Power flow transfer(PFT) analysis under various anticipated faults in advance is important for securing power system operations. In China, PSD-BPA software is the most widely used tool for power system analysis, but i...Power flow transfer(PFT) analysis under various anticipated faults in advance is important for securing power system operations. In China, PSD-BPA software is the most widely used tool for power system analysis, but its input/output interface is easily adapted for PFT analysis,which is also difficult due to its computationally intensity.To solve this issue, and achieve a fast and accurate PFT analysis, a modular parallelization framework is developed in this paper. Two major contributions are included. One is several integrated PFT analysis modules, including parameter initialization, fault setting, network integrity detection, reasonableness identification and result analysis.The other is a parallelization technique for enhancing computation efficiency using a Fork/Join framework. The proposed framework has been tested and validated by the IEEE 39 bus reference power system. Furthermore, it has been applied to a practical power network with 11052 buses and 12487 branches in the Yunnan Power Grid ofChina, providing decision support for large-scale power system analysis.展开更多
A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed S...A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.展开更多
The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow a...The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.展开更多
The optimization method by adjusting load and distances between two adjacent coils( or resonators) is presented on basis of wireless power transfer( WPT) system with relay resonators. 2-port network and impedance matc...The optimization method by adjusting load and distances between two adjacent coils( or resonators) is presented on basis of wireless power transfer( WPT) system with relay resonators. 2-port network and impedance matching theory are applied to analyzing power flow of incidence and reflection in WPT system,then setting up power flow model. The maximum power transmission efficiency can be obtained when the load and distance between secondary resonator and output coil meets impedance matching at 2-port network's output port. The simulation and experimental results shown the impedance matching method can effectively improve and maintain transmission efficiency by adjusting load and distances between coils or relay resonators.展开更多
An overview on the application and achievements of physico-mathematicalmodeling of metallurgical processes in China is briefly declared. The important role of coefficientsin model formulation is shown from our experie...An overview on the application and achievements of physico-mathematicalmodeling of metallurgical processes in China is briefly declared. The important role of coefficientsin model formulation is shown from our experience. The mass transfer coefficients of the slag-metalreactions and the gas-metal reactions are discussed referring to the flow conditions near theinterface. The influence of the surface-active species on the mass transfer and the interfacialreaction is also discussed briefly.展开更多
微通道散热器是应对电子器件散热的有效方法,但目前常规通道存在功耗大等问题。分形结构被认为是质能运输效率最高结构之一。按照Murray定律和“黄金比例phi”设计Y型和Ψ-Y型微通道的结构,得到4种微通道:Ψ-Y-M、Y-M、Ψ-Y-phi、Y-phi...微通道散热器是应对电子器件散热的有效方法,但目前常规通道存在功耗大等问题。分形结构被认为是质能运输效率最高结构之一。按照Murray定律和“黄金比例phi”设计Y型和Ψ-Y型微通道的结构,得到4种微通道:Ψ-Y-M、Y-M、Ψ-Y-phi、Y-phi。研究采用Fluent进行数值模拟,结果表明,phi型结构比Murray型结构底面温度低;Ψ型结构比Y型结构的底面温度分布更均匀。引入性能系数(coefficient of performance,COP)来评价各结构的综合性能,Ψ-Y-M的COP相较于Y-M增长了约3%,Ψ-Y-phi和Y-phi的COP都小于Y-M,前者减小约6%,后者减小约18%。展开更多
为了解决大规模风电接入所导致的可用输电能力(available transfer capability,ATC)受限问题,提出了一种提升风电接入系统ATC的混合型潮流控制器(hybrid power flow controller,HPFC)选址定容方法。首先,基于功率注入法建立HPFC的数学模...为了解决大规模风电接入所导致的可用输电能力(available transfer capability,ATC)受限问题,提出了一种提升风电接入系统ATC的混合型潮流控制器(hybrid power flow controller,HPFC)选址定容方法。首先,基于功率注入法建立HPFC的数学模型,并采用改进K均值(K-means)聚类算法削减风电、负荷概率场景;其次,建立了计及ATC的HPFC双层优化配置模型,上层优化模型以最小化HPFC配置成本和节点电压偏移为目标,下层以最大化系统ATC为目标;最后,应用改进多目标粒子群(multi-objective particle swarm optimization,MOPSO)算法计算所提双层优化模型的Pareto解集,根据解集中每个解的模糊满意度函数确定最优解。展开更多
基金supported by the Major International Joint Research Project from the National Nature Science Foundation of China (No. 51210014)Major Program of National Natural Science Foundation of China (No. 91547201)
文摘Power flow transfer(PFT) analysis under various anticipated faults in advance is important for securing power system operations. In China, PSD-BPA software is the most widely used tool for power system analysis, but its input/output interface is easily adapted for PFT analysis,which is also difficult due to its computationally intensity.To solve this issue, and achieve a fast and accurate PFT analysis, a modular parallelization framework is developed in this paper. Two major contributions are included. One is several integrated PFT analysis modules, including parameter initialization, fault setting, network integrity detection, reasonableness identification and result analysis.The other is a parallelization technique for enhancing computation efficiency using a Fork/Join framework. The proposed framework has been tested and validated by the IEEE 39 bus reference power system. Furthermore, it has been applied to a practical power network with 11052 buses and 12487 branches in the Yunnan Power Grid ofChina, providing decision support for large-scale power system analysis.
基金supported by National Natural Science Foundation of China (Nos.50836007, 10921062)
文摘A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.
文摘The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.
基金Human Provincial Natural Science Foudation of China(No.2016JJ4043)Youth Foundation of Education Bureau of Hunan Province,China(No.16B137)Science and Technology Projects of Loudi City,China
文摘The optimization method by adjusting load and distances between two adjacent coils( or resonators) is presented on basis of wireless power transfer( WPT) system with relay resonators. 2-port network and impedance matching theory are applied to analyzing power flow of incidence and reflection in WPT system,then setting up power flow model. The maximum power transmission efficiency can be obtained when the load and distance between secondary resonator and output coil meets impedance matching at 2-port network's output port. The simulation and experimental results shown the impedance matching method can effectively improve and maintain transmission efficiency by adjusting load and distances between coils or relay resonators.
文摘An overview on the application and achievements of physico-mathematicalmodeling of metallurgical processes in China is briefly declared. The important role of coefficientsin model formulation is shown from our experience. The mass transfer coefficients of the slag-metalreactions and the gas-metal reactions are discussed referring to the flow conditions near theinterface. The influence of the surface-active species on the mass transfer and the interfacialreaction is also discussed briefly.
文摘微通道散热器是应对电子器件散热的有效方法,但目前常规通道存在功耗大等问题。分形结构被认为是质能运输效率最高结构之一。按照Murray定律和“黄金比例phi”设计Y型和Ψ-Y型微通道的结构,得到4种微通道:Ψ-Y-M、Y-M、Ψ-Y-phi、Y-phi。研究采用Fluent进行数值模拟,结果表明,phi型结构比Murray型结构底面温度低;Ψ型结构比Y型结构的底面温度分布更均匀。引入性能系数(coefficient of performance,COP)来评价各结构的综合性能,Ψ-Y-M的COP相较于Y-M增长了约3%,Ψ-Y-phi和Y-phi的COP都小于Y-M,前者减小约6%,后者减小约18%。
文摘为了解决大规模风电接入所导致的可用输电能力(available transfer capability,ATC)受限问题,提出了一种提升风电接入系统ATC的混合型潮流控制器(hybrid power flow controller,HPFC)选址定容方法。首先,基于功率注入法建立HPFC的数学模型,并采用改进K均值(K-means)聚类算法削减风电、负荷概率场景;其次,建立了计及ATC的HPFC双层优化配置模型,上层优化模型以最小化HPFC配置成本和节点电压偏移为目标,下层以最大化系统ATC为目标;最后,应用改进多目标粒子群(multi-objective particle swarm optimization,MOPSO)算法计算所提双层优化模型的Pareto解集,根据解集中每个解的模糊满意度函数确定最优解。
