## 4 Next Generation HSRS with Higher Speed
### Wear Evolution Regulation under Rational Condition of Wheel-Rail Matching  
Taking the trailer vehicle as the research project, the normal wear regulation is formed with the nonlinear variation of wheel-rail contact geometry, as shown in Figures 13-15, including the three main stages of uniform wear at low conicity, rapid wear evolution, and stable wear at high conicity. Figure 13: Hunting motion stabilization at low conicity of \(\lambda_{e}\) = 0.06 when running in tangent lines. (**a**) Influence of vehicle speed increase on distribution characteristics of wheel wear index. (**b,c**) Variation patterns of wheel spin and longitudinal creepae when running at 575 km/h, which is maintained with the hypothesis of small creepage and non-spin. (**d,e**) Left and right wheel unloading rates of 1 st wheelset when running at 575 km/h, the maximum value 0.60 has small occurrence probability of \(\leq\)5%. Figure 14: Concept of limit speed explained as suddenly transition from hunting motion stability to instability hunting oscillation at \(\lambda_{e}\) = 0.10, which becomes High Creepage Issue. (**a**) Influence of vehicle speed on distribution characteristics of wheel wear index in tangent line operations. (**b**) Lateral acceleration PSD of rear bogie frame changes suddenly into forced resonance, ca. 5.6 Hz, when \(v\) = 650 km/h. (**c,d**) High Creepage Issue represented through variation patterns of wheel spin and longitudinal creepage for left and right wheels of 1 st wheelest. Figure 15: Gradual transition from hunting motion stability to instability hunting oscillation at \(\lambda_{e}\) = 0.16. (**a**) Influence of vehicle speed on distribution characteristics of wheel wear index in tangent line operations. (**b**) Lateral acceleration PSD of rear bogie frame changes gradually into forced resonance, ca. 6.0 Hz, when \(v\) = 600 km/h. (**c,d**) Variation patterns of wheel spin and longitudinal creepage, which is one of main characteristics of stable wear stage at high conicity. (1) Uniform wear at low conicity.Under the collaborative and innovative efforts between vehicle and rail disciplines, the self-adaptive improved design of higher speed bogies returns to the rational condition of wheel-rail matching, i.e., \(\lambda_{emit}\) = (0.03-0.06), as shown in Figure 13, and the uniform wear stage at low conicity will bring considerable cost effectiveness to Chinese HSR practices. These beneficial findings are mainly manifested in the following three aspects: (i) When running in tangent lines or in a large radius curving negotiations, as shown in Figure 13a, the low wear area becomes wider and the amplitude of wheelset hunting motion increases correspondingly; (ii) The hypothesis of small creepage and non-spin is valid, by which the stability robustness performance can be gained against aerodynamic disturbances such as crosswind, sidewind, or wake, as shown in Figure 13b,c; (iii) Because the rubber pad and pressing buckle are the only damping elements for ballastless track bed with seamless rails, when approaching the limit speed, as shown in Figure 13d,e, the maximum rate > 0.60 of wheel unloading becomes a small occurrence probability event of \(\leq\)0.15%. These findings once again demonstrate that the rational condition of wheel-rail matching cannot be easily abandoned, which is one of the necessary conditions for the successful commercial applications of HSRS in the high-tech manufacturing industry. This rational condition is unique to Chinese HSR parameter system, which does not require the improved design of the wheel-rail relationship, such as rail grinding treatment or wheel profile renewal design. However, as a classic research case of large-scale MDO, HSRS must emphasize the significance of actively recommending and introducing the dynamic design methodology, in which the analysis graph of full-vehicle stability properties and variation patterns becomes one of the key technologies. As a result, the correct direction of self-adaptive improved design is clarified for higher-speed bogies by using PODA.