Addressing cargo stability in the container loading problem


Speaker:Antonio Galrão Ramos , Polytechnic Institute of Porto
Date: Thursday 2 February 2017
Time: 11:30 - 13:30
Location: Building One Kolade Teaching

Further details

Addressing cargo stability in the container loading problem

António Galrão Ramos1,2, José F. Oliveira1,3


2 School of Engineering, Polytechnic of Porto

3 Faculty of Engineering, University of Porto

The container loading problem is a real-world driven NP-hard combinatorial optimization problem that addresses the optimization of the spatial arrangement of cargo inside containers so that the utilization of the containers’ space is maximized. As an assignment problem it can have two basic objectives, the maximization of the value of the cargo loaded, when the number of containers is not sufficient to accommodate all the cargo, or the minimization of the value of containers when there are sufficient containers to accommodate all cargo.

The problem is of great relevance in the field of transport management since it impacts on customer satisfaction, operational efficiency and transport safety. Cargo damage, efficient use of space and workers’ safety are just a few examples of the influence of cargo arrangements in transportation.

It is the large number of real-world constraints, such as cargo stability, container weight limit or cargo orientation constraints that limits the use in real-world scenarios of the classic approaches to the problem. These approaches only consider the existence of geometric constraints such as non-overlapping of boxes and the total inclusion of boxes inside the container and have as goal, the optimization of the space used.

Cargo stability is considered in the literature as one of the most important real-world constraints of the container loading problem. It is usually approached by making a distinction between static (vertical) and dynamic (horizontal) stability, that is, the stability of the cargo during the loading process into the container and the stability of the cargo during transportation.

The majority of authors only focus on static stability, and the way that it is guaranteed in container loading algorithms is by enforcing the full base support constrain, which requires the entire base of a box be in contact with the base of the container or with the top surface of other boxes. The full support constraint is excessively restrictive for the container space utilization and does not necessarily meet real-world needs.

Dynamic stability has been addressed in the literature in an over-simplified way which does not actually translate real-world stability. It is treated as a soft constraint and is evaluated by measuring the boxes' interlocking and lateral movement.

The aim of this work is to address cargo stability under a realistic framework, within the container loading problem. The approach to static stability is based on the static mechanical equilibrium conditions applied to rigid bodies derived from Newton’s laws of motion, and to dynamic stability by using a physics simulation tool based on a physics engine, which can be used to translate real-world stability.

Keywords: static stability, dynamic stability, container loading problem, physics engine