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Data publikacji: 6 września 2023

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1

Valivarthi, Mohan Varma, and 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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2

Alpert, David N. "Enriched Space-Time Finite Element Methods for Structural Dynamics Applications." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377870451.

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Kashefi, Ali. "A Finite-Element Coarse-GridProjection Method for Incompressible Flows." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79948.

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Coarse grid projection (CGP) methodology is a novel multigrid method for systems involving decoupled nonlinear evolution equations and linear elliptic Poisson equations. The nonlinear equations are solved on a fine grid and the linear equations are solved on a corresponding coarsened grid. Mapping operators execute data transfer between the grids. The CGP framework is constructed upon spatial and temporal discretization schemes. This framework has been established for finite volume/difference discretizations as well as explicit time integration methods. In this article we present for the first time a version of CGP for finite element discretizations, which uses a semi-implicit time integration scheme. The mapping functions correspond to the finite-element shape functions. With the novel data structure introduced, the mapping computational cost becomes insignificant. We apply CGP to pressure correction schemes used for the incompressible Navier Stokes flow computations. This version is validated on standard test cases with realistic boundary conditions using unstructured triangular meshes. We also pioneer investigations of the effects of CGP on the accuracy of the pressure field. It is found that although CGP reduces the pressure field accuracy, it preserves the accuracy of the pressure gradient and thus the velocity field, while achieving speedup factors ranging from approximately 2 to 30. Exploring the influence of boundary conditions on CGP, the minimum speedup occurs for velocity Dirichlet boundary conditions, while the maximum speedup occurs for open boundary conditions. We discuss the CGP method as a guide for partial mesh refinement of incompressible flow computations and show its application for simulations of flow over a backward facing step and flow past a cylinder.<br>Master of Science

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4

Wang, Bao. "Numerical Simulation of Detonation Initiation by the Space-Time Conservation Element and Solution Element Method." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1293461692.

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5

Dosopoulos, Stylianos. "Interior Penalty Discontinuous Galerkin Finite Element Method for the Time-Domain Maxwell's Equations." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337787922.

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6

Nagai, Toshiki. "Space-time Extended Finite Element Method with Applications to Fluid-structure Interaction Problems." Thesis, University of Colorado at Boulder, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10844711.

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<p> This thesis presents a space-time extended finite element method (space-time XFEM) based on the Heaviside enrichment for transient problems with moving interfaces, and its applications to the fluid-structure interaction (FSI) analysis. The Heaviside-enriched XFEM is a promising method to discretize partial differential equations with discontinuities in space. However, significant approximation errors are introduced by time stepping schemes when the interface geometry changes in time. The proposed space-time XFEM applies the finite element discretization and the Heaviside enrichment in both space and time with elements forming a space-time slab. A simple space-time scheme is introduced to integrate the weak form of the governing equations. This scheme considers spatial intersection configuration at multiple temporal integration points. Standard spatial integration techniques can be applied for each spatial configuration. Nitsche's method and the face-oriented ghost-penalty method are extended to the proposed space-time XFEM formulation. The stability, accuracy and flexibility of the space-time XFEM for various interface conditions including moving interfaces are demonstrated with structural and fluid problems. Moreover, the space-time XFEM enables analyzing complex FSI problems using moving interfaces, such as FSI with contact. Two FSI methods using moving interfaces (full-Eulerian FSI and Lagrangian-immersed FSI) are studied. The Lagrangian-immersed FSI method is a mixed formulation of Lagrangian and Eulerian descriptions. As solid and fluid meshes are independently defined, the FSI is computed between non-matching interfaces based on Nitsche's method and projection techniques adopted from computational contact mechanics. The stabilized Lagrange multiplier method is used for contact. Numerical examples of FSI and FSI-contact problems provide insight into the characteristics of the combination of the space-time XFEM and the Lagrangian-immersed FSI method. The proposed combination is a promising method which has the versatility for various multi-physics simulations and the applicability such as optimization.</p><p>

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7

Vikas, Sharma. "Development of Space-Time Finite Element Method for Seismic Analysis of Hydraulic Structures." Kyoto University, 2018. http://hdl.handle.net/2433/235094.

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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第21374号<br>農博第2298号<br>新制||農||1066(附属図書館)<br>学位論文||H30||N5147(農学部図書室)<br>京都大学大学院農学研究科地域環境科学専攻<br>(主査)教授村上章, 教授藤原正幸, 教授渦岡良介<br>学位規則第4条第1項該当

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8

KALARICKEL, RAMAKRISHNAN PRAVEEN. "Reliability of finite element method for time harmonic electromagnetic problems involving moving bodies." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/930777.

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This work is mainly concerned about the time-harmonic electromagnetic problems involving moving bodies. Such a formulation is possible when the boundaries between different moving objects are stationary and the sources involved are time-harmonic. Even simple media present bianisotropic properties when they are in motion. This kind of problems find applications in diverse fields. Numerical solution is required for most of the practical problems. We examined the reliability of finite element simulator developed for solving such problems.

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9

Wang, Shumin. "Improved-accuracy algorithms for time-domain finite methods in electromagnetics." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1061225243.

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10

Campbell-Kyureghyan, Naira Helen. "Computational analysis of the time-dependent biomechanical behavior of the lumbar spine." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1095445065.

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Thesis (Ph. D.)--Ohio State University, 2004.<br>Title from first page of PDF file. Document formatted into pages; contains xix, 254 p.; also includes graphics. Includes bibliographical references (p. 234-254).

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11

YU, CHUNG-CHYI. "FINITE-ELEMENT ANALYSIS OF TIME-DEPENDENT CONVECTION DIFFUSION EQUATIONS (PETROV-GALERKIN)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183930.

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Petrov-Galerkin finite element methods based on time-space elements are developed for the time-dependent multi-dimensional linear convection-diffusion equation. The methods introduce two parameters in conjunction with perturbed weighting functions. These parameters are determined locally using truncation error analysis techniques. In the one-dimensional case, the new algorithms are thoroughly analyzed for convergence and stability properties. Numerical schemes that are second order in time, third order in space and stable when the Courant number is less than or equal to one are produced. Extensions of the algorithm to nonlinear Navier-Stokes equations are investigated. In this case, it is found more efficient to use a Petrov-Galerkin method based on a one parameter perturbation and a semi-discrete Petrov-Galerkin formulation with a generalized Newmark algorithm in time. The algorithm is applied to the two-dimensional simulation of natural convection in a horizontal circular cylinder when the Boussinesq approximation is valid. New results are obtained for this problem which show the development of three flow regimes as the Rayleigh number increases. Detailed calculations for the fluid flow and heat transfer in the cylinder for the different regimes as the Rayleigh number increases are presented.

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12

Arpaci, Erdogan. "Analysis Of Sinusoidal And Helical Buckling Of Drill String In Horizontal Wells Using Finite Element Method." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611003/index.pdf.

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The number of horizontal wells is increasing rapidly in all over the world with the growth of new technological developments. During horizontal well drilling, much more complex problems occur when compared with vertical well drilling, such as decrease in load transfer to the bit, tubular failure, tubular fatigue and tubular lock-up. This makes selection of appropriate tubular and making the right drill string design more important. As the total compression load on the horizontal section increases, the behavior of the tubular changes from straight to sinusoidal buckling, and if the total compression load continues to increase the behavior of the tubular changes to helical buckling. Determination of critical buckling loads with finite element method (FEM) in horizontal wells is the main objective of this study. Initially, a computer program (ANSYS) that uses FEM is employed to simulate different tubular and well conditions. Four different pipe sizes, four different wellbore sizes and three different torque values are used to model the cases. Critical buckling load values corresponding to significant variables are collected from these simulated cases. The results are classified into different buckling modes according to the applied weight on bit values and the main properties of the simulated model, such as modulus of elasticity, moment of inertia of tubular cross section, weight per unit length of tubular and radial clearance between the wellbore and the tubular. Then, the boundary equations between the buckling modes are obtained. The equations developed in this thesis by simulating the cases for the specific tubular sizes are used to make a comparison between the critical buckling load values from the models in the literature and this work. It is observed that the results of this work fit with literature models as the tubular size increases. The influence of torque on critical buckling load values is investigated. It is observed that torque has a slight effect on critical buckling load values. Also the applicability of ANSYS for buckling problems was revealed by comparing the ANSYS results with the literature models&amp<br>#8217<br>results and the experimental study in the literature.

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13

Warner, Michael S. "Numerical solutions to optimal-control problems by finite elements in time with adaptive error control." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/11844.

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14

Cloete, Renier. "A simplified finite element model for time-dependent deflections of flat slabs." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-05302005-123208/.

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15

Marais, Neilen. "Efficient high-order time domain finite element methods in electromagnetics." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1499.

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Thesis (DEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009.<br>The Finite Element Method (FEM) as applied to Computational Electromagnetics (CEM), can beused to solve a large class of Electromagnetics problems with high accuracy and good computational efficiency. For solving wide-band problems time domain solutions are often preferred; while time domain FEM methods are feasible, the Finite Difference Time Domain (FDTD) method is more commonly applied. The FDTD is popular both for its efficiency and its simplicity. The efficiency of the FDTD stems from the fact that it is both explicit (i.e. no matrices need to be solved) and second order accurate in both time and space. The FDTD has limitations when dealing with certain geometrical shapes and when electrically large structures are analysed. The former limitation is caused by stair-casing in the geometrical modelling, the latter by accumulated dispersion error throughout the mesh. The FEM can be seen as a general mathematical framework describing families of concrete numerical method implementations; in fact the FDTD can be described as a particular FETD (Finite Element Time Domain) method. To date the most commonly described FETD CEM methods make use of unstructured, conforming meshes and implicit time stepping schemes. Such meshes deal well with complex geometries while implicit time stepping is required for practical numerical stability. Compared to the FDTD, these methods have the advantages of computational efficiency when dealing with complex geometries and the conceptually straight forward extension to higher orders of accuracy. On the downside, they are much more complicated to implement and less computationally efficient when dealing with regular geometries. The FDTD and implicit FETD have been combined in an implicit/explicit hybrid. By using the implicit FETD in regions of complex geometry and the FDTD elsewhere the advantages of both are combined. However, previous work only addressed mixed first order (i.e. second order accurate) methods. For electrically large problems or when very accurate solutions are required, higher order methods are attractive. In this thesis a novel higher order implicit/explicit FETD method of arbitrary order in space is presented. A higher order explicit FETD method is implemented using Gauss-Lobatto lumping on regular Cartesian hexahedra with central differencing in time applied to a coupled Maxwell’s equation FEM formulation. This can be seen as a spatially higher order generalisation of the FDTD. A convolution-free perfectly matched layer (PML) method is adapted from the FDTD literature to provide mesh termination. A curl conforming hybrid mesh allowing the interconnection of arbitrary order tetrahedra and hexahedra without using intermediate pyramidal or prismatic elements is presented. An unconditionally stable implicit FETD method is implemented using Newmark-Beta time integration and the standard curl-curl FEM formulation. The implicit/explicit hybrid is constructed on the hybrid hexahedral/tetrahedral mesh using the equivalence between the coupled Maxwell’s formulation with central differences and the Newmark-Beta method with Beta = 0 and the element-wise implicitness method. The accuracy and efficiency of this hybrid is numerically demonstrated using several test-problems.

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16

Sakai, Kotaro. "Seismic Performance Analysis of Fill Dams Using Velocity Based Space-Time Finite Element Method." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263700.

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17

Luckshetty, Harish Kumar. "Space-Time Finite Element Analysis on Graphics Processing Unit Computing Platform." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1331296560.

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18

Chirputkar, Shardool U. "Bridging Scale Simulation of Lattice Fracture and Dynamics using Enriched Space-Time Finite Element Method." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313753940.

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19

Kung, Christopher W. "Development of a time domain hybrid finite difference/finite element method for solutions to Maxwell's equations in anisotropic media." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1238024768.

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20

Larsson, Karl. "Finite element methods for threads and plates with real-time applications." Licentiate thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-38198.

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Thin and slender structures are widely occurring both in nature and in human creations. Clever geometries of thin structures can produce strong constructions while using a minimal amount of material. Computer modeling and analysis of thin and slender structures has its own set of problems stemming from assumptions made when deriving the equations modeling their behavior from the theory of continuum mechanics. In this thesis we consider two kinds of thin elastic structures; threads and plates. Real-time simulation of threads are of interest in various types of virtual simulations such as surgery simulation for instance. In the first paper of this thesis we develop a thread model for use in interactive applications. By viewing the thread as a continuum rather than a truly one dimensional object existing in three dimensional space we derive a thread model that naturally handles both bending, torsion and inertial effects. We apply a corotational framework to simulate large deformation in real-time. On the fly adaptive resolution is used to minimize corotational artifacts. Plates are flat elastic structures only allowing deflection in the normal direction. In the second paper in this thesis we propose a family of finite elements for approximating solutions to the Kirchhoff-Love plate equation using a continuous piecewise linear deflection field. We reconstruct a discontinuous piecewise quadratic deflection field which is applied in a discontinuous Galerkin method. Given a criterion on the reconstruction operator we prove a priori estimates in energy and L2 norms. Numerical results for the method using three possible reconstructions are presented.

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21

Kabir, S. M. Raiyan. "Finite element time domain method with a unique coupled mesh system for electromagnetics and photonics." Thesis, City University London, 2015. http://openaccess.city.ac.uk/14523/.

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The finite difference time domain (FDTD) method is a popular technique, being used successfully to analyse the electromagnetic properties of many structures, including a range of optical or photonic devices. This method offers several major advantages such as, a minimum level of calculation is required for each of the cells into which the structure is divided, as well as data parallelism and explicit and easy implementation. However, due to the use of the Finite Difference grid, this method suffers from higher numerical dispersion and inaccurate discretisation due to staircasing at slanted and curve edges. The rectangular computational domain in 2D and cuboid computational domain in 3D sometimes makes the method very resource intensive especially for large simulations. Although the finite element (FE) approach is superior for the discretisation of both 2D and 3D structures, most of the FE-based time domain approaches reported so far suffer from limitations due to the implicit or iterative form or the mass matrix formulation, for example. Therefore, the speed of the simulation is much slower than the FDTD method. Time domain analysis of electromagnetic is a very resource intensive numerical technique. Due to the slow performance the FE based techniques are not as popular as the FDTD method. In this research work a new FE based time domain technique has been proposed for both 2D and 3D problems which is similar to the FDTD method explicit and data parallel in nature. The method proposed does not requires any matrix formulation or iteration. It uses minimum possible CPU cycles among any FE-based techniques. The method also utilises a unique meshing scheme to reduce the number of calculation to at least half for 2D and one fifth for 3D compared to any full mesh FE based technique. The method also shows very low numerical dispersion when used with equilateral elements in both 2D and 3D. Thus the proposed method effectively produces results with less numerical dispersion error with lower density mesh compared to the FDTD method. When the advantage in resolution is taken into consideration, calculation of each time-step using the proposed method is significantly faster than the FDTD method.

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22

Ma, Jie. "A new space-time finite element method for the dynamic analysis of TRUSS-type structures." Thesis, Edinburgh Napier University, 2015. http://researchrepository.napier.ac.uk/Output/9165.

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Truss-type structures are widely used in contemporary constructions. The dynamic analysis is very important to ensure the safety and the functionalities of these structures. The aim of this research was to propose a new method tailored for the dynamic analysis of linear truss-type structures. The proposed method is a single-step method underpinned by Unconventional Hamilton-type Variational Principles, and employing the finite element discretisation in both spatial and temporal domains. To develop the proposed method, five Unconventional Hamilton-type Variational Principles tailor-made for truss-type structures were derived, preserving naturally all necessary conditions for the dynamic analysis without the introduction of any artificial factors. The resultant one-field and the two-filed formulations were used to build algorithms for the proposed method. The semi-discretisation treatment of the spatial and temporal domains was applied to these formulations. While the spatial discretisation was undertaken in the standard fashion, temporal discretisation was attempted with four different types of time finite elements. The convergence of the algorithms was examined in terms of the stability and the consistency properties. Numerical examples with different types of truss-type structures were given to verify the proposed method, and also to compare the performance of these algorithms against the existing analysis methods. The proposed algorithms were shown to be second- or higher-order accurate when various time finite elements were employed. Compared to the widely used Average Acceleration Method (AAM), the proposed method produces highly accurate results. Larger time steps can be used without compromising the accuracy hence the computational costs may be reduced. Therefore, the proposed method can provide a fast and high-precision analysis solution for applications where these attributes are desired.

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23

Johansson, August. "Duality-based adaptive finite element methods with application to time-dependent problems." Doctoral thesis, Umeå : Institutionen för matematik och matematisk statistik, Umeå universitet, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-33872.

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24

Bilyeu, David Lawrence. "Numerical Simulation of Chemical Reactions Inside a Shock-Tube by the Space-Time Conservation Element and Solution Element Method." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213363652.

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25

Mello, Frank James. "Weak formulations in analytical dynamics, with applications to multi-rigid-body systems, using time finite elements." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/32854.

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Szumski, Ricard Gerard. "A finite element formulation for the time domain vibration analysis of an elastic-viscoelastic structure." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17053.

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27

Chilton, Ryan Austin. "H-, P- and T-Refinement Strategies for the Finite-Difference-Time-Domain (FDTD) Method Developed via Finite-Element (FE) Principles." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1219064270.

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Rieben, Robert N. "A novel high order time domain vector finite element method for the simulation of electromagnetic devices /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

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Bhamare, Sagar D. "High Cycle Fatigue Simulation using Extended Space-Time Finite Element Method Coupled with Continuum Damage Mechanics." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352490187.

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Hou, Lin-Jun. "Development and application of displacement and mixed hp-version space-time finite elements." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/20708.

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Bourgeois, Jacqueline M. "A complete three-dimensional electromagnetic simulation of ground-penetrating radars using the finite-difference time-domain method." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/14845.

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32

Sjösten, William, and Victor Vadling. "Finite Element Approximations of 2D Incompressible Navier-Stokes Equations Using Residual Viscosity." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-354590.

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Chorin’s method, Incremental Pressure Correction Scheme (IPCS) and Crank-Nicolson’s method (CN) are three numerical methods that were investigated in this study. These methods were here used for solving the incompressible Navier-Stokes equations, which describe the motion of an incompressible fluid, in three different benchmark problems. The methods were stabilized using residual based artificial viscosity, which was introduced to avoid instability. The methods were compared in terms of accuracy and computational time. Furthermore, a theoretical study of adaptivity was made, based on an a posteriori error estimate and an adjoint problem. The implementation of the adaptivity is left for future studies. In this study we consider the following three well-known benchmark problems: laminar 2D flow around a cylinder, Taylor-Green vortex and lid-driven cavity problem. The difference of the computational time for the three methods were in general relatively small and differed depending on which problem that was investigated. Furthermore the accuracy of the methods also differed in the benchmark problems, but in general Crank-Nicolson’s method gave less accurate results. Moreover the stabilization technique worked well when the kinematic viscosity of the fluid was relatively low, since it managed to stabilize the numerical methods. In general the solution was affected in a negative way when the problem could be solved without stabilization for higher viscosities.

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33

Palmerini, Claudia. "On the smoothed finite element method in dynamics: the role of critical time step for linear triangular elements." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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Il metodo agli elementi finiti (FEM) è molto utilizzato per risolvere problemi strutturali in diversi ambiti dell’ingegneria. Negli anni, è stata sviluppata una famiglia di nuovi metodi ottenuta combinando il FEM standard con la tecnica “strain smoothing”, giungendo ai cosiddetti “smoothed finite element method” (SFEM). In questa tesi, l’attenzione è stata concentrata sul node-based SFEM (NS-FEM) e sull'edge-based SFEM (ES-FEM), che appartengono a questa nuova famiglia di metodi. Dopo una literature review, volta a metterne in luce le proprietà e gli aspetti fondamenti, i due metodi sono stati confrontati con il FEM standard. L'implementazione dei due metodi è stata eseguita con il software MATLAB. Lo studio è stato fatto in ambito dinamico, utilizzando due metodi di integrazione numerica nel tempo: il metodo delle differenze centrali e il metodo di Runge-Kutta. Come problema test è stato studiato il problema delle vibrazioni libere di un elemento strutturale in stato piano di tensione. Il confronto è stato portato avanti su due fronti: il costo computazionale dei metodi ed il calcolo del “critical time step”. I risultati hanno mostrato che il NS-FEM e l'ES-FEM hanno un costo maggiore rispetto al FEM standard, mentre, lato critical time step, sono paragonabil al FEM standard.

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34

Rawat, Vineet. "Finite Element Domain Decomposition with Second Order Transmission Conditions for Time-Harmonic Electromagnetic Problems." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243360543.

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Srisukh, Yudhapoom. "Development of hybrid explicit/implicit and adaptive h and p refinement for the finite element time domain method." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1135879014.

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36

Wassef, Karim N. "Nonlinear transient finite element analysis of conductive and ferromagnetic regions using a surface admittance boundary condition." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/13318.

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Alsuleimanagha, Zaid, and Jing Liang. "Dynamic analysis of the Baozhusi dam using FEM." Thesis, KTH, Mark- och vattenteknik (flyttat 20130630), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-171817.

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High magnitude earthquakes have devastating effects that leads to severe human and material losses; when affecting concrete gravity dams, seisms devastate the surrounding habitat through sudden release of reservoir. Dam safety is therefore a significant issue to be accounted in order to prevent the failure of dams located in seismic regions. The Baozhusi dam, the case study of this thesis, was exposed to 8.0 Ms (at the Mercalli scale) Wenchuan earthquake 2008 with intensity of (0.148 g) at the dam site. The earthquake intensity exceeded the design level of the dam (0.1 g); yet, the Baozhusi dam was not severely damaged as showed by tests. The present study case is a modeling and analyzing of the dynamical behavior of the Baozhusi dam during the earthquake duration. The results show that the horizontal component of the ground motion predominate the dynamic response of the dam. It is confirmed that the horizontal component of the ground motion crossed the dam at its axis and therefore minimizing the damages on the concrete gravity dam.

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Maczugowski, Maciej. "Numerical simulation of residual stresses in a weld seam : An application of the Finite Element Method." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-65867.

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Articulated haulers are fundamental equipment to transport material. The load carrying structure on a hauler consists mainly of welded frames. During welding of the frames high residual stress will be introduced. These stresses may have a significant impact on the fatigue life of the frames. This is the reason for having good knowledge of the weld residual stresses. The finite element method was used to calculate the residual stress distributions in a butt weld and a T-join weld. Simulation of the welding process with thermal and mechanical analysis was prepared by means of welding GUI implemented in LS-PrePost. The welding simulation is a computer intensive operation with high CPU time. That is why it is important to investigate which process factors that have the largest impact on welding simulation results. The aim of this thesis is to investigate the correlation between designed models in FEA software with published results of weld residual stress measurements and conclude which parameters should be mainly taken into consideration.

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Fernández, Bravo Elena. "Modelling and testing of a solar panel structure for KNATTE (Kinesthetic Node and Autonomous Table-Top Emulator)." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-87200.

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One of the challenges that satellites face is the interaction between control movement and vibration of flexible appendages such as solar arrays and antennas that can negatively affect the performance of the spacecraft. The aim of this thesis is to develop a numerical model of a solar panel structure for KNATTE, a frictionless platform developed by the Onboard Space Systems group at Luleå University of Technology, and develop a control law that reduces the flexible vibration of the solar arrays when attitude control manoeuvres are performed. A set of solar panel structures have been designed and tested, the mathematical model of the multibody system, which consists of KNATTE and two flexible solar panels, has been developed in MATLAB by applying the finite element method. A finite element analysis has been performed in MATLAB to extract the natural frequencies of the system. The model has been numerically verified using a commercial software, and experimentally verified by performing testing on the frictionless vehicle, KNATTE, equipped with the solar panel structures and a number of piezoelectric sensors. Once the model has been verified, a Linear Quadratic Gaussian (LQG) controller has been developed using the results from the finite element model in order to reduce the amplitude of the vibrations of the flexible solar panel structure. The behaviour of the system has been simulated when the spacecraft performs an attitude manoeuvre. The finite element model provides the modal behaviour of the multibody system, obtaining its natural frequencies with low relative error. The LQG controller reduces the amplitude of the vibrations of the flexible solar panel structure.

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Ireland, David John. "Dielectric Antennas and Their Realisation Using a Pareto Dominance Multi-Objective Particle Swarm Optimisation Algorithm." Thesis, Griffith University, 2010. http://hdl.handle.net/10072/365312.

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Antennas utilising a dielectric medium are technologies that have become popular in modern wireless platforms. They offer several desirable features such as high efficiency, electrically small and resistance to proximity detuning. Being a volumetric radiator however, realising a final, commercially competitive solution, often requires the use of a computational optimisation algorithm. In the realm of antenna design the practice of optimisation typically involves an automated routine consisting of a heuristic algorithm and a forward solving engine such as the finite element method (FEM) or finite difference time domain (FDTD) method. The solving engine is used to derive a post-processed performance value typically referred to as an objective or fitness function, while the heuristic method uses the objective function data to determine the next trial solution or solutions that approach a design goal. Nowadays, commercially viable antenna platforms are not characterised by a single performance value, but rather, a series of objective functions that are often inherently conflicting. Thus, an increase in one objective function results in a decrease in another. The optimisation algorithm is therefore required to seek a solution dictated by the preferences of the designer. Classical literature dominantly featured preference articulation, a priori, where the set of objectives are transformed into a scalar using a predefined preference arrangement. Contemporary theory implements the articulation a posteriori, where the complete set of compromise solutions are sought by the optimisation algorithm. It is hypothesised that modern multi-objective optimisation (MOO) theory, using a posteriori preference articulation, can be more useful for contemporary antenna design. By treating the objectives as individual dimensions in a mathematical space, it allows for independent, simultaneous optimisation. At the time of writing this dissertation, all commercial simulation software that include an optimisation algorithm use a predefined preference to the performance criteria. Thus, where a large set of equally potential solutions exist, only one final solution is delivered. This thesis examines two novel dielectric antenna technologies and uses modern MOO theory to obtain new solutions that supersede their prototypes. Taking a commercial perspective by optimising the electromagnetic performance and the physical size of the antenna simultaneously, it is hypothesised this allows an unprecedented insight into the inherent tradeoffs of practical antenna configurations.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Griffith School of Engineering<br>Science, Environment, Engineering and Technology<br>Full Text

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Zhao, Bo. "THE APPLICATION OF DISCONTINUOUS GALKERIN FINITE ELEMENT TIME-DOMAIN METHOD IN THE DESIGN, SIMULATION AND ANALYSIS OF MODERN RADIO FREQUENCY SYSTEMS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/186.

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The discontinuous Galerkin finite element time-domain (DGFETD) method has been successfully applied to the solution of the coupled curl Maxwell’s equations. In this dissertation, important extensions to the DGFETD method are provided, including the ability to model lumped circuit elements and the ability to model thin-wire structures within a discrete DGFETD solution. To this end, a hybrid DGFETD/SPICE formulation is proposed for high-frequency circuit simulation, and a hybrid DGFETD/Thin-wire formulation is proposed for modeling thin-wire structures within a three-dimensional problem space. To aid in the efficient modeling of open-region structures, a Complex Frequency Shifted-Perfectly Matched Layer (CFS-PML) absorbing medium is applied to the DGFETD method for the first time. An efficient CFS-PML method that reduces the computational complexity and improves accuracy as compared to previous PML formulations is proposed. The methods have been successfully implemented, and a number of test cases are provided that validate the proposed methods. The proposed hybrid formulations and the new CFS-PML formulation dramatically enhances the ability of the DGFETD method to be efficiently applied to simulate complex, state of the art radio frequency systems.

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Kitchen, Ryan L. "Improving Steering Module Efficiency for Incremental Loading Finite Element Numeric Models." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1248.pdf.

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Minami, Takuto. "Numerical simulation of the tsunami-induced electromagnetic field using a time-domain finite element method: application to the 2011 Tohoku Earthquake tsunami." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188496.

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Ellis, Brian. "A real-time hybrid method based on blade tip timing for diagnostics and prognostics of cracks in turbomachine rotor blades." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/73315.

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This dissertation proposes hybrid models for (i) diagnosis and (ii) remaining useful life estimation of a single fatigue crack in a low-pressure turbine blade. The proposed hybrid methods consist of physics-based methods and data-driven methods. In this dissertation, blade tip timing is used to measure the relative tip displacement of a rotor blade. The natural frequency of the blade is determined by detecting the critical speeds of the blade using a newly derived least squares spectral analysis method. The method shares its origin from the Lomb-Scargle periodogram and can detect resonance frequencies in the blade’s displacement while the rotor is in operation. A Campbell diagram is then used to convert the critical speed into a natural frequency. Two kinds of shaft transients are considered, a run-up run-down crossing the same critical speed, is used to test the new method. This dissertation shows that the relative displacement of the blade tip is comparable to those simulated from an analytical single degree of freedom model. It is also shown that the newly proposed resonance detection method estimates the natural frequency of the blade to a high degree of accuracy when compared to the measurements from a modal impact hammer test. The natural frequency obtained from the real time measurement is then used in a pre-constructed hybrid diagnostics model. The diagnostics model provides a probability density function estimation of the surface crack length given the measured natural frequency. A Gaussian Process Regression model is trained on data collected during experiments and finite element simulations of a fatigue crack in the blade. The final part of this dissertation is a sequential inference model for improving the estimation of the crack length and the prediction of the crack growth. The suggested model uses an unscented Kalman filter that improves estimations of the crack length and the rate of crack growth from Paris’ Law coefficients. The model is updated each time a diagnosis is performed on the blade. The RUL of the blade is then determined from an integration of Paris’s Law given the uncertainty estimates of the current damage in the blade. The result of the algorithm is an estimation of the remaining number of cycles to failure. The algorithm is shown to improve the overall estimation of the RUL; however, it is suggested that future work looks at the convergence rate of the method.<br>Dissertation (MEng)--University of Pretoria, 2019.<br>Eskom Power Plant Engineering Institute (EPPEI)<br>Mechanical and Aeronautical Engineering<br>MEng<br>Unrestricted

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Anees, Asad [Verfasser], Lutz [Akademischer Betreuer] Angermann, Reza [Akademischer Betreuer] Abedi, and Muhammad Ozair [Akademischer Betreuer] Ahmad. "Time domain finite element method for linear and nonlinear models in electromagnetics and optics / Asad Anees ; Lutz Angermann, Reza Abedi, Muhammad Ozair Ahmad." Clausthal-Zellerfeld : Technische Universität Clausthal, 2020. http://d-nb.info/123136260X/34.

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Abenius, Erik. "Direct and Inverse Methods for Waveguides and Scattering Problems in the Time Domain." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6013.

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Malheiro, Ana Paula Resende. "Construção de separadores globalmente suaves para conjuntos de pontos no R2 e geração de base mínima." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/275758.

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Orientador: Jorge Stolfi<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Computação<br>Made available in DSpace on 2018-08-18T02:35:56Z (GMT). No. of bitstreams: 1 Malheiro_AnaPaulaResende_D.pdf: 11382454 bytes, checksum: 9ea58ac7af766674dc90224444666560 (MD5) Previous issue date: 2011<br>Resumo: Esta tese tem duas partes relativamente independentes. A primeira estuda o problema de construir uma curva suave (C1) que separa dois conjuntos de pontos do plano. Especificamente, a curva é definida por uma equação implícita F(x, y) = 0 onde F é uma spline polinomial de grau 2 com continuidade adequada. O objetivo é determinar uma única cônica se possível, senão uma curva que minimiza uma função quadrática de "energia". O problema é reduzido a um problema de minimização quadrática com restrições, que é resolvido por uma biblioteca existente (CGAL). A segunda parte descreve um algoritmo geral para determinar uma base de elementos finitos em um espaço de splines arbitrário, definido por exemplo por restrições lineares homogêneas de continuidade ou contorno. Neste caso o problema é caracterizado como o problema de encontrar uma base de peso máximo em um matróide e, portanto, pode ser resolvido pelo algoritmo guloso de Edmonds. Esse algoritmo tem custo exponencial no número n de células da malha. Entretanto, esta tese mostra que para casos de interesse - onde existe uma base de elementos finitos com suporte de k células, no máximo - o algoritmo pode ser melhorado de modo a terminar em tempo O(n km3), onde m é a dimensão do espaço (que é geralmente O(n))<br>Abstract: This thesis has two relatively independent parts. The first part considers the problem of constructing a smooth (C1) curve separating two sets of points of the plane. Specifically, the curve is defined by an implicit equation F(x, y) = 0, where F is a polynomial spline of degree 2 with appropriate continuity. The goal is to determine a unique conic wherever possible, or a piecewise-defined curve that minimizes a quadratic "energy" function. The problem is reduced to a quadratic minimization problem with constraints, which is solved by an existing library (CGAL). The second part describes a general algorithm to determine a finite-element basis on an arbitrary space of splines; for example, a space defined by homogeneous linear boundary or continuity constraints. In this case the problem is defined as the problem of finding a maximum weight basis in a matroid, and therefore can be solved by the greedy algorithm of Edmonds. This algorithm has exponential cost in the number n of mesh cells. However, we show that for cases of interest - wherever there is a finite-element basis with maximum support of ? cells - the algorithm can be improved so as to finish in time O(n km3), where m is the dimension of the space (which is usually O(n))<br>Doutorado<br>Ciência da Computação<br>Doutor em Ciência da Computação

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Carreño, Sánchez Amanda María. "Integration methods for the time dependent neutron diffusion equation and other approximations of the neutron transport equation." Doctoral thesis, Universitat Politècnica de València, 2020. http://hdl.handle.net/10251/144771.

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[ES] Uno de los objetivos más importantes en el análisis de la seguridad en el campo de la ingeniería nuclear es el cálculo, rápido y preciso, de la evolución de la potencia dentro del núcleo del reactor. La distribución de los neutrones se puede describir a través de la ecuación de transporte de Boltzmann. La solución de esta ecuación no puede obtenerse de manera sencilla para reactores realistas, y es por ello que se tienen que considerar aproximaciones numéricas. En primer lugar, esta tesis se centra en obtener la solución para varios problemas estáticos asociados con la ecuación de difusión neutrónica: los modos lambda, los modos gamma y los modos alpha. Para la discretización espacial se ha utilizado un método de elementos finitos de alto orden. Diversas características de cada problema espectral se analizan y se comparan en diferentes reactores. Después, se investigan varios métodos de cálculo para problemas de autovalores y estrategias para calcular los problemas algebraicos obtenidos a partir de la discretización espacial. La mayoría de los trabajos destinados a la resolución de la ecuación de difusión neutrónica están diseñados para la aproximación de dos grupos de energía, sin considerar dispersión de neutrones del grupo térmico al grupo rápido. La principal ventaja de la metodología que se propone es que no depende de la geometría del reactor, del tipo de problema de autovalores ni del número de grupos de energía del problema. Tras esto, se obtiene la solución de las ecuaciones estacionarias de armónicos esféricos. La implementación de estas ecuaciones tiene dos principales diferencias respecto a la ecuación de difusión neutrónica. Primero, la discretización espacial se realiza a nivel de pin. Por tanto, se estudian diferentes tipos de mallas. Segundo, el número de grupos de energía es, generalmente, mayor que dos. De este modo, se desarrollan estrategias a bloques para optimizar el cálculo de los problemas algebraicos asociados. Finalmente, se implementa un método modal actualizado para integrar la ecuación de difusión neutrónica dependiente del tiempo. Se presentan y comparan los métodos modales basados en desarrollos en función de los diferentes modos espaciales para varios tipos de transitorios. Además, también se desarrolla un control de paso de tiempo adaptativo, que evita la actualización de los modos de una manera fija y adapta el paso de tiempo en función de varias estimaciones del error.<br>[CAT] Un dels objectius més importants per a l'anàlisi de la seguretat en el camp de l'enginyeria nuclear és el càlcul, ràpid i precís, de l'evolució de la potència dins del nucli d'un reactor. La distribució dels neutrons pot modelar-se mitjançant l'equació del transport de Boltzmann. La solució d'aquesta equació per a un reactor realístic no pot obtenir's de manera senzilla. És per això que han de considerar-se aproximacions numèriques. En primer lloc, la tesi se centra en l'obtenció de la solució per a diversos problemes estàtics associats amb l'equació de difusió neutrònica: els modes lambda, els modes gamma i els modes alpha. Per a la discretització espacial s'ha utilitzat un mètode d'elements finits d'alt ordre. Algunes de les característiques dels problemes espectrals s'analitzaran i es compararan per a diferents reactors. Tanmateix, diversos solucionadors de problemes d'autovalors i estratègies es desenvolupen per a calcular els problemes obtinguts de la discretització espacial. La majoria dels treballs per a resoldre l'equació de difusió neutrònica estan dissenyats per a l'aproximació de dos grups d'energia i sense considerar dispersió de neutrons del grup tèrmic al grup ràpid. El principal avantatge de la metodologia exposada és que no depèn de la geometria del reactor, del tipus de problema d'autovalors ni del nombre de grups d'energia del problema. Seguidament, s'obté la solució de les equacions estacionàries d'harmònics esfèrics. La implementació d'aquestes equacions té dues principals diferències respecte a l'equació de difusió. Primer, la discretització espacial es realitza a nivell de pin a partir de l'estudi de diferents malles. Segon, el nombre de grups d'energia és, generalment, major que dos. D'aquesta forma, es desenvolupen estratègies a blocs per a optimitzar el càlcul dels problemes algebraics associats. Finalment, s'implementa un mètode modal amb actualitzacions dels modes per a integrar l'equació de difusió neutrònica dependent del temps. Es presenten i es comparen els mètodes modals basats en l'expansió dels diferents modes espacials per a diversos tipus de transitoris. A més a més, un control de pas de temps adaptatiu es desenvolupa, evitant l'actualització dels modes d'una manera fixa i adaptant el pas de temps en funció de vàries estimacions de l'error.<br>[EN] One of the most important targets in nuclear safety analyses is the fast and accurate computation of the power evolution inside of the reactor core. The distribution of neutrons can be described by the neutron transport Boltzmann equation. The solution of this equation for realistic nuclear reactors is not straightforward, and therefore, numerical approximations must be considered. First, the thesis is focused on the attainment of the solution for several steady-state problems associated with neutron diffusion problem: the $\lambda$-modes, the $\gamma$-modes and the $\alpha$-modes problems. A high order finite element method is used for the spatial discretization. Several characteristics of each type of spectral problem are compared and analyzed on different reactors. Thereafter, several eigenvalue solvers and strategies are investigated to compute efficiently the algebraic eigenvalue problems obtained from the discretization. Most works devoted to solve the neutron diffusion equation are made for the approximation of two energy groups and without considering up-scattering. The main property of the proposed methodologies is that they depend on neither the reactor geometry, the type of eigenvalue problem nor the number of energy groups. After that, the solution of the steady-state simplified spherical harmonics equations is obtained. The implementation of these equations has two main differences with respect to the neutron diffusion. First, the spatial discretization is made at level of pin. Thus, different meshes are studied. Second, the number of energy groups is commonly bigger than two. Therefore, block strategies are developed to optimize the computation of the algebraic eigenvalue problems associated. Finally, an updated modal method is implemented to integrate the time-dependent neutron diffusion equation. Modal methods based on the expansion of the different spatial modes are presented and compared in several types of transients. Moreover, an adaptive time-step control is developed that avoids setting the time-step with a fixed value and it is adapted according to several error estimations.<br>Carreño Sánchez, AM. (2020). Integration methods for the time dependent neutron diffusion equation and other approximations of the neutron transport equation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/144771<br>TESIS

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Le, Thanh Nam. "Corotational formulation for nonlinear analysis of flexible beam structures." Licentiate thesis, KTH, Bro- och stålbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94880.

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Flexible beam structures are popular in civil and mechanical engineering. Many of these structures undergo large displacements and finite rotations, but with small deformations. Their dynamic behaviors are usually investigated using finite beam elements. A well known method to derive such beam elements is the corotational approach. This method has been extensively used in nonlinear static analysis. However, its application in nonlinear dynamics is rather limited. The purpose of this thesis is to investigate the nonlinear dynamic behavior of flexible beam structures using the corotational method. For the 2D case, a new dynamic corotational beam formulation is presented. The idea is to adopt the same corotational kinetic description in static and dynamic parts. The main novelty is to use cubic interpolations to derive both inertia terms and internal terms in order to capture correctly all inertia effects. This new formulation is compared with two classic formulations using constant Timoshenko and constant lumped mass matrices. This work is presented in the first appended journal paper. For the 3D case, update procedures of finite rotations, which are central issues in development of nonlinear beam elements in dynamic analysis, are discussed. Three classic and one new formulations of beam elements based on the three different parameterizations of the finite rotations are presented. In these formulations, the corotational method is used to develop expressions of the internal forces and the tangent stiffness matrices, while the dynamic terms are formulated into a total Lagrangian context. Many aspects of the four formulations are investigated. First, theoretical derivations as well as practical implementations are given in details. The similarities and differences between the formulations are pointed out. Second, numerical accuracy and computational efficiency of these four formulations are compared. Regarding efficiency, the choice of the predictor at each time step and the possibility to simplify the tangent inertia matrix are carefully investigated. This work is presented in the second appended journal paper. To make this thesis self-contained, two chapters concerning the parametrization of the finite rotations and the derivation of the 3D corotational beam element in statics are added.<br>QC 20120521

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Fasora, Pavel. "Modelování vlnovodů metodou konečných prvků v časové oblasti." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-217800.

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The thesis deals with frequency domain finite elements and time domain finite elements. Derivation of the wave equation, generation of the discretization mesh and the composition of matrices for solving wave equation are presented. Exploitation of COMSOL Multiphysics for the analysis of the electromagnetic wave propagation in a wave guide is explained. Finally, in this thesis is described the m-file of MATLAB for analyzing electric field intensity of the waveguide in longitudinal direction to both domain. In last part is concisely exposed perfect match layers.

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