Larsen, Jesper

Lusby, Richard Martin

Vilhelmsen, Charlotte

Many bulk ships have multiple tanks and can thereby carry multiple inhomogeneous products at a time. A major challenge when operating such ships is how to best allocate cargoes to available tanks while taking tank capacity, safety restrictions, ship stability and strength as well as other operational constraints into account. The complexity of the allocation problem varies with the number of tanks and the number and type of dierent products transported at the same time, and the problem of nding a feasible solution has been shown to be NP-Complete. The Tank Allocation Problem (TAP) as described above is an operational planning problem but it also arises as a subproblem in tactical planning when routing bulk ship eets. For each considered route, the TAP must be solved to assess route feasibility with respect to stowage. If the routing problem is solved in a way that requires assessment of numerous routes, as for instance in column generation and local search based methods, the solution time for the entire procedure will only be acceptable if the TAP can be solved eciently. We consider the TAP from a tactical perspective where the main objective is to quickly assessfeasibility of a given ship route. We have developed a randomised heuristic for eciently nding feasible allocations and computational results show that it can solve 99% of the considered instances within 0.5 seconds and all of them if allowed longer time. The heuristic is designed to work as an ecient subproblem solver and in such a setting with running times below e.g. 5 seconds, the heuristic clearly outperforms an earlier method by consistently solving more instances and eectively cutting 84% of the average running time. Furthermore, we have combined our heuristic with a modied version of the earlier method to derive a hybrid method that can eciently solve all instances. Compared to the earlier method, this hybrid method cuts 93% of the average running times and consistently solves more instances than the other method within any given time limit

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017A Heuristic and Hybrid Method for the Tank Allocation Problem in Maritime BulkShippingVilhelmsen, Charlotte; Larsen, Jesper; Lusby, Richard MartinPublication date:2014Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Vilhelmsen, C., Larsen, J., & Lusby, R. M. (2014). A Heuristic and Hybrid Method for the Tank AllocationProblem in Maritime Bulk Shipping. Abstract from 3rd International Symposium on Combinatorial Optimization ,Lisbon, Portugal.A Heuristic and Hybrid Method for the Tank AllocationProblem in Maritime Bulk ShippingCharlotte Vilhelmsen, Jesper Larsen and Richard LusbyDepartment of Management Engineering, Technical University of Denmarkchaan@dtu.dk, jesla@dtu.dk and rmlu@dtu.dkMany bulk ships have multiple tanks and can thereby carry multiple inhomogeneous products ata time. A major challenge when operating such ships is how to best allocate cargoes to availabletanks while taking tank capacity, safety restrictions, ship stability and strength as well as otheroperational constraints into account. The complexity of the allocation problem varies with thenumber of tanks and the number and type of different products transported at the same time, andthe problem of finding a feasible solution has been shown to be NP-Complete.The Tank Allocation Problem (TAP) as described above is an operational planning problembut it also arises as a subproblem in tactical planning when routing bulk ship fleets. For eachconsidered route, the TAP must be solved to assess route feasibility with respect to stowage. If therouting problem is solved in a way that requires assessment of numerous routes, as for instance incolumn generation and local search based methods, the solution time for the entire procedure willonly be acceptable if the TAP can be solved efficiently.We consider the TAP from a tactical perspective where the main objective is to quickly assessfeasibility of a given ship route. We have developed a randomised heuristic for efficiently findingfeasible allocations and computational results show that it can solve 99% of the considered instanceswithin 0.5 seconds and all of them if allowed longer time. The heuristic is designed to work asan efficient subproblem solver and in such a setting with running times below e.g. 5 seconds,the heuristic clearly outperforms an earlier method by consistently solving more instances andeffectively cutting 84% of the average running time. Furthermore, we have combined our heuristicwith a modified version of the earlier method to derive a hybrid method that can efficiently solveall instances. Compared to the earlier method, this hybrid method cuts 93% of the average runningtimes and consistently solves more instances than the other method within any given time limit.1

A Heuristic and Hybrid Method for the Tank Allocation Problem in Maritime Bulk Shipping

In bulk shipping, ships often have multiple tanks and carry multiple inhomogeneous products at a time. When operating such ships it is therefore a major challenge to decide how to best allocate cargoes to available tanks while taking into account tank capacity, safety restrictions, ship stability and strength as well as other operational constraints. The problem of finding a feasible solution to this tank allocation problem has been shown to be NP-Complete. We approach the problem on a tactical level where requirements for computation time are strict while solution quality is less important than simply finding a feasible solution. We have developed a heuristic that can efficiently find feasible cargo allocations. Computational results show that it can solve 99% of the considered instances within 0.4 seconds and all of them if allowed longer time. We have also modified an optimality based method from the literature. The heuristic is much faster than this modified method on the vast majority of considered instances. However, the heuristic struggles on two instances which are relatively quickly solved by the modified optimality based method. These two methods therefore complement each other nicely and so, we have created a hybrid method that first runs the heuristic and if the heuristic fails to solve the problem, then runs the modified optimality based method on the parts of the problem that the heuristic did not solve. This hybrid method cuts between 90% and 94% of the average running times compared to the other methods and consistently solves more instances than the other methods within any given time limit. In fact, this hybrid method is fast enough to be used in a tactical setting

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A Heuristic and Hybrid Method for the Tank Allocation Problem in Maritime Bulk Shipping

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