To investigate the effect of rail pad viscoelasticity on vehicle-track-bridge coupled vibration,the fractional Voigt and Maxwell model in parallel(FVMP)was used to characterize the viscoelastic properties of the rail ...To investigate the effect of rail pad viscoelasticity on vehicle-track-bridge coupled vibration,the fractional Voigt and Maxwell model in parallel(FVMP)was used to characterize the viscoelastic properties of the rail pad based on dynamic performance test results.The FVMP model was then incorporated into the vehicle-track-bridge nonlinear coupled model,and its dynamic response was solved using a cross-iteration algorithm with a relaxation factor.Results indicate that the nonlinear coupled model achieves good convergence when the time step is less than 0.001 s,with the cross-iteration algorithm adjusting the wheel-rail force.In particular,the best convergence is achieved when the relaxation factor is within the range of 0.3-0.5.The FVMP model effectively characterizes the viscoelasticity of rail pads across a temperature range of±20℃and a frequency range of 1-1000 Hz.The viscoelasticity of rail pads significantly affects high-frequency vibrations in the coupled system,particularly around 50 Hz,corresponding to the wheel-rail coupled resonance range.Considering rail pad viscoelasticity is essential for accurately predicting track structure vibrations.展开更多
针对目前黄连(Coptis chinensis)人工收获劳动强度大、效率低的问题,该研究在分析黄连种植农艺特性的基础上,提出了一种交替式黄连挖掘装置。首先,在对挖掘装置关键部件曲柄摇杆机构运动学建模的基础上,利用遗传算法,将黄连根土复合体...针对目前黄连(Coptis chinensis)人工收获劳动强度大、效率低的问题,该研究在分析黄连种植农艺特性的基础上,提出了一种交替式黄连挖掘装置。首先,在对挖掘装置关键部件曲柄摇杆机构运动学建模的基础上,利用遗传算法,将黄连根土复合体被抛出时的最大速度作为目标函数,以杆长、最小传动角、挖掘深度、最小切土厚度、入土角、切土轨迹、抛出位置为约束条件对曲柄摇杆机构各杆杆长进行了优化求解。进一步,采用图像重建法建立了黄连根茎的三维模型,运用离散元法(discrete element method,DEM)构建了挖掘装置-黄连根茎-土壤的离散元复合模型,并联合多体动力学软件RecurDyn进行了挖掘过程的耦合仿真分析,黄连根土复合体的运动过程及状态变化表明,挖掘装置挖掘性能符合设计要求。最后,制作试验样机进行挖掘性能试验,得到了挖掘装置在前进速度为0.5m/s、曲柄转速为300r/min时挖掘性能最优,其抛送合格率、挖松率、损伤率分别为93.15%、99.28%、2.95%。试验结果表明,该挖掘装置的挖掘性能满足黄连根茎的挖掘要求,可为黄连机械化收获装备的开发提供参考。展开更多
掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body ...掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body dynamics,离散单元法-多柔性体动力学)双向耦合技术的回转台疲劳寿命预测方法。首先,建立了掘进机截割部与回转台的空间受力模型,明确了截割部与回转台的受力规律。然后,联合RecurDyn与EDEM软件对回转台进行双向刚柔耦合动力学仿真分析,获得了回转台在工作状态下的应力分布。最后,利用拉丁超立方抽样法选取15组掘进机服役参数作为输入,以回转台疲劳寿命为响应,建立了对应的Kriging代理模型,并利用粒子群优化算法对代理模型进行寻优,得到了回转台在最佳服役参数下的疲劳寿命。结果表明,当掘进机的截割头转速为54 r/min、回转台横摆速度为1.003 m/min、截割臂垂直摆角为7°时,回转台的疲劳寿命最长。结合DEM-MFBD双向耦合技术、Kriging代理模型与粒子群优化算法来探究掘进机的最佳服役参数,可为回转类部件的优化设计提供新思路。展开更多
为提高现有作物生长模型单产模拟精度,明确土壤水分供需变化与产量之间的动态关系,该研究构建了水文—作物生长耦合模型SWAT-EPIC(soil and water assessment tool-environmental policy integrated climate)。基于参数敏感性优化的扩...为提高现有作物生长模型单产模拟精度,明确土壤水分供需变化与产量之间的动态关系,该研究构建了水文—作物生长耦合模型SWAT-EPIC(soil and water assessment tool-environmental policy integrated climate)。基于参数敏感性优化的扩展傅里叶幅度敏感性检验算法(extended fourier amplitude sensitivity test,E-FAST),在陕北黄土高原建立包含土壤碳动态评估的苹果单产评估体系。结果表明,优化后的模型在旱作苹果单产的模拟精度误差减少了38.98%,模拟RMSE=2.56%,RRMSE≈9.8%,具有良好的模拟性能。降水对果园浅层土壤水分补给具有直接作用,而深层水分持续消耗加剧干旱胁迫,成为限制苹果单产提升的关键因素。此外,农地改种果园后0~10m土壤有机碳储量提升了14.85%。本研究表明,通过整合水文过程与作物生长机制,SWAT-EPIC耦合模型能够更全面反演区域水分与产量的响应关系,为干旱区果园水分管理与可持续高产提供科学依据。展开更多
基金Project(2023ZDZX0008)supported by the Sichuan Major Science and Technology Project,ChinaProject(52308468)supported by the National Natural Science Foundation of ChinaProject(2022JBQY009)supported by the Fundamental Research Funds for the Central Universities(Science and Technology Leading Talent Team Project),China。
文摘To investigate the effect of rail pad viscoelasticity on vehicle-track-bridge coupled vibration,the fractional Voigt and Maxwell model in parallel(FVMP)was used to characterize the viscoelastic properties of the rail pad based on dynamic performance test results.The FVMP model was then incorporated into the vehicle-track-bridge nonlinear coupled model,and its dynamic response was solved using a cross-iteration algorithm with a relaxation factor.Results indicate that the nonlinear coupled model achieves good convergence when the time step is less than 0.001 s,with the cross-iteration algorithm adjusting the wheel-rail force.In particular,the best convergence is achieved when the relaxation factor is within the range of 0.3-0.5.The FVMP model effectively characterizes the viscoelasticity of rail pads across a temperature range of±20℃and a frequency range of 1-1000 Hz.The viscoelasticity of rail pads significantly affects high-frequency vibrations in the coupled system,particularly around 50 Hz,corresponding to the wheel-rail coupled resonance range.Considering rail pad viscoelasticity is essential for accurately predicting track structure vibrations.
文摘针对目前黄连(Coptis chinensis)人工收获劳动强度大、效率低的问题,该研究在分析黄连种植农艺特性的基础上,提出了一种交替式黄连挖掘装置。首先,在对挖掘装置关键部件曲柄摇杆机构运动学建模的基础上,利用遗传算法,将黄连根土复合体被抛出时的最大速度作为目标函数,以杆长、最小传动角、挖掘深度、最小切土厚度、入土角、切土轨迹、抛出位置为约束条件对曲柄摇杆机构各杆杆长进行了优化求解。进一步,采用图像重建法建立了黄连根茎的三维模型,运用离散元法(discrete element method,DEM)构建了挖掘装置-黄连根茎-土壤的离散元复合模型,并联合多体动力学软件RecurDyn进行了挖掘过程的耦合仿真分析,黄连根土复合体的运动过程及状态变化表明,挖掘装置挖掘性能符合设计要求。最后,制作试验样机进行挖掘性能试验,得到了挖掘装置在前进速度为0.5m/s、曲柄转速为300r/min时挖掘性能最优,其抛送合格率、挖松率、损伤率分别为93.15%、99.28%、2.95%。试验结果表明,该挖掘装置的挖掘性能满足黄连根茎的挖掘要求,可为黄连机械化收获装备的开发提供参考。
文摘掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body dynamics,离散单元法-多柔性体动力学)双向耦合技术的回转台疲劳寿命预测方法。首先,建立了掘进机截割部与回转台的空间受力模型,明确了截割部与回转台的受力规律。然后,联合RecurDyn与EDEM软件对回转台进行双向刚柔耦合动力学仿真分析,获得了回转台在工作状态下的应力分布。最后,利用拉丁超立方抽样法选取15组掘进机服役参数作为输入,以回转台疲劳寿命为响应,建立了对应的Kriging代理模型,并利用粒子群优化算法对代理模型进行寻优,得到了回转台在最佳服役参数下的疲劳寿命。结果表明,当掘进机的截割头转速为54 r/min、回转台横摆速度为1.003 m/min、截割臂垂直摆角为7°时,回转台的疲劳寿命最长。结合DEM-MFBD双向耦合技术、Kriging代理模型与粒子群优化算法来探究掘进机的最佳服役参数,可为回转类部件的优化设计提供新思路。
