## 4 Next Generation HSRS with Higher Speed
### Design Optimization of Service Car Body System  
In order to ensure the 30-year service life of the aluminum alloy car body, as shown in Figures 16-18, the passenger transport discipline should carry out optimal route planning and design so as to remove and eliminate the negative impacts of central hollow tread wear on the lateral coupling vibration of the service car body. _(1) External excitation source belongs to unsaturated and unsteady state._ As shown in Figure 16, a mutual influence will occasionally take place between the parametric disturbance of wheel spin and the forced vibration of the bogie frame. As for slight central hollow tread wear, the local conformal or bad contact is occasionally constructed on specific rail sections, the rail running light band becomes widened, and the wheel wear is concentrated on the central tread. Different from the bogie hunting instability failure caused by the primary or secondary hunting phenomenon, the slight central hollow tread wear forces the wheels to produce spin creepage. As a result, the wheelsets produce a small-amplitude instability hunting oscillation, and the bogie frame has a forced vibration response, which is not the modal vibration of bogie frame lateral or yaw motion. This forced vibration response can only change into resonance when the vehicle speed is greater than 450 km/h, the dominant frequency of which changes to ca. 6.0 Hz. Therefore, within the service speed of (300-450) km/h, the above forced vibration response has obvious broadband characteristics, with the dominant frequency of ca. (7.0-8.0) Hz and the leading frequency of 10 Hz or more in general, which constructs a sufficiently strong external excitation source. Specifically, in the general curving negotiation with a speed of 250 km/h, the UK small defect spectrum does not change the wear characteristics shown in Figure 16c. In order to avoid the further deterioration of such forced vibration responses, it is necessary for the passenger transport discipline to carry out the planning and design optimization of the operating routes, as shown in Figure 17, to enhance the self-cleaning capability of central hollow tread wear. The German track spectrum of high interference does not weaken the excitation inputs for small defects of wavelength \(\leq\)3 m and long-wave irregularities. Especially, the long-wave horizontal irregularity excitation input can cause the roll and rock of service car body. Figure 16: Central hollow tread wear results occasionally in local conformal or bad contact between worn wheel and rail on some rail sections, which forces bogie frame to produce lateral forced vibration when running in tangent lines. (**a,b**) Equivalent conicity and RRD curves calculated by slight central hollow tread wear. (**c**) Travelling wide light band is formed on top surface of railhead while concentrated wear is evolved on wheel tread. (**d**) Bogie frame thereby generates forced resonance with dominant frequency of ca. 6 Hz and leading frequency is close to or more than 10 Hz. (**e**) Influence of vehicle speed on lateral acceleration (_RMS_)\({}_{2,\sigma}\) of bogie frame. **(2)** _Correlative excitations come from internal lateral resonances._ By applying MMRT, the transaction strategy of the flexible body-to-MBS interface was improved, as shown in Figure 18, so as to remove and eliminate completely the lateral coupling relationship between running gear and the service car body. As mentioned above, through the collaborative and innovative efforts of vehicle, rail, and passenger transport disciplines, the slight central hollow tread wear provides the necessary conditions for the structural experts to better realize the structural dynamic response design optimization of an aluminum alloy car body.