Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computa...Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computational treatments.The flow velocity has a large spatial differentiation which is more likely to produce non-linear flow and additional head losses on and nearby intersections in such shaped fractures,therefore it is necessary to understand and quantify them.In this study,both laboratory experiments and numerical simulations were performed to investigate the total head loss on and nearby the intersections as well as the local head loss exactly on the intersections,which were not usually paid sufficient attention or even ignored.The investigation results show that these two losses account for 29.17%-84.97%and 0-73.57%of the entire total head loss in a fracture,respectively.As a result,they should be necessarily considered for groundwater modeling in fractured rocks.Furthermore,both head losses become larger when aperture and flow rate increase and intersection length decreases.Particularly,the ratios of these two head losses to the entire total head loss in a fracture could be well statistically explained by power regression equations with variables of aperture,intersection length,and flow rates,both of which achieved high coefficients of determination.It could be feasible through this type of study to provide a way on how to adjust the groundwater head from those obtained by numerical simulations based on the traditional linear flow model.Finally,it is practicable and effective to implement the investigation approach combining laboratory experiments with numerical simulations for quantifying the head losses on and nearby the intersections between disc-shaped fractures.展开更多
Manufacturing micro-holes in non-conductive ceramics presents significant challenges in precision machining,particularly due to the absence of central abrasive grains in micro-grinding wheels.This study investigates h...Manufacturing micro-holes in non-conductive ceramics presents significant challenges in precision machining,particularly due to the absence of central abrasive grains in micro-grinding wheels.This study investigates helical grinding under conditions where the central abrasive grain is absent,focusing on the formation of undeformed chips.It was observed that nearly all microgrinding wheels,regardless of their manufacturing process or grain size,exhibit a central grain absence,with larger grain sizes leading to more extensive absence areas.Analysis revealed that residual patterns at the bottom of machined holes depend on the ratio of the absence zone diameter to the wheel's eccentricity.Analytical models were developed to describe the heights of cylindrical and disc-shaped residues,which were subsequently validated through kinematic simulations.The removal mechanisms for these residues differ;cylindrical residues,which cannot be removed by grinding,cause interference and should be avoided,while disc-shaped residues removal depends on the protrusion height of the first grain,influencing contact with the wheel's end face and subsequent grinding actions.Experimental validation using SiC_(p)/Al demonstrated that cylindrical residues create distinct ring-shaped wear marks,significantly increasing cutting forces,whereas discshaped residues result in hat-shaped wear marks and higher cutting forces when the first grain's protrusion is insufficient.Additionally,inadequate lubrication and chip removal can lead to chip adhesion starting from the absence zone.These findings enhance the theoretical framework of helical grinding/milling and provide valuable insights for precision machining of micro-holes in nonconductive ceramics.展开更多
基金supported by National Key Research and Development Program of China(No.2020 YFC1807100,No.2019YFC1806205)National Natural Science Foundation of China(No.41572240)。
文摘Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computational treatments.The flow velocity has a large spatial differentiation which is more likely to produce non-linear flow and additional head losses on and nearby intersections in such shaped fractures,therefore it is necessary to understand and quantify them.In this study,both laboratory experiments and numerical simulations were performed to investigate the total head loss on and nearby the intersections as well as the local head loss exactly on the intersections,which were not usually paid sufficient attention or even ignored.The investigation results show that these two losses account for 29.17%-84.97%and 0-73.57%of the entire total head loss in a fracture,respectively.As a result,they should be necessarily considered for groundwater modeling in fractured rocks.Furthermore,both head losses become larger when aperture and flow rate increase and intersection length decreases.Particularly,the ratios of these two head losses to the entire total head loss in a fracture could be well statistically explained by power regression equations with variables of aperture,intersection length,and flow rates,both of which achieved high coefficients of determination.It could be feasible through this type of study to provide a way on how to adjust the groundwater head from those obtained by numerical simulations based on the traditional linear flow model.Finally,it is practicable and effective to implement the investigation approach combining laboratory experiments with numerical simulations for quantifying the head losses on and nearby the intersections between disc-shaped fractures.
基金supported by the National Natural Science Foundation of China(No.U1737201)。
文摘Manufacturing micro-holes in non-conductive ceramics presents significant challenges in precision machining,particularly due to the absence of central abrasive grains in micro-grinding wheels.This study investigates helical grinding under conditions where the central abrasive grain is absent,focusing on the formation of undeformed chips.It was observed that nearly all microgrinding wheels,regardless of their manufacturing process or grain size,exhibit a central grain absence,with larger grain sizes leading to more extensive absence areas.Analysis revealed that residual patterns at the bottom of machined holes depend on the ratio of the absence zone diameter to the wheel's eccentricity.Analytical models were developed to describe the heights of cylindrical and disc-shaped residues,which were subsequently validated through kinematic simulations.The removal mechanisms for these residues differ;cylindrical residues,which cannot be removed by grinding,cause interference and should be avoided,while disc-shaped residues removal depends on the protrusion height of the first grain,influencing contact with the wheel's end face and subsequent grinding actions.Experimental validation using SiC_(p)/Al demonstrated that cylindrical residues create distinct ring-shaped wear marks,significantly increasing cutting forces,whereas discshaped residues result in hat-shaped wear marks and higher cutting forces when the first grain's protrusion is insufficient.Additionally,inadequate lubrication and chip removal can lead to chip adhesion starting from the absence zone.These findings enhance the theoretical framework of helical grinding/milling and provide valuable insights for precision machining of micro-holes in nonconductive ceramics.
