stiffness method) or displacements to corresponding (flexibility method) at discrete, preselected points on the structure. These methods offer many advantages: 1. Capability for complete automation 2. The structure geometry can be described easily 3. The real structure can be represented easily by a mathematical model composed of various structural elements. 4. Ability to treat anisotropic material. 5. Ability to treat discontinuities. 6. Ability to implement residual stresses, prestress conditions, and thermal loadings. 7. Ability to treat nonlinear structural problems. viii 8. Ease of handling multiple load conditions. The finite element matrix methods have gained great prominence throughout the industries owing to their unlimited applications in the solution of practical design problems of high complexity. The basic concept of the finite element matrix method in structural analysis is that the real structure can be represented by an equivalent mathematical model which consists of a discrete number of finite structural elements. The structural behaviour of each these elements may be described by different sets of functions which normally are chosen such that continuity of stresses and/or strains throughout the structure is ensured. The types of elements which are commonly used in structural idealisation are the truss, beam, two-dimensional membrane, shell and plate bending, and three dimensional solid elements. The mathematical relationships which govern the structural behaviour of an element are derived on the basis of an idealised element model. For example, once the element shape is selected, it is discretized by placing a finite number of nodes at various locations on the element surface. Generally speaking, the accuracy increases with an increase in nodal points considered on the element. Likewise, the smaller the element size, the more accurate the analytical results become for a given structural system. Note that the core storage requirement increases rapidly with an increase in the number of element nodes and the number of elements considered in a structure. In the first chapter, the concept of the design of automotive vechiles is explained as well. The headlines of the process are these:. conventional improvement duration. computer aided improvement duration. Errors in FE-method a) Principle errors b) Geometric errors c) Errors due to the material d) Errors due to the boundary conditions In the second chapter the analysis of FE-method is explained:. Coordinate system IX . Forces, displacements and their sign convention. Stiffness method concept. Formulation procedures for element structural relation ships. Element stiffness matrices. From element to system formulations. Special finite elements and global stiffness matrices for each In the third chapter, geometric models of a midibus are drawn and truck chassis data are prepared for the program. A list of the program and the solution of the models are given in the appendix. The program capacity is enlarged from an other program. The old program is in Basics and the new one is in Visual Basics. The old program is in DOS and the new one is in Excel under Windows 95 system though it can solve greater problems in less time. Note that the program solves only beam element which is a special finite element (Figure 1) Figure 1. Beam Element