Modify Kaunda | Cape peninsula University of technology (original) (raw)
Conference Presentations by Modify Kaunda
This paper presents a new mathematical approach for optimizing the geometry of a thermoacoustic r... more This paper presents a new mathematical approach for optimizing the geometry of a thermoacoustic regenerator, aimed at producing efficient thermoacoustic engines. Optimal set of parameters describing the device are computed for a chosen thermoacoustic couple to illustrate this approach. Hence, a non-linear multiobjective problem is formulated in GAMS and solved using Lindoglobal solver. Lexicographic optimization is presented as an alternative optimization technique to the common used weighting methods. This approach establishes a hierarchical order among all the optimization objectives instead of giving them a specific (and most of the time, arbitrary) weight. In this work, the optimization criteria are chosen as work output, viscous resistance as well as thermal losses that are typically disregarded when modeling the device. A practical example is given, in a hypothetical scenario, showing how the proposed optimization technique may help thermoacoustic regenerator designers to identify Pareto optimal solutions when dealing with geometric parameters.
This work proposes a multi-objective optimization approach to model and optimize small scale stan... more This work proposes a multi-objective optimization approach to model and optimize small scale standing wave thermoacoustic
refrigerator (TAR). This study aims to optimize the geometric variables namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing thermoacoustic refrigerators. Unlike most previous studies, these variables are considered interdependent. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). A practical example considering three different gases is given to illustrate the approach. This approach has been implemented in the software GAMS (General Algebraic modelling System) and Pareto optimal solutions describing the most preferred geometry for maximum performance of the device are computed using the augmented Epsilon-constraint
method.
Thermoacoustic heat engines provide a practical solution to the problem of heat management where ... more Thermoacoustic heat engines provide a practical solution to the problem of heat management where heat can be pumped or spot cooling can be produced. However, the most inhibiting characteristic of thermoacoustic cooling is their current lack of efficiencies. This paper illustrates the use of the augmented ε-constraint method implemented in GAMS (General Algebraic Modeling Software), aimed at optimizing the geometry of a thermoacoustic regenerator. Lexicographic optimization is presented as an alternative optimization technique to the common used weighting methods.
Papers by Modify Kaunda
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
International Journal for Numerical Methods in Engineering
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
International Journal of Impact Engineering, 1996
The paper reviews work that has been carried out in recent years in the Centre for Research in Co... more The paper reviews work that has been carried out in recent years in the Centre for Research in Computational and Applied Mechanics (CERECAM) at the University of Cape Town on the compact internal variable formulation of the problem of an elastic-plastic body subject to incremental loading. The fundamental problem is expressed as a convex nonlinear programming problem. The simplest two
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
2013 IEEE International Conference on Industrial Technology (ICIT), 2013
As a result of miniaturisation, electronic products are shrinking in size and weight but with gre... more As a result of miniaturisation, electronic products are shrinking in size and weight but with greater pressure for cost reduction. Heat fluxes have increased considerably and hence thermal management becomes crucial from the reliability point of view. Thermoacoustic heat engines provide a practical solution to the problem of heat management in microcircuits where they can be used to pump heat or produce spot cooling of specific circuit elements. However, the most inhibiting characteristic of thermoacoustic cooling is its current lack of efficiency. A multiobjective optimization approach is presented to model and optimize a small-scale thermoacoustic regenerator.
Abstract Purpose – This paper aims to illustrate the use of the augmented epsilon-constraint meth... more Abstract
Purpose – This paper aims to illustrate the use of the augmented epsilon-constraint method
implemented in general algebraic modelling system (GAMS), aimed at optimizing the geometry of a
thermoacoustic regenerator. Thermoacoustic heat engines provide a practical solution to the problem of
heat management where heat can be pumped or spot cooling can be produced. However, the most
inhibiting characteristic of thermoacoustic cooling is their current lack of efficiencies.
Design/methodology/approach – Lexicographic optimization is presented as an alternative
optimization technique to the common used weighting methods. This approach establishes a
hierarchical order among all the optimization objectives instead of giving them a specific (and most of
the time, arbitrary) weight.
Findings – A practical example is given, in a hypothetical scenario, showing how the proposed
optimization technique may help thermoacoustic regenerator designers to identify Pareto optimal
solutions when dealing with geometric parameters. This study highlights the fact that the geometrical
parameters are interdependent, which support the use of a multi-objective approach for optimization in
thermoacoustic.
Originality/value – The research output from this paper can be a valuable resource to support
designers in building efficient thermoacoustic device. The research illustrates the use of a lexicographic
optimization to provide more meaningful results describing the geometry of thermoacoustic
regenerator. It applies the epsilon-constraint method (AUGMENCON) to solve a five-criteria mixed
integer non-linear problem implemented in GAMS (GAM software).
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing thermoacoustic refrigerators. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multi-objective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple thermoacoustic refrigerator.
Computers & Structures, 2015
ABSTRACT One-step multiple-value methods are developed which involve an accurate predictor method... more ABSTRACT One-step multiple-value methods are developed which involve an accurate predictor method with higher derivatives, followed by a corrector method cast in form of an enhanced Newton-Raphson scheme. The generalized Newmark (GNpj) method may be recovered as a special case. The algorithms serve to match the accuracy of the fourth-order Runge-Kutta-Fehlberg method. Challenges to solve more reliably, accurately and efficiently non-linear differential equations are highlighted as stemming from amplitude and phase shift errors introduced by discretization in space and time - a continuous-discrete transformation. The classical stability tool of spectral radius is performed on linear systems whereas Liapunov method on nonlinear systems.
IUTAM BookSeries, 2008
The fundamental problem of an elastic-plastic body subjected to incremental loading is reviewed u... more The fundamental problem of an elastic-plastic body subjected to incremental loading is reviewed using a compact internal variable approach which is expressed as a convex nonlinear mathematical programming problem. The approach is based on work carried out by Martin and co-workers [1–6] at the University of Cape Town. Additional contributions are introduced in the area of solution algorithms. Algorithms are
International Journal of Impact Engineering, 1996
The paper reviews work that has been carried out in recent years in the Centre for Research in Co... more The paper reviews work that has been carried out in recent years in the Centre for Research in Computational and Applied Mechanics (CERECAM) at the University of Cape Town on the compact internal variable formulation of the problem of an elastic-plastic body subject to incremental loading. The fundamental problem is expressed as a convex nonlinear programming problem. The simplest two
As a result of miniaturisation, electronic products are shrinking in size and weight but with gre... more As a result of miniaturisation, electronic products are shrinking in size and weight but with greater pressure for cost reduction. Heat fluxes have increased considerably and hence thermal management becomes crucial from the reliability point of view. Thermoacoustic heat engines provide a practical solution to the problem of heat management in microcircuits where they can be used to pump heat or produce spot cooling of specific circuit elements. However, the most inhibiting characteristic of thermoacoustic cooling is its current lack of efficiency. A multiobjective optimization approach is presented to model and optimize a small-scale thermoacoustic regenerator. Optimization of multiple objectives components is considered and global optimal solutions have been identified using the epsilon constraint method.
This work illustrates the use of a multi-objective optimization approach to model and optimize th... more This work illustrates the use of a multi-objective optimization approach to model and optimize the performance of a simple thermoacoustic engine. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the model. Work output, viscous loss, conductive heat loss, convective heat loss and radiative heat loss have been used to measure the performance of the engine. The optimization task is formulated as a five-criterion mixed-integer non-linear programming problem. Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the design would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using the augmented E-constraint method. This approach has been implemented in GAMS (General Algebraic Modelling System).
This paper presents a new mathematical approach for optimizing the geometry of a thermoacoustic r... more This paper presents a new mathematical approach for optimizing the geometry of a thermoacoustic regenerator, aimed at producing efficient thermoacoustic engines. Optimal set of parameters describing the device are computed for a chosen thermoacoustic couple to illustrate this approach. Hence, a non-linear multiobjective problem is formulated in GAMS and solved using Lindoglobal solver. Lexicographic optimization is presented as an alternative optimization technique to the common used weighting methods. This approach establishes a hierarchical order among all the optimization objectives instead of giving them a specific (and most of the time, arbitrary) weight. In this work, the optimization criteria are chosen as work output, viscous resistance as well as thermal losses that are typically disregarded when modeling the device. A practical example is given, in a hypothetical scenario, showing how the proposed optimization technique may help thermoacoustic regenerator designers to identify Pareto optimal solutions when dealing with geometric parameters.
This work proposes a multi-objective optimization approach to model and optimize small scale stan... more This work proposes a multi-objective optimization approach to model and optimize small scale standing wave thermoacoustic
refrigerator (TAR). This study aims to optimize the geometric variables namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing thermoacoustic refrigerators. Unlike most previous studies, these variables are considered interdependent. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). A practical example considering three different gases is given to illustrate the approach. This approach has been implemented in the software GAMS (General Algebraic modelling System) and Pareto optimal solutions describing the most preferred geometry for maximum performance of the device are computed using the augmented Epsilon-constraint
method.
Thermoacoustic heat engines provide a practical solution to the problem of heat management where ... more Thermoacoustic heat engines provide a practical solution to the problem of heat management where heat can be pumped or spot cooling can be produced. However, the most inhibiting characteristic of thermoacoustic cooling is their current lack of efficiencies. This paper illustrates the use of the augmented ε-constraint method implemented in GAMS (General Algebraic Modeling Software), aimed at optimizing the geometry of a thermoacoustic regenerator. Lexicographic optimization is presented as an alternative optimization technique to the common used weighting methods.
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
International Journal for Numerical Methods in Engineering
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
International Journal of Impact Engineering, 1996
The paper reviews work that has been carried out in recent years in the Centre for Research in Co... more The paper reviews work that has been carried out in recent years in the Centre for Research in Computational and Applied Mechanics (CERECAM) at the University of Cape Town on the compact internal variable formulation of the problem of an elastic-plastic body subject to incremental loading. The fundamental problem is expressed as a convex nonlinear programming problem. The simplest two
Heat and Mass Transfer, 2014
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing TARs. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multiobjective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple TAR.
2013 IEEE International Conference on Industrial Technology (ICIT), 2013
As a result of miniaturisation, electronic products are shrinking in size and weight but with gre... more As a result of miniaturisation, electronic products are shrinking in size and weight but with greater pressure for cost reduction. Heat fluxes have increased considerably and hence thermal management becomes crucial from the reliability point of view. Thermoacoustic heat engines provide a practical solution to the problem of heat management in microcircuits where they can be used to pump heat or produce spot cooling of specific circuit elements. However, the most inhibiting characteristic of thermoacoustic cooling is its current lack of efficiency. A multiobjective optimization approach is presented to model and optimize a small-scale thermoacoustic regenerator.
Abstract Purpose – This paper aims to illustrate the use of the augmented epsilon-constraint meth... more Abstract
Purpose – This paper aims to illustrate the use of the augmented epsilon-constraint method
implemented in general algebraic modelling system (GAMS), aimed at optimizing the geometry of a
thermoacoustic regenerator. Thermoacoustic heat engines provide a practical solution to the problem of
heat management where heat can be pumped or spot cooling can be produced. However, the most
inhibiting characteristic of thermoacoustic cooling is their current lack of efficiencies.
Design/methodology/approach – Lexicographic optimization is presented as an alternative
optimization technique to the common used weighting methods. This approach establishes a
hierarchical order among all the optimization objectives instead of giving them a specific (and most of
the time, arbitrary) weight.
Findings – A practical example is given, in a hypothetical scenario, showing how the proposed
optimization technique may help thermoacoustic regenerator designers to identify Pareto optimal
solutions when dealing with geometric parameters. This study highlights the fact that the geometrical
parameters are interdependent, which support the use of a multi-objective approach for optimization in
thermoacoustic.
Originality/value – The research output from this paper can be a valuable resource to support
designers in building efficient thermoacoustic device. The research illustrates the use of a lexicographic
optimization to provide more meaningful results describing the geometry of thermoacoustic
regenerator. It applies the epsilon-constraint method (AUGMENCON) to solve a five-criteria mixed
integer non-linear problem implemented in GAMS (GAM software).
This work develops a novel mathematical programming model to optimize the performance of a simple... more This work develops a novel mathematical programming model to optimize the performance of a simple thermoacoustic refrigerator (TAR). This study aims to optimize the geometric parameters namely the stack position, the stack length, the blockage ratio and the plate spacing involved in designing thermoacoustic refrigerators. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the models. The cooling load, the coefficient of performance and the acoustic power loss have been used to measure the performance of the device. The optimization task is formulated as a three-criterion nonlinear programming problem with discontinuous derivatives (DNLP). Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the geometrical parameters describing would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using a lexicographic multi-objective optimization scheme. Additionally, this approach illustrates the difference between a design for maximum cooling and best coefficient of performance of a simple thermoacoustic refrigerator.
Computers & Structures, 2015
ABSTRACT One-step multiple-value methods are developed which involve an accurate predictor method... more ABSTRACT One-step multiple-value methods are developed which involve an accurate predictor method with higher derivatives, followed by a corrector method cast in form of an enhanced Newton-Raphson scheme. The generalized Newmark (GNpj) method may be recovered as a special case. The algorithms serve to match the accuracy of the fourth-order Runge-Kutta-Fehlberg method. Challenges to solve more reliably, accurately and efficiently non-linear differential equations are highlighted as stemming from amplitude and phase shift errors introduced by discretization in space and time - a continuous-discrete transformation. The classical stability tool of spectral radius is performed on linear systems whereas Liapunov method on nonlinear systems.
IUTAM BookSeries, 2008
The fundamental problem of an elastic-plastic body subjected to incremental loading is reviewed u... more The fundamental problem of an elastic-plastic body subjected to incremental loading is reviewed using a compact internal variable approach which is expressed as a convex nonlinear mathematical programming problem. The approach is based on work carried out by Martin and co-workers [1–6] at the University of Cape Town. Additional contributions are introduced in the area of solution algorithms. Algorithms are
International Journal of Impact Engineering, 1996
The paper reviews work that has been carried out in recent years in the Centre for Research in Co... more The paper reviews work that has been carried out in recent years in the Centre for Research in Computational and Applied Mechanics (CERECAM) at the University of Cape Town on the compact internal variable formulation of the problem of an elastic-plastic body subject to incremental loading. The fundamental problem is expressed as a convex nonlinear programming problem. The simplest two
As a result of miniaturisation, electronic products are shrinking in size and weight but with gre... more As a result of miniaturisation, electronic products are shrinking in size and weight but with greater pressure for cost reduction. Heat fluxes have increased considerably and hence thermal management becomes crucial from the reliability point of view. Thermoacoustic heat engines provide a practical solution to the problem of heat management in microcircuits where they can be used to pump heat or produce spot cooling of specific circuit elements. However, the most inhibiting characteristic of thermoacoustic cooling is its current lack of efficiency. A multiobjective optimization approach is presented to model and optimize a small-scale thermoacoustic regenerator. Optimization of multiple objectives components is considered and global optimal solutions have been identified using the epsilon constraint method.
This work illustrates the use of a multi-objective optimization approach to model and optimize th... more This work illustrates the use of a multi-objective optimization approach to model and optimize the performance of a simple thermoacoustic engine. System parameters and constraints that capture the underlying thermoacoustic dynamics have been used to define the model. Work output, viscous loss, conductive heat loss, convective heat loss and radiative heat loss have been used to measure the performance of the engine. The optimization task is formulated as a five-criterion mixed-integer non-linear programming problem. Since we optimize multiple objectives simultaneously, each objective component has been given a weighting factor to provide appropriate user-defined emphasis. A practical example is given to illustrate the approach. We have determined a design statement of a stack describing how the design would change if emphasis is given to one objective in particular. We also considered optimization of multiple objectives components simultaneously and identify global optimal solutions describing the stack geometry using the augmented E-constraint method. This approach has been implemented in GAMS (General Algebraic Modelling System).