The creation of three-dimensional models from an unorganized set of points is an active research area in computer graphics.One of the purposes of this study is to explore the 3D reconstruction of a cube-type artificia...The creation of three-dimensional models from an unorganized set of points is an active research area in computer graphics.One of the purposes of this study is to explore the 3D reconstruction of a cube-type artificial reef(CTAR)set by linear structured light and binocular stereo vision technology in an underwater environment.The experimental setup is composed of two ca-meras in a stereo vision configuration.The alpha shapes method can be used to construct a surface that most closely reflects the arti-ficial reef set described by the points.A parameter study is conducted to assess the scales of the set(i.e.,usable volume,surface area,projected area,height,and base diameter)on the basis of 3D reconstruction.Experimental results show that the quality of 3D recon-struction in an underwater environment is acceptable for estimating the scale size of the CTAR set.According to the measurement of the scale sizing of the CTAR set,the relationships between the parameters of the CTAR set and the number of CTAR modules were determined.Moreover,the usable volume of the CTAR set can be estimated depending on the basis of the number of CTAR modules.展开更多
From an ingot to a wafer then to a die,wafer thinning plays an important role in the semiconductor industry.To reveal the material removal mechanism of semiconductor at nanoscale,molecular dynamics has been widely use...From an ingot to a wafer then to a die,wafer thinning plays an important role in the semiconductor industry.To reveal the material removal mechanism of semiconductor at nanoscale,molecular dynamics has been widely used to investigate the grinding process.However,most simulation analyses were conducted with a single phase space trajectory,which is stochastic and subjective.In this paper,the stress field in wafer thinning simulations of 4H-SiC was obtained from 50 trajectories with spatial averaging and phase space averaging.The spatial averaging was conducted on a uniform spatial grid for each trajectory.A variable named mask was assigned to the spatial point to reconstruct the shape of the substrate.Different spatial averaging parameters were applied and compared.The result shows that the summation of Voronoi volumes of the atoms in the averaging domain is more appropriate for spatial averaging.The phase space averaging was conducted with multiple trajectories after spatial averaging.The stress field converges with increasing the number of trajectories.The maximum and average relative difference(absolute value)of Mises stress was used as the convergence criterion.The obtained hydrostatic stress in the compression zone is close to the phase transition pressure of 4H-SiC from first principle calculations.展开更多
Rotor clearance is necessary for the safe operation of twin-screw compressors,and it has a major impact on the performance of twin-screw compressors.The purpose of this study was to obtain a rotor tooth profile with r...Rotor clearance is necessary for the safe operation of twin-screw compressors,and it has a major impact on the performance of twin-screw compressors.The purpose of this study was to obtain a rotor tooth profile with reasonable meshing clearance on the rotor end surface,so that the clearance on the rotor contact line would be uniform and the rotor could be smoothly meshed.Under ideal conditions,the rotor of a screw compressor should have no clearance or interference.However,owing to assembly errors,thermal compression,stress deformation,and other factors,a rotor without backlash modification will inevitably produce interference during operation.A new design method based on the Alpha shape solution was proposed to achieve an efficient and high-precision design of the clearance of the twin-screw rotor profile.This method avoids the complex analytical calculations in the traditional envelope principle.The best approximation of the points on the rotor conjugate motion sweeping surface in the points is illuminated using a specific color.The sweeping surface of the screw rotor single-tooth profile is roughly scanned to capture the base point set of the sweeping surface boundary points.The chord length and tilt angle of each interval are calculated using the value of the base point set to adjust the position,phase,and magnification of each interval sweeping surface.Finally,the data point set is converted to the same coordinate system to generate the conjugated rotor profile.An example was used to verify the feasibility and adaptability of this method.Based on the equidistant profile method,the clearance between male and female rotors of a screw compressor was obtained under actual operation conditions.Therefore,this study provides a basis for the meshing clearance design in the machining of twin-screw compressor rotors.展开更多
针对室内环境中超宽带(Ultra-Wideband,UWB)信号易受障碍物遮挡导致非视距(Non Line of Sight,NLOS)误差的问题,本文提出了一种基于激光雷达(Light Detection And Ranging,LiDAR)点云识别UWB NLOS的融合定位方法,该方法利用LiDAR点云信...针对室内环境中超宽带(Ultra-Wideband,UWB)信号易受障碍物遮挡导致非视距(Non Line of Sight,NLOS)误差的问题,本文提出了一种基于激光雷达(Light Detection And Ranging,LiDAR)点云识别UWB NLOS的融合定位方法,该方法利用LiDAR点云信息辅助UWBNLOS识别,并通过UWB视距(LineofSight,LOS)测距值消除LiDAR同时定位与建图(Simultaneous Localization and Mapping,SLAM)过程中的累计误差,从而提高室内融合定位精度和鲁棒性。首先,采用八叉树对LiDAR点云进行处理,根据UWB基准站位置信息构建测距方向,并从LiDAR点云中提取测距方向上相关区域的点云数据。然后,通过3D Alpha Shape算法对所提取点云中可能阻碍UWB信号传播的障碍物进行轮廓提取。此外,根据分析提取的障碍物轮廓和UWB测距方向的空间关系,以此有效判定UWB信号是否存在NLOS测距情况。最后,剔除UWB测距过程中存在的NLOS测距值,通过紧组合方式,采用扩展卡尔曼滤波(EKF)将UWB LOS测距值和LiDAR SLAM的定位信息进行融合解算,消除LiDAR SLAM定位结果中的累积误差,以此提高融合定位精度和鲁棒性。为验证本文所提出的融合定位算法的有效性,通过搭建的融合定位实验平台在教学楼大厅进行了NLOS静态识别实验,在地下停车场进行了动态NLOS识别与动态定位实验。实验结果表明,该方法能够显著提高在室内复杂环境中的NLOS识别与定位的准确性,相较于单传感器定位与UWB原始测距值与LiDAR SLAM紧组合EKF的定位方法,NLOS识别准确率为93.22%,定位精度分别提高了49.24%、47.03%、96.13%,定位误差为0.067 m,实现了亚分米级室内定位。展开更多
基金This research was supported by the National Key R&D Program of China(No.2019YFD0901302)the National Natural Science Foundation of China(No.31802349).
文摘The creation of three-dimensional models from an unorganized set of points is an active research area in computer graphics.One of the purposes of this study is to explore the 3D reconstruction of a cube-type artificial reef(CTAR)set by linear structured light and binocular stereo vision technology in an underwater environment.The experimental setup is composed of two ca-meras in a stereo vision configuration.The alpha shapes method can be used to construct a surface that most closely reflects the arti-ficial reef set described by the points.A parameter study is conducted to assess the scales of the set(i.e.,usable volume,surface area,projected area,height,and base diameter)on the basis of 3D reconstruction.Experimental results show that the quality of 3D recon-struction in an underwater environment is acceptable for estimating the scale size of the CTAR set.According to the measurement of the scale sizing of the CTAR set,the relationships between the parameters of the CTAR set and the number of CTAR modules were determined.Moreover,the usable volume of the CTAR set can be estimated depending on the basis of the number of CTAR modules.
基金supported by National Natural Science Foundation of China(52075208)National Natural Science Foundation of China(U20A6004)+1 种基金National Natural Science Foundation of China(Number:51675211)Shanghai Municipal Science and Technology Major Project(No.2018SHZDZX01)and ZJLab.
文摘From an ingot to a wafer then to a die,wafer thinning plays an important role in the semiconductor industry.To reveal the material removal mechanism of semiconductor at nanoscale,molecular dynamics has been widely used to investigate the grinding process.However,most simulation analyses were conducted with a single phase space trajectory,which is stochastic and subjective.In this paper,the stress field in wafer thinning simulations of 4H-SiC was obtained from 50 trajectories with spatial averaging and phase space averaging.The spatial averaging was conducted on a uniform spatial grid for each trajectory.A variable named mask was assigned to the spatial point to reconstruct the shape of the substrate.Different spatial averaging parameters were applied and compared.The result shows that the summation of Voronoi volumes of the atoms in the averaging domain is more appropriate for spatial averaging.The phase space averaging was conducted with multiple trajectories after spatial averaging.The stress field converges with increasing the number of trajectories.The maximum and average relative difference(absolute value)of Mises stress was used as the convergence criterion.The obtained hydrostatic stress in the compression zone is close to the phase transition pressure of 4H-SiC from first principle calculations.
文摘Rotor clearance is necessary for the safe operation of twin-screw compressors,and it has a major impact on the performance of twin-screw compressors.The purpose of this study was to obtain a rotor tooth profile with reasonable meshing clearance on the rotor end surface,so that the clearance on the rotor contact line would be uniform and the rotor could be smoothly meshed.Under ideal conditions,the rotor of a screw compressor should have no clearance or interference.However,owing to assembly errors,thermal compression,stress deformation,and other factors,a rotor without backlash modification will inevitably produce interference during operation.A new design method based on the Alpha shape solution was proposed to achieve an efficient and high-precision design of the clearance of the twin-screw rotor profile.This method avoids the complex analytical calculations in the traditional envelope principle.The best approximation of the points on the rotor conjugate motion sweeping surface in the points is illuminated using a specific color.The sweeping surface of the screw rotor single-tooth profile is roughly scanned to capture the base point set of the sweeping surface boundary points.The chord length and tilt angle of each interval are calculated using the value of the base point set to adjust the position,phase,and magnification of each interval sweeping surface.Finally,the data point set is converted to the same coordinate system to generate the conjugated rotor profile.An example was used to verify the feasibility and adaptability of this method.Based on the equidistant profile method,the clearance between male and female rotors of a screw compressor was obtained under actual operation conditions.Therefore,this study provides a basis for the meshing clearance design in the machining of twin-screw compressor rotors.
文摘针对室内环境中超宽带(Ultra-Wideband,UWB)信号易受障碍物遮挡导致非视距(Non Line of Sight,NLOS)误差的问题,本文提出了一种基于激光雷达(Light Detection And Ranging,LiDAR)点云识别UWB NLOS的融合定位方法,该方法利用LiDAR点云信息辅助UWBNLOS识别,并通过UWB视距(LineofSight,LOS)测距值消除LiDAR同时定位与建图(Simultaneous Localization and Mapping,SLAM)过程中的累计误差,从而提高室内融合定位精度和鲁棒性。首先,采用八叉树对LiDAR点云进行处理,根据UWB基准站位置信息构建测距方向,并从LiDAR点云中提取测距方向上相关区域的点云数据。然后,通过3D Alpha Shape算法对所提取点云中可能阻碍UWB信号传播的障碍物进行轮廓提取。此外,根据分析提取的障碍物轮廓和UWB测距方向的空间关系,以此有效判定UWB信号是否存在NLOS测距情况。最后,剔除UWB测距过程中存在的NLOS测距值,通过紧组合方式,采用扩展卡尔曼滤波(EKF)将UWB LOS测距值和LiDAR SLAM的定位信息进行融合解算,消除LiDAR SLAM定位结果中的累积误差,以此提高融合定位精度和鲁棒性。为验证本文所提出的融合定位算法的有效性,通过搭建的融合定位实验平台在教学楼大厅进行了NLOS静态识别实验,在地下停车场进行了动态NLOS识别与动态定位实验。实验结果表明,该方法能够显著提高在室内复杂环境中的NLOS识别与定位的准确性,相较于单传感器定位与UWB原始测距值与LiDAR SLAM紧组合EKF的定位方法,NLOS识别准确率为93.22%,定位精度分别提高了49.24%、47.03%、96.13%,定位误差为0.067 m,实现了亚分米级室内定位。
