Rozprawy doktorskie: „Finite Element”

1

Teng, Puay Tan Andy. "Intelligent Finite Element". Thesis, University of Exeter, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506062.

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Starkloff, Hans-Jörg. "Stochastic finite element method with simple random elements". Universitätsbibliothek Chemnitz, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200800596.

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We propose a variant of the stochastic finite element method, where the random elements occuring in the problem formulation are approximated by simple random elements, i.e. random elements with only a finite number of possible values.

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Roberts, D. P. "Finite element modelling of rockbolts and reinforcing elements". Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638679.

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The aim of this research was to produce a generic rockbolt model for inclusion in two and three dimensional explicit finite element analyses of mining problems. Installation of rockbolts is completely automated. Algorithms for the automatic placement of rockbolt nodes within continuum elements are developed and described. The rockbolts are described independently of the continuum degrees of freedom. Continuum elements and the rockbolt elements are connected through bond elements. Displacements from the continuum are transferred to the rockbolt system through these elements, and the resultant reactions passed to the continuum as external loads. In this way, the solution procedures for the continuum and the rockbolts are separated, thus creating an explicit-explicit subcycle. Using this form or nodal partitioning, rockbolts may have much higher stiffness than the parent continuum without effecting the overall timestep for the problem. Rockbolt systems are constructed of interconnected layers of bond elements and axial structural elements. The constitutive models for both these types of elements are effectively one-dimensional and therefore may be expressed algebraically. The most appropriate bond models from the literature are discussed and implemented. In addition, there is the capacity for elements crossing discontinuities to generate reactions consistent with transverse shearing of rockbolts. The model is tested by performing numerical pull-tests, based on experimental data from the literature. The sensitivity of rockbolt system to the relative bond and axial stiffness is demonstrated. The numerical axial and bond stress distributions were consistent with the experimental results. The model is applied to an excavation problem, with various rockbolt types and support patterns being analysed. The capacity of rockbolts to reduce the occurrence and depth of fracturing around the excavation is demonstrated. The model is also used to represent reinforcing bars in a concrete beam.

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Adams, Leila. "Finite element method using vector finite elements applied to eddy current problems". Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/9992.

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Vector fields found in electromagnetics are fundamentally different to vector fields found in other research areas such as structural mechanics. Electromagnetic vector fields possess different physical behaviour patterns and different properties in comparison to the other vector fields and therein lies the necessity of the development of a finite element which would be able to cater for these differences . The vector finite element was then developed and used within the finite element method specifically for the approximation of electromagnetic problems. This dissertation investigates the partial differential equation that governs eddy current behaviour. A finite element algorithm is coded and used to solve this partial differential equation and produce vector field simulations for fundamental eddy current problems.

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Larsson, Jesper. "Spring Element Evaluation Using Finite Element Analysis". Thesis, Högskolan i Jönköping, Tekniska Högskolan, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-45837.

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Margetts, Lee. "Parallel finite element analysis". Thesis, University of Manchester, 2002. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:70784.

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Finite element analysis is versatile and used widely in a range of engineering andscientific disciplines. As time passes, the problems that engineers and designers areexpected to solve are becoming more computationally demanding. Often theproblems involve the interplay of two or more processes which are physically andtherefore mathematically coupled. Although parallel computers have been availablefor about twenty years to satisfy this demand, finite element analysis is still largelyexecuted on serial machines. Parallelisation appears to be difficult, even for thespecialist. Parallel machines, programming languages, libraries and tools are used toparallelise old serial programs with mixed success. In some cases the serialalgorithm is not naturally suitable for parallel computing. Some argue that rewritingthe programs from scratch, using an entirely different solution strategy is a betterapproach. Taking this point of view, using MPI for portability, a mesh free elementby element method for simple data distribution and the appropriate iterative solvers,a general parallel strategy for finite element analysis is developed and assessed.

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Mohseninia, Mohsen. "Concurrent finite element optimisation". Thesis, University of Hertfordshire, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358479.

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Rabadi, Kairas. "PERFORMANCE OF INTERFACE ELEMENTS IN THE FINITE ELEMENT METHOD". Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2188.

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The objective of this research is to assess the performance of interface elements in the finite element method. Interface elements are implemented in the finite element codes such as MSC.NASTRAN, which is used in this study. Interface elements in MSC.NASTRAN provide a tool to transition between a shell-meshed region to another shell-meshed region as well as from a shell-meshed region to a solid-meshed region. Often, in practice shell elements are layered on shell elements or on solid elements without the use of interface elements. This is potentially inaccurate arising in mismatched degrees of freedom. In the case of a shell-to-shell interface, we consider the case in which the two regions have mismatched nodes along the boundary. Interface elements are used to connect these mismatched nodes. The interface elements are especially useful in global/local analysis, where a region with a dense mesh interfaces to a region with a less dense mesh. Interface elements are used to help avoid using special transition elements between two meshed regions. This is desirable since the transition elements can be severely distorted and cause poor results. Accurate results are obtained in shell-shell and shell-solid combinations. The most interesting result is that not using interface elements can lead to severe inaccuracies. This difficulty is illustrated by computing the stress concentration of a sharp elliptical hole.
M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering

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Dietzsch, Julian. "Implementierung gemischter Finite-Element-Formulierungen für polykonvexe Verzerrungsenergiefunktionen elastischer Kontinua". Master's thesis, Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-217381.

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In der vorliegenden Arbeit wird ein gemischtes Element gegen Locking-Effekte untersucht. Dazu wird ein Fünf-Feld-Hu-Washizu-Funktional (CoFEM-Element) für lineare und quadratische Hexaeder-Elemente unter einer hyperelastischen, isotropen, polykonvexen sowie einer transversal-isotropen Materialformulierung implementiert. Die resultierenden nichtlinearen Gleichungen werden mithilfe eines Mehrebenen-NEWTON-RAPHSON-Verfahren unter Beachtung einer konsistenten Linearisierung gelöst. Als repräsentatives Beispiel der numerischen Untersuchungen dient der einseitig eingespannte Cook-Balken mit einer quadratischen Druckverteilung am Rand. Zur Beurteilung des CoFEM-Elements wird das räumliche Konvergenzverhalten für unterschiedliche Polynomgrade und für verschiedene Netze unter Beachtung der algorithmischen Effizienz untersucht
This paper presents a mixed finite element formulation of Hu-Washizu type (CoFEM) designed to reduce locking effects with respect to a linear and quadratic approximation in space. We consider a hyperelastic, isotropic, polyconvex material formulation as well as transverse isotropy. The resulting nonlinear algebraic equations are solved with a multilevel NEWTON-RAPHSON method. As a numerical example serves a cook-like cantilever beam with a quadratic distribution of in-plane load on the Neumann boundary. We analyze the spatial convergence with respect to the polynomial degree of the underlying Lagrange polynomials and with respect to the level of mesh refinement in terms of algorithmic efficiency

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Nava, JoseÌ Manuel Franco. "Finite element versus boundary element analysis of finite strain elastic and elastoplastic fracture mechanics". Thesis, Cranfield University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401612.

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Monaghan, Dermot James. "Automatically coupling elements of dissimilar dimension in finite element analysis". Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326293.

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12

Berger, Stephanie 1981. "Experimental and finite element analysis of high pressure packer elements". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28879.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.
Includes bibliographical references (leaf 30).
Packer elements are traditionally rubber seals that can operate under specified downhole conditions and provide a seal for either a short-term, retrievable, or a long-term, permanent, completion. In this case a retrievable 19.7cm (7-3/4") packer element for a high-pressure high-temperature (HPHT) environment was designed and tested. The element created a seal between the mandrel, or tubing, and the casing. At high temperature and pressure rubber needs to be contained so that it will create and maintain an energized seal. In this study only Aflas rubber was tested. Various backup systems were examined; some more traditional designs such as the carbon steel foldback ring were compared to more experimental ideas. Results of theoretical simulations were compared to actual test results in order to gain a greater understanding of element behavior. Experiments were also performed to study the process of element setting, which is difficult to observe due to the high pressures and temperatures required. In a related study alternative materials to rubber such as annealed high-conductivity oxygen-free copper were tested to determine if the properties could be applied for packer element applications. The most successful design was the foldback ring with an anti-extrusion PEEK ring under the gage ring. This design passed a liquid test at 134 MPa (19.5k psi) differential pressure and a gas test at 87.6 MPa (12.7k psi) differential pressure. New designs such as the split ring with mesh and the garter spring with mesh did not pass fixture tests but could be successful with further modifications. FEA was used as an analytical tool to create simulations of the element after a setting force is applied. The modeling was shown to correlate to the actual test results and therefore it would be a good tool to use in future studies.
by Stephanie Berger.
S.M.

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13

Cenanovic, Mirza. "Finite element methods on surfaces". Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-28424.

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The purpose of this thesis is to improve numerical simulations of surface problems. Two novel computational concepts are analyzed and applied on two surface problems; minimal surface problems and elastic membrane problems. The concept of tangential projection implies that direct computation on the surface is made possible compared to the classical approach of mapping 2D parametric surfaces to 3D surfaces by means of differential geometry operators. The second concept presented is the cut finite element method, in which the basic idea of discretization is to embed the d- 1-dimensional surface in a d-dimensional mesh and use the basis functions of a higher dimensional mesh but integrate over the surface. The aim of this thesis is to present the basics of the two main approaches and to provide details on the implementation.

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Kolstad, Gaute Thorson. "Finite Element Modelling of Weldments". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19322.

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Brittle fracture is a large problem for steel structures in the arctic region. It is thus important to qualify materials and welds so they do not behave in a brittle manner. Since fracture testing of the heat affected zone (HAZ) around a weld gives a lot of scatter, doing weld simulated testing is proposed as an alternative method. In this thesis cracks in weld simulated HAZ specimens are compared to cracks in real welds, by use of finite element simulations. A weld simulated specimen is usually more brittle than a real weld. The goal of this thesis is thus to find a general rule for how much more brittle a weld simulated test specimen is, compared to a real weld on a structure. It would then be possible to establish how brittle a real weld is based on the result from the weld simulated testing. As a fracture criterion the Weibull stress is used, which is a statistical criterion. Crack tip opening displacement (CTOD) is used as a measure on how brittle a specimen is. To compare weld simulated specimens with real welds, two 2D modified boundary layer (MBL) models are used. One homogeneous model to represent weld simulated specimens, and one with three different materials to represent a real weld. The three materials in the weld model are base material, welded material and heat affected zone. On the two models a large parameter study is performed. The variables investigated are: - Position of the crack relative to the HAZ. - Size of the HAZ. - Geometry constraint. - Mismatch in WM. - Mismatch in HAZ. - Hardening. - The Weibull exponent m. There have also been made 3D models to investigate the size effect on the weld simulated specimen. This is because a weld simulated specimen is limited to a cross-section of $10$x$10$~mm. The parameter study concludes that it is mainly the size of the HAZ, the yield stress mismatch and the geometry constraint, that make weld simulated specimens more brittle than welds. The 3D simulations are however concluding that the geometry constraint effect can not be included, due to the size of the small test specimen. Based on these results a general relationship is proposed between the critical CTOD for a weld simulated specimen, and the critical CTOD for a real weld. There are three requirements for this relationship to be valid: - At least 10% overmatch in HAZ compared to base material. - No more than 10% undermatch in HAZ compared to welded material. - Maximal brittle HAZ thickness of 0.5 mm.

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梁耀華 i Yew-wah Leung. "Finite element solution on microcomputers". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31209300.

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Stevens, Nicholas P. C. "Finite element simulations in electrochemistry". Thesis, University of Bath, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285310.

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Kang, David Sung-Soo. "Hybrid stress finite element method". Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14973.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO
Bibliography: leaves 257-264.
by David Sung-Soo Kang.
Ph.D.

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Olivier, Albertus Hendrik. "Object-oriented finite element framework". Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52971.

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Thesis (MScEng)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: The role of the computer has changed from a calculation tool to a tool that supports human thinking. In this thesis fundamental aspects of the Finite Element method are mapped to an object model with a well defined structure which provides for local and distributed analysis work. To achieve this the following was investigated: • An object-oriented framework for the Finite Element analysis method • An associated graphical user interface that enables the user to create and modify Finite Element models in an effective way • Requirements for the sharing of analysis information in a communication network Proposed solutions are implemented in a pilot application which indicates their potential.
AFRIKAANSE OPSOMMING: Die rol van die rekenaar het verander vanaf 'n gereedskapstuk wat berekening doen na 'n gereedskapstuk wat menslike denke ondersteun. In hierdie tesis word die fundamentele aspekte van die Eindige Element metode oorgedra na 'n objek model met 'n goed gedefinieerde struktuur wat lokale en verspreide analisering werk ondersteun. Om dit te bereik is die volgende ondesoek: • 'n Objek orienteerde raamwerk vir die Eindige Element metode • 'n Geassosieerde grafiese raamwerk wat die gebruiker in staat stelom objekte te skep en te verander • Vereistes vir die deel van analise inligting in 'n kommunikasie netwerk Die voorgestelde oplossing is geimplimenteer in 'n loodsimplementering wat die voordele van die benadering uitlig.

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Sitapati, Kartik. "Mixed-Field Finite-Element Computations". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11195.

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A new method called the Direct Method is developed to solve for the propagating modes in waveguides via the finite-element method. The variational form of the Direct method is derived to ensure that an extremum is reached. The Direct method uses Maxwell's equations directly, both zero and first-order, scalar and vector bases that are used in the finite-element formulation. The direct solution method solves for both the magnetic and electric fields simultaneously. Comparisons are made with the traditionally used vector-Helmholtz equation set. The advantages and disadvantages of the newly developed method is described as well as several results displayed using the WR-90 waveguide and a circular waveguide as test waveguides. Results include a partially filled dielectric loaded rectangular waveguide. The effects of including the divergence of the fields in the functional as penalty terms on the quality of results obtained by the Direct method and the vector-Helmholtz method is explored. The quality of results is gauged on the accuracy of the computed modes as well as the elimination or a significant reduction in the number of 'spurious modes' that are often encountered in solutions to waveguide problems. It is shown that computational time for the solution and computer storage requirements exceed the typically used Helmholtz equation method but the results obtained can be more accurate. Future work may include developing a sparse eigenvalue solution method that could reduce the solution time and storage requirements significantly. The Direct method of solution in dynamics resulted after an initial search in magnetostatics for methods to solve for the magnetic field without using the magnetic-vector potential using finite-element methods. A variational derivation that includes the boundary conditions is developed for the magnetic-vector potential method. Several techniques that were used to attempt accurate solutions for the magnetostatic fields with multiple materials and without the use of the magnetic-vector potential are described. It was found that some of the newly developed general techniques for magnetostatics are only accurate when homogeneous media are present. A method using two curl equations is developed which is a Direct method in magnetostatics and reveals the interaction between the bases used. The transition from magnetostatics to dynamics is made and similar Direct methods are applied to the waveguide problem using different bases.
Ph. D.

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Leung, Yew-wah. "Finite element solution on microcomputers /". [Hong Kong] : University of Hong Kong, 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12754948.

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Dogan, Abdulkadir. "Petrov-Galerkin finite element methods". Thesis, Bangor University, 1997. https://research.bangor.ac.uk/portal/en/theses/petrovgalerkin-finite-element-methods(4d767fc7-4ad1-402a-9e6e-fd440b722406).html.

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Lai, Zhi Cheng. "Finite element analysis of electrostatic coupled systems using geometrically nonlinear mixed assumed stress finite elements". Diss., Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-05052008-101337/.

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Irfanoglu, Bulent. "Boundary Element-finite Element Acoustic Analysis Of Coupled Domains". Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605360/index.pdf.

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This thesis studies interactions between coupled acoustic domain(s) and enclosing rigid or elastic boundary. Boundary element-finite element (BE-FE) sound-structure interaction models are developed by coupling frequency domain BE acoustic and FE structural models using linear inviscid acoustic and elasticity theories. Flexibility in analyses is provided by discontinuous triangular and quadrilateral elements in the BE method (BEM), and a rectangular plate and a triangular shell element in the FE method (FEM). An analytical formulation is developed for an extended fundamental sound-structure interaction problem that involves locally reacting sound absorptive treatment on interior elastic boundary. This new formulation is built upon existing analytical solutions for a configuration known as the cavity-backed-plate problem. Results from developed analytical formulation are compared against those from independent BE-FE analyses. Analytical and BE-FE analysis results for a selection of cavity-plate(s) interaction cases are given. Single- and multi-domain BE analyses of cavity-Helmholtz resonator interaction are provided as an alternative to modal method of acoustoelasticity. A discrete-form of the existing BE acoustic particle velocity formulation is presented and demonstrated on a basic case study. Both the existing and the discretized BE acoustic particle velocity formulations could be utilized in acoustic studies. A selection of case studies involving fundamental configurations are studied both analytically and computationally (by BE or BE-FE methods). These studies could provide a basis for benchmark case development in the field of acoustics.

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24

Jacobs, Ralf Theo. "Finite element-boundary element analysis of conformal microstrip antennas". Thesis, Heriot-Watt University, 2001. http://hdl.handle.net/10399/531.

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Wong, S.-W. "Element-by-element methods in transient analysis". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383902.

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Yilmaz, Asim Egemen. "Finite Element Modeling Of Electromagnetic Scattering Problems Via Hexahedral Edge Elements". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608587/index.pdf.

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In this thesis, quadratic hexahedral edge elements have been applied to the three dimensional for open region electromagnetic scattering problems. For this purpose, a semi-automatic all-hexahedral mesh generation algorithm is developed and implemented. Material properties inside the elements and along the edges are also determined and prescribed during the mesh generation phase in order to be used in the solution phase. Based on the condition number quality metric, the generated mesh is optimized by means of the Particle Swarm Optimization (PSO) technique. A framework implementing hierarchical hexahedral edge elements is implemented to investigate the performance of linear and quadratic hexahedral edge elements. Perfectly Matched Layers (PMLs), which are implemented by using a complex coordinate transformation, have been used for mesh truncation in the software. Sparse storage and relevant efficient matrix ordering are used for the representation of the system of equations. Both direct and indirect sparse matrix solution methods are implemented and used. Performance of quadratic hexahedral edge elements is deeply investigated over the radar cross-sections of several curved or flat objects with or without patches. Instead of the de-facto standard of 0.1 wavelength linear element size, 0.3-0.4 wavelength quadratic element size was observed to be a new potential criterion for electromagnetic scattering and radiation problems.

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Bravo, Victor. "Finite element simulation of flow in twin screw extruder mixing elements". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0005/NQ42727.pdf.

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Weber, Marc Anton. "The study of creep in machine elements using finite element methods". Master's thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/21954.

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Bibliography: pages 92-98.
In this thesis a simplified analysis procedure is developed, in which creep laws are decoupled from damage laws, for the purposb of constructing methods of use in the early stages of high temperature design. The procedure is based on the creep and damage laws proposed by Kachanov and Rabotnov. The creep laws are normalised. with respect to a convenient normalising stress. As a consequence of this normalisation, the dependence of the creep law on the stress constant, the time and temperature functions, and the actual load level is removed. In addition, if the reference stress of the component is chosen as the normalising stress, the creep law becomes insensitive to the stress exponent. The non-dimensional creep laws are then implemented in a standard finite element scheme, from which the results of a stationary state creep analysis are then in non-dimensional form. In order to estimate rupture times, the maximum stationary stresses in a component are used together with the damage laws. Conservative failure criteria are derived from the creep and damage laws to extend the method to residual life assessment and damage monitoring. The procedure is illustrated and tested against simple examples and case studies.

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Tseng, Gordon Bae-Ji. "Investigation of tetrahedron elements using automatic meshing in finite element analysis /". Online version of thesis, 1992. http://hdl.handle.net/1850/10699.

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Svensson, Daniel, i Tomas Walander. "Evaluation of an Interphase Element using Explicit Finite Element Analysis". Thesis, University of Skövde, School of Technology and Society, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-3895.

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A research group at University of Skövde has developed an interphase element for implementation in the commercial FE-software Abaqus. The element is using the Tvergaard & Hutchinson cohesive law and is implemented in Abaqus Explicit version 6.7 using the VUEL subroutine. This bachelor degree project is referring to evaluate the interphase element and also highlight problems with the element.

The behavior of the interphase element is evaluated in mode I using Double Cantilever Beam (DCB)-specimens and in mode II using End Notch Flexure (ENF)-specimens. The results from the simulations are compared and validated to an analytical solution.

FE-simulations performed with the interphase element show very good agreement with theory when using DCB- or ENF-specimens. The only exception is when an ENF-specimen has distorted elements.

When using explicit finite element software the critical time step is of great importance for the results of the analyses. If a too long time step is used, the simulation will fail to complete or complete with errors. A feasible equation for predicting the critical time step for the interphase element has been developed by the research group and the reliability of this equation is evaluated.

The result from simulations shows an excellent agreement with the equation when the interphase element governs the critical time step. However when the adherends governs the critical time step the equation gives a time step that is too large. A modification of this equation is suggested.

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Galuta, Ezeedin M. "Combined boundary element and finite element analysis of composite bridges". Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6814.

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In this thesis, the coupling of boundary element and finite element methods and its application to analyze bridges are studied for the first time. The coupling technique is implemented to analyze slab on girders and box girder bridges. The boundary element method is employed to model the bridge deck while the finite element method is used to model the girders. The finite elements and boundary elements are connected at a number of interface nodes in the longitudinal direction. For the finite element region, a static condensation technique is applied to condense the non-interface degrees of freedom. Then the finite element equations are transformed into boundary element equations and the compatibility interface mechanism required to combine the two methods is developed. A computer program which combines boundary element and finite element methods in one solution is developed in this thesis. Different types of bridges with different load cases are considered in the study in order to test the performance of the combined method. It has been shown that the results obtained by the combined method (BEM-FEM) are in good agreement with the finite strip solution. The numerical examples, considered in this thesis, demonstrated the accuracy of the results and the simplicity and reduction of the input data.

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32

Johnson, Sean (Sean Michael). "Modeling a bender element test using Abaqus Finite Element Program". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/64573.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 253-255).
Finite Element Methods hold promise for modeling the behavior of an unsaturated soil specimen subjected to bender element agitation. The immediate objective of this research project is to reproduce a bender element test using Abaqus Finite Element Software assuming elastic and isotropic conditions. Extensive compressions were made of bender element testing of unsaturated Ticino Sand specimens uniaxially compressed and the Abaqus Finite Element Method program simulation. The research determined that the mesh resolution of a numerical analysis are optimal at a resolution of a twentieth of the shear wavelength and the integration time step has a negligible effect on the observed wave velocity. Moreover, it is possible to reproduce an uniaxially stressed bender element experiments of unsaturated Ticino sand in an Abaqus Finite Element Method program with relatively minimal error of the body wave velocity measurements if the source receiver distance is beyond two shear wavelengths and the reflected signals from the boundaries are suppressed.
by Sean Johnson.
S.M.

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33

Thompson, Ronald H. "Plane frame element addition to the MESS finite element program". Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/80052.

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A plane frame element based on linear, elastic theory is developed and implemented into the MESS finite element program. Post-processed results include nodal displacements, end reactions, maximum tensile and average shear stress, and a deformed geometry plot. The element is tested for accuracy relative to simple beam theory and by comparison with results generated using another finite element program. In both cases agreement to within 6 significant figures was achieved. Because the intended use is educational, a survey of its benefit as a design aid in undergraduate instruction is included. These benefits are based on test cases from senior design class projects. Results generated using analysis techniques presently available are contrasted with those using the plane frame element. Students' work that was examined contained mistakes resulting from large amounts of hand calculations. Conversely, results generated using the finite element method proved to be easily obtained and to have a higher degree of accuracy. A recommendation for further improvements in program capability is provided at the end of the study.
Master of Science

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Abou, Ghadir Mohamed Mohamed Moustafa. "Combined finite strip and finite element methods in structural analysis". Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.446434.

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Sevilla, Cárdenas Rubén. "NURBS-Enhanced Finite Element Method (NEFEM)". Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/5857.

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Aquesta tesi proposa una millora del clàssic mètode dels elements finits (finite element method, FEM) per a un tractament eficient de dominis amb contorns corbs: el denominat NURBS-enhanced finite element method (NEFEM). Aquesta millora permet descriure de manera exacta la geometría mitjançant la seva representació del contorn CAD amb non-uniform rational B-splines (NURBS), mentre que la solució s'aproxima amb la interpolació polinòmica estàndard. Per tant, en la major part del domini, la interpolació i la integració numèrica són estàndard, retenint les propietats de convergència clàssiques del FEM i facilitant l'acoblament amb els elements interiors. Només es requereixen estratègies específiques per realitzar la interpolació i la integració numèrica en elements afectats per la descripció del contorn mitjançant NURBS.

La implementació i aplicació de NEFEM a problemes que requereixen una descripció acurada del contorn són, també, objectius prioritaris d'aquesta tesi. Per exemple, la solució numèrica de les equacions de Maxwell és molt sensible a la descripció geomètrica. Es presenta l'aplicació de NEFEM a problemes d'scattering d'ones electromagnètiques amb una formulació de Galerkin discontinu. S'investiga l'habilitat de NEFEM per obtenir solucions precises amb malles grolleres i aproximacions d'alt ordre, i s'exploren les possibilitats de les anomenades malles NEFEM, amb elements que contenen singularitats dintre d'una cara o aresta d'un element. Utilitzant NEFEM, la mida de la malla no està controlada per la complexitat de la geometria. Això implica una dràstica diferència en la mida dels elements i, per tant, suposa un gran estalvi tant des del punt de vista de requeriments de memòria com de cost computacional. Per tant, NEFEM és una eina poderosa per la simulació de problemes tridimensionals a gran escala amb geometries complexes. D'altra banda, la simulació de problemes d'scattering d'ones electromagnètiques requereix mecanismes per aconseguir una absorció eficient de les ones scattered. En aquesta tesi es discuteixen, optimitzen i comparen dues tècniques en el context de mètodes de Galerkin discontinu amb aproximacions d'alt ordre.

La resolució numèrica de les equacions d'Euler de la dinàmica de gasos és també molt sensible a la representació geomètrica. Quan es considera una formulació de Galerkin discontinu i elements isoparamètrics lineals, una producció espúria d'entropia pot evitar la convergència cap a la solució correcta. Amb NEFEM, l'acurada imposició de la condició de contorn en contorns impenetrables proporciona resultats precisos inclús amb una aproximació lineal de la solució. A més, la representació exacta del contorn permet una imposició adequada de les condicions de contorn amb malles grolleres i graus d'interpolació alts. Una propietat atractiva de la implementació proposada és que moltes de les rutines usuals en un codi d'elements finits poden ser aprofitades, per exemple rutines per realitzar el càlcul de les matrius elementals, assemblatge, etc. Només és necessari implementar noves rutines per calcular les quadratures numèriques en elements corbs i emmagatzemar el valor de les funciones de forma en els punts d'integració. S'han proposat vàries tècniques d'elements finits corbs a la literatura. En aquesta tesi, es compara NEFEM amb altres tècniques populars d'elements finits corbs (isoparamètics, cartesians i p-FEM), des de tres punts de vista diferents: aspectes teòrics, implementació i eficiència numèrica. En els exemples numèrics, NEFEM és, com a mínim, un ordre de magnitud més precís comparat amb altres tècniques. A més, per una precisió desitjada NEFEM és també més eficient: necessita un 50% dels graus de llibertat que fan servir els elements isoparamètrics o p-FEM per aconseguir la mateixa precisió. Per tant, l'ús de NEFEM és altament recomanable en presència de contorns corbs i/o quan el contorn té detalls geomètrics complexes.
This thesis proposes an improvement of the classical finite element method (FEM) for an efficient treatment of curved boundaries: the NURBSenhanced FEM (NEFEM). It is able to exactly represent the geometry by means of the usual CAD boundary representation with non-uniform rational Bsplines (NURBS), while the solution is approximated with a standard piecewise polynomial interpolation. Therefore, in the vast majority of the domain, interpolation and numerical integration are standard, preserving the classical finite element (FE) convergence properties, and allowing a seamless coupling with standard FEs on the domain interior. Specifically designed polynomial interpolation and numerical integration are designed only for those elements affected by the NURBS boundary representation.

The implementation and application of NEFEM to problems demanding an accurate boundary representation are also primary goals of this thesis. For instance, the numerical solution of Maxwell's equations is highly sensitive to geometry description. The application of NEFEM to electromagnetic scattering problems using a discontinuous Galerkin formulation is presented. The ability of NEFEM to compute an accurate solution with coarse meshes and high-order approximations is investigated, and the possibilities of NEFEM meshes, with elements containing edge or corner singularities, are explored. With NEFEM, the mesh size is no longer subsidiary to geometry complexity, and depends only on the accuracy requirements on the solution, whereas standard FEs require mesh refinement to properly capture the geometry. This implies a drastic difference in mesh size that results in drastic memory savings, and also important savings in computational cost. Thus, NEFEM is a powerful tool for large-scale scattering simulations with complex geometries in three dimensions. Another key issue in the numerical solution of electromagnetic scattering problems is using a mechanism to perform the absorption of outgoing waves. Two perfectly matched layers are discussed, optimized and compared in a high-order discontinuous Galerkin framework.

The numerical solution of Euler equations of gas dynamics is also very sensitive to geometry description. Using a discontinuous Galerkin formulation and linear isoparametric elements, a spurious entropy production may prevent convergence to the correct solution. With NEFEM, the exact imposition of the solid wall boundary condition provides accurate results even with a linear approximation of the solution. Furthermore, the exact boundary representation allows using coarse meshes, but ensuring the proper implementation of the solid wall boundary condition. An attractive feature of the proposed implementation is that the usual routines of a standard FE code can be directly used, namely routines for the computation of elemental matrices and vectors, assembly, etc. It is only necessary to implement new routines for the computation of numerical quadratures in curved elements and to store the value of shape functions at integration points.

Several curved FE techniques have been proposed in the literature. In this thesis, NEFEM is compared with some popular curved FE techniques (namely isoparametric FEs, cartesian FEs and p-FEM), from three different perspectives: theoretical aspects, implementation and performance. In every example shown, NEFEM is at least one order of magnitude more accurate compared to other techniques. Moreover, for a desired accuracy NEFEM is also computationally more efficient. In some examples, NEFEM needs only 50% of the number of degrees of freedom required by isoparametric FEs or p-FEM. Thus, the use of NEFEM is strongly recommended in the presence of curved boundaries and/or when the boundary of the domain has complex geometric details.

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Maag, Hans. "Interaktive Steuerung nichtlinearer Finite-Element-Berechnungen /". Zürich, 1985. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=7808.

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Korsawe, Johannes Rudolf. "Multilevelverfahren für nichtlineare Finite-Element-Ausgleichsprobleme". [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963621874.

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Mekchay, Khamron. "Convergence of adaptive finite element methods". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3216.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Mathematics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Elofsson, Johan, i Per Martinsson. "Welding simulation with Finite Element Analysis". Thesis, University West, Department of Technology, Mathematics and Computer Science, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-827.

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Nygårds, Mikael. "Microstructural finite element modeling of metals". Doctoral thesis, KTH, Solid Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3496.

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The mechanical properties of metals have been investigated.This has been done by creating micromechanical models based onthe microstructural data available for the materials ofinterest. Thus, models containing a grain structure withappropriate constitutive equations have been created. Periodiccells on the micrometer scale have been shown to be sufficientto represent the materials, when macroscopic properties areevaluated.

Micromechanical modeling by the finite element method can bedivided into three different parts: geometry, boundaryconditions and constitutive equations. These parts have more orless been illustrated and used in the seven appendedpapers.

The geometric outlines of the grain structures arerepresented by the Voronoi algorithm. Hence, polyheadrons areused to represent three-dimensional grain structures, whiletwo-dimensional models are represented by polygons. Twodifferent approaches are used. Either, space is divided intograins by application of the Voronoi algorithm. Thus, grainboundaries are represented by planes or lines. Thereafter, thegrains are meshed with an adaptive mesh generator.Alternatively, a mesh is created before the Voronoi algorithmis applied. The grain boundaries will in the latter case bekinky, since the outline of the predefined mesh is followedwhen grains are formed. The former method results in smallerelements close to grain boundaries. This fact is used to studytwo-phase ferrite-pearlite steels, since pearlite and the smallelements have the same location.

Representative volume elements (RVEs) of the materials arecreated by considering a sufficient number of grains, and it isshown how this number depends on anisotropy and loading. Toavoid edge effects in the models, the volume elements are madeperiodic and periodic boundary conditions are utilized toconstrain the models. In the present implementation of periodicboundary conditions, average stresses and/or average strainsare prescribed over the periodic cell.

A non-local crystal plasticity theory that incorporates slipgradients in the hardening has been implemented. It is shownthat this concept can be used to account for the effectsmaller is harder. Furthermore, the effect ofnon-local plasticity on the deformation of a free surface isinvestigated in detail. It is shown that the surface roughnessdecreases as an effect of strain gradients.

Lastly, all numerical work done here aims to mimicexperiments that have been performed. This includes microscopicinvestigations, tensile testing, investigations by atomic forcemicroscopy, but also experimental data from the literature.

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Hellborg, Simon. "Finite Element Simulation of Roll Forming". Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8312.

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A finite element model has been developed to simulate the forming of a channel section profile with the roll forming method. The model has been optimized to experimental results with respect to strains at the edge of the sheet and spring back of the sides of the profile. Finite element models with a coarse mesh have been compared to models with a finer mesh. The models with to fine mesh become instable and a model with a rather coarse mesh was finally chosen.

Both the models with shell elements and the models with solid elements have been used in the simulations. The simulations with shell elements gave very good results both for the geometry shape and the strains at the edge of the sheet. The reaction forces at the tools found in the simulations was only half of the reaction forces fond in the experiments.

The simulations with the solid element model showed very good results for the reaction forces while the geometry shape of the sheet was really bad. The spring back was much larger in the simulations than in the experiments.

The shell element model was chosen because of the excessive spring back with the solid element model. The spring back of the sides of the sheet differs only a few percent between the simulation and the experiment results when using the shell element model. The reaction forces at the tools in the simulation are only half of the reaction forces measured in the experiments but the results from the simulations are linearly proportional to the results in the experiments. The model that finally was chosen describe both the spring back and the strains at the edge of the sheet very well. Like in the experiments there were no signs of wrinkles at the sheet in any of the simulations.

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Johannessen, Kjetil André. "An adaptive isogeometric finite element analysis". Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9936.

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In this thesis we will explore the possibilities of making a finite element solver for partial differential equations using the isogeometric framework established by Hughes et al. Whereas general B-splines and NURBS only allow for tensor product refinement, a new technology called T-splines will open for true local refinement. We will give an introduction into T-splines along with B-splines and NURBS on which they are built, presenting as well a refinement algorithm which will preserve the exact geometry of the T-spline and allow for more control points in the mesh. For the solver we will apply a residual-based a posteriori error estimator to identify elements which contribute the most to the error, which in turn allows for a fully automatic adaptive refinement scheme. The performance of the T-splines is shown to be superior on problems which contains singularities when compared with more traditional splines. Moreover the T-splines along with a posteriori error estimators are shown to have a very positive effect on badly parametrized models, as it seem to make the solution grid independent of the original parametrization.

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Zeng, Yang. "Finite Element Methods for Microelectromechanical Systems". Thesis, Uppsala University, Department of Information Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-110896.

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The stationary Joule heating problem is a crucial multiphysical problem for many microelectromechanical (MEMS) applications. In our paper, we derive a finite element method for this problem and introduce iterative solution-techniques to compute the numerical simulation. Further we construct an adaptive algorithm for mesh refinement based on a posteriori error estimation.Finally, we present two numerical tests: convergences analysis of different iterative methods for distinct materials which are classified by electrical conductivities, and a test of the new adaptive refinement algorithm. All the numerical implementations have been done in MATLAB.

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Grosman, Sergey. "Adaptivity in anisotropic finite element calculations". Doctoral thesis, Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600815.

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When the finite element method is used to solve boundary value problems, the corresponding finite element mesh is appropriate if it is reflects the behavior of the true solution. A posteriori error estimators are suited to construct adequate meshes. They are useful to measure the quality of an approximate solution and to design adaptive solution algorithms. Singularly perturbed problems yield in general solutions with anisotropic features, e.g. strong boundary or interior layers. For such problems it is useful to use anisotropic meshes in order to reach maximal order of convergence. Moreover, the quality of the numerical solution rests on the robustness of the a posteriori error estimation with respect to both the anisotropy of the mesh and the perturbation parameters. There exist different possibilities to measure the a posteriori error in the energy norm for the singularly perturbed reaction-diffusion equation. One of them is the equilibrated residual method which is known to be robust as long as one solves auxiliary local Neumann problems exactly on each element. We provide a basis for an approximate solution of the aforementioned auxiliary problem and show that this approximation does not affect the quality of the error estimation. Another approach that we develope for the a posteriori error estimation is the hierarchical error estimator. The robustness proof for this estimator involves some stages including the strengthened Cauchy-Schwarz inequality and the error reduction property for the chosen space enrichment. In the rest of the work we deal with adaptive algorithms. We provide an overview of the existing methods for the isotropic meshes and then generalize the ideas for the anisotropic case. For the resulting algorithm the error reduction estimates are proven for the Poisson equation and for the singularly perturbed reaction-difussion equation. The convergence for the Poisson equation is also shown. Numerical experiments for the equilibrated residual method, for the hierarchical error estimator and for the adaptive algorithm confirm the theory. The adaptive algorithm shows its potential by creating the anisotropic mesh for the problem with the boundary layer starting with a very coarse isotropic mesh.

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Risa, Adrian Opheim. "Finite element analysis of marine umbilical". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15368.

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Background: Marine umbilicals play a vital role in oil and gas production fields. The oil and gas industry is in constant change, as the resources in the reservoirs are ever decreasing. Today oil and gas exploration takes place at increasing depths, and in harsher environments. This means that components like marine umbilicals are getting more advanced. Thus accurate structural analysis is important. The focus in this thesis is an umbilical consisting of 19 copper conductors. The goal is to model it in ABAQUS, and compare the results with laboratory testing. Results: Stress distribution and fatigue calculations were the main focus. Ultimately, it was proven that ABAQUS was able to represent the umbilical's general behavior. However, due to computational limitations and limits in the material model, the result proved inaccurate. In particular, values for axial stress and strain, exceeds the expected values. Conclusion: The model was able to represent the general behavior from the laboratory results. Effort should be made in the future to overcome the computational problems, and the material model should be revised.

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Valivarthi, Mohan Varma, i Hema Chandra Babu Muthyala. "A Finite Element Time Relaxation Method". Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-17728.

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In our project we discuss a finite element time-relaxation method for high Reynolds number flows. The key idea consists of using local projections on polynomials defined on macro element of each pair of two elements sharing a face. We give the formulation for the scalar convection–diffusion equation and a numerical illustration.

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Witte, Holger. "Magnet design using finite element analysis". Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491607.

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This thesis applies the method of finite element software to calculate pulsed high field magnets. The calculations address the structural and thermal load of pulsed magnets during discharge and at peak field. The most successful currently-used coil designs from different magnet laboratories are assessed with these methods. The results are compared against wellestablished analytic programs; arising differences are discussed. Particular emphasis is on the coil designs developed for the pulsed field facility in the Clarendon Laboratory, Oxford, UK. The facility, named after Nikolas Kurti, is described and classified. The coil designs are based on a novel high strength copper-silver conductor, which is compared to other common conductors. In combination with the novel calculation methods this established a new quality of high magnetic fields: the local record was broken in March 2007 by creating the highest magnetic field to date in the Clarendon Laboratory. Present and future trends in pulsed magnet design are discussed and evaluated. These include a discussion of foil coils, braiding of conductors and the matching of conductors with suitable reinforcement. Particular emphasis is placed on the verification of the simulation results. To this end a finite element method is developed which can be used to predict the irreversible change of the inductance of pulsed magnets due to plastic deformation. Preliminary results of residual strains in a magnet using neutron scattering are also considered. Another focus is on reducing the cool-down time of pulsed magnets by using rapid cooling methods. The concept of the so-called 'cooling disc' is new in this respect. Experimental and theoretical results are contrasted with other methods. Other work has contributed to the design of the magnetic channel of the international Muon Ionization Cooling Experiment; this thesis gives a summary. The work comprises force calculations, quench considerations and magnetic shielding issues.

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Wagner, Roy E. "Finite element analysis of wire coating". Thesis, University of Ottawa (Canada), 1987. http://hdl.handle.net/10393/5236.

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Nowzartash, Farhood. "Elasto-plastic finite element for pipelines". Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6180.

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An efficient pipe element for the modeling of the inelastic behaviour of three-dimensional pipes is presented. The formulation is based on a two-node element with twelve degrees of freedom. The element consists of an elastic portion and two potentially plastic generalized 3D hinges located at both nodes. The formulation is based on a lumped plasticity approach. The behaviour of plastic hinges is characterized using recently developed interaction relations for pipe sections. The interaction relations are exact and include the effects of axial force, bi-axial bending moments, bi-axial shear, torsion and internal and/or external pressure. The element models shear deformation effects both in the elastic and plastic ranges. Therefore, it is suitable for predicting the behaviour of pipe segments subject to high shear forces. The analysis is implemented using the displacement control scheme in order to capture the peak point of the load deformation response without numerical difficulty. The normality condition concept in conjunction with the yield hyper-surface at stress resultant level is used to approximately simulate the material nonlinearity effects. The developed technique models material nonlinearity in a very efficient way when compared to full 3D or shell finite element analysis. The model is thus particularly suitable for long pipeline systems. Solutions for simple problems are provided and compared to several other well-established elements in the ABAQUS(TM) library in order to assess the validity of the results and demonstrate their scope of applicability. A discussion of additional features that can be added to the analysis is also presented.

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Hellwig, Felix Lutz. "Finite element studies of femoroacetabular impingement". Thesis, University of Portsmouth, 2013. https://researchportal.port.ac.uk/portal/en/theses/finite-element-studies-of-femoroacetabular-impingement(d908629c-3ecc-4c80-ba06-eeb211aeffcd).html.

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Recently, femoroacetabular impingement (FAI) was introduced as a pathomechanical concept that could explain idiopathic cartilage and labral degeneration. FAI can be subdivided into three mechanisms: 'Cam'- and 'pincer'-type impingement and the 'contracoupe' mechanism. The suggested concept aims to create a link between retrospective findings of cartilaginous tissue degeneration and mild abnormal structural deformations of the hip joint. The theoretical concept focuses on abnormal articulation rather than increased axial-overloading. Although clinical evidence seems to be given, prospective biomechanical verification would be desirable to provide further justification for early joint reconstruction surgery. A comprehensive research program has been carried out to highlight elevated stresses, contact pressures, affected fluid-load support, abnormal articulation and increased femoral head motion evoked by mild to severe abnormal conditions of the hip joint. Contact pressure, stress distributions and femoral head motion, indicating joint stability, were studied using three dimensional finite element models of normal and abnormal hip joint conditions; the considered abnormal conditions included a varying degree of acetabular and femoral version and manifestation of femoral protrusions (hump) at the femoral head-neck junction. The cartilogenous tissues were considered as linear elastic isotropic materials. The highlighted abnormal articulation confirmed the suggested concept of FAI; the predicted abnormal stress and contact pressure distribution corresponded to clinical findings. The fluid-load support, solid-on-solid stress, stress components, within the solid extracellular matrix of the cartilaginous tissues, and total contact pressure were studied during normal and isolated 'cam'-type impinged articulation. The cartilogenous tissues were considered as linear biphasic orthotropic materials. While the maximum total contact pressure, predicted during distinct 'cam'-type impingement, did not exceed the maxima obtained for normal articulation, the fluid-load support was severely affected at the zone of impingement. Vigorous elevated solid-on-solid stresses found at the zone of impingement, suggest a local increase in the coefficient of friction, which might lead to cartilage wear and progresses to severe osteoarthritis.

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