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Sole versus dual-sourcing under order dependent lead-times and prices [electronic resource]
, Article Computers And Operations Research, Published in: Elsevier Journals ; Volume 36, Issue 12, December 2009, Pages 3272–3280 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, we consider a dual-sourcing model with constant demand and stochastic lead times. Two suppliers may be different in terms of purchasing prices and lead-time parameters. The ordering takes place when the inventory level depletes to a reorder level, and the order is split among two suppliers. Unlike previous works in the order splitting literature, the supply lead time between vendor and buyer as well as unit purchasing prices is considered to be order quantity dependent. The proposed model finds out the optimal reorder point, order quantity and splitting proportion, using a solution procedure. Numerical results show that neglecting the relationship between ordering batch size...
A genetic fuzzy expert system to optimize profit function
, Article Economic Computation and Economic Cybernetics Studies and Research ; Volume 8 , 2012 ; 0424267X (ISSN) ; Shavandi, H ; Sharif University of Technology
2012
Abstract
In this paper we develop a fuzzy system to obtain the demand based on input variables of price, warranty length and lead time of order delivery. We use linguistic terms to illustrate the situation of input and output variables and construct a fuzzy rule base. The fuzzy rule base is integrated with a genetic algorithm to construct a hybrid solution method. The best value of price, warranty length and lead time are obtained by maximizing the manufacturer profit. Finally a numerical example is presented to show the performance of proposed approach
A new order splitting model with stochastic lead times for deterioration items
, Article International Journal of Systems Science ; Vol. 45, Issue. 9 , 2014 , pp. 1936-1954 ; ISSN: 00207721 ; Jokar, M. R. A ; Baboli, A ; Sharif University of Technology
Abstract
In unreliable supply environments, the strategy of pooling lead time risks by splitting replenishment orders among multiple suppliers simultaneously is an attractive sourcing policy that has captured the attention of academic researchers and corporate managers alike. While various assumptions are considered in the models developed, researchers tend to overlook an important inventory category in order splitting models: deteriorating items. In this paper, we study an order splitting policy for a retailer that sells a deteriorating product. The inventory system is modelled as a continuous review system (s, Q) under stochastic lead time. Demand rate per unit time is assumed to be constant over...
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...
Sole versus dual sourcing under order dependent lead times and prices
, Article Computers and Operations Research ; Volume 36, Issue 12 , 2009 , Pages 3272-3280 ; 03050548 (ISSN) ; Eshghi, K ; Sharif University of Technology
Abstract
In this paper, we consider a dual-sourcing model with constant demand and stochastic lead times. Two suppliers may be different in terms of purchasing prices and lead-time parameters. The ordering takes place when the inventory level depletes to a reorder level, and the order is split among two suppliers. Unlike previous works in the order splitting literature, the supply lead time between vendor and buyer as well as unit purchasing prices is considered to be order quantity dependent. The proposed model finds out the optimal reorder point, order quantity and splitting proportion, using a solution procedure. Numerical results show that neglecting the relationship between ordering batch size...
DMLS gets an expert once-over
, Article Metal Powder Report ; Volume 61, Issue 4 , 2006 , Pages 10-13 ; 00260657 (ISSN) ; Pohl, H ; Simchi, A ; Alcantara, B ; Sharif University of Technology
Elsevier Ltd
2006
Abstract
Direct Metal Laser Sintering has real potential for rapid-manufacture applications in the PM arena, reducing lead times and cutting costs. But it has been hampered by the limited range of suitable powders available and their cost. A research group led by Fraunhofer scientists made their own powders and took a closer look.... © 2006 Elsevier Ltd. All rights reserved
Order Splitting in Supply Chain for Deteriorating Items
, M.Sc. Thesis Sharif University of Technology ; Akbari Jokar, Mohammad Reza (Supervisor)
Abstract
Pooling Lead-time risk by splitting replenishment orders simultaneously among multiple suppliers is a sourcing policy that has attracted the attention of academic researchers for some years. While they consider many different assumptions in their models, they don’t pay attention to deterioration items in order splitting models. In this thesis, we have considered order splitting policy about products with constant deteriorating rate and developed two inventory models. In the first model, it is assumed that the whole requirement supply from only one source, whereas in the second two suppliers are accessible. Then after determining the optimal policy, by numerical search and use of MAPLE...
Optimization of Raw Material Inventory Control System in Khorramshahr Oil Extraction Company Based on ( r,Q ) Optimal Inventory Policy
, M.Sc. Thesis Sharif University of Technology ; Hajji, Rasool (Supervisor)
Abstract
This thesis is related to applying survey of scientific inventory control methods in Khoramshahr Oil Extraction Company (KHOEC). KHOEC is the producer of edible oils in I.R of Iran and is a subset of E.T.K.A holding organization. The inventory costs of high consuming items are studied and optimized based on the optimal ordering policy (r, Q). First, the company raw materials are identified and classified based on ABC analysis method. For developing the new method of inventory control, the demand for each item is predicted, and the probability distribution of demand during the lead time is determined. Then according to this information and the desired service level of management, order point...
Developing a coordinated vendor-buyer model in two-stage supply chains with stochastic lead-times
, Article Computers and Operations Research ; Volume 36, Issue 8 , 2009 , Pages 2484-2489 ; 03050548 (ISSN) ; AkbariJokar, M. R ; Modarres, M ; Sharif University of Technology
2009
Abstract
This paper develops an approach to determine the optimal production and shipment policy for an integrated vendor-buyer problem. The vendor manufactures the product in batches at a finite rate and ships the output to the buyer. All shipments to the buyer are equal-sized batches. Despite previous papers in the literature, we assume that the supply lead-time between vendor and buyer is stochastic and shortage is also allowed. The objective is to minimize the expected total cost of both buyer and vendor. We derive the expected annual integrated total cost function and propose an analytic solution procedure to determine the optimal policy. To illustrate the significance of cost-reduction of the...
Pricing and Lead Time Decisions in Decentralized Supply Chains Under Competition
,
M.Sc. Thesis
Sharif University of Technology
;
Shavandi, Hasan
(Supervisor)
Abstract
This thesis investigated a two-echelon supply chain consists of one retailer and several manufacturers that faces a price and lead time sensitive demand. We use a Stackelberg game for decision analysis of prices and lead times determined by manufacturers as Leader and retailer as a Follower. We assume that demand depends to the retailer’s price. Market share of each manufacturer, is also price and lead time sensitive. Objective of each firm is to determine price and planned lead time to maximize her own profit. We first determine the best response of the retailer to manufacturers’ decision and next at manufacturers’ level, we will solve the problem for one manufacturer at first and then we...
Inventory Control and Carrier Mode Selection in a Two-echelon Supply Chain with Deteriorating Items
, M.Sc. Thesis Sharif University of Technology ; Modarres Yazdi, Mohammad (Supervisor)
Abstract
This study investigates a two-echelon supply consists of a vendor and a buyer with deteriorating items. The deterioration rate of product is assumed to be constant and independent of time. The buyer’s order is shipped in equal-sized batches. Moreover, in order to ship products from vendor to buyer, two carrier’s modes with different travelling time and cost are considered. What distinguishes this study from literature is that the deterioration of product continues during the travelling time which depends on the carrier’s mode to ship batches from vendor to buyer.
The objective is to minimize the cost of both buyer and vendor simultaneously. The cost functions of buyer and vendor are...
The objective is to minimize the cost of both buyer and vendor simultaneously. The cost functions of buyer and vendor are...
A new up-to level inventory model for deteriorating products with non-linear holding cost
, Article IFAC Proceedings Volumes (IFAC-PapersOnline) ; 2013 , Pages 1702-1707 ; 14746670 (ISSN) ; 9783902823359 (ISBN) ; Rekik, Y ; Akbari Jokar, M. R ; Baboli, A ; Mirzapour Al E Hashem, S. M. J ; Sharif University of Technology
2013
Abstract
Inventory management of deteriorating items faces major challenges by uncertain demand, uncertain lead time, perishability, and high customer service level requirements. So, this issue is extremely important in many corporations today. The periodic up-to level policy for deteriorating products under stochastic demand and stochastic lead time is not paid enough attention up to now. In this paper we propose a new approach to study inventory up-to level policy of deteriorating products under normal distributed demand and lead time by considering service level requirements. To model deterioration process, a non-linear increasing holding cost function is considered. After developing the...
Multiple-buyer multiple-vendor multi-product multi-constraint supply chain problem with stochastic demand and variable lead-time: A harmony search algorithm
, Article Applied Mathematics and Computation ; Volume 217, Issue 22 , July , 2011 , Pages 9234-9253 ; 00963003 (ISSN) ; Niaki, S. T. A ; Barzinpour, F ; Sharif University of Technology
2011
Abstract
In this paper, a multi-buyer multi-vendor supply chain problem is considered in which there are several products, each buyer has limited capacity to purchase products, and each vendor has warehouse limitation to store products. In this chain, the demand of each product is stochastic and follows a uniform distribution. The lead-time of receiving products from a vendor to a buyer is assumed to vary linearly with respect to the order quantity of the buyer and the production rate of the vendor. For each product, a fraction of the shortage is backordered and the rest are lost. The ordered product quantities are placed in multiple of pre-defined packets and there are service rate constraints for...
Queueing system with inventory for two-echelon supply chain
, Article 2009 International Conference on Computers and Industrial Engineering, CIE 2009, 6 July 2009 through 9 July 2009, Troyes ; 2009 , Pages 835-838 ; 9781424441365 (ISBN) ; Haji, R ; Sharif University of Technology
Abstract
In this paper a two-echelon supply chain consisting of a supplier and aretailer is considered, Customers refer to retailer according to a Poissonprocess and retailer uses one for one inventory policy. Supplier followscontinuous review (r,Q) policy. Satisfying each demand which arrives to thesupplier needs an on hand-inventory and a process/service. Process/service andreplenishment lead times are random variables which are exponentiallydistributed. During a period that supplier has non zero on-hand inventory,arriving demands from retailer join the queue. But when supplier has no on-handinventory retailer buys product from the other source with zero lead time andadditional cost. In this paper...
An integrated vendor-buyer cooperative model under stochastic supply lead-time
, Article International Journal of Advanced Manufacturing Technology ; Volume 41, Issue 9-10 , 2009 , Pages 1043-1050 ; 02683768 (ISSN) ; Akbari Jokar, M. R ; Sharif University of Technology
2009
Abstract
This paper presents a single-vendor, single-buyer integrated inventory model. We relax the assumption of deterministic lead-time in the hitherto existing joint economic lot sizing (JELS) models and analyze the problem where the buyer lead-time is a stochastic variable. Moreover, we consider the situation in which shortage is allowed. The vendor produces the product in batches and periodically delivers final goods at a fixed lot size to the customer, who has a constant demand rate. The proposed model, based on the integrated expected total relevant costs of both buyer and vendor finds out optimal values of reorder point, order quantity, and number of shipments, using a solution procedure....
An efficient optimal algorithm for the quantity discount problem in material requirement planning
, Article Computers and Operations Research ; Volume 36, Issue 6 , 2009 , Pages 1780-1788 ; 03050548 (ISSN) ; Shadrokh, S ; Kianfar, F ; Sharif University of Technology
2009
Abstract
An optimal algorithm based on branch-and-bound approach is presented in this paper to determine lot sizes for a single item in material requirement planning environments with deterministic time-phased demand and constant ordering cost with zero lead time, where all-units discounts are available from vendors and backlog is not permitted. On the basis of the proven properties of optimal order policy, a tree-search procedure is presented to construct the sequence of optimal orders. Some useful fathom rules have been proven, which make the algorithm very efficient. To compare the performance of this algorithm with the other existing optimal algorithms, an experimental design with various...
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...
Due date assignment for multistage assembly systems
, Article Optimization Letters ; Volume 3, Issue 2 , 2009 , Pages 199-210 ; 18624472 (ISSN) ; Kianfar, F ; Sharif University of Technology
2009
Abstract
This paper is concerned with the study of the constant due-date assignment policy in a multistage assembly system. The multistage assembly system is modeled as an open queueing network. It is assumed that the product order arrives according to a Poisson process. In each service station, there is either one or infinite machine with exponentially distributed processing time. The transport times between every pair of service stations are independent random variables with generalized Erlang distributions. It is assumed that each product has a penalty cost that is some linear function of its due-date and its actual completion time. The due date is found by adding a constant to the time that the...
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....
Centralized replenishment policy for deteriorating items in a three echelon supply chain under stochastic lead time
, Article IFAC Proceedings Volumes (IFAC-PapersOnline) ; Volume 14, Issue PART 1 , 2012 , Pages 493-498 ; 14746670 (ISSN) ; 9783902661982 (ISBN) ; Akbari Jokar, M ; Baboli, A ; Campagne, J. P ; Sharif University of Technology
2012
Abstract
One of the significant problems faced in inventory management is how to control and maintain the inventories of deteriorating items. Most of studies developed in this field, assumed supply lead time is fixed while that is hard to be exactly determined in the majority procurement systems. Also, most of integration inventory models for supply chains with a deterioration item have been developed for two-echelon supply chains. In this paper, in order to fill these gaps, we focus on optimally determining replenishment policy for deteriorating items among all the partners in a three echelon supply chain with stochastic supply lead time for the buyer. For modeling the deterioration process, a...