Using traditional particle tracking velocimetry based on optical flow for measuring areas with large velocity gradient changes may cause oversmoothing,resulting in significant measurement errors.To address this proble...Using traditional particle tracking velocimetry based on optical flow for measuring areas with large velocity gradient changes may cause oversmoothing,resulting in significant measurement errors.To address this problem,the traditional particle tracking velocimetry method based on an optical flow was improved.The level set segmentation algorithm was used to obtain the boundary contour of the region with large velocity gradient changes,and the non-uniform flow field was divided into regions according to the boundary contour to obtain sub-regions with uniform velocity distribution.The particle tracking velocimetry method based on optical flow was used to measure the granular flow velocity in each sub-region,thus avoiding the problem of granular flow distribution.The simulation results show that the measurement accuracy of this method is approximately 10%higher than that of traditional methods.The method was applied to a velocity measurement experiment on dense granular flow in silos,and the velocity distribution of the granular flow was obtained,verifying the practicality of the method in granular flow fields.展开更多
This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moo...This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.展开更多
Stereoscopic particle image velocimetry technology was employed to investigate the planar three-dimensional velocity field and the process of proppant entry into branch fractures in a fracture configuration of“vertic...Stereoscopic particle image velocimetry technology was employed to investigate the planar three-dimensional velocity field and the process of proppant entry into branch fractures in a fracture configuration of“vertical main fracture-vertical branch fracture”intersecting at a 90°angle.This study analyzed the effects of pumping rate,fracturing fluid viscosity,proppant particle size,and fracture width on the transport behavior of proppant into branch fractures.Based on the deflection behavior of proppant,the main fractures can be divided into five regions:pre-entry transition,pre-entry stabilization,deflection entry at the fracture mouth,rear absorption entry,and movement away from the fracture mouth.Proppant primarily deflects into the branch fracture at the fracture mouth,with a small portion drawn in from the rear of the intersection.Increasing the pumping rate,reducing the proppant particle size,and widening the branch fracture are conducive to promoting proppant deflection into the branch.With increasing fracturing fluid viscosity,the ability of proppant to enter the branch fracture first improves and then declines,indicating that excessively high viscosity is unfavorable for proppant entry into the branch.During field operations,a high pumping rate and micro-to small-sized proppant can be used in the early stage to ensure effective placement in the branch fractures,followed by medium-to large-sized proppant to ensure adequate placement in the main fracture and enhance the overall conductivity of the fracture network.展开更多
文摘Using traditional particle tracking velocimetry based on optical flow for measuring areas with large velocity gradient changes may cause oversmoothing,resulting in significant measurement errors.To address this problem,the traditional particle tracking velocimetry method based on an optical flow was improved.The level set segmentation algorithm was used to obtain the boundary contour of the region with large velocity gradient changes,and the non-uniform flow field was divided into regions according to the boundary contour to obtain sub-regions with uniform velocity distribution.The particle tracking velocimetry method based on optical flow was used to measure the granular flow velocity in each sub-region,thus avoiding the problem of granular flow distribution.The simulation results show that the measurement accuracy of this method is approximately 10%higher than that of traditional methods.The method was applied to a velocity measurement experiment on dense granular flow in silos,and the velocity distribution of the granular flow was obtained,verifying the practicality of the method in granular flow fields.
文摘This paper addresses the challenges of insufficient navigation accuracy,low path-planning efficiency,and poor environmental adaptability faced by deep space rovers in complex extraterrestrial environments(e.g.,the Moon and Mars).A novel autonomous navigation scheme is proposed that integrates laser Doppler velocimetry(LDV)with star trackers(ST)and inertial navigation system(INS).The scheme suppresses slip errors from wheel odometry through non-contact,high-precision laser speed measurement(accuracy better than 0.1%).By deeply fusing multi-source data via a Kalman filter algorithm,high-precision positioning is realized under extreme extraterrestrial conditions such as weak illumination and dust coverage.This solution features high accuracy,non-contact measurement,and anti-interference capabilities,significantly improving the navigation accuracy and autonomy of deep space rovers in complex environments.
基金Supported by Joint Funds of the National Natural Science Foundation of China(U23B6004).
文摘Stereoscopic particle image velocimetry technology was employed to investigate the planar three-dimensional velocity field and the process of proppant entry into branch fractures in a fracture configuration of“vertical main fracture-vertical branch fracture”intersecting at a 90°angle.This study analyzed the effects of pumping rate,fracturing fluid viscosity,proppant particle size,and fracture width on the transport behavior of proppant into branch fractures.Based on the deflection behavior of proppant,the main fractures can be divided into five regions:pre-entry transition,pre-entry stabilization,deflection entry at the fracture mouth,rear absorption entry,and movement away from the fracture mouth.Proppant primarily deflects into the branch fracture at the fracture mouth,with a small portion drawn in from the rear of the intersection.Increasing the pumping rate,reducing the proppant particle size,and widening the branch fracture are conducive to promoting proppant deflection into the branch.With increasing fracturing fluid viscosity,the ability of proppant to enter the branch fracture first improves and then declines,indicating that excessively high viscosity is unfavorable for proppant entry into the branch.During field operations,a high pumping rate and micro-to small-sized proppant can be used in the early stage to ensure effective placement in the branch fractures,followed by medium-to large-sized proppant to ensure adequate placement in the main fracture and enhance the overall conductivity of the fracture network.
