| The suspended monorail transit(SMT),as a new type of rail transit form,can be used as the main rail transit of medium and small-sized cities and an important component of the rail transit system of large cities because of its many advantages with high operation security,strong climbing capability,sharp curve,small ground occupation,less manufacturing cost,low noise,etc.It could have a broad application prospect in our country.Compared with the traditional railway system,the SMT has the special vehicle structure,the bridge structure and the wheel-track contact relation;both the vehicle-bridge interactive features and the safety assessment of the vehicle operation have also significant discrepancies.The domestic research on the vehicle-bridge dynamic theory of the SMT is still at the initial stage,and the field test has been reported rarely.Therefore,it is meaningful to systematically conduct the theoretical and experimental research on the coupled vehicle-bridge vibration of the SMT,and to analyze the vehicle-bridge dynamic interaction features under different operation conditions and the reasonable values of key design parameters with the aims of establishing and improving the coupled vehicle-bridge dynamic theory of the SMT,conducting the dynamic optimization design of the vehicle-bridge system,and ensuring the train operating security and comfort.In this thesis,the main research contents are drawn as follows:1.The development history,system composition and structural characteristic of the SMT are introduced.At the same time,a detailed review is presented concerning the vehicle dynamics,bridge dynamics and coupled vehicle-bridge vibration for the SMT at home and abroad,and the research topic and contents of this thesis are also pointed out.2.Based on the tyre characteristics used in the SMT,a more accurate and reasonable tyre model with patch contact is developed.Subsequently,an experimental research on mechanical properties of a full-scale driving tyre is conducted.Then,the dynamic parameters of the established tyre model with patch contact are accordingly identified with the test data.At the same time,to accurately and efficiently model the dynamic behavior among the structural components of the suspended monorail vehicle,a dynamic decoupling method of using the oblique springs to model the oblique links is proposed for the four-link suspended device of the vehicle;thus,the suspended monorail vehicle is regarded as a coupled system with five rigid bodies connected by the spring-damping elements.The motion equations of each component are derived based on the D'Alemenbert principal.On this basis,according to the vehicle-bridge interaction theory and the finite element method,a coupled dynamic model of suspended monorail train and bridge considering a wheel-track relation with patch contact is established.Then,a corresponding dynamic simulation system is developed by applying the secondary development language of the finite software ANSYS.Finally,the proposed dynamic model is systemically validated by the field test.3.Based on the developed dynamic simulation system of the SMT,the coupled vibration characteristics between the train and bridge are investigated in detail,revealing the vehicle-bridge interaction features,the dynamic behavior characteristics of the vehicle and the dynamic performance of the bridge.Referring to the relevant rail transit standards,the vehicle-bridge dynamic performances are comprehensively evaluated.Results indicate that the first-order lateral and vertical vibration frequencies of the straight bridge with a 25 m span are 2.39 Hz and 5.41 Hz,respectively;the vehicle-bridge vibration level and bridge deformation of the SMT are significantly larger than those of the traditional railway vehicle-bridge system.As the train operating speed rises gradually,the bridge vibration would gradually become stronger and the vehicle running stability would gradually decrease;and the lateral stability of the vehicle is worse than its vertical stability and the lateral vibration of the bridge is stronger than its vertical vibration;additionally,the train load has a small dynamic impact on the bridge,and the dynamic amplification coefficients of the displacements and stress of the bridge are less than 1.15.4.The interaction features and dynamic performances of the vehicle and bridge are investigated in detail when the suspended monorail train passes through the curve line.Then,the influences of the vehicle running speed and the curve radius on the vehicle-curved bridge dynamic performances are analyzed.Results show that when the train passes through the curve line,the left and right driving tyres of the bogie will appear obvious unbalance load;at the same time,the vehicle will also appear obvious lateral displacement and wobble;the change rules of the vehicle stability,the bridge vibration and the bridge deformation along with vehicle running speed under the curve line are similar with those under the straight line;the overhigh vehicle running speed would cause an instantaneous derailment of the driving tyre at the side of loading decrease and significantly increase the wheel-track force of the driving tyre at the side of loading increment.Therefore,in addition to meeting the requirements of ride comfort,the wheel-track dynamic interaction should be reduced as much as possible in the design of the vehicle running speed limit of the SMT at the curve lines.5.The optimization analysis of key design parameters of suspended monorail vehicle under different operating conditions is carried out in detail.The secondary suspension parameters and the reasonable value of bogie wheelbase are analyzed by using the out-of-round tyre as the excitation;then,the influences of key design parameters of the guiding tyre,the anti-roll shock absorber and the four-link suspended device of the vehicle on the vehicle-bridge dynamic performances are analyzed when the train passes the curve line aiming at studying the reasonable ranges of the crucial performance parameters of the abovementioned core components.Results indicate that when the vertical stiffness of secondary suspension is less than 0.2 MN/m,the influences of the periodic excitation caused by the out-of-round tyre on the vehicle vibration could be effectively eliminated;the reasonable value of the vertical damping of the secondary suspension is 17 k N·s/m;the bogie wheelbase and the circumference of the driving tyre should be avoided to be a close design value as much as possible;the design parameters of the guide wheel,anti-roll shock absorber and four-link suspended device have significant influences on the dynamic performances of the vehicle running on the curve line.By comprehensively considering the vehicle-bridge dynamic indexes,the installation height of the guiding tyre is suggested to be close to the bogie mass center,and the anti-roll shock absorber damping of the vehicle and the initial angle of the four-link suspended device are recommended to be 20?30 k N·s/m and65?70°,respectively.6.Based on the linear filter method of auto-regressive(AR)model,the modelling of the three-dimensional fluctuating wind field is carried out,obtaining the time-history samples of the turbulent wind velocities.Then,considering the influence of the stochastic wind,the vehicle-bridge dynamic responses with and without wind load are compared,revealing the discrepancies between them.Then,the effects of wind level and train running speed on the vibration responses of the STM are systematically investigated and the operating security and stability of the suspended monorail vehicle and the bridge vibration level are assessed by referring to the relevant rail transit standards.Finally,taking the driving tyre force as the evaluation index,some suggestions for the train speed limit under different wind levels are proposed.7.Dynamic experiment is carried out to evaluate the dynamic performances of train-bridge system in the first suspended monorail test line with the new energy in China.The vehicle-bridge dynamic responses under different line conditions and train running speeds are tested,and the dynamic performances of the vehicle and the bridge are assessed by referring to the relevant rail transit standards.Results show that the first-order natural frequencies in the lateral and vertical directions are 2.27 Hz and 5.60 Hz,respectively.As the train speed gradually rises,the bridge vibration would gradually become stronger and the train running stability would gradually decrease under different line conditions;meanwhile,the lateral stability of the vehicle is worse than its vertical stability and the lateral vibration of the bridge is stronger than its vertical vibration;additionally,the train load has a small dynamic impact on the bridge,and the dynamic amplification coefficient of bridge displacement is less than 1.15.The experimental results are positively consistent with the modelling results.Under all test conditions,the maximum values of the deflection-span ratios and vertical rotary angles of beam end are 1.82‰ rad and 1/1099 respectively,which meet the requirements of relevant standard limits.The circumference of the driving tyre,the wheelbase of the bogie and the stiffness space of the bridge are the sensitive wavelengths that aggravate the vehicle vibration,which should be paid more attention in the design of the suspended monorail vehicle and bridge. |
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