该研究的目的是将能量辐射传递法(radiative energy transfer method,RETM)推广到功能梯度板模型中,以预测结构的高频振动响应。基于一阶剪切变形理论推导了功能梯度板的振动控制方程,获得了波传播特性参数。在该方法中,结构内部的能量...该研究的目的是将能量辐射传递法(radiative energy transfer method,RETM)推广到功能梯度板模型中,以预测结构的高频振动响应。基于一阶剪切变形理论推导了功能梯度板的振动控制方程,获得了波传播特性参数。在该方法中,结构内部的能量响应由激励产生的直接场与边界虚源产生的反射场叠加得到。在临界频率以下,能量响应由一种传播波控制;而在临界频率以上,由三种传播波控制。数值算例结果与模态叠加法和功率流分析进行了对比,验证了RETM在计算不同物理参数下功能梯度板高频振动响应的准确性。研究了不同厚度下剪切变形和转动惯量对能量响应的影响,讨论了材料梯度因子、结构阻尼和激励频率对高频振动能量的影响。结果表明,材料梯度因子的变化会导致结构波传播特性和能量分布特征的变化,越大能量的衰减速度越快,衰减幅度越大。展开更多
The main objective of this paper is to show an overview analysis of market power issues.Market power reflects the scarcity of power supply.It is the ability of a particular seller or group of sellers to maintain price...The main objective of this paper is to show an overview analysis of market power issues.Market power reflects the scarcity of power supply.It is the ability of a particular seller or group of sellers to maintain prices profitably above competitive levels for a significant period of time.Because the electric power system has its own characteristics that are different to other economic systems,both physical factors and economic factors of power system are key elements on this definition.We study some cases here,including different line limit levels,load levels and bid strategy through a market model based on OPF (optimal power flow) with a decommitment algorithm.展开更多
The international standard IEC 61400-12-1 Wind turbines--Part 12-1： Power performance measurements of electricity producing wind turbines＂ aims to provide a uniform methodology that will ensure consistency, accuracy...The international standard IEC 61400-12-1 Wind turbines--Part 12-1： Power performance measurements of electricity producing wind turbines＂ aims to provide a uniform methodology that will ensure consistency, accuracy and reproducibility in the measurement and analysis of power performance by wind turbines. Annex G of this standard provides a methodology for the appropriate arrangement of instruments on the meteorological mast to ensure accurate measurement. For cup anemometers it provides recommendations about their location relative to the mast so that the effect of mast and boom interference on their output may be minimised. These recommendations are given for both tubular masts and lattice masts. This paper compares the flow distortion predicted by the IEC standard and the results of a 3D CFD （computational fluid dynamics） simulation of a triangular lattice mast. Based on the results of wind tunnel and CFD simulation it was found that the flow distortion surrounding the lattice mast was overpredicted by the method suggested in appendix G oflEC61400-12-1. Using the CFD data it was possible to determine, for a range of flow directions and mast heights, the distance from the mast that anemometers would need to be in order to be outside the flow distortion field.展开更多
This paper performs a numerical simulation of three-dimensional flow field in a centrifugal compressor with long inlet and outlet pipes using CFX software.By arranging virtual probes at different positions in both inl...This paper performs a numerical simulation of three-dimensional flow field in a centrifugal compressor with long inlet and outlet pipes using CFX software.By arranging virtual probes at different positions in both inlet and outlet planes,the aerodynamic performance of the centrifugal compressor is measured and compared with each other.Then effects of measuring positions on measurement results are discussed.The results show that it will generate notable measuring errors of the pressure ratio and efficiency if the inlet total pressure is measured using a single-point probe.The inlet total pressure data can be accurate when they are measured using a 3-point rake.The outlet total pressure and total temperature data can not be accurate if they are respectively measured at one circumferential position even using a multi-point rake.Increasing tangential measuring positions at the outlet is effective to improve the test accuracy.When the outlet total pressure and total temperature are respectively measured at 3 tangential positions,the data can be almost accurate.展开更多
文摘该研究的目的是将能量辐射传递法(radiative energy transfer method,RETM)推广到功能梯度板模型中,以预测结构的高频振动响应。基于一阶剪切变形理论推导了功能梯度板的振动控制方程,获得了波传播特性参数。在该方法中,结构内部的能量响应由激励产生的直接场与边界虚源产生的反射场叠加得到。在临界频率以下,能量响应由一种传播波控制;而在临界频率以上,由三种传播波控制。数值算例结果与模态叠加法和功率流分析进行了对比,验证了RETM在计算不同物理参数下功能梯度板高频振动响应的准确性。研究了不同厚度下剪切变形和转动惯量对能量响应的影响,讨论了材料梯度因子、结构阻尼和激励频率对高频振动能量的影响。结果表明,材料梯度因子的变化会导致结构波传播特性和能量分布特征的变化,越大能量的衰减速度越快,衰减幅度越大。
基金This paper supported by National Natural Science Foundation of China (50079006).
文摘The main objective of this paper is to show an overview analysis of market power issues.Market power reflects the scarcity of power supply.It is the ability of a particular seller or group of sellers to maintain prices profitably above competitive levels for a significant period of time.Because the electric power system has its own characteristics that are different to other economic systems,both physical factors and economic factors of power system are key elements on this definition.We study some cases here,including different line limit levels,load levels and bid strategy through a market model based on OPF (optimal power flow) with a decommitment algorithm.
文摘The international standard IEC 61400-12-1 Wind turbines--Part 12-1： Power performance measurements of electricity producing wind turbines＂ aims to provide a uniform methodology that will ensure consistency, accuracy and reproducibility in the measurement and analysis of power performance by wind turbines. Annex G of this standard provides a methodology for the appropriate arrangement of instruments on the meteorological mast to ensure accurate measurement. For cup anemometers it provides recommendations about their location relative to the mast so that the effect of mast and boom interference on their output may be minimised. These recommendations are given for both tubular masts and lattice masts. This paper compares the flow distortion predicted by the IEC standard and the results of a 3D CFD （computational fluid dynamics） simulation of a triangular lattice mast. Based on the results of wind tunnel and CFD simulation it was found that the flow distortion surrounding the lattice mast was overpredicted by the method suggested in appendix G oflEC61400-12-1. Using the CFD data it was possible to determine, for a range of flow directions and mast heights, the distance from the mast that anemometers would need to be in order to be outside the flow distortion field.
基金funded by Chinese Key Laboratory Fund,Grant No.9140C3310040705the National Natural Science Foundation of China,Grant No.50776004+1 种基金supported by the 111 Project,No.B07009973 Project,No.2007CB210103
文摘This paper performs a numerical simulation of three-dimensional flow field in a centrifugal compressor with long inlet and outlet pipes using CFX software.By arranging virtual probes at different positions in both inlet and outlet planes,the aerodynamic performance of the centrifugal compressor is measured and compared with each other.Then effects of measuring positions on measurement results are discussed.The results show that it will generate notable measuring errors of the pressure ratio and efficiency if the inlet total pressure is measured using a single-point probe.The inlet total pressure data can be accurate when they are measured using a 3-point rake.The outlet total pressure and total temperature data can not be accurate if they are respectively measured at one circumferential position even using a multi-point rake.Increasing tangential measuring positions at the outlet is effective to improve the test accuracy.When the outlet total pressure and total temperature are respectively measured at 3 tangential positions,the data can be almost accurate.
