严寒地区冰雪飞溅问题对高速铁路运营安全性有直接影响,现场调研发现多处冰块脱落击打应答器的现象,而国内外对此研究尚未见文献报道。采用基于离散元-多柔性体动力学-计算流体力学(discrete element method-multi flexible body dynami...严寒地区冰雪飞溅问题对高速铁路运营安全性有直接影响,现场调研发现多处冰块脱落击打应答器的现象,而国内外对此研究尚未见文献报道。采用基于离散元-多柔性体动力学-计算流体力学(discrete element method-multi flexible body dynamics-computational fluid dynamics, DEM-MFBD-CFD)耦合分析法,建立车厢底板结冰脱落击打应答器模型,并借助风洞和现场试验结果,验证了模型的可靠性;基于建立的分析模型研究不同列车速度、风压变化、冰块质量等因素对应答器击打的受力影响。结果表明:应答器受到的最大应力随列车运行速度呈现幂函数增长关系,当行车速度增大到350 km/h时,最大应力达15.591 MPa,约为150 km/h时的3.5倍;且随冰块质量增加应答器最大应力呈现先迅速增加后缓慢增长趋势;当横风风速为5~20 m/s作用时,应答器表面所受到的最大应力相差不大,表明横风对冰雪击打应答器作用可忽略不计;为减小冰雪飞溅击打应答器危害,可采取除融雪手段、列车降速等措施。展开更多
Under barometric pressure, groundwater flow in well-aquifer systems is a kind of hydromechanical coupling problem. Applying the flux boundary conditions on borehole wall and water pressure equilibrium conditions insid...Under barometric pressure, groundwater flow in well-aquifer systems is a kind of hydromechanical coupling problem. Applying the flux boundary conditions on borehole wall and water pressure equilibrium conditions inside and outside the borehole wall under barometric pressure （BP）, an analytic solution to well-water level changes has been proposed in this paper. The formulation shows that the BP coefficients increase with time and tend to BP constant. The Change of BP coefficients over time depends only on the ratio of transmissivity （T） to the well radius squared （ r2, ） , and has nothing to do with the change in BP. The BP constant only relates to aquifer loading efficiency （B）, and has nothing to do with the aquifer transmissivity and well radius. The BP coefficients＇ change over time in the analytic formulation is consistent with the analysis of measured data from the Nanxi wells. Based on the BP coefficient changes over time, a parameter estimation method is suggested and discussed in its application to the estimation of the aquifer BP constant （or B） and transmissivity by using the Nanxi well data.展开更多
We propose a numerical solution of Faraday＇s law of induction based on the knowledge of the time-varying, non-uniform vector potential inside arbitrarily shaped electrical coils. The vector potential can be related t...We propose a numerical solution of Faraday＇s law of induction based on the knowledge of the time-varying, non-uniform vector potential inside arbitrarily shaped electrical coils. The vector potential can be related to the magnetic induction which yields the well-known form of Faraday＇s law. The algorithm applies for non-retarding fields within the quasi-stationary regime. The model is intended to help to understand the behavior of electromagnetic fields inside the discharge chambers of radio-frequency ion thrusters. This provides a basis for modeling an inductively-coupled plasma which is kept burning by absorbing electromagnetic energy. In the long run, this plasma model will be used to support development processes of electric and electronic control devices which are needed for driving radio-frequency ion thrusters more efficiently. To predict the induced radio frequency fields more precisely, the skin effect along the coil wire is modeled. Furthermore, an impedance model of the coil, which incorporates the skin effect, is introduced. The simulated data are compared to measured values obtained by a generic electric field probe. Although the probe was uncalibrated, the observed values were highly similar to the expected values as determined by the numerical solution.展开更多
为消除有限元法(finite element method,FEM)处理切屑分离及大变形问题的局限,使用光滑粒子流体动力学法(smooth particle hydrodynamics,SPH)耦合FEM模拟此类问题。工件使用SPH建模,弹丸使用FEM建模,二者通过接触算法实现耦合,通过仿...为消除有限元法(finite element method,FEM)处理切屑分离及大变形问题的局限,使用光滑粒子流体动力学法(smooth particle hydrodynamics,SPH)耦合FEM模拟此类问题。工件使用SPH建模,弹丸使用FEM建模,二者通过接触算法实现耦合,通过仿真实验研究锐边弹丸在不同入射条件下撞击工件时,弹丸的翻转效应对工件表面弹坑深度、切屑堆积高度的影响。结果表明:当前倾角较大时,弹丸向前翻转,对工件表面产生碾压作用,形成尖锐的弹坑,切屑堆积在弹坑前部边缘不与工件分离;当前倾角较小时,弹丸向后翻转,对工件表面产生铲削作用,切屑与工件分离,弹坑横截面光滑而平缓。通过与相关实验及理论数据的比较,验证了仿真模型及结果的正确性,为锐边弹丸侵蚀工件表面的仿真研究提供新的手段。展开更多
This paper describes the calculation method for unsteady state conditions in the secondary air systems in gas turbines. The 1D-3D-Structure coupled method was applied. A 1D code was used to model the standard componen...This paper describes the calculation method for unsteady state conditions in the secondary air systems in gas turbines. The 1D-3D-Structure coupled method was applied. A 1D code was used to model the standard components that have typical geometric characteristics. Their flow and heat transfer were described by empirical correlations based on experimental data or CFD calculations. A 3D code was used to model the non-standard components that cannot be described by typical geometric languages, while a finite element analysis was carried out to compute the structural deformation and heat conduction at certain important positions. These codes were coupled through their interfaces. Thus, the changes in heat transfer and structure and their interactions caused by exterior disturbances can be reflected. The results of the coupling method in an unsteady state showed an apparent deviation from the existing data, while the results in the steady state were highly consistent with the existing data. The difference in the results in the unsteady state was caused primarily by structural deformation that cannot be predicted by the 1D method. Thus, in order to obtain the unsteady state performance of a secondary air system more accurately and efficiently, the 1D-3D-Structure coupled method should be used.展开更多
文摘为了进一步研究切缝药包爆破机理,在AUTODYN内运用光滑粒子流体动力学与有限单元(SPH FEM)耦合法构建了装药不耦合系数为2.0的切缝药包爆破模型,分析装药爆炸初期的爆轰产物膨胀过程、爆轰产物粒子运动速度及炮孔周围岩体损伤演化历程。结果表明:对于切缝方向,由于没有切缝管的约束作用,爆轰产物粒子能够以较高的速度向前运动,粒子最大运动速度可达到4750m s^-1,最前端粒子在3.5μs到达孔壁,切缝方向岩体开始产生损伤破坏,且随着切缝管内爆轰产物的继续膨胀,切缝方向岩体进一步受到破坏;对于非切缝方向,切缝管的约束作用使得爆轰产物粒子膨胀受阻,粒子最大运动速度仅为800 m s^-1,同时切缝管在爆轰产物的推动下缓慢向炮孔壁运动,12.6μs切缝管到达炮孔壁,非切缝方向岩体开始产生损伤,但损伤展布区域较小,且非切缝方向炮孔壁保持了较好的完整性。
基金supported by special funds for Public Welfare Scientific Research of Ministry of Science and Technology,PRC(200808055)Scientific Research Project of Education Department,Hebei Province(Z2009104),China
文摘Under barometric pressure, groundwater flow in well-aquifer systems is a kind of hydromechanical coupling problem. Applying the flux boundary conditions on borehole wall and water pressure equilibrium conditions inside and outside the borehole wall under barometric pressure （BP）, an analytic solution to well-water level changes has been proposed in this paper. The formulation shows that the BP coefficients increase with time and tend to BP constant. The Change of BP coefficients over time depends only on the ratio of transmissivity （T） to the well radius squared （ r2, ） , and has nothing to do with the change in BP. The BP constant only relates to aquifer loading efficiency （B）, and has nothing to do with the aquifer transmissivity and well radius. The BP coefficients＇ change over time in the analytic formulation is consistent with the analysis of measured data from the Nanxi wells. Based on the BP coefficient changes over time, a parameter estimation method is suggested and discussed in its application to the estimation of the aquifer BP constant （or B） and transmissivity by using the Nanxi well data.
文摘We propose a numerical solution of Faraday＇s law of induction based on the knowledge of the time-varying, non-uniform vector potential inside arbitrarily shaped electrical coils. The vector potential can be related to the magnetic induction which yields the well-known form of Faraday＇s law. The algorithm applies for non-retarding fields within the quasi-stationary regime. The model is intended to help to understand the behavior of electromagnetic fields inside the discharge chambers of radio-frequency ion thrusters. This provides a basis for modeling an inductively-coupled plasma which is kept burning by absorbing electromagnetic energy. In the long run, this plasma model will be used to support development processes of electric and electronic control devices which are needed for driving radio-frequency ion thrusters more efficiently. To predict the induced radio frequency fields more precisely, the skin effect along the coil wire is modeled. Furthermore, an impedance model of the coil, which incorporates the skin effect, is introduced. The simulated data are compared to measured values obtained by a generic electric field probe. Although the probe was uncalibrated, the observed values were highly similar to the expected values as determined by the numerical solution.
文摘为消除有限元法(finite element method,FEM)处理切屑分离及大变形问题的局限,使用光滑粒子流体动力学法(smooth particle hydrodynamics,SPH)耦合FEM模拟此类问题。工件使用SPH建模,弹丸使用FEM建模,二者通过接触算法实现耦合,通过仿真实验研究锐边弹丸在不同入射条件下撞击工件时,弹丸的翻转效应对工件表面弹坑深度、切屑堆积高度的影响。结果表明:当前倾角较大时,弹丸向前翻转,对工件表面产生碾压作用,形成尖锐的弹坑,切屑堆积在弹坑前部边缘不与工件分离;当前倾角较小时,弹丸向后翻转,对工件表面产生铲削作用,切屑与工件分离,弹坑横截面光滑而平缓。通过与相关实验及理论数据的比较,验证了仿真模型及结果的正确性,为锐边弹丸侵蚀工件表面的仿真研究提供新的手段。
基金supported by funds from National natural science foundation of China(Grant No.51176004)
文摘This paper describes the calculation method for unsteady state conditions in the secondary air systems in gas turbines. The 1D-3D-Structure coupled method was applied. A 1D code was used to model the standard components that have typical geometric characteristics. Their flow and heat transfer were described by empirical correlations based on experimental data or CFD calculations. A 3D code was used to model the non-standard components that cannot be described by typical geometric languages, while a finite element analysis was carried out to compute the structural deformation and heat conduction at certain important positions. These codes were coupled through their interfaces. Thus, the changes in heat transfer and structure and their interactions caused by exterior disturbances can be reflected. The results of the coupling method in an unsteady state showed an apparent deviation from the existing data, while the results in the steady state were highly consistent with the existing data. The difference in the results in the unsteady state was caused primarily by structural deformation that cannot be predicted by the 1D method. Thus, in order to obtain the unsteady state performance of a secondary air system more accurately and efficiently, the 1D-3D-Structure coupled method should be used.
