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Tesi sul tema "Finite element modelling"
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1
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.
Testo completoAbstract (sommario):
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.
2
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.
Testo completoAbstract (sommario):
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.
3
Pires, F. M. A. "Issues on the finite element modelling". Thesis, Swansea University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638539.
Testo completoAbstract (sommario):
Aspects of constitutive modelling and numerical prediction of failure in finitely straining ductile metals are investigated in this thesis. Attention is focused on the construction of a framework for prediction of failure. The development of a model for finite strain elasto-(visco)plastic damage; a low order finite element for the numerical treatment of incompressibility and an adaptive mesh refinement strategy for this class of problems, constitute the building blocks of the overall approach. Emphasis is given to the efficient numerical simulation of the proposed theories in large scale problems. The characterisation of material response has to account for the interaction between the different phenomena that precede fracture initiation. The derivation of constitutive models is addressed within Continuum Damage Mechanics theory. Particular, the effect of micro-crack closure which may dramatically decrease the rate of damage growth under compression is emphasised. With regard to the computational treatment of incompressibility, a new technique which allows the use of simplex finite elements in the large strain analysis of nearly incompressible solids is proposed. It is based on relaxation of the excessive volumetric constrain by the enforcement of near-incompressibility over a patch of elements. The new elements are implemented within an implicit quasi-static and an explicit transient dynamic finite element environment. The algorithms for numerical integration of the corresponding path dependent constitutive equations are discussed in detail. The strategy for numerical simulation of the associated incremental boundary value problems relies on fully implicit and explicit displacement based finite element procedures.
4
Bayrakdar, Haluk. "Finite element modelling of transportation tunnels". Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5175/.
Testo completoAbstract (sommario):
The aim of this thesis is to determine the ground deformation and stress distribution around highway tunnels at various stages of excavation and for several support conditions using finite element modelling techniques. When ground is excavated and material removed the subsequent redistribution of stress in the remaining surrounding material needs to be treated by one of three methods. These are the gravity difference method, the stress reversal technique and the relaxation approach. The first two methods were chosen for the simulation of excavation in this study. The tunnel data are in the form of the dimensions of the tunnel, heights of the rock layers, details of the shotcrete lining and tunnel support systems. A pre-processing program was written to transform this information into a finite element mesh in a format suitable for use by PAFEC-FE software. This enables different tunnel models and meshes to be produced with minimum error and time. The lack of adequate post-processing facilities available in PAFEC-FE dictated that computer programs needed to be written in order to reformat the textual output files and process the mesh stress and displacement outputs for graphical display using UNIRAS. In this way repeated use could be made of PAFEC-FE without time-consuming and error-prone manual retrieval of data. The tunnels were modelled at various stages of excavation and with such support provided at those stages as to allow the computed displacements to be compared with measurements made on highway tunnels in Turkey. The stresses generated in the tunnel supports and surrounding ground were also calculated to enable the possibility of damage or failure of the support structure or ground to be assessed and the selection of an optimal support system. Insertion of a support system into the model has a marginal effect on the development of rock strength around an excavation boundary.
5
Knock, Clare. "Finite element modelling of estuarine hydrodynamics". Thesis, University of the West of England, Bristol, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258716.
Testo completo
6
Datta, Kanyakumari. "Finite element modelling of hot rolling". Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242200.
Testo completo
7
Adam, Alexandros. "Finite element, adaptive spectral wave modelling". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/45307.
Testo completoAbstract (sommario):
The ability to predict the wave climate has a great impact on a wide range of sectors, including coastal and offshore engineering, marine renewable energy and shipping. The state of the art in wave prediction is called spectral wave modelling and is based on a phase-averaged, spectral description of the sea-surface elevation. The governing equation, called the action balance equation, is five-dimensional and describes the generation, propagation and evolution of action density in geographic space, spectral space and time. Due to the multidimensional nature of the equation the feasible resolutions are restricted by the computational costs. The aim of this work is to propose schemes which can increase the range of possible resolutions in spectral wave modelling, with the use of adaptivity in space and angle. Thus, this work focuses on the development of an unstructured, adaptive finite element spectral wave model (Fluidity-SW). A sub-grid scale model for the spatial discretisation is used, which retains the stability of discontinuous systems, with continuous degrees of freedom. Then, a new framework for angular adaptivity is developed, with results in dynamic angular and spatial anisotropy of the angular mesh. Finally a spatially h−adaptive scheme is implemented, which can dynamically treat the spatial gradients of the solution fields. The resulting framework is thoroughly verified and validated in a wide range of test cases and realistic scenarios, against analytical solutions, wave measurements and the results obtained with the widely used SWAN model. Thus, the overall ability of the code to simulate surface gravity wind-waves in fixed and adaptive spatial and angular meshes is demonstrated.
8
Bates, Paul David. "Finite element modelling of floodplain inundation". Thesis, University of Bristol, 1992. http://hdl.handle.net/1983/edf8eb51-e701-4c18-a482-7f0dac785f84.
Testo completoAbstract (sommario):
Flood inundation phenomena typically occur over reach lengths of 5- 30 km and incorporate a number of complex flow mechanisms. These include a momentum transfer between the main channel and floodplain and turbulent mixing caused by the delivery of water to the floodplain from the channela nd its subsequenrte turn. However, currently available one dimensional schemes applicable at scales appropriate to floodplain inundation processes cannot effectively simulate such processes. This is due to both an incomplete description of the flow physics and a failure to treat floodplain areas in realistic fashion. More complex two and three dimensional models, which have these capabilities, have only been applied over very short reach lengths (c. 0.5 -2 km) and rarely to compound meandering channels. This thesis reports on the further development of a generalized two dimensional, finite element code (RMA-2) to meet this research need. This is achieved via a series of modifications to the numerical model and to the physical representation by finite elements that enable river channel/floodplain flow at the long reach scale to be effectively simulated. Evaluationo f the enhancedR MA-2 schemef ollows a three stages trategy. Firstly, the assumptions underlying the scheme are examined to identify possible inconsistencies. Secondly, tests are undertaken to assess whether the specified physical model has been correctly transferred into computer code. This is achieved via sensitivity analysis, examination of numerical stability issues and investigation of model response to abnormal parameterization. Thirdly, model predictions of flow field information are compared to observed field data in the context of an application of the enhanced model to an 11 km reach of the River Culm, Devon, UK. Results from this evaluation process indicate that the enhanced RMA-2 model is capable of simulating main channel/floodplain momentum transfer and the two dimensionale ffects associatedw ith compoundm eanderingc hannelsa t this scale. Model simulations compare favourably to field data, both for specific cross sections and over the entire mesh. Finally, extension of this core modelling capability is begun via the development of two model application scenarios. These demonstrate the likely utility of the enhanceds chemef or the assessmenotf flood risk and the investigationo f sediment depositionp rocessesin floodplain systems.
9
Swarbrick, Sean James. "Finite element simulation of viscoelastic flow". Thesis, Teesside University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278423.
Testo completo
10
Kukula, S. J. "Finite element modelling of delaminations in composites". Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/7711.
Testo completo
11
Power, Philip William. "Error measures for finite element ocean modelling". Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485614.
Testo completoAbstract (sommario):
This thesis presents goal-based error measures and applies them, via appropriate metric tensors, to the adaptation of three dimensional anisotropic tetrahedral finite element meshes for a range of oceanographic modelling problems. The overall aim of this work is to produce error measures which are able to resolve the flow features of an ocean over a wide range of spatial and temporal scales simultaneously. For example, western boundary currents, the Antarctic Circumpolar Current (ACC), equatorial jets, meddies (mid-latitude eddies) and Open Ocean Deep Convection. Conventional numerical ocean models generally use static meshes. The use of dynamically-adaptive meshes has many potential advantages but needs to be guided by an error measure. Mesh quality is gauged with respect to the metric tensor which embodies the error measure, such that an ideal element has sides of unit length when measured with respect to this metric tensor. The result is meshes in which each finite element node has approximately equal (subject to certain boundary conforming constraints and the performance of the mesh optimization procedure)'error contribution. Error measures are formulated which measure the error contribution of each solution variable to an overall goal, which encompasses important features of the flow structure and is embodied in an integral form, e.g. the integral of the solution in a small region of the domain of interest. The sensitivity of the functional, taken with respect to the solution variables, is used as the basis from which error measures are derived. The error measures then act to predict those areas of the domain where resolution should be changed and lead to the solution of so-called forward and adjoint (backward) problems. Focus is given to developing relatively simple methods that refer to information readily accessible from the discretized equation sets and do not explicitly use equation residuals.
12
Piefort, Vincent. "Finite element modelling of piezoelectric active structures". Doctoral thesis, Universite Libre de Bruxelles, 2001. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211645.
Testo completo
13
Pamudji, Rahardjo A. "Finite element modelling of river bed dynamics". Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638405.
Testo completoAbstract (sommario):
Numerical modelling of Bed Dynamics in 1-D and 2-D poblems using the Two-Step Taylor Galerkin Finite Element scheme has been proposed. It has been shown that the scheme is capable of handling the coupled system that exists between unsteady hydrodynamics and a mobile bed. Fully coupled codes have been developed with an option to semi-couple the system while maintaining numerical accuracy for both the hydrodynamics and the bed level change. The semi-coupled extension enables the modelling of the hydrodynamics and the bed level change with different time steps. Coupling is maintained at common time terminals and, or, with separate computational meshes, where coupling is achieved by means of interpolation between the meshes. The Two-Step Taylor Galerkin scheme has been verified extensively for hydraulic problems related to bed dynamics, especially the interaction of progressive waves and the development of steady state flow in channels. Treatment of the boundary condition allowing waves to leave the computational domain both for the fluid and the bed have been proposed and work well. For the hydrodynamic equations, it is also demonstrated that the boundary treatment is capable of absorbing outgoing waves while incoming waves are simultaneously prescribed. These treatments are based on an examination of the characteristics of the bed dynamic system. The results of the analysis can be used to approximate the Reimann invariant vector of the bed dynamic system and this is especially useful when the fully coupled method is applied. A Von Neumann linear stability analysis of the 1-D Taylor-Galerkin scheme for a system including a source term is presented. The anlaysis is based on the graphical interpretation of an Argand Diagram representation for the amplification factor. It is found that the presence of a strong source term may reduce the time step limit.
14
Kabir, Saiful. "Finite element modelling of photonic crystal fibres". Thesis, City University London, 2007. http://openaccess.city.ac.uk/8592/.
Testo completoAbstract (sommario):
Photonic crystal fibre (PCF), a new kind of optical fibre, has many air-holes in their cross-section and has potential applications to new optical communication systems. The main objective of this research is the modelling of photonic crystal fibre to identify the fundamental and higher order quasi-TE and TM modes with square, ,rectangular and circular air holes in a square and hexagonal matrix, by using a rigorous full-vectorial H-field based finite element method (FEM). Besides the modal solutions of the effective indices, mode field profiles, spot sizes, modal hybridness, polarization beat length and group velocity dispersion values for equal and unequal air holes; research was carried out to optimize and design highly birefringent PCF. The variation of modal birefringence is shown through the effect of hole diameters, air hole arrangement, structural asymmetry, operating wavelength, and pitch-distance. Birefringence was enhanced by breaking the structural symmetry and this was verified by using unequal air holes. The diameter of two air holes and four air holes in the first ring was changed to break the rotational symmetry and a comparison between the two designs is made in this work. In this work, highly birefringent PCF is designed with higher operating wavelength, larger d2/A value, lower pitch length for a given structural asymmetry. It is identified that birefringence value increases rapidly when d2 is much larger than d. At lower pitch value, one of the highest birefringence values reported so far at wavelertgth of 1.55 J.Jm for an asymmetric PCF using circular air holes. A single polarization guide PCF structure is also achieved. In this study, it has been identified that for fixed d/A and d2/A value, as operating wavelength is increased, birefringence increases significantly. It can also be identified that for higher d/A values, birefringence changes rapidly with A as their corresponding cutoff condition also approaches. One important validation of this work is the existence of modal birefringence for PCF with six-fold rotational symmetry. It is shown that birefringence value of a simple PCF incorporating circular holes but of different diameters is high compared to polarization maintaining Panda or Bow-tie fibres. This research also aims to investigate the modal leakage losses of PCF, by using a semi-vectorial beam propagation method (BPM) based on the versatile FEM. The robust perfectly matched layer (PML) boundary condition has been introduced to the modal solution approach. The effects of d2/A, operating wavelength and number of air holes have been thoroughly detailed and explained. In this study, it has been identified that the confinement loss decreases significantly with the increased number of rings, lower operating wavelength and lower d2/A value. For special case, PCF with large spot-size provides higher leakage loss.
15
Hiett, Ben. "Photonic crystal modelling using finite element analysis". Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274031.
Testo completo
16
Abosaf, Mohamed. "Finite element modelling of multi-point forming". Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8012/.
Testo completoAbstract (sommario):
The general aim of this study is to develop a 3-D FE model for multi-point forming dies using ABAQUS software and use this to study the effect of process parameters related to tool geometry such as radius of curvature of deformed parts, pin size, elastic cushion thickness and coefficient of friction. Doubly curved parts will be investigated in this research. The material properties for two blanks were determined for use as required parameters for the simulation analysis. Finite element models of the doubly curved forming process were developed and validated for two materials: DC05 steel sheet and 5251-0 aluminium sheet. The mesh sensitivity, reliability of the numerical model, suitable blank holder force, effect of gap distance between punch and blank holder on the thickness distribution, and the comer defect were studied. A parametric study was carried to investigate the effect of certain parameters on the deviation from target shape, wrinkling, and thickness variation. A test rig for the experimental work was designed and manufactured. In parallel, experiments with the forming of doubly curved parts were conducted to validate the simulation results. The numerical analysis results were compared with the experimental results and good agreement was generally found. The methodology developed in this research could help to build a reliable numerical model to predict the common defects in sheet forming using the multi-point forming process.
17
Mayne, David A. "Finite element modelling of cohesive sediment transport". Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/15300.
Testo completoAbstract (sommario):
The movement of cohesive sediment is of great importance in many coastal and estuarine engineering problems. Navigation channels often used to be dredged to maintain navigable depths, allowing for the effect of a harbour or wharf on the local sediment transport regime. Contaminants are readily absorbed by silt and clay particles, causing a range of water quality problems. This thesis describes the development and testing of a finite element program to model cohesive sediment transport. The program solves the coupled Navier-Stokes and scalar-transport equations along with several complex numerical algorithms for settling velocity, flocculation, non-Newtonian flow and turbulence. The program also uses h-adaptivity and unstructured mesh generation to capture important flow features. The program is benchmarked against the thermally driven cavity problem, producing results that compare well with existing solutions without any special scheme for advection dominated flow. This is possible by modelling the transient problem using h-adaptivity. The programme is also applied to realistic cohesive sediment transport problems. It predicts the formation of a hindered settling layer and uses h-adaptivity to capture sharp density interfaces. It also solves settling of dredged material onto a inclined bed and non-Newtonian flow in a race-track flume. The program produces results that compare well with experimental data. The h-adaptive finite element method is found to be a very successful in modelling the transport of cohesive sediment and its associated physical processes.
18
Conradie, Johan. "Finite Element Modelling of Off-Road Tyres". Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/45957.
Testo completoAbstract (sommario):
Most tyre models developed to date require a fair amount of data before an accurate representation of the tyre can be obtained. This study entails the development of a simplified, yet accurate, non-linear Finite Element (FE) model of an “off-road” tyre to study the behaviour of the tyre due to radial loading conditions. The study aims to develop a FE tyre model that can solve fast and be accurate enough to be used in multibody dynamic vehicle simulations. A model that is less complex than conventional detailed FE models is developed.
The work explores the use of superimposed finite elements to model the varying stiffness in the respective orthogonal directions of the sidewall and tread of the tyre. Non-linear elements defined by Neo-Hookean or Ogden models and elements with different linear orthogonal stiffnesses are superimposed onto each other to simulate the global material properties of the tread and the sidewall of the tyre investigated.
The geometry of the tyre studied was measured experimentally using laser displacement transducers and digital image correlation techniques. Material properties of segments of the tyre were obtained by performing tensile tests on samples. Since the rubber slipped against the clamps during the experiment, deformation of the segments was also measured using digital image correlation. These geometrical and material properties were used as input to develop a finite element model of an “off-road” tyre.
Measurements were conducted using laser displacement transducers, load cells mounted to actuators, etc. to obtain accurate sidewall deformation profiles and global radial load vs. displacement curves for different radial loading conditions. The data obtained from the results was used to validate the tyre model developed.
Numerous analyses are performed with different combinations of moduli of elasticity in the respective orthogonal directions of the sidewall stiffness and the tread to investigate its influence on the global behaviour of the tyre model.
The main focus of the project was to develop a tyre model from data obtained from laser and photogrammetry measurements in a laboratory that accurately represents tyre behaviour due to radial forces. A finite element model that can simulate the effect of radial forced and obstacles on a tyre was developed. The use of two subsets of elements, superimposed onto each other to simulate global material properties of the rubbers, steel wires, polyester and nylon threads, was investigated.
The combination of material properties that gave the best fit for all the load cases investigated were determined. The finite element model correlated well with the load vs. displacement graphs and sidewall displacement profiles determined experimentally.
The solving time is still fairly high and is still not quite suitable for real-time dynamic simulation. However, it solves faster than more complex tyre models where details of steel wires, etc. are included in the model.
For future studies it is recommended that different element types be investigated in the tyre model.
The study proves that equivalent material properties can be used to simulate the composite properties of the materials in tyres. Most tyres can be divided into a few regions that each has its own material structure right through the region. These regions can be characterized by simple tests and the input can be used as a first estimation of the tyre’s material properties for the model.
Accurate validation criteria should be used to validate the tyre model if time does not allow for excessive testing of the material properties of all the rubber, steel wires, polyester threads, etc. Geometric displacement data at various loading conditions can be used for validation of the tyre model.
The model developed can be used to investigate the effect of different stiffnesses and other material changes in the sidewall or tread of a tyre. Useful insight can be obtained from the finite element model developed for dynamic simulation where the force vs. global displacement data is important.Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Mechanical and Aeronautical Engineering
MEng
Unrestricted
19
Oliveira, Ana Carolina Carius de. "Hierarchical modelling for the heat equation in a heterogeneous". Laboratório Nacional de Computação Científica, 2006. http://www.lncc.br/tdmc/tde_busca/arquivo.php?codArquivo=68.
Testo completoAbstract (sommario):
In this dissertation, we study the stationary heat equation in a heterogeneous tridimensional plate, using a "dimension reduction" techinique called hierarchical modelling and we generate model the original problem in a two-dimensional domain. To estimate the error modelling, we develop an asymptotic expansion for the original problem solution and for the aproximate solution. Comparing both solutions with their own asymptotic expansions, we obtain an estimative of the error modelling. We perform some computational experiments, using the Residual Free Bubbles (RFB) Method and the Multiscale Finite Element Method for the diffusion problem and for the diffusion-reaction problem in a two-dimensional domain, with small parameters. Finally, we extend the numeric solutions found the original tridimensional problem.Neste trabalho, estudamos a equação do calor estacionária em uma placa heterogênea tridimensional. Para a modelagem deste problema, utilizamos uma técnica de redução de dimensão conhecida por Modelagem Hierárquica. Desta forma, geramos um modelo para o problema original em um domínio bidimensional. Com o objetivo de estimar o erro de modelagem, desenvolvemos a expansão assintótica da solução do problema original e da solução aproximada. Comparando as soluções com suas respectivas expansões assintóticas, obtemos uma estimativa para o erro de modelagem. Realizamos alguns experimentos computacionais, desenvolvendo o método Residual Free Bubbles (RFB) e o método de Elementos Finitos Multiescala (MEFM) para o problema de difusão e para o problema de difusão-reação em um domínio bidimensional, com parâmetros pequenos. Com base nestes experimentos, encontramos algumas soluções numéricas para o problema da placa tridimensional.
20
Unosson, Mattias. "On failure modelling in finite element analysis : material imperfections and element erosion". Doctoral thesis, Linköping : Linköpings universitet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-4679.
Testo completo
21
Di, Meglio Alberto. "Finite element-boundary elements modelling of acoustic scattering from viscoelastic anechoic structures". Thesis, University of Birmingham, 2000. http://etheses.bham.ac.uk//id/eprint/488/.
Testo completoAbstract (sommario):
This research work focuses on the analysis of multi-layered, anechoic tiles for underwater applications, especially in the field of communications. It is firstly shown how the sound absorbing properties of viscoelastic materials can be modified and enhanced by the proper use of fillers, such as lead oxide and mica. Successively, a new method for identifying the viscoelastic frequency-dependent properties of such materials from experimental data is presented. The method is based on a variational method analogous to the Hamilton Principle. It allows calculating hard-to-find properties such as the complex viscoelastic response functions and the complex Poisson ratio. After the materials properties have been determined, it is shown how they can be incorporated into the combined finite-element-boundary element method to provide accurate numerical solutions to the acoustic scattering problem. A tile made of three layers, a reflecting aluminium layer, an absorbing butyl rubber layer and a matching layer made of a regular grid of polyurethane cones is finally analysed in several scattering and geometrical configurations. The scattering patterns produced by a plane wave incident on the tile are plotted, discussed and compared with experimental data obtained from in-tank scattering measurements of a model tile.
22
Runnemalm, Henrik. "Efficient finite element modelling and simulation of welding". Doctoral thesis, Luleå, 1999. http://epubl.luth.se/1402-1544/1999/20/index.html.
Testo completo
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Elkhouri, Nidal. "Finite-element modelling of the gerbil middle ear". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98957.
Testo completoAbstract (sommario):
Hearing loss is the third leading chronic disability after arthritis and hypertension, and the most frequent birth defect. Non-invasive diagnoses and middle-ear prostheses are often unsatisfactory, partly because of a lack of understanding of middle-ear mechanics. The focus of this thesis is to develop a 3-D finite-element model to quantify the mechanics of the gerbil middle ear. An MRM dataset with a voxel size of 45 &mgr;m, and an x-ray micro-CT dataset with a voxel size of 5 um, supplemented by histological images, are the basis for 3-D reconstruction and finite-element mesh generation. The eardrum model is based on moire shape measurements. The material properties of all the structures in the model are based on a priori estimates from the literature.The behaviour of the finite-element model in response to a static pressure of 1 Pa is analyzed. Overall, the model demonstrates good agreement with low-frequency experimental data. For example, (1) the ossicular ratio is found to be about 3.5; (2) maximum footplate displacements are about 34.2 run +/- 0.04 nm; (3) the motion of the stapes is predominantly piston-like; (4) the displacement pattern of the eardrum shows two points of maximum displacements, one in the posterior region and one in the anterior region. The results also include a series of sensitivity tests to evaluate the significance of the different parameters in the finite-element model. Finally, in an attempt to understand how the overall middle-ear mechanics is influenced by the anterior mallear ligament and the posterior incudal ligament, results are shown for cutting or stiffening the ligaments.
24
Mikhael, Chadia. "Finite-element modelling of the human middle ear". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82619.
Testo completoAbstract (sommario):
Most models of the middle ear are based on oversimplified geometries and iterative material-property fitting to experimental data which may yield physiologically incorrect estimates.The aim of our work was to build an accurate human middle-ear finite-element model that is based on accurate geometry and a priori material-property estimates.
A human temporal-bone specimen was obtained for which the middle-ear response had been measured by means of laser Doppler vibrometry. High-resolution micro-computed tomography data for the specimen were used for accurately defining structure geometry. This model comprises the tympanic membrane, the ossicles, two joints, and four ligaments. We assigned estimated material-property values derived from the literature.
We compared the response of our model with those of other human middle-ear models, and with experimental measurements including those from the same ear. Sensitivity of the model to several of its parameters was also investigated.
25
Thomas, Sadiq. "Comprehensive finite element modelling of electromagnetic acoustic transducers". Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509874.
Testo completo
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Mohd, Ihsan A. K. A. "Powder compaction, finite element modelling and experimental validation". Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638216.
Testo completoAbstract (sommario):
In the modelling of powder compaction, the behaviour of powders is assumed to be rate-independent elastoplastic, and the process may be described by a large displacement based finite element formulation. Three constitutive relationships to describe the mechanical behaviour of the powders were examined, namely a Mohr-Coulomb yield surface, an elliptical cap yield surface and a combined yield surface model. Of all the models tested, an elliptical cap was shown to be the most appropriate for the compaction phase. An incremental elastoplastic material model was used to simulate the relaxation phase and a plasticity theory for friction was employed in the treatment of the powder-tooling interface for the ejection phase. The model was extended to provide a decoupled thermal solution where the plastic and friction work during the compaction process was considered as sources of energy and the consequent temperature fields were calculated. In parallel, a series of experimental studies were carried out in the laboratory and factory for a plain bush and multi-level component. The parameters which were measured were force, displacement and density. The friction coefficient was derived from the plain bush compaction and shear yield tests were conducted to establish the shear behaviour of the powders. The powders tested are typical of those used in industrial applications. The results detailed information concerning the behaviour of the powders in terms of their material parameters for modelling and in validation of the numerical simulation work. Finally the numerical simulation results were validated against the experimental data to gain confidence in the model developed. The comparisons showed good agreement. The versatility of the simulation allows the complete representation of the green compact generation cycle.
27
Trigo, Teixeira A. A. "Finite element modelling of hydrodynamics in coastal zones". Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639260.
Testo completoAbstract (sommario):
A Finite Element Model is developed and implemented in order to study the hydrodynamics of coastal zones. The Shallow Water Equations for well mixed waters are derived integrating the Reynolds Equations along the water depth, using the surface and bottom stress laws, and taking into account the geostrophic acceleration. The system of equations is derived in conservation form. The Euler-Taylor-Galerkin scheme is used to discretize the system of equations, with the temporal discretization preceding the spatial discretization. In the process, triangular elements are used, taking advantage of exact quadrature laws and of the meshing flexibility that such elements provide. Marching in time is done explicitly and stability controlled by the smallest element present in the grid. Analytical solutions for the linearized shallow water equations are revisited and used to assess the model's performance. A rectangular and a polar basin with constant bathymetry and closed at one end are used to test the model. Two algorithms are presented for mesh generation, one generates unstructured meshes and the other structured meshes. A methodology is devised in order to blend both types of meshes to produce an unstructured-structured hybrid mesh and the final connectivity matrix from the contribution of each individual mesh. Particular emphasis is put on the bathymetry modelling process. A new methodology is developed to obtain the information from hydrographic charts converting it into digital format using a digitizer device driver, written with the specific needs of the problem at hand. A Delaunay triangular irregular network is used to encode bathymetric information. The bathymetric information is then automatically transferred, superimposing the computational grid to the triangular irregular network, solving a point-in-triangulation query and interpolating linearly from the background grid. Two case studies are presented simulating tidal flow.
28
Herbert, Rolf China. "Modelling insect wings using the finite element method". Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370012.
Testo completo
29
Rabbani, Khawar. "Material behaviour modelling for finite element crash simulation". Thesis, Birmingham City University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430363.
Testo completo
30
Hanspal, Navraj S. "Finite element modelling of high performance aeronautical filters". Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/14001.
Testo completoAbstract (sommario):
The primary aim of this study is to develop and validate a computer model for the design of pleated cartridge filters. Mathematical modelling of incompressible creeping flow and low permeability Darcy flow are well established and a number of reliable schemes for the simulation of these regimes are available in the literature. In the context of the present studies a computer model for modelling of combined Stokes/Darcy flows encountered in pleated cartridge filters has been developed. A two-dimensional simulation code that can model fluid hydrodynamics in permeable media as in dead-end pleated cartridge filters has been developed in FORTRAN. The developed code named as ACFAMP- Aircraft Cartridge Filter Analysis Modelling Program has been used to evaluate the performance and design of pleated cartridge filter elements. The governing equations of the flow model can be well represented by the Continuity, Stokes and Darcy equations respectively. Viscosity variations and non-Newtonian effects have been introduced to model the behaviour of shear-thickening fluids used in aircraft hydraulic circuits. The governing equations of the flow model are solved by using a weighted residuals finite element method. Two separate modelling approaches have been adopted in the model development. The first approach is based on modelling of flow through porous media by employing a slightly compressible form of continuity equation utilising nine-noded Lagrangian elements for domain discretisation in conjunction with a U-V -P finite element scheme. The second strategy is based on modelling of coupled Free/Porous regimes making the model industrially complaint. This scheme utilises the stabilised C0 continuous Taylor-Hood element, which generates stable solutions for incompressible flows without any problems of numerical locking. Initial numerical experiments were based on simple geometries and the complexity of the geometries was finally extended to model the pleated cartridge filters. A permeability model that interprets medium compression effects and which is based on data obtained from flat sheets of the filter material used in the fabrication of the filter cartridge is incorporated within the main model. During pleating, bending and creasing the medium deforms and leads to a loss of permeability and/or effective filtering area results. The combined effects of compression and reduction in filtration area cause deviations from Darcy's law. The effects of medium compression, pleat deformation and pleat crowding have also been analysed. The present work is directed towards the prediction of accurate values of compression factors and percentage losses in the filtration area, which assist in designing pleated cartridge filter elements. The simulated results have been compared against the experimental data for purposes of validation.
31
Arabshahi, Saeed. "Finite element idealisation in a solid modelling environment". Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305391.
Testo completo
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El-Shawish, Jamal M. "Investigation of variable transformers by finite element modelling". Thesis, City University London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412619.
Testo completo
33
Rui, Yi. "Finite element modelling of thermal piles and walls". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708657.
Testo completo
34
Cotton, John. "Finite element modelling of concrete at elevated temperatures". Thesis, Cardiff University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630477.
Testo completoAbstract (sommario):
This thesis presents a new plastic damage constitutive model for concrete subjected to elevated temperatures. The proposed Cardiff Concrete Temperature (CARCOT) model combines the original theory presented by Lubliner et al. (1989) with newly derived temperature dependent material parameters developed for normal and high strength concrete. The temperature dependent material parameters have been obtained from a laboratory based experimental study conducted by the author. The CARCOT model has been implemented into the finite element code LUSAS after a successful validation programme using a single point constitutive driver. The overall aim of the CARCOT model is to accurately represent the non-linear behaviour of concrete in both tension and compression for temperatures up to 600· C with a single set of constitutive equations. This is achieved by using the Lubliner yield surface to asses the current stress level and the Mohr Coulomb surface to control the change in volume caused by plastic deformation, i.e. a non associated flow rule is adopted. The proposed model also incorporates the comer indicators proposed by Crisfield (1987) to assess the comers present on the yield surface. Depending on the current stress level and its position on the yield surface a multi vector return algorithm is employed to bring the stress increment back to the yield surface. The thermal damage mechanisms are dealt with in a staged approach in which the temperature damage effects are accounted for at the start of every load increment of finite element computations by a subroutine incorporating the temperature dependent functions.
35
Cronje, M. "Finite element modelling of shielded metal arc welding". Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/2649.
Testo completoAbstract (sommario):
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005.This study involved the modelling and verification of the Shielded Metal Arc Welding of mild steel with the focus on displacement and temperature distribution prediction of welded plates. The project was divided into three phases namely; the literature survey into finite element modelling of welding processes, the modelling of a welding process and verification of the modelling with experimental results. A working welding model was created using a commercial finite element software package with the capabilities to model welding processes. The welding model was systematically developed from a two-dimensional model into a threedimensional full physics process model. Experimental measured welding heat input parameters were applied in the model, temperature dependent material properties were applied and actual structural restraints from the experiments were modelled. Displacement and temperature distributions were measured on mild steel plates welded with the Shielded Metal Arc Welding process. The plate temperature was measured at various locations with K-type thermocouples spot welded onto the plates. Plate deformation was measured at various stages of the manufacturing process. Tendencies in plate displacement were investigated with a change in certain welding parameters. The finite element model was verified and good correlations were found, especially for the temperature distribution in the welded plates.
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Elmasoudi, Solayman. "Finite element modelling of a pedestrian impact dummy". Thesis, KTH, Neuronik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183557.
Testo completo
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Kormendy, Imre, e Mustafa Muwaili. "Timber Shear Wall Analysis : Parameterized Finite Element Modelling". Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-77199.
Testo completoAbstract (sommario):
This paper investigates the linear elastic behavior of timber shear walls under monotonic prescribed displacement. ABAQUS© 16.4-5, is a numerical finite element software used as the primary analysis methodology. Parameterized models are created for two shear wall specimens of different geometry concerning door and window configurations. The shear walls are simulated as solid timber framing which is mechanically connected to gypsum sheathing board through fasteners. The primary findings are the linear elastic shear force distribution of the mechanical joints. Additionally, deformations and reaction forces of the shear walls are determined. The overall horizontal shear wall behavior of each specific wall was also studied in the presence of door and window openings. The simulations indicate there is a clear deformation difference in the behaviors of the two shear walls. Furthermore, the highest shear force values of the fasteners are located around the corners of the openings. The findings are supported by other researcher’s experiments and analytical tests, timber shear wall theory and Eurocode design requirements.
38
Cheng, Yew Bie. "Finite element modelling and optimization of solenoid actuators". Thesis, University of Southampton, 1994. https://eprints.soton.ac.uk/47958/.
Testo completoAbstract (sommario):
This thesis is concerned with the application of electromagnetic finite element (FE) analysis, using a general purpose package, OPERA-2d, and optimization techniques to the design of solenoid actuators used in hydraulic control valves. Different methods of force calculations are reviewed, including Maxwell Stress Tensor (MST), multi-solution Virtual Work Principle (VWP), and single-solution based VWP methods. While the MST method enables the calculation of force using a single solution and provides the distribution of force transmitted across various sections of the integration surface enclosing the armature of the actuator, it requires a finer mesh for accurate force calculation compared to VWP. There is no advantage of MST and single-solution VWP methods over multi-solution VWP technique in computing force-displacement characteristics of a d.c. solenoid actuator with constant current source because in all methods a set of FE solutions has to be found anyway at several armature displacements. However, for solenoids where current varies with displacement, e.g. a.c. solenoids, the multi-solution VWP requires a large number of solutions. In this thesis both multi-solution VWP and MST methods are used. Implementation of single-solution methods is not possible using the current version of OPERA-2d. To understand the effect of armature geometry on the shape of the force-displacement characteristic, a parametric study using OPERA-2d has been conducted. A customized design shell environment (CusOP) is developed to aid and simplify the repetitive process of using OPERA-2d. The results of this study were used to design a new proportional solenoid actuator, which was built and tested. It was found that more desirable force displacement characteristics have indeed been achieved. A comprehensive review of available optimization techniques is presented. The most promising of these techniques, including Broyden-Fletcher-Goldfarb-Shanno (BFGS) variable metric procedure, Nelder-Mead simplex method, Gauss-Newton method, Levenberg-Marquardt procedure, Trust region method and Simulated Annealing, have been extensively evaluated by comparing their performance (in terms of number of function evaluations) in the optimization of eighteen general unconstrained problems and eighteen nonlinear least-squares problems. The Levenberg-Marquardt procedure shows clear advantage, displaying consistent performance over the range of problems tested. This method which can only find local optima is preferred to the Simulated Annealing global optimization method, because it does not require too many function calls. Finding local optima is usually sufficient in optimization of solenoid actuators and, therefore, it is chosen for this application. A program called Electromechanical Actuator Modelling and Optimization (EAMON) has been created for the implementation of constrained automated optimization by interfacing the Levenberg-Marquardt technique to OPERA-2d. The program has been used successfully to optimize the design of a proportional solenoid actuator to produce a specified force-displacement characteristic. It has also been used in optimizing an actuator, which was subsequently successfully tested, where the area under the force-displacement characteristic is maximized. The research demonstrates the advantages of using FE modelling and optimization techniques to improve the performance of practical solenoid actuators.
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Saksono, Prihambodo Hendro. "On finite element modelling of surface tension phenomena". Thesis, Swansea University, 2002. https://cronfa.swan.ac.uk/Record/cronfa42392.
Testo completoAbstract (sommario):
The objective of this work is to develop a computational framework for modelling the motion of liquid phase between moving particles associated with the processing of complex multiphase materials. The liquid phase may be present at various levels of saturation and necessarily includes numerous and irregular free surfaces. In this kind of situation the surface tension is dominant and governs the interparticle motion that plays a fundamental role during material processing. This work focuses on surface tension modelling using the finite element method. Two issues related to the modelling of surface tension are addressed in this thesis, the first one is the development of a finite element procedure capable of modelling accurately the motion of the free surface boundaries between the gas and liquid phases. The second issue is finite element modelling of surface tension at such boundaries. The finite element formulation is based on the use of the incremental flow formulation of the Lagrangian form of the initial boundary value problem governing the free surface flow. The incompressibility constraint associated with the Newtonian fluid employed in this work is imposed using the penalty method. With regard to the surface tension model, the constitutive model commonly known as the Laplace-Young equation is employed. In the Lagrangian framework the surface tension formulation emerges naturally through the weak form of the Laplace-Young equation and the use of the surface divergence theorem reduces the continuity requirement across the element boundary from to C[1] to C[0]. The performance of the finite element model of surface tension is validated by means of numerical examples for both equilibrium and dynamic cases. The finite element results are compared against both analytical solutions and experimental results.
40
Li, Chenfeng. "Stochastic finite element modelling of elementary random media". Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42770.
Testo completoAbstract (sommario):
Following a stochastic approach, this thesis presents a numerical framework for elastostatics of random media. Firstly, after a mathematically rigorous investigation of the popular white noise model in an engineering context, the smooth spatial stochastic dependence between material properties is identified as a fundamental feature of practical random media. Based on the recognition of the probabilistic essence of practical random media and driven by engineering simulation requirements, a comprehensive random medium model, namely elementary random media (ERM), is consequently defined and its macro-scale properties including stationarity, smoothness and principles for material measurements are systematically explored. Moreover, an explicit representation scheme, namely the Fourier-Karhunen-Loeve (F-K-L) representation, is developed for the general elastic tensor of ERM by combining the spectral representation theory of wide-sense stationary stochastic fields and the standard dimensionality reduction technology of principal component analysis. Then, based on the concept of ERM and the F-K-L representation for its random elastic tensor, the stochastic partial differential equations regarding elastostatics of random media are formulated and further discretized, in a similar fashion as for the standard finite element method, to obtain a stochastic system of linear algebraic equations. For the solution of the resulting stochastic linear algebraic system, two different numerical techniques, i.e. the joint diagonalization solution strategy and the directed Monte Carlo simulation strategy, are developed. Original contributions include the theoretical analysis of practical random medium modelling, establishment of the ERM model and its F-K-L representation, and development of the numerical solvers for the stochastic linear algebraic system. In particular, for computational challenges arising from the proposed framework, two novel numerical algorithms are developed: (a) a quadrature algorithm for multidimensional oscillatory functions, which reduces the computational cost of the F-K-L representation by up to several orders of magnitude; and (b) a Jacobi-like joint diagonalization solution method for relatively small mesh structures, which can effectively solve the associated stochastic linear algebraic system with a large number of random variables.
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Qureshi, Jawed Qureshi. "Finite element modelling of steel-concrete composite structures". Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/21112/.
Testo completoAbstract (sommario):
The main objective of this research is to contribute to the knowledge and understanding of the behaviour of the headed stud shear connector in composite beams with trapezoidal profiled metal decking laid perpendicular to the axis of the beam through experimental and numerical studies. Push tests are used to study the behaviour of composite beams. A three-dimensional finite element model of the push test is developed using the general purpose finite element program ABAQUS and the push test is analysed using different concrete material models, and analysis procedures. The Concrete Damaged Plasticity model with dynamic explicit analysis procedure is found to have matched with experimental results very well in terms of the shear connector resistance, load-slip behaviour and failure mechanisms. The post-failure behaviour of the push test, which has not been modelled in the past, is accurately predicted in this study with the help of this modelling technique. The experimental investigation is conducted with a single-sided horizontal push test arrangement to study the influence of various parameters such as normal load, number of shear studs, reinforcement bar at the bottom trough, number of layers of mesh, position of mesh, position of normalload and various push test arrangements. To assess the accuracy and reliability of the developed finite element model, it is validated against push test experiments conducted in this study and variety of push tests carried out by other authors with different steel decks and shear stud dimensions, positions of the shear stud within a rib and push test arrangements. The results obtained from the finite element analysis showed excellent agreement with the experimental studies. The validated finite element model is used in a parametric study to investigate the effect of shear stud position, thickness of the profiled sheeting, shear connector spacing and staggering of shear studs on the performance of the shear stud. The results of the parametric study are evaluated and findings are used to propose the design equations for shear connector resistance taking into account the position of the shear stud and thickness of the profiled sheeting. The coefficient of correlation between experimental and predicted results is nearly equal to one, which indicates that the predicted results are accurate, and the proposed equations are suitable for future predictions.
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Ljungberg, Björn. "3D Finite Element Modelling of ICRH in JET". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-253263.
Testo completoAbstract (sommario):
This master's thesis assesses the possibility of using the nite element method to solve the electromagneticwave equation in a fusion plasma in 3D. In particular, the frequency is chosen to match that of ioncyclotron resonance heating in the fusion experiment JET. In this work, a brief introduction on fusion isgiven, followed by an explanation of the damping process in a plasma. A projection of the 3D wave eldonto a poloidal plane is compared to the 2D wave eld produced by the code FEMIC for validation ofthe developed 3D code. The comparison was done with good results.The power spectrum and coupling resistance per toroidal mode obtained from the 3D model arealso compared to the corresponding quantities obtained from an analytical slab model. Though somediscrepancies can be seen near the toroidal mode number n = 0 and for higher mode numbers (jnj > 70),the appearance of the power spectra are similar. The dierence near n = 0 is attributed to inducedcurrents in the reactor wall, whereas for higher mode numbers, the dierence is likely due to bad resolution.The induced currents in the wall causes singularities in the chosen model of the coupling resistance. Thisproduces unreliable predictions of the coupling resistance.Denna masteruppsats utvärderar möjligheten att använda finita elementmetoden till att lösa den elektro-magnetiska vågekvationen i ett fusionsplasma i 3D. Speciellt väljs frekvensen för att matcha frekvensen för uppvärmning genom joncyklotronresonans i fusionsexperimentet JET. I detta arbete ges en översiktlig introduktion till fusion, åtföljd av en förklaring av dämpningsprocessen i ett plasma. En projektion av 3D-vågfältet på ett poloidalt plan jämförs med 2D-vågfältet producerat av 2D-koden FEMIC för att validera den utvecklade 3D-koden. Jämförelsen gjordes med gott resultat.| |Effektspektrumet och kopplingsresistansen per toroidal mod från 3D-modellen jämförs också med motsvarande storheter från en analytisk 1D-modell. Trots att vissa skillnader kan ses nära det toroidala modtalet n = 0 och för högre modtal ( n > 70), är utseendet på effektspektrumen lika. Skillnaden nära n = 0 tillskrivs de inducerade strömmarna i reaktorväggen, medan för högre modtal beror skillnaden troligen på dålig upplösning. De inducerade strömmarna i väggen ger upphov till singulariteter i den valda modellen för kopplingsresistansen. Det resulterar i otillförlitliga värden tansen.
43
Gong, Nai-Guang. "Finite element analysis of masonry arch bridges". Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335791.
Testo completo
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Dávalos, Chargoy César Emilio. "Particle finite element methods for modelling granular material flows". Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/276169.
Testo completoAbstract (sommario):
The aim of this work is to present a new procedure for modelling industrial processes that involve granular material flows, using a numerical model based on the Particle Finite Element Method (PFEM). The numerical results herein presented show the potential of this methodology when applied to different branches of industry. Due to the phenomenological richness exhibited by granular materials, the present work will exclusively focus on the modelling of cohesionless dense granular flows.
The numerical model is based on a continuum approach in the framework of large-deformation plasticity theory. For the constitutive model, the yield function is defined in the stress space by a Drucker-Prager yield surface characterized by two constitutive parameters, the cohesion and the internal friction coefficient, and equipped with a non-associative deviatoric flow rule. This plastic flow condition is considered nearly incompressible, so the proposal is integrated in a mixed formulation with a stabilization of the pressure term via the Polynomial Pressure Projection (PPP). In order to characterize the non-linear dependency on the shear rate when flowing a visco-plastic regularization is proposed.
The numerical integration is developed within the Impl-Ex technique, which increases the robustness and reduces the iteration number, compared with a typical implicit integration scheme. The spatial discretization is addressed within the framework of the PFEM which allows treating the large deformations and motions associated to granular flows with minimal distortion of the involved finite element meshes. Since the Delaunay triangulation and the reconnection process minimize such distortion but does not ensure its elimination, a dynamic particle discretization of the domain is proposed, regularizing, in this manner, the smoothness and particle density of the mesh. Likewise, it is proposed a method that ensures conservation of material or Lagrangian surfaces by means of a boundary constraint, avoiding in this way, the geometric definition of the boundary through the classic a-shape method.
For modelling the interaction between the confinement boundaries and granular material, it is advocated for a method, based on the Contact Domain Method (CDM) that allows coupling of both domains in terms of an intermediate region connecting the potential contact surfaces by a domain of the same dimension than the contacting bodies. The constitutive model for the contact domain is posed similarly to that for the granular material, defining a correct representation of the wall friction angle.
In order to validate the numerical model, a comparison between experimental results of the spreading of a granular mass on a horizontal plane tests, and finite element predictions, is carried out. These sets of examples allow us validating the model according to the prediction of the different kinematics conditions of granular materials while spreading ¿ from a stagnant condition, while the material is at rest, to a transition to a granular flow, and back to a deposit profile.
The potential of the numerical method for the solution and optimization of industrial granular flows problems is achieved by focusing on two specific industrial applications in mining industry and pellet manufacturing: the silo discharge and the calculation of the power draw in tumbling mills. Both examples are representative when dealing with granular flows due to the presence of variations on the granular material mechanical response.El objetivo principal de este trabajo es presentar una nueva metodología para la simulación de procesos industriales que involucren flujos de materiales granulares, mediante un modelo numérico basado en el Método de Elementos Finitos de Partículas (PFEM, por sus siglas en inglés). Los resultados numéricos que se presentan en este documento, muestran el potencial de aplicar esta metodología a diferentes ramas de la industria. Debido a la riqueza fenomenológica exhibida por los materiales granulares, el presente trabajo se centrará exclusivamente en la simulación de flujos granulares densos sin cohesión. El modelo numérico se basa en un enfoque del medio continuo, en el marco teórico de plasticidad en grandes deformaciones. Para el modelo constitutivo, la función de fluencia se define en el espacio de tensiones mediante una superficie de fluencia del tipo Drucker-Prager caracterizada por dos parámetros constitutivos, la cohesión y el coeficiente de fricción interna, y equipado con una regla de flujo desviadora no asociada. Esta condición de flujo plástico se considera incompresible, por lo que se propone su integración mediante una formulación mixta del tipo u- p y estabilizando la expresión de la presión a través de una proyección polinomial (Polynomial Pressure Projection, PPP). A su vez, se propone una regularización visco-plástica con el fin de caracterizar la no linealidad de la velocidad de cizallamiento del material cuando fluye. La integración numérica se desarrolla en el marco de la técnica Impl-Ex, aumentando la robustez y reduciendo el número de iteraciones, en comparación con un esquema típico de integración implícito. La discretización espacial se aborda en el marco del PFEM, permitiendo el manejo de grandes deformaciones y del movimiento asociado a los flujos granulares con una distorsión mínima de las mallas de elementos finitos. La triangulación de Delaunay y el proceso de reconexión minimizan tales distorsiones pero no aseguran su eliminación; por esto, se propone una discretización en partículas del dominio dinámica y constante, regularizando de esta manera, la suavidad y la densidad de las partículas en la malla. Asimismo, se propone un método para asegura la conservación de las superficies materiales o Lagrangeanas por medio de una restricción de la frontera, evitando de esta manera, su definición geométrica a través del método clásico alpha-shape. Para el modelado de la interacción entre el material granular y las superficies de su confinamiento, se apuesta por un método basado en el Contact Domain Method (CDM) que permite el acoplamiento de ambos dominios en términos de una región intermedia que conecta las superficies potenciales de contacto – siendo este dominio de la misma dimensión que los cuerpos en contacto. El modelo constitutivo a emplear para el dominio de contacto se plantea de manera similar al del material granular, definiendo una correcta representación del ángulo de pared. Con el fin de validar el modelo numérico, se llevó a cabo una comparación entre los resultados experimentales de la difusión o desmoronamiento de una masa granular en un plano horizontal y las predicciones obtenidas mediante la simulación por medio de elementos finitos. Este conjunto de ejemplos nos permite validar el modelo de acuerdo a la predicción de las diferentes condiciones de la cinemática de los materiales granulares: desde una condición de confinamiento, con el material en reposo, a una transición hacia el flujo granular y de nuevo, a un estancamiento del material hasta definir su depósito final. El potencial del método numérico, para la solución y optimización de los problemas industriales que involucran flujos granulares, se logra enfocándose en dos aplicaciones industriales específicas en la industria minera y la fabricación de pellets: la descarga de un silo y el cálculo del consumo de energía en molinos rotacionales (tumbling mills). Ambos ejemplos son representativos en cuanto a los flujos granulares en la industria debido a la presencia de variaciones en la respuesta mecánica del material granular.
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Stenius, Ivan. "Finite element modelling of hydroelasticity in hull-water impacts". Licentiate thesis, KTH, Aeronautical and Vehicle Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4304.
Testo completoAbstract (sommario):
The work in this thesis focuses on the use of explicit finite element analysis (FEA) in the modelling of fluid-structure interaction of panel-water impacts. Paper A, considers modelling of a two-dimensional rigid wedge impacting a calm water surface. From analytical methods and results of a systematic parameter study a generalised approach for determination of fluid discretization and contact parameters in the modelling of arbitrary hull-water impact situations is developed and presented. In paper B the finite element modelling methodology suggested in paper A is evaluated for elastic structures by a convergence study of structural response and hydrodynamic load. The structural hydroelastic response is systematically studied by a number of FE-simulations of different impact situations concerning panel deadrise, impact velocity and boundary conditions. In paper B a tentative method for dynamic characterization is also derived. The results are compared with other published results concerning hydroelasticity in panel water impacts. The long-term goal of this work is to develop design criteria, by which it can be determined whether the loading situation of a certain vessel type should be regarded as quasi-static or dynamic, and which consequence on the design a dynamic loading has.
46
Antypas, Dionyssios. "Structural response modelling using the stochastic finite element method". Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/8314.
Testo completo
47
Cai, Qingbo. "Finite element modelling of cracking in concrete gravity dams". Thesis, Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-01302008-160623.
Testo completo
48
Suriyachat, Phanuwat. "Modelling of mine openings using nonlinear finite element method". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39380.
Testo completoAbstract (sommario):
A nonlinear finite element model, called MINE-PAL, has been developed for elasto-plastic, large deformation analysis of underground and surface mining excavations. The model accounts for both material nonlinearity due to yielding and strain-hardening and strain-softening effects and geometric nonlinearity due to large deformations. The finite element equations are formulated using incremental plasticity theory with Total Lagrangian approach where the Kirchhoff stress tensor and Green strain increment tensor are used. The model is developed for use on microcomputer system and is designed to perform 2-D nonlinear analysis of mine excavations in multiple-material domain, thus predicting the distribution of elastic, strain-softening, strain-hardening and residual strength zones. The model accommodates any arbitrary stope geometry and it allows for a variety of mining-type loading conditions in situ stresses, gravity loading and boundary tractions. Special provision has been made to permit the simulation of backfill as in situ stress-free material. Stress-space strain-softening is invoked into model using the concept of damage parameter in the incremental stress-strain relation.In addition to model verification and sensitivity analysis, two numerical modelling case studies have been undertaken. The first case study is of a narrow vein mine with backfill which is located in the province of Karnchanaburi, Thailand. The second case study is about a room-and-pillar design of a potash deposit in the province of Chaiyaphum, Thailand.
49
Wadham-Gagnon, Matthew. "Hyperelastic modelling of rubber behaviour in finite element software". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99797.
Testo completoAbstract (sommario):
Experimental characterisation of rubber in uniaxial, equi-biaxial and planar tension under cyclic quasi-static loading shows strain-induced stress softening, hysteresis and unrecoverable strain. The objective of this work is to study the applications and limitations involved in predicting the behaviour of rubber with hyperelastic models. To assume a preconditioned perfectly elastic material, the data obtained from experiments must first be simplified. The data is then fitted to popular hyperelastic models in the finite element analysis (FEA) software ANSYS(TM). A single hyperelastic model (with given coefficients) is shown to only provide a good fit to a single characterisation test and level of preconditioning at the time. A two-iteration preconditioning method is developed using different hyperelastic models for a given material to approximate the softening effect of cyclic loading in a static FEA simulation. A biaxiality test is developed, providing information on the dominant mode of simple strain in the elements of a FE model. FEA simulations and experimental tests of a cantilevered rubber plate subjected to a bending load at its free end as well as a rubber guide lug subjected to a transverse deflection are presented and discussed. It is shown that using a single hyperelastic model is insufficient to predict the behaviour of these experiments in FEA simulations. The preconditioning iteration, when applied to these simulations, shows very good agreement with the experiments, both qualitatively and quantitatively. The biaxiality test provides insight on which characterisation test is the most appropriate for curve fitting hyperelastic models for a given analysis.
50
Ladak, Hanif M. "Finite-element modelling of middle-ear prostheses in cat". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68035.
Testo completoAbstract (sommario):
Discontinuity of the middle-ear ossicular chain results in conductive hearing loss. Two prostheses commonly used to surgically repair the ossicular chain are the MSA and the MFA. In the MSA, a strut is connected between the malleus and the head of the stapes, while in the MFA a strut is connected between the malleus and the footplate of the stapes. In this work, finite-element models of the MSA, MFA and normal cat middle ear are developed. The models are valid for low frequencies (below 300 Hz) and for physiological sound levels. The mechanical behaviour of the normal middle-ear model is compared with that of the MFA and MSA models. Several parameters are then varied in order to study their relative importance in the models. The effects of strut placement on the behaviour of the MSA and MFA models are also investigated.