Dynamic simulation and safety evaluation of high-speed trains meeting in open air

Dynamic responses of a carriage under excitation with the German high-speed low-interference track spectrum together with the air pressure pulse generated as high-speed trains passing each other are investigated with a multi-body dynamics method.The variations of degrees of freedom（DOFs：horizontal movement,roll angle,and yaw angle）,the lateral wheel-rail force,the derailment coefficient and the rate of wheel load reduction with time when two carriages meet in open air are obtained and compared with the results of a single train travelling at specifie speeds.Results show that the rate of wheel load reduction increases with the increase of train speed and meets some safety standard at a certain speed,but exceeding the value of the rate of wheel load reduction does not necessarily mean derailment.The evaluation standard of the rate of wheel load reduction is somewhat conservative and may be loosened.The pressure pulse has significan effects on the train DOFs,and the evaluations of these safety indexes are strongly suggested in practice.The pressure pulse has a limited effect on the derailment coefficien and the lateral wheel-rail force,and,thus,their further evaluations may be not necessary.

Evaluation of Pt and Au pressure scales based on MgO absolute pressure scale

The equations of state(EOSs)of MgO produced by two independent scale-free methods,(1)the simultaneous elastic wave velocity and in situ synchrotron X-ray measurements(Kono et al.,2010;Li et al.,2006)and(2)the first-principles calculations(Wu et al.,2008),agree well with each other to at least 150 GPa and 2000 K.Furthermore,the EOS from first-principles calculations also agrees well with shock wave data,another pressure-scale-free data.These agreements strongly support that these EOSs provide reliable absolute pressure scales.Here we evaluate Au and Pt EOSs based on the EOS of Wu et al.(2008)using the simultaneously measured volume data of MgO,Au,and Pt from the literature.The primary pressure scales developed by Tange et al.(2009)and Yokoo et al.(2009)using only pressure-scale-free experimental data of MgO,Au,and Pt produce internal consistent pressure and agree with EOS of Wu et al.(2008).The Au EOS by Tsuchiya(2003)works well at room temperature but underestimates pressure at high temperature.The Au EOS by Fei et al.(2007)can well describe thermal pressure.The EOSs of Pt by Holmes et al.(1989)and Ono et al.(2011)work well at both room temperature and high temperature.The results also suggest that the discrepancy between bulk modulus of iron from experiments(Mao et al.,1990)and those from Earth's core(Dziewonski and Anderson,1981)is not originated from the overestimation of pressure by the EOS of Holmes et al.(1989).At high pressure and temperature,pressure uncertainty resulted from volume error becomes similarly important as the accuracy of the pressure scale.

Gas Expansion Process in the Dynamic Vacuum Calibration

By analyzing the gas expansion process from the upstream chamber via an orifice and a very rapid-opening ultra-high vacuum(UHV)gate valve to downstream one,the standard pressure analytical model basedon the dvnamic vacuum calibration apparatus in millisecond range developed by Lanzhou Institute of Physics(LIP)is deduced theoretically and corrected by real gas characteristics and temperature changes.According to the Kuudsen criterion,there is no free molecular fow regime in the area in front of the orifice during the gas expansion,so the chocked fow approximation is adopted to reduce the difficulty of numerical computation Under this anproxiuatiou and the full opening of the rapid valve,the standard pressure expression is calculated theoretically,and the upstream chamber pressure and temperature changes are obtained by numerical simulation during the gas expansion from 100 kPa to 10kPa.Also,experiments are performed using capacitance diaphragmgauges(model CDG045Dhs),The uncertainties between the measured pressure and the simulated and theoretical ones are 10%and 4.65%,respectively,which indicates that the apparatus can generate predictable pressure changes in the millisecond rauge and the conceptual model can better approximate the calibration results.Einally,the orifice conductance,and the correction factors of real gas characteristics and temperature change to the standard pressure are calculated accordins to the simulation results:the corrected staudard pressure expression is obtained.