Multi-objective optimisation focuses on optimising multiple objectives simultanuously. Evolutionary and immune-based algorithms have been developed in order to solve multi-objective optimisation problems. These algorithms often include a property called elitism, a method of preserving good solutions. This study has focused on how different approaches of elitism affect an algorithm's ability to find optimal solutions in a multi-objective optimisation problem with a discrete and highly discontinuous decision space. Three state-of-the-art algorithms, NSGA-II, SPEA2+ and NNIA2, were implemented, validated and tested against a multi-objective optimisation problem of a miniature plant. Final populations yielded from all the algorithms were included in an analysis. The results of this study indicate that external populations are important in order for algorithms to find optimal solutions in multi-objective optimisation problems with a discrete and highly discontinuous decision spaces.

A mobile ad hoc network (MANET) is an infrastructure-less multi-hop network where each node communicates with other nodes directly or indirectly through intermediate nodes. Thus, all nodes in a MANET basically function as mobile routers participating in some routing protocol required for deciding and maintaining the routes. Since MANETs are infrastructure-less, self-organizing, rapidly deployable wireless networks, they are highly suitable for applications such as military tactical operations, search and rescue missions, disaster relief operations, and target tracking. Building such ad-hoc networks poses a significant technical challenge because of energy constraints and specifically in relation to the application of wireless network protocols. As a result of its highly dynamic and distributed nature, the routing layer within the wireless network protocol stack, presents one of the key technical challenges in MANETs. In particular, energy efficient routing may be the most important design criterion for MANETs since mobile nodes are powered by batteries with limited capacity and variable recharge frequency, according to application demand. In order to conserve power it is essential that a routing protocol be designed to guarantee data delivery even should most of the nodes be asleep and not forwarding packets to other nodes. Load distribution constitutes another important approach to the optimisation of active communication energy. Load distribution enables the maximisation of the network lifetime by facilitating the avoidance of over-utilised nodes when a route is in the process of being selected. Routing algorithms for mobile networks that attempt to optimise routes while at- tempting to retain a small message overhead and maximise the network lifetime has been put forward. However certain of these routing protocols have proved to have a negative impact on node and network lives by inadvertently over-utilising the energy resources of a small set of nodes in favour of others. The conservation of power and careful sharing of the cost of routing packets would ensure an increase in both node and network lifetimes. This thesis proposes simultaneously, by using an ant colony optimisation (ACO) approach, to optimise five power-aware metrics that do result in energy-efficient routes and also to maximise the MANET's lifetime while taking into consideration a realistic mobility model. By using ACO algorithms a set of optimal solutions - the Pareto-optimal set - is found. This thesis proposes five algorithms to solve the multi-objective problem in the routing domain. The first two algorithms, namely, the energy e±ciency for a mobile network using a multi-objective, ant colony optimisation, multi-pheromone (EEMACOMP) algorithm and the energy efficiency for a mobile network using a multi-objective, ant colony optimisation, multi-heuristic (EEMACOMH) algorithm are both adaptations of multi-objective, ant colony optimisation algorithms (MOACO) which are based on the ant colony system (ACS) algorithm. The new algorithms are constructive which means that in every iteration, every ant builds a complete solution. In order to guide the transition from one state to another, the algorithms use pheromone and heuristic information. The next two algorithms, namely, the energy efficiency for a mobile network using a multi-objective, MAX-MIN ant system optimisation, multi-pheromone (EEMMASMP) algorithm and the energy efficiency for a mobile network using a multi-objective, MAX- MIN ant system optimisation, multi-heuristic (EEMMASMH) algorithm, both solve the above multi-objective problem by using an adaptation of the MAX-MIN ant system optimisation algorithm. The last algorithm implemented, namely, the energy efficiency for a mobile network using a multi-objective, ant colony optimisation, multi-colony (EEMACOMC) algorithm uses a multiple colony ACO algorithm. From the experimental results the final conclusions may be summarised as follows:<ul><li> Ant colony, multi-objective optimisation algorithms are suitable for mobile ad hoc networks. These algorithms allow for high adaptation to frequent changes in the topology of the network. </li><li> All five algorithms yielded substantially better results than the non-dominated sorting genetic algorithm (NSGA-II) in terms of the quality of the solution. </li><li> All the results prove that the EEMACOMP outperforms the other four ACO algorithms as well as the NSGA-II algorithm in terms of the number of solutions, closeness to the true Pareto front and diversity. </li></ul> / Thesis (PhD)--University of Pretoria, 2010. / Computer Science / unrestricted

In the recent years there has been a great deal of attention on the optimal demand and supply side strategy. The increase in renewable energy sources and the expansion in demand response programmes has shown the need for a robust power system. These changes in power system require the control of the uncertain generation and load at the same time. Therefore, it is important to provide an optimal scheduling strategy that can meet an adequate energy mix under demand response without affecting the system reliability and economic performance. This thesis addresses the following four aspects to these changes. First, a renewable obligation model is proposed to maintain an adequate energy mix in the economic dispatch model while minimising the operational costs of the allocated spinning reserves. This method considers a minimum renewable penetration that must be achieved daily in the energy mix. If the renewable quota is not achieved, the generation companies are penalised by the system operator. The uncertainty of renewable energy sources are modelled using the probability density functions and these functions are used for scheduling output power from these generators. The overall problem is formulated as a security constrained economic dispatch problem. Second, a combined economic and demand response optimisation model under a renewable obligation is presented. Real data from a large-scale demand response programme are used in the model. The model finds an optimal power dispatch strategy which takes advantage of demand response to minimise generation cost and maximise renewable penetration. The optimisation model is applied to a South African large-scale demand response programme in which the system operator can directly control the participation of the electrical water heaters at a substation level. Actual load profile before and after demand reduction are used to assist the system operator in making optimal decisions on whether a substation should participate in the demand response programme. The application of these real demand response data avoids traditional approaches which assume arbitrary controllability of flexible loads. Third, a stochastic multi-objective economic dispatch model is presented under a renewable obligation. This approach minimises the total operating costs of generators and spinning reserves under renewable obligation while maximising renewable penetration. The intermittency nature of the renewable energy sources is modelled using dynamic scenarios and the proposed model shows the effectiveness of the renewable obligation policy framework. Due to the computational complexity of all possible scenarios, a scenario reduction method is applied to reduce the number of scenarios and solve the model. A Pareto optimal solution is presented for a renewable obligation and further decision making is conducted to assess the trade-offs associated with the Pareto front. Four, a combined risk constrained stochastic economic dispatch and demand response model is presented under renewable obligation. An incentive based optimal power dispatch strategy is implemented to minimise generation costs and maximise renewable penetration. In addition, a risk-constrained approach is used to control the financial risks of the generation company under demand response programme. The coordination strategy for the generation companies to dispatch power using thermal generators and renewable energy sources while maintaining an adequate spinning reserve is presented. The proposed model is robust and can achieve significant demand reduction while increasing renewable penetration and decreasing the financial risks for generation companies. / Thesis (PhD (Electrical Engineering))--University of Pretoria, 2020. / Electrical, Electronic and Computer Engineering / PhD (Electrical Engineering) / Unrestricted

To ensure that wave power reaches its full potential it is important to optimise all aspects of the technology. The optimisation process requires us to consider computationally heavy simulations and several objective functions, so one should carefully choose which optimisation algorithm is most suitable. This study has reviewed three different multi-objective optimisation algorithms: NSGA-II, MO-CMA-ES and MOPSO. The algorithms will optimise a wave park in respect to its generated power, power fluctuation, cost and park area. Multi-objective optimisation results in a so-called Pareto front of many optimal solutions, and this study has investigated how to choose one preferred solution from the Pareto front to best satisfy the user's requirements. The results show that NSGA-II and MOPSO are fast algorithms that can reliably converge towards non-dominated solutions, although NSGA-II may miss essential parts of the solution space and MOPSO is reliant on uncertain parameters. MO-CMA-ES also converges reliably, but computationally heavy parameters make it unsuitable for high-dimensional problems. The preferred solution depends on how all objective functions are weighed against each other, and the results show that the values of the weights will change depending on the specific problem setup. In the end, the identification of the preferred solution from the Pareto front depends on subjective decisions made by human decision makers.

The complex co-evolutionary systems approach -CCeSA - provides a well-suited framework for analysing agricultural systems, serving as a bridge between physical and socioeconomic sciences, alowing for the explaination of phenomena, and for the use of metaphors for thinking and action. By studying agricultural systems as self-generated, hierarchical, complex co-evolutionary farming systems - CCeFSs -, one can investigate the interconnections between the elements that constitute CCeFSs, along with the relationships between CCeFSs and other sytems, as a fundamental step to understanding sustainability as an emergent property of the system. CCeFSs are defined as human activity systems emerging from the purposes, gestalt, mental models, history and weltanschauung of the farm manager, and from his dynamic co-evolution with the environment while managing the resources at his hand to achieve his own multiple, conflicting, dynamic, semi-structured, and often incommensurable and conflicting purposes while performing above thresholds for failure, and enough flexibility to dynamically co-evolve with its changing biophysical and socioeconomic environment for a given future period. Fitness and flexibility are essential features of sustainable CCeFSs because they describe the systems' dynamic capacity to explore and exploit their dynamic phase space while co-evolving with it. This implies that a sustainable CCeFS is conceived as a set of dynamic, co-evolutionary processes, contrasting with the standard view of sustainability as an equilibrium or steady-state. Achieving sustainable CCeFSs is a semi-structured, constrained, multi-objective and dynamic optimisation management problem, with an intractable search space, that can be solved within CCeSA with the help of a multi-objective co-evolutionary optimisation tool. Carnico-ICSPEA2, a co-evolutionary navigator - CoEvoNav -used as a CCeSA's tool for harnessing the complexity of the CCeFS of interest and its environment towards sustainability, is introduced. The software was designed by its end-user - the farm manager and author of this thesis - as an aid for the analysis and optimisation of the San Francisco ranch, a beef cattle enterprise running on temperate pastures and fodder crops in the Central Plateau of Mexico. By combining a non-linear simulator and a multi-objective evolutionary algorithm with a deterministic and stochastic framework, the CoEvoNav imitates the co-evolutionary pattern of the CCeFS of interest. As such, the software was used by the farm manager to navigate through his CCeFS's co-evolutionary phase space towards achieving sustainability at farm level. The ultimate goal was to enhance the farm manager's decision-making process and co-evolutionary skills, through an increased understanding of his system, the co-evolutionary process between his mental models, the CCeFS, and the CoEvoNav, and the continuous discovery of new, improved sets of heuristics. An overview of the methodological, theoretical and philosophical framework of the thesis is introduced. Also, a survey of the Mexican economy, its agricultural sector, and a statistical review of the Mexican beef industry is presented. Concepts such as modern agriculture, the reductionist approach to agricultural research, models, the system's environment, sustainability, conventional and sustainable agriculture, complexity, evolution, simulators, and multi-objective optimisation tools are extensively reviewed. Issues concerning the impossibility of predicting the long-term future behaviour of CCeFSs, along with the use of simulators as decision support tools in the quest for sustainable CCeFSs are discussed. The rationale behind the simulator used for this study, along with that of the multi-objective evolutionary tools used as a makeup of Carnico-ICSPEA2 are explained. A description of the San Francisco ranch, its key on-farm sustainability indicators in the form of objective functions, constraints, and decision variables, and the semi-structured, multi-objective, dynamic, constrained management problem posed by the farm manager's planned introduction of a herd of bulls for fattening as a way to increase the fitness of his CCeFS via a better management of the system's feed surpluses and the acquisition of a new pick-up truck are described as a case study. The tested scenario and the experimental design for the simulations are presented as well. Results from using the CoEvoNav as the farm manager's extended phenotype to solve his multi-objective optimisation problem are described, along with the implications for the management and sustainability of the CCeFS. Finally, the approach and tools developed are evaluated, and the progress made in relation to methodological, theoretical, philosophical and conceptual notions is reviewed along with some future topics for research.

The complex co-evolutionary systems approach -CCeSA - provides a well-suited framework for analysing agricultural systems, serving as a bridge between physical and socioeconomic sciences, alowing for the explaination of phenomena, and for the use of metaphors for thinking and action. By studying agricultural systems as self-generated, hierarchical, complex co-evolutionary farming systems - CCeFSs -, one can investigate the interconnections between the elements that constitute CCeFSs, along with the relationships between CCeFSs and other sytems, as a fundamental step to understanding sustainability as an emergent property of the system. CCeFSs are defined as human activity systems emerging from the purposes, gestalt, mental models, history and weltanschauung of the farm manager, and from his dynamic co-evolution with the environment while managing the resources at his hand to achieve his own multiple, conflicting, dynamic, semi-structured, and often incommensurable and conflicting purposes while performing above thresholds for failure, and enough flexibility to dynamically co-evolve with its changing biophysical and socioeconomic environment for a given future period. Fitness and flexibility are essential features of sustainable CCeFSs because they describe the systems' dynamic capacity to explore and exploit their dynamic phase space while co-evolving with it. This implies that a sustainable CCeFS is conceived as a set of dynamic, co-evolutionary processes, contrasting with the standard view of sustainability as an equilibrium or steady-state. Achieving sustainable CCeFSs is a semi-structured, constrained, multi-objective and dynamic optimisation management problem, with an intractable search space, that can be solved within CCeSA with the help of a multi-objective co-evolutionary optimisation tool. Carnico-ICSPEA2, a co-evolutionary navigator - CoEvoNav -used as a CCeSA's tool for harnessing the complexity of the CCeFS of interest and its environment towards sustainability, is introduced. The software was designed by its end-user - the farm manager and author of this thesis - as an aid for the analysis and optimisation of the San Francisco ranch, a beef cattle enterprise running on temperate pastures and fodder crops in the Central Plateau of Mexico. By combining a non-linear simulator and a multi-objective evolutionary algorithm with a deterministic and stochastic framework, the CoEvoNav imitates the co-evolutionary pattern of the CCeFS of interest. As such, the software was used by the farm manager to navigate through his CCeFS's co-evolutionary phase space towards achieving sustainability at farm level. The ultimate goal was to enhance the farm manager's decision-making process and co-evolutionary skills, through an increased understanding of his system, the co-evolutionary process between his mental models, the CCeFS, and the CoEvoNav, and the continuous discovery of new, improved sets of heuristics. An overview of the methodological, theoretical and philosophical framework of the thesis is introduced. Also, a survey of the Mexican economy, its agricultural sector, and a statistical review of the Mexican beef industry is presented. Concepts such as modern agriculture, the reductionist approach to agricultural research, models, the system's environment, sustainability, conventional and sustainable agriculture, complexity, evolution, simulators, and multi-objective optimisation tools are extensively reviewed. Issues concerning the impossibility of predicting the long-term future behaviour of CCeFSs, along with the use of simulators as decision support tools in the quest for sustainable CCeFSs are discussed. The rationale behind the simulator used for this study, along with that of the multi-objective evolutionary tools used as a makeup of Carnico-ICSPEA2 are explained. A description of the San Francisco ranch, its key on-farm sustainability indicators in the form of objective functions, constraints, and decision variables, and the semi-structured, multi-objective, dynamic, constrained management problem posed by the farm manager's planned introduction of a herd of bulls for fattening as a way to increase the fitness of his CCeFS via a better management of the system's feed surpluses and the acquisition of a new pick-up truck are described as a case study. The tested scenario and the experimental design for the simulations are presented as well. Results from using the CoEvoNav as the farm manager's extended phenotype to solve his multi-objective optimisation problem are described, along with the implications for the management and sustainability of the CCeFS. Finally, the approach and tools developed are evaluated, and the progress made in relation to methodological, theoretical, philosophical and conceptual notions is reviewed along with some future topics for research.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In a minerals processing environment, stable production processes, cost minimisation and energy efficiency are key to operational excellence, safety and profitability. At an ilmenite smelter, typically found in the heavy minerals industry, it is no different. Management of an ilmenite smelting process is a complex, multi-variable challenge with high costs and safety risks at stake. A by-product of ilmenite smelting is superheated carbon monoxide (CO) gas, or furnace off-gas. This gas is inflammable and extremely poisonous to humans. At the same time the gas is a potential energy source for various on-site heating applications. Re-using furnace off-gas can increase the energy efficiency of the energy intensive smelting process and can save on the cost of procuring other gas for heating purposes. In this research project, the management of CO gas from the Tronox KZN Sands ilmenite smelter in South Africa was studied with the aim of optimising the current utilisation of the gas. In the absence of any buffer capacity in the form of a pressure vessel, the stability of the available CO gas is directly dependent on the stability of the furnaces. The CO gas has been identified as a partial replacement for methane gas which is currently purchased for drying and heating of feed material and pre-heating of certain smelter equipment. With no buffer capacity between the furnaces and the gas consuming plants, a dynamic prioritisation approach had to be found if the CO was to replace the methane. The dynamics of this supply-demand problem, which has been termed the “CO gas problem”, needed to be studied. A discrete-event simulation model was developed to match the variable supply of CO gas to the variable demand for gas over time – the demand being a function of the availability of the plants requesting the gas, and the feed rates and types of feed material processed at those plants. The problem was formulated as a multi-objective optimisation problem with the two main, conflicting objectives, identified as: 1) the average production time lost per plant per day due to CO-methane switchovers; and 2) the average monthly saving on methane gas costs due to lower consumption thereof. A metaheuristic, namely multi-objective optimisation using the cross-entropy method, or MOO CEM, was applied as optimisation algorithm to solve the CO gas problem. The performance of the MOO CEM algorithm was compared with that of a recognised benchmark algorithm for multi-objective optimisation, the NSGA II, when both were applied to the CO gas problem. The background of multi-objective optimisation, metaheuristics and the usage of furnace off-gas, particularly CO gas, were investigated in the literature review. The simulation model was then developed and the optimisation algorithm applied. The research aimed to comment on the merit of the MOO CEM algorithm for solving the dynamic, stochastic CO gas problem and on the algorithm’s performance compared to the benchmark algorithm. The results served as a basis for recommendations to Tronox KZN Sands in order to implement a project to optimise usage and management of the CO gas. / AFRIKAANSE OPSOMMING: In mineraalprosessering is stabiele produksieprosesse, kostebeperking en energie-effektiwiteit sleuteldrywers tot bedryfsprestasie, veiligheid en wins. ‘n Ilmenietsmelter, tipies aangetref in swaarmineraleprosessering, is geen uitsondering nie. Die bestuur van ‘n ilmenietsmelter is ‘n komplekse, multi-doelwit uitdaging waar hoë kostes en veiligheidsrisiko’s ter sprake is. ‘n Neweproduk van die ilmenietsmeltproses is superverhitte koolstofmonoksiedgas (CO gas). Hierdie gas is ontvlambaar en uiters giftig vir die mens. Terselfdertyd kan hierdie gas benut word as energiebron vir allerlei verhittingstoepassings. Die herbenutting van CO gas vanaf die smelter kan die energie-effektiwiteit van die energie-intensiewe smeltproses verhoog en kan verder kostes bespaar op die aankoop van ‘n ander gas vir verhittingsdoeleindes. In hierdie navorsingsprojek is die bestuur van die CO gasstroom wat deur die ilmenietsmelter van Tronox KZN Sands in Suid-Afrika geproduseer word, ondersoek met die doel om die huidige benuttingsvlak daarvan te verbeter. Weens die afwesigheid van enige bufferkapasiteit in die vorm van ‘n drukbestande tenk, is die stabiliteit van CO gas beskikbaar vir hergebruik direk afhanklik van die stabiliteit van die twee hoogoonde wat die gas produseer. Die CO gas kan gedeeltelik metaangas, wat tans aangekoop word vir die droog en verhitting van voermateriaal en vir die voorverhitting van sekere smeltertoerusting, vervang. Met geen bufferkapasiteit tussen die hoogoonde en die aanlegte waar die gas verbruik word nie, was die ondersoek van ‘n dinamiese prioritiseringsbenadering nodig om te kon vasstel of die CO die metaangas kon vervang. Die dinamika van hierdie vraag-aanbod probleem, getiteld die “CO gasprobleem”, moes bestudeer word. ‘n Diskrete-element simulasiemodel is ontwikkel as probleemoplossingshulpmiddel om die vraag-aanbodproses te modelleer en die prioritiseringsbenadering te ondersoek. Die doel van die model was om oor tyd die veranderlike hoeveelhede van geproduseerde CO teenoor die veranderlike gasaanvraag te vergelyk. Die vlak van gasaanvraag is afhanklik van die beskikbaarheidsvlak van die aanlegte waar die gas verbruik word, sowel as die voertempo’s en tipes voermateriaal in laasgenoemde aanlegte. Die probleem is geformuleer as ‘n multi-doelwit optimeringsprobleem met twee hoof, teenstrydige doelwitte: 1) die gemiddelde verlies aan produksietyd per aanleg per dag weens oorgeskakelings tussen CO en metaangas; 2) die gemiddelde maandelikse besparing op metaangaskoste weens laer verbruik van dié gas. ‘n Metaheuristiek, genaamd MOO CEM (multi-objective optimisation using the cross-entropy method), is ingespan as optimeringsalgoritme om die CO gasprobleem op te los. Die prestasie van die MOO CEM algoritme is vergelyk met dié van ‘n algemeen aanvaarde riglynalgoritme, die NSGA II, met beide toepas op die CO gasprobleem. The agtergrond van multi-doelwit optimering, metaheuristieke en die benutting van hoogoond af-gas, spesifiek CO gas, is ondersoek in die literatuurstudie. Die simulasiemodel is daarna ontwikkel en die optimeringsalgoritme is toegepas.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Society is continually in search of ways to optimise various objectives. When faced with multiple and con icting objectives, humans are in need of solution techniques to enable optimisation. This research is based on a recent venture in the eld of multi-objective optimisation, the use of the cross-entropy method to solve multi-objective problems. The document provides a brief overview of the two elds, multi-objective optimisation and the cross-entropy method, touching on literature, basic concepts and applications or techniques. The application of the method to two problems is then investigated. The rst application is to the multi-objective vehicle routing problem with soft time windows, a widely studied problem with many real-world applications. The problem is modelled mathematically with a transition probability matrix that is updated according to cross-entropy principles before converging to an approximation solution set. The highly constrained problem is successfully modelled and the optimisation algorithm is applied to a set of benchmark problems. It was found that the cross-entropy method for multi-objective optimisation is a valid technique in providing feasible and non-dominated solutions. The second application is to a real world case study in blood management done at the Western Province Blood Transfusion Service. The conceptual model is derived from interviews with relevant stakeholders before discrete event simulation is used to model the system. The cross-entropy method is used to optimise the inventory policy of the system by simultaneously maximising the combined service level of the system and minimising the total distance travelled. By integrating the optimisation and simulation model, the study shows that the inventory policy of the service can improve signi cantly, and the use of the cross-entropy algorithm adequately progresses to a front of solutions. The research proves the remarkable width and simplicity of possible applications of the cross-entropy algorithm for multi-objective optimisation, whilst contributing to literature on the vehicle routing problem and blood management. Results on benchmark problems for the vehicle routing problem with soft time windows are provided and an improved inventory policy is suggested to the Western Province Blood Transfusion Service. / AFRIKAANSE OPSOMMING: Die mensdom is voortdurend op soek na maniere om verskeie doelwitte te optimeer. Wanneer die mens konfrontreer word met meervoudige en botsende doelwitte, is oplossingsmetodes nodig om optimering te bewerkstellig. Hierdie navorsing is baseer op 'n nuwe wending in die veld van multi-doelwit optimering, naamlik die gebruik van die kruisentropie metode om multi-doelwit probleme op te los. Die dokument verskaf 'n bre e oorsig oor die twee velde { multi-doelwit optimering en die kruis-entropie-metode { deur kortliks te kyk na die beskikbare literatuur, basiese beginsels, toepassingsareas en metodes. Die toepassing van die metode op twee onafhanklike probleme word dan ondersoek. Die eerste toepassing is di e van die multi-doelwit voertuigroeteringsprobleem met plooibare tydvensters. Die probleem word eers wiskundig modelleer met 'n oorgangswaarskynlikheidsmatriks. Die matriks word dan deur kruis-entropie beginsels opdateer voor dit konvergeer na 'n benaderingsfront van oplossings. Die oplossingsruimte is onderwerp aan heelwat beperkings, maar die probleem is suksesvol modelleer en die optimeringsalgoritme is gevolglik toegepas op 'n stel verwysingsprobleme. Die navorsing het gevind dat die kruis-entropie metode vir multi-doelwit optimering 'n geldige metode is om 'n uitvoerbare front van oplossings te beraam. Die tweede toepassing is op 'n gevallestudie van die bestuur van bloed binne die konteks van die Westelike Provinsie Bloedoortappingsdiens. Na aanleiding van onderhoude met die relevante belanghebbers is 'n konsepmodel geskep voor 'n simulasiemodel van die stelsel gebou is. Die kruis-entropie metode is gebruik om die voorraadbeleid van die stelsel te optimeer deur 'n gesamentlike diensvlak van die stelsel te maksimeer en terselfdetyd die totale reis-afstand te minimeer. Deur die optimerings- en simulasiemodel te integreer, wys die studie dat die voorraadbeleid van die diens aansienlik kan verbeter, en dat die kruis-entropie algoritme in staat is om na 'n front van oplossings te beweeg. Die navorsing bewys die merkwaardige wydte en eenvoud van moontlike toepassings van die kruis-entropie algoritme vir multidoelwit optimering, terwyl dit 'n bydrae lewer tot die afsonderlike velde van voertuigroetering en die bestuur van bloed. Uitslae vir die verwysingsprobleme van die voertuigroeteringsprobleem met plooibare tydvensters word verskaf en 'n verbeterde voorraadbeleid word aan die Westelike Provinsie Bloedoortappingsdiens voorgestel.

L'hydrogène produit à partir de sources renouvelables et utilisé dans les piles à combustible pour diverses applications, tant mobiles que stationnaires, constitue un vecteur énergétique très prometteur, dans un contexte de développement durable. Les « feuilles de route » stratégiques, élaborées au niveau européen, national ou régional, consacrées aux potentialités énergétiques de l’hydrogène, ainsi que l’analyse des publications scientifiques ont cependant identifié le manque d'infrastructures, comme l'un des principaux obstacles au développement de l'économie « hydrogène ». Cette étude s’inscrit dans le cadre du développement d’une méthodologie de conception d'une chaîne logistique « hydrogène » (production, stockage et transport). La formulation, basée sur une procédure de programmation mathématique linéaire en variables mixtes, implique une approche multicritère concernant la minimisation du prix de revient de l’hydrogène, l’impact sur le réchauffement climatique et un indice de risque, en prenant en compte une échelle tant régionale que nationale. L’optimisation multi-objectif repose sur une stratégie Ɛ-contrainte développée à partir d’une méthode lexicographique menant à la construction de fronts de Pareto offrant un grand nombre de solutions. La procédure d’aide à la décision M-TOPSIS est ensuite utilisée pour choisir le meilleur compromis. Le modèle est appliqué à une étude de cas en Grande-Bretagne, issue de la littérature spécialisée, qui sert de référence pour comparer les approches mono- et multi-objectif. Ensuite, la modélisation et l'optimisation de la chaîne d'approvisionnement d'hydrogène pour la région Midi-Pyrénées ont été étudiées dans le cadre du projet «H2 vert carburant». Un problème mono/multi-période est traité selon des scénarios d'optimisation basés sur la stratégie Ɛ-contrainte développée à partir d’une méthode lexicographique. Le système d’information ArcGIS® est ensuite utilisé pour valider les solutions obtenues par optimisation multi-objectif. Cette technologie permet d'associer une période de temps aux configurations de la chaîne logistique hydrogène et d’analyser plus finement les résultats de la conception du réseau H2. L’extension au cas de la France répond à un double objectif : d'une part, tester la robustesse de la méthode à une échelle géographique différente et, d’autre part, examiner si les résultats obtenus au niveau régional sont cohérents avec ceux de l'échelle nationale. Dans cette étude de cas, l'outil spatial ArcGIS® est utilisé avant optimisation pour identifier les contraintes géographiques. Un scénario prenant en compte un cycle économique est également traité. Les optimisations mono et multi-objectif présentent des différences relatives au mode de déploiement de filière, centralisé ou décentralisé, et au type de technologie des unités production, ainsi qu’à leur taille. Les résultats confirment l'importance d'étudier différentes échelles spatiales. / Hydrogen produced from renewable sources and used in fuel cells both for mobile and stationary applications constitutes a very promising energy carrier in a context of sustainable development. Yet the strategic roadmaps that were currently published about the energy potentialities of hydrogen at European, national and regional level as well as the analysis of the scientific publications in this field have identified the lack of infrastructures as a major barrier to the development of a « hydrogen » economy. This study focuses on the development of a methodological framework for the design of a hydrogen supply chain (HSC) (production, storage and transportation). The formulation based on mixed integer linear programming involves a multi-criteria approach where three objectives have to be optimised simultaneously, i.e., cost, global warming potential and safety risk, either at national or regional scale. This problem is solved by implementing lexicographic and Ɛ-constraint methods. The solution consists of a Pareto front, corresponding to different design strategies in the associated variable space. Multiple choice decision making based on M-TOPSIS (Modified Technique for Order Preference by Similarity to Ideal Solution) analysis is then selected to find the best compromise. The mathematical model is applied to a case study reported in the literature survey and dedicated to Great Britain for validation purpose, comparing the results between mono- and multi-objective approaches. In the regional case, the modelling and optimisation of the HSC in the Midi-Pyrénées region was carried out in the framework of the project “H2 as a green fuel”. A mono/multi period problem is treated with different optimisation scenarios using Ɛ-constraint and lexicographic methods for the optimisation stage. The geographic information system (GIS) is introduced and allows organising, analysing and mapping spatial data. The optimisation of the HSC is then applied to the national case of France. The objective is twofold: on the one hand, to examine if the methodology is robust enough to tackle a different geographic scale and second to see if the regional approach is consistent with the national scale. In this case study, the ArcGIS® spatial tool is used before optimisation to identify the geographic items that are further used in the optimisation step. A scenario with an economic cycle is also considered. Mono- and multi-objective optimisations exhibit some differences concerning the degree of centralisation of the network and the selection of the production technology type and size. The obtained results confirm that different spatial and temporal scales are required to encompass the complexity of the problem.

Depuis une dizaine d’années, les matériaux composites sont de plus en plus utilisés dans de nombreuses applications, et en particulier dans l'aéronautique grâce à leurs excellentes propriétés mécaniques et leur faible densité. Ainsi les derniers modèles d'Airbus (A350) et de Boeing (B787) utilisent plus de 50% en masse de composites, principalement des polymères renforcés de fibres de carbone (CFRP). Toutefois, l'augmentation de l'utilisation des CFRP soulève des préoccupations environnementales quant à leur fin de vie à travers l'élimination des déchets, la consommation de ressources non renouvelables ainsi que la nécessité de recycler les déchets CFRP. Dans ces travaux de thèse, un modèle générique est développé afin de proposer une gestion optimale des déchets de CFRP aéronautiques en prenant en compte simultanément des objectifs économiques et environnementaux. Ainsi, dans un premier temps une approche systémique suivant les lignes directrices d’une approche par Analyse de Cycle de Vie est effectuée afin de modéliser les impacts environnementaux des procédés de recyclage des CFRP, avec une attention toute particulière sur l’impact de réchauffement climatique. Ensuite, toute la chaîne logistique du recyclage des déchets CFRP est modélisée en partant des sites de démantèlement des avions jusqu’à la réutilisation des fibres recyclées vers d’autres applications possibles. Une stratégie d’optimisation multi-objectif de programmation mathématique, d’-contrainte et de technique lexicographique est développé mettent également en jeu des techniques d’aide à la décision appropriées (M-TOPSIS, PROMETHEE-GAIA). Différentes configurations de chaînes logistiques de déchet CFRP sont ainsi proposées et plusieurs scénarios sont étudiés et optimisés de façon à prendre en compte les sites de recyclage déjà existants dans une vision mono-période ainsi que déploiement de nouveaux sites selon une approche multipériode. Le cas de la France sert d’illustration à la démarche et les configurations proposées pour implanter de nouveaux sites de façon optimale traitant une fibre recyclée facilement valorisable pour des applications ciblées sont analysées et discutées minimisant le coût ou maximisant le profit pour un critère économique et minimisant un critère environnemental basé sur le potentiel de réchauffement climatique. / Composites have been increasingly used in different applications in the last decade, especially in aerospace due to their high strength and lightweight characteristics. Indeed, the latest models of Airbus (A350) and Boeing (B787) have employed more than 50 wt% of composites, mainly Carbon Fibre Reinforced Polymers (CFRP). Yet, the increased use of CFRP has raised the environmental concerns about their end-of-life related to waste disposal, consumption of non-renewable resources for manufacturing and the need to recycle CFRP wastes. In this study, a generic model is developed in order to propose an optimal management of aerospace CFRP wastes taking into account economic and environmental objectives. Firstly, a life-cycle systemic approach is used to model the environmental impacts of CFRP recycling processes focusing on Global Warming Potential (GWP) following the guidelines of Life Cycle Assessment (LCA). The whole supply chain for recycling CFRP pathways is then modelled from aircraft dismantling sites to the reuse of recycled fibres in various applications. A multi-objective optimisation strategy based on mathematical programming, -constraint and lexicographic methods with appropriate decisionmaking techniques (M-TOPSIS, PROMETHEE-GAIA) has been developed to determine CFRP waste supply chain configurations. Various scenarios have been studied in order to take account the potential of existing recycling sites in a mono-period visions as well as the deployment of new sites in a multi-period approach considering the case study of France for illustration purpose. The solutions obtained from optimisation process allow developing optimal strategies for the implementation of CFRP recovery with recycled fibres (of acceptable quality) for the targeted substitution use while minimising cost /maximising profit for an economic criterion and minimising an environmental impact based on GWP.