With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train ...With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces (moments), possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objectives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load reduction factor was reduced by up to 1.72%.展开更多
对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身...对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身及桩周土层沉降变化情况,得到高填方夯实地基未处理填土层桩侧负摩阻力变化规律。试验结果表明,未处理填土层桩侧摩阻力沿深度呈现"负-正"变化的现象,随着固结时间的增加,端承桩负摩阻力区段大于摩擦桩。端承桩桩侧土层提供的最大负摩阻力约是摩擦桩的1.18~2.56倍,桩周土层密实度对桩侧最大负摩阻力有影响。采用一阶负指数函数拟合得到桩身下拉荷载预测模型,随着固结时间的增加,作用于桩身的下拉荷载趋于定值,作用于端承桩的下拉荷载比摩擦桩高41.2%~55.4%,从控制负摩阻力角度推导出高填方夯实地基摩擦桩桩长设计计算方法。桩身中性点位置均随固结时间增加而逐渐下移,端承桩中性点深度较摩擦桩平均大0.7 m。展开更多
Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions,which may exceed the settlement limit and threaten the safe operation of high-speed trains.However,the effect of ground...Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions,which may exceed the settlement limit and threaten the safe operation of high-speed trains.However,the effect of groundwater reduction on a long-pile group(greater than 20 m in length)has not been fully understood,especially in respect of repeated reductions.In this study,a centrifuge test was conducted to investigate the responses of pile groups in silty soils subjected to repeated falls in the water table.The behavior of the piles was discussed based both on the test and on 3D numerical analyses.With the derived coef-ficientβfor the axial force evaluation of the pile,the effect of lowering the water table on the railway pile foundation could be seen.Results of the tests and numerical analyses indicated that the water table decline significantly increased the down-drag and axial force of the pile,causing significant settlement.A longer pile presented a larger axial force at the neutral point.Nevertheless,the incremental percentage of the axial force decreased with increasing pile length with the same water table reduction.Because of group effect,the displacement of soil next to the center pile was smaller than that near the corner piles and showed a similar trend as the axial force of the pile.As the water table fell,the static load ratio affecting the progress of pile settlement increased dis-advantageously,possibly inducing excessive pile settlement.A design method for railway pile foundations taking account of lowering groundwater was proposed with an example application,which provided a reference for similar projects.展开更多
In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea sta...In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.展开更多
基金Project supported by the National Natural Science Foundation of China (No. 50823004)the National Key Technology R&D Program of China (No. 2009BAG12A01-C09)+1 种基金the 2013 Doctoral Innovation Funds of Southwest Jiaotong Universitythe Fundamental Research Funds for the Central Universities, China
文摘With the continuous improvement of the train speed, the dynamic environment of trains turns out to be aerodynamic domination. Solving the aerodynamic problems has become one of the key factors of the high-speed train head design. Given that the aerodynamic drag is a significant factor that restrains train speed and energy conservation, reducing the aerodynamic drag is thus an important consideration of the high-speed train head design. However, the reduction of the aerodynamic drag may increase other aerodynamic forces (moments), possibly deteriorating the operational safety of the train. The multi-objective optimization design method of the high-speed train head was proposed in this paper, and the aerodynamic drag and load reduction factor were set to be optimization objectives. The automatic multi-objective optimization design of the high-speed train head can be achieved by integrating a series of procedures into the multi-objective optimization algorithm, such as the establishment of 3D parametric model, the aerodynamic mesh generation, the calculation of the flow field around the train, and the vehicle system dynamics. The correlation between the optimization objectives and optimization variables was analyzed to obtain the most important optimization variables, and a further analysis of the nonlinear relationship between the key optimization variables and the optimization objectives was obtained. After optimization, the aerodynamic drag of optimized train was reduced by up to 4.15%, and the load reduction factor was reduced by up to 1.72%.
文摘对原为沟壑的场地,经回填全风化泥质粉砂岩形成高填方地基。对高填方地基采用3000 k N·m能级强夯预处理后,打设钻孔灌注桩,通过在桩身钢筋笼主筋上安装应力计,在桩身截面和桩周土层分别埋设沉降杆、分层沉降仪,测试桩身轴力、桩身及桩周土层沉降变化情况,得到高填方夯实地基未处理填土层桩侧负摩阻力变化规律。试验结果表明,未处理填土层桩侧摩阻力沿深度呈现"负-正"变化的现象,随着固结时间的增加,端承桩负摩阻力区段大于摩擦桩。端承桩桩侧土层提供的最大负摩阻力约是摩擦桩的1.18~2.56倍,桩周土层密实度对桩侧最大负摩阻力有影响。采用一阶负指数函数拟合得到桩身下拉荷载预测模型,随着固结时间的增加,作用于桩身的下拉荷载趋于定值,作用于端承桩的下拉荷载比摩擦桩高41.2%~55.4%,从控制负摩阻力角度推导出高填方夯实地基摩擦桩桩长设计计算方法。桩身中性点位置均随固结时间增加而逐渐下移,端承桩中性点深度较摩擦桩平均大0.7 m。
基金Project supported by the Basic Science Center Program for Multiphase Evolution in Hypergravity at the National Natural Science Foundation of China(No.51988101)the Chinese Program of Introducing Talents of Discipline to University(111 Project)(No.B18047)the Key Research and Development Program of Zhejiang Province(No.2019C03111),China。
文摘Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions,which may exceed the settlement limit and threaten the safe operation of high-speed trains.However,the effect of groundwater reduction on a long-pile group(greater than 20 m in length)has not been fully understood,especially in respect of repeated reductions.In this study,a centrifuge test was conducted to investigate the responses of pile groups in silty soils subjected to repeated falls in the water table.The behavior of the piles was discussed based both on the test and on 3D numerical analyses.With the derived coef-ficientβfor the axial force evaluation of the pile,the effect of lowering the water table on the railway pile foundation could be seen.Results of the tests and numerical analyses indicated that the water table decline significantly increased the down-drag and axial force of the pile,causing significant settlement.A longer pile presented a larger axial force at the neutral point.Nevertheless,the incremental percentage of the axial force decreased with increasing pile length with the same water table reduction.Because of group effect,the displacement of soil next to the center pile was smaller than that near the corner piles and showed a similar trend as the axial force of the pile.As the water table fell,the static load ratio affecting the progress of pile settlement increased dis-advantageously,possibly inducing excessive pile settlement.A design method for railway pile foundations taking account of lowering groundwater was proposed with an example application,which provided a reference for similar projects.
文摘In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.
