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  • 1.
    Bredström, David
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Models and solution methods for large-scale industrial mixed integer programming problems2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with large-scale industrial problems that can be formulated using mixed integer linear programming (MIP) models. Because of the large problem size, it is not often possible to apply standard solution methods. Therefore special techniques must be used. In this thesis, both full optimization and optimization based heuristic approaches are developed.

    The body of this thesis consists of five research papers. In the papers we consider industrial cases based on three applications: production planning at Södra Cell AB, ship routing and distribution at Södra Cell AB, and staff routing and scheduling in the Swedish home care.

    We develop two large-scale MIP models for the production-planning problem. For solving, we use both a direct approach, and a combination of column generation and constraint branching. The latter is a technique to control the branching rules in a branch and bound framework and takes into account application specific properties.

    For the ship routing problem, we present a MIP model and develop two solution methods. The first is based on an iterative rolling time horizon. In each step a part of the model is solved and later fixed. This is repeated until the full problem is solved. The second approach is to combine a genetic algorithm and linear programming. From the MIP model, we obtain solution bounds rarely present in genetic algorithm frameworks.

    In the staff routing problem there are special synchronization constraints and we introduce a new MIP model. An exact solution approach based on column generation and branch and bound is developed. We also suggest a variable fixing heuristic, which we use for solving the more general problem with requirements on equal workload.

    In the computational experiments, we use data instances obtained from real-world cases, and generated instances based on real-world cases. The numerical results show that high quality solutions can be obtained within reasonable time limits in all applications.

    Delarbeid
    1. Combined vehicle routing and scheduling with temporal precedence and synchronization constraints
    Åpne denne publikasjonen i ny fane eller vindu >>Combined vehicle routing and scheduling with temporal precedence and synchronization constraints
    2006 (engelsk)Inngår i: EconPapers, Vol. 18Artikkel i tidsskrift (Annet vitenskapelig) Published
    Abstract [en]

    We present a mathematical programming model for the combined vehicle routing and scheduling problem with time windows and additional temporal constraints. The temporal constraints allow for imposing pairwise synchronization and pairwise temporal precedence between customer visits, independently of the vehicles. We describe some real world problems where the temporal constraints, in the literature, usually are remarkably simplified in the solution process, even though these constraints may significantly improve the solution quality and/or usability. We also propose an optimization based heuristic to solve real size instances. The results of numerical experiments substantiate the importance of the temporal constraints in the solution approach. We also make a computational study by comparing a direct usage of a commercial solver against the proposed heuristic where the latter approach can find high quality solutions within distinct time limits.

    Emneord
    Routing; Scheduling; Temporal Constraints; Synchronization; Branch and Bound
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13128 (URN)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2009-02-17
    2. A branch and price algorithm for the combined vehicle routing and scheduling problem with synchronization constraints
    Åpne denne publikasjonen i ny fane eller vindu >>A branch and price algorithm for the combined vehicle routing and scheduling problem with synchronization constraints
    2007 (engelsk)Inngår i: Social Science Research Network, Vol. 7Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper we present a branch and price algorithm for the combined vehicle routing and scheduling problem with synchronization constraints. The synchronization constraints are used to model situations when two or more customers need simultaneous service. The synchronization constraints impose a temporal dependency between vehicles, and it follows that a classical decomposition of the vehicle routing and scheduling problem is not directly applicable. With our algorithm, we have solved 44 problems to optimality from the 60 problems used for numerical experiments. The algorithm performs time window branching, and the number of subproblem calls is kept low by adjustment of the columns service times.

    Emneord
    Routing, Scheduling, Synchronization, Branch and Price
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13129 (URN)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2009-04-15
    3. Supply chain optimization in the pulp mill industry: IP models, column generation and novel constraint branches
    Åpne denne publikasjonen i ny fane eller vindu >>Supply chain optimization in the pulp mill industry: IP models, column generation and novel constraint branches
    Vise andre…
    2004 (engelsk)Inngår i: European Journal of Operational Research, ISSN 0377-2217, Vol. 156, nr 1, s. 2-22Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study the supply chain problem of a large international pulp producer with five pulp mills located in Scandinavia. The company currently uses manual planning for most of its supply chain, which includes harvesting and transportation of pulp, production scheduling and distribution of products to customers. We have developed two new mixed integer models that determine daily supply chain decisions over a planning horizon of three months. One model is based on column generation, where the generation phase is to find new production plans using a shortest path network. The second, slightly less flexible, has the daily production decisions explicitly included in the model. In order to solve the models within practical time limits we use a flexible approach that aggregates together the less immediate decisions. We also introduce a novel constraint branching heuristic. The models and solution approaches are intended to become an integrated component in the company’s new management system. In tests and comparisons with today’s manual planning, we have found new strategic policies that significantly reduce the company’s supply chain costs.

    Emneord
    Branch and bound, Integer programming, Production, Scheduling, Supply chain management
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13130 (URN)10.1016/j.ejor.2003.08.001 (DOI)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2013-11-05
    4. Supply chain optimization in pulp distribution using a rolling horizon solution approach
    Åpne denne publikasjonen i ny fane eller vindu >>Supply chain optimization in pulp distribution using a rolling horizon solution approach
    2006 (engelsk)Rapport (Annet vitenskapelig)
    Abstract [en]

    In this paper we consider a combined supply chain and ship routing problem for a large pulp producer in Scandinavia. The problem concerns the distribution of pulp to customers, with route scheduling of ships as a central part of modeling. It is an operative planning problem with daily ship routing decisions over a 40 days period. The pulp supply is determined by fixed production plans, and the transport flows and storages are modeled with the requirement to satisfy the demand in a cost-optimal way. We develop a mixed integer programming model with binary variables for route usage of a vessel.

    The problem is solved with a heuristic solution method, based on a rolling time horizon and a standard branch and bound algorithm. We apply the heuristic on problem instances with real world data, and compare results from reduced problem instances with the results from an exact branch and bound search. The computational experiments indicate that real world problems are solvable with the solution method and that it in many cases can be very effcient.

     

    Serie
    LiTH-MAT-R ; 2003-25
    Emneord
    Supply chain, Ships, Scheduling, Mixed integer programming
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13131 (URN)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2013-11-05
    5. A hybrid algorithm for a pulp distribution problem
    Åpne denne publikasjonen i ny fane eller vindu >>A hybrid algorithm for a pulp distribution problem
    2005 (engelsk)Inngår i: IEEE Intelligent Systems, ISSN 1541-1672, Vol. 20, nr 4, s. 19-25Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Distribution is a major factor in the supply chain for Sodra Cell, a leading manufacturer of pulp intended for paper production. Each year, the company transports large quantities of pulp using ships, trains, and trucks; here we focus on scheduling the ships and optimizing deliveries to minimize distribution costs.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13132 (URN)10.1109/MIS.2005.59 (DOI)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2015-12-29
  • 2.
    Bredström, David
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Optimization models and methods for production planning and ship scheduling in the pulp industry2003Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    To use optimization models and methods is an increasingly acknowledged element of supply chain management for large industries. Concurrently with the increasing global market competition and modern business policies, an already effective organization needs to find new possibilities to improve their planning procedures and resource utilization. To incorporate the planning in a more comprehensive context, in an overall supply chain, provides new possibilities to efficiently manage several planning steps than if considered individually.

    This thesis considers production planning and ship scheduling problems at Södra Cell, a large Scandinavian pulp manufacturer. The main purpose of the thesis is to suggest optimization models and methods that can support production and distribution planners to objectively consider the supply chain impact in the short-term decision making process. The production planning and the ship scheduling problems are approached separately. Optimization models are formulated for both problems, and specially adapted solution methods are developed that account the characteristics of the problems.

    The thesis consists of three research papers. In the first paper two mixed integer models (MIPs) are developed for the production planning problem. The first model has binary variables for every possible production plan and a column generation approach with a constraint branching heuristic is used to solve the otherwise very large model. The second model has the production choices formulated in constraints and is solved with a standard branch and bound search. The results are compared with manual planning and potential large savings are indicated.

    The second and the third paper both consider the pulp distribution problem where ship routing and scheduling decisions have a key role. In the second paper the problem is solved with a rolling time horizon method. An MIP model is solved repeatedly over short ranges of time until eventually the whole planning period is covered. The third paper presents a genetic algorithm with integrated linear programming models for the distribution problem. The solutions from the different solution strategies for the distribution problem are mutually compared in the third paper.

    Delarbeid
    1. Supply chain optimization in the pulp mill industry: IP models, column generation and novel constraint branches
    Åpne denne publikasjonen i ny fane eller vindu >>Supply chain optimization in the pulp mill industry: IP models, column generation and novel constraint branches
    Vise andre…
    2004 (engelsk)Inngår i: European Journal of Operational Research, ISSN 0377-2217, Vol. 156, nr 1, s. 2-22Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study the supply chain problem of a large international pulp producer with five pulp mills located in Scandinavia. The company currently uses manual planning for most of its supply chain, which includes harvesting and transportation of pulp, production scheduling and distribution of products to customers. We have developed two new mixed integer models that determine daily supply chain decisions over a planning horizon of three months. One model is based on column generation, where the generation phase is to find new production plans using a shortest path network. The second, slightly less flexible, has the daily production decisions explicitly included in the model. In order to solve the models within practical time limits we use a flexible approach that aggregates together the less immediate decisions. We also introduce a novel constraint branching heuristic. The models and solution approaches are intended to become an integrated component in the company’s new management system. In tests and comparisons with today’s manual planning, we have found new strategic policies that significantly reduce the company’s supply chain costs.

    Emneord
    Branch and bound, Integer programming, Production, Scheduling, Supply chain management
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13130 (URN)10.1016/j.ejor.2003.08.001 (DOI)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2013-11-05
    2. Supply chain optimization in pulp distribution using a rolling horizon solution approach
    Åpne denne publikasjonen i ny fane eller vindu >>Supply chain optimization in pulp distribution using a rolling horizon solution approach
    2006 (engelsk)Rapport (Annet vitenskapelig)
    Abstract [en]

    In this paper we consider a combined supply chain and ship routing problem for a large pulp producer in Scandinavia. The problem concerns the distribution of pulp to customers, with route scheduling of ships as a central part of modeling. It is an operative planning problem with daily ship routing decisions over a 40 days period. The pulp supply is determined by fixed production plans, and the transport flows and storages are modeled with the requirement to satisfy the demand in a cost-optimal way. We develop a mixed integer programming model with binary variables for route usage of a vessel.

    The problem is solved with a heuristic solution method, based on a rolling time horizon and a standard branch and bound algorithm. We apply the heuristic on problem instances with real world data, and compare results from reduced problem instances with the results from an exact branch and bound search. The computational experiments indicate that real world problems are solvable with the solution method and that it in many cases can be very effcient.

     

    Serie
    LiTH-MAT-R ; 2003-25
    Emneord
    Supply chain, Ships, Scheduling, Mixed integer programming
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13131 (URN)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2013-11-05
    3. A genetic algorithm for a pulp distribution problem
    Åpne denne publikasjonen i ny fane eller vindu >>A genetic algorithm for a pulp distribution problem
    2003 (engelsk)Rapport (Annet vitenskapelig)
    Abstract [en]

    In this paper we present a genetic algorithm for the pulp distribution problem at a large pulp producer in Scandinavia. The distribution is a major part of the company's supply chain and includes transports with cargo vessels, by train and trucks and storages at terminals in port, at pulp mills and in customer locations. The problem we focus on is to find ship schedules and pulp deliveries in order to minimize the total cost of distribution.

    The genetic algorithm utilizes two linear programming models. The first model optimizes all transport flows given a schedule and the second model approximates the performance of a schedule, measured in the total distribution cost. In the computational experiments we use instances from the real world and compare the results with an exact mixed integer programming approach.

    sted, utgiver, år, opplag, sider
    Linköping: Linköpings universitet, 2003. s. 21
    Serie
    LiTH-MAT-R, ISSN 0348-2960 ; 26
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-22364 (URN)1572 (Lokal ID)1572 (Arkivnummer)1572 (OAI)
    Tilgjengelig fra: 2009-10-07 Laget: 2009-10-07 Sist oppdatert: 2013-11-05
  • 3.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Carlsson, Dick
    Södra Cell AB, Växjö, Sweden.
    Lundgren, Jan T.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Mason, Andrew
    Department of Engineering Science, The University of Auckland, Auckland, New Zealand.
    Rönnqvist, Mikael
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Supply chain optimization in the pulp mill industry: IP models, column generation and novel constraint branches2004Inngår i: European Journal of Operational Research, ISSN 0377-2217, Vol. 156, nr 1, s. 2-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the supply chain problem of a large international pulp producer with five pulp mills located in Scandinavia. The company currently uses manual planning for most of its supply chain, which includes harvesting and transportation of pulp, production scheduling and distribution of products to customers. We have developed two new mixed integer models that determine daily supply chain decisions over a planning horizon of three months. One model is based on column generation, where the generation phase is to find new production plans using a shortest path network. The second, slightly less flexible, has the daily production decisions explicitly included in the model. In order to solve the models within practical time limits we use a flexible approach that aggregates together the less immediate decisions. We also introduce a novel constraint branching heuristic. The models and solution approaches are intended to become an integrated component in the company’s new management system. In tests and comparisons with today’s manual planning, we have found new strategic policies that significantly reduce the company’s supply chain costs.

  • 4.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Rönnqvist, Mikael
    Norwegian School of Economics and Business Administration (NHH), Bergen, Norway.
    A branch and price algorithm for the combined vehicle routing and scheduling problem with synchronization constraints2007Inngår i: Social Science Research Network, Vol. 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we present a branch and price algorithm for the combined vehicle routing and scheduling problem with synchronization constraints. The synchronization constraints are used to model situations when two or more customers need simultaneous service. The synchronization constraints impose a temporal dependency between vehicles, and it follows that a classical decomposition of the vehicle routing and scheduling problem is not directly applicable. With our algorithm, we have solved 44 problems to optimality from the 60 problems used for numerical experiments. The algorithm performs time window branching, and the number of subproblem calls is kept low by adjustment of the columns service times.

  • 5.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Rönnqvist, Mikael
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    A genetic algorithm for a pulp distribution problem2003Rapport (Annet vitenskapelig)
    Abstract [en]

    In this paper we present a genetic algorithm for the pulp distribution problem at a large pulp producer in Scandinavia. The distribution is a major part of the company's supply chain and includes transports with cargo vessels, by train and trucks and storages at terminals in port, at pulp mills and in customer locations. The problem we focus on is to find ship schedules and pulp deliveries in order to minimize the total cost of distribution.

    The genetic algorithm utilizes two linear programming models. The first model optimizes all transport flows given a schedule and the second model approximates the performance of a schedule, measured in the total distribution cost. In the computational experiments we use instances from the real world and compare the results with an exact mixed integer programming approach.

  • 6.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Rönnqvist, Mikael
    Norwegian School of Economics and Business Administration, Bergen.
    Combined vehicle routing and scheduling with temporal precedence and synchronization constraints2006Inngår i: EconPapers, Vol. 18Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    We present a mathematical programming model for the combined vehicle routing and scheduling problem with time windows and additional temporal constraints. The temporal constraints allow for imposing pairwise synchronization and pairwise temporal precedence between customer visits, independently of the vehicles. We describe some real world problems where the temporal constraints, in the literature, usually are remarkably simplified in the solution process, even though these constraints may significantly improve the solution quality and/or usability. We also propose an optimization based heuristic to solve real size instances. The results of numerical experiments substantiate the importance of the temporal constraints in the solution approach. We also make a computational study by comparing a direct usage of a commercial solver against the proposed heuristic where the latter approach can find high quality solutions within distinct time limits.

  • 7.
    Bredström, David
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Rönnqvist, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Matematiska institutionen, Optimeringslära.
    Ship routing and scheduling in the pulp mill industry2003Inngår i: 18th International Symposium on Mathematical Programming,2003, 2003Konferansepaper (Annet vitenskapelig)
  • 8.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Rönnqvist, Mikael
    Norwegian School of Economics and Business Administration, Bergen.
    Supply chain optimization in pulp distribution using a rolling horizon solution approach2006Rapport (Annet vitenskapelig)
    Abstract [en]

    In this paper we consider a combined supply chain and ship routing problem for a large pulp producer in Scandinavia. The problem concerns the distribution of pulp to customers, with route scheduling of ships as a central part of modeling. It is an operative planning problem with daily ship routing decisions over a 40 days period. The pulp supply is determined by fixed production plans, and the transport flows and storages are modeled with the requirement to satisfy the demand in a cost-optimal way. We develop a mixed integer programming model with binary variables for route usage of a vessel.

    The problem is solved with a heuristic solution method, based on a rolling time horizon and a standard branch and bound algorithm. We apply the heuristic on problem instances with real world data, and compare results from reduced problem instances with the results from an exact branch and bound search. The computational experiments indicate that real world problems are solvable with the solution method and that it in many cases can be very effcient.

     

  • 9.
    Bredström, David
    et al.
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Rönnqvist, Mikael
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Carlsson, Dick
    A hybrid algorithm for a pulp distribution problem2005Inngår i: IEEE Intelligent Systems, ISSN 1541-1672, Vol. 20, nr 4, s. 19-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Distribution is a major factor in the supply chain for Sodra Cell, a leading manufacturer of pulp intended for paper production. Each year, the company transports large quantities of pulp using ships, trains, and trucks; here we focus on scheduling the ships and optimizing deliveries to minimize distribution costs.

1 - 9 of 9
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