Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static me...Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.展开更多
The dynamic response stability of the vibrating screen is an important factor affecting the screening effect and the structural performance of the vibrating screen.In this paper,to improve dynamic response stability a...The dynamic response stability of the vibrating screen is an important factor affecting the screening effect and the structural performance of the vibrating screen.In this paper,to improve dynamic response stability and screening efficiency,we optimized the configuration of linear screening process parameters based on the co-optimization method with dual objectives via the virtual experiment.Firstly,a coupled DEM-MBK simulation model was established according to the dynamics of linear screen,and the dy-namic response law of the screen machine under material impact was investigated.Secondly,the quantitative index of dynamic response stability according to the time-domain characteristics of the centroid amplitude was established.The trend and significance of three types of screening process pa-rameters,including excitation,damping and structure,on the screening efficiency and dynamic response stability were analyzed through virtual orthogonal experiments.Finally,a parameter configuration scheme to achieve co-optimization was proposed based on the comprehensive balance method.The virtual experiment results show that the screening efficiency and dynamic response stability of the proposed scheme are improved by 3.28%and 49.07%,respectively,compared with the empirical parameter configuration.Obviously,the co-optimization method can maintain high screening efficiency and dynamic response stability at the same time,which is beneficial to improve the service life of the screen surface and screen body.展开更多
Based on the unified Hauser-Feshbach and exciton model for light nuclei, the calculations of reaction cross sections and the double-differential cross sections for n + 6Li are performed. Since all of the first-particl...Based on the unified Hauser-Feshbach and exciton model for light nuclei, the calculations of reaction cross sections and the double-differential cross sections for n + 6Li are performed. Since all of the first-particle emissions are from the compound nucleus to the discrete levels, the angular momentum coupling effect in pre-equilibrium mechanism must be taken into account. The fitting of the measured data indicates that the three-body break-up process needs to be involved, and the pre-equilibrium reaction mechanism dominates the reaction processes. In light nucleus reactions the recoil effect must be taken into account.展开更多
In the face of complicated, diversified three-dimensional world, the existing 3D GIS data models suffer from certain issues such as data incompatibility, insufficiency in data representation and representation types, ...In the face of complicated, diversified three-dimensional world, the existing 3D GIS data models suffer from certain issues such as data incompatibility, insufficiency in data representation and representation types, among others. It is often hard to meet the requirements of multiple application purposes(users) related to GIS spatial data management and data query and analysis, especially in the case of massive spatial objects. In this study, according to the habits of human thinking and recognition, discrete expressions(such as discrete curved surface(DCS), and discrete body(DB)) were integrated and two novel representation types(including function structure and mapping structure) were put forward. A flexible and extensible ubiquitous knowledgeable data representation model(UKRM) was then constructed, in which structurally heterogeneous multiple expressions(including boundary representation(B-rep), constructive solid geometry(CSG), functional/parameter representation, etc.) were normalized. GIS's ability in representing the massive, complicated and diversified 3D world was thus greatly enhanced. In addition, data reuse was realized, and the bridge linking static GIS to dynamic GIS was built up. Primary experimental results illustrated that UKRM was overwhelmingly superior to the current data models(e.g. IFC, City GML) in describing both regular and irregular spatial objects.展开更多
The study of soil and rigid body system interactions is very important for the exploration of the Moon and Mars worldwide.The discrete element method(DEM)is a relatively accurate simulation method to study dry sand so...The study of soil and rigid body system interactions is very important for the exploration of the Moon and Mars worldwide.The discrete element method(DEM)is a relatively accurate simulation method to study dry sand soil mechanical properties.However,it is not suitable for bodies that are in mutual contact,connected due to constraints or have complex inertia properties due to their geometry.An efficient combination of the two-dimensional discrete element and multibody dynamic modeling method is proposed to solve the problem,in which the contacts and frictions among the granular spheres and the multibody system,including the smooth and rough rigid bodies,are taken into account.In this work,the soil field is modeled by a two-dimensional DEM,and the dynamics of the constrained rigid body system are modeled by the Cartesian method.A detection algorithm is developed to address the interactions between spherical discrete elements and roughly shaped rigid bodies.The advantage of this coupled method is that it enables the simultaneous capture of both responses.Finally,the program is verified by simulation experiments of the three-ball collision and the collision among the rectangular bars and the three balls.Based on this,the movement of the toothed wheel in the granular matter is analyzed,and the results show that the wheel with six teeth and 30°inclination has the fastest forward speed.In extraterrestrial objects,the wheel grip worsens,but the forward speed first increases and then decreases with decreasing gravity acceleration and loads on wheels,which proves that the coupled two-dimensional DEM and multibody dynamic program is effective in solving engineering problems.展开更多
A numerical model is developed for dynamic analysis of large-cylinder breakwaters embedded in soft soil. In the model, the large cylinder is taken as a rigid body divided into elements and the soft soil is replaced by...A numerical model is developed for dynamic analysis of large-cylinder breakwaters embedded in soft soil. In the model, the large cylinder is taken as a rigid body divided into elements and the soft soil is replaced by discrete 3D nonlinear spring-dashpot systems. The numerical model is used to simulate the dynamic response of a large-cylinder breakwater to breaking wave excitation. The effects of the dynamic stress-strain relationship models of the soil, the radius and embedded depth of the cylinder, the nonlinear behaviors of the soil, and the limit strength condition of the soil on the dynamic responses of the large-cylinder structure are investigated with an example given. It is indicated that the above-mentioned factors have significant effects on the dynamic responses of an embedded large cylinder breakwater under breaking wave excitation.展开更多
为研究采煤机螺旋滚筒在多种赋存条件下的振动特性,以MG2×55/250–BWD型薄煤层采煤机为工程对象,优化煤岩接触模型,建立与实际赋存条件相似的多种不同截割工况下煤壁离散元模型。结合DEM–MFBD(Discrete Element Method-Multi Flex...为研究采煤机螺旋滚筒在多种赋存条件下的振动特性,以MG2×55/250–BWD型薄煤层采煤机为工程对象,优化煤岩接触模型,建立与实际赋存条件相似的多种不同截割工况下煤壁离散元模型。结合DEM–MFBD(Discrete Element Method-Multi Flexible Body Dynamics)双向耦合数值模拟方法搭建采煤机截割部刚柔耦合虚拟样机模型与煤壁离散元模型的双向耦合试验平台,通过仿真试验得到不同煤岩工况下螺旋滚筒的截割过程,并分别对其振动特性的变化规律展开分析。研究结果表明:螺旋滚筒在截割过程中,三向均出现不同程度的振动,其中截割阻力方向振动加速度最大,牵引阻力方向振动加速度次之,侧向力方向振动加速度最小。随着模型中夹矸硬度以及层数比例的增加,截割过程中螺旋滚筒的振动强度不断加剧,最大振动加速度有效值的差值达到4403.149 mm/s^(2)。利用短时傅里叶变换将一维振动信号转化为二维时频谱图像,得到不同煤岩工况下振动信息变化特征在时频域中完成较好保留,其时频谱图像的特征样本效果优于各工况的时域一维信号曲线,主频能量位置、范围大小、特征团形状等信息具有明显区别,即使遇到夹矸层数不同,夹矸坚固性系数也存在差异的复杂工况,其时频谱图像中能量特征的分布形式也具有显著差别。通过振动模态分析发现,随着煤壁中含有夹矸硬度的增加,各部位的变形量均发生变化,其中截齿部位变化最为强烈。基于相似理论搭建采煤机振动信号测试试验平台,对不同煤岩工况条件下螺旋滚筒截割过程进行了测试研究,通过追踪螺旋滚筒的振动状态,发现其振动变化规律与双向耦合数值模拟一致。试验测试得到DEM–MFBD数值模拟方法获取的螺旋滚筒振动加速度有效值与依据相似比反推的试验数据之间的误差小于DEM离散元数值模拟方法与实验数据之间的误差,�展开更多
基金the project supported by the National Natural Science Foundation of China(Grant No.52372425)the Fundamental Research Funds for the Central Universities(Science and technology leading talent team project)(Grant No.2022JBXT010).
文摘Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.
基金supported by the Unveils Major Projects of Hubei Province(grant No.2019AEE015)The authors acknowledge the help by Ezhou City Machinery and Equipment Green Intelligent Manufacturing Enterprise and School Joint Innovation Center.
文摘The dynamic response stability of the vibrating screen is an important factor affecting the screening effect and the structural performance of the vibrating screen.In this paper,to improve dynamic response stability and screening efficiency,we optimized the configuration of linear screening process parameters based on the co-optimization method with dual objectives via the virtual experiment.Firstly,a coupled DEM-MBK simulation model was established according to the dynamics of linear screen,and the dy-namic response law of the screen machine under material impact was investigated.Secondly,the quantitative index of dynamic response stability according to the time-domain characteristics of the centroid amplitude was established.The trend and significance of three types of screening process pa-rameters,including excitation,damping and structure,on the screening efficiency and dynamic response stability were analyzed through virtual orthogonal experiments.Finally,a parameter configuration scheme to achieve co-optimization was proposed based on the comprehensive balance method.The virtual experiment results show that the screening efficiency and dynamic response stability of the proposed scheme are improved by 3.28%and 49.07%,respectively,compared with the empirical parameter configuration.Obviously,the co-optimization method can maintain high screening efficiency and dynamic response stability at the same time,which is beneficial to improve the service life of the screen surface and screen body.
文摘Based on the unified Hauser-Feshbach and exciton model for light nuclei, the calculations of reaction cross sections and the double-differential cross sections for n + 6Li are performed. Since all of the first-particle emissions are from the compound nucleus to the discrete levels, the angular momentum coupling effect in pre-equilibrium mechanism must be taken into account. The fitting of the measured data indicates that the three-body break-up process needs to be involved, and the pre-equilibrium reaction mechanism dominates the reaction processes. In light nucleus reactions the recoil effect must be taken into account.
基金supported by the National Natural Science Foundation of China(Grant No.41271196)the Key Project of the 12th Five-year Plan,Chinese Academy of Sciences(Grant No.KZZD-EW-07-02-003)
文摘In the face of complicated, diversified three-dimensional world, the existing 3D GIS data models suffer from certain issues such as data incompatibility, insufficiency in data representation and representation types, among others. It is often hard to meet the requirements of multiple application purposes(users) related to GIS spatial data management and data query and analysis, especially in the case of massive spatial objects. In this study, according to the habits of human thinking and recognition, discrete expressions(such as discrete curved surface(DCS), and discrete body(DB)) were integrated and two novel representation types(including function structure and mapping structure) were put forward. A flexible and extensible ubiquitous knowledgeable data representation model(UKRM) was then constructed, in which structurally heterogeneous multiple expressions(including boundary representation(B-rep), constructive solid geometry(CSG), functional/parameter representation, etc.) were normalized. GIS's ability in representing the massive, complicated and diversified 3D world was thus greatly enhanced. In addition, data reuse was realized, and the bridge linking static GIS to dynamic GIS was built up. Primary experimental results illustrated that UKRM was overwhelmingly superior to the current data models(e.g. IFC, City GML) in describing both regular and irregular spatial objects.
基金supported by the Key Program of National Natural Science Foundation of China(Grant No.11932001)the General Program of National Natural Science Foundation of China(Grant Nos.11772186 and 11772188)for which the authors are grateful.This research was also supported by the Key Laboratory of Hydrodynamics(Ministry of Education).
文摘The study of soil and rigid body system interactions is very important for the exploration of the Moon and Mars worldwide.The discrete element method(DEM)is a relatively accurate simulation method to study dry sand soil mechanical properties.However,it is not suitable for bodies that are in mutual contact,connected due to constraints or have complex inertia properties due to their geometry.An efficient combination of the two-dimensional discrete element and multibody dynamic modeling method is proposed to solve the problem,in which the contacts and frictions among the granular spheres and the multibody system,including the smooth and rough rigid bodies,are taken into account.In this work,the soil field is modeled by a two-dimensional DEM,and the dynamics of the constrained rigid body system are modeled by the Cartesian method.A detection algorithm is developed to address the interactions between spherical discrete elements and roughly shaped rigid bodies.The advantage of this coupled method is that it enables the simultaneous capture of both responses.Finally,the program is verified by simulation experiments of the three-ball collision and the collision among the rectangular bars and the three balls.Based on this,the movement of the toothed wheel in the granular matter is analyzed,and the results show that the wheel with six teeth and 30°inclination has the fastest forward speed.In extraterrestrial objects,the wheel grip worsens,but the forward speed first increases and then decreases with decreasing gravity acceleration and loads on wheels,which proves that the coupled two-dimensional DEM and multibody dynamic program is effective in solving engineering problems.
文摘A numerical model is developed for dynamic analysis of large-cylinder breakwaters embedded in soft soil. In the model, the large cylinder is taken as a rigid body divided into elements and the soft soil is replaced by discrete 3D nonlinear spring-dashpot systems. The numerical model is used to simulate the dynamic response of a large-cylinder breakwater to breaking wave excitation. The effects of the dynamic stress-strain relationship models of the soil, the radius and embedded depth of the cylinder, the nonlinear behaviors of the soil, and the limit strength condition of the soil on the dynamic responses of the large-cylinder structure are investigated with an example given. It is indicated that the above-mentioned factors have significant effects on the dynamic responses of an embedded large cylinder breakwater under breaking wave excitation.
文摘为研究采煤机螺旋滚筒在多种赋存条件下的振动特性,以MG2×55/250–BWD型薄煤层采煤机为工程对象,优化煤岩接触模型,建立与实际赋存条件相似的多种不同截割工况下煤壁离散元模型。结合DEM–MFBD(Discrete Element Method-Multi Flexible Body Dynamics)双向耦合数值模拟方法搭建采煤机截割部刚柔耦合虚拟样机模型与煤壁离散元模型的双向耦合试验平台,通过仿真试验得到不同煤岩工况下螺旋滚筒的截割过程,并分别对其振动特性的变化规律展开分析。研究结果表明:螺旋滚筒在截割过程中,三向均出现不同程度的振动,其中截割阻力方向振动加速度最大,牵引阻力方向振动加速度次之,侧向力方向振动加速度最小。随着模型中夹矸硬度以及层数比例的增加,截割过程中螺旋滚筒的振动强度不断加剧,最大振动加速度有效值的差值达到4403.149 mm/s^(2)。利用短时傅里叶变换将一维振动信号转化为二维时频谱图像,得到不同煤岩工况下振动信息变化特征在时频域中完成较好保留,其时频谱图像的特征样本效果优于各工况的时域一维信号曲线,主频能量位置、范围大小、特征团形状等信息具有明显区别,即使遇到夹矸层数不同,夹矸坚固性系数也存在差异的复杂工况,其时频谱图像中能量特征的分布形式也具有显著差别。通过振动模态分析发现,随着煤壁中含有夹矸硬度的增加,各部位的变形量均发生变化,其中截齿部位变化最为强烈。基于相似理论搭建采煤机振动信号测试试验平台,对不同煤岩工况条件下螺旋滚筒截割过程进行了测试研究,通过追踪螺旋滚筒的振动状态,发现其振动变化规律与双向耦合数值模拟一致。试验测试得到DEM–MFBD数值模拟方法获取的螺旋滚筒振动加速度有效值与依据相似比反推的试验数据之间的误差小于DEM离散元数值模拟方法与实验数据之间的误差,�
