In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method(BEM) was carr...In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method(BEM) was carried out. By dividing the problem into a pitted half-plane and an upper closed domain as an alluvial hill and applying continuity/boundary conditions at the interface, coupled equations were constructed and ultimately, the problem was solved step-by-step in the time domain to obtain the boundary values. After solving some verification examples, a semi-sine shaped alluvial hill located on an underground circular cavity was successfully analyzed to determine the amplification ratio of the hill surface. For sensitivity analysis, the effects of the impedance factor and shape ratio of the hill were also considered. The ground surface responses are illustrated as three-dimensional graphs in the time and frequency domains. The results show that the material properties of the hill and their heterogeneity with the underlying half-space had a significant effect on the surface response.展开更多
Optically pumped wavelength-tunable vertical-cavity surface-emitting lasers(VCSELs)operating in the ultraviolet A(UVA)spectrum were demonstrated.The VCSELs feature double dielectric distributed brag reflectors and a w...Optically pumped wavelength-tunable vertical-cavity surface-emitting lasers(VCSELs)operating in the ultraviolet A(UVA)spectrum were demonstrated.The VCSELs feature double dielectric distributed brag reflectors and a wedge-shaped cavity fabricated using the substrate transfer technique and laser lift off,resulting in a graded cavity length in one device.A resonant period gain structure is used in the InGaN/GaN multi-quantum well active region to enhance the coupling between the cavity mode field and the active layers.The optical field inside the cavity is modulated by the cavity length;thus,tunable lasing at different wavelengths is realized at different points of a single VCSEL chip.The lasing wavelength extends from 376 to 409 nm,covering most of the UVA band below the band gap of GaN.The threshold pumping power density of the UVA VCSELs at different wavelengths ranges from 383 to 466 kW/cm^(2),which is among the lowest values for ultraviolet(UV)VCSELs.This study is promising for the development of small-footprint,power-efficient UV light sources.展开更多
The effect of the tilt angle on mixed convection and related heat transfer in a“T”shaped double enclosure with four heated obstacles on the bottom surface is numerically investigated.The considered obstacles are con...The effect of the tilt angle on mixed convection and related heat transfer in a“T”shaped double enclosure with four heated obstacles on the bottom surface is numerically investigated.The considered obstacles are constantly kept at a relatively high(fixed)temperature,while the cavity’s upper wall is cooled.The finite volume approach is used to solve the mass,momentum,and energy equations with the SIMPLEC algorithm being exploited to deal with the pressure-velocity coupling.Emphasis is put on the influence of the tilt angle on the solution symmetry,flow structure,and heat exchange through the walls.The following parameters and related ranges are considered:Rayleigh number 104≤Ra≤5.105,tilt angle 0°≤φ≤90°,Reynolds number 100≤Re≤1000,Prandtl number Pr=0.72,block height B=0.5,opening width C=0.15,and distance between blocks D=0.5.The results reveal different branches of solutions on varying Re andφ.They also show that the symmetry of the solution regarding the P_(2)axis is retained for all cases with no tilt and for values of Re between 100 and 1000.展开更多
The present study concerns the modelization and numerical simulation for the heat and flow exchange characteristics in a novel configuration saturated with a nonNewtonian Ag-MgO hybrid nanofluid.The wavy shaped enclos...The present study concerns the modelization and numerical simulation for the heat and flow exchange characteristics in a novel configuration saturated with a nonNewtonian Ag-MgO hybrid nanofluid.The wavy shaped enclosure is equipped with onequarter of a conducting solid cylinder.The system of equations resulting from the mathematical modeling of the physical problem in its dimensionless form is discretized via the higher-order Galerkin-based finite element method(GFEM).The dependency of various factors and their interrelationships affecting the hydro-thermal behavior and heat exchange rate are delineated.The numerical experiments reveal that the best heat transfer rate is achieved for the pseudo-plastic hybrid nanoliquid with high Rayleigh number and thermal conductivity ratio and low Hartmann number.Besides,the power-law index has a major effect in deteriorating the heat convection at high Rayleigh number.展开更多
文摘In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method(BEM) was carried out. By dividing the problem into a pitted half-plane and an upper closed domain as an alluvial hill and applying continuity/boundary conditions at the interface, coupled equations were constructed and ultimately, the problem was solved step-by-step in the time domain to obtain the boundary values. After solving some verification examples, a semi-sine shaped alluvial hill located on an underground circular cavity was successfully analyzed to determine the amplification ratio of the hill surface. For sensitivity analysis, the effects of the impedance factor and shape ratio of the hill were also considered. The ground surface responses are illustrated as three-dimensional graphs in the time and frequency domains. The results show that the material properties of the hill and their heterogeneity with the underlying half-space had a significant effect on the surface response.
基金supported by the National Key Research and Development Program of China(Grants No.2017YFE0131500 and 2016YFB0400803)the National Natural Science Foundation of China(Grants No.U1505253 and 62104204).
文摘Optically pumped wavelength-tunable vertical-cavity surface-emitting lasers(VCSELs)operating in the ultraviolet A(UVA)spectrum were demonstrated.The VCSELs feature double dielectric distributed brag reflectors and a wedge-shaped cavity fabricated using the substrate transfer technique and laser lift off,resulting in a graded cavity length in one device.A resonant period gain structure is used in the InGaN/GaN multi-quantum well active region to enhance the coupling between the cavity mode field and the active layers.The optical field inside the cavity is modulated by the cavity length;thus,tunable lasing at different wavelengths is realized at different points of a single VCSEL chip.The lasing wavelength extends from 376 to 409 nm,covering most of the UVA band below the band gap of GaN.The threshold pumping power density of the UVA VCSELs at different wavelengths ranges from 383 to 466 kW/cm^(2),which is among the lowest values for ultraviolet(UV)VCSELs.This study is promising for the development of small-footprint,power-efficient UV light sources.
文摘The effect of the tilt angle on mixed convection and related heat transfer in a“T”shaped double enclosure with four heated obstacles on the bottom surface is numerically investigated.The considered obstacles are constantly kept at a relatively high(fixed)temperature,while the cavity’s upper wall is cooled.The finite volume approach is used to solve the mass,momentum,and energy equations with the SIMPLEC algorithm being exploited to deal with the pressure-velocity coupling.Emphasis is put on the influence of the tilt angle on the solution symmetry,flow structure,and heat exchange through the walls.The following parameters and related ranges are considered:Rayleigh number 104≤Ra≤5.105,tilt angle 0°≤φ≤90°,Reynolds number 100≤Re≤1000,Prandtl number Pr=0.72,block height B=0.5,opening width C=0.15,and distance between blocks D=0.5.The results reveal different branches of solutions on varying Re andφ.They also show that the symmetry of the solution regarding the P_(2)axis is retained for all cases with no tilt and for values of Re between 100 and 1000.
文摘The present study concerns the modelization and numerical simulation for the heat and flow exchange characteristics in a novel configuration saturated with a nonNewtonian Ag-MgO hybrid nanofluid.The wavy shaped enclosure is equipped with onequarter of a conducting solid cylinder.The system of equations resulting from the mathematical modeling of the physical problem in its dimensionless form is discretized via the higher-order Galerkin-based finite element method(GFEM).The dependency of various factors and their interrelationships affecting the hydro-thermal behavior and heat exchange rate are delineated.The numerical experiments reveal that the best heat transfer rate is achieved for the pseudo-plastic hybrid nanoliquid with high Rayleigh number and thermal conductivity ratio and low Hartmann number.Besides,the power-law index has a major effect in deteriorating the heat convection at high Rayleigh number.
