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Flisberg, Patrik
Publications (10 of 11) Show all publications
Carlsson, D., Flisberg, P. & Roennqvist, M. (2014). Using robust optimization for distribution and inventory planning for a large pulp producer. Computers & Operations Research, 44, 214-225
Open this publication in new window or tab >>Using robust optimization for distribution and inventory planning for a large pulp producer
2014 (English)In: Computers & Operations Research, ISSN 0305-0548, E-ISSN 1873-765X, Vol. 44, p. 214-225Article in journal (Refereed) Published
Abstract [en]

Sodra Cell is a world leading producer of pulp and has a large distribution network for its pulp products. This network includes production mills in Sweden and Norway, terminals in European harbours and inland locations, and many customers. The company uses several transport modes including long chartered vessels, spot vessels, trains, barges and trucks. The company uses a supplier managed inventory with a large proportion of its customers. This makes the logistic planning including transportation and inventory critical, as Sodra Cell has direct responsibility of their customers inventories. However, there is still some uncertainty regarding customer demand and Sodra Cell has traditionally used a safety stock inventory approach to handle this. In this paper, we introduce a robust optimization approach to handle the uncertainty and to establish a distribution plan, together with related inventory management. With this approach there is no need for explicit safety stock levels. This is instead taken into account directly through the robust solution. In the proposed model, we can use practical characterization and historical information on the uncertainty. An important result with this is that we can avoid solutions that are too conservative and costly as in standard robust models. A large case study from Sodra Cell is used to validate the proposed approach against the traditional approach with safety stock. The analysis is based on simulations and it shows that the robust approach is more cost efficient and can be used as a basis in a decision support system.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Value chain management; Robust optimization; Uncertainty; Inventory management; Transportation; Distribution
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-105568 (URN)10.1016/j.cor.2013.11.010 (DOI)000331498900019 ()
Available from: 2014-03-31 Created: 2014-03-27 Last updated: 2017-12-05
Flisberg, P., Lidén, B. & Rönnqvist, M. (2009). A hybrid method based on linear programming and tabu search for routing of logging trucks. Computers & Operations Research, 36(4), 1122-1144
Open this publication in new window or tab >>A hybrid method based on linear programming and tabu search for routing of logging trucks
2009 (English)In: Computers & Operations Research, ISSN 0305-0548, E-ISSN 1873-765X, Vol. 36, no 4, p. 1122-1144Article in journal (Refereed) Published
Abstract [en]

In this paper, we consider an operational routing problem to decide the daily routes of logging trucks in forestry. This industrial problem is difficult and includes aspects such as pickup and delivery with split pickups, multiple products, time windows, several time periods, multiple depots, driver changes and a heterogeneous truck fleet. In addition, the problem size is large and the solution time limited. We describe a two-phase solution approach which transforms the problem into a standard vehicle routing problem with time windows. In the first phase, we solve an LP problem in order to find a destination of flow from supply points to demand points. Based on this solution, we create transport nodes which each defines the origin(s) and destination for a full truckload. In phase two, we make use of a standard tabu search method to combine these transport nodes, which can be considered to be customers in vehicle routing problems, into actual routes. The tabu search method is extended to consider some new features. The solution approach is tested on a set of industrial cases from major forest companies in Sweden.

Keywords
Forestry, Routing, Tabu search, Linear Programming, OR in Practice
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85519 (URN)10.1016/j.cor.2007.12.012 (DOI)
Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2017-12-07
Flisberg, P., Ronnqvist, M. & Nilsson , S. (2009). Billerud Optimizes Its Bleaching Process Using Online Optimization. INTERFACES, 39(2), 119-131
Open this publication in new window or tab >>Billerud Optimizes Its Bleaching Process Using Online Optimization
2009 (English)In: INTERFACES, ISSN 0092-2102 , Vol. 39, no 2, p. 119-131Article in journal (Refereed) Published
Abstract [en]

Billerud, a Swedish company with four integrated pulp and paper mills, serves specific packaging-market segments. In 2000, the process-engineering department at Billeruds mill in Skarblacka sought to improve the mills bleaching process. It contacted Linkoping University, which collaborated with Eurocon Automation AB to develop a decision-support system, OptCab. Eurocon Automation AB now offers OptCab as a general tool in the market. Its core is an online optimization system that dynamically updates a process description and optimizes the bleaching control process. The system, which has been fully operational since 2004, has provided numerous benefits to Billerud. Chemical use has decreased by approximately 10 percent, saving approximately two million euros since its installation; the environmental impact has also been reduced; and the brightness quality of paper that the mill produces is more uniform and stable. Moreover, OptCab requires less operator time, freeing the operators for development and analysis work.

Keywords
decision-support system, nonlinear, applications, planning, chemical, lumber/wood
National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-17894 (URN)10.1287/inte.1080.0404 (DOI)
Available from: 2009-04-26 Created: 2009-04-24 Last updated: 2009-04-26
Flisberg, P. (2007). Application of operations research in operative planning in the forest industry. (Doctoral dissertation). Matematiska institutionen
Open this publication in new window or tab >>Application of operations research in operative planning in the forest industry
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is the use of Operations Research for pplications in the forest industry. Optimization models and methods have been developed for problems in the forest supply chain and they have been integrated in decision support systems. The problems considered in this thesis are operative with a planning horizon of less than a month. Short solution times for the methods and the feasibility of the models used are important aspects. The body of this thesis consists of eight research papers where six of them consider operative problems and follows the forest supply chain. The industrial applications include routing of forwarders, routing of logging trucks, a process control problem, and roll cutting problems. The other two papers consider an operative planning problem in the home care sector. They are spin offs from one of the other projects in this thesis. In these applications both linear and nonlinear problems occur.

The forwarding problem is to decide routes for forwarders to pick up the small piles of logs the harvesters have left in the harvest areas. The forwarders then put the logs adjacent to forest roads. The logging truck problem is to decide routes for logging trucks to pick up the piles created by the forwarders and transport them to demand points, for example pulp or paper mills. The process control problem appear in the bleaching stage of a pulp mill where the control variables are the bleaching chemical charges. The cost of bleaching chemicals is minimized while a finishing brightness within target values is ensured. Mainly two roll cutting problems are studied. One is to minimize the number of cutting patterns and one is to minimize the number of reels when defects in the papper reels are considered. The solution methods developed for the forwarding problem have also been applied to a routing problem which appears in staff planning for home care operations.

The different DSS developed and implemented have been tested and several are in daily industrial use. In each of the papers, we have developed robust OR models and quick and effective OR methods. The savings from using the systems vary but are typically in the range 5-20%.

Place, publisher, year, edition, pages
Matematiska institutionen, 2007. p. 31
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1104
Keywords
operative planning, routing, forestry, modelling, Decision Support System, optimization, OR in practice
National Category
Computational Mathematics
Identifiers
urn:nbn:se:liu:diva-8806 (URN)978-91-85831-91-3 (ISBN)
Public defence
2007-05-30, C3, Hus C, Campus Valla, Linköpings Universitet, Linköping, 10:10 (English)
Opponent
Supervisors
Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2012-11-22
Flisberg, P., Forsberg, M. & Ronnqvist, M. (2007). Optimization based planning tools for routing of forwarders at harvest areas. Canadian Journal of Forest Research, 37(11), 2153-2163
Open this publication in new window or tab >>Optimization based planning tools for routing of forwarders at harvest areas
2007 (English)In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 37, no 11, p. 2153-2163Article in journal (Refereed) Published
Abstract [en]

The forwarding of logs at harvest areas once the harvesting is done is planned manually by experienced operators. To improve their efficiency and simplify the planning we have developed and tested a decision support system at a major Swedish forest company. The system is based on a combination of a geographic information system (GIS), global positioning system (GPS), and optimization routines to solve the underlying vehicle routing problem. The routes for the forwarders are found by using a repeated matching algorithm. The solution time is short, and it is possible to find routes dynamically in a real-time environment. The geographic information required is found by using a GPS together with data obtained from the bucking software in the harvesters. To show the routes and location of the forwarder, we make use of a GIS that is connected to the GPS. We report on a study with savings in the distance travelled of 8% and numerical tests on the solution methodology. We also compare the proposed solution method with some well-known routing methods.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47900 (URN)10.1139/X07-065 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Flisberg, P., Nilsson, S. & Rönnqvist, M. (2007). Optimized on-line process control of bleaching operations with OptCab. Norges Handelshoeyskole. Institutt for Foretaksoekonomi. Discussion Paper
Open this publication in new window or tab >>Optimized on-line process control of bleaching operations with OptCab
2007 (English)In: Norges Handelshoeyskole. Institutt for Foretaksoekonomi. Discussion Paper, ISSN 1500-4066Article, review/survey (Refereed) Published
Abstract [en]

To produce pulp for paper production or as market pulp is a complicated on-line process with many integrated stages that impact the final quality. In the bleaching plant which is at the end of pulp production, the main objective is to increase pulp brightness within specified limits. Here chemical treatments are applied in sequential stages to achieve the right brightness while striving to maintain the pulp strength as unaffected as possible. The raw material, i.e. pulp logs and wood chips from saw mills, differ in quality and properties. Due to this, it is important to continuously update the amount of chemicals added to the pulp in real-time. This is typically done by experienced operators. In this paper, we describe an on-line optimization based decision support system called OptCab that controls the bleaching process at Billerud AB's paper mill in Skärblacka. The solution approach is based on two phases. In phase one, we establish approximations of each of the processes based on process data collected on-line. These approximations are found by solving a set of constrained least square problems and are updated every 15 minutes. In phase two, we formulate an overall nonlinear control problem that links all stages together and aims to minimize the cost of chemicals. This is solved on-line every five minutes. The system has been in operation during the last three years providing a 10% reduction in the use of chemicals. Additional benefits include a more stable brightness quality.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85523 (URN)
Note

This is a working paper.

Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2012-11-22
Eveborn, P., Flisberg, P. & Rönnqvist, M. (2006). Laps Care: an operational system for staff planning of home care. European Journal of Operational Research, 171(3), 962-976
Open this publication in new window or tab >>Laps Care: an operational system for staff planning of home care
2006 (English)In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 171, no 3, p. 962-976Article in journal (Refereed) Published
Abstract [en]

The health care system in Sweden and many other countries is facing increasing costs. The major reason is the changing age distribution of the population with more elderly people in need of support. At the same time, health care systems are often very labor and staff intensive. In this paper, we focus on a staff planning problem arising in Sweden where people receive home care from the local authorities. The objective is to develop visiting schedules for care providers that incorporate some restrictions and soft objectives. Each visit has a particular task to be performed, for example: cleaning, washing, personal hygiene and/or nursing activities. Each staff member has skills and each client should, if possible, be visited by the same contact person. The operational situation is continuously changing and planning is done each day. We describe the development of a decision support system Laps Care to aid the planners. The system consists of a number of components including information data bases, maps, optimization routines, and report possibilities. We formulate the problem using a set partitioning model and, for a solution method, we make use of a repeated matching algorithm. The system is currently in operation at a number of home care organizations. We report on the practical impact of the system in the health care organization which was involved in the development. The savings are considerably in terms of saved planning time and in the quality of the routes, as well as the measured quality for the clients. Numerical experiments of the system are presented.

Keywords
health care; home care; staff planning; modelling; heuristics; optimization; practice of OR
National Category
Social Sciences
Identifiers
urn:nbn:se:liu:diva-53494 (URN)10.1016/j.ejor.2005.01.011 (DOI)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12
Flisberg, P., Nilsson, S. & Rönnqvist, M. (2005). Pulp fact, not fiction. OR/MS Today, 32(2), 42-47
Open this publication in new window or tab >>Pulp fact, not fiction
2005 (English)In: OR/MS Today, ISSN 1085-1038, Vol. 32, no 2, p. 42-47Article in journal (Refereed) Published
Abstract [en]

By taking the guesswork out of the equation, operations research-based process control system helps cut costs, reduce environmental impact at Swedish paper mill.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85522 (URN)
Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2012-11-27
Rönnqvist, M., Flisberg, P. & Eveborn, P. (2004). Home care operations. OR/MS today, April, 38-43
Open this publication in new window or tab >>Home care operations
2004 (English)In: OR/MS today, ISSN 1085-1038, Vol. April, p. 38-43Article in journal (Refereed) Published
Abstract [en]

No abstract available.

National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-22746 (URN)2060 (Local ID)2060 (Archive number)2060 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2012-11-22
Flisberg, P., Eveborn, P. & Rönnqvist, M. (2003). Staff planning in the Swedish home care system. Linköping: Linköpings universitet
Open this publication in new window or tab >>Staff planning in the Swedish home care system
2003 (English)Report (Other academic)
Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2003
Series
LiTH-MAT-R ; 11
National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-22365 (URN)1573 (Local ID)1573 (Archive number)1573 (OAI)
Available from: 2009-10-07 Created: 2009-10-07
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