J.K. Jha

Two-echelon supply chain inventory model with controllable lead time and service level constraint

This paper considers a two-echelon supply chain inventory problem consisting of a single-vendor and a single-buyer. In the system under study, a vendor produces a product in a batch production environment and supplies it to a buyer facing a stochastic demand, which is assumed to be normally distributed. Also, buyers lead time is controllable which can be shortened at an added cost and all shortages are backordered. A model has been formulated for an integrated vendor-buyer problem to jointly determine the optimal order quantity, lead time and the number of shipments from the vendor to the buyer during a production cycle while minimizing the total expected cost of the vendor-buyer integrated system. It is often difficult to estimate the shortage cost in inventory systems. Therefore, instead of having a shortage cost term in the objective function, a service level constraint (SLC) is included in the model that requires a certain proportion of demands to be met in each cycle. An efficient procedure has been suggested to find the bounds on number of shipments and then, an algorithm is developed to obtain the optimal solution of the proposed model. A numerical example is included to illustrate the algorithmic procedure and the effects of key parameters are studied to analyze the behavior of the model. Finally, the savings of buyer and vendor are investigated from implementation of joint optimization model over the model in which they minimize their own cost independently.

A single-vendor single-buyer production-inventory model with controllable lead time and service level constraint for decaying items

This paper presents a production-inventory model in a single-vendor single-buyer system for decaying items which deplete with constant decay rate. It is assumed that the lead time demand follows a normal distribution and shortages are backordered. Also, buyers lead time can be reduced at an added cost. A model has been formulated to find the optimal order quantity, lead time and the number of shipments from the vendor to the buyer during one production cycle while minimising the total expected cost per unit time of the vendor-buyer integrated system. It is often difficult to estimate the stock-out cost in inventory systems. Therefore, instead of having a stock-out term in the objective function, a service level constraint is included in the model. Due to mathematical complexities involved, it is difficult to establish the solutions analytically. An iterative procedure is developed to find the optimal solution using LINGO 10, and a numerical example is given to illustrate the results of the proposed model. Furthermore, the effects of key parameters are also studied to provide the insight into the structure of the solution. In addition, the savings of buyer and vendor are investigated from implementation of joint optimisation model over the model in which they minimise their own cost independently.

Implementing National Food Security Act in India: issues and challenges

Purpose – National Food Security Act 2013 (NFSA) is a unique step taken by Indian government to fight against hunger and protect right of the people for food. With its peculiarities like the life cycle approach, women empowerment, consideration of vulnerable sections in society and proposed reforms in public distribution system (PDS), NFSA is a promising effort for food security in India. The purpose of this paper is to put forth various aspects of NFSA and to identify issues and challenges for its implementation in the light of Indian PDS. Design/methodology/approach – Understanding the implications of NFSA, mapping the existing system of foodgrains distribution in India and analysing existing literature and secondary data available from assorted sources are the steps followed in this endeavour. Findings – Limited resources and exponentially increasing population, lack of infrastructure, operational inefficiencies and poor performance of the PDS are the major hurdles in successful implementation of the proposed act. This study gives emphasis on the need of major reforms in procurement, storage, movement and distribution of foodgrains strategies. Research limitations/implications – This paper focusses mainly on the operational and strategic aspects of PDS and its implications on NFSA. There is a wide scope for future research on sustainability of the act through agricultural and biotechnological innovations, financial analysis and strategic aspects. Originality/value – This study is an unique attempt of mapping and auditing of the entire complex value chain of the Indian PDS for implementation of NFSA. As NFSA is going to redefine the food security aspects, this pioneering work will be useful for researchers and policy makers working in this field in India and other developing countries.

A coordinated two-phase approach for operational decisions with vehicle routing in a single-vendor multi-buyer system

This study considers a two-echelon system in which a vendor produces a product at a finite production rate and supplies it to several buyers facing independent normally-distributed demands. The product is delivered to the buyers using a set of different speed vehicles with identical capacity and different operating costs. The issues of lead time reduction and the service level constraint on the buyers have been incorporated in the model. A model is formulated to determine the optimal production–inventory policy, vehicle routes and vehicle type for each route by minimising the related production, inventory, lead time crashing and transportation costs of the system while satisfying the service level constraint on each buyer. A coordinated two-phase iterative approach is proposed to solve the model. Finally, a numerical example is included to describe the solution approach and illustrate the results.

Production-inventory model for two-echelon closed-loop supply chain with finite manufacturing and remanufacturing rates

ABSTRACTThis research develops a two-echelon closed-loop supply chain production-inventory model consisting of a manufacturer, a remanufacturer and a retailer. The retailer faces a constant demand from the customers, which is satisfied by new and remanufactured product received from the manufacturer and the remanufacturer, respectively. The manufacturer and remanufacturer produce the product in batches with finite production rate. The manufacturer procures raw material in batches from outside supplier, and the remanufacturer receives the used product from the customers at a constant return rate. Many studies in the area of forward supply chain have established that the centralised production-inventory control models provide better results than the decentralised models. Hence, with synchronised activities of the supply chain players, this research proposes to find an optimal production-inventory policy of the players by minimising the joint total cost of the two-echelon closed-loop supply chain. Numerical ...

Two-echelon closed-loop supply chain deterministic inventory models in a batch production environment

Abstract This paper considers a two-echelon closed-loop supply chain consisting of a manufacturer and a remanufacturer at the upper echelon and a retailer at the lower echelon. The retailer faces a constant demand from customers, which is satisfied through recovered and new products received from the remanufacturer and the manufacturer, respectively. The manufacturer produces the product with finite rate, whereas the recovery of returned product is instantaneous at the remanufacturer. We develop three models to determine the optimal production-inventory policy of the players for minimizing the joint total cost of the system. In the first model, the retailer receives the product in batches from the manufacturer and the remanufacture simultaneously, whereas in the second and third models, the batches are received alternatively. In the third model, however, the procurement of raw material at the manufacturer is also considered. Numerical illustration is presented to examine the impact of certain key parameters.

Optimizing a two-echelon serial supply chain with different carbon policies

Abstract In recent years, organizations are becoming environment conscious due to stringent laws, competitive advantages and increasing awareness of customers. They are integrating environmental practices into their operations to curb carbon emissions. Regulatory bodies are also imposing carbon policies to check emission. In this paper, we developed three models considering three carbon policies (I. carbon tax, II. strict cap and III. cap-and-trade) and have determined the optimal order quantity and number of shipments for a two-echelon supply chain. The objective is to minimize the total supply chain cost which comprises the ordering, setup, production, inventory holding and transportation costs. In Model I tax on carbon emissions has been included in the cost function; in Model II we have considered a strict carbon cap on the total carbon emission; and in Model III trading price of carbon is included in the cost function. A numerical study is given to illustrate the solution procedure. Further, sensitivity analyses are performed to examine the impact of the various parameters on the total cost and total emission.

A closed-form solution for the distribution free continuous review integrated inventory model

In this paper, we develop an integrated inventory model in a single-vendor single-buyer supply chain under an unknown demand distribution at the buyer. It is assumed that each lot delivered to the buyer contains a random fraction of defective items, and lead time can be reduced at an extra crashing cost. We also consider that the unmet demand at the buyer during the stockout period is partially backordered. A model is formulated to minimize the total expected relevant costs of the system considering an exact expression of the service level constraint to ensure that a certain percentage of customer orders are filled by the buyer. Closed-form expressions are derived for the optimal order quantity and safety factor for given lead time and shipment frequency, and then an algorithm is proposed to find the global optimal solution. Finally, a numerical example is presented to illustrate the solution procedure and sensitivity analysis is carried out to analyze the proposed model.

A novel constraint propagation approach for airline schedule design problem

In this paper, we propose a novel finite domain constraint programming formulation using constraint propagation (CP) approach with variable and value ordering for solving flight scheduling problem. We subsequently model the same problem using time-space network representation and integer linear programming (ILP) technique. The performance of the CP and ILP models are evaluated on simulated and a real life case. The ILP and CP models are solved using CPLEX 12.2 solver and CP optimiser 12.2, respectively. We observe that the ILP model generates better first feasible solutions, while the CP model produces faster feasible solutions. In few cases, the CP model takes longer time compared to the ILP model. For the case data with 600 aircrafts and 1,000 markets, the CP model generates feasible solution rather faster, while the ILP model could not find feasible solution in a day for defined time-space network flow problem with some additional constraints.

Developing decision support system for heterogeneous fleet vehicle routing problem using hybrid heuristic

In the last few years, there has been an increasing use of optimisation packages and decision support system (DSS) for the efficient and effective decision making. A significant variant of vehicle routing problem (VRP) arises when a fleet of vehicles is characterised by different capacities and operating costs, which is known as heterogeneous fleet vehicle routing problem (HFVRP). This paper aims at determining the optimal composition of fleet and set of routes to be accomplished by a fleet of heterogeneous vehicles for serving a given set of customers with the objective of minimising the total routing cost. To obtain the solution of the HFVRP, implementations of construction heuristics (savings algorithm, nearest neighbour, branch and cut) and improvement heuristics (2-opt and or-opt) are achieved through development of a DSS which eventually leads to proposal of a hybrid heuristic for route optimisation.