Tunnel portal sections often suffer serious damage in strong earthquake events.Earthquake waves may propagate in different directions,producing various dynamic responses in the tunnel portal.Based on the Galongla tunn...Tunnel portal sections often suffer serious damage in strong earthquake events.Earthquake waves may propagate in different directions,producing various dynamic responses in the tunnel portal.Based on the Galongla tunnel,which is located in a seismic region of China,three-dimensional seismic analysis is conducted to investigate the dynamic response of a tunnel portal subjected to earthquake waves with different vibration directions.In order to simulate the mechanic behavior of slope rock effectively,an elastoplastic damage model is adopted and applied to ABAQUS software by a self-compiled user material(UMAT)subroutine.Moreover,the seismic wave input method for tunnel portal is established to realize the seismic input under vertically incident earthquake waves with different vibration directions,e.g.,S waves with a vibration direction perpendicular or parallel to the tunnel axis and P waves with a vibration direction perpendicular to the tunnel axis.The numerical results indicate that the seismic response and damage mechanisms of the tunnel portal section are related to the vibration direction of the earthquake waves.For vertically incident S waves running perpendicular to the tunnel axis,the hoop tensile strain at the spandrel and arch foot and the hoop shear strain at the vault and arch bottom are the main contributors to the plastic damage of the tunnel.The strain is initially concentrated around the tunnel foot and spandrel,before shifting to the tunnel vault and bottom farther away from the tunnel entrance.For vertically incident S waves running parallel to the tunnel axis,very large hoop shear strain and plastic damage appear at the tunnel haunches.This strain first increases and then decreases with distance from the tunnel entrance.For vertically incident P waves running perpendicular to the tunnel axis,the maximum damage factor of the slope rock and the maximum plastic strain of the tunnel are significantly lower than for S waves.Moreover,with increasing distance from the tunnel entrance,the plastic damage to the tunnel lining rapidly decreases.展开更多
Ultrasonic elliptical vibration cutting(UEVC)with clockwise elliptical vibration has made notable achievements in precision machining;however,its critical cutting speed limits its application to low-speed machining ta...Ultrasonic elliptical vibration cutting(UEVC)with clockwise elliptical vibration has made notable achievements in precision machining;however,its critical cutting speed limits its application to low-speed machining tasks.Meanwhile,rotary ultrasonic elliptical machining(RUEM)with clockwise elliptical vibration has been validated as an effective high-speed cutting technology.Unfortunately,conventional RUEM leads to increased surface roughness.To address this issue and enhance machining quality,we propose a novel RUEM method employing an anticlockwise vibration direction,called anticlockwise rotary ultrasonic elliptical machining(ARUEM).The mechanisms of surface formation and subsurface strengthening for ARUEM are analyzed.Experimental validations were performed on Ti-6Al-4V alloy,revealing that ARUEM achieved substantially lower ridge heights and up to a 50%reduction in surface roughness compared to conventional RUEM.Additionally,relative to conventional milling,ARUEM resulted in up to 122.6%thicker plastic deformation layers,53.4%higher surface residual compressive stress,and 19.3%greater surface micro-hardness.This study showcases a promising method for high-performance milling of Ti-6Al-4V,offers new insights into RUEM by examining the influence of vibration direction,and enhances understanding of surface formation and subsurface strengthening in the ARUEM method.展开更多
In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction o...In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction of rockets and directional tubes when clearances exist, the method of estimating initial disturbances for the rocket by using vibration data of the directional tube has been given. The estimated results have been compared with the simulation results computed by the dynamic simulating software ADAMS. Results computed by the two methods are basically consistent and the computing errors do not increase with the variation of the clearance. The validity of the proposed method has been proved.展开更多
基金support from the Beijing Natural Science Foundation Program(JQ19029)the National Natural Science Foundation of China(41672289+1 种基金U183920151421005).
文摘Tunnel portal sections often suffer serious damage in strong earthquake events.Earthquake waves may propagate in different directions,producing various dynamic responses in the tunnel portal.Based on the Galongla tunnel,which is located in a seismic region of China,three-dimensional seismic analysis is conducted to investigate the dynamic response of a tunnel portal subjected to earthquake waves with different vibration directions.In order to simulate the mechanic behavior of slope rock effectively,an elastoplastic damage model is adopted and applied to ABAQUS software by a self-compiled user material(UMAT)subroutine.Moreover,the seismic wave input method for tunnel portal is established to realize the seismic input under vertically incident earthquake waves with different vibration directions,e.g.,S waves with a vibration direction perpendicular or parallel to the tunnel axis and P waves with a vibration direction perpendicular to the tunnel axis.The numerical results indicate that the seismic response and damage mechanisms of the tunnel portal section are related to the vibration direction of the earthquake waves.For vertically incident S waves running perpendicular to the tunnel axis,the hoop tensile strain at the spandrel and arch foot and the hoop shear strain at the vault and arch bottom are the main contributors to the plastic damage of the tunnel.The strain is initially concentrated around the tunnel foot and spandrel,before shifting to the tunnel vault and bottom farther away from the tunnel entrance.For vertically incident S waves running parallel to the tunnel axis,very large hoop shear strain and plastic damage appear at the tunnel haunches.This strain first increases and then decreases with distance from the tunnel entrance.For vertically incident P waves running perpendicular to the tunnel axis,the maximum damage factor of the slope rock and the maximum plastic strain of the tunnel are significantly lower than for S waves.Moreover,with increasing distance from the tunnel entrance,the plastic damage to the tunnel lining rapidly decreases.
基金supported by the National Natural Science Foundation of China(Nos.91960203 and 52375399)the Chinese Aeronautical Establishment Aeronautical Science Foundation(No.2022Z045051001).
文摘Ultrasonic elliptical vibration cutting(UEVC)with clockwise elliptical vibration has made notable achievements in precision machining;however,its critical cutting speed limits its application to low-speed machining tasks.Meanwhile,rotary ultrasonic elliptical machining(RUEM)with clockwise elliptical vibration has been validated as an effective high-speed cutting technology.Unfortunately,conventional RUEM leads to increased surface roughness.To address this issue and enhance machining quality,we propose a novel RUEM method employing an anticlockwise vibration direction,called anticlockwise rotary ultrasonic elliptical machining(ARUEM).The mechanisms of surface formation and subsurface strengthening for ARUEM are analyzed.Experimental validations were performed on Ti-6Al-4V alloy,revealing that ARUEM achieved substantially lower ridge heights and up to a 50%reduction in surface roughness compared to conventional RUEM.Additionally,relative to conventional milling,ARUEM resulted in up to 122.6%thicker plastic deformation layers,53.4%higher surface residual compressive stress,and 19.3%greater surface micro-hardness.This study showcases a promising method for high-performance milling of Ti-6Al-4V,offers new insights into RUEM by examining the influence of vibration direction,and enhances understanding of surface formation and subsurface strengthening in the ARUEM method.
文摘In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction of rockets and directional tubes when clearances exist, the method of estimating initial disturbances for the rocket by using vibration data of the directional tube has been given. The estimated results have been compared with the simulation results computed by the dynamic simulating software ADAMS. Results computed by the two methods are basically consistent and the computing errors do not increase with the variation of the clearance. The validity of the proposed method has been proved.
