The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experi...The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.展开更多
A finite-volume charge method has been proposed to simulate PIN diodes and insulated-gate bipolar transistor(IGBT)devices using SPICE simulators by extending the lumped-charge method.The new method assumes local quasi...A finite-volume charge method has been proposed to simulate PIN diodes and insulated-gate bipolar transistor(IGBT)devices using SPICE simulators by extending the lumped-charge method.The new method assumes local quasi-neutrality in the undepleted N^(-)base region and uses the total collector current,the nodal hole density and voltage as the basic quantities.In SPICE implementation,it makes clear and accurate definitions of three kinds of nodes—the carrier density nodes,the voltage nodes and the current generator nodes—in the undepleted N^(-)base region.It uses central finite difference to approximate electron and hole current generators and sets up the current continuity equation in a control volume for every carrier density node in the undepleted N^(-)base region.It is easy to increase the number of nodes to describe the fast spatially varying carrier density in transient processes.We use this method to simulate IGBT devices in SPICE simulators and get a good agreement with technology computer-aided design simulations.展开更多
A one-dimensional pipe flow model of single-cylinder diesel engine is established to investigate the intake and exhaust flow characteristics of diesel engine in the condition of high power density(HPD).A space-lime co...A one-dimensional pipe flow model of single-cylinder diesel engine is established to investigate the intake and exhaust flow characteristics of diesel engine in the condition of high power density(HPD).A space-lime conservation element and solution element(CE/SE)method is used to derive the discrete equations of the partial differential equation for the intake and exhaust systems.The performance parameters of diesel engine with speed of 2100 r/min are simulated.The simulated results are in accordance with the experimental data.The effect of increased power density on charging coefficient is analyzed using a validated model.The results show that the charging coefficient is slowly improved with the increase in intake pressure,and is obviously reduced with the increase in engine speed.展开更多
基于非线性3D模拟软件AN SY S/LS-DYNA和LS-REPO ST,用ALE算法模拟线性聚能装药射流形成以及射流对某均质钢靶切割侵彻的过程。在模拟过程中考虑到射流、空气和钢靶的流固耦合问题,故计算模型基本合理。经过计算,得到了线性聚能装药爆...基于非线性3D模拟软件AN SY S/LS-DYNA和LS-REPO ST,用ALE算法模拟线性聚能装药射流形成以及射流对某均质钢靶切割侵彻的过程。在模拟过程中考虑到射流、空气和钢靶的流固耦合问题,故计算模型基本合理。经过计算,得到了线性聚能装药爆轰波的传播过程、射流形成过程以及钢靶切割过程的3D模拟结果,用LS-RE-PO ST软件也得到了射流头部压力、速度和加速度变化曲线。将数值模拟和计算结果进行对比,结果令人满意、可信,3D数值模拟较以前的2D模拟更形象逼真,显示了ALE算法解决此类问题的优越性。展开更多
基金supported by National Natural Science Foundation of China(Nos.92066108 and 51277061)。
文摘The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.
文摘A finite-volume charge method has been proposed to simulate PIN diodes and insulated-gate bipolar transistor(IGBT)devices using SPICE simulators by extending the lumped-charge method.The new method assumes local quasi-neutrality in the undepleted N^(-)base region and uses the total collector current,the nodal hole density and voltage as the basic quantities.In SPICE implementation,it makes clear and accurate definitions of three kinds of nodes—the carrier density nodes,the voltage nodes and the current generator nodes—in the undepleted N^(-)base region.It uses central finite difference to approximate electron and hole current generators and sets up the current continuity equation in a control volume for every carrier density node in the undepleted N^(-)base region.It is easy to increase the number of nodes to describe the fast spatially varying carrier density in transient processes.We use this method to simulate IGBT devices in SPICE simulators and get a good agreement with technology computer-aided design simulations.
文摘A one-dimensional pipe flow model of single-cylinder diesel engine is established to investigate the intake and exhaust flow characteristics of diesel engine in the condition of high power density(HPD).A space-lime conservation element and solution element(CE/SE)method is used to derive the discrete equations of the partial differential equation for the intake and exhaust systems.The performance parameters of diesel engine with speed of 2100 r/min are simulated.The simulated results are in accordance with the experimental data.The effect of increased power density on charging coefficient is analyzed using a validated model.The results show that the charging coefficient is slowly improved with the increase in intake pressure,and is obviously reduced with the increase in engine speed.
文摘基于非线性3D模拟软件AN SY S/LS-DYNA和LS-REPO ST,用ALE算法模拟线性聚能装药射流形成以及射流对某均质钢靶切割侵彻的过程。在模拟过程中考虑到射流、空气和钢靶的流固耦合问题,故计算模型基本合理。经过计算,得到了线性聚能装药爆轰波的传播过程、射流形成过程以及钢靶切割过程的3D模拟结果,用LS-RE-PO ST软件也得到了射流头部压力、速度和加速度变化曲线。将数值模拟和计算结果进行对比,结果令人满意、可信,3D数值模拟较以前的2D模拟更形象逼真,显示了ALE算法解决此类问题的优越性。
