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Investigation of the bullwhip effect using spreadsheet simulation
Borut Buchmeister, 2008, original scientific article

Abstract: Superior supply chains are one of the best ways to compete in today's marketplaces. In Supply Chain Management, overall supply chain evaluation needs to include an important logistical effect known as the Bullwhip Effect. It shows how small changes at the demand end of a supply chain are progressively amplified up the supply chain. Production plans are based on demand forecasting and suppliers not only react an changed demand, they adapt the level of safety stock (variation of stocks and orders increases). In this paper two special situations in a four-stage supply chain are studied: i) stable demand with a single 5 % change in demand (with application of four different stock keeping policies), and ii) changing demand with alternating 5 % changes in demand (up and down, with another three stock keeping policies). The results of spreadsheet simulations are shown in tables and charts. Increasing variability of production orders and stock levels up the supply chain is evident. The Bullwhip Effect is measured by the standard deviation of orders. The comparison of the results shows that the Bullwhip Effect can be partially reduced by appropriate stock keeping policy.
Keywords: supply chain, changing demand, bullwhip effect, ordering policy
Published: 31.05.2012; Views: 1363; Downloads: 78
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Bullwhip effect problem in supply chains
Borut Buchmeister, Jože Pavlinjek, Iztok Palčič, Andrej Polajnar, 2008, original scientific article

Abstract: In Supply Chain Management, a phenomenon called the "Bullwhip Effect" has attracted considerable attention. Overall supply chain evaluation needs to include the Bullwhip Effect. The Bullwhip Effect shows how small changes at the demand end of a supply chain are progressively amplified for operations further back in the chain. It is understood that demand forecast variance contributes to that effect in the chain. With this understanding, the authorsexperimented with two cases: stable demand with a single 5 % change in demand, and changing demand in periodic 10 % increases and later in the same decreases. Two stock keeping policies for all stages in the chain have been studied: to keep in stock i) one, and ü) two periods' demand. Results are shown in tables and charts. Increasing variability of production orders and stocks up the supply chain is evident. The effect indicates a lack of synchronization among supply chain members because of corrupt key information about actual demand. When we understand the nature of supply chain dynamics, there are several actions concerned with coordinating the activities of the operations in the chain, which is discussed in the last part of the paper.
Keywords: supply chain, demand fluctuation, bullwhip effect, production rate variability, stock level variability
Published: 01.06.2012; Views: 1215; Downloads: 19
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Inventory cost consequences of variability demand process within a multi-echelon supply chain
Francisco Campuzano Bolarín, Andrej Lisec, Francisco Cruz Lario Esteban, 2008, original scientific article

Abstract: The bullwhip effect (Lee et al, 1997a) is a known supply chain phenomenon where small variations in end item demand create oscillations that amplify throughout the chain. Different price elasticity of demand influence different changes of demand when prices of items are changing on the time horizon. The variance of the orders at the end user placed on suppliers or on manufacturer increases with the orders flow upstream in the logistics chain. This creates harmful consequences in inventory levels and all kind of inventory costs that may affect added value of activities along the logistics chain and finally affect Net Present Value of all activities in the chain. Traditional model of dynamic supply chain structures is used for this particular study, based on the seminal work of Forrester Diagrams (Forrester 1961). Simulation platform for supply chain management at stochastic demand developed by Campuzano (2006) has been used. VENSIM Simulation Software was previously used for developing these supply chain dynamic models. In the development platform generalised supply chain models are constructed graphically and also analytically. Our study here is to get a dipper insight into the processes in a logistics chain, measuring the inventory cost consequences due to variability demand amplification.
Keywords: bullwhip effect, demand amplification, logistic chain, system dynamics
Published: 05.06.2012; Views: 824; Downloads: 23
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Matevž Močilnikar, 2014, undergraduate thesis

Abstract: In this assignment we discuss the issues of line balancing in a complex production line in the example of Hella KGaA Hueck & Co. The assignment describes the terms and constraints needed to successfully balance a line. With different scenarios we can evaluate all the possibilities in a production line. Based on the data we have from the production line, such as time of a station, customer demand and output, we can calculate the best way to balance our production lines, so that we meet our customer demands. The question of the optimum number of workers comes into consideration. Taking into account the trend of performance-based pay, we also consider the extra performance of a workgroup or worker. We also consider the loss of productivity while qualifying a worker in a station as well as the effect of qualification. The goal of this research is to determine the differences in a balanced line within a time wage performance, performance-based work groups and the performance related to the qualification of a worker.
Keywords: line balancing, bottleneck, cycle time, customer demand, efficiency
Published: 13.10.2014; Views: 976; Downloads: 81
.pdf Full text (1,53 MB)

A fuzzy model of power supply system control
Janez Usenik, 2012, original scientific article

Abstract: In this article, a mathematical model of control of a dynamic system is described; one such system could be a power supply system. Analytical approaches that have been developed to describe the influence of production and stock, i.e. additional capacities, require a hierarchical spatial pattern and demand. Demand is usually an inherently stochastic process, but in this article we simulate it as an output fuzzy variable in a fuzzy system, in which all the input variables are also fuzzy. Furthermore, an interesting use of neural sets is shown, which is presented as an efficient method for the optimisation of the fuzzy system. At the end, a numerical example is given.
Keywords: power supply system, energy capacities, demand, fuzzy logic, neural net
Published: 10.07.2015; Views: 1248; Downloads: 19
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Matjaž Klopčič, 2016, bachelor thesis/paper

Abstract: V Sloveniji ima zaradi neustreznega planiranja, veliko število proizvodnih podjetij težave z izpolnjevanjem naročil, oziroma preveliko vezavo kapitala v zaloge končnih izdelkov, surovin, embalaže. Cilj vsakega podjetja je zanesljiva dobava izdelkov ob minimalnih stroških zaloge. Čeprav gre za nasprotujoča si pojma, lahko s premišljenim načrtovanjem materialnih potreb v proizvodnem procesu bistveno pripomoremo k optimalnemu poslovanju podjetja. Namen diplomske naloge je optimizacija konfiguracije procesa operativnega planiranja v šaržni proizvodnji s pomočjo celovite programske rešitve SAP ERP 6.0. V diplomski nalogi je predstavljen predlog izboljšav celotnega procesa MRP(materials requirement planning) planiranja v podjetju JUB. Diplomska naloga je izdelana po metodi študija primera.
Keywords: SAP, ERP, MRP, planiranje, demand
Published: 30.11.2016; Views: 977; Downloads: 9
.pdf Full text (6,10 MB)

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