碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数...碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。展开更多
船舶在冰区海域中航行会受到冰水环境阻力的影响,是冰区船舶快速性研究中的重要影响因素。为合理分析冰区船舶的快速性能,该文采用基于离散元(discrete element method,DEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)...船舶在冰区海域中航行会受到冰水环境阻力的影响,是冰区船舶快速性研究中的重要影响因素。为合理分析冰区船舶的快速性能,该文采用基于离散元(discrete element method,DEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法的流固耦合模型模拟船舶冰区航行过程,获得不同航速下的船舶阻力和推进力,进一步计算出螺旋桨的推力、扭矩以及定速航行所需的螺旋桨转速等参数。为研究船体结构、海冰与海水之间的流固耦合作用,文中通过SPH粒子与固定粒子边界相对运动的拟合项直接计算固体与流体之间的相互作用力,建立船体结构、海冰与海水耦合的DEM-SPH模型,并基于该模型分别对船舶在冰区的航行阻力和推进力进行模拟,通过拟合的方式匹配航行阻力和推进力,并考虑尾部流场导致的船体阻力增额,从而预报船舶在特定航速下实现自航所需的螺旋桨转速。此外,文中还模拟了DTMB 5415船模在浮冰区和层冰区中航行的阻力和不同螺旋桨转速下的推力,对船模在不同工况下实现特定航速航行所需的螺旋桨转速进行了预报。计算结果表明:DEM-SPH耦合模型对船-冰、桨-冰作用中的流固耦合过程模拟效果出色,可完整描述船体及尾部伴流场对海冰的拖曳作用;通过文中所述阻力-推力模拟算例及强制力的拟合分析,所形成的基于数值模拟方法的船舶自航下螺旋桨转速预报,可为进一步的试验验证和工程应用推广奠定基础。展开更多
针对鱼类大小分级问题设计了一种自动化高效分级设备,结合鱼的体态形状特征,利用其体厚参数可以较平缓、温和地将鱼进行大小分级,同时增加了倾角调节装置,可根据不同种类的鱼调节设备的结构参数。对设备分级鲫鱼的过程进行了离散元(Disc...针对鱼类大小分级问题设计了一种自动化高效分级设备,结合鱼的体态形状特征,利用其体厚参数可以较平缓、温和地将鱼进行大小分级,同时增加了倾角调节装置,可根据不同种类的鱼调节设备的结构参数。对设备分级鲫鱼的过程进行了离散元(Discrete Element Method,DEM)仿真;设计正交试验,对设备的辊轴转速、倾斜角度以及每秒进鱼量进行了优化,得到设备分级准确率和效率的最优值,为进一步设计优化结构提供参考。展开更多
The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on th...The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on the real shape of coarse particles.First,an improved Viola-Jones algorithm is employed to establish a digitalized 2D particle database for coarse particle shape evaluation and discrete modeling purposes of subgrade filler.Shape indexes of 2D subgrade filler are then computed and statistically analyzed.Finally,numerical simulations are performed to quantitatively investigate the effects of the aspect ratio(AR)and interparticle friction coefficient(μ)on the macro-and micro-mechanical compaction characteristics of subgrade filler based on the discrete element method(DEM).The results show that with the increasing AR,the coarse particles are narrower,leading to the increasing movement of fine particles during compaction,which indicates that it is difficult for slender coarse particles to inhibit the migration of fine particles.Moreover,the average displacement of particles is strongly influenced by the AR,indicating that their occlusion under power relies on particle shapes.The dis-placement and velocity of fine particles are much greater than those of the coarse particles,which shows that compaction is primarily a migration of fine particles.Under the cyclic load,the interparticle friction coefficientμhas little effect on the internal structure of the sample;under the quasi-static loads,however,the increase inμwill lead to a significant increase in the porosity of the sample.This study could not only provide a novel approach to investigate the compaction mechanism but also establish a new theoretical basis for the evaluation of intelligent subgrade compaction.展开更多
文摘碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。
文摘针对鱼类大小分级问题设计了一种自动化高效分级设备,结合鱼的体态形状特征,利用其体厚参数可以较平缓、温和地将鱼进行大小分级,同时增加了倾角调节装置,可根据不同种类的鱼调节设备的结构参数。对设备分级鲫鱼的过程进行了离散元(Discrete Element Method,DEM)仿真;设计正交试验,对设备的辊轴转速、倾斜角度以及每秒进鱼量进行了优化,得到设备分级准确率和效率的最优值,为进一步设计优化结构提供参考。
基金This work was supported by the National Key R&D Program‘Transportation Infrastructure’project(No.2022YFB2603400).
文摘The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on the real shape of coarse particles.First,an improved Viola-Jones algorithm is employed to establish a digitalized 2D particle database for coarse particle shape evaluation and discrete modeling purposes of subgrade filler.Shape indexes of 2D subgrade filler are then computed and statistically analyzed.Finally,numerical simulations are performed to quantitatively investigate the effects of the aspect ratio(AR)and interparticle friction coefficient(μ)on the macro-and micro-mechanical compaction characteristics of subgrade filler based on the discrete element method(DEM).The results show that with the increasing AR,the coarse particles are narrower,leading to the increasing movement of fine particles during compaction,which indicates that it is difficult for slender coarse particles to inhibit the migration of fine particles.Moreover,the average displacement of particles is strongly influenced by the AR,indicating that their occlusion under power relies on particle shapes.The dis-placement and velocity of fine particles are much greater than those of the coarse particles,which shows that compaction is primarily a migration of fine particles.Under the cyclic load,the interparticle friction coefficientμhas little effect on the internal structure of the sample;under the quasi-static loads,however,the increase inμwill lead to a significant increase in the porosity of the sample.This study could not only provide a novel approach to investigate the compaction mechanism but also establish a new theoretical basis for the evaluation of intelligent subgrade compaction.
