Efficient management of port resources plays a crucial role in reducing vessel stay times and avoiding the payment of demurrage charges. In this paper, we focus on the integrated Laycan and Berth Allocation and Quay Crane Assignment Problem (LBACAP), which considers three problems in an integrated way: the Laycan Allocation Problem, the dynamic continuous Berth Allocation Problem and the time-invariant Quay Crane Assignment Problem. Since these problems have different decision levels, a change of decision time scale is made inside the planning horizon. To ensure that this integrated problem is as close as possible to reality, we consider non-working periods and tidal ports with multiple quays that have different water depths. The integer programming model proposed for the LBACAP aims to find an efficient schedule for berthing chartered vessels with an efficient quay crane assignment, and to propose laycans (laydays and canceling) to new vessels to charter. In a second part, we focus on the integrated Laycan and Berth Allocation and Specific Quay Crane Assignment Problem (LBACASP), which extends the LBACAP model to include the assignment of a set of specific quay cranes to each vessel, considering the productivity of quay cranes (homogeneous or heterogeneous) and their maximum outreach. Moreover, we use predicates in the formulation of both models, which ensure maximum flexibility in their implementation, thereby improving significantly their computational performance. Finally, the computational study on several classes of generated test instances shows that problems with up to 100 vessels can be solved to optimality.
The standardization of partially substitutable components destined to meet a set of needs is studied. The monocriterion approach to standardization proposed in the last century is highlighted by taking into account several criteria and an economic valorization through modeling by linear programming. The notion of diversity is analyzed in this perspective and some cost problems of this method are discussed.
Reasoned fertilization, which is a major concern for sustainable and efficient agriculture, consists of applying customized fertilizers which requires a very large increase in the number of fertilizer formulae, involving increasing costs due to the multiplication of production batch, of storage areas and of transportation constraints. An alternative solution is given by adopting a Reverse Blending approach, which is a new Blending Problem where inputs are non-pre-existing composite materials that need to be defined in both number and composition, simultaneously with the quantities to be used in the blending process, such as to meet the specifications of a wide variety of outputs, while keeping their number as small as possible. This would replace the production of a large variety of small batches of fertilizers by few large batches of new composite materials whose blending may be performed close to end-users (delayed differentiation), delivering substantial production and logistics cost savings, well in excess of remote blending costs. Reverse Blending presents some analogies with the Pooling Problem which is a two-stage Blending Problem where primary inputs are existing raw materials. An adapted version of this problem may be used to facilitate the design of new composite materials used by Reverse Blending. This paper presents the Reverse Blending approach, whose modelling is based on a quadratic programming formulation, and a large case study to demonstrate its feasibility. Reverse Blending, therefore, may be a disruptive approach to successfully reengineer not only the fertilizer supply chain but any other industry operating in blending contexts to meet a great diversity.
RésuméPlusieurs formulations partielles du problème d'ordonnancement sur lignes de production ou d'assemblage dédiées à une production de masse fortement diversifiée -l'industrie automobile constituant l'exemple le plus cité -ont été proposées. Des hypothèses implicites limitent la portée de beaucoup d'entre elles. On proposera ici une formulation générale du problème d'ordonnancement s'appuyant sur des hypothèses réalistes de description du processus physique et prenant en compte l'incidence économique des décisions d'ordonnancement, notamment au niveau de l'appel momentané de renforts et de la prise en compte de l'incidence de rafales sur certains coûts de lancement (atelier de peinture, par exemple). Le modèle linéaire obtenu permet une description explicite et complète de ce problème complexe. La résolution de problèmes réels par la programmation mathématique est difficile en raison de la taille du problème. La description proposée facilite la mise au point d'heuristiques pertinentes.Mots clefs: ligne de production et d'assemblage, ordonnancement sur ligne de produits hétérogènes , contraintes d'espacement, rafales, personnel de renfort, évaluation économique.
AbstractSeveral formulations to the mixed-model assembly line have been proposed in the literature. Such a problem is concerned with the production of a variety of product models. Vehicles fall into that category. The underlying assumptions of those models are often restrictive, therefore limiting their applicability. Our incentive is to develop a general formulation of the car sequencing problem that explicitly takes into account the constraints of the paint shop, those of the body shop and finally the constraints emanating from the assembly shop. The resultant linear program captures the whole complexity of the problem as it is encountered in practice. Solving real-sized instances to optimality would require too much computation time. The proposed description provides a starting point to the development of relevant heuristic solution approaches.
this article seeks to consider the service concepts currently used from a process oriented perspective. The authors examine service definition of well know authors and offer a new good-service continuum definition. A new process oriented service classification is proposed which helps authors to challenge the validity of the service characteristics.
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