Logistique durable

Article for general public (2008)

Un problème de chargement/déchargement profitable d'une flotte de véhicules soumise à des fenêtres de temps

Conference (2008, February 26)

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or ... [more ▼]

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or visited integraly. So, the total earning is supposed to be constant. Conversely, the costs related to trip length or duration or either to the fleet size are consequences of the operations management efficiency. Therefore, typically the objective function is reduced to a cost minimization. On the contrary, this model tends to maximize the global profit. Let’s consider a fleet of vehicles starting at different initial times from different locations and oblige to return to their final depots before fixed maximal times. On their way-back, these vehicles are performing full-truck-load transportation between pickup and delivery points and have to respect time windows for the loading and unloading operations. Realized transportation orders add positive contributions while linking paths generate costs. In summary, the goal for the fleet resides in the selection of transportations orders among available ones while fullfilling the final time requirements and the time restrictions for the un/loading operations. [less ▲]

Politiques d’approvisionnement dans les systèmes à plusieurs fournisseurs et Optimisation des décisions dans les chaînes logistiques décentralisées

Doctoral thesis (2008)

Coordinating product flows between the partners of a supply chain is a difficult task because of random variations in demand and supply processes and the antagonistic nature of the individual economic ... [more ▼]

Coordinating product flows between the partners of a supply chain is a difficult task because of random variations in demand and supply processes and the antagonistic nature of the individual economic objectives of the partners. This study concentrates on the management of interorganizational product flows in supply chains. Two approaches are analyzed with the aim of improving performances of production/inventory systems controlled by base stock type product flow control policies. In the first approach, the effects of multi-supplier strategies on the performances of supply chains are studied. It is shown that a multi-supplier strategy decreases the expected replenishment delay and the expected inventory holding and shortage costs. The second approach deals with the deviations from the set of supply chain optimal actions due to the decentralisation of decision rights in a two-stage supply chain. In the game theory framework, the partners play a two-stage game of the Stackelberg type. A coordination contract is proposed and it is shown that the optimal supply chain performance is achievable using the proposed contract. [less ▲]

Inventory control in a decentralized two-stage make-to-stock queuing system

in INCOM 06, 12th IFAC Symposium on Information Control Problems in Manufacturing, Saint-Etienne, France, 17-19 May 2006 (2006, May 17)

In an Enterprise network, several companies interact to produce families of goods. Each member company seeks to optimize his own production and inventory policy to maximize his profit. These objectives ... [more ▼]

In an Enterprise network, several companies interact to produce families of goods. Each member company seeks to optimize his own production and inventory policy to maximize his profit. These objectives are generally antagonistic and can lead to contradictory choices in the context of a network with a high degree of local decisional autonomy. To avoid a global loss of economic efficiency, the network should be equipped with a coordination mechanism. The present paper describes a coordination contract negotiated between a manufacturer and a supplier. The purpose of the negotiation is to determine the price of the supplied intermediate goods and the delay penalty in case of a late delivery. For a manufacturer with a dominant contracting position, the outcome of the negotiation can be computed as a Stackelberg equilibrium point. Under the resulting contract, the two-stage supply chain reaches globally optimal running conditions with the maximal possible profit obtained by the manufacturer and the smallest acceptable profit obtained by the supplier. [less ▲]

Coordination de chaînes logistiques, une approache par la théorie des jeux

in MOSIM 06, 6e Conférence Francophone de MOdélisation et SIMulation, Rabat, Maroc, 3-5 Avril 2006 (2006, April 03)

Les chaînes logistiques étudiées sont constituées de différentes entreprises qui interviennent dans le processus de fabrication d’une famille de produits. Pour chaque entreprise, il s’agit principalement ... [more ▼]

Les chaînes logistiques étudiées sont constituées de différentes entreprises qui interviennent dans le processus de fabrication d’une famille de produits. Pour chaque entreprise, il s’agit principalement d’optimiser sa politique de production et d’approvisionnement par rapport à ses propres critères économiques. Puisque les objectifs des acteurs sont souvent antagonistes, le caractère distribué de la structure décisionnelle peut conduire à une perte d’efficacité pour l’ensemble de la chaîne et nécessite des mécanismes de coordination permettant d’améliorer les performances globales, tout en limitant les risques encourus par chacun des partenaires. Dans cet article, nous analysons un maillon élémentaire à deux niveaux d’une chaîne logistique, composé d’un producteur confronté à une demande aléatoire et d’un fournisseur qui gère sa production et son stock de produit intermédiaire. Nous étudions les effets des décisions locales sur les délais de livraison et nous proposons un contrat de coordination qui permet d’amener les performances du système distribué vers les performances théoriques du modèle centralisé. [less ▲]

Inventory control in a multi-supplier system

in International Journal of Production Economics (2006), 104

An enterprise network is analyzed from the viewpoint of an end-product manufacturer who receives customer orders and organises his production and supply policy so as to minimize the sum of his average ... [more ▼]

An enterprise network is analyzed from the viewpoint of an end-product manufacturer who receives customer orders and organises his production and supply policy so as to minimize the sum of his average holding cost and average stockout cost. For each main component to be ordered, the producer has several possible suppliers. The arrivals of customers’ orders are random and delivery times from suppliers are also supposed random. This supply system is represented as a queuing network where the producer uses a base-stock inventory control policy that keeps constant the inventory position level (current inventory level+pending replenishment orders). The decision variables are the reference inventory position level and the percentages of orders sent to the different suppliers. In the queuing network model, the percentages of orders are implemented as Bernoulli branching parameters. A close-form expression of the expected cost criterion is obtained as a complex non-linear function of decision variables. A decomposed approach is proposed for solving the optimization problem in an approximate manner. The quality of the approximate solution is evaluated by comparison to the exact solution, which can be computed numerically in some simple cases, in particular in the two-supplier case. Numerical applications show the important economic advantage for the producer of sending orders to several suppliers rather than to a single one. [less ▲]

Impact des délais d'approvisionnement sur les performances de chaînes logistiques

Conference (2005, May 19)

Les chaînes logistiques sont souvent constituées de différentes entreprises qui interviennent dans le processus de fabrication d’une famille de produits. Pour chaque entreprise particulière, il s’agit ... [more ▼]

Les chaînes logistiques sont souvent constituées de différentes entreprises qui interviennent dans le processus de fabrication d’une famille de produits. Pour chaque entreprise particulière, il s’agit principalement d’optimiser sa politique de production et d’approvisionnement par rapport à ses propres critères. Puisque les objectifs des acteurs sont souvent concurrentiels, la décentralisation des décisions conduit à une perte d’efficacité pour l’ensemble de la chaîne et nécessite des mécanismes de coordination permettant d’améliorer les performances du fonctionnement global, tout en limitant les risques encourus par chacun des partenaires. Dans cet article, nous analysons une chaîne logistique élémentaire à deux niveaux dont le stock de produit intermédiaire est géré par le fournisseur et le stock de produit fini par le producteur, qui est confronté à une demande aléatoire. Nous étudions les effets de délais d’approvisionnement aléatoires et nous proposons un contrat de coordination qui permet d’amener les performances du système à celles du modèle centralisé. [less ▲]

Inventory control in a multi-supplier system

in IGLS 04, 13th International Working Seminar on Production Economics, Igls/Innsbruck, Austria, 16-20 February 2004 (2004, February 16)

An enterprise network is analyzed from the viewpoint of an end-product manufacturer who receives customer orders and organises his production and supply policy so as to minimize the sum of his average ... [more ▼]

An enterprise network is analyzed from the viewpoint of an end-product manufacturer who receives customer orders and organises his production and supply policy so as to minimize the sum of his average holding cost and average stock-out cost. For each main component to be ordered, the producer has several possible suppliers. The arrivals of customers’ orders are random and delivery times from suppliers are also supposed random. This supply system is represented as a queuing network and the producer uses a base-stock inventory control policy that keeps constant the position inventory level (current inventory level + pending replenishment orders). The decision variables are the reference position inventory level and the percentages of orders sent to the different suppliers. In the queuing network model, the percentages of orders are implemented as Bernoulli branching parameters. A close-form expression of the expected cost criterion is obtained as a complex non-linear function of decision variables. A decomposed approach is proposed for solving the optimization problem in an approximate manner. The quality of the approximate solution is evaluated by comparison to the exact solution, which can be computed numerically in some simple cases, in particular in the two-supplier case. Numerical applications show the important economic advantage for the producer of sending orders to several suppliers rather than to a single one. [less ▲]

Analyse de politiques de gestion de stocks au sein d'une chaîne logistique

Master's dissertation (2003)

Cette étude s'intéresse au problème de gestion de stock d’une entreprise dont le stock est approvisionné par des fournisseurs extérieurs. Les demandes arrivent en suivant un processus de Poisson simple et ... [more ▼]

Cette étude s'intéresse au problème de gestion de stock d’une entreprise dont le stock est approvisionné par des fournisseurs extérieurs. Les demandes arrivent en suivant un processus de Poisson simple et les délais d’approvisionnement sont des variables aléatoires à distribution de probabilité exponentielle. L’objectif est de minimiser le coût moyen de l’entreprise, qui comprend les coûts de stockage et de rupture de stock. Dans le cas d’un seul fournisseur disponible, le niveau de stock peut être modélisé comme une chaîne de Markov en temps continu et le critère à minimiser a la même forme que dans le modèle du Newsboy. Le problème qui tient compte de l’existence de plusieurs fournisseurs est plus complexe, puisque dans ce cas l’entreprise doit aussi choisir les fournisseurs pour passer les commandes en minimisant ses coûts. Si l’entreprise effectue les commandes chez le même fournisseur pendant la période analysée, elle doit choisir le fournisseur qui possède le taux de service maximal et par conséquent qui offre le coût minimal. Dans le cas du choix d’un fournisseur, éventuellement diffèrent, à chaque déclenchement de réapprovisionnement du stock, nous supposons que l’entreprise choisit les fournisseurs selon un processus de sélection de Bernoulli. Nous modélisons le système d’approvisionnement comme un réseau ouvert de files d’attente et en utilisant les fonctions de génération de probabilité, nous obtenons la distribution de probabilité du nombre total de commandes dans le réseau ouvert. Cette approche nous permet d’exprimer le critère à minimiser en fonction des variables de décision. Nous proposons aussi une heuristique pour résoudre ce problème. [less ▲]

Integration of fuzzy optimization and stochastic programming in multi-commodity network flow problems

Master's dissertation (2001)

This study analyzes the problem of transporting vital commodities and emergency personnel during the response stage of a disaster relief operation by integrating fuzzy linear optimization and stochastic ... [more ▼]

This study analyzes the problem of transporting vital commodities and emergency personnel during the response stage of a disaster relief operation by integrating fuzzy linear optimization and stochastic programming. This transportation system is treated as a probabilistic, multi-commodity, multi-modal network flow problem and first a fuzzy model that allows the satisfaction of demand requirements through different supply nodes over a fuzzy network is developed. Since the available information in case of disasters is generally vague and imprecise about the values of model parameters, fuzzy linear optimization is employed to deal with this uncertainty and to generate different scenarios depending upon the preferences of the decision maker. Then these scenarios are handled within the framework of stochastic programming by defining a scenario as a joint realization of the uncertain parameters. Multi-commodity network flow problem is decomposed into uncapacitated single-commodity network flow problems by using Lagrangian relaxation. An exact algorithm is developed for each subproblem, and a sequential structure is designed to maintain consistency and feasibility between the solutions of these subproblems. [less ▲]