Two types of dendrite tip splitting including dendrite orientation transition and twinned-like dendrites in Fe-C alloys were investigated by phase-field method. In equiaxed growth, the possible dendrite growth directi...Two types of dendrite tip splitting including dendrite orientation transition and twinned-like dendrites in Fe-C alloys were investigated by phase-field method. In equiaxed growth, the possible dendrite growth directions and the effect of supersaturation on tip splitting were discussed; the dendrite orientation transition was observed, and it was found that the orientation regions of anisotropy parameters were reduced from three to two with increasing the supersaturation, which was due to the effect of interracial anisotropy controlled by the solute in front of S/L interface changing with the increase of supersaturation. In directional solidification, it was found that the twinned like dendrites were formed with the fixed anisotropy couples and no seaweed dendrites were observed; these were concluded from the results of competition between process anisotropy and inherent anisotropy. The formation process of twinned-like dendrite was investigated by tip splitting phenomenon, which was related to the chan ges of dendrite tips growth velocity. Then, the critical speed of tips splitting and solute concentration of twinned-like dendrites were investigated, and a new type of microsegregation in Fe-C alloys was proposed to supplement the dendrite growth theories.展开更多
Tip splitting instability of cellular interface morphology in directional solidification is analyzed based on the bias field method proposed recently by Glicksman. The physical mechanism of tip instability is explaine...Tip splitting instability of cellular interface morphology in directional solidification is analyzed based on the bias field method proposed recently by Glicksman. The physical mechanism of tip instability is explained by analyzing the interface potential, the tangential energy flux, and the normal energy flux. A rigorous criterion for tip-splitting instability is established analytically, i.e., the ratio of the cellular tip radius to the cellular width α 〉3/2/π≈ 0.3899, which is in good agreement with simulation results. This study also reveals that the cellular tip splitting instability is attributable to weak Gibbs–Thomson energy acting on the interface.展开更多
目的:观测钩状突尖端(uncinate process tip,UPT)、椎弓根峡部和颈神经之间的位置关系,为单孔分体脊柱内镜辅助颈椎前路椎间盘切除减压融合术中钩状突精准切除实现颈神经彻底减压提供临床数据参考。方法:选取2016年8月至2021年1月滨州...目的:观测钩状突尖端(uncinate process tip,UPT)、椎弓根峡部和颈神经之间的位置关系,为单孔分体脊柱内镜辅助颈椎前路椎间盘切除减压融合术中钩状突精准切除实现颈神经彻底减压提供临床数据参考。方法:选取2016年8月至2021年1月滨州医学院附属医院的26例神经根型颈椎病病人资料,并在Mimics21.0上观测C3~4至C7~T1相关参数:UPT分别至UPT所在矢状面的颈神经前缘前后距离(a)、UPT所在矢状面的颈神经下缘垂直距离(b)、颈神经起点上缘左右距离(c)、颈神经起点上缘垂直距离(d)、颈神经起点下缘垂直距离(e)、椎弓根峡部外侧缘前后距离(f)、椎弓根峡部外侧缘左右距离(g)、颈神经外展角(∠A)、前倾角(∠B)。结果:C_(3~4)至C_(7)~T_(1),同节段不同性别、不同侧别之间差异无统计学意义;同节段b、e之间差异无统计学意义,表明减压UPT所在矢状面的颈神经下缘即可实现颈神经起点下缘减压;随着C_(3~4)至C_(7)~T_(1)节段降低,a逐渐减小;b、d、e、g、∠A、∠B逐渐增加;c、f先增加后减小(P<0.05)。结论:以UPT作为重要骨性标志点,明确颈神经减压范围并精准切除钩状突。UPT向前(0.9±0.5)mm至(2.3±1.3)mm至椎弓根峡部外侧缘,向外磨透钩状突,可完成UPT至椎弓根区出口处颈神经腹侧减压;向上(5.5±2.1)mm至(8.0±3.0)mm、向内(1.1±0.5)mm至(1.9±0.9)mm分别磨除部分上位椎体和钩状突后外侧壁增生骨赘,可显露硬脊膜外侧缘和颈神经起点上缘,完成UPT至颈神经起点减压,为手术精准切除钩状突安全减压颈神经提供理论依据。展开更多
According to the behaviors of a bubble in the ship wake flow, the numericai simulation is divided into two stages, quasi-spherical motion and non-spherical motion, based on whether the bubble is captured by the vortex...According to the behaviors of a bubble in the ship wake flow, the numericai simulation is divided into two stages, quasi-spherical motion and non-spherical motion, based on whether the bubble is captured by the vortex or not. The one-way coupled particle tracking method （PTM） and the boundary element method （BEM） are adopted to simulate these two stages, respectively. Meanwhile, the initial condition of the second stage is taken as the output of the first one, and the entire simulation is connected and completed. Based on the numerical results and the published experimental data, the cavitation inception is studied, and the wake bubble is tracked. Besides, the split of the bubble captured by the vortex and the following sub-bubbles are simulated, including motion, deformation, and collapse. The results provide some insights into the control on wake bubbles and optimization of the wake flow.展开更多
基金funded by International Cooperation Project of the Ministry of Science and Technology of China(2014DFA50320)National Natural Science Foundation of China(51574207,51574206,51204147, 51274175)International Science and Technology Cooperation Project of Shanxi Province of China (2013081017,2012081013)
文摘Two types of dendrite tip splitting including dendrite orientation transition and twinned-like dendrites in Fe-C alloys were investigated by phase-field method. In equiaxed growth, the possible dendrite growth directions and the effect of supersaturation on tip splitting were discussed; the dendrite orientation transition was observed, and it was found that the orientation regions of anisotropy parameters were reduced from three to two with increasing the supersaturation, which was due to the effect of interracial anisotropy controlled by the solute in front of S/L interface changing with the increase of supersaturation. In directional solidification, it was found that the twinned like dendrites were formed with the fixed anisotropy couples and no seaweed dendrites were observed; these were concluded from the results of competition between process anisotropy and inherent anisotropy. The formation process of twinned-like dendrite was investigated by tip splitting phenomenon, which was related to the chan ges of dendrite tips growth velocity. Then, the critical speed of tips splitting and solute concentration of twinned-like dendrites were investigated, and a new type of microsegregation in Fe-C alloys was proposed to supplement the dendrite growth theories.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB610401)the National Natural Science Foundation of China(Grant No.51371151)the Free Research Fund of State Key Laboratory of Solidification Processing,China(Grant No.100-QP-2014)
文摘Tip splitting instability of cellular interface morphology in directional solidification is analyzed based on the bias field method proposed recently by Glicksman. The physical mechanism of tip instability is explained by analyzing the interface potential, the tangential energy flux, and the normal energy flux. A rigorous criterion for tip-splitting instability is established analytically, i.e., the ratio of the cellular tip radius to the cellular width α 〉3/2/π≈ 0.3899, which is in good agreement with simulation results. This study also reveals that the cellular tip splitting instability is attributable to weak Gibbs–Thomson energy acting on the interface.
文摘目的:观测钩状突尖端(uncinate process tip,UPT)、椎弓根峡部和颈神经之间的位置关系,为单孔分体脊柱内镜辅助颈椎前路椎间盘切除减压融合术中钩状突精准切除实现颈神经彻底减压提供临床数据参考。方法:选取2016年8月至2021年1月滨州医学院附属医院的26例神经根型颈椎病病人资料,并在Mimics21.0上观测C3~4至C7~T1相关参数:UPT分别至UPT所在矢状面的颈神经前缘前后距离(a)、UPT所在矢状面的颈神经下缘垂直距离(b)、颈神经起点上缘左右距离(c)、颈神经起点上缘垂直距离(d)、颈神经起点下缘垂直距离(e)、椎弓根峡部外侧缘前后距离(f)、椎弓根峡部外侧缘左右距离(g)、颈神经外展角(∠A)、前倾角(∠B)。结果:C_(3~4)至C_(7)~T_(1),同节段不同性别、不同侧别之间差异无统计学意义;同节段b、e之间差异无统计学意义,表明减压UPT所在矢状面的颈神经下缘即可实现颈神经起点下缘减压;随着C_(3~4)至C_(7)~T_(1)节段降低,a逐渐减小;b、d、e、g、∠A、∠B逐渐增加;c、f先增加后减小(P<0.05)。结论:以UPT作为重要骨性标志点,明确颈神经减压范围并精准切除钩状突。UPT向前(0.9±0.5)mm至(2.3±1.3)mm至椎弓根峡部外侧缘,向外磨透钩状突,可完成UPT至椎弓根区出口处颈神经腹侧减压;向上(5.5±2.1)mm至(8.0±3.0)mm、向内(1.1±0.5)mm至(1.9±0.9)mm分别磨除部分上位椎体和钩状突后外侧壁增生骨赘,可显露硬脊膜外侧缘和颈神经起点上缘,完成UPT至颈神经起点减压,为手术精准切除钩状突安全减压颈神经提供理论依据。
基金Project supported by the Key Program of National Natural Science Foundation of China(No.50939002)the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (No.10976008)the National Defense Basic Scientific Research Program of China (No.B2420110011)
文摘According to the behaviors of a bubble in the ship wake flow, the numericai simulation is divided into two stages, quasi-spherical motion and non-spherical motion, based on whether the bubble is captured by the vortex or not. The one-way coupled particle tracking method （PTM） and the boundary element method （BEM） are adopted to simulate these two stages, respectively. Meanwhile, the initial condition of the second stage is taken as the output of the first one, and the entire simulation is connected and completed. Based on the numerical results and the published experimental data, the cavitation inception is studied, and the wake bubble is tracked. Besides, the split of the bubble captured by the vortex and the following sub-bubbles are simulated, including motion, deformation, and collapse. The results provide some insights into the control on wake bubbles and optimization of the wake flow.
