Optimization of mixed air cargo transportation network

In order to optimize the air cargo transportation network with the mixed characteristics of point-to-point and hub-and-spoke, a bi-level optimization model was built based on the OD flow of air cargo transportation companies. The objective of upper model was designed to minimize the total transportation cost, and the air cargo transportation network structure and the configuration capacity were optimized. The equilibrium cargo flow on each link was calculated in the lower model. The bi-level optimization model was verified by using the related data of fourteen cities served by Shunfeng Airlines, under the premise of setting 4 hub airports, the cases with 4-6 cargo aircrafts were analyzed respectively. Analysis result indicates that in the three cases, four airports of Beijing, Shanghai, Nanjing and Shenzhen are all set as hub airports. When 4 cargo aircrafts are used, the cargo aircrafts are arranged on the flight segments of Beijing-Nanjing, Beijing-Shenzhen, Shanghai-Shenzhen and Nanjing-Shenzhen respectively. The transshipping ratios of 4 hub airports are 24.3%, 24.2%, 47.8% and 14.9% respectively, and the transshipping ratio of Nanjing Airport is the largest, while the ratio of Shenzhen Airport is the smallest. When 5 cargo aircrafts are used, the fifth cargo aircraft is arranged on the flight segment of Beijing-Shanghai, the flight segments of the other 4 cargo aircrafts remain unchanged. The transshipping ratios of 4 hub airports are 38.6%, 50.9%, 44.3% and 11.9% respectively, and the transshipping ratio of Shanghai Airport is the largest, while the ratio of Shenzhen Airport is the smallest. When 6 cargo aircrafts are used, all flight segments between hub airports are arranged with cargo aircrafts. The transshipping ratios of 4 hub airports are 38.5%, 74.0%, 79.5% and 10.2% respectively, and the transshipping ratio of Nanjing Airport is the largest, while the ratio of Shenzhen Airport is the smallest. Therefore Nanjing is a typical transshipping hub city, and Shenzhen is a typical hinterland hub city. The airports in the cities with large transport demand are determined to be hubs easily. Both hub airports and non-hub airports may transship cargos. Two nearby airports may be determined as hub airports simultaneously.