Multi-Objective Optimization of High-Speed Train Nose Shape Using the Vehicle Modeling Function

Abstract

To reduce a micro-pressure wave and an aerodynamic drag of a high-speed train, twostep optimization is performed on the train nose shape using the vehicle modeling function. In the first step, the cross-sectional area distribution of a train nose is optimized to reduce a micro-pressure wave. The optimized cross-sectional area distributions of a train nose have an extremely blunt front end and a negative gradient around a middle section. The steep change of the cross-sectional area from the positive to negative gradient causes a strong expansion effect. This phenomenon divides one large compression wave into two small waves. Compared to the previous optimization results, the optimized shapes reduce the maximum micro-pressure wave by 12-19%. To generate 3-D nose shapes from the optimized crosssectional area distribution, the vehicle modelin g function is proposed. This mathematical function makes a simple curve with a rounded front end, and the curve shape is controlled by two parameters. Modeling of a complex curve can be achieved by a combination of several functions. To make the 3-D nose shape, the 2-D side and top view shapes are defined firstly, and the cross sections are produced along the length of a train. One of the most important features of the vehicle modeling function is that it can make various 3-D nose shapes for a given cross-sectional area. The 3-D nose shape optimization is done with the optimized cross-sectional area distribution. Through the second optimization, the aerodynamic drag force is reduced by 5.6% preserving the minimum micro-pressure wave.