Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and pu...Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.展开更多
针对在负压干扰条件下,控制器局域网(Control Area Network,CAN)总线接收器存在工作异常以及传输延时较大的问题,设计了一种超宽共模输入范围的可变速率的CAN(CAN with Flexible Data rate,CAN FD)接收器。该设计通过电平移位与共射级...针对在负压干扰条件下,控制器局域网(Control Area Network,CAN)总线接收器存在工作异常以及传输延时较大的问题,设计了一种超宽共模输入范围的可变速率的CAN(CAN with Flexible Data rate,CAN FD)接收器。该设计通过电平移位与共射级相结合的方式,以减少总线信号对输入级静态工作点影响,拓展接收器的负压输入范围;采用电阻分压的方式衰减总线信号电平,以减轻输入级差分对管的耐压负担;引入低温漂电压,以产生高精度的翻转阈值;在输出级模块增添限幅晶体管,以限制接收器输出摆幅,提升传输速度。芯片采用0.18μm 60 V双极、互补、双扩散金属氧化物半导体工艺进行电路设计。仿真结果表明,在5 V电源电压条件下,设计接收器的共模输入范围为-60~60 V,阈值电压为0.71 V,迟滞门限为120 mV,温漂为0.057 mV/℃,平均传输延时小于55 ns。与相关设计相比,设计的接收器具有较宽的共模输入范围,传输延时较小,符合CAN协议规范。展开更多
针对传统超声波测风装置测风精度不高、抗噪声能力弱,提出了一种改进多重信号分类(multiple signal classification,MUSIC)算法的超声波测风方法。采用一种弧形6阵元超声波传感器阵列的测风结构,推导其阵列流型;在此基础上,添加小波阈...针对传统超声波测风装置测风精度不高、抗噪声能力弱,提出了一种改进多重信号分类(multiple signal classification,MUSIC)算法的超声波测风方法。采用一种弧形6阵元超声波传感器阵列的测风结构,推导其阵列流型;在此基础上,添加小波阈值降噪算法提高信号信噪比,降低噪声信号协方差矩阵的秩;再使用PHAT加权广义互相关时延估计算法以提高时延估计的准确性,同时根据时延关系对传统MUSIC算法矢量矩阵进行改进;最后通过MUSIC算法实现对风速风向的测量。理论分析与仿真结果表明:改进后的MUSIC算法具有较好的抗噪性能和较高的风参数测量精度,测量风速绝对误差达到0.15 m/s,风向绝对误差达到2°,可以应用于对风参数要求较高的场景。展开更多
Based on the continuous development of motion capture technology for ordinary video images, unmarked optical motion capture has become the fastest human posture recognition technology. Compared with other technical pr...Based on the continuous development of motion capture technology for ordinary video images, unmarked optical motion capture has become the fastest human posture recognition technology. Compared with other technical products, Google’s 3D human body recognition framework—Mediapipe is the most mature representative in this field. However, Mediapipe also has many defects in the detection of 3D human posture. In this paper, firstly, to solve the problem of inaccurate detection of human posture by Mediapipe, the accuracy of 2D human posture detection is improved through the speed threshold correction method for each joint;According to the problem that the monocular camera can not detect the depth Z value in the human posture data accurately, the Z value of the joint point is corrected for the human tilt angle through statistics;Then, according to the inaccurate recognition of Z value caused by large body posture, the accurate correction of Z value of human posture under different body posture is realized by normalizing the simulation proportion of each body limb;Finally, in order to solve the problem of jitter, lag problem and periodic noise in multiple frames caused by the speed change of human joints, one euro filtering and mean filtering of joint data are carried out. This paper verifies that the accuracy of 3D human posture detection based on the improved Mediapipe is more than 90% through the multi-pose recognition test for people of different heights, weights, ages and gender.展开更多
A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flot...A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.展开更多
基金supported by the National Natural Science Foundation of China(Project no.52078489)and the Fundamental Research Funds for the Central Universities of Central South University(Project no.2021zzts0772)to which the authors are most grateful.
文摘Purpose–This paper aims to study the influence of aerodynamics force of trains passing each other on the dynamic response of vehicle bridge coupling system based on numerical simulation and multi-body dynamics and put forward the speed threshold for safe running of train under different crosswind speeds.Design/methodology/approach–The computational fluid dynamics method is adopted to simulate the aerodynamic force in the whole process of train passing each other by using dynamic grid technology.The dynamic model of vehicle-bridge coupling system is established considering the effects of aerodynamic force of train passing each other under crosswind,the dynamic response of train intersection on the bridge under crosswind is computed and the running safety of the train is evaluated.Findings–The aerodynamic force of trains’intersection has little effects on the derailment factor,lateral wheel-rail force and vertical acceleration of train,but it increases the offload factor of train and significantly increases the lateral acceleration of train.The crosswind has a significant effect on increasing the derailment factor,lateral wheel-rail force and offload factor of train.The offload factor of train is the key factor to control the threshold of train speed.The impact of the aerodynamic force of trains’intersection on running safety cannot be ignored.When the extreme values of crosswind wind speed are 15 m$s1,20 m$s1 and 25 m$s1,respectively,the corresponding speed thresholds for safe running of train are 350 km$h1,275 km$h1 and 200 km$h1,respectively.Originality/value–The research can provide a more precise numerical method to study the running safety of high-speed trains under the aerodynamic effect of trains passing each other on bridge in crosswind.
文摘针对传统超声波测风装置测风精度不高、抗噪声能力弱,提出了一种改进多重信号分类(multiple signal classification,MUSIC)算法的超声波测风方法。采用一种弧形6阵元超声波传感器阵列的测风结构,推导其阵列流型;在此基础上,添加小波阈值降噪算法提高信号信噪比,降低噪声信号协方差矩阵的秩;再使用PHAT加权广义互相关时延估计算法以提高时延估计的准确性,同时根据时延关系对传统MUSIC算法矢量矩阵进行改进;最后通过MUSIC算法实现对风速风向的测量。理论分析与仿真结果表明:改进后的MUSIC算法具有较好的抗噪性能和较高的风参数测量精度,测量风速绝对误差达到0.15 m/s,风向绝对误差达到2°,可以应用于对风参数要求较高的场景。
文摘Based on the continuous development of motion capture technology for ordinary video images, unmarked optical motion capture has become the fastest human posture recognition technology. Compared with other technical products, Google’s 3D human body recognition framework—Mediapipe is the most mature representative in this field. However, Mediapipe also has many defects in the detection of 3D human posture. In this paper, firstly, to solve the problem of inaccurate detection of human posture by Mediapipe, the accuracy of 2D human posture detection is improved through the speed threshold correction method for each joint;According to the problem that the monocular camera can not detect the depth Z value in the human posture data accurately, the Z value of the joint point is corrected for the human tilt angle through statistics;Then, according to the inaccurate recognition of Z value caused by large body posture, the accurate correction of Z value of human posture under different body posture is realized by normalizing the simulation proportion of each body limb;Finally, in order to solve the problem of jitter, lag problem and periodic noise in multiple frames caused by the speed change of human joints, one euro filtering and mean filtering of joint data are carried out. This paper verifies that the accuracy of 3D human posture detection based on the improved Mediapipe is more than 90% through the multi-pose recognition test for people of different heights, weights, ages and gender.
文摘A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.
文摘植被物候动态是多重因子影响的结果,尤其在对外界扰动响应敏感的青藏高原草地生态系统。本研究利用2000-2020年MODIS 16 d合成的归一化植被指数(normalization difference vegetation index, NDVI)数据,选用动态阈值法提取了青藏高原逐年的植被物候期,探究了青藏高原草地物候动态变化及其对驱动因子的响应。结果表明:1) 2000-2020年青藏高原草地生长季始期(start of the growing season, SOS)从西北向东南呈提前趋势,每年提前约0.19 d;草地生长季末期(end of the growing season, EOS)整体呈推迟趋势,每年推迟约0.19 d;草地生长季长度(length of the growing season, LOS)由西北向东南逐渐增长。2)风速和连续5 d最大降雨(yearly maximum five-day precipitation, RX5day)是影响草地LOS的主要因素,且因子间两两交互作用要强于单个因子对植被物候的影响,尤其表现在RX5day与温度和风速与温度之间的交互。3)草地LOS与风速和RX5day的回归系数有明显的空间异质性。藏北高原草地LOS随风速增大而变长,随RX5day增大而变短。青海高原和藏南谷地的草地LOS随风速增大而变短。川藏高山峡谷区草地LOS随RX5day增大而变长。综上,本研究可为研究区内生态系统保护和畜牧业的发展提供一定科学依据。
