published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

published_or_final_version / abstract / toc / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

No description available.

To evaluate and test control systems designed for heavy duty hydraulic excava-tor, it is important to simulate the force acting on the bucket during its excavation process. The study of soil-tool interaction contributes to the prediction and simula-tion of resistive forces experienced at the tool during digging. Even though many different finite element (FE) models have been developed in the past to study soil-tool interaction process, there is still needs to study the effects of soil-tool friction coefficient. The main objective of this thesis is to utilize finite element model to simulate the soil-tool interaction process, with the focus on the application of excavation, to study the effects of soil-tool friction coefficient on soil failure zone, soil resistive force, and stress distribution on the cutting tool by utilizing finite element model to simulate the soil-tool interaction process. / October 2016

No description available.

Chan Kit Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 90-93). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Model Elliptic Boundary-Value Problems --- p.2 / Chapter 1.2 --- Applications of the Model Boundary-Value Problem --- p.4 / Chapter 1.2.1 --- Curl-Curl Formulation --- p.4 / Chapter 1.2.2 --- Vector Potential Formulation --- p.6 / Chapter 1.2.3 --- Darwin Model and Quasistatic Model --- p.7 / Chapter 1.3 --- Spurious Solutions --- p.8 / Chapter 2 --- Finite Element Formulation --- p.11 / Chapter 2.1 --- Preliminaries --- p.11 / Chapter 2.2 --- Weak Formulation --- p.14 / Chapter 2.2.1 --- Galerkin Method --- p.17 / Chapter 2.2.2 --- The Rayleigh-Ritz Method --- p.19 / Chapter 2.3 --- H1(Ω) Conforming Finite Element Method --- p.23 / Chapter 2.3.1 --- The Dirichlet Problem --- p.24 / Chapter 2.3.2 --- The Neumann Problem --- p.27 / Chapter 3 --- Numerical Implementations --- p.29 / Chapter 3.1 --- Introduction --- p.29 / Chapter 3.2 --- Implementation of Boundary Conditions --- p.32 / Chapter 3.3 --- Numerical Integration Formula --- p.39 / Chapter 3.4 --- Discrete L2-norms --- p.40 / Chapter 3.5 --- Solution of Linear System of Equations --- p.42 / Chapter 3.6 --- Automatic Mesh Generation --- p.43 / Chapter 3.6.1 --- The Cubic Domain Ω --- p.44 / Chapter 3.6.2 --- The Spherical Shell Domain Ωs --- p.44 / Chapter 4 --- Numerical Experiments --- p.50 / Chapter 4.1 --- Numerical Experiments for Dirichlet Problem --- p.50 / Chapter 4.1.1 --- Original Formulation --- p.50 / Chapter 4.1.2 --- Experiments --- p.52 / Chapter 4.1.3 --- Penalty Factor Effect --- p.56 / Chapter 4.2 --- Numerical Experiment for Neumann Problem --- p.61 / Chapter 4.2.1 --- Original Formulation --- p.61 / Chapter 4.2.2 --- Experiments --- p.62 / Chapter 4.2.3 --- Penalty Factor Effect --- p.66 / Chapter 4.2.4 --- Comparison with the Dirichlet Problem --- p.70 / Chapter 4.3 --- Numerical Experiment of Dirichlet Problem with Boundary Condition E = E --- p.71 / Chapter 4.3.1 --- Original Formulation --- p.71 / Chapter 4.3.2 --- Experiments --- p.73 / Chapter 4.3.3 --- Penalty Factor Effect --- p.76 / Chapter 4.4 --- Numerical Experiment on Spherical Shell Domain --- p.81 / Chapter 4.4.1 --- The Spherical Shell Domain --- p.81 / Chapter 4.4.2 --- Dirichlet Problem --- p.82 / Chapter 4.5 --- Some Numerical Phenomena --- p.86 / Chapter 4.5.1 --- GMRES Convergence Accelerator --- p.86 / Chapter 4.5.2 --- Sparsity Improvement --- p.88 / Bibliography --- p.90 / List of Tables --- p.94

"It is well known that singularities occur when solving elliptic value problems with non-convex domains or when some part of the data or the coefficients of the PDE are not smooth. Such problems and correspondent singularities often arise in practice, for instance, in fracture mechanics, in the material science with heterogeneities, or when dealing with mixed boundary conditions. A great deal is known about the nature of the singularities, which arise in some of these problems. In this thesis, we consider the scalar transmission problems with straight interfaces and with cross points across coefficients and possibly on a non-convex region ($L$-shaped domain). It is known that only $H^{1+au}$ ($0 < au< 1$) regularity on the solution is obtained and therefore the use of finite element method with the piecewise linear continuous function space does not give optimal accuracy. In this thesis, we introduce a new algorithm which are second order accurate on the (weighted) $L_2$, first order accurate on the (weighted) $H_1$ norm and second order accurate for the Stress Intensive Factor (SIF). The new methods take advantage of Mortar techniques. The main feature of the proposed algorithms is that we use primal singular functions {it without} cutting-off functions. The old algorithms use cutting-off functions as a tool of satisfying boundary conditions. In algorithms proposed in this thesis, use instead Mortar finite element technique to match the boundary and interfaces conditions. In this thesis, we also consider non-matching meshes sizes for different coefficients. We note that a new Mortar Lagrange multiplier is required in order to obtain optimal consistence errors for transmission problems. The proposed algorithms are very appealing over other methods because they are very accurate, do not require complicated numerical quadratures or interpolations, it is simple to design PCGs, and it can be generalized to other PDEs and to higher order methods."

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

In this thesis, numerical experiments are performed to test the numerical stability of the finite element method for analyzing incompressible materials from boundary displacements. The significance of the study relies on the fact that incompressibility, or density preservation during deformation, is an important property of materials such as rubber and soft tissue.<p>It is well known that the finite element analysis (FEA) of incompressible materials is less straightforward than for materials which are compressible. The FEA of incompressible materials using the usual displacement based finite element method results in an unstable solution for the stress field. Hence, a different formulation called the mixed u-p formulation (u displacement, p pressure) is used for the analysis. The u-p formulation results in a stable solution but only when the forces and/or stress tractions acting on the structure are known. There are, however, certain situations in the real world where the forces or stress tractions acting on the structure are unknown, but the deformation (i.e. displacements) due to the forces can be measured. One example is the stress analysis of soft tissues. High resolution images of initial and deformed states of a tissue can be used to obtain the displacements along the boundary. In such cases, the only inputs to the finite element method are the structural geometry, material properties, and boundary displacements. When finite element analysis of incompressible materials with displacement boundary conditions is performed, even the mixed u-p formulation results in highly unstable calculations of the stress field. Here, a hypothesis for solving this problem is developed and tested. Theories of linear and nonlinear stress analysis are reviewed to demonstrate that it may be possible to determine the von Mises stress uniquely in spite of the numerical instability inherent in the calculations.<p>To validate this concept, four different numerical examples representing different deformation processes are considered using ANSYS®: a plate in simple shear; expansion of a thick-walled cylinder; a plate in uniform strain; and Cooks membrane. Numerical results show that, unlike the normal stress components Sx, Sy, and Sz, the calculated values of the von Mises stress are reasonably accurate if measurement errors in the displacement data are small. As the measurement error increases, the error in the von Mises stress increases approximately linearly for linear problems, but can become unacceptably large in nonlinear cases, to the point where solution process encounter fatal errors. A quasi-Dirichlet patch test in association with this problem is also introduced.