Study On Fluid-solid Coupling Vibration And Running Safety Of High Speed Trains

A series of key technical issues that should be urgently solved has arisen as the coupling vibration between the train and airflow intensifies along with the high-speed and light-weight development of train. The issues include dynamic performance deterioration of the tailing vehicle, threat to running safety of train from side wind, effect on train's structure and dynamic performance of the pressure wave and aerodynamic load impulse when two trains pass by each other at high speed, safty issues caused by fluid-solid vibration when a train passes through the platform at high speed, and so on. Although considerable achievements have been obtained in the field of train aerodynmics with development of high-speed rail transport, the coupling vibration relationship has been taken into account rarely. Safety is the all-important one among issues regarding train system. The train-airfow coupling vibration is an important engineering and technical issue concerning safety, also one of the key technical issues needed to be solved for railway development.In this paper, an analysis method for train-airflow coupling vibration including off-line and on-line coupling analysis method was proposed by establishing a train-ailfow coupling model on the basis of Arbitrary Lagrangian-Eulerian (ALE) through integrating the theory of computation fluid mechanics and train system dynamics. With regard to off-line coupling analysis method, the train's vibration state is not taken into consideration in flow field anlysis, but the aerodynamic load is taken into account in the anlysis on dynamic response of train system. The on-line coupling analysis method includes explicit and implicit ones. The train's dynamic response and flow field characteristic are analyzed synchronously for the explicit coupling analysis method, which focuses on the process of interaction between fluid and solid and needs more time. Whereas, for the implicit method, it focuses on the final condition of interaction between fluid and solid and needs less time as the train's dynamic response and flow field characteristic are analyzed with selective link. The research on fluid-solid coupling vibration and running safety of high-speed train was conducted by adopting the foregoing coupling vibration analysis method in the paper, of which details are as follows:(1)For coupling vibration between airflow and train in the calm open space, the study analyzes running stationarity and stability of a high-speed train under the influence of airflow with the off-line and explicit coupling analysis method and compares relevant results with those based on conventional method. (2)As for safety problem of a train running in side wind, considering the attitude change, the study analyzes running safety of the train in specific condition with the off-line, explicit and implicit coupling analysis methods and compares relevant results acquired from these different analysis methods. At the same time, running safety of a train in different conditions is analyzed with implicit coupling analysis method and safety domain of a train in side wind is defined.(3)Adopting the off-method and explicit method, from the perspective of surface pressure wave, aerodynamic load impulse, carbody response and running stability, the study analyzes safey of two trains passing by each other in different wind environments. The differences of safety of a train in different wind environmets and acquired from different coupling methods are compared. Additionally, a comparative analysis is made with running test data.(4)With respect to the safety issue, the study compares collision risk and running stability of a train with the intial fixed attitude and the stable attitude in side wind when the train passes through the railway platform at high speed, analyzes safety of a train passing through the platform in different conditions, defines safety domain of a train passing through the platform and researches the peressure wave of shield door when a train passing through the platform at high-speed.Main conclusions as following are reached according to above discussions.(l)The train-airflow coupling analysis for a train running in the calm open space shows that train's running stationarity and stability acquired from off-line coupling method diminish somewhat compared to those acquired from conventional computing method. After the fluid-solid coupling relationship is taken into consideration with explicit coupling analysis method, the lateral stability of leading vehicle, middle vehicle and the front end of the tailing vehicle improve slightly, but the lateral stability of the back end of tailing vehicle decreases. In addition, the upward transfer of wheel-rail vibration is influenced to some extent due to the limition of airflow to carbody's motion, thus the train's running stability descreaes.(2)Different coupling anlysis methods for safety of a train running in side wind show that the adaptive process to side wind's action results in attitude change of a train. Accurate result of attitude change needs the on-line coupling analysis method. The implicit coupling method can meet the demands of study on safety of a train running side wind with considering the attitude changes. Influence of attitude changes on aerodynamic is well consistent with running test data in relevant literatures. Critical speeds of a train running safely in different side winds are found and the safety domain of train in side wind is defined with consideration of attitude changes in the implicit coupling analyses. The faster a train runs, the lower capability to withstand side wind it has, and the more sensitive to side wind the critical speed is.(3)The fluid-solid analyses on two trains passing by each other at high-speed show that, some surface pressure waves and aerodynamic load impulses rise, and others descrease in the environment with side wind compared to a calm envirement without wind. The aerodynamic load impulses of the leeward train are bigger than that of windward train. The surface pressure waves, aerodynamic load impulses, carbody responses and running stabilities obtained in the explicit coupling analysis are bigger than those in the off-line coupling analysis. Moreover, simulation results of surface pressure waves and carbody responses are well consistent with concerned running test data.(4)The safety analyses on a train with different attitudes passing through platform show that, the train with initial fixed attitude can meet the analysis demand. The analysis on different side wind speeds and running speeds indicate the abscissa of the closest point is proportional to the wind speed when a train passing through the platform at the same speed. The safety domain of a train passing through platform in side wind is the union of collision safety domain and operating stability safety domain. There is a pressure wave on the shield door when a train passes through at high-speed, which is similar to the pressure wave when two train pass by each other. The maximum and minimum values will appear respectively when the leading vehicle runs into and out of the shield door.(5) Proper methods should be taken to analyze different problems in order to ensure accuracy of analysis result and enhance analysis efficiency. For example, the implicit coupling analysis method was adopted to research the attitude changes of a train running in side wind. And the analysis on pressure wave of shield door doesn't need to consider train's vibration.In conclusion, the paper discusses mechanisms of a series of key issue caused by coupling vibration between high-speed train and airflow. The influence pattern of airflow on train's running stationarity and stability is found by explicit coupling analysis. The on-line coupling analysis on a train in side wind reveals that attitude changes pose an effect that can not be ignored on aerodynamic load and running stability. The safety issue of trains passing by each other becomes more prominent after fluid-solid coupling relationship being taken into consideration. The attention should be paid to the influence of fluid-solid coupling on train's running stability and the collsion risk between train and platform. In order to ensure train's running safety, it is very necessary to consider the fluid-solid coupling vibration relationship for train's running safety analysis. As the coupling analysis method is verified by test datum, it throws a light on train's dynamic behaviour study under fluid-solid coupling relationship and offers a thought for cross-sectional studies on train's aerodynamics and system dynamics.