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continuous-reviews
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A new approach to find the optimal solution for base stock policies
, Article Journal of Applied Sciences ; Volume 9, Issue 4 , 2009 , Pages 789-793 ; 18125654 (ISSN) ; Eshraghniaye Jahromi, A ; Modarres, M ; Sharif University of Technology
2009
Abstract
In this study, the cost function of the defined system is derived first. Then, we prove this function is convex in the system's base stock level. Finally, based on the convexity of the cost function, the optimal solution for the base stock model is determined. For demonstrating the applicability of the proposed method, we resort to solving an example. © 2009 Asian Network for Scientific Information
A theoretical game approach for two- echelon stochastic inventory system
, Article Acta Polytechnica Hungarica ; Volume 12, Issue 4 , 2015 , Pages 221-239 ; 17858860 (ISSN) ; Hajji, A ; Alaei, R ; Behravesh, M ; Sharif University of Technology
Budapest Tech Polytechnical Institution
2015
Abstract
In this paper, we study the differences between the Centralized and Decentralized approaches in a two-echelon stochastic inventory system under the lost sale policy. We formulate the condition in which the retailer applies (r, Q) inventory policy, and his relation with the upper echelon who acts as a manufacturer. This situation has not been considered in the literature before. The Centralized approach results in optimal solution of the system and the Decentralized one is based on Stackelberg game in which the manufacturer is the leader. The demand arrives according to the stationary Poisson process. We drive the long-run average cost functions, then a set of computational steps are...
Optimal solution for a two-level inventory system with information exchange leading to a more computationally efficient search
, Article Applied Mathematics and Computation ; Volume 189, Issue 2 , 2007 , Pages 1341-1349 ; 00963003 (ISSN) ; Haji, R ; Sharif University of Technology
2007
Abstract
In this paper we consider a two-level inventory system with one warehouse and one retailer with information exchange. The retailer applies fixed order size continuous review policy. The supplier starts with m initial batches of the same order size of the retailer, and places an order to an outside source immediately after the retailer's inventory position reaches an amount equal to the retailer's order point plus a fixed value s. Transportation times are constant and the retailer faces independent Poisson demand. In a recent paper it was pointed out that the optimal supplier policy in this inventory system is an open question. To obtain the optimal policy for this system, first we find the...
A parameter-tuned genetic algorithm to optimize two-echelon continuous review inventory systems
, Article Expert Systems with Applications ; Volume 38, Issue 9 , September , 2011 , Pages 11708-11714 ; 09574174 (ISSN) ; Niaki, S. T. A ; Tokhmehchi, N ; Sharif University of Technology
2011
Abstract
This paper deals with a two-echelon inventory system for a non-repairable item where the system consists of one warehouse and m identical retailers and uses continuous-review (R, Q) ordering policy. To find an effective stocking policy for this system, a mathematical model with the objective of minimizing the total annual inventory investment subject to constraints on the average annual order frequency, expected number of backorders, and budget is formulated. The mathematical model of the problem at hand is shown to be nonlinear integer-programming and hence a parameter-tuned genetic algorithm is proposed to solve it efficiently. A numerical example is provided at the end to illustrate the...
A Game Theoretic Inventory Model for a Two-Echelon Supply Chain with Poisson Demand
, M.Sc. Thesis Sharif University of Technology ; Hajji, Alireza (Supervisor)
Abstract
In this research, we study the differences between the centralized and decentralized approaches in a two-stage serial supply chain including a manufacturer and a retailer under the lost sale policy. The centralized approach results in optimal solution of the system and the decentralized one is based on Stackelberg game in which the manufacturer is the leader. The retailer uses the continuous review (r, Q) policy and the demand arrives according to the stationary Poisson process. In order to obtain the solution for two approaches, a set of computational steps are developed. Furthermore, we provide a numerical example and the corresponding sensitivity analysis to compare the two approaches....
Shared information in a serial inventory system [electronic resource]
, Article International Journal of Advanced Operations Management - IJAOM ; 2011 Vol.3, No.2 pp.101 - 121 ; Eshraghniaye Jahromi, Abdolhamid ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this study, a supply chain model consisting of a single product, one supplier and one retailer is considered. Transportation times are constant and demands at the retailer are assumed to be generated by a stationary Poisson process. Demands not covered immediately from inventory are backordered. The retailer carries inventory and replenishes stock according to a (Q, R) policy. The supplier has online information about the demand at the retailer and uses this information to replenish its stock. The order size at the supplier is a multiple integer to the retailer's order size. Considering order costs for the retailer and the supplier, we derive the exact cost function for this inventory...
Determination of the economical policy of a three-echelon inventory system with (R, Q) ordering policy and information sharing
, Article International Journal of Advanced Manufacturing Technology ; Volume 55, Issue 5-8 , 2011 , Pages 831-841 ; 02683768 (ISSN) ; Sajadifar, S. M ; Haji, R ; Sharif University of Technology
2011
Abstract
In this work, we consider a three-echelon serial inventory system with two warehouses (suppliers) and one retailer with information exchange. The retailer applies continuous review (R, Q) policy. The warehouses have online information on the inventory position and demand activities of the retailer. We present a new ordering policy to share information among inventory echelons. The warehouse I and II start with m 1 and m 2 initial batches of the same order size of the retailer, respectively. The warehouse I places an order to an outside source immediately after the retailer's inventory position reaches an amount equal to the retailer's order point plus a fixed value s 1, and the warehouse II...
Exact evaluation of a two sourcing supply chain with order splitting and information sharing
, Article 2008 IEEE International Conference on Industrial Engineering and Engineering Management, IEEM 2008, Singapore, 8 December 2008 through 11 December 2008 ; 2008 , Pages 1835-1839 ; 9781424426300 (ISBN) ; Hendi, A. M ; Haji, R ; Sharif University of Technology
2008
Abstract
We consider a single item, two-level inventory system which consisting of two suppliers and one retailer. Transportation times are constant. The retailer faces Poisson demands and applies continuous (R,Q) policy. Each supplier starts with m initial batches of size Q/2 and places an order in a batch of size Q/2 to an outside source immediately after the retailer's inventory position reaches R+s. In this paper using the idea of the one-for-one ordering policy, we derive the exact value of the expected total cost in the convergent coordinated supply chain. © 2008 IEEE
Exact evaluation of a two-echelon inventory system with a different batch size and information exchange
, Article 37th International Conference on Computers and Industrial Engineering 2007, Alexandria, 20 October 2007 through 23 October 2007 ; Volume 3 , 2007 , Pages 1715-1720 ; 9781627486811 (ISBN) ; Haji, R ; Sharif University of Technology
2007
Abstract
In this paper we consider a dyadic supply chain consisting of one warehouse and one retailer with an unequal order batch size and information exchange. Transportation times are constant and retailer faces independent Poisson demand. The retailer applies continuous review (R,Q)-policy. The supplier starts with m initial batches (of size Q), and places an order in a batch of size nQ to an outside source immediately after the retailer's inventory position reaches R+s. In this paper using the idea of the onefor- one ordering policy we obtain the exact value of the expected system costs
Cost derivation of a dyadic supply chain with time lag information sharing
, Article 37th International Conference on Computers and Industrial Engineering 2007, Alexandria, 20 October 2007 through 23 October 2007 ; Volume 3 , 2007 , Pages 1709-1714 ; 9781627486811 (ISBN) ; Haji, R ; Shenas, N. Y ; Sharif University of Technology
2007
Abstract
In this paper we consider a dyadic supply chain consisting of one warehouse and one retailer with information exchange. We assume that the demand process to the retailer is a Poisson process and transportation times are constant. The retailer applies continuous review (R,Q)-policy. When the retailer's inventory position reaches R+s she sends information about her customer demand and inventory activities to the supplier. The supplier receives this information after a constant time lag. The supplier starts with m initial batches (of size Q), and places an order in a batch of size Q to an outside source immediately after receiving the information from the retailer. In this paper using the idea...
Inventory Ordering System with Fuzzy Parameters in Supply Chain
, M.Sc. Thesis Sharif University of Technology ; Hajji, Rasool (Supervisor)
Abstract
Inventory control has been always considered important due to its prominent role in managing and better application of resources in the field of operational systems. Ordering system or review stock policy in supply chain management can be mentioned as one of the inventory control study fields of management. A lot of researches have been done in investigating ordering system in supply chain under certainty conditions; however, since the real world is full of uncertainties, parameters such as demand cannot be predicted exactly and we encounter with ambiguity. In this case, using crisp (exact) values can cause to decide wrongly (a wrong decision). On the other hand, due to absence of sufficient...
A queueing system with inventory and mixed exponentially distributed lead times
, Article International Journal of Advanced Manufacturing Technology ; Volume 53, Issue 9-12 , August , 2011 , Pages 1231-1237 ; 02683768 (ISSN) ; Haji, R ; Hassanzadeh, F ; Sharif University of Technology
2011
Abstract
We consider M/M/1/∞ systems with inventory in which completing each service in the queueing system requires an on-hand inventory. Continuous review (r, Q) policy is considered for the inventory system, and lead times are assumed to be mixed exponentially distributed. During stockout, arriving demands get rejected from the queue and become lost (lost sale situation). We derive stationary distribution of product form of joint queue length and on-hand inventory. The resulting distribution is employed to compute performance measures which can be used to derive the optimal policy. Optimal order size for predetermined reorder policy is initially determined and finally, optimal reorder point and...
Optimizing multi-product multi-constraint inventory control systems with stochastic replenishments
, Article Journal of Applied Sciences ; Volume 8, Issue 7 , 2008 , Pages 1228-1234 ; 18125654 (ISSN) ; Aryanezhad, M. B ; Akhvan Niaki, S. T ; Sharif University of Technology
Asian Network for Scientific Information
2008
Abstract
Multi-periodic inventory control problems are mainly studied employing two assumptions. The first is the continuous review, where depending on the inventory level orders can happen at any time and the other is the periodic review, where orders can only happen at the beginning of each period. In this study, we relax these assumptions and assum that the periodic replenishments are stochastic in nature. Furthermore, we assume that the periods between two replenishments are independent and identically random variables. For the problem at hand, the decision variables are of integer-type and there are two kinds of space and service level constraints for each product. We develop a model of the...
Measuring the bullwhip effect in order-up-to policies with continuous and periodic review: A system dynamics simulation approach
, Article International Conference on Risk Management and Engineering Management, Toronto, ON, 18 April 2008 through 18 April 2008 ; 2008 , Pages 24-29 ; 9780978348458 (ISBN) ; Saeidi, A ; Esfahani, N. N ; Akbari, R ; Sharif University of Technology
2008
Abstract
The inventory replenishment policy exploited by a supply chain has a principle role in amplification of order variability compared to fluctuations in customers' demands. This phenomenon is known as the bullwhip effect. In this paper, a four echelon supply chain is simulated and the impacts of continuous and periodic review order-up-to policies on the bullwhip effect are examined. Experiments have been conducted to analyze the influence of the lead time in deterministic conditions, and also the variance of demand and lead time in stochastic circumstances on the bullwhip effect and the corresponding cost. It was observed that in low demand and lead time variances, it is more efficient to...
A replenishment policy for perishable products with non-linear holding cost under stochastic supply lead time
, Article International Journal of Advanced Manufacturing Technology ; Volume 64, Issue 5-8 , 2013 , Pages 1087-1098 ; 02683768 (ISSN) ; Baboli, A ; Akbari Jokar, M. R ; Sharif University of Technology
2013
Abstract
The development and application of inventory models for deteriorating items is one of the main concerns of subject matter experts. The inventory models developed in this field have focused mainly on supply chains under the assumption of constant lead time. In this study, we develop an inventory model for a main class of deteriorating items, namely perishable products, under stochastic lead time assumption. The inventory system is modeled as a continuous review system (r, Q). Demand rate per unit time is assumed to be constant over an infinite planning horizon and the shortages could be backordered completely. For modeling the deterioration process, a non-linear holding cost is considered....
A hybrid method of fuzzy simulation and genetic algorithm to optimize constrained inventory control systems with stochastic replenishments and fuzzy demand
, Article Information Sciences ; Volume 220 , 2013 , Pages 425-441 ; 00200255 (ISSN) ; Niaki, S. T. A ; Aryanezhad, M. B ; Shafii, N ; Sharif University of Technology
2013
Abstract
Multi-periodic inventory control problems are mainly studied by employing one of two assumptions. First, the continuous review, where depending on the inventory level, orders can happen at any time, and next the periodic review, where orders can only be placed at the beginning of each period. In this paper, we relax these assumptions and assume the times between two replenishments are independent random variables. For the problem at hand, the decision variables (the maximum inventory of several products) are of integer-type and there is a single space-constraint. While demands are treated as fuzzy numbers, a combination of back-order and lost-sales is considered for the shortages. We...
A genetic algorithm to optimize multiproduct multiconstraint inventory control systems with stochastic replenishment intervals and discount
, Article International Journal of Advanced Manufacturing Technology ; Volume 51, Issue 1-4 , November , 2010 , Pages 311-323 ; 02683768 (ISSN) ; Akhavan Niaki, S.T ; Aryanezhad, M. B ; Fallah Tafti, A ; Sharif University of Technology
2010
Abstract
There are two main assumptions in multiperiodic inventory control problems. The first is the continuous review, where, depending on the inventory level, orders can happen at any time, and the other is the periodic review, where orders can only happen at the beginning of each period. In this paper, these assumptions are relaxed, and the periods between two replenishments are assumed independent and identically distributed random variables. Furthermore, the decision variables are assumed integer-type and that there are two kinds of space and budget constraints. The incremental discounts to purchase products are considered, and a combination of backorder and lost sales are taken into account...
General bounds for the optimal value of retailers' reorder point in a two-level inventory control system with and without information sharing
, Article International Journal of Advanced Manufacturing Technology ; Volume 48, Issue 1-4 , April , 2010 , Pages 383-393 ; 02683768 (ISSN) ; Eshragh Jahromi, A ; Akhavan Niaki, S ; Sharif University of Technology
2010
Abstract
In this study, an inventory system consisting of a single product, one supplier, and multiple identical retailers is considered. Each retailer replenishes inventory from the supplier according to the well known (R,Q) policy. Transit times are constant and retailers face independent Poisson demand. The supplier utilizing the retailers' information in decision making for replenishment policy with a given order size starts with m initial batches (of size Q) and places an order in a batch of size Q to an outside source when a new order is placed. In this inventory system, excess demand is backordered, delayed orders are satisfied on a first-come first-serve basis, and no partial shipment is...
An efficient procedure for computing an optimal (R, Q) policy in continuous review systems with poisson demands and constant lead time
, Article Scientia Iranica ; Volume 16, Issue 2 E , 2009 , Pages 128-137 ; 10263098 (ISSN) ; Eshraghnia Jahromi, A ; Modarres Yazdi, M ; Sharif University of Technology
Abstract
In this paper, a continuous review inventory system is considered in which an order in a batch of size Q is placed immediately after the inventory position reaches R. Transportation time is constant and demands are assumed to be generated by a stationary Poisson process with one unit demand at a time. Demands not covered immediately from the inventory are backordered. In a recent paper, the exact evaluation of batch-ordering policies for two-level inventory systems was derived. This evaluation is based on a recursive procedure for determining the exact policy costs in case of one-for-one replenishment policies. In this paper, we show how this result can be applied to find the optimal...