Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model de...Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.展开更多
In practice,different design methods are used in solving geotechnical problems depending on the type of issue such as the tunneling,braced excavation,or bearing capacity of a foundation,that is,the basic mechanism of ...In practice,different design methods are used in solving geotechnical problems depending on the type of issue such as the tunneling,braced excavation,or bearing capacity of a foundation,that is,the basic mechanism of the design method differs depending on the problems even for the same ground.A numerical analysis using the finite element method has recently become familiar owing to an improved computing performance;however,it is not widely used in the design of geotechnical problems including tunnel excavation owing to the reliability of the constitutive model of the ground material.If a constitutive model of soils can properly express the properties of the ground material,a numerical analysis will play a vital role in solving the geotechnical problems.In this paper,the current state of a numerical analysis and its applicability in tunnel design are discussed.Herein,the simulation of the ground behavior during tunnel excavation is carried out using sandy and clay ground parameters for shallow and deep tunnel excavations.This paper is mainly focused on the effects of tunnel excavation under three-dimensional(3D)conditions,as well as the current design method.Non-linear 2D and 3D finite element analyses have been conducted,in which the elastoplastic sub-loading tij model has been used as a constitutive model of the soil.The performance and acceptability of the constitutive model have already been proven to reproduce the results of various model tests on different geotechnical problems such as the tunneling,braced excavation,and bearing capacity of a foundation,as well as the measured field data.It was found that a 2D finite element analysis where the rate of stress release is considered,can be used for the prediction of the ground deformation and surface settlement;however,it does not provide rational information in the prediction of tunnel lining forces such as the stress,bending moment,and axial force,which emphasize the necessity of a 3D analysis with a proper construction process in a tunnel design.展开更多
The three-dimensional （3D） deformation effect of the slope engineering under the step-by-step excavation for the Antaibao surface mine was analyzed using the FLAC^3D technique. An optimal excavated scheme with a rel...The three-dimensional （3D） deformation effect of the slope engineering under the step-by-step excavation for the Antaibao surface mine was analyzed using the FLAC^3D technique. An optimal excavated scheme with a relatively steeper slope angle of 47° instead of 30° was successfully implemented at the west wall in the geological section 73200 of the mine area, where the 3D effect of the nonlinear large deformation of the slope was taken into account. Based on the above research conclusion, put forward the countermeasures of shortening mining length, excavating by different regions, timely foot backfilling to protect the excavated slope, and monitoring and feedback adjustment by studying the nonlinear effect. The results show that these countermeasures are effective in controlling maximum deformation and increasing the stability of the slope.展开更多
During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a chang...During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree of inhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.展开更多
The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux...The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.展开更多
Effective atomic numbers for photon energy absorption(ZPEA_(eff)) and their corresponding electron numbers (NPEA_(eff)), and effective macroscopic removal cross sections of fast neutrons(RR) were calculated for 27 dif...Effective atomic numbers for photon energy absorption(ZPEA_(eff)) and their corresponding electron numbers (NPEA_(eff)), and effective macroscopic removal cross sections of fast neutrons(RR) were calculated for 27 different types of three-dimensional dosimeters, four types of phantom materials, and water. The values of ZPEA_(eff) and NPEA_(eff) were obtained using the direct method for energies ranging from 10 keV to 20 MeV. Results are presented relative to water, for direct comparison over the range of examined energies. The effect of monomers that are used in polymer gel dosimeters on the water equivalence is discussed. The relation between Σ_R and hydrogen content was studied. Micelle gel dosimeters are highly promising because our results demonstrate perfect matching between the effective atomic number, electron density number, and fast neutron attenuation coefficient of water.展开更多
目的探究基于全息3D投影技术的沉浸式宣教在儿童内镜检查中的应用效果。方法采用便利抽样法选取2023年4月—2023年8月来杭州市儿童医院需全麻下实施内镜检查的108例患儿实施前瞻性研究,按照随机数字表法分为研究组(54例)、对照组(54例)...目的探究基于全息3D投影技术的沉浸式宣教在儿童内镜检查中的应用效果。方法采用便利抽样法选取2023年4月—2023年8月来杭州市儿童医院需全麻下实施内镜检查的108例患儿实施前瞻性研究,按照随机数字表法分为研究组(54例)、对照组(54例)。对照组实施常规宣教,研究组实施基于全息3D投影技术的沉浸式宣教。比较两组焦虑程度[中文版耶鲁术前焦虑量表(Chinese version of the Yale Preoperative Anxiety Scale,mYPAS-SF)]、依从性、检查顺利性及家长满意度的差异。结果重复测量显示,两组mYPAS-SF评分的时点效应、组间效应、交互效应比较,差异均有统计学意义(P<0.05),与T1时刻比较[(55.31±6.06)分/(55.43±6.19)分],T2时刻、T3时刻、T4时刻两组mYPAS-SF评分[(45.19±3.56)分/(50.28±3.19)分、(38.06±2.23)分/(43.20±3.21)分、(28.09±1.19)分/(30.28±2.30)分]均降低(P<0.05),且研究组低于对照组(P<0.05)。与对照组相比[(1.33±0.48)分、(1.04±0.19)分、(1.91±0.29)分、(1.83±0.38)分、(1.59±0.50)分],研究组检查前准备、配合意识、体位摆放、检查中配合、其他配合得分[(1.94±0.23)分、(1.98±0.14)分、(2.02±0.14)分、(1.96±0.27)分、(1.98±0.14)分]均更高(P<0.05)。与对照组相比[(13.24±3.16)min、(9.17±1.31)min、(6.50±0.95)分、87.04%],研究组患儿进入检查室至医生准备操作时间、医生开始操作至操作结束时间更少[(10.20±2.33)min、(7.24±1.39)min、(8.20±1.05)分、98.15%],肠道清洁度、一次性成功率[(8.20±1.05)分、98.15%]均更高,差异均有统计学意义(均P<0.05)。等级资料秩和检验显示,与对照组相比,研究组家庭满意度更好(94.44%vs.81.48%),差异有统计学意义(P<0.05)。结论基于全息3D投影技术的沉浸式宣教应用于儿童内镜检查中效果较好,可有效降低焦虑程度,改善依从性,促进检查顺利性,提升家长满意度。展开更多
A method for predicting effective thermal conductivities(ETCs) of three-dimensional five-directional(3D5D) braided composites is presented. The effective thermal conductivity prediction method contains a digital image...A method for predicting effective thermal conductivities(ETCs) of three-dimensional five-directional(3D5D) braided composites is presented. The effective thermal conductivity prediction method contains a digital image processing technology. Multiple scanning electron microscopy(SEM)images of composites are analyzed to obtain actual microstructural features. These actual microstructural features of 3D5D braided composites are introduced into representative volume element(RVE) modeling. Apart from applying actual microstructural features,compression effects between yarns are considered in the modeling of RVE,making the RVE more realistic. Therefore,the ETC prediction method establishes a representative unit cell model that better reflects the true microstructural characteristics of the 3D5D braided composites. The ETCs are predicted with the finite element method. Then thermal conductivity measurements are carried out for a 3D5D braided composite sample.By comparing the predicted ETC with the measured thermal conductivity, the whole process of the ETC prediction method is proved to be effective and accurate,where a relative error of only 2.9 % is obtained.Furthermore,the effects of microstructural features are investigated,indicating that increasing interior braiding angles and fiber fill factor can lead to higher transverse ETCs. Longitudinal ETCs decrease with increasing interior braiding angles,but increase with increasing fiber fill factor. Finally,the influence of variations of microstructure parameters observed in digital image processing are investigated. To explore the influence of variations in microstructural features on variations in predicted ETCs,the actual probability distributions of microstructural features obtained from the 3D5D braided composite sample are introduced into the ETC investigation. The results show that,compared with the interior braiding angle,variations in the fiber fill factor exhibit more significant effects on variations in ETCs.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51239007 and 51179077)the Sino-UK Higher Education Research Partnership for Ph.D.Studies
文摘Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio Dd/Dc and thickness ratio td/Dc is studied by a 3D （three-dimensional） numerical model developed in this paper, and compared with the results obtained through 2D （two-dimensional） numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns： ωx has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ωy along the radial axis is smaller than that of ωx along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ωz of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio Dd/Dc and thickness ratio td/Dc are discussed in detail.
文摘In practice,different design methods are used in solving geotechnical problems depending on the type of issue such as the tunneling,braced excavation,or bearing capacity of a foundation,that is,the basic mechanism of the design method differs depending on the problems even for the same ground.A numerical analysis using the finite element method has recently become familiar owing to an improved computing performance;however,it is not widely used in the design of geotechnical problems including tunnel excavation owing to the reliability of the constitutive model of the ground material.If a constitutive model of soils can properly express the properties of the ground material,a numerical analysis will play a vital role in solving the geotechnical problems.In this paper,the current state of a numerical analysis and its applicability in tunnel design are discussed.Herein,the simulation of the ground behavior during tunnel excavation is carried out using sandy and clay ground parameters for shallow and deep tunnel excavations.This paper is mainly focused on the effects of tunnel excavation under three-dimensional(3D)conditions,as well as the current design method.Non-linear 2D and 3D finite element analyses have been conducted,in which the elastoplastic sub-loading tij model has been used as a constitutive model of the soil.The performance and acceptability of the constitutive model have already been proven to reproduce the results of various model tests on different geotechnical problems such as the tunneling,braced excavation,and bearing capacity of a foundation,as well as the measured field data.It was found that a 2D finite element analysis where the rate of stress release is considered,can be used for the prediction of the ground deformation and surface settlement;however,it does not provide rational information in the prediction of tunnel lining forces such as the stress,bending moment,and axial force,which emphasize the necessity of a 3D analysis with a proper construction process in a tunnel design.
基金Supported by the National Natural Science Foundation of China(10572008)the Natural Science Foundation of Beijing(3063019)Doctor Foundation of Yanshan University(B245)
文摘The three-dimensional （3D） deformation effect of the slope engineering under the step-by-step excavation for the Antaibao surface mine was analyzed using the FLAC^3D technique. An optimal excavated scheme with a relatively steeper slope angle of 47° instead of 30° was successfully implemented at the west wall in the geological section 73200 of the mine area, where the 3D effect of the nonlinear large deformation of the slope was taken into account. Based on the above research conclusion, put forward the countermeasures of shortening mining length, excavating by different regions, timely foot backfilling to protect the excavated slope, and monitoring and feedback adjustment by studying the nonlinear effect. The results show that these countermeasures are effective in controlling maximum deformation and increasing the stability of the slope.
基金Prqject(50335060) supported by the National Natural Science Foundation for Key Program of China Project (50225518) supported by the National Science Found of China for Distinguished Young Scholars
文摘During cold ring rolling process, changing the sizes of forming rolls including driver roll and idle roll will lead to a change of amount of feed Ah and contact areas between ring blank and forming rolls, thus a change of the shape and dimension of deformation zone located in the gap of forming rolls is found. It has a significant effect on metal flow and the forming quality of deformed ring. So the size effect of forming rolls on cold ring rolling was investigated by three-dimensional dynamic explicit FEM under ABAQUS environment. The obtained results thoroughly reveal the influence laws of the sizes of forming rolls on the average spread, fishtail coefficient, degree of inhomogeneous deformation and force and power parameters etc not only provide an important basis for design of the forming rolls and optimization of cold ring rolling process, but also reveal the plastic deformation mechanism of cold ring rolling.
基金funded by the National Science and Technology Major Project of the Ministry of Science and Technology of China under Project No.2016YFB1100703
文摘The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.
文摘Effective atomic numbers for photon energy absorption(ZPEA_(eff)) and their corresponding electron numbers (NPEA_(eff)), and effective macroscopic removal cross sections of fast neutrons(RR) were calculated for 27 different types of three-dimensional dosimeters, four types of phantom materials, and water. The values of ZPEA_(eff) and NPEA_(eff) were obtained using the direct method for energies ranging from 10 keV to 20 MeV. Results are presented relative to water, for direct comparison over the range of examined energies. The effect of monomers that are used in polymer gel dosimeters on the water equivalence is discussed. The relation between Σ_R and hydrogen content was studied. Micelle gel dosimeters are highly promising because our results demonstrate perfect matching between the effective atomic number, electron density number, and fast neutron attenuation coefficient of water.
文摘目的探究基于全息3D投影技术的沉浸式宣教在儿童内镜检查中的应用效果。方法采用便利抽样法选取2023年4月—2023年8月来杭州市儿童医院需全麻下实施内镜检查的108例患儿实施前瞻性研究,按照随机数字表法分为研究组(54例)、对照组(54例)。对照组实施常规宣教,研究组实施基于全息3D投影技术的沉浸式宣教。比较两组焦虑程度[中文版耶鲁术前焦虑量表(Chinese version of the Yale Preoperative Anxiety Scale,mYPAS-SF)]、依从性、检查顺利性及家长满意度的差异。结果重复测量显示,两组mYPAS-SF评分的时点效应、组间效应、交互效应比较,差异均有统计学意义(P<0.05),与T1时刻比较[(55.31±6.06)分/(55.43±6.19)分],T2时刻、T3时刻、T4时刻两组mYPAS-SF评分[(45.19±3.56)分/(50.28±3.19)分、(38.06±2.23)分/(43.20±3.21)分、(28.09±1.19)分/(30.28±2.30)分]均降低(P<0.05),且研究组低于对照组(P<0.05)。与对照组相比[(1.33±0.48)分、(1.04±0.19)分、(1.91±0.29)分、(1.83±0.38)分、(1.59±0.50)分],研究组检查前准备、配合意识、体位摆放、检查中配合、其他配合得分[(1.94±0.23)分、(1.98±0.14)分、(2.02±0.14)分、(1.96±0.27)分、(1.98±0.14)分]均更高(P<0.05)。与对照组相比[(13.24±3.16)min、(9.17±1.31)min、(6.50±0.95)分、87.04%],研究组患儿进入检查室至医生准备操作时间、医生开始操作至操作结束时间更少[(10.20±2.33)min、(7.24±1.39)min、(8.20±1.05)分、98.15%],肠道清洁度、一次性成功率[(8.20±1.05)分、98.15%]均更高,差异均有统计学意义(均P<0.05)。等级资料秩和检验显示,与对照组相比,研究组家庭满意度更好(94.44%vs.81.48%),差异有统计学意义(P<0.05)。结论基于全息3D投影技术的沉浸式宣教应用于儿童内镜检查中效果较好,可有效降低焦虑程度,改善依从性,促进检查顺利性,提升家长满意度。
文摘A method for predicting effective thermal conductivities(ETCs) of three-dimensional five-directional(3D5D) braided composites is presented. The effective thermal conductivity prediction method contains a digital image processing technology. Multiple scanning electron microscopy(SEM)images of composites are analyzed to obtain actual microstructural features. These actual microstructural features of 3D5D braided composites are introduced into representative volume element(RVE) modeling. Apart from applying actual microstructural features,compression effects between yarns are considered in the modeling of RVE,making the RVE more realistic. Therefore,the ETC prediction method establishes a representative unit cell model that better reflects the true microstructural characteristics of the 3D5D braided composites. The ETCs are predicted with the finite element method. Then thermal conductivity measurements are carried out for a 3D5D braided composite sample.By comparing the predicted ETC with the measured thermal conductivity, the whole process of the ETC prediction method is proved to be effective and accurate,where a relative error of only 2.9 % is obtained.Furthermore,the effects of microstructural features are investigated,indicating that increasing interior braiding angles and fiber fill factor can lead to higher transverse ETCs. Longitudinal ETCs decrease with increasing interior braiding angles,but increase with increasing fiber fill factor. Finally,the influence of variations of microstructure parameters observed in digital image processing are investigated. To explore the influence of variations in microstructural features on variations in predicted ETCs,the actual probability distributions of microstructural features obtained from the 3D5D braided composite sample are introduced into the ETC investigation. The results show that,compared with the interior braiding angle,variations in the fiber fill factor exhibit more significant effects on variations in ETCs.
