Wind Turbulence And Aerodynamic Forces Relative To Moving Vehicle And Its Overturning Risk Under Crosswind

In the last decade,high-speed railway has been widely built around the world,especially in China,due to its many advantages,such as high running speed,high safety and comfortable performance.However,high-speed railway is so long that high-speed trains often run through rivers,high embankment,high mountains and canyon regions with complicated wind environment.With the increasing running speed and reducing weight,high speed trains with bluff bodies are more sensitive to crosswind.Under strong crosswind,the side force and lift force loading on moving vehicle can increase the rolling moment around leeward rail,then the overturning risk will increase significantly.So,this dissertation will systematically research the wind turbulence and aerodynamic forces relative to moving vehicle,and the dynamic responses and overturning risk of moving vehicle under crosswind,and the overturning risk of vehicle running on bridge.Include following major respects:Firstly,the wind turbulence model is proposed with considering the effect of moving vehicle.Based on the Taylor’s frozen turbulence hypothesis,the relationship between wind turbulence relative to moving vehicle and wind turbulence relative to stationary ground is derived.Furthermore,the correlation function of wind turbulence relative to stationary ground is used to describe the correlation function of wind turbulence relative to moving vehicle.Then,the wind spectra relative to moving vehicle is derived by Fourier Transform.With considering Kaimal’s spectrum,the characteristics of wind turbulence relative to moving vehicle are investigated,and the time histories of wind turbulence relative to moving vehicle are simulated with superposition of harmonic.Based on any kind wind spectra and coherence function relative to stationary ground,the wind spectra relative to moving vehicle with any vehicle speed along any moving direction under any wind speed environment can be calculated by this new proposed wind model.Secondly,the new unsteady aerodynamic forces model relative to moving vehicle is presented with considering longitudinal,lateral and vertical turbulence,which makes simulate the unsteady aerodynamic forces relative to moving vehicle more closely to the reality.The reduction effect induced by spatially partial correlation wind tunnel turbulence is removed by joint acceptance function,then the advanced method for extracting vehicle aerodynamic admittance functions is proposed based on the proposed unsteady aerodynamic forces model,which ensures the 9 complex admittance functions can be identified.The effect of phase existing in unsteady aerodynamic forces response is analyzed in theory.Based on the method developed by Chen,the time domain expression of complex admittance function of vehicle is derived,which makes it possible to consider the complex admittance function in simulating the time histories of aerodynamic forces relative to moving vehicle.At last,the time histories of unsteady aerodynamic force are simulated,and the effect of the admittance phase on the unsteady aerodynamic forces is investigated.Thirdly,a spectral analysis framework for calculating the response and assessing overturning risk of high-speed trains under strong crosswind is introduced.Based on previous research,the aerodynamic force spectra loading on moving vehicle are simulated and the vehicle dynamic response spectra and standard deviation are calculated.Furthermore,the cumulative probability distribution of vehicle extreme response is introduced based on the extreme value distribution model.And the probability of overturning risk of moving vehicle is evaluated.Using the software Matlab,the codes for calculating vehicle response and evaluating overturning risk are developed.The influence of track irregularities and wind turbulence on the response of moving vehicle are investigated.Moreover,the probabilistic characteristic wind curve composed by critical wind speed is given,and the overturning probability of vehicle running along the railway is calculated.Fourthly,based on multi-body dynamic and mode superposition method,the framework for calculating the overturning probability of vehicle running on the bridge is developed.In this framework,the simplified wheel-track contact model is used,and the equation of motion of vehicle-bridge system is proposed.The mode superposition method can effectively reduce the freedom of bridge and the calculation of time domain analysis.The codes for evaluating the overturning probability of vehicle running on the bridge is developed using software Matlab.The simply supported beam with 32 meter length is used to analyze the effect of moving vehicle on the bridge and the effect of bridge vibration on the moving vehicle.Base on the aerodynamic experimental data,the responses of vehicle moving on ground and bridge under crosswind are calculated,and the response difference between vehicles moving on ground and bridge are investigated.The reasons about the response difference are discussed.