چكيده به لاتين
Planning to meet customer demands in a timely manner and with the lowest cost and best quality, is always one of the key issues in the growth and survival of service organizations. This issue is even more important in freight rail companies, because if all the customers' cargo is not shipped on time, they do not wait and quickly turn to road transportation.
These companies to raise the level of service and prevent changes in the way customers , are always looking to increase the inventory level of their wagons in the rail network to achieve this goal, their managers usually decided to buy or rent a new fleet. however, buying a wagon requires a lot of initial capital and it is usually not possible to finance its initial funding and renting wagons without estimating the exact number required it increases costs and reduces the company's profitability. Therefore, determine the number of real estate and rental fleets and how to use them optimally to meet all customer demands in order to reduce the direct and indirect costs of the company, it becames important.
The present project seeks to meet this need of rail freight companies. This research presents an applied model in addition to determining the optimal size required for the rail freight fleet to meet existing demands, it also provides the method of distributing empty wagons at the loading points of the railway network of the Islamic Republic of Iran. Objective function in this model is seeks to reduce fixed (lost customer demand) and variable costs (rent, maintenance, "repairs" and pregnant and empty wagons). The limitations of the model include the demands between principles and destinations taking into account the time window, inventory and balance of arrival and departure of loaded and empty wagons at each station, unloading and loading capacity at destinations and bases, donot to unload specific wagons at specified destinations, And the maximum and minimum number of daily train trains sent from each station and their constituent wagons.
The model results also show the inventory of each station,the optimal number of required real estate, rental wagons, and how to send them among the bases and destinations of the rail network, and presents the lost demand in all time periods.
Application of this model for rail freight companies assuming that the type of wagons is heterogeneous, and the number of depots varies and the demand and travel time are definite, static environment with time window is suitable.
To validate the proposed model used from the statistical data of Parsian Rail Shargh Private Freight transport Company active in the field of rail transportation of basic goods such as cereals. . The results shows the proposed model in addition to specifying the optimal fleet size to meet customer demand ,it also presents the distribution of empty wagons at loading points in different time periods and while increasing the level of customer service, it increases the company's productivity.
