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inventory-system
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Inventory Management in Two-Echelon Chain with Shortage
, M.Sc. Thesis Sharif University of Technology ; Haji, Alireza (Supervisor)
Abstract
The thesis has considered a two-echelon supply chain which consists of one central warehouse and multiple retailers. Assume all retailers and the warehouse follow a continuous review inventory model. The costumer’s demand comes to retailers in a Poisson process. The retailers replenish their stocks from the warehouse in an (S-1, S) inventory control policy and the warehouse replenishes its stocks in an (r, Q) inventory control policy from an external supplier with an infinite capacity. It may be more representative to model stockouts as lost sales when the retailers are in a competitive market or in monopoly markets all demand will be backorder. Therefore, if the market situation goes...
A New Inventory Control Policy for a Two-level Supply Chain with Perishable Products
, Ph.D. Dissertation Sharif University of Technology ; Hajji, Alireza (Supervisor) ; Hajji, Rasoul (Co-Advisor)
Abstract
The assumption of infinite lifetime is common in most of the inventory models. However, the perishability of products is a major problem of some industry sectors in which by disregarding the finite lifetime of their products the resulting model may give inaccurate results. Although, significant studies have been carried out for inventory control of perishable products, yet the literature needs more studies to develop or optimize the inventory policies. In this thesis, the inventory control of perishable products is considered. For the case of stochastic demand, it was well known that there is no inventory control policy in which both the order size and the order interval are constant with an...
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...
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 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...
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...
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...
One for one period policy for perishable inventory
, Article Computers and Industrial Engineering ; Volume 79 , January , 2015 , Pages 10-17 ; 03608352 (ISSN) ; Haji, A ; Haji, R ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Recently, for zero ordering cost a new ordering policy named (1, T), in which the time interval between two consecutive orders and the value of the order size are both constant, have been developed for nonperishable products. In this paper, the (1, T) policy is developed for perishable products. Using an analogy among this inventory model, a queueing model with impatient customers, and a finite dam model, the long-run average total cost function of the inventory system is derived. It is observed that the total cost rate is independent from the lead time as is for nonperishable products. Since analyzing the convexity of the model is extremely complicated, a proposition is proved to define a...
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...
An investigation of vendor-managed inventory application in supply chain: The EOQ model with shortage
, Article International Journal of Advanced Manufacturing Technology ; Volume 49, Issue 1-4 , July , 2010 , Pages 329-339 ; 02683768 (ISSN) ; Akhavan Niaki, S. T ; Roozbeh Nia, A ; Sharif University of Technology
2010
Abstract
Recent researches have shown the importance of improving the supply chain competitiveness by means of strategic alliances. This study considers the retailer-supplier partnership through a vendor-managed inventory (VMI) system and develops an analytical model to explore the effect of important supply chain parameters on the cost savings realized from collaborative initiatives. This model is developed for a two-level supply chain consisting of a single supplier and a single retailer and examines the inventory management practices before and after implementation of VMI. The results of analytical examination show that VMI implementation in economic order quantity model when shortage is...
A queueing approach to production-inventory planning for supply chain with uncertain demands: Case study of PAKSHOO Chemicals Company
, Article Journal of Manufacturing Systems ; Volume 29, Issue 2-3 , July , 2010 , Pages 55-62 ; 02786125 (ISSN) ; Modarres, M ; Ghasemzadeh, F ; Fathi, M ; Sharif University of Technology
2010
Abstract
In some industries such as the consumable product industry because of small differences between products made by various companies, customer loyalty is directly related to the availability of products required at that time. In other words, in such industries demand cannot be backlogged but can be totally or partly lost. So companies of this group use make-to-stock (MTS) production policy. Therefore, in these supply chains, final product warehouses play a very important role, which will be highlighted by considering the demand uncertainty as it happens in real world, especially in the consumable product industries in which demand easily varies according to the customer's taste variation,...
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...
Joint order (1, T) policy for a two-echelon, single-item, multi-retailer inventory system with Poisson demand
, Article Computers and Industrial Engineering ; Volume 119 , 2018 , Pages 353-359 ; 03608352 (ISSN) ; Haji, R ; Ghalebsaz Jeddi, B ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
This study considers a two-echelon inventory system with one central warehouse and a number of non-identical retailers with Poisson demands, constant lead times, and lost sales for a single item. The warehouse works as a cross-docking terminal with no inventory and coordinates shipments to retailers. We apply the Joint order (1, T) policy in such an inventory system. In the standard (1, T) policy, the warehouse sends one unit of the item to each retailer in a fixed cycle time, which is calculated by considering each retailer separately. In the joint order (1, T) policy, the warehouse decides to replenish one unit of the item for each retailer in a cycle time which is adjusted to be an...
Introducing a new ordering policy in a two-echelon inventory system with Poisson demand
, Article International Journal of Production Economics ; Volume 117, Issue 1 , 2009 , Pages 212-218 ; 09255273 (ISSN) ; Neghab, M. P ; Baboli, A
Elsevier
2009
Abstract
In this paper we introduce a new ordering policy for inventory control in a two-echelon inventory system consisting of one central warehouse and a number of non-identical retailers. The warehouse uses a modified one-for-one policy, but the retailers apply a new policy which is different from the traditional inventory policies described in the literature of inventory and production control systems. In this system, each retailer constantly places an order for one unit of product to the central warehouse in a pre-determined time interval; i.e., the time interval between any two consecutive orders from each retailer is a fixed number and the quantity of each order is one. We then show how the...
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
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...
Cost differential for deciding about installing information sharing technology in a two-echelon inventory system
, Article IIE Annual Conference and Expo 2007 - Industrial Engineering's Critical Role in a Flat World, Nashville, TN, 19 May 2007 through 23 May 2007 ; 2007 , Pages 1139-1144 ; Sajadifar, M ; Sharif University of Technology
2007
Abstract
We consider a dyadic supply chain. Retailer applies (R,Q)-policy. Supplier starts with m initial batches of size Q and places an order of the same size to an outside source. The supplier can select one of the two following cases. Case 1, whenever the retailer places an order, the supplier will also place an order. Case 2, whenever the retailer's inventory position reaches R+s, the supplier will place an order. This paper derives the cost differential between these cases for any value of s, which enables the supply chain managers to decide whether to install an information sharing technology
Cost evaluation of a two-echelon inventory system with lost sales and approximately normal demand
, Article Scientia Iranica ; Volume 13, Issue 1 , 2006 , Pages 105-112 ; 10263098 (ISSN) ; Seifbarghy, M ; Sharif University of Technology
Sharif University of Technology
2006
Abstract
The inventory system under consideration consists of one central warehouse and an arbitrary number of retailers controlled by a continuous review inventory policy (R,Q). Independent Poisson demands are assumed with constant transportation times for all retailers and a constant lead time for replenishing orders from an external supplier for the warehouse. Unsatisfied demands are assumed to be lost in the retailers and unsatisfied retailer orders are backordered in the warehouse. An approximate cost function is developed to find optimal reorder points for given batch sizes in all installations and the related accuracy is assessed through simulation. © Sharif University of Technology, January...
Developing a model for a two-echelon two-item inventory system with lost sale and demand substitution
, Article 2006 IEEE International Conference on Management of Innovation and Technology, ICMIT 2006, Singapore, 21 June 2006 through 23 June 2006 ; Volume 2 , 2006 , Pages 926-930 ; 1424401488 (ISBN); 9781424401482 (ISBN) ; Zangeneh, S ; Sharif University of Technology
2006
Abstract
Almost all multi-echelon inventory models assume that demands which are not satisfied immediately can be backordered. In some situations, this assumption may not be realistic. For example, we can model stockouts as lost sales when the retailers are in a competitive market and customers can easily turn to another retailer for purchasing goods. So, in this study, assuming lost sales at the retailers, we consider a one-warehouse, several retailers, two-item inventory system where the items can be interchangeably used. Using the well-known METRIC-approximation as a framework, we present a heuristic for finding cost effective base-stock policies. In a numerical study with simulation, we find that...
A constrained multi-item EOQ inventory model for reusable items: Reinforcement learning-based differential evolution and particle swarm optimization
, Article Expert Systems with Applications ; Volume 207 , 2022 ; 09574174 (ISSN) ; Amani Bani, E ; Akhavan Niaki, S. T ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
The growing environmental concerns, governmental regulations, and significant cost savings are the primary motivations for companies to consider the reuse and recovery of products in their inventory system. The previous research ignored several realistic features of reusable items inventory systems, such as the presence of multiple products and operational constraints. For the first time, this paper presents a new multiproduct economic order quantity inventory model for an inventory system of reusable products. The goal of the model is to determine the optimal replenishment quantity and reuse quantity of each item so that the system's total cost is minimized. Several operational constraints...