Urban tunnels crossing faults are always at the risk of severe damages.In this paper,the efects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D fini...Urban tunnels crossing faults are always at the risk of severe damages.In this paper,the efects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D finite difference analysis.After verifying the accuracy of the numerical simulation predictions with the centrifuge physical model results,a parametric study is then conducted.That is,theleffects of various parameters such as the sprayed concrete thickness,the geo-mechanical properties of soil,the tunnel depth,and the fault plane dip angle are studied on the displacements of the ground surface and the tunnel structure,and on the plastic strains of the soil mass around tunnel.The results of each case of reverse and normal faulting are independently discussed and then compared with each other.It is obtained that deeper tunnels show greater displacements for both types of faulting.展开更多
Current guidelines recommend using single-degree-of-freedom(SDOF) method for dynamic analysis of reinforced concretec (RC) structures against blast loads, which is not suitable for retrofitted members. Thus, a finite ...Current guidelines recommend using single-degree-of-freedom(SDOF) method for dynamic analysis of reinforced concretec (RC) structures against blast loads, which is not suitable for retrofitted members. Thus, a finite difference procedure developed in another study was used to accurately and efficiently analyze the dynamic response of fibre reinforced polymer (FRP) plated members under blast loads. It can accommodate changes in the mechanical properties of a member's cross section along its length and through its depth in each time step, making it possible to directly incorporate both strain rate effects (which will vary along the length and depth of a member) and non-uniform member loading to solve the partial differential equation of motion. The accuracy of the proposed method was validated in part using data from field blast testing. The finite difference procedure is implemented easily and enables accurate predictions of FRP-plated-member response.展开更多
The finite-difference time-domain （FDTD） method is proposed for analyzing the surface acoustic wave （SAW） propagation in two-dimensional （2D） piezoelectric phononic crystals （PCs） at radio frequency （RF）, an...The finite-difference time-domain （FDTD） method is proposed for analyzing the surface acoustic wave （SAW） propagation in two-dimensional （2D） piezoelectric phononic crystals （PCs） at radio frequency （RF）, and also experiments are established to demonstrate its analysis result of the PCs＇ band gaps. The FDTD method takes the piezoelectric effect of PCs into account, in which periodic boundary conditions are used to decrease memory/time consumption and the perfectly matched layer boundary conditions are adopted as the SAW absorbers to attenuate artificial reflections. Two SAW delay lines are established with/without piezoelectric PCs located between interdigital transducers. By removing several echoes with window gating function in time domain, delay lines transmission function is achieved. The PCs＇ transmission functions and band gaps are obtained by comparing them in these two delay lines. When Aluminum/128°YX-LiNbO3 is adopted as scatter and substrate material, the PCs＇ band gap is calculated by this FDTD method and COMSOL respectively. Results show that computational results of FDTD agree well with experimental results and are better than that of COMSOL.展开更多
This paper presents a new design of dual polarized aperture coupled printed antenna array. The finite difference time domain (FDTD) analysis of an aperture coupled microstrip element is performed, and the effects ...This paper presents a new design of dual polarized aperture coupled printed antenna array. The finite difference time domain (FDTD) analysis of an aperture coupled microstrip element is performed, and the effects of antenna parameters on its characteristics are obtained to guide the design of the printed array. Then an 8×2 dual polarized array design in X band is introduced with configuration plots. In order to improve its isolation and cross polarization, an outphase displacement feeding technique is adopted in the feed network. Also, the round bends are used instead of conventional right angle bends so as to achieve better VSWR performance. Experimental results are presented, indicating the validity of the design. This dual polarized array can be applied as a sub array of spaceborne SAR systems.展开更多
High temperatures are generated due to the sliding contacts between the rubbing surfaces of the friction clutch system.In this work,by considering the effective thermal contact conductance under sliding conditions,a s...High temperatures are generated due to the sliding contacts between the rubbing surfaces of the friction clutch system.In this work,by considering the effective thermal contact conductance under sliding conditions,a simulation model of a two-dimensional transient temperature field of the clutch disc was developed.A numerical solution to obtain the surface temperature at different radii was presented based on the finite difference method.Compared with the experimental data,the proposed model for estimating the surface temperature is more accurate than the conventional prediction method.The results showed that the errors of the calculated temperatures at radii of 114 and 106 mm have obviously reduced by 12.98%and 12.60%,respectively.In addition,the influences of pressure and relative speed on the surface temperature were investigated.The temperature increases with the increase of the relative speed and pressure during the sliding period,and there is an interaction effect between pressure and speed on the surface temperature rise.展开更多
The pile responses induced by adjacent tunnel excavation have been a hot research topic in geotechnical engineering.Tunnel excavation may exert disturbance to the surrounding soil mass and then influence the adjacent ...The pile responses induced by adjacent tunnel excavation have been a hot research topic in geotechnical engineering.Tunnel excavation may exert disturbance to the surrounding soil mass and then influence the adjacent pile foundations.In this paper,the random finite difference analysis considering the spatial variations of soil properties is conducted to explore the effect of tunnel excavation on the adjacent pile response by varying the distance of pile away from the tunnel centerline(D),the pile length(L),the pile diameter(d_(p)),the tunnel depth(h),and the anisotropic ratio between the horizontal and the vertical scales of fluctuation(δ_(x)/δ_(y)).A set of pile response curves are developed to assess the influence of tunnel excavation on the adjacent passive pile foundations in spatially variable clays and provide guidelines for the tunnel excavation in the complex constructed environment.展开更多
文摘Urban tunnels crossing faults are always at the risk of severe damages.In this paper,the efects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D finite difference analysis.After verifying the accuracy of the numerical simulation predictions with the centrifuge physical model results,a parametric study is then conducted.That is,theleffects of various parameters such as the sprayed concrete thickness,the geo-mechanical properties of soil,the tunnel depth,and the fault plane dip angle are studied on the displacements of the ground surface and the tunnel structure,and on the plastic strains of the soil mass around tunnel.The results of each case of reverse and normal faulting are independently discussed and then compared with each other.It is obtained that deeper tunnels show greater displacements for both types of faulting.
文摘Current guidelines recommend using single-degree-of-freedom(SDOF) method for dynamic analysis of reinforced concretec (RC) structures against blast loads, which is not suitable for retrofitted members. Thus, a finite difference procedure developed in another study was used to accurately and efficiently analyze the dynamic response of fibre reinforced polymer (FRP) plated members under blast loads. It can accommodate changes in the mechanical properties of a member's cross section along its length and through its depth in each time step, making it possible to directly incorporate both strain rate effects (which will vary along the length and depth of a member) and non-uniform member loading to solve the partial differential equation of motion. The accuracy of the proposed method was validated in part using data from field blast testing. The finite difference procedure is implemented easily and enables accurate predictions of FRP-plated-member response.
基金supported by the National Natural Science Foundation of China(11174318,11304346,61106081)Chinese Postdoctoral Science Foundation(2011M501204,2013T60718)+2 种基金National High Technology Research and Development Program(863 Program)(SS2013AA041103)Beijing Municipal Science and Technology Commission Project(Z141100003814016)the Fundamental Research Funds for the Central Universities(HUST:2013QN038)
文摘The finite-difference time-domain （FDTD） method is proposed for analyzing the surface acoustic wave （SAW） propagation in two-dimensional （2D） piezoelectric phononic crystals （PCs） at radio frequency （RF）, and also experiments are established to demonstrate its analysis result of the PCs＇ band gaps. The FDTD method takes the piezoelectric effect of PCs into account, in which periodic boundary conditions are used to decrease memory/time consumption and the perfectly matched layer boundary conditions are adopted as the SAW absorbers to attenuate artificial reflections. Two SAW delay lines are established with/without piezoelectric PCs located between interdigital transducers. By removing several echoes with window gating function in time domain, delay lines transmission function is achieved. The PCs＇ transmission functions and band gaps are obtained by comparing them in these two delay lines. When Aluminum/128°YX-LiNbO3 is adopted as scatter and substrate material, the PCs＇ band gap is calculated by this FDTD method and COMSOL respectively. Results show that computational results of FDTD agree well with experimental results and are better than that of COMSOL.
文摘This paper presents a new design of dual polarized aperture coupled printed antenna array. The finite difference time domain (FDTD) analysis of an aperture coupled microstrip element is performed, and the effects of antenna parameters on its characteristics are obtained to guide the design of the printed array. Then an 8×2 dual polarized array design in X band is introduced with configuration plots. In order to improve its isolation and cross polarization, an outphase displacement feeding technique is adopted in the feed network. Also, the round bends are used instead of conventional right angle bends so as to achieve better VSWR performance. Experimental results are presented, indicating the validity of the design. This dual polarized array can be applied as a sub array of spaceborne SAR systems.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52105232)the Fundamental Research Funds for the Central Universities(Grant No.2022YQJD02).
文摘High temperatures are generated due to the sliding contacts between the rubbing surfaces of the friction clutch system.In this work,by considering the effective thermal contact conductance under sliding conditions,a simulation model of a two-dimensional transient temperature field of the clutch disc was developed.A numerical solution to obtain the surface temperature at different radii was presented based on the finite difference method.Compared with the experimental data,the proposed model for estimating the surface temperature is more accurate than the conventional prediction method.The results showed that the errors of the calculated temperatures at radii of 114 and 106 mm have obviously reduced by 12.98%and 12.60%,respectively.In addition,the influences of pressure and relative speed on the surface temperature were investigated.The temperature increases with the increase of the relative speed and pressure during the sliding period,and there is an interaction effect between pressure and speed on the surface temperature rise.
基金National Natural Science Foundation of China(Grant Nos.52078086 and 52108299)the National Major Scientific Instruments Development Project of China(Grant no.5202780029)Program of Distinguished Young Scholars,Natural Science Foundation of Chongqing,China(cstc2020jcyj-jq0087).
文摘The pile responses induced by adjacent tunnel excavation have been a hot research topic in geotechnical engineering.Tunnel excavation may exert disturbance to the surrounding soil mass and then influence the adjacent pile foundations.In this paper,the random finite difference analysis considering the spatial variations of soil properties is conducted to explore the effect of tunnel excavation on the adjacent pile response by varying the distance of pile away from the tunnel centerline(D),the pile length(L),the pile diameter(d_(p)),the tunnel depth(h),and the anisotropic ratio between the horizontal and the vertical scales of fluctuation(δ_(x)/δ_(y)).A set of pile response curves are developed to assess the influence of tunnel excavation on the adjacent passive pile foundations in spatially variable clays and provide guidelines for the tunnel excavation in the complex constructed environment.
