In this study,a combination of acoustic emission(AE)method(AEM)and wave transmission method(WTM)is used to investigate the behaviors of AE and ultrasonic properties corresponding to initial fracturing in granitic rock...In this study,a combination of acoustic emission(AE)method(AEM)and wave transmission method(WTM)is used to investigate the behaviors of AE and ultrasonic properties corresponding to initial fracturing in granitic rocks.The relationships of AE characteristics,frequency spectra,and spatial locations with crack initiation(CI)are studied.The anisotropic ultrasonic characteristics,velocity distributions in different ray paths,wave amplitudes,and spectral characters of transmitted waves are investigated.To identify CI stress,damage initiations characterized by strain-based method(SBM),AEM and WTM are compared.For granite samples,it shows that the ratio of CI stress to peak strength estimated by SBM ranges from 0.4 to 0.55,and 0.49-0.6 by WTM,which are higher than that of AEM(0.38-0.46).The CI stress identified by AEM indicates the onset of microcracking,and the combination of AEM and WTM provides an insight into the detection of rock damage initiation and anisotropy.展开更多
With rapid development of urban rail transit,maglev trains,benefiting from its comfortable,energy-saving and environmentally friendly merits,have gradually entered people's horizons.In this paper,aiming at improvi...With rapid development of urban rail transit,maglev trains,benefiting from its comfortable,energy-saving and environmentally friendly merits,have gradually entered people's horizons.In this paper,aiming at improving the aerodynamic performance of an urban maglev train,the aerodynamic optimization design has been performed.An improved two-point infill criterion has been adopted to construct the cross-validated Kriging model.Meanwhile,the multi-objective genetic algorithm and complex three-dimensional geometric parametrization method have been used,to optimize the streamlined head of the train.Several optimal shapes have been obtained.Results reveal that the optimization strategy used in this paper is sufficiently accurate and time-efficient for the optimization of the urban maglev train,and can be applied in practical engineering.Compared to the prototype of the train,optimal shape benefits from higher lift of the leading car and smaller drag of the whole train.Sensitivity analysis reveals that the length and height of the streamlined head have a great influence on the aerodynamic performance of the train,and strong nonlinear relationships exist between these design variables and aerodynamic performance.The conclusions drawn in this study offer the chance to derive critical reference values for the optimization of the aerodynamic characteristics of urban maglev trains.展开更多
The irregularities on trains bodies are normally ignored or greatly simplified in studies concerned with aerodynamics.However,surface roughness is known to affect the flow characteristics in the boundary layer near th...The irregularities on trains bodies are normally ignored or greatly simplified in studies concerned with aerodynamics.However,surface roughness is known to affect the flow characteristics in the boundary layer near the wall,hence potentially influencing the aerodynamic performance of a train.This work investigates the effects of roughness on the overall aerodynamic characteristics of a high-speed train subjected to crosswinds.Both experimental work and numerical work have been conducted to simulate a typical high-speed train with a 90?yaw angle,with both a smooth and rough surface.Roughness is applied to the roof of the train surface in the form of longitudinal strips.Results reveal that the addition of roughness is able to reduce the surface pressure on the roof and leeside of the train.Numerical results agree well with experimental ones and confirm that an increase in the roughness relative size can effectively restrain flow separation and reduce surface pressure.Moreover,numerical simulation results show that side force coefficient and roll moment coefficient subjected to rough model significantly decreased compared with smooth model.The conclusions drawn in this study offer the chance to derive critical reference values for the optimization of the aerodynamic characteristics of high-speed trains.展开更多
Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms ...Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance.We conduct non-equilibrium molecular dynamics(NEMD)simulation and X-ray diffraction(XRD)simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg(NP-Mg).Two different deformation modes govern the shock consolidation in NP-Mg,i.e.,deformation twinning at up≤1.5 km s^(-1)and structural disordering,at up≥2.0 km s^(-1).They accelerate the collapse of nanopores and void compaction,giving rise to the final consolidation of NP-Mg.Three types of deformation twinning are emitted in NP-Mg,i.e.,the extension twinning for{1121}(1126),and{1102}〈1101>,and the compression{1122}(1123)twinning.They are prompted via coupling atomic shuffles and slips.Deformation twinning prefers to occur within the grains as shock along<1120>or its approaching direction(A-and B-type grains),originated from the high-angle grain boundaries(HAGB)at compression stage.They are inhibited within the ones as shocking along<0001>and the approaching ones(C-and D-type grains).The release and tension loading facilitates the reversible and irreversible detwinning,for the extension and compression twinning,respectively,within the A-and B-type grains.It also contributes to a compression-tension asymmetry for twinning,i.e.,release and tension induced extension twinning within the C-and D-type grains.The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at up≤1.5 km s^(-1),and structural disordering at up≥2.0 km s^(-1).展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51809137)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180480)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.2017015)。
文摘In this study,a combination of acoustic emission(AE)method(AEM)and wave transmission method(WTM)is used to investigate the behaviors of AE and ultrasonic properties corresponding to initial fracturing in granitic rocks.The relationships of AE characteristics,frequency spectra,and spatial locations with crack initiation(CI)are studied.The anisotropic ultrasonic characteristics,velocity distributions in different ray paths,wave amplitudes,and spectral characters of transmitted waves are investigated.To identify CI stress,damage initiations characterized by strain-based method(SBM),AEM and WTM are compared.For granite samples,it shows that the ratio of CI stress to peak strength estimated by SBM ranges from 0.4 to 0.55,and 0.49-0.6 by WTM,which are higher than that of AEM(0.38-0.46).The CI stress identified by AEM indicates the onset of microcracking,and the combination of AEM and WTM provides an insight into the detection of rock damage initiation and anisotropy.
基金This work was supported by Advanced Rail Transportation Special Plan in National Key Research and Development Project(Grants 2016YFB1200601-B13 and 2016YFB1200602-09)Youth Innovation Promotion Association CAS(2019020).
文摘With rapid development of urban rail transit,maglev trains,benefiting from its comfortable,energy-saving and environmentally friendly merits,have gradually entered people's horizons.In this paper,aiming at improving the aerodynamic performance of an urban maglev train,the aerodynamic optimization design has been performed.An improved two-point infill criterion has been adopted to construct the cross-validated Kriging model.Meanwhile,the multi-objective genetic algorithm and complex three-dimensional geometric parametrization method have been used,to optimize the streamlined head of the train.Several optimal shapes have been obtained.Results reveal that the optimization strategy used in this paper is sufficiently accurate and time-efficient for the optimization of the urban maglev train,and can be applied in practical engineering.Compared to the prototype of the train,optimal shape benefits from higher lift of the leading car and smaller drag of the whole train.Sensitivity analysis reveals that the length and height of the streamlined head have a great influence on the aerodynamic performance of the train,and strong nonlinear relationships exist between these design variables and aerodynamic performance.The conclusions drawn in this study offer the chance to derive critical reference values for the optimization of the aerodynamic characteristics of urban maglev trains.
基金The work was financed by the program of China Scholarships Council,Youth Innovation Promotion Association CAS(2019020)a University of Birmingham(UK)funded scholarship and was supported by the EU H2O2O project LiftTRAIN(701693)。
文摘The irregularities on trains bodies are normally ignored or greatly simplified in studies concerned with aerodynamics.However,surface roughness is known to affect the flow characteristics in the boundary layer near the wall,hence potentially influencing the aerodynamic performance of a train.This work investigates the effects of roughness on the overall aerodynamic characteristics of a high-speed train subjected to crosswinds.Both experimental work and numerical work have been conducted to simulate a typical high-speed train with a 90?yaw angle,with both a smooth and rough surface.Roughness is applied to the roof of the train surface in the form of longitudinal strips.Results reveal that the addition of roughness is able to reduce the surface pressure on the roof and leeside of the train.Numerical results agree well with experimental ones and confirm that an increase in the roughness relative size can effectively restrain flow separation and reduce surface pressure.Moreover,numerical simulation results show that side force coefficient and roll moment coefficient subjected to rough model significantly decreased compared with smooth model.The conclusions drawn in this study offer the chance to derive critical reference values for the optimization of the aerodynamic characteristics of high-speed trains.
基金financially supported by the Natural Science Foundation(NSF)of China(Nos.11802092 and U2230401)NSF of Hunan Province(Nos.2019JJ50221,2019JJ40127,2020JJ5260,and 2020JJ4375)+5 种基金the Funding of the Hunan Education Department Project(Nos.20A248 and 22B0225)the Double first-class construction project of Hunan Agricultural University(No.SYL2019063)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20230682)the Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20230682)the Postgraduate Scientific Research Innovation Project of Hunan Agricultural University(No.2023XC019)We also acknowledge the support of the computation platform of the National Super Computer Center in Changsha(NSCC).
文摘Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials,and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance.We conduct non-equilibrium molecular dynamics(NEMD)simulation and X-ray diffraction(XRD)simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg(NP-Mg).Two different deformation modes govern the shock consolidation in NP-Mg,i.e.,deformation twinning at up≤1.5 km s^(-1)and structural disordering,at up≥2.0 km s^(-1).They accelerate the collapse of nanopores and void compaction,giving rise to the final consolidation of NP-Mg.Three types of deformation twinning are emitted in NP-Mg,i.e.,the extension twinning for{1121}(1126),and{1102}〈1101>,and the compression{1122}(1123)twinning.They are prompted via coupling atomic shuffles and slips.Deformation twinning prefers to occur within the grains as shock along<1120>or its approaching direction(A-and B-type grains),originated from the high-angle grain boundaries(HAGB)at compression stage.They are inhibited within the ones as shocking along<0001>and the approaching ones(C-and D-type grains).The release and tension loading facilitates the reversible and irreversible detwinning,for the extension and compression twinning,respectively,within the A-and B-type grains.It also contributes to a compression-tension asymmetry for twinning,i.e.,release and tension induced extension twinning within the C-and D-type grains.The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at up≤1.5 km s^(-1),and structural disordering at up≥2.0 km s^(-1).
