Gemischt-autonome Flotten in der urbanen Logistik

We consider a city logistics application in which a service provider seeks a repeatable plan to transport commodities from distribution centers to satellites. The service provider uses a mixed autonomous fleet that is composed of autonomous vehicles and manually operated vehicles. The autonomous vehicles are only able to travel independently on feasible streets of the heterogeneous infrastructure but elsewhere need to be pulled by manually operated vehicles in platoons. We introduce the service network design problem with mixed autonomous fleets to determine a tactical plan that minimizes the total costs over a medium-term time horizon. The tactical plan determines the size and mix of the fleet, schedules transportation services, and decides on the routing or outsourcing of commodities. We model this problem as an integer program on a time-expanded network and study the impact of different problem characteristics on the solutions. To precisely depict the synchronization requirements of the problem, the time-expanded networks need to consider narrow time intervals. Thus, we develop an exact solution approach based on the dynamic discretization discovery scheme that refines partially time-expanded networks containing only a fraction of the nodes and arcs of the fully time-expanded network. Further methodological contributions of this work include the introduction of valid inequalities, two enhancements that exploit linear relaxations, and a heuristic search space restriction. Computational experiments show that all evaluated variants of the solution approach outperform a commercial solver. For transferring a tactical plan to an operational solution that minimizes the transshipment effort on a given day, we present a post-processing technique that specifically assigns commodities to vehicles and vehicles to platoons. Finally, we solve a case study on a real-world based network resembling the city of Braunschweig, Germany. Analyzing the tactical and operational solutions, we assess the value of using a mixed autonomous fleet and derive practical implications.Wir betrachten eine Anwendung der urbanen Logistik, bei der ein Dienstleister einen wiederholbaren Plan für den Gütertransport von Distributionszentren zu Satelliten anstrebt. Dafür setzt der Dienstleister eine gemischt-autonome Flotte ein, die sich aus autonomen Fahrzeugen und manuell gesteuerten Fahrzeugen zusammensetzt. Die autonomen Fahrzeuge können nur auf bestimmten Straßen der heterogenen Infrastruktur selbstständig fahren, außerhalb dieser müssen sie von manuell gesteuerten Fahrzeugen mittels Platooning gezogen werden. Wir führen das „service network design problem with mixed autonomous fleets“ ein, um einen taktischen Plan zu ermitteln, der die Gesamtkosten über einen mittelfristigen Zeithorizont minimiert. Der taktische Plan bestimmt die Größe und Zusammensetzung der Flotte, legt die Transportdienste fest und entscheidet über das Routing oder das Outsourcing von Gütern. Wir modellieren dieses Problem als ganzzahliges Programm auf einem zeiterweiterten Netzwerk und untersuchen die Auswirkungen verschiedener Problemeigenschaften auf die Lösungen. Um die Synchronisationsanforderungen des Problems präzise darzustellen, müssen die zeiterweiterten Netzwerke kleine Zeitintervalle berücksichtigen. Daher entwickeln wir einen exakten Lösungsansatz, der auf dem Schema des „dynamic discretization discovery“ basiert und partiell zeiterweiterte Netzwerke entwickelt, die nur einen Teil der Knoten und Kanten des vollständig zeiterweiterten Netzwerks enthalten. Weitere methodische Beiträge dieser Dissertation umfassen die Einführung von Valid Inequalities, zweier Erweiterungen, die lineare Relaxationen verwenden, und einer heuristischen Suchraumbegrenzung. Experimente zeigen, dass alle evaluierten Varianten des Lösungsansatzes einen kommerziellen Solver übertreffen. Um einen taktischen Plan in eine operative Lösung zu überführen, die die Umladevorgänge an einem bestimmten Tag minimiert, stellen wir eine Post-Processing-Methode vor, mit der Güter zu Fahrzeugen und Fahrzeuge zu Platoons eindeutig zugeordnet werden. Schließlich lösen wir eine Fallstudie auf einem realitätsnahen Netzwerk, das der Stadt Braunschweig nachempfunden ist. Anhand der taktischen und operativen Lösungen bewerten wir den Nutzen einer gemischt-autonomen Flotte und leiten Implikationen für die Praxis ab

Motor Carrier Service Network Design

This chapter introduces service network design (SND) operations research models and solution methodologies specifically focused on problems that arise in the planning of operations in the trucking, or motor freight, industry. Consolidation carriers such as less-than-truckload and package trucking companies face flow planning problems to decide how to route freight between transfer terminals, and load planning problems to decide how to consolidate shipments into trailerloads and containerloads for dispatch. Integer programming models are introduced for these network design decision problems as well as exact and heuristic solution methods

Greedy Approaches for Large-Scale Flow and Load Planning

The flow and load planning problem is to determine freight flows through a network and to schedule containerized dispatches to accommodate these flows. The problem is perhaps the core decision problem faced by parcel express companies, LTL carriers, and large online retailers that operate private consolidation networks. Cost minimization is achieved by consolidating goods into common trailers along their journey. Goods are released to the network at specified times and must be delivered before their due date. Goods are typically grouped into sets with common origin, release time, destination, and due date; such a group is referred to as a commodity. The scale of the problems faced in industry can involve thousands of locations and millions of commodities; however, most approaches in the literature are exact and are only able to solve instances with hundreds of commodities. The work in this thesis focuses on developing heuristic approaches that can solve industry-scale instances. In Chapter 2, we provide a sequential marginal cost path based approach to solve the flow and load planning problem. Commodities are sequentially pathed on a partially time-expanded network with optimistically mapped arcs. Heuristic dynamic discretization discovery (DDD) is used to detect when consolidations are not possible due to mapping error and to specify which time points must be added to prevent the infeasibility. Several improvements are made to the shortest path algorithm to exploit the repeated structure of the time-expanded network. Computational experiments show that the approach has an optimality gap of 4-18% on instances which can be solved with exact methods (~300 commodities). Further experiments show that the approach outperforms a commonly used slope scaling heuristic by 16-34% on both small and realistic sized (~100k commodities) instances. In Chapter 3, we develop a different sequential marginal cost path approach that removes the requirement for maintaining and altering a time-expanded network. The approach maintains a set of dispatches currently in the solution, and a time window associated with each dispatch representing when it can depart. At each iteration, a shortest path algorithm on an expanded state space is solved to determine for a commodity a collection of new or existing dispatches which deliver it from its origin to its destination within its delivery window. Then the set of existing dispatches is updated, and the optimal set of dispatch windows is determined. We prove that finding the optimal set of dispatch windows is equivalent to solving a minimum mean cost path on a dispatch dependency graph. We use the Bellman-Ford algorithm to solve this problem and use a creative way to maintain labels between iterations to improve the efficiency of the approach. Computational experiments were performed and demonstrate that this approach outperforms the approach from the first chapter in plan cost by up to 10% with approximately one tenth of the solution time. Finally, in Chapter 4, we incorporate many practical constraints into the model. In the literature, most works either ignore the structure of flow plans or force them to adhere to in-tree structures where each flow class has exactly one next stop. In practice, more general structures are used where flow classes can have multiple possible next stops. We present a model for generating flow and load plans where commodities are aggregated into flow classes that may be independently directed at every building. Our model produces plans that guarantee each package will be delivered on time despite the aggregated level of control. We give a general heuristic template that we prove can preserve the flow-rule feasibility of solutions. We give four possible implementations adhering to this template. One of these heuristics was shown to produce cost savings of up to 3.4% and savings in trailer-miles of up to 8.5% on large-scale industry instances in under one hour.Ph.D

Coupled structural, thermal, phase-change and electromagnetic analysis for superconductors, volume 1

This research program has dealt with the theoretical development and computer implementation of reliable and efficient methods for the analysis of coupled mechanical problems that involve the interaction of mechanical, thermal, phase-change and electromagnetic subproblems. The focus application has been the modeling of superconductivity and associated quantum-state phase-change phenomena. In support of this objective the work has addressed the following issues: (1) development of variational principles for finite elements; (2) finite element modeling of the electromagnetic problem; (3) coupling of thermal and mechanical effects; and (4) computer implementation and solution of the superconductivity transition problem. The research was carried out over the period September 1988 through March 1993. The main accomplishments have been: (1) the development of the theory of parametrized and gauged variational principles; (2) the application of those principled to the construction of electromagnetic, thermal and mechanical finite elements; and (3) the coupling of electromagnetic finite elements with thermal and superconducting effects; and (4) the first detailed finite element simulations of bulk superconductors, in particular the Meissner effect and the nature of the normal conducting boundary layer. The grant has fully supported the thesis work of one doctoral student (James Schuler, who started on January 1989 and completed on January 1993), and partly supported another thesis (Carmelo Militello, who started graduate work on January 1988 completing on August 1991). Twenty-three publications have acknowledged full or part support from this grant, with 16 having appeared in archival journals and 3 in edited books or proceedings

Arc flow formulations based on dynamic programming: Theoretical foundations and applications

Network flow formulations are among the most successful tools to solve optimization problems. Such formulations correspond to determining an optimal flow in a network. One particular class of network flow formulations is the arc flow, where variables represent flows on individual arcs of the network. For NP-hard problems, polynomial-sized arc flow models typically provide weak linear relaxations and may have too much symmetry to be efficient in practice. Instead, arc flow models with a pseudo-polynomial size usually provide strong relaxations and are efficient in practice. The interest in pseudo-polynomial arc flow formulations has grown considerably in the last twenty years, in which they have been used to solve many open instances of hard problems. A remarkable advantage of pseudo-polynomial arc flow models is the possibility to solve practical-sized instances directly by a Mixed Integer Linear Programming solver, avoiding the implementation of complex methods based on column generation. In this survey, we present theoretical foundations of pseudo-polynomial arc flow formulations, by showing a relation between their network and Dynamic Programming (DP). This relation allows a better understanding of the strength of these formulations, through a link with models obtained by Dantzig-Wolfe decomposition. The relation with DP also allows a new perspective to relate state-space relaxation methods for DP with arc flow models. We also present a dual point of view to contrast the linear relaxation of arc flow models with that of models based on paths and cycles. To conclude, we review the main solution methods and applications of arc flow models based on DP in several domains such as cutting, packing, scheduling, and routing

Optimization strategies for efficient dosage of H2O2 in Fenton and photo-Fenton processes

This Thesis work addresses the challenge of designing hydrogen peroxide (H2O2) dosage Strategies for improving Fenton and photo-Fenton applications. The determination of the H2O2 dosage scheme that minimizes hydrogen peroxide consumption while meeting the specified treatment outcome is crucial for the practicality of Fenton and photo-Fenton processes, as well as for further understanding the effect of the dosage. A first part of the research addresses this challenge by providing a problem formulation, identifying and discussing objectives and constraints, and the nature of the optimal solution. From this point, the Thesis presents a novel dosage model and a consequent methodology aimed at experimentally optimizing the dosage profile along a discretized time horizon following recipe optimization concepts. The approach is parallel to the numerical solution of the model-based optimization problem posed by H2O2. The methodology is validated in the remediation of a Paracetamol (PCT) solution, and the obtained results are assessed and discussed in regard of the evolution of the concentration of hydrogen peroxide, the contaminant (PCT), and Total Organic Carbon (TOC). The concentration of dissolved oxygen (DO), which is also monitored, allows providing a more comprehensive explanation of the nature of the process. A second part focuses on the practical limitations of this scheme by adopting a hybrid methodology between open and closed loop approaches and it is based on three different stages: (i) one-shot initial H2O2 addition (ii) continuous H2O2 dosage until reaching a specific dissolved oxygen (DO) level and (iii) on-off control of H2O2 dosage using DO slope as control variable. The proposed strategy is validated in the remediation of a Paracetamol solution (100 mg L-1) and the results are assessed using H2O2 consumption and mineralization rate and level as performance criteria. The final tuning of the proposed strategy consists of: (i) only 40% of the stoichiometric H2O2 concentration, (ii) continuous feeding of H2O2 until a 4 mg L-1 DO concentration is attained, and (iii) on-off control dosage selecting DO slope set-points in 0.1 and 0.2 mg L-1 1 min-1. The dosage scheme and settings developed in this second part show an improvement of the process performance by ~ 15% with respect to the same H2O2 amount in a single-addition. Finally, the third part generalizes this strategy by expanding its application and exploring and assessing its performance on different water matrix (natural water and distilled water), different contaminant concentrations, and different contaminants (paracetamol and sulfamethazine) and mixtures. Towards this end, a set of assays were planned and executed involving Paracetamol and Sulfamethazine. In particular, assays performed on sulfamethazine presented higher efficiency (mg of TOC removed per mg of H2O2 consumed), which increased 25-35% with respect to the results obtained with only one-shot initial addition. Furthermore, a deeper analysis of the results allowed detecting and assessing the option of a redesign of the dosage scheme by removing the idea of a specific DO set point and directly addressing the control of the DO slope. Hence, this thesis also opens new research lines in regard to increasing the simplicity and robustness of this efficient control strategy of the photo-Fenton process.Aquest treball de tesi aborda el repte de dissenyar estratègies de dosificació de peròxid d'hidrogen (H2O2) per millorar les aplicacions dels processos Fenton i foto-Fenton. La determinació d'una estratègia de dosificació d'H2O2 que en minimitzi el consum mentre s'assoleixen els objectius del tractament especificat és crucial per a l'aplicació pràctica dels processos de Fenton i foto-Fenton, així com per a la millor comprensió de l'efecte de la dosificació. Una primera part de la investigació aborda aquest repte proporcionant una formulació del problema, identificant i discutint objectius i restriccions, i la naturalesa de la solució òptima. A partir d'aquest punt, la tesi presenta un nou model de dosificació i una metodologia derivada que pretén optimitzar experimentalment el perfil de dosificació al llarg d'un horitzó temporal convenientment discretitzat seguint conceptes d'optimització de receptes. L'enfocament és paral·lel a la solució numèrica del problema d'optimització basat en models i la metodologia que se'n deriva es valida en el tractament d'una solució de paracetamol (PCT). Els resultats obtinguts s'avaluen i es discuteixen en relació amb l'evolució de la concentració de peròxid d'hidrogen, el contaminant (PCT) i el carboni orgànic total (TOC). La concentració d'oxigen dissolt (DO), que també es controla, permet donar una explicació més completa de la naturalesa del procés . Una segona part se centra en les limitacions pràctiques d'aquest esquema mitjançant l'adopció d'una metodologia híbrida entre el control en llaç obert i el control en llaç tancat. La metodologia es basa en tres etapes diferents: (i) addició inicial H2O2 inicial (ii) dosificació contínua d'H2O2 fins a arribar a un determinat nivell d'oxigen dissolt (DO) i (iii) control on-off de la dosi d'H2O2 utilitzant el pendent de DO com a variable de control. L'estratègia proposada es valida en el tractament d'una solució de paracetamol (100 mg L-1) i els resultats s'avaluen utilitzant el consum de H2O2 i la taxa i el nivell de mineralització com a criteris de rendiment. L'ajust final de l'estratègia proposada es concreta de la següent manera: (i) només el 40% de la concentració estequiomètrica de H2O2, (ii) alimentació contínua de H2O2 fins a l'assoliment d'una concentració de 4 mg de L-1 DO i (iii) dosificació sota un control on-off seleccionant els valors de pendent de DO entre 0,1 i 0,2 mg L-1 1 min-1. L'esquema de dosificació i la configuració desenvolupats en aquesta segona part mostren una millora del rendiment del procés d'un 15% respecte al que s'obté amb mateixa quantitat de H2O2 en una única addició. Finalment, la tercera part generalitza aquesta estratègia ampliant la seva aplicació, explorant i avaluant el seu rendiment en diferents matrius d'aigua (aigua natural i aigua destil·lada), diferents concentracions de contaminants, diferents contaminants (paracetamol i sulfametazina) i mescles. Amb aquesta finalitat, es van planificar i executar un conjunt d'assajos que van incloure paracetamol i sulfametazina. En particular, els assajos realitzats amb sulfametazina van presentar una eficiència més elevada (mg de TOC eliminats per mg d'H2O2 consumit), que va augmentar entre un 25 i un 35% respecte als resultats obtinguts amb només una única incorporació inicial. A més, una anàlisi més profunda dels resultats va permetre detectar i avaluar l'opció d'un redisseny de l'esquema de dosificació eliminant la idea d'un punt de referència específic de DO i abordant directament el control del pendent de DO. Per tant, aquesta tesi també obre noves línies de recerca per augmentar la simplicitat i robustesa d'aquesta estratègia de control eficient del procés de foto-Fenton.Enginyeria de processos químic

逐次探索による多目的最適化および宇宙往還機の複合領域概念設計への応用

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 土屋 武司, 東京大学教授 鈴木 真二, 東京大学教授 鈴木 宏二郎, 東京大学准教授 今村 太郎, 防衛大学校准教授 横山 信宏University of Tokyo(東京大学

Efficient sharing mechanisms for virtualized multi-tenant heterogeneous networks

The explosion in data traffic, the physical resource constraints, and the insufficient financial incentives for deploying 5G networks, stress the need for a paradigm shift in network upgrades. Typically, operators are also the service providers, which charge the end users with low and flat tariffs, independently of the service enjoyed. A fine-scale management of the network resources is needed, both for optimizing costs and resource utilization, as well as for enabling new synergies among network owners and third-parties. In particular, operators could open their networks to third parties by means of fine-scale sharing agreements over customized networks for enhanced service provision, in exchange for an adequate return of investment for upgrading their infrastructures. The main objective of this thesis is to study the potential of fine-scale resource management and sharing mechanisms for enhancing service provision and for contributing to a sustainable road to 5G. More precisely, the state-of-the-art architectures and technologies for network programmability and scalability are studied, together with a novel paradigm for supporting service diversity and fine-scale sharing. We review the limits of conventional networks, we extend existing standardization efforts and define an enhanced architecture for enabling 5G networks' features (e.g., network-wide centralization and programmability). The potential of the proposed architecture is assessed in terms of flexible sharing and enhanced service provision, while the advantages of alternative business models are studied in terms of additional profits to the operators. We first study the data rate improvement achievable by means of spectrum and infrastructure sharing among operators and evaluate the profit increase justified by a better service provided. We present a scheme based on coalitional game theory for assessing the capability of accommodating more service requests when a cooperative approach is adopted, and for studying the conditions for beneficial sharing among coalitions of operators. Results show that: i) collaboration can be beneficial also in case of unbalanced cost redistribution within coalitions; ii) coalitions of equal-sized operators provide better profit opportunities and require lower tariffs. The second kind of sharing interaction that we consider is the one between operators and third-party service providers, in the form of fine-scale provision of customized portions of the network resources. We define a policy-based admission control mechanism, whose performance is compared with reference strategies. The proposed mechanism is based on auction theory and computes the optimal admission policy at a reduced complexity for different traffic loads and allocation frequencies. Because next-generation services include delay-critical services, we compare the admission control performances of conventional approaches with the proposed one, which proves to offer near real-time service provision and reduced complexity. Besides, it guarantees high revenues and low expenditures in exchange for negligible losses in terms of fairness towards service providers. To conclude, we study the case where adaptable timescales are adopted for the policy-based admission control, in order to promptly guarantee service requirements over traffic fluctuations. In order to reduce complexity, we consider the offline pre­computation of admission strategies with respect to reference network conditions, then we study the extension to unexplored conditions by means of computationally efficient methodologies. Performance is compared for different admission strategies by means of a proof of concept on real network traces. Results show that the proposed strategy provides a tradeoff in complexity and performance with respect to reference strategies, while reducing resource utilization and requirements on network awareness.La explosion del trafico de datos, los recursos limitados y la falta de incentivos para el desarrollo de 5G evidencian la necesidad de un cambio de paradigma en la gestion de las redes actuales. Los operadores de red suelen ser tambien proveedores de servicios, cobrando tarifas bajas y planas, independientemente del servicio ofrecido. Se necesita una gestion de recursos precisa para optimizar su utilizacion, y para permitir nuevas sinergias entre operadores y proveedores de servicios. Concretamente, los operadores podrian abrir sus redes a terceros compartiendolas de forma flexible y personalizada para mejorar la calidad de servicio a cambio de aumentar sus ganancias como incentivo para mejorar sus infraestructuras. El objetivo principal de esta tesis es estudiar el potencial de los mecanismos de gestion y comparticion de recursos a pequei\a escala para trazar un camino sostenible hacia el 5G. En concreto, se estudian las arquitecturas y tecnolog fas mas avanzadas de "programabilidad" y escalabilidad de las redes, junto a un nuevo paradigma para la diversificacion de servicios y la comparticion de recursos. Revisamos los limites de las redes convencionales, ampliamos los esfuerzos de estandarizacion existentes y definimos una arquitectura para habilitar la centralizacion y la programabilidad en toda la red. La arquitectura propuesta se evalua en terminos de flexibilidad en la comparticion de recursos, y de mejora en la prestacion de servicios, mientras que las ventajas de un modelo de negocio alternativo se estudian en terminos de ganancia para los operadores. En primer lugar, estudiamos el aumento en la tasa de datos gracias a un uso compartido del espectro y de las infraestructuras, y evaluamos la mejora en las ganancias de los operadores. Presentamos un esquema de admision basado en la teoria de juegos para acomodar mas solicitudes de servicio cuando se adopta un enfoque cooperativo, y para estudiar las condiciones para que la reparticion de recursos sea conveniente entre coaliciones de operadores. Los resultados ensei\an que: i) la colaboracion puede ser favorable tambien en caso de una redistribucion desigual de los costes en cada coalicion; ii) las coaliciones de operadores de igual tamai\o ofrecen mejores ganancias y requieren tarifas mas bajas. El segundo tipo de comparticion que consideramos se da entre operadores de red y proveedores de servicios, en forma de provision de recursos personalizada ya pequei\a escala. Definimos un mecanismo de control de trafico basado en polfticas de admision, cuyo rendimiento se compara con estrategias de referencia. El mecanismo propuesto se basa en la teoria de subastas y calcula la politica de admision optima con una complejidad reducida para diferentes cargas de trafico y tasa de asignacion. Con particular atencion a servicios 5G de baja latencia, comparamos las prestaciones de estrategias convencionales para el control de admision con las del metodo propuesto, que proporciona: i) un suministro de servicios casi en tiempo real; ii) una complejidad reducida; iii) unos ingresos elevados; y iv) unos gastos reducidos, a cambio de unas perdidas insignificantes en terminos de imparcialidad hacia los proveedores de servicios. Para concluir, estudiamos el caso en el que se adoptan escalas de tiempo adaptables para el control de admision, con el fin de garantizar puntualmente los requisitos de servicio bajo diferentes condiciones de trafico. Para reducir la complejidad, consideramos el calculo previo de las estrategias de admision con respecto a condiciones de red de referenda, adaptables a condiciones inexploradas por medio de metodologias computacionalmente eficientes. Se compara el rendimiento de diferentes estrategias de admision sobre trazas de trafico real. Los resultados muestran que la estrategia propuesta equilibra complejidad y ganancias, mientras se reduce la utilizacion de recursos y la necesidad de conocer el estado exacto de la red.Postprint (published version

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 336)

This bibliography lists 111 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during April 1990. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance