This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters...This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters. Three depth-averaged two-equation turbulence closure models, k-ε,k-w, and k-w, were used to close the non-simplified quasi-three-dimensional hydrodynamic fundamental governing equations. The discretized equations were solved with the advanced multi-grid iterative method using non-orthogonal body-fitted coarse and fine grids with collocated variable arrangement. Except for steady flow computation, the processes of contaminant inpouring and plume development at the beginning of discharge, caused by a side-discharge of a tributary, have also been numerically investigated. The three depth-averaged two-equation closure models are all suitable for modeling strong mixing turbulence. The newly established turbulence models such as the k-w model, with a higher order of magnitude of the turbulence parameter, provide a possibility for improving computational precision.展开更多
To transmit customer power data collected by smart meters(SMs)to utility companies,data must first be transmitted to the corresponding data aggregation point(DAP)of the SM.The number of DAPs installed and the installa...To transmit customer power data collected by smart meters(SMs)to utility companies,data must first be transmitted to the corresponding data aggregation point(DAP)of the SM.The number of DAPs installed and the installation location greatly impact the whole network.For the traditional DAP placement algorithm,the number of DAPs must be set in advance,but determining the best number of DAPs is difficult,which undoubtedly reduces the overall performance of the network.Moreover,the excessive gap between the loads of different DAPs is also an important factor affecting the quality of the network.To address the above problems,this paper proposes a DAP placement algorithm,APSSA,based on the improved affinity propagation(AP)algorithm and sparrow search(SSA)algorithm,which can select the appropriate number of DAPs to be installed and the corresponding installation locations according to the number of SMs and their distribution locations in different environments.The algorithm adds an allocation mechanism to optimize the subnetwork in the SSA.APSSA is evaluated under three different areas and compared with other DAP placement algorithms.The experimental results validated that the method in this paper can reduce the network cost,shorten the average transmission distance,and reduce the load gap.展开更多
Based on analysis of the discharging course in double grid air counter (DGAC),the dischargin model is built up by applying the conception of average ionizing free path. An effective algorithm is presented for the wor...Based on analysis of the discharging course in double grid air counter (DGAC),the dischargin model is built up by applying the conception of average ionizing free path. An effective algorithm is presented for the working voltage of DGAC using this model. The working voltage is nearly related to the geometric parameters of DGAC, the sensitivity of the circuitry and the number of discharges. Computing results confirm that the working voltage increases with the ratio of the radius of the anode to that of the cathode. The number of discharges follows the similar rule.展开更多
With the characteristics of diversity, randomness, concurrency and decomposability, tasks in manufacturing field are very complicated, and so manufacturing grid (MG) should have considerable flexibility to deal with t...With the characteristics of diversity, randomness, concurrency and decomposability, tasks in manufacturing field are very complicated, and so manufacturing grid (MG) should have considerable flexibility to deal with this problem. With the definition of node and arc, MG structure is converted into a small-world network. Given construction cost constraint, the problem of shortest task waiting time is transformed into the constrained optimization problem, and a corresponding ?exibility analysis model based on average path length (APL) is proposed, and the premise of arc-length and node-distance are defined. The results of application example show that the analysis model is effiective.展开更多
In this paper, we present the a posteriori error estimate of two-grid mixed finite element methods by averaging techniques for semilinear elliptic equations. We first propose the two-grid algorithms to linearize the m...In this paper, we present the a posteriori error estimate of two-grid mixed finite element methods by averaging techniques for semilinear elliptic equations. We first propose the two-grid algorithms to linearize the mixed method equations. Then, the averaging technique is used to construct the a posteriori error estimates of the two-grid mixed finite element method and theoretical analysis are given for the error estimators. Finally, we give some numerical examples to verify the reliability and efficiency of the a posteriori error estimator.展开更多
电网同步锁相是光伏跟网型并网系统稳定可靠运行的关键技术之一。高比例新能源场景下,电网面临着电压扰动、电压不平衡、谐波畸变及直流偏置等诸多问题。为此,提出一种基于同步参考坐标系锁相环和环前型滑动平均滤波结构(pre-loop movin...电网同步锁相是光伏跟网型并网系统稳定可靠运行的关键技术之一。高比例新能源场景下,电网面临着电压扰动、电压不平衡、谐波畸变及直流偏置等诸多问题。为此,提出一种基于同步参考坐标系锁相环和环前型滑动平均滤波结构(pre-loop moving average filter,PMAF)的新型锁相环。该锁相环采用相位补偿方法校正频率偏移时的锁相误差。同时,考虑PMAF的相频耦合特性,设计了一种角频率补偿方法以提高锁相环的动态性能,建立其小信号模型并进行稳定性分析。接着设计了一种故障检测模块,实现两种补偿支路的投入和切除以适应不同工况。仿真验证了该新型锁相环在相位跳变、频率偏移、电压畸变等复杂电网条件下的有效性。最后,在高比例新能源电网中进行了新型锁相环的暂态性能测试。结果表明该锁相环能快速锁定电网电压相位,避免电压电流的振荡发散,有利于系统在故障后快速平稳地恢复。展开更多
为解决应用于LCL型并网逆变器的传统反步控制策略所存在的计算量大、测量噪声被成倍放大的问题,提出一种基于加权平均电流控制WACC(weighted average current control )的改进反步控制策略。首先,利用WACC策略将LCL三阶滤波系统降阶为一...为解决应用于LCL型并网逆变器的传统反步控制策略所存在的计算量大、测量噪声被成倍放大的问题,提出一种基于加权平均电流控制WACC(weighted average current control )的改进反步控制策略。首先,利用WACC策略将LCL三阶滤波系统降阶为一阶,在有效减少整体计算量的同时,降低对虚拟控制量的求导次数;然后,利用滑模观测器对加权平均电流进行观测,以减小LCL滤波器参数摄动对加权平均电流精度的影响;最后,依据所建立的等效系统模型设计反步控制器,控制并网电流。仿真与实验结果表明,所提控制策略具有良好的稳态性能和较高的鲁棒性。展开更多
A depth averaged nonlinear k ε model for turbulent flows in complex geometries has been developed in a boundary fitted coordinate system. The SIMPLEC procedure is used to develop an economical discrete method for ...A depth averaged nonlinear k ε model for turbulent flows in complex geometries has been developed in a boundary fitted coordinate system. The SIMPLEC procedure is used to develop an economical discrete method for staggered grids to analyze flows in a 90° bend. This paper describes how to change a program in rectangular coordinate into a boundary fitted coordinate. The results compare well with experimental data for flow in a meandering channel showing the efficiency of the model and the discrete method.展开更多
基金supported by FAPESP (Foundation for Supporting Research in So Paulo State), Brazil, of the PIPE Project (Grant No. 2006/56475-3)
文摘This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters. Three depth-averaged two-equation turbulence closure models, k-ε,k-w, and k-w, were used to close the non-simplified quasi-three-dimensional hydrodynamic fundamental governing equations. The discretized equations were solved with the advanced multi-grid iterative method using non-orthogonal body-fitted coarse and fine grids with collocated variable arrangement. Except for steady flow computation, the processes of contaminant inpouring and plume development at the beginning of discharge, caused by a side-discharge of a tributary, have also been numerically investigated. The three depth-averaged two-equation closure models are all suitable for modeling strong mixing turbulence. The newly established turbulence models such as the k-w model, with a higher order of magnitude of the turbulence parameter, provide a possibility for improving computational precision.
基金supported by the Fujian University of Technology under Grant GYZ20016,GY-Z18183,and GY-Z19005partially supported by the National Science and Technology Council under Grant NSTC 113-2221-E-224-056-.
文摘To transmit customer power data collected by smart meters(SMs)to utility companies,data must first be transmitted to the corresponding data aggregation point(DAP)of the SM.The number of DAPs installed and the installation location greatly impact the whole network.For the traditional DAP placement algorithm,the number of DAPs must be set in advance,but determining the best number of DAPs is difficult,which undoubtedly reduces the overall performance of the network.Moreover,the excessive gap between the loads of different DAPs is also an important factor affecting the quality of the network.To address the above problems,this paper proposes a DAP placement algorithm,APSSA,based on the improved affinity propagation(AP)algorithm and sparrow search(SSA)algorithm,which can select the appropriate number of DAPs to be installed and the corresponding installation locations according to the number of SMs and their distribution locations in different environments.The algorithm adds an allocation mechanism to optimize the subnetwork in the SSA.APSSA is evaluated under three different areas and compared with other DAP placement algorithms.The experimental results validated that the method in this paper can reduce the network cost,shorten the average transmission distance,and reduce the load gap.
文摘Based on analysis of the discharging course in double grid air counter (DGAC),the dischargin model is built up by applying the conception of average ionizing free path. An effective algorithm is presented for the working voltage of DGAC using this model. The working voltage is nearly related to the geometric parameters of DGAC, the sensitivity of the circuitry and the number of discharges. Computing results confirm that the working voltage increases with the ratio of the radius of the anode to that of the cathode. The number of discharges follows the similar rule.
基金supported by the National Natural Science Foundation of China (Grant No.50805089)the Science Foundation of Science and Technology Commission of Shanghai Municipality (Grant Nos.08DZ1123402,08DZ1124502)
文摘With the characteristics of diversity, randomness, concurrency and decomposability, tasks in manufacturing field are very complicated, and so manufacturing grid (MG) should have considerable flexibility to deal with this problem. With the definition of node and arc, MG structure is converted into a small-world network. Given construction cost constraint, the problem of shortest task waiting time is transformed into the constrained optimization problem, and a corresponding ?exibility analysis model based on average path length (APL) is proposed, and the premise of arc-length and node-distance are defined. The results of application example show that the analysis model is effiective.
文摘In this paper, we present the a posteriori error estimate of two-grid mixed finite element methods by averaging techniques for semilinear elliptic equations. We first propose the two-grid algorithms to linearize the mixed method equations. Then, the averaging technique is used to construct the a posteriori error estimates of the two-grid mixed finite element method and theoretical analysis are given for the error estimators. Finally, we give some numerical examples to verify the reliability and efficiency of the a posteriori error estimator.
文摘电网同步锁相是光伏跟网型并网系统稳定可靠运行的关键技术之一。高比例新能源场景下,电网面临着电压扰动、电压不平衡、谐波畸变及直流偏置等诸多问题。为此,提出一种基于同步参考坐标系锁相环和环前型滑动平均滤波结构(pre-loop moving average filter,PMAF)的新型锁相环。该锁相环采用相位补偿方法校正频率偏移时的锁相误差。同时,考虑PMAF的相频耦合特性,设计了一种角频率补偿方法以提高锁相环的动态性能,建立其小信号模型并进行稳定性分析。接着设计了一种故障检测模块,实现两种补偿支路的投入和切除以适应不同工况。仿真验证了该新型锁相环在相位跳变、频率偏移、电压畸变等复杂电网条件下的有效性。最后,在高比例新能源电网中进行了新型锁相环的暂态性能测试。结果表明该锁相环能快速锁定电网电压相位,避免电压电流的振荡发散,有利于系统在故障后快速平稳地恢复。
文摘为解决应用于LCL型并网逆变器的传统反步控制策略所存在的计算量大、测量噪声被成倍放大的问题,提出一种基于加权平均电流控制WACC(weighted average current control )的改进反步控制策略。首先,利用WACC策略将LCL三阶滤波系统降阶为一阶,在有效减少整体计算量的同时,降低对虚拟控制量的求导次数;然后,利用滑模观测器对加权平均电流进行观测,以减小LCL滤波器参数摄动对加权平均电流精度的影响;最后,依据所建立的等效系统模型设计反步控制器,控制并网电流。仿真与实验结果表明,所提控制策略具有良好的稳态性能和较高的鲁棒性。
文摘文中提出了一种用于估计电网频率的带滑动平均滤波器(moving average filter,MAF)半正切锁相环(half-tangent phase-locked loop,HTan-PLL)。所提出的PLL(phase-locked loop)采用半正切鉴相器(phase detector,PD),并在锁相环中引入MAF(mass air flow)解决电网中的谐波干扰。与常规SRF-PLL(self resonant frequency phase-locked loop)和HTan-PLL(half-tangent phase-locked loop)相比,当电网频率发生跳变时,所提出的带滑动平均滤波器半切锁相环(moving average filter half-tangent phase-locked loop,MAF-HTan-PLL)具有更高的动态特性;此外,当电网包含谐波干扰时,它具有理想的稳态精度和动态性能。通过实验与常规方法进行对比分析,验证了该方法的优越性。结果表明,相比于常规方法,所提方法在频率发生较大跳变以及存在谐波干扰的情况下,仍然能够快速而准确的实现频率估计。
文摘A depth averaged nonlinear k ε model for turbulent flows in complex geometries has been developed in a boundary fitted coordinate system. The SIMPLEC procedure is used to develop an economical discrete method for staggered grids to analyze flows in a 90° bend. This paper describes how to change a program in rectangular coordinate into a boundary fitted coordinate. The results compare well with experimental data for flow in a meandering channel showing the efficiency of the model and the discrete method.
