Modeling and simulation have emerged as an indispensable approach to create numerical experiment platforms and study engineering systems.However,the increasingly complicated systems that engineers face today dramatica...Modeling and simulation have emerged as an indispensable approach to create numerical experiment platforms and study engineering systems.However,the increasingly complicated systems that engineers face today dramatically challenge state-of-the-art modeling and simulation approaches.Such complicated systems,which are composed of not only continuous states but also discrete events,and which contain complex dynamics across multiple timescales,are defined as generalized hybrid systems(GHSs)in this paper.As a representative GHS,megawatt power electronics(MPE)systems have been largely integrated into the modern power grid,but MPE simulation remains a bottleneck due to its unacceptable time cost and poor convergence.To address this challenge,this paper proposes the numerical convex lens approach to achieve state-discretized modeling and simulation of GHSs.This approach transforms conventional time-discretized passive simulations designed for pure-continuous systems into state-discretized selective simulations designed for GHSs.When this approach was applied to a largescale MPE-based renewable energy system,a 1000-fold increase in simulation speed was achieved,in comparison with existing software.Furthermore,the proposed approach uniquely enables the switching transient simulation of a largescale megawatt system with high accuracy,compared with experimental results,and with no convergence concerns.The numerical convex lens approach leads to the highly efficient simulation of intricate GHSs across multiple timescales,and thus significantly extends engineers’capability to study systems with numerical experiments.展开更多
The key and bottleneck of research on the tip-jet rotor compound helicopter lies in the power system. Computational Fluid Dynamics (CFD) was used to numerically simulate the gas generator and rotor inner passage of th...The key and bottleneck of research on the tip-jet rotor compound helicopter lies in the power system. Computational Fluid Dynamics (CFD) was used to numerically simulate the gas generator and rotor inner passage of the tip-jet rotor composite power system, studying the effects of intake mode, inner cavity structure, propellant components, and injection amount on the characteristics of the composite power system. The results show that when a single high-temperature exhaust gas enters, the gas generator outlet fluid is uneven and asymmetric;when two-way high-temperature exhaust gas enters, the outlet temperature of the gas generator with a tilted inlet is more uniform than that with a vertical inlet;adding an inner cavity improves the temperature and velocity distribution of the gas generator's internal flow field;increasing the energy of the propellant is beneficial for improving the available moment.展开更多
The solar power conversion efficiency of a gallium indium phosphide(GaInP)/silicon(Si)tandem solar cell has been investigated by means of a physical device simulator considering both mechanically stacked and monolithi...The solar power conversion efficiency of a gallium indium phosphide(GaInP)/silicon(Si)tandem solar cell has been investigated by means of a physical device simulator considering both mechanically stacked and monolithic structures.In particular,to interconnect the bottom and top sub-cells of the monolithic tandem,a gallium arsenide(GaAs)-based tunnel-junction,i.e.GaAs(n+)/GaAs(p+),which assures a low electrical resistance and an optically low-loss connection,has been considered.The J–V characteristics of the single junction cells,monolithic tandem,and mechanically stacked structure have been calculated extracting the main photovoltaic parameters.An analysis of the tunnel-junction behaviour has been also developed.The mechanically stacked cell achieves an efficiency of 24.27%whereas the monolithic tandem reaches an efficiency of 31.11%under AM1.5 spectral conditions.External quantum efficiency simulations have evaluated the useful wavelength range.The results and discussion could be helpful in designing high efficiency monolithic multijunction GaInP/Si solar cells involving a thin GaAs(n+)/GaAs(p+)tunnel junction.展开更多
以脱酸塔内旋转雾化器为研究对象,基于VOF(Volume of fluid)和DPM(Discrete particle model)方法,采用Fluent软件模拟了石灰浆液的一次破碎过程和雾化后的粒径分布特征,分析了雾化盘转速、单喷孔、平行双/3喷孔及孔间距对喷孔射流一次...以脱酸塔内旋转雾化器为研究对象,基于VOF(Volume of fluid)和DPM(Discrete particle model)方法,采用Fluent软件模拟了石灰浆液的一次破碎过程和雾化后的粒径分布特征,分析了雾化盘转速、单喷孔、平行双/3喷孔及孔间距对喷孔射流一次破碎效果和粒径分布的影响。结果表明,高速射流条件下的液滴破碎主要由周向表面波和轴向波叠加导致,并呈现出关于主流对称的形态;多喷孔射流的聚合射程与孔间距成正比关系,增加喷孔数将导致射流提前聚合;提高雾化盘转速、喷孔间距和喷孔数目均有利于减小雾化后液滴平均直径;多喷孔结构下的液滴平均直径与孔间距呈简单的线性关系。展开更多
基金the Major Program of National Natural Science Foundation of China(51490683).
文摘Modeling and simulation have emerged as an indispensable approach to create numerical experiment platforms and study engineering systems.However,the increasingly complicated systems that engineers face today dramatically challenge state-of-the-art modeling and simulation approaches.Such complicated systems,which are composed of not only continuous states but also discrete events,and which contain complex dynamics across multiple timescales,are defined as generalized hybrid systems(GHSs)in this paper.As a representative GHS,megawatt power electronics(MPE)systems have been largely integrated into the modern power grid,but MPE simulation remains a bottleneck due to its unacceptable time cost and poor convergence.To address this challenge,this paper proposes the numerical convex lens approach to achieve state-discretized modeling and simulation of GHSs.This approach transforms conventional time-discretized passive simulations designed for pure-continuous systems into state-discretized selective simulations designed for GHSs.When this approach was applied to a largescale MPE-based renewable energy system,a 1000-fold increase in simulation speed was achieved,in comparison with existing software.Furthermore,the proposed approach uniquely enables the switching transient simulation of a largescale megawatt system with high accuracy,compared with experimental results,and with no convergence concerns.The numerical convex lens approach leads to the highly efficient simulation of intricate GHSs across multiple timescales,and thus significantly extends engineers’capability to study systems with numerical experiments.
文摘The key and bottleneck of research on the tip-jet rotor compound helicopter lies in the power system. Computational Fluid Dynamics (CFD) was used to numerically simulate the gas generator and rotor inner passage of the tip-jet rotor composite power system, studying the effects of intake mode, inner cavity structure, propellant components, and injection amount on the characteristics of the composite power system. The results show that when a single high-temperature exhaust gas enters, the gas generator outlet fluid is uneven and asymmetric;when two-way high-temperature exhaust gas enters, the outlet temperature of the gas generator with a tilted inlet is more uniform than that with a vertical inlet;adding an inner cavity improves the temperature and velocity distribution of the gas generator's internal flow field;increasing the energy of the propellant is beneficial for improving the available moment.
文摘The solar power conversion efficiency of a gallium indium phosphide(GaInP)/silicon(Si)tandem solar cell has been investigated by means of a physical device simulator considering both mechanically stacked and monolithic structures.In particular,to interconnect the bottom and top sub-cells of the monolithic tandem,a gallium arsenide(GaAs)-based tunnel-junction,i.e.GaAs(n+)/GaAs(p+),which assures a low electrical resistance and an optically low-loss connection,has been considered.The J–V characteristics of the single junction cells,monolithic tandem,and mechanically stacked structure have been calculated extracting the main photovoltaic parameters.An analysis of the tunnel-junction behaviour has been also developed.The mechanically stacked cell achieves an efficiency of 24.27%whereas the monolithic tandem reaches an efficiency of 31.11%under AM1.5 spectral conditions.External quantum efficiency simulations have evaluated the useful wavelength range.The results and discussion could be helpful in designing high efficiency monolithic multijunction GaInP/Si solar cells involving a thin GaAs(n+)/GaAs(p+)tunnel junction.
文摘以脱酸塔内旋转雾化器为研究对象,基于VOF(Volume of fluid)和DPM(Discrete particle model)方法,采用Fluent软件模拟了石灰浆液的一次破碎过程和雾化后的粒径分布特征,分析了雾化盘转速、单喷孔、平行双/3喷孔及孔间距对喷孔射流一次破碎效果和粒径分布的影响。结果表明,高速射流条件下的液滴破碎主要由周向表面波和轴向波叠加导致,并呈现出关于主流对称的形态;多喷孔射流的聚合射程与孔间距成正比关系,增加喷孔数将导致射流提前聚合;提高雾化盘转速、喷孔间距和喷孔数目均有利于减小雾化后液滴平均直径;多喷孔结构下的液滴平均直径与孔间距呈简单的线性关系。
