Studien genomfördes på industriföretaget Gränges Finspång AB som är en producent av valsade aluminiumprodukter för värmeväxlare vilka används som komponenter främst inom bilindustrin och värme, ventilation och luftkonditionering. Aluminium är en miljöeffektiv råvara tack vare materialets naturliga egenskaper samt dess återanvändbarhet vilket har lett till att allt fler företag vill ta vara på dessa egenskaper vid tillverkning av klimatsmarta produkter. För Gränges Finspång AB har materialets aktualitet på marknaden inneburit en ökad efterfrågan på företagets produkter vilket i sin tur har satt ökad press på företagets produktionseffektivitet. Den produktionsprocess som studerades på företaget var en uppsättning maskiner – även kallade kallvalsverk – vilka kan liknas med en funktionell verkstad. Syftet med studien var att, med hjälp av optimeringsmetoder, ta fram en modell som kan användas som beslutsunderlag för sekvensering av produkter i företagets kallvalsverk. Utifrån intervjuer, granskning av interna dokument och en kvantitativ dataanalys genomfördes en kartläggning av Gränges Finspång AB:s hela produktionsflöde såväl som de processer unika för kallvalsprocessen. För sekvensering av företagets produkter tillämpades en linjär heltalsmodell vilken anger optimum för maximalt 14 produkter. Studien bekräftar att företagets kallvalsning är ett komplext produktionssystem ur ett schemaläggningsperspektiv. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

Is battery energy storage a feasible solution for lowering the operational costs of electric vehicle fast charging and reducing its impact on local grids? The thesis project aims at answering this question for the Swedish scenario. The proposed solution (fast charging station coupled with storage) is modelled in MATLAB, and its performance is tested in the framework provided by Swedish regulation and electricity tariff structure. The analysis is centred on the economic performance of the system. Its cost-effectiveness is assessed by means of an optimisation algorithm, designed for delivering the optimal control strategy and the required equipment sizing. A mixed-integer linear programming (MILP) formulation is utilised. The configuration and operative costs of conventional fast charging stations are used as a benchmark for the output of the optimisation. Sensitivity analysis is conducted on most relevant parameters: charging load, battery price and tariff structure. The modelling of the charging demand is based on statistics from currently implemented 50 kW DC chargers in Sweden. Overall, results show that with current figures the system may be an economically viable solution for both reducing costs and lowering the impact on the local distribution grid, at least during peak-period pricing. However, sensitivity analysis illustrates how system design and performance are highly dependent on input parameters. Among these, electricity tariff was identified as the most important. Consequently, detailed discussion on the influence of this parameter is conducted. Finally, the study shows how the system is in line with most recent directives proposed by the European Commission.

Swedish home care industry has been facing both external and internal problems, such as ageing population, varying quality and unsatisfactory continuity. Accordingly, workforce scheduling system, as one of the most common and useful software within home care planning nowadays, is in need of constant improvement and upgrading. This master’s thesis aimed to explore and analyze improvement potential of an established workforce scheduling system for an IT-company. The thesis was divided into two phases, of which a pre-study in Phase I tried to understand the planning process for planners and identify the perceived problems and shortcomings of the current system from a planner’s perspective. Based on the analysis from the pre-study, the caregiver continuity was chosen as the research area for Phase II. The current system was re-implemented and was modelled as an optimization problem. Furthermore, the system mainly consisted of two key parts, mixed integer linear programming (MILP) and heuristics. Different approaches in terms of modifications in both MILP and heuristics were applied to the re-implemented system. The performance of the modifications was measured by multiple evaluation indicators. The test results showed that there was a potential to improve caregiver continuity with 1.2% to almost 13% depending on the modification type. The modifications were lastly suggested for further examination regarding their practical appropriateness by applying them to the current running algorithm. / Den svenska hemtjänsten möter både yttre och inre problem såsom åldrande befolkning, varierande kvalitet och bristande kontinuitet. Schemaläggningssystemet som är en av de vanligaste och användbaraste programvarorna inom hemtjänsten behöver därmed en ständig förbättring och uppgradering som bemöter de existerande utmaningarna. Detta examensarbete hade som syfte att utforska och analysera förbättringspotentialen av ett etablerat schemaläggningssystem för ett ITföretag. Arbetet var indelat i två faser, varav förstudien i Fas I försökte förstå planerarnas planeringsprocesser och identifiera upplevda problem och brister i det nuvarande systemet utifrån ett planerares perspektiv. Baserat på analysen från förstudien, personalkontinuitet valdes som ett forskningsområde för Fas II. Nuvarande systemet implementerades om och det modellerades som ett optimeringsproblem. Systemet bestod huvudsakligen av två nyckeldelar, blandat heltalslinjärprogrammering (MILP) och heuristik. Olika metoder i form av modifieringar i både MILP och heuristik tillämpades på det omimplementerade systemet. Modifieringarnas prestanda mättes sedan med flera utvärderingsindikatorer. Testresultaten visade att, beroende på vilken modifiering det gäller, fanns det en potential att förbättra personalkontinuiteten med 1,2% till nästan 13%. Det föreslogs slutligen att modifieringarnas praktiska lämplighet behövs undersökas ytterligare genom att applicera det på det nuvarande systemet som är i drift.

With increasing shares of variable renewable energy sources in the power mix, the need for energy storage solutions is projected to increase as well. Storage can in such combined systems help mitigate the issues with relying on intermittent sources by time-shifting the supply and smoothing out frequency fluctuations, to name some examples. This thesis has focused on Azelio ABs flagship product, the TES.POD, which is a long-duration thermal energy storage technology. When integrated with, for example, solar PV power, the TES.POD can store excess energy and dispatch it during times of low supply or when during the evening/night. The aim of the thesis has been the development of a day-ahead dispatch optimization tool for systems that include multiple TES.PODs, combined into a Cluster, and solar PV. The model was to be built using the Python programming language and based on Mixed-Integer-Linear-Programming (MILP) methods. The PV+storage system was then allowed to be connected to supplementary power sources such as a larger electric grid, or diesel generators in off-grid locations. The purpose of the optimization model is to find the most economic way to operate the individual TES.PODs while also keeping track of other system components, using a cost-based objective function (minimize costs). A focus has been on using high time resolution (small time step) in order to investigate the impact that the TES.PODs dynamic constraints has on operation. Another strength compared to pre-existing models was the ability to operate individual units indifferent to each other, as opposed to having them all operated in unison. Final results from benchmarking tests and two case studies indicated that using the optimization tool with smaller time steps had an effect on key indicators, and could lead to improved economy in the system. It was observed in both cases that the cost of electricity was reduced by running the optimization tool with time steps of either two or three minutes when compared with using an hourly resolution. Furthermore, several usage parameters for the TES.PODs, notably the total amount of operated hours and energy output per cycle, saw improvements which could lead to reduced cost of operation and maintenance. While not the main intent, testing different Cluster sizes and amount of installed PV capacity with the model, it could also be used in strategic decisions for system sizing. However, due to rapidly growing computational times in systems with large TES.POD clusters and using smaller time steps, the possibility of adding more complexity to the model in future work must be done with caution. To combat this issue, either improvements to the model formulation could be attempted, or by using more powerful hardware or optimizer (imported software algorithm that handles solving the model).

There is an ever-increasing usage of mobile data with global traffic having reached 115 exabytes per month at the end of 2022 for mobile data traffic including fixed wireless access. This is projected to grow up to 453 exabytes at the end of 2028, according to Ericssons 2022 mobile data traffic outlook report. To meet the increasing demand radio access networks (RAN) used for mobile communication are continuously being improved with the current generation enabling larger virtualization of the network through the Cloud RAN (C-RAN) architecture. This facilitates the usage of commercial off-the-shelf servers (COTS) in the network replacing specialized hardware servers and making it easier to scale up or down the network capacity after traffic demand. This thesis looks at how we can efficiently identify servers needed to meet traffic demand in a network consisting of both COTS servers and specialized hardware servers while trying to reduce the energy consumption of the network. We model the problem as a network where the antennas and radio heads are connectedto the core network through a C-RAN and a specialized hardware layer. The network is then represented using a graph where the nodes represent servers in the network. Using this problem model as a base we then generate problem instances with varying topologies, server profiles, and traffic demands. To find out how the traffic should be passed through the network we test two different methods: A mixed integer linear programming (MILP) method focused on energy minimization and a graph attention network (GAT) predictor combined with the energy minimization MILP. To help evaluate the results we also create three other methods: a MILP model that tries to spread the traffic as evenly as possible, a random predictor combined with the energy minimization MILP and a greedy method. Our results show that the energy optimization MILP method can be used to create optimal solutions, but it suffer from a slow computation time compared to the other methods. The GAT model shows promising results in making predictions regarding what servers should be included in a network making it possible to reduce the problem size and solve it faster with MILP. The mean energy cost of the solutions created using the combined GAT/MILP method was 4% more than just using MILP but the time gain was substantial for problems of similar size as the GAT was trained on. With regards to computation time the combined GAT/MILP method used was 85% faster than using only MILP. For networks of almost double the size than the ones that the GAT model was trained on the solutions of the combined GAT and MILP methods had a mean energy cost increase of 7% while still showing a strong speedup, being 93% faster than when only using MILP.

There is growing interest in commercial aircraft formation flight as a means of reducing both airspace congestion and the carbon footprint of air transportation. Wake vortex surfing has been researched extensively and proven to have significant fuel-saving benefits, however, commercial air transportation has yet to take advantage of these formation benefits due to understandable safety concerns. The realization of these formations requires serious consideration of formation contingencies and safety during closer-in maneuvering of large commercial aircraft. Formation contingency scenarios are much more complex than those of individual aircraft and have not yet been studied in depth. This thesis investigates the utility of optimization modeling in providing insight into generation of aircraft escape paths for formation contingency planning. Three high-altitude commercial aircraft formation scenarios are presented; formation join, formation emergency exit, and formation escape. The model-generated paths are compared with pilot-generated escape plans using the author’s pilot expertise. The model results compare well with pilot intuition and are useful in presenting solutions not previously considered, in evaluating separation requirements for improvement of escape path planning and in confirming the viability of the pilot-generated plans. The novel optimization model formulation presented in this thesis is the first model shown to be capable of generating escape paths comparable to pilot- generated escape plans and is also the first to incorporate avoidance of persistent and drifting wake turbulence within the formation.

High electricity prices have become the title of several news articles recently in Sweden and the prices have experienced large sudden fluctuations during certain periods. In this thesis work, a smart control model for the electricity usage in three different households has been developed with the main purpose to minimize the electricity cost. This has been implemented by using mixed-integer linear programming (MILP) to optimize the cost 24 hours ahead, and by forecasting two of the main inputs; the load and the electricity spot prices for bidding zone three (SE3) in Sweden. The units included in the model are the photovoltaic system, the batteries, the electricity consumption in the house and the electric vehicles. However, the main task of the smart control was to determine when and in which amount the energy should flow from one unit to another, or to/from the grid. In other words, it decides the charging/discharging of the batteries, the selling/buying of electricity and the charging of the electric vehicle (EV). Different amounts of cost savings/profits have been obtained when applying the smart control on the three houses, which have different annual consumption, capacities of the components, heating systems and more. The results showed that it is most optimal to run the model between the time interval 13.00-00.00, when the spot prices for the next day are known, in order to avoid the remarkable impact accompanied with the use of forecasted electricity prices as input to the model. The forecasting of the load is, on the other hand, required to run the model, but this thesis showed that the effect of the uncertainties in this forecast is relatively small. Three types of machine learning methods were implemented to perform the forecasts, namely linear regression (LR), decision tree regression and random forest regression. After measuring especially the mean absolute error (MAE) to validate the results, the random forest regression showed the least error and the other methods showed close results when looking at the electric load prognosis.

Tesis por compendio / [EN] Since its birth in the fifties, the maritime container has revolutionised freight international transport providing support to a global production system, marked by the industry offshoring looking for competitive advantages and the configuration of increasingly complex and global supply chains. Within this context, the container has gained a great importance becoming a basic logistic element in supply chains where it plays the role of a transport, production and distribution unit. The success of container is evident if we analyse the evolution of container port traffic, which has been growing at a pace of over 10 % surpassing 600 million TEU of traffic since 2012. The container is, therefore, a key element in global supply chains and container logistics is a field of work and study of enormous interest due to its impact in the efficiency of these supply chains, due to the cost incurred for the operating account of shipping companies and operators (cost which is transferred to the final user and has an impact in the price of the goods being transported), and due to the social and environmental cost associated to the externalities of transport derived from the management of the container fleet. Container logistics has to do with the efficient management of the container fleet, minimising the transport, warehousing and maintenance costs, and maximising the use of the equipment. In container logistics it is possible to categorise, generally, two different categories or levels depending on the geographical scope and the transport modes involved: The international level and the local or regional level. This thesis addresses container logistics at a local or regional level, insofar as in relation to the management of stock, transport and internal movements, trying to react and identify solutions to some of the problems currently facing the port-logistics sector. The research result allows, firstly, knowing in an integral and structured manner the complexity of maritime container logistics. Secondly, specific real problems are identified and addressed for its modelling and analysis that allows for contributing to the improvement of the current logistics system. The following specific problems are addressed: -Modal choice problems for the configuration of internal logistics corridors or chains for maritime container transport. -Problems locating networks of nodal infrastructures facilitating the logistics needs of maritime containers. -Problems related to the movements and management of empty maritime containers. The interest and the academic contribution of this thesis lies as much in the definition and modelling of the specific problems with a significant theoretical discussion, as the empirical application to a real environment and real situations. This has been possible due to the direct contact of the author with the port-logistics sector and the participation in many consultancy and research projects in the cluster of the port of Valencia and also at European and international level. The thesis is outlined as a collection of six scientific articles. The articles have been presented in the thesis in such a way as to follow a logical sequence and not in relation with the chronological order of their publication. / [ES] Desde su aparición en los años 50, el contenedor marítimo ha revoluciona-do el transporte internacional de mercancías dando soporte a un sistema global de producción, marcado por la multilocalización de las industrias en busca de ventajas competitivas y la configuración de cadenas de suministro cada vez más complejas y globales. En este contexto, el contenedor ha adquirido un gran protagonismo convirtiéndose en un elemento logístico básico en las cadenas de suministro en las que actúa como unidad de transporte, producción y distribución. El éxito del contenedor queda puesto de manifiesto al analizar la evolución del tráfico portuario de contenedores, que ha estado creciendo a ritmos superiores al 10 %, superando los 600 millones TEU desde 2012. El contenedor es, por tanto, un elemento clave de las cadenas de suministro globales y la logística del contenedor es un área de estudio y trabajo de enorme interés por el impacto que tiene en la eficiencia de dichas cadenas, por el coste que supone a navieras y operadores en sus cuentas de explotación (coste que se traslada al usuario final y repercute en el precio de las mercancías transportadas) y por el coste social y ambiental asociado a las externalidades del transporte derivadas de esta gestión de la flota de contenedores. La logística del contenedor tiene que ver con la gestión eficiente del parque de contenedores, minimizando los costes de transporte, almacenamiento y mantenimiento, y maximizando la utilización del equipo. En la logística del contenedor se pueden identificar, por lo general, dos categorías o niveles diferenciados en función del ámbito geográfico y de los modos de transporte implicados: El nivel internacional y el nivel local o regional. Este trabajo aborda la logística del contenedor a nivel regional o local, es decir, en lo relativo a la gestión del stock, transporte y movimientos interiores, tratando de dar respuesta y plantear soluciones a algunos de los problemas con los que se encuentra el sector logístico-portuario en la actualidad. El resultado de la investigación permite, en primer lugar, conocer de una forma integral y estructurada la complejidad de la logística del contenedor marítimo. En segundo lugar, se identifican y abordan problemas específicos reales para su modelización y análisis, que permiten contribuir a la mejora del sistema logístico actual. En concreto se abordan los siguientes problemas: -Problemas de elección modal en la configuración de las cadenas o corredores logísticos interiores en el transporte de contenedores marítimos. -Problemas de localización o vertebración de una red de infraestructuras nodales para atender las necesidades logísticas de los contenedores marítimos. -Problemas asociados a los movimientos en vacío y gestión de contenedores marítimos. El interés y contribución académica de este trabajo reside tanto en la definición y modelización de los problemas específicos con una profunda discusión teórica, como en la aplicación empírica a situaciones y entornos reales, cosa que ha sido posible gracias al contacto directo del autor con el sector logístico-portuario y su participación en numerosos proyectos de consulto-ría e investigación tanto en el clúster del Puerto de Valencia como a nivel europeo e internacional. El trabajo se plantea como una colección de seis artículos científicos. El orden en que están situados los artículos en la tesis permite mantener una secuencia lógica construida a posteriori y no según el orden cronológico en el que fueron publicados. / [CA] Des del seu naixement als anys 50, el contenidor marítim ha revolucionat el transport internacional de mercaderies donant suport a un sistema global de producció, marcat per la multilocalització de les indústries en busca d'avantatges competitives i la configuració de cadenes de subministrament cada vegada més complexes i globals. En aquest context, el contenidor ha adquirit un gran protagonisme convertintse en un element logístic bàsic en les cadenes de subministrament en les quals actua com a unitat de transport, producció i distribució. L'èxit del contenidor s'evidencia en analitzar l'evolució del tràfic portuari de contenidors, que ha estat creixent a ritmes superiors al 10 % superant els 600 milions TEU des de 2012. El contenidor és, per tant, un element clau de les cadenes subministrament globals i la logística del contenidor és un àrea d'estudi i treball d'enorme interès per l'impacte que té en l'eficiència d'aquestes cadenes, pel cost que suposa a navilieres i operadors en els seus comptes d'explotació (cost que es trasllada a l'usuari final i repercuteix en el preu de les mercaderies transportades) i pel cost social i ambiental associat a les externalitats del transport derivades d'aquesta gestió de la flota de contenidors. La logística del contenidor té a veure amb la gestió eficient del parc de contenidors, minimitzant els costos de transport, emmagatzematge i manteniment, i maximitzant la utilització de l'equip. En la logística del contenidor es poden identificar, en general, dues categories o nivells diferenciats en funció de l'àmbit geogràfic i de les modalitats de transport implicats: el nivell internacional i el nivell local o regional. Aquest treball aborda la logística del contenidor a nivell regional o local, és a dir, quant a la gestió de l'estoc, transport i moviments interiors, tractant de donar resposta i plantejar solucions a alguns dels problemes amb els quals es troba el sector logístic-portuari en l'actualitat. El resultat de la recerca permet, en primer lloc, conèixer d'una forma integral i estructurada la complexitat de la logística del contenidor marítim. En segon lloc, s'identifiquen i aborden problemes específics reals per a la seua modelització i anàlisi, que permeten contribuir a la millora del sistema logístic actual. En concret s'aborden els següents problemes: -Problemes d'elecció modal en la configuració de les cadenes o corredors logístics interiors en el transport de contenidors marítims. -Problemes de localització o vertebració d'una xarxa d'infraestructures nodals per a atendre les necessitats logístiques dels contenidors marítims. -Problemes associats als moviments en buit i gestió de contenidors marítims. L'interès i contribució acadèmica d'aquest treball resideix tant en la definició i modelització dels problemes específics amb una profunda discussió teòrica, com en l'aplicació empírica a situacions i entorns reals, cosa que ha sigut possible gràcies al contacte directe de l'autor amb el sector logístic-portuari i la seua participació en nombrosos projectes de consultoria i recerca tant en el clúster del Port de València com a nivell europeu i internacional. El treball es planteja com una col·lecció de sis articles científics. L'ordre en què estan situats els articles en la tesi permet mantenir una seqüència lògica construïda a posteriori i no segons l'ordre cronològic en el qual van ser publicats. / Furió Pruñonosa, S. (2016). Modelos y métodos avanzados para la logística del contenedor. Aplicación al Puerto de Valencia [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63248 / Compendio

This paper presents the development and mathematical implementation of a production scheduling model utilizing mixed-integer linear programming (MILP). A simplified model of a real-world multi-product batch plant constitutes the basis. The paper shows practical extensions to the model, resulting in a digital twin of the plant. Apart from sequential arrangement, the final model contains maintenance periods, campaign planning and storage constraints to a limited extend. To tackle weak computational performance and missing model features, a condensed mathematical formulation is introduced at first. After stating that these measures do not suffice for applicability in a restrained time period, a novel solution strategy is proposed. The overall non-iterative algorithm comprises a multi-step decomposition approach, which starts with a reduced scope and incrementally complements the schedule in multiple subproblem stages. Each of those optimizations holds less decision variables and makes use of warmstart information obtained from the predecessor model. That way, a first feasible solution accelerates the subsequent improvement process. Furthermore, the optimization focus can be shifted beneficially leveraging the Gurobi solver parameters. Findings suggest that correlation may exist between certain characteristics of the scheduling scope and ideal parameter settings, which yield potential for further investigation. Another promising area for future research addresses the concurrent multi-processing of independent MILPs on a single machine. First observations indicate that significant performance gains can be achieved in some cases, though sound dependencies were not discovered yet.

Nous nous intéressons au Problème de Dimensionnement de Lots mono-produit (PDL) dans une chaîne logistique composée d'un détaillant et d'un fournisseur en y intégrant le contrat buyback et l'approvisionnement par batch. L'objectif est de déterminer un plan d'approvisionnement pour le détaillant pour satisfaire ses demandes déterministes sur un horizon fini, tout en minimisant ses coûts d'approvisionnement et de stockage. Concernant le coût d'approvisionnement, nous supposons deux structures différentes : FTL (Full Truck Load) et OFB (Only Full Batch). Trois types de contrat buyback sont étudiés : avec des périodes de retour fixes, avec une limite de temps sur les retours, et avec des retours uniquement dans les périodes d'approvisionnement. Chaque contrat est caractérisé par un pourcentage de retour maximal qui peut être égal à 100% (retour total) ou inférieur à 100% (retour partiel). Pour le PDL sous le contrat buyback avec des périodes de retour fixes, nous supposons le cas de ventes perdues (lost sales). En outre, un autre concept ajouté dans les PDL sous les trois types de contrat buyback réside dans le fait que le détaillant peut jeter la quantité invendue et non retournée au fournisseur, appelé mise au rebut (disposal). Nous avons modélisé ces différentes extensions du PDL par des Programmes Linéaires en Nombres Entiers (PLNE). Nous avons ensuite développé des algorithmes exacts polynomiaux de programmation dynamique pour certaines extensions, et montré la NP-difficulté pour d'autres. Pour chaque problème résolu en temps polynomial, nous avons comparé l'efficacité et les limites de l'algorithme proposé avec celles des quatre formulations en PLNE. Nous avons également proposé des modèles mathématiques pour les PDL sous d'autres types de contrats de réservation de capacité dans le cas déterministe à multi-périodes. / We study the single-item Lot Sizing Problem (LSP) in a supply chain composed of a retailer and a supplier by integrating the buyback contract and the batch ordering. The purpose is to determine a replenishment planning for the retailer to satisfy his deterministic demands over a finite horizon, while minimizing the procurement and inventory costs. Regarding the procurement cost, we assume two different structures: FTL (Full Truck Load) and OFB (Only Full Batch). We consider three types of buyback contract: with fixed return periods, with a time limit on returns, and with returns permitted only in procurement periods. Each contract is characterized by the maximum return percentage being either equal to 100% (full return) or less than 100% (partial return). For the LSP under the buyback contract with fixed return periods, we assume the concept of lost sales. Another concept considered in the LSP's under the three types of buyback contract is the disposal of the unsold and unreturned quantities. We model these different LSP extensions as a Mixed Integer Linear Program (MILP). Thereafter, we develop exact polynomial time dynamic programming algorithms for some extensions and show the NP-hardness of others. For each problem solved in polynomial time, we compare the efficiency and the limits of the proposed algorithm with those of four MILP formulations by performing different tests. Finally, we propose mathematical models for the LSP's under other types of the capacity reservation contract in the deterministic and multi-period case.