thesis statement : In today’s turbulent markets, maintaining an efficient and flexible supply chain is critical for every enterprise, especially given the prevailing volatilities in the business environment with constantly shifting and increasing customer expectations. The increasing competitive pressures in the global marketplace coupled with the rapid advances in information technology have brought supply chain planning into the forefront of the business practices of most manufacturing and service organizations (Gupta and Maranas 2003). A major issue in supply chain planning is inventory management. Inventory usually represents from 20% to 60% of the total assets of manufacturing firms. Therefore, inventory management policies prove critical in determining the profit of such firms (Giannoccaro et al. 2003).
یک مشاور حرفه ای برای انجام پایان نامه شما Lack of a coordinated inventory management throughout the Supply Chain (SC) often causes the bullwhip effect, namely an amplification of demand variability moving toward the upstream stages. This causes excessive inventory investments, lost revenues, misguided capacity plans, ineffective transportation, missed production schedules, and poor customer service. In addition, the time necessary to have the upstream SC stages perceive changes in market demand increases, thus making the whole SC less responsive to customer requirements (Giannoccaro et al. 2003). Under competitive market conditions, customer satisfaction level is recognized as an important index that must be monitored and maintained at a high level. thesis Ph.D A high level of customer satisfaction can be achieved by maintaining increased inventory levels to hedge against demand uncertainties (Jung et al. 2004).Although additional inventory improves customer satisfaction, it entails increased inventory holding cost. Thus, cost-effective and agile inventory and production management can provide a competitive advantage for a company in a highly dynamic market. Therefore, it is of significant importance to integrate the tactical planning decisions with inventory management decisions, and coordinate the activities of purchase, production, storage, and sale to minimize the total cost (You and Grossmann 2011). Supply chain planning is concerned with determining supply, production and stock levels in raw materials, subassemblies at different levels of the given Bills of Material (BoM), end products and information exchange through a set of factories, depots and dealer centers of a given production and service network to meet fluctuating demand requirements (Alonso-Ayuso et al. 2003) and its main objective is to achieve acceptable financial returns together with the desired customer satisfaction levels (Mele et al. 2007). The main focus is on supporting the material flow across a supply chain and related business functions: procurement, production, transport and distribution as well as sales (Stadtler 2005). The decision making process in supply chains can be decomposed according to the time horizons considered. This results in the following classification of the models.The strategic level concerns those decisions that will have along-lasting effect on the firm. It is focused on SC design and entails determining the optimal configuration for entire network, i.e., deciding on the production topology, plant sizing, product selection, product allocation among plants and vendor selection for raw materials over a relatively long time horizon ranging from 5 to 10 years (Alonso-Ayuso et al. 2003; Gupta and Maranas 2003 thesis statement; Mele et al. 2007; Peidro et al. 2009; Santoso et al. 2005). Short-term operational scheduling models constitute the other extreme of the spectrum of planning models. These models are characterized by very short timeframes, such as 1-2 weeks, over which they address day-to-day decisions such as scheduling, lead-time quotations, lot size, assigning loads and vehicle routes (Alonso-Ayuso et al. 2003 thesis statement; Gupta and Maranas 2003; Mele et al. 2007; Peidro et al. 2009; Santoso et al. 2005). The third class encompasses midterm tactical models which address planning horizons of 3 months to 2 years. These include overall purchasing and production decisions, inventory policies, transport and distribution strategies and incorporate some features from both the strategic and operational models. The tactical planning problem assumes that the supply chain topology is given. The most important difference between strategic and tactical planning problems is that tactical planning is devoted to better utilization of available resources and strategic planning is devoted to better acquisition of resources (Alonso-Ayuso et al. 2003; Gupta and Maranas, 2003; Mele et al. 2007; Peidro et al. 2009; Santoso et al. 2005). Cost of master thesisTactical planning has to coordinate activities and processes along a SC and thus has to capture decisions in procurement, transport, production and distribution adequately. Given the structure of the SC, tactical planning looks for the most efficient way to fulfill demand forecasts over a medium-term planning interval (Stadtler 2005).An important issue in the process of supply chain planning is the need to make decisions in the face of uncertainty (Gumus et al. 2010). Deterministic planning models which do not recognize the uncertainty in the future forecasts, can be expected to result in inferior planning decisions as compared to models that explicitly account for the uncertainty (Cristobal et al. 2007 thesis statement; Gupta et al. 2000; Gupta and Maranas 2003). Galbraith (1973) defines uncertainty as the difference between the amount of information required to perform a task and the amount of information already possessed (Mula et al. 2006; Peidro et al. 2009). Underestimating uncertainty and its impact can lead to planning decisions that neither safeguard a company against the threats nor take advantage of the opportunities that higher levels of uncertainty provide (Gupta and Maranas 2003). Majority of researchers classified the source of uncertainty into three groups: demand, process/ manufacturing and supply. Uncertainty in supply is caused by the variability brought about by how the supplier operates because of the faults or delays in the supplier’s deliveries. Uncertainty in the process is a result of the poorly reliable production process due to, for example, machine holdups. Finally, demand uncertainty, is the most important of the three and is presented as a volatile demand or as inexact forecasting demands (Peidro et al. 2009). The longer the planning horizon the greater the portion of forecasted demand. Accurate demand forecasts are an important input to decision models used in supply chain planning. Forecast errors are directly related to required safety stocks, while frequent adjustments of demand forecasts can lead to dramatic changes in plans. Hence, great emphasis has to be put on choosing correct forecasting models (Stadtler 2005 thesis statement). To incorporate uncertainty in a supply chain model a suitable means of representing it must be found. Three methods are frequently used for representing uncertainty (Gumus et al. 2010; Gupta and Maranas 2003): The scenario-based approach attempts to represent a random parameter by forecasting all its possible future outcomes. Each scenario is associated with a probability level representing the decision maker’s expectation of the occurrence of a particular scenario. The main drawback of this technique is that the number of scenarios increases exponentially with the number of uncertain parameters, leading to an exponential increase in the problem size (Gumus et al. 2010; Gupta and Maranas 2000; Gupta and Maranas 2003).
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