Using a numerical method to simulate the Metal-Organic Chemical Vapor Deposition (MOCVD). A study of the GaN films were growth on sapphire substrates, and a new design method which The position of carrier gas inlets and outlets, the gas in inlets by a showerhead reactor, the modified susceptor. The purpose of this research is to maintain deposited GaN film thickness variation range by controlling those parameters which may affect the deposition.

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Made available in DSpace on 2015-03-04T18:50:40Z (GMT). No. of bitstreams: 1 Resultados e conclusoes.pdf: 472056 bytes, checksum: c1292d32ce76370a06e53954042acc70 (MD5) Previous issue date: 2005-06-22 / Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A numerical method is presented to solve single species population dynamics problems, with focus on the spread if invading organisms. This problem is mathematically modeled by a non-linear advection-diffusion-reaction transport equation, which is numerically solved by a finite element methodology. Some examples are conducted, showing the stability and accuracy of the proposed methodology. The role of the weak and strong Alee effects is analyzed on the spread of a single species invading organism in a one-dimensional domain. In this case the population dynamics describes propagation of traveling population fronts that represent either single-species invasion or single-species retreat. Some scenarios are investigated so as to evaluate the interaction of traveling population fronts under different parameter values, allowing to derive numerically whether they can reverse or block the species invasion. / Uma solução numérica é presentada para resolver problemas da dinâmica populacional de uma única espécie, com ênfase na dispersão de um organismo invasor. Este problema é matematicamente modelado por uma equação de transporte não linear de advecção-difusão-reação e resolvido numericamente usando o método de elementos finitos. Os exemplos apresentados demonstram a estabilidade e precisão da metodologia proposta. A influência do efeito Allee forte e fraco é analisada na dispersão de uma espécie de organismo invasor em um domínio uni-dimensional. Neste caso a dinâmica populacional descreve a propagação de frentes populacionais que representam a invasão ou o recuo da espécie. Alguns cenários são investigados para avaliar a interação da frente de ondas populacionais para diferentes valores de parâmetros indicando numéricamente quando é possível reverter ou bloquear a invasão de espécies.

Differential-algebraic equations (DAEs) result in many areas of science and engineer- ing. In this thesis, numerical methods for solving DAEs are compared for two prob- lems, energy-economic models and traffic flow models. An energy-economic model is presented based on the Hubbert model of oil production and is extended to include economic factors for the first time. Using numerical methods to simulate the DAE model, the resulting graphs break the symmetry of the traditional Hubbert curve. For the traffic flow models, a numerical method is developed to solve the steady-state flow pattern including the linearly unstable regime, i.e. solutions which cannot be found with an initial value solver. / UOIT

Circular cylinders in cross-flow or the motion of circular cylinders in a fluid at rest are especially of interest in fields such as offshore and civil engineering or heat exchanger design in particular. A time-independent finite difference scheme, the basic equations are written in the form of the primitive-variable method, is developed to simulate the viscous flow across a streamwise oscillating circular cylinder. The mov-ing boundary of the oscillating cylinder is mapped to a fixed boundary and the boundary condition, therefore, becomes time independent. The finite difference ap-proximation and algorithm were first validated by the reported numerical simulation and flow visualization of the phenomenon £\ and phenomenon £] for a flow across a fixed circular cylinder. Detailed streamline patterns developed in the process are then described and discussed. Surface pressure distribution and position of separation point versus phases of various stationary and oscillating stages are discussed. The flow be-haviors of various amplitudes of exciting velocity and frequency of moving cylinder are simulated and compared. The relation between Keulegan-Carpenter and the drag force on cylinder during cylinder oscillation was also calculated under various Reynolds number.

In preparation for, and for decision support during, CBRN (chemical, biological, radiological and nuclear) emergencies it is essential to know how such an event would turn out, so that one can prepare a possible evacuation. Afterwards it might be good to know how to backtrack and see what caused the emergency, and in the case of e.g. a gas leak, where did it begin? The Swedish Defence Research Agency (FOI) develops models for such scenarios. In this thesis FOI's model, "The Nordic Urban Dispersion model" (NUD), has been studied. The system of equations set up by this model was originally solved using Intel's PARDISO solver, which is a direct solver. An evaluation on how an iterative multigrid method would work to solve the system has been done in this thesis. The wind model is a mass-consistent model which sets up a diagnostic initial wind field. The final wind field is later minimized under the constraint of the continuity equation. The minimization problem is solved using Lagrange multipliers and the system turns into a Poisson-like problem. The iterative algebraic multigrid solver (AMG) which has been evaluated had difficulties solving the problem of an asymmetric system matrix generated by NUD. The AMG solver was then tried on a symmetric discrete Poisson problem instead, and the solution turns out to be the same as for the PARDISO solver. A comparison was made between the AMG and PARDISO solver, and for the discrete Poisson case the AMG solver turned out on top for both larger system size and less computational time. To try out the solvers for the original NUD case a modification of the boundary conditions was made to make the system matrix symmetric. This modification turns the problem into a mathematical problem rather than a physical one, as the wind fields generated are not physically correct. For this modified case both the solvers get the same solution in essentially the same computational time. A method of how to in the future solve the original (asymmetric) problem, by modifying the discretization of the boundary conditions, has been discussed.

Differential-algebraic equations (DAEs) result in many areas of science and engineer- ing. In this thesis, numerical methods for solving DAEs are compared for two prob- lems, energy-economic models and traffic flow models. An energy-economic model is presented based on the Hubbert model of oil production and is extended to include economic factors for the first time. Using numerical methods to simulate the DAE model, the resulting graphs break the symmetry of the traditional Hubbert curve. For the traffic flow models, a numerical method is developed to solve the steady-state flow pattern including the linearly unstable regime, i.e. solutions which cannot be found with an initial value solver.

A numerical method is presented to solve single species population dynamics problems, with focus on the spread if invading organisms. This problem is mathematically modeled by a non-linear advection-diffusion-reaction transport equation, which is numerically solved by a finite element methodology. Some examples are conducted, showing the stability and accuracy of the proposed methodology. The role of the weak and strong Alee effects is analyzed on the spread of a single species invading organism in a one-dimensional domain. In this case the population dynamics describes propagation of traveling population fronts that represent either single-species invasion or single-species retreat. Some scenarios are investigated so as to evaluate the interaction of traveling population fronts under different parameter values, allowing to derive numerically whether they can reverse or block the species invasion. / Uma solução numérica é presentada para resolver problemas da dinâmica populacional de uma única espécie, com ênfase na dispersão de um organismo invasor. Este problema é matematicamente modelado por uma equação de transporte não linear de advecção-difusão-reação e resolvido numericamente usando o método de elementos finitos. Os exemplos apresentados demonstram a estabilidade e precisão da metodologia proposta. A influência do efeito Allee forte e fraco é analisada na dispersão de uma espécie de organismo invasor em um domínio uni-dimensional. Neste caso a dinâmica populacional descreve a propagação de frentes populacionais que representam a invasão ou o recuo da espécie. Alguns cenários são investigados para avaliar a interação da frente de ondas populacionais para diferentes valores de parâmetros indicando numéricamente quando é possível reverter ou bloquear a invasão de espécies.

The distributed point source method, or DPSM, developed in the last decade has been used for solving various engineering problems-such as elastic and electromagnetic wave propagation, electrostatic, and fluid flow problems. Based on a semi-analytical formulation, the DPSM solution is generally built by superimposing the point source solutions or Green's functions. However, the DPSM solution can be also obtained by superimposing elemental solutions of volume sources having some source density called the equivalent source density (ESD). In earlier works mostly point sources were used. In this paper the DPSM formulation is modified to introduce a new kind of ESD, replacing the classical single point source by a family of point sources that are referred to as quantum sources. The proposed formulation with these quantum sources do not change the dimension of the global matrix to be inverted to solve the problem when compared with the classical point source-based DPSM formulation. To assess the performance of this new formulation, the ultrasonic field generated by a circular planer transducer was compared with the classical DPSM formulation and analytical solution. The results show a significant improvement in the near field computation.