Browsing by Author "Vera, Jorge"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemA robust optimization approach to wine grape harvesting scheduling(ELSEVIER, 2010) Bohle, Carlos; Maturana, Sergio; Vera, JorgeOptimization models are increasingly being used in agricultural planning. However, the inherent uncertainties present in agriculture make it difficult. In recent years, robust optimization has emerged as a methodology that allows dealing with uncertainty in optimization models, even when probabilistic knowledge of the phenomenon is incomplete. In this paper, we consider a wine grape harvesting scheduling optimization problem subject to several uncertainties, such as the actual productivity that can be achieved when harvesting. We study how effective robust optimization is solving this problem in practice. We develop alternative robust models and show results for some test problems obtained from actual wine industry problems. (C) 2008 Elsevier B.V. All rights reserved.
- ItemAn optimization approach for scheduling wine grape harvest operations(ELSEVIER, 2008) Ferrer, Juan Carlos; Mac Cawley, Alejandro; Maturana, Sergio; Toloza, Sergio; Vera, JorgeThis article presents a practical tool for optimally scheduling wine grape harvesting operations taking into account both operational costs and grape quality. We solve a mixed-integer linear programming model to support harvest scheduling, labor allocation, and routing decisions. A quality loss function is used to represent wine quality reduction at each vineyard block due to premature or deferred harvest with respect to an optimal date. We present computational results which show that the proposed tool could be used to support grape harvest planning in a large vineyard, at both a tactical and operational level, (C) 2007 Elsevier B.V. All rights reserved.
- ItemMorphological trends in main stem of Pinus radiata D. Don: Transition between vegetative and reproductive phase(TAYLOR & FRANCIS AS, 2007) Fernandez, Maria Paulina; Norero, Aldo; Barthelemy, Daniel; Vera, JorgeDevelopmental patterns of structural units of the main tree axis of Pinus radiata were investigated in two plantations in Chile growing under different ecological conditions. Environmental characteristics of sites were recorded and structural features of sample trees were measured. Annual shoot length, number of growth units per annual shoot, growth unit length, and number of branches and cones per growth unit were statistically compared between sites and between vegetative and reproductive phases of trees. No clear pattern of stand development was apparent when variables were directly examined in terms of actual dimensions ( cm) and time scale ( years). In contrast, common patterns of development of structural parameters were indicated after dimensions and time were normalized so as to express them on a ontogenetic scale. The number of growth units per annual shoot and average length of annual shoot increased during the juvenile stage of development. Transition from juvenile to mature stages brought about a change in this trend, either stabilizing or reversing the pattern of development and size of these structural elements. The practical consequence of these changes on wood quality for industrial purposes is discussed.
- ItemRisk averse retail pricing with robust demand forecasting(ELSEVIER SCIENCE BV, 2012) Ferrer, Juan Carlos; Oyarzun, Diego; Vera, JorgeGood demand estimates are the key to effective pricing decision-making. However, they are subject to a high degree of uncertainty due to various factors that are unpredictable or difficult to model, thus making pricing decisions risky. This research provides a simple proposal for a robust optimization methodology that incorporates both demand uncertainty and the decision maker's degree of risk aversion. Uncertainty is explicitly considered for two coefficients of a linear demand function, price expressions are derived, and a criterion is proposed for defining the degree of risk aversion. The resulting model is also applied to an exponential demand case to better reflect a more realistic retail setting. (C) 2011 Elsevier B.V. All rights reserved.
- ItemScheduling production for a sawmill: A comparison of a mathematical model versus a heuristic(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Maturana, Sergio; Pizani, Enzo; Vera, JorgeSawmill production scheduling is complex. It involves determining which logs to process taking into account the diameter, length, and grade of each log, on one hand, and the finished products that are needed to fulfill the orders, on the other. The cutting pattern determines which products are generated and also the yield, which is how much of the volume of the log ends as finished products. We used two approaches to solve the problem: a mathematical model, which calculates the volume and the schedule of various types of logs, and a heuristic that solves the problem by systematically applying the criteria used by a sawmill programmer in southern Chile. We compare the results of using both approaches under various scenarios in a 6 week planning horizon, with the mathematical model showing a superior performance in almost all instances except two, were both found the optimal solution. The proposed mathematical model can be solved in a relatively short time, which makes it a suitable basis of a practical optimization-based decision support system. (C) 2010 Elsevier Ltd. All rights reserved.