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[es] OPTIMIZACIÓN DE FORMA DE MODELOS BIDIMENSIONALES DE ELEMENTOS FINITOS CON COMPORTAMIENTO ELÁSTICO-PLÁSTICO / [pt] OTIMIZAÇÃO DE FORMA DE MODELOS BIDIMENSIONAIS DE ELEMENTOS FINITOS COM COMPORTAMENTO ELASTO-PLÁSTICO / [en] SHAPE OPTIMIZATION OF 2D FINITE ELEMENT MODELS CONSIDERING ELASTO-PLASTIC BEHAVIOURCARLOS EDUARDO KUBRUSLY DA SILVA 04 October 2001 (has links)
[pt] Este trabalho tem por objetivo apresentar um sistema
integrado para otimização de forma de estruturas planas que
tenham comportamento elasto-plástico. A metodologia
implementada propõe uma alternativa à forma conservadora
com que tradicionalmente as estruturas têm sido otimizadas,
ou seja, admitindo-se que as mesmas possuam comportamento
linear elástico.
O sistema computacional é denominado integrado pois reúne
diversos módulos distintos para o tratamento do problema,
como modelagem geométrica, geração de malhas de elementos
finitos, análise não-linear da resposta da estrutura,
análise de sensibilidade,programação matemática e
otimização de estruturas.
A geometria do contorno da estrutura plana é definida por
meio de curvas (paramétricas)B-splines cúbicas. Estas, por
sua vez, são determinadas em função de um conjunto de
pontos de interpolação (pontos-chave) e condições de
contorno em seus vértices extremos.
A correta definição da geometria da estrutura é responsável
pelo sucesso do processo de otimização.
A resposta da estrutura às solicitações do carregamento
externo é avaliada pelo método dos elementos finitos. Para
isso, é necessário que o domínio da estrutura seja
discretizado. No presente trabalho foi empregado um gerador
automático de malhas não estruturadas de elementos finitos
isoparamétricos. A configuração de equilíbrio da estrutura
é obtida através de um procedimento iterativo/incremental
envolvendo o método de Newton-Raphson. Localmente, o
equilíbrio é satisfeito pela aplicação de um algoritmo
implícito de integração de tensões nos pontos que violarem
o critério de plastificação do material. A matriz tangente
de rigidez é atualizada a cada iteração da análise e é
obtida de forma consistente com o algoritmo de integração
das tensões, preservando as características de convergência
quadrática assintótica inerentes ao método de Newton-
Raphson.
No procedimento iterativo de otimização é empregado um
algoritmo de programac¸ ão quadrática recursiva que requer
a avaliação dos gradientes da função-objetivo e restrições.
Para tal, foi implementado um método semi-analítico para a
determinação das sensibilidades da resposta estrutural
envolvidas nas expressôes dos gradientes citados. O método
leva em consideração os efeitos da plastificação ocorrida
durante o carregamento da estrutura e é dito -exato- por
apresentar imprecisões apenas nos casos em que a magnitude
da perturbação da variável é muito pequena, não podendo ser
representada corretamente pelo hardware.
Os exemplos analisados mostram que a consideração do
comportamento elastoplástico da estrutura na otimização de
sua forma leva a configurações mais eficientes do que
aquelas obtidas admitindo-se a relação linear elástica
entre deformações e tensões. / [en] The main goal of this work is to present an integrated
system for the optimization of plane structures with
elastoplastic behavior. The methodology proposes an
alternative for the conservative way in which structures
traditionally have been optimized, i.e., that they
present linear elastic behavior. The computational system
is said to be integrated because it congregates distinct
modules for the solution of the problem, such as geometric
modelling, finite element mesh generation, non-linear
structural response analysis, sensitivity analysis,
mathematical programming and optimization of structures.
The geometry of the plane structure`s boundary is defined
by cubic (parametric) B-splines curves. Those, in turn, are
determined by a set of interpolation points (key points)
and boundary constraints at their ends. The correct
definition of the structure`s geometry is responsible for
the success of the optimization process.The structural
response to the applied loading is evaluated by the finite
element method. For that, the domain of the structure must
be discretized. In the present work, an automatic
unstructured mesh generator of isoparametric finite
elements has been used. The equilibrium layout of the
structure is obtained by an iterative/incremental procedure
using the standard Newton-Raphson method. Locally, the
equilibrium is satisfied by applying an implicit stress
return mapping algorithm at points which violate the yield
criterion of the material. The tangent stiffness matrix is
updated at each analysis iteration and it is obtained in
a way which is consistent with the return mapping
algorithm, so that the asymptotic quadratic rate of
convergence of the Newton-Raphson method is preserved.
The use of a quadratic recursive programming algorithm in
the optimization procedure involves the gradient evaluation
of the objective function and constraints. For that, a
semi-analytical method for the calculation of the response
sensitivities, which appear in the gradient expressions,
has been implemented. The technique takes into account the
plastic effects which take place during the loading of the
structure and is considered - exact- up to round-off
errors, which occurs when the magnitude of the perturbation
is so small that the hardware cannot accurately represent
it.The examples presented demonstrate that the
consideration of the elastoplastic behavior of the material
during the optimization process leads to structural layouts
which are more efficient than of those obtained under the
assumption of linear elastic relationship between
strains and stresses. / [es] Este trabajo tiene por objetivo presentar un sistema
integrado para otimización de forma de extructuras planas
que tengan comportamiento elástico-plástico. LA metodología
implementada propone una alternativa a la forma
conservadora con que tradicionalmente las extructuras han
sido optimizadas, o sea, admitiendo que las poseen um
comportamiento lineal-elástico. EL sistema computacional se
denomina integrado pues reúne diversos módulos para el
tratamiento del problema, como modelage geométrica,
generación de mallas de elementos finitos, análisis no
lineal de la respuesta de la extructura, análisis de
sensibilidad,programación matemática y otimización de
extructuras. LA geometría del contorno de la extructura
plana es definida por medio de curvas (paramétricas)B
splines cúbicas. Estas, por su vez, son determinadas en
función de un conjunto de puntos de interpolación (puntos
claves) y condiciones de contorno en sus vértices extremos.
La definición correta de la geometría de la extructura es
responsable por el éxito del proceso de otimización. La
respuesta de la extructura a las solicitudes de carga
externa se evalúa por el método de los elementos finitos.
Para esto, es necesario que el dominio de la extructura sea
discretizado. En este trabajo se utiliza un generador
automático de mallas no extructuradas de elementos finitos
isoparamétricos. La configuración de equilíbrio de la
extructura se obtiene a través de un procedimiento
iterativo/incremental que envuelve el método de Newton
Raphson. Localmente, el equilíbrio es satisfecho por la
aplicación de un algoritmo implícito de integración de
tensiones en los puntos que violen el critério de
plastificación del material. La matriz tangente de rigidez
se actualiza a cada iteración del análisis y se obtiene de
forma consistente con el algoritmo de integración de las
tensiones, preservando las características de convergencia
cuadrática asintótica inherentes al método de Newton
Raphson. En el procedimiento iterativo de otimización se
utiliza un algoritmo de programación cuadrática recursiva
que requiere la evaluación de los gradientes de la función
objetivo y restricciones. Para tal, se implementó un método
semi analítico para la determinación de las sensibilidades
de la respuesta extructural envolvidas en las expresóes de
los gradientes citados. EL método lleva en consideración el
hecho de que la plastificación que ocurre durante la carga
de la extructura y se dice exacta por presentar
imprecisiones apenas en los casos en que la magnitud de la
perturbación de la variable es muy pequeña, no puede ser
representada correctamente por el hardware. Los ejemplos
analizados muestran que la consideración del comportamiento
elástico-plástico de la extructura en la otimización de su
forma lleva la configuraciones más eficientes de que
aquellas obtenidas admitiendo la relación lineal elástica
entre deformaciones y tensiones.
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[pt] AUTO-ADAPTAÇÃO E OTIMIZAÇÃO DE FORMA EM CASCAS / [en] SELF-ADAPTIVITY AND SHAPE OPTIMIZATION OF SHELLSJOAO BATISTA MARQUES DE SOUSA JUNIOR 26 October 2001 (has links)
[pt] Este trabalho consiste no desenvolvimento e implementação
de um sistema computacional integrado para Modelagem Geo-
étrica, Geração de Malhas, Análise Numérica, Auto-
Adaptação
do tipo h e Otimização de Forma e Espessura em Cascas.
O Modelo Geométrico adotado consiste em representar a
superfície por meio de B-Splines Racionais Recortadas,
admitindo variação de espessura segundo as mesmas funções
que descrevem a superfície.
Para a utilização nos módulos de Auto-Adaptação e
Otimização, Geradores de Malhas Não-Estruturadas
sobre superfícies paramétricas foram empregados. Com base
em um gerador de malhas triangulares que utiliza a
técnica
de avanço de Fronteira, dois geradores de malhas
quadrilaterais foram desenvolvidos.
Os elementos finitos empregados são baseados nas
hipóteses
de Reissner-Mindlin e no conceito de degeneração de
sólidos. São considerados os elementos tradicionais,
baseados puramente em deslocamentos, bem como elementos
de
formulação mais robusta, com base em campos assumidos
de deformação.
Um procedimento para Auto-Adaptação de Malhas do tipo
foi desenvolvido para o Modelo Geométrico e para os
elementos considerados. As malhas obtidas a partir de
níveis de erro prescritos permitem aos modelos a
obtenção
de suas taxas de convergência mesmo em problemas
com singularidades e efeitos de fronteira.
A Análise de Sensibilidade, ferramenta essencial nos
procedimentos de Otimização, é feita com a utilização do
Método Semi-Analítico, considerando as características
especiais dos elementos de casca. Foi desenvolvida para
elementos degenerados de casca uma versão do Método Semi-
Analítico que elimina sua imprecisão eventual, através da
diferenciação exata das componentes de deslocamento de
corpo rígido. Para os elementos baseados puramente em
deslocamentos, o Método Analítico também foi desenvolvido.
Os módulos de Otimização de Forma e Espessura trabalham
sobre diversas possibilidades de definição das variáveis
de
projeto e com diferentes algoritmos de Programação Matemá
tica. Permitem também a Otimização de Forma com
consideração de Auto-Adaptatividade para obter as malhas
durante o processo de mudança de forma.
Devido à interconexão entre os diversos módulos e com o
objetivo de facilitar a comunicação e a implementação dos
mesmos, o sistema computacional foi completamente
desenvolvido utilizando técnicas de Programação Orientada
para Objetos. / [en] The purpose of this thesis is the development of an
integrated computational system for Geometric Modelling,
Unstructured Mesh Generation, Numerical Analysis,
Adaptivity and Shape Optimization of Shells.The Geometric
Model is composed of Non-Uniform Rational B-Spline Surfaces
(NURBS), further modified by trimming loops described in
the parametric plane. Smooth thickness variations
may be modelled by means of the same functions that
describe the surface geometry.For Unstructured Mesh
Generation, two algorithms were implemented for
quadrilateral elements and one for triangles. The
triangular Mesh Generator is based on the Advancing Front
Technique applied to parametric surfaces. The quadrilateral
Mesh Generators employ the indirect approach for converting
the triangular meshes to pure quadrilateral ones.
The Finite Element formulation is based on the degenerated
isoparametric approach. Pure displacement based elements,
as well as assumed strain robust shell elements, are
employed in the Analysis, Adaptivity and Optimization
modules. A procedure for h-Adaptive Mesh Refinement was
developed for the shell models. For this purpose an Error
Estimator scheme, based upon a Zienkiewicz-Zhu Patch
Recovery Technique, adapted to handle curved shell
surfaces, was employed. The adaptive procedure allows the
convergence rates of the Finite Element Model to be
maintained even in the presence of singularities and
boundary layers.For the Sensitivity Evaluation, the well-
known Semi-Analytical Method is employed and adapted for
the degenerated solid shell element approach. In order to
solve the inaccuracy problems inherent to the application
of the method for certain types of structures, the recent
Refined Semi- Analytical Method, is extended for
degenerated shell elements. For the pure displacement-based
elements, the Analytical Method is also developed.
The Shape and Thickness Optimization modules work with a
wide variety of design variable descriptions, different
mathematical Programming algorithms, Sensitivity schemes
and Finite Element Models. The possibility of h-Adaptive
Mesh refinement in conjunction with Shape Optimization
is also considered in this stage. In order to ease up code
expansion, communication and data exchange between the
modules,the computational system was fully developed
employing Object-Oriented Programming techniques.
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Shape optimization of coronashield geometry : Simulation techniques for minimizing electricfield with COMSOL 6.0Bjerned, Erik, Persson, Mattias, Danielsson, Axel January 2022 (has links)
This report focuses on the practicality and results of using the COMSOL 6.0 Optimization Module on a HVDC bushing corona shield model provided by Hitachi Energy to minimize electric field. The Optimization Module has several functions and parameters for altering the geometry of a model. Parameter Optimization, Polynomial Boundary and Free Shape Boundary was the primary methods used. The best results in minimizing the electric field was found with the Polynomial Boundary. The optimized shape decreased the maximum electric field by about 15% and when run with constraints to the change in volume the optimization showed similar results. Tests with Parameter Optimization did decrease the electric field but lacked the ability to fine-tune the shape like Polynomial Boundary can. Free Shape Boundaryseemed to have great potential in the documentation but we did not finda successful way of implementing the method. Through testing of different setups for methods and solvers we have concluded that the Optimization Module is both useful and practical for the given model and a clear improvement in electric field was observed in the new shape. Polynomial Boundary is the best option for the given model but more research is needed about Free Shape Boundary.
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Exploring Immersed FEM, Material Design, and Biological Tissue Material ModelingKaudur, Srivatsa Bhat 13 March 2024 (has links)
This thesis utilizes the Immersed Interface Finite Element Method (IIFEM) for shape optimization and material design, while also investigating the modeling and parameterization of lung tissue for Diver Underwater Explosion (UNDEX) simulations.
In the first part, a shape optimization scheme utilizing a four-noded rectangular immersed-interface element is presented. This method eliminates the need for interface fitted mesh or mesh morphing, reducing computational costs while maintaining solution accuracy. Analytical design sensitivity analysis is performed to obtain gradients for the optimization formulation, and various parametrization techniques are explored. The effectiveness of the approach is demonstrated through verification and case studies.
For material design, the study combines topological shape optimization with IIFEM, providing a computational approach for architecting materials with desired effective properties. Numerical homogenization evaluates effective properties, and level set-based topology optimization evolves boundaries within the unit cell to generate optimal periodic microstructures. The design space is parameterized using radial basis functions, facilitating a gradient-based optimization algorithm for optimal coefficients. The method produces geometries with smooth boundaries and distinct interfaces, demonstrated through numerical examples.
The thesis then delves into modeling the mechanical response of lung tissues, particularly focusing on hyperelastic and hyperviscoelastic models. The research adopts a phased approach, emphasizing hyperelastic model parametrization while reserving hyperviscoelastic model parametrization for future studies. Alternative methods are used for parametrization, circumventing direct experimental tests on biological materials. Representative material properties are sourced from literature or refit from existing experimental data, incorporating both empirically derived data and practical values suitable for simulations. Damage parameter quantification relies on asserted quantitative relationships between injury levels and the regions or percentages of affected lung tissue. / Doctor of Philosophy / This research explores the following themes: optimizing shapes, designing materials using repetitive identical building blocks, and understanding how divers' lungs respond to underwater explosions. When computationally analyzing structures with multiple materials, the conventional method involves creating meshes that align with material interfaces, which can be intricate and time-consuming. The Immersed Interface Finite Element Method (IIFEM) is introduced as a computational approach that simplifies this process, utilizing a uniform grid for analysis regardless of interface shape.
Consider a plate with a hole or other inclusions. Shape optimization seeks the optimal hole/inclusion shape for withstanding specific loading. Traditional optimization processes necessitate iterative mesh recreation, a step circumvented by employing IIFEM. This technique also extends to creating micro-building blocks of materials, enabling the architectural design of materials with desired qualities. Materials with specific properties, like strength or flexibility can be achieved.
This thesis also addresses the challenge of understanding how divers' lungs respond to underwater explosions, a crucial aspect of safety. Advanced computer models are used to mimic the behavior of lung tissue under shock loads. Directly testing materials and tissues can be difficult and restricted. Techniques like gathering data from scientific papers and refitting existing experimental data are utilized to obtain the information needed. Also, it is hard to directly measure how much damage an underwater explosion does to a diver's lungs.
Thus, the level of damage was quantified based on assertions about the relationship between different injury severities and how much lung tissue is affected.
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Implementing automatic design optimisation in an interactive environmentUgail, Hassan, Bloor, M.I.G., Wilson, M.J. January 2000 (has links)
Yes
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Hydrodynamic Design Optimization and Wave Tank Testing of Self-Reacting Two-Body Wave Energy ConverterMartin, Dillon Minkoff 09 November 2017 (has links)
As worldwide energy consumption continues to increase, so does the demand for renewable energy sources. The total available wave energy resource for the United States alone is 2,640 TWh/yr; nearly two thirds of the 4,000 TWh of electricity used in the United States each year. It is estimated that nearly half of that available energy is recoverable through wave energy conversion techniques. In this thesis, a two-body 'point absorber' type wave energy converter with a mechanical power-takeoff is investigated. The two-body wave energy converter extracts energy through the relative motion of a floating buoy and a neutrally buoyant submerged body. Using a linear frequency-domain model, analytical solutions of the optimal power and the corresponding power-takeoff components are derived for the two-body wave energy converter. Using these solutions, a case study is conducted to investigate the influence of the submerged body size on the absorbed power of the device in regular and irregular waves. Here it is found that an optimal mass ratio between the submerged body and floating buoy exists where the device will achieve resonance. Furthermore, a case study to investigate the influence of the submerged body shape on the absorbed power is conducted using a time-domain numerical model. Here it is found that the submerged body should be designed to reduce the effects of drag, but to maintain relatively large hydrodynamic added mass and excitation force. To validate the analytical and numerical models, a 1/30th scale model of a two-body wave energy converter is tested in a wave tank. The results of the wave tank tests show that the two-body wave energy converter can absorb nearly twice the energy of a single-body 'point absorber' type wave energy converter. / Master of Science
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Optimization Under Uncertainty and Total Predictive Uncertainty for a Tractor-Trailer Base-Drag Reduction DeviceFreeman, Jacob Andrew 07 September 2012 (has links)
One key outcome of this research is the design for a 3-D tractor-trailer base-drag reduction device that predicts a 41% reduction in wind-averaged drag coefficient at 57 mph (92 km/h) and that is relatively insensitive to uncertain wind speed and direction and uncertain deflection angles due to mounting accuracy and static aeroelastic loading; the best commercial device of non-optimized design achieves a 12% reduction at 65 mph. Another important outcome is the process by which the optimized design is obtained. That process includes verification and validation of the flow solver, a less complex but much broader 2-D pathfinder study, and the culminating 3-D aerodynamic shape optimization under uncertainty (OUU) study.
To gain confidence in the accuracy and precision of a computational fluid dynamics (CFD) flow solver and its Reynolds-averaged Navier-Stokes (RANS) turbulence models, it is necessary to conduct code verification, solution verification, and model validation. These activities are accomplished using two commercial CFD solvers, Cobalt and RavenCFD, with four turbulence models: Spalart-Allmaras (S-A), S-A with rotation and curvature, Menter shear-stress transport (SST), and Wilcox 1998 k-ω. Model performance is evaluated for three low subsonic 2-D applications: turbulent flat plate, planar jet, and NACA 0012 airfoil at α = 0°.
The S-A turbulence model is selected for the 2-D OUU study. In the 2-D study, a tractor-trailer base flap model is developed that includes six design variables with generous constraints; 400 design candidates are evaluated. The design optimization loop includes the effect of uncertain wind speed and direction, and post processing addresses several other uncertain effects on drag prediction. The study compares the efficiency and accuracy of two optimization algorithms, evolutionary algorithm (EA) and dividing rectangles (DIRECT), twelve surrogate models, six sampling methods, and surrogate-based global optimization (SBGO) methods. The DAKOTA optimization and uncertainty quantification framework is used to interface the RANS flow solver, grid generator, and optimization algorithm. The EA is determined to be more efficient in obtaining a design with significantly reduced drag (as opposed to more efficient in finding the true drag minimum), and total predictive uncertainty is estimated as ±11%. While the SBGO methods are more efficient than a traditional optimization algorithm, they are computationally inefficient due to their serial nature, as implemented in DAKOTA.
Because the S-A model does well in 2-D but not in 3-D under these conditions, the SST turbulence model is selected for the 3-D OUU study that includes five design variables and evaluates a total of 130 design candidates. Again using the EA, the study propagates aleatory (wind speed and direction) and epistemic (perturbations in flap deflection angle) uncertainty within the optimization loop and post processes several other uncertain effects. For the best 3-D design, total predictive uncertainty is +15/-42%, due largely to using a relatively coarse (six million cell) grid. That is, the best design drag coefficient estimate is within 15 and 42% of the true value; however, its improvement relative to the no-flaps baseline is accurate within 3-9% uncertainty. / Ph. D.
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Optimal Shape Design for Polymer Electrolyte Membrane Fuel Cell Cathode Air Channel: Modelling, Computational and Mathematical AnalysisAl-Smail, Jamal Hussain 19 March 2012 (has links)
Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right.
The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.
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Optimal Shape Design for Polymer Electrolyte Membrane Fuel Cell Cathode Air Channel: Modelling, Computational and Mathematical AnalysisAl-Smail, Jamal Hussain 19 March 2012 (has links)
Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right.
The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.
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Shape Optimization Using A Meshless Flow Solver And Modern Optimization TechniquesSashi Kumar, G N 11 1900 (has links)
The development of a shape optimization solver using the existing Computational Fluid
Dynamics (CFD) codes is taken up as topic of research in this thesis. A shape optimizer
was initially developed based on Genetic Algorithm (GA) coupled with a CFD solver
in an earlier work. The existing CFD solver is based on Kinetic Flux Vector Splitting
and uses least squares discretization. This solver requires a cloud of points and their
connectivity set, hence this CFD solver is a meshless solver. The advantage of a meshless
solver is utilised in avoiding re-gridding (only connectivity regeneration is required) after each shape change by the shape optimizer. The CFD solver is within the optimization loop, hence evaluation of CFD solver after each shape change is mandatory. Although the earlier shape optimizer developed was found to be robust, but it was taking enoromous amount of time to converge to the optimum solution (details in Appendix). Hence a new evolving method, Ant Colony Optimization (ACO), is implemented to replace GA. A shape optimizer is developed coupling ACO and the meshless CFD solver. To the best of the knowledge of the present author, this is the first time when ACO is implemented for aerodynamic shape optimization problems. Hence, an exhaustive validation has become mandatory. Various test cases such as regeneration problems of
(1) subsonic - supersonic nozzle with a shock in quasi - one dimensional flow
(2) subsonic - supersonic nozzle in a 2-dimensional flow field
(3) NACA 0012 airfoil in 2-dimensional flow and
(4) NACA 4412 airfoil in 2-dimensional flow
have been successfully demonstrated. A comparative study between GA and ACO at
algorithm level is performed using the travelling salesman problem (TSP). A comparative study between the two shape optimizers developed, i.e., GA-CFD and ACO-CFD is carried out using regeneration test case of NACA 4412 airfoil in 2-dimensional flow. GA-CFD performs better in the initial phase of optimization and ACO-CFD performs
better in the later stage. We have combined both the approaches to develop a hybrid
GA-ACO-CFD solver such that the advantages of both GA-CFD and ACO-CFD are retained with the hybrid method. This hybrid approach has 2 stages, namely,
(Stage 1) initial optimum search by GA-CFD (coarse search), the best members from
the optimized solution from GA-CFD are segregated to form the input for the fine search by ACO-CFD and
(Stage 2) final optimum search by ACO-CFD (fine search).
It is observed that this hybrid method performs better than either GA-CFD or ACO-
CFD, i.e., hybrid method attains better optimum in less number of CFD calls. This
hybrid method is applied to the following test cases:
(1) regeneration of subsonic-supersonic nozzle with shock in quasi 1-D flow and
(2) regeneration of NACA 4412 airfoil in 2-dimensional flow.
Two applications on shape optimization, namely,
(1) shape optimization of a body in strongly rotating viscous flow and
(2) shape optimization of a body in supersonic flow such that it enhances separation of binary species, have been successfully demonstrated using the hybrid GA-ACO-CFD method. A KFVS based binary diffusion solver was developed and validated for this purpose.
This hybrid method is now in a state where industrial shape optimization applications
can be handled confidently.
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