| 1. |
|
|
| 2. |
- Berg, Sofia, et al.
(author)
-
Ekologisk funktionalitet av värdekärnor för barrskogar inom Västra Götalands län : Ett strategiskt underlag för planering av förändrad skogsskötsel av barrskogsområden inom Västra Götalands län i syfte att stärka skogarnas förutsättningar att stödja biologisk mångfald och skogens klimatnytta
- 2022
-
Reports (pop. science, debate, etc.)abstract
- Skogsstyrelsen redovisar i sin utvärdering av miljömålet Levande skogar 2019 att centrala hinder för uppfyllelse av miljömålet är minskande och fragmenterade livsmiljöer och minskande och/eller små populationer av ett antal hotade arter knutna till skogsekosystemet. En väg framåt för att vända denna trend är att framtidens skogsbruk bland annat bör utvecklas utifrån ett landskapsperspektiv och där hyggesfria skogsbruksmetoder ökar i omfattning.Länsstyrelserna i Sverige har genom sitt arbete med regionala handlingsplaner för grön infrastruktur identifierat så kallade värdekärnor – områden av stor betydelse för skogsarternas överlevnad. I denna studie har Västra Götalands läns värdekärnor analyserats med avseende på deras förmåga att stödja biologisk mångfald i ett landskapsperspektiv. Arbetet har gjorts i samverkan med Länsstyrelsen för Västra götalands län.Metoden som använts är Biotope Biodiversity Capacity Indicator (BBCI). Metoden har utvecklats inom forskningsprojektet “Landscape biodiversity capacity: a tool for measuring, monitoring and managing” finansierat av Naturvårdsverkets miljöforskningsanslag (2019-2022).Resultaten visar vilka geografiskt avgränsade värdekärnor som idag har hög ekologisk funktionalitet och som utgör biologiska överlevnads- och spridningshotspots för arter knutna till barrskogar. Vidare visar resultaten att endast sju kommuner har BBCI-värden över 1, det vill säga, ett hållbart skogslandskap som kan hålla fokusarten i ett 100-årsperspektiv.För att nå de svenska miljömålen Levande skogar och Ett rikt växt- och djurliv samt skapa bättre förutsättningar för skogens biologiska mångfald att fortleva behöver nuvarande skogsmetoder med trakthyggesbruk anpassas till brukningsformer som tar större hänsyn till skogens ekosystem. Resultaten från denna studie kan ge prioriteringsunderlag för inom vilka produktionsskogar en så kallad återvildning genom förändrad brukningsmetod skulle kunna resultera i betydelsefull ökad ekologisk funktionalitet på landskapsnivå för de västgötska barrskogarna.
|
|
| 3. |
- Jonsson, Annie, et al.
(author)
-
Landskapets förmåga att hålla biologisk mångfald : – en indikator för biologisk mångfald och ett planeringsverktyg för prioritering av markanvändning
- 2022
-
Reports (other academic/artistic)abstract
- Rapporten beskriver ett nytt verktyg framtaget för att underlätta planering av grön infrastruktur på landskapsnivå och ger via fallstudier exempel på hur verktyget kan användas. Projektet har utförts i ett samarbete med expertis inom teoretisk ekologi, ekologi, biodiversitetsinformatik och tillämpad matematik.Forskningsprojektet har utvecklat en modell för att uppskatta ett landskaps för-måga att hålla biologisk mångfald i dess olika biotoper (Biotope Biodiversity Capacity Indicator, BBCI). Ett teoretiskt ramverk baserat på ekologisk kunskap har tagits fram som grund för modellen.Syftet med BBCI är att modellen ska kunna användas som ett planeringsverktyg för att:stärka biologisk mångfald i ett landskap,förbättra förutsättningarna för arter att använda hela landskapet ochskapa bättre förutsättningar för hänsyn till biologisk mångfald i samband med samhällsutveckling.För att testa och beskriva verktygets användbarhet har fyra fallstudier genomförts med olika fokus:Analys av fragmenteringen i ett barrskogslandskap som sköts med särskild naturhänsyn i Västernorrlands län.Analys av barrskogsvärdekärnors kapacitet för biologisk mångfald inom Västra Götalands län som synliggör vikten av kommunöverskridande samverkan.Analys av potentiella målkonflikter mellan två biotoper, ädellövskog och öppen mark med skyddsvärda träd i Valle.Analys av kapacitet för biologisk mångfald hos äldre ädellövträd i ett landskap mixat med urbana miljöer och landsbygd, Mjölby kommun.Parallellt med utvcklingen av BBCI har en tät dialog och samverkan skett med olika intressenter och slutanvändare. Den breda dialogen har medfört ett effektivt kun-skapsutbyte mellan olika parter.Rapporten avslutas med att beskriva utmaningar och verktygets utvecklings-potential både avseende pedagogik och teknik men även hur modellen kan byggas på och utvecklas med ytterligare funktioner för en breddad tillämpning.
|
|
| 4. |
- Larsson, Madeleine, 1984-, et al.
(author)
-
Towards a more circular biobased economy and nutrient use on Gotland : finding suitable locations for biogas plants
- 2023
-
Reports (other academic/artistic)abstract
- In this study we have investigated the role of biogas solutions to support increased resource efficiency on the island Gotland, including recovery and redistribution of nitrogen (N) and phosphorus (P) within the agricultural sector. First, we analyzed the potential for expanding energy and nutrient recovery from organic residues using biogas solutions. Our findings suggest that the biogas production could expand to 165 GWh, from the current 36 GWh (2020), with manure accounting for a potential 110 GWh biogas annually if all were digested. Comparing the nutrients contained in organic feedstock with the crop nutrient demand on Gotland showed that for N the demand is 2.4 times higher than the supply. In contrast, the calculations showed a 137 tonnes P surplus, with distinct excess areas in the center and southern part of the island.We then compared scenarios with different numbers (3 - 15) of biogas plants with respect to efficient nutrient redistribution and transport costs. Spatial constraints for new plants, e.g. need for roads with a certain capacity and permit issues, were accounted for by adding local information to a national data set. We identified 104 potential locations (1 km$^2$ grid cells) and used an optimization model to identify the most suitable locations for minimized transport costs. Optimal (meeting the crop demand with no excess) redistribution of all nutrients contained in the feedstock, as raw digestate from biogas plants, would result in an export of 127 tonnes of P from the island. The model results indicated that if all potential feedstock would be digested in three additional biogas plants and nutrients redistributed for optimal reuse, the total transport cost would be 2.6 million SEK annually, excluding the costs for nutrient export from the island (3.7 million SEK). If instead 10 or 15 smaller plants would be built, the transport cost would drop to 1.8 million SEK, with the same amount of P being exported. Comparing the scenarios with different number of biogas plants (3 - 15), showed that some locations are more suitable than others in terms of distance to feedstock andto fields with fertilizer demands. Finally, a preliminary analysis of the amount of crop residues indicated that this type of feedstock could add a substantial amount of biogas production, but more extensive analyses are needed to assess the feasibility to realize part of that potential.
|
|
| 5. |
- Larsson, Torbjörn, et al.
(author)
-
A Lagrangian bounding and heuristic principle for bi-objective discrete optimization
- 2024
-
In: Operational Research. - : SPRINGER HEIDELBERG. - 1109-2858 .- 1866-1505. ; 24:2
-
Journal article (peer-reviewed)abstract
- Lagrangian relaxation is a common and often successful way to approach computationally challenging single-objective discrete optimization problems with complicating side constraints. Its aim is often twofold; first, it provides bounds for the optimal value, and, second, it can be used to heuristically find near-optimal feasible solutions, the quality of which can be assessed by the bounds. We consider bi-objective discrete optimization problems with complicating side constraints and extend this Lagrangian bounding and heuristic principle to such problems. The Lagrangian heuristic here produces non-dominated candidates for points on the Pareto frontier, while the bounding forms a polyhedral outer approximation of the Pareto frontier, which can be used to assess the quality of the candidate points. As an illustration example we consider a facility location problem in which both CO2 emission and cost should be minimized. The computational results are very encouraging, both with respect to bounding and the heuristically found non-dominated solutions. In particular, the Lagrangian bounding is much stronger than the outer approximation given by the Pareto frontier of the problem's linear programming relaxation.
|
|
| 6. |
- Larsson, Torbjörn, et al.
(author)
-
A theoretical justification of the set covering greedy heuristic of Caprara et al
- 2022
-
In: Discrete Optimization. - : Elsevier. - 1572-5286 .- 1873-636X. ; 45
-
Journal article (peer-reviewed)abstract
- Large scale set covering problems have often been approached by constructive greedy heuristics, and much research has been devoted to the design and evaluation of various greedy criteria for such heuristics. A criterion proposed by Caprara et al. (1999) is based on reduced costs with respect to the yet unfulfilled constraints, and the resulting greedy heuristic is reported to be superior to those based on original costs or ordinary reduced costs. We give a theoretical justification of the greedy criterion proposed by Caprara et al. by deriving it from a global optimality condition for general nonconvex optimisation problems. It is shown that this criterion is in fact greedy with respect to incremental contributions to a quantity which at termination coincides with the deviation between a Lagrangian dual bound and the objective value of the feasible solution found.
|
|
| 7. |
- Larsson, Torbjörn, et al.
(author)
-
Column generation extensions of set covering greedy heuristics
- 2022
-
In: Operations Research Letters. - : Elsevier. - 0167-6377 .- 1872-7468. ; 50:6, s. 738-744
-
Journal article (peer-reviewed)abstract
- Large-scale set covering problems are often approached by constructive greedy heuristics, and many selection criteria for such heuristics have been considered. These criteria are typically based on measures of the cost of setting an additional variable to one in relation to the number of yet unfulfilled constraints that it will satisfy. We show how such greedy selections can be performed on column-oriented set covering models, by using a fractional optimization formulation and solving sequences of ordinary column generation problems for the application at hand.
|
|
| 8. |
- Larsson, Torbjörn, et al.
(author)
-
One-parametric analysis of column-oriented linear programs
- 2023
-
In: Oncoscience. - : ELSEVIER. - 0255-0156 .- 2214-7160. ; 10
-
Journal article (peer-reviewed)abstract
- A linear optimization problem which is amenable to column generation and contains a single parameter in the objective function is considered. We extend and adapt the standard linear programming column generation scheme to effectively and efficiently solve this problem for all values of the parameter. As a potential application we consider bi-objective discrete optimization and describe how the one-parametric column generation scheme can be used to form an outer approximation of the Pareto frontier for such a problem.
|
|
| 9. |
- Metson, Genevieve, et al.
(author)
-
Not all sites are created equal - Exploring the impact of constraints to suitable biogas plant locations in Sweden
- 2022
-
In: Journal of Cleaner Production. - : Elsevier Science Ltd. - 0959-6526 .- 1879-1786. ; 349
-
Journal article (peer-reviewed)abstract
- Biogas production from manure is attractive to support plans towards a circular economy as it allows for renewable energy production and nutrient recycling in agriculture. Finding optimal locations for biogas plants, which minimize transport distances to and from farms, while accounting for multiple feasibility constraints, remains a challenge. We developed 1 km2 spatially-explicit datasets for known feasibility constraints such as distance to housing, compatible land-use zoning, and the presence of roads with sufficient weight bearing capacity. These datasets were used to improve the realism of an optimization model designed to minimize transportation costs in Sweden. At a national level, the presence of durable enough roads most limited the number of suitable locations for a plant. We further focused our analysis on a case study region where a company wanted to invest in a new manure-based biogas plant. In contrast to the national level, the constraint for remaining at least 500 m from housing/buildings had the greatest limiting impact, excluding 71% of grids in the Sjo center dot bo or Tomelilla municipalities of Southern Sweden. Still, we identified 105 suitable locations for a new biogas plant. The most suitable location, accounting for feasibility and minimized transportation costs, changed when simultaneously accounting for another proposed plant in a neighboring municipality. Our results indicate that utilizing both local and national datasets can help narrow down potential biogas development sites and that long-term planning is necessary for actors with ambitions to build several plants to minimize costs and maximize energy and nutrient recycling benefits.
|
|
| 10. |
- Metson, Genevieve S., 1988-, et al.
(author)
-
Optimizing transport to maximize nutrient recycling and green energy recovery
- 2020
-
In: Resources, Conservation & Recycling: X. - : Elsevier. - 2590-289X. ; 9-10
-
Journal article (peer-reviewed)abstract
- A circular biobased economy must be able to sustainably manage multiple resources simultaneously. Nutrient (nitrogen, phosphorus, and potassium) recycling and renewable energy production (biogas) can be compatible practices but require substantial transport of heavy organic waste. We combine a spatial optimization model and Life Cycle Assessment (LCA) to explore how Sweden could maximize its use of excreta resources. We use 10×10 km2 resolution data on the location of animal and human excreta and crop demand and model both optimal biogas plant locations and transport of nutrients to and from these plants. Each type of biogas plant (given 4 realistic mixes of excreta) is then evaluated for global warming potential, primary energy use and financial resource costs. Moving excreta through biogas plants, as opposed to simply reapplying on fields, to meet crop nutrient demands comes at a similar cost but the climate and primary energy savings are substantial. As much as 91% of phosphorus and 44% of nitrogen crop demand could be met via optimally transported excreta and the country would avoid about 1 450 kt of CO2-eq, save 3.6 TWh (13 000 tera-joules) of primary energy, and save 90 million euros per year. Substituting mineral fertilizers with recycled nutrients results in savings across all indicators, but the added energy and avoided greenhouse gas emissions associated with biogas production make a large difference in the attractiveness of nutrient recycling. Although the numeric values are theoretical, our results indicate that carefully coordinated and supported biogas production could help maximize multi-resource benefits.
|
|
| 11. |
- Metson, Genevieve, et al.
(author)
-
Swedish food system transformations : Rethinking biogas transport logistics to adapt to localized agriculture
- 2022
-
In: Sustainable Production and Consumption. - : Elsevier. - 2352-5509. ; 29, s. 370-386
-
Journal article (peer-reviewed)abstract
- Ensuring future food and energy security will require large changes in consumption and production pat-terns, including enhanced animal and human excreta recycling. Although these shifts are considered in many scenario studies, their implications on the logistical requirements for effective recycling are rarely analysed. Here we translated two existing stakeholder co-designed food system scenarios for Sweden to 5 x 5 km resolution maps of animals, crops, and humans. We used optimization modelling to identify biogas plant locations to minimize transport costs and maximize nutrient reuse. We then compared sce-narios, including full recycling under current landscape configuration, through Life Cycle Assessment. The reduction in meat consumption and imported food in both co-designed scenarios, by definition, led to less nutrients available in manure for recycling back on cropland, and less material available for diges-tion. Less excreta meant lower national benefits, for example 50% less greenhouse gas emissions savings in the most divergent scenario. However on a per transport basis the benefits of recycling were more important: recycling remained a net financial benefit even if transport costs were to increase. Although fewer biogas plant locations were necessary (184 and 228 for alternative futures, vs 236 under current conditions) to process human and animal excreta, the regional clustering of locations did not change substantially across scenarios. Regions such as Skane and Vastra Gotaland consistently required the most biogas plant locations across scenarios. Focusing early construction investments in these regions would be resilient to a large array of food system futures. Our spatially-explicit open access scenario maps can be used to explore logistics for such planning, and explore the impact of landscape configuration on other sustainability priority areas. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.
|
|
| 12. |
- Ngulo, Uledi, 1983-, et al.
(author)
-
A Dissection of the Duality Gap of Set Covering Problems
- 2020
-
In: Operations Research Proceedings 2019. - Cham : Springer International Publishing. - 9783030484385 ; , s. 175-181
-
Conference paper (peer-reviewed)abstract
- Set covering problems are well-studied and have many applications. Sometimes the duality gap is significant and the problem is computationally challenging. We dissect the duality gap with the purpose of better understanding its relationship to problem characteristics, such as problem shape and density. The means for doing this is a set of global optimality conditions for discrete optimization problems. These decompose the duality gap into two terms: near-optimality in a Lagrangian relaxation and near-complementarity in the relaxed constraints. We analyse these terms for numerous instances of large size, including some real-life instances. We conclude that when the duality gap is large, typically the near-complementarity term is large and the near-optimality term is small. The large violation of complementarity is due to extensive over-coverage. Our observations should have implications for the design of solution methods, and especially for the design of core problems.
|
|
| 13. |
- Ngulo, Uledi, 1983-
(author)
-
Decomposition Methods for Combinatorial Optimization
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- This thesis aims at research in the field of combinatorial optimization. Problems within this field often posses special structures allowing them to be decomposed into more easily solved subproblems, which can be exploited in solution methods. These structures appear frequently in applications. We contribute with both re-search on the development of decomposition principles and on applications. The thesis consists of an introduction and three papers. In Paper I, we develop a Lagrangian meta-heuristic principle, which is founded on a primal-dual global optimality condition for discrete and non-convex optimization problems. This condition characterizes (near-)optimal solutions in terms of near-optimality and near-complementarity measures for Lagrangian relaxed solutions. The meta-heuristic principle amounts to constructing a weighted combination of these measures, thus creating a parametric auxiliary objective function (which is a close relative to a Lagrangian function), and embedding a Lagrangian heuristic in a search procedure in the space of the weight parameters. We illustrate and assess the Lagrangian meta-heuristic principle by applying it to the generalized assignment problem and to the set covering problem. Our computational experience shows that the meta-heuristic extension of a standard Lagrangian heuristic principle can significantly improve upon the solution quality. In Paper II, we study the duality gap for set covering problems. Such problems sometimes have large duality gaps, which make them computationally challenging. The duality gap is dissected with the purpose of understanding its relationship to problem characteristics, such as problem shape and density. The means for doing this is the above-mentioned optimality condition, which is used to decompose the duality gap into terms describing near-optimality in a Lagrangian relaxation and near-complementarity in the relaxed constraints. We analyse these terms for numerous problem instances, including some large real-life instances, and conclude that when the duality gap is large, the near-complementarity term is typically large and the near-optimality term small. The large violation of complementarity is due to extensive over-coverage. Our observations have implications for the design of solution methods, especially for the design of core problems. In Paper III, we study a bi-objective covering problem stemming from a real-world application concerning the design of camera surveillance systems for large-scale outdoor areas. It is prohibitively costly to surveil the entire area, and therefore relevant to be able to present a decision-maker with trade-offs between total cost and the portion of the area that is surveilled. The problem is stated as a set covering problem with two objectives, describing cost and portion of covering constraints that are fulfilled, respectively. Finding the Pareto frontier for these objectives is very computationally demanding and we therefore develop a method for finding a good approximate frontier in a reasonable computing time. The method is based on the ε−constraint reformulation, an established heuristic for set covering problems, and subgradient optimization.
|
|
| 14. |
- Olsson, Jonas, et al.
(author)
-
Automating the planning of container loading for Atlas Copco: Coping with real-life stacking and stability constraints
- 2020
-
In: European Journal of Operational Research. - : ELSEVIER. - 0377-2217 .- 1872-6860. ; 280:3, s. 1018-1034
-
Journal article (peer-reviewed)abstract
- The Atlas Copco* distribution center in Allen, TX, supplies spare parts and consumables to mining and construction companies across the world. For some customers, packages are shipped in sea containers. Planning how to load the containers is difficult due to several factors: heterogeneity of the packages with respect to size, weight, stackability, positioning and orientation; the set of packages differs vastly between shipments; it is crucial to avoid cargo damage. Load plan quality is ultimately judged by shipping operators. This container loading problem is thus rich with respect to practical considerations. These are posed by the operators and include cargo and container stability as well as stacking and positioning constraints. To avoid cargo damage, the stacking restrictions are modeled in detail. For solving the problem, we developed a two-level metaheuristic approach and implemented it in a decision support system. The upper level is a genetic algorithm which tunes the objective function for a lower level greedy-type constructive placement heuristic, to optimize the quality of the load plan obtained. The decision support system shows load plans on the forklift laptops and has been used for over two years. Management has recognized benefits including reduction of labour usage, lead time, and cargo damage risk. (C) 2019 Elsevier B.V. All rights reserved.
|
|
| 15. |
- Quttineh, Nils-Hassan, et al.
(author)
-
An optimization approach to the design of outdoor thermal fire detection systems
- 2022
-
In: Fire safety journal. - : Elsevier Science Ltd. - 0379-7112 .- 1873-7226. ; 129
-
Journal article (peer-reviewed)abstract
- With the recent growing usage of bio-fuels the need for fire detection in outdoor bio-fuel depots has increased, and several fire detection technologies for this purpose have been proposed. We consider the use of thermal cameras and present the problem of designing the placement of such cameras. Bio-fuel depots are often large and it might be prohibitively expensive to surveil the complete areas of interest, and it is therefore required to generate compromise solutions between area coverage and cost, to be presented to a customer. We give a bi-objective mathematical optimization formulation of the problem and fast heuristics that find compromise solutions, and present results from calculating camera placements for several real-world bio-fuel depots. Our approach has been implemented in a decision support software, which is currently in use.
|
|
| 16. |
- Quttineh, Nils-Hassan, et al.
(author)
-
Applying heuristics in supply chain planning in the process industry
- 2020
-
In: International Journal of Industrial Engineering Computations. - : GROWING SCIENCE. - 1923-2926 .- 1923-2934. ; 11:4, s. 585-606
-
Journal article (peer-reviewed)abstract
- In this paper a mixed-integer linear programming (MILP) model is developed to be used as a decision support tool for the chemical company Perstorp Oxo AB. The intention with the mathematical model is to maximize the profit and the model can be used in the process of planning the supply chain for the company. Perstorp Oxo is classified as a global company in the process industry and is has production sites in Gent, Castellanza, Stenungsund and Perstorp. The site in Stenungsund is in focus in this paper. The company produces chemicals that later are used for example in textiles, plastic and glass production. Perstorp Oxo also uses inventories in other countries for enabling the selling abroad. It has two larger inventories in Antwerp and in Tees and two smaller in Philadelphia and in Aveiro. The larger facilities store five different products and the smaller take care of one type each. To be able to find feasible and profitable production plans for the company we have developed and implemented rolling horizon techniques for a time horizon of one year and used real sales data. The outcomes from the model show the transportation of products between different production sites, the different production rates, the levels of inventory, setups and purchases from external suppliers. The numerical results are promising and we conclude that a decision support tool based on an optimization model could improve the situation for the planners at Perstorp Oxo AB. (C) 2020 by the authors; licensee Growing Science, Canada
|
|
| 17. |
- Quttineh, Nils-Hassan, 1979-, et al.
(author)
-
Approximating the Pareto frontier for a challenging real-world bi-objective covering problem
- 2022
-
In: INFOR. Information systems and operational research. - : Taylor & Francis Inc. - 0315-5986 .- 1916-0615. ; 60:3, s. 342-358
-
Journal article (peer-reviewed)abstract
- We study a bi-objective covering problem stemming from a real-world application concerning the design of camera surveillance systems for large-scale outdoor areas. It is in this application prohibitively costly to surveil the entire area, and therefore necessary to be able to present a decision-maker with trade-offs between total cost and the portion of the area that is surveilled. The problem can be stated as a set covering problem with two objectives, describing cost and portion of covering constraints that are fulfilled. Finding the Pareto frontier for these objectives is very computationally demanding and we therefore derive a method for finding a good approximate frontier in a practically feasible computing time. The method is based on the epsilon-constraint reformulation, an established heuristic for set covering problems, and subgradient optimization.
|
|
| 18. |
- Quttineh, Nils-Hassan, 1979-, et al.
(author)
-
Dissecting the duality gap : the supporting hyperplane interpretation revisited
- 2022
-
In: Optimization Letters. - : Springer Nature. - 1862-4472 .- 1862-4480. ; 16, s. 1093-1102
-
Journal article (peer-reviewed)abstract
- We revisit the classic supporting hyperplane illustration of the duality gap for non-convex optimization problems. It is refined by dissecting the duality gap into two terms: the first measures the degree of near-optimality in a Lagrangian relaxation, while the second measures the degree of near-complementarity in the Lagrangian relaxed constraints. We also give an example of how this dissection may be exploited in the design of a solution approach within discrete optimization.
|
|
| 19. |
- Quttineh, Nils-Hassan, et al.
(author)
-
Integrated solution for electric bus timetabling and vehicle scheduling combined with choices of charging locations
- 2023
-
In: Journal of Public Transportation. - : ELSEVIER. - 1077-291X. ; 25
-
Journal article (peer-reviewed)abstract
- This paper presents a novel mathematical model, integrating timetabling and vehicle scheduling problems for electric buses. The objective is to minimize the number of buses while satisfying constraints concerning routing and charging, including design choices for where to install charging stations. The aim of the paper is to illustrate and discuss the effects of solving the timetabling and vehicle scheduling of electric buses (including where to install charging infrastructure) separately, compared to solving them jointly in one single step. For that purpose, we perform tests with: i) given timetable, that is, solving only the vehicle scheduling problem, ii) fixed headways for each line, and iii) variable headways. A small test case based on actual bus lines from Va center dot stra Fro center dot lunda, Gothenburg, Sweden, is used. From the numerical experiments, we verify that combining the two planning steps can significantly reduce the number of vehicles needed.
|
|
| 20. |
- Tadaros, Marduch
(author)
-
New Modelling Approaches for Location and Routing Problems towards Sustainable Logistic Systems
- 2022
-
Licentiate thesis (other academic/artistic)abstract
- Transportations are paramount for a well-functioning society and necessary to secure essential products and maintain our standard of living. These are operations and activities related to distributing packages and goods and providing services by society such as waste collection, postal services, health care, or emergency response. Transports thus affect all of us – companies, the public sector, and individuals – in our daily lives. However, the transportation sector is also one of the most polluting sectors, and in recent years the number distributed goods has increased significantly. Based on the importance of transportation and logistics services and their impact on the economy, environment, and people’s lives, it is in everyone’s interest that these transports are as efficient as possible.The supply chain's underlying infrastructure affects the efficiency and design of distribution routes. As such infrastructure is associated with substantial capital investments, it is crucial to consider the network design and the location of various facilities. The supply chain network design in this context encompasses two major problem classes; the vehicle routing problem aiming to find optimal routes to serve a set of customers by a fleet of vehicles from a central facility, and the facility location problem aiming to find the optimal location for various facilities. Moreover, these problems are interconnected as the facilities affect the demand fulfillment and the vehicle routing. Such problems are often solved with optimization techniques within the field of Operations Research, which is concerned with the mathematical modeling and algorithmic solution of decision-making problems.The objective of this thesis is to contribute to the advancement of the field of supply chain network design, by; I. exploring and identifying opportunities and needs for modeling and solution approaches that cope with the increased complexity of real-life industrial applications in facility location and distribution systems of goods, and II. to propose new modeling approaches and solution methods that cope with such opportunities and needs. The thesis is based on three appended papers. Paper A presents a network design modeling approach for a reverse supply chain of a newly introduced product with difficulties in demand estimations. Paper B is a literature review covering multi-objective location-routing problems; these are strategic models aiming to determine the location of facilities considering aspects of tour planning and multi-stop routes. An annotated review is presented based on the application area of the various models, and an analysis of objectives and solution approaches used. Paper C introduces the Hierarchical Multi-Switch Multi-Echelon VRP, which is a new variant of the vehicle routing problem based on a real-life operational problem originating from the policies of a Nordic distribution company. A mixed-integer formulation of the problem is proposed, and its relations to other previously stated VRP variants are analyzed and discussed.
|
|
