n/a

This paper addresses the wholesale hub location problem in food supply chains. The paper aims to design an optimal hub location network to serve food consumption markets through efficient connections with production sites. These optimal locations can be compared with the current locations of hubs to determine whether changes could lead to greater efficiencies. The model is mathematically formulated as a mixed-integer programming problem. The model minimizes the total network costs, which include the transportation of goods and the construction of hubs. The mathematical program considers several constraints on travel distance, hub capital cost and capacity, road condition, and transportation cost. Several experiments are conducted to test the sensitivity of the model to changes in parameters such as the food's average travel distance, the maximum hub capacity, and the transportation cost. Then, a real-world application is made to the Northeast United States livestock industry. Finally, the results show the effect of the changes in model parameters on the optimal hub network design (i.e., the number of hubs and the selection of hub locations).

An optimum control approach for a wind turbine drivetrain with a variable ratio gearbox is presented. The objective is to find the optimum shifting sequence of the variable ratio gearbox in order to maximize power generation and extend gear life. The employment of a variable ratio gearbox enhances the capabilities of the wind turbine to cope with wind speed variations. Based on our preliminary study, the gear ratios of the variable ratio gearbox were carefully selected to increase the wind energy capture. We then propose a new control approach to extend the gear service life. It finds the gear shifting sequence that will minimize the tangential force on the gear tooth. The wind turbine drivetrain with a variable ratio gearbox is modeled and simulation results for two sets of recorded wind data are presented and compared.