عنوان مقاله [English]
In this paper, a multi-phase bi-objective mathematical model is presented for a transportation planning. It is assumed that there is a planning horizon which includes some planning periods. In each phase, its related decisions are made. In the first phase, a transportation planning is done for each planning period considering products inconsistency features and other real conditions. In mentioned model steaming decision is made to solve products inconsistency before transporting the new product and the model considers transportation, steaming and other related costs to define optimal tour plan for each vehicle in each time period. The model is solved for each period separately according to the products demands and supplies in mentioned period. In the second phase, according to the total benefit and cost of each vehicle in each period, an optimal portfolio of vehicles is determined. The proposed model of the second phase considers average and risk of using various vehicles and tries to select proper ones. By the proposed portfolio, the transportation company will face to a strategic number of vehicles plan and according to observed periods may have more profit in the future. In the third phase, a bi-objective model is proposed for tactical decisions of purchasing or sale of each vehicle considering their age, their potential profits, their maintenance and other costs at the beginning of each time period. The first objective tries to maximize the total benefit of the transportation company while the second one minimizes the deviation of number of vehicles with their target value which was determined in the second phase by the portfolio selection model. By the third model, the transportation company will decide to purchase or sale each vehicle types to be used for the next time period. This decision is made considering the required demands or supplies, different costs and benefits. Finally, a fuzzy goal programming approach is used to solve the bi-objective model. Sensitivity analysis is done to consider models validity. Comparison of the proposed three phased approach with a classic transportation problem for a numerical example confirms efficacy of the proposed approach.