随着电力系统中新能源机组渗透率的快速提高,系统惯量水平下降将威胁系统频率稳定性,惯量的空间分布特征也将更加凸显,频率响应的分散性将不能被忽略。针对以上问题,提出一种考虑频率响应分散性及系统分区的含风电电力系统等效惯量估计...随着电力系统中新能源机组渗透率的快速提高,系统惯量水平下降将威胁系统频率稳定性,惯量的空间分布特征也将更加凸显,频率响应的分散性将不能被忽略。针对以上问题,提出一种考虑频率响应分散性及系统分区的含风电电力系统等效惯量估计方法。首先,为降低频率响应分散性对估计精度的影响,基于谱聚类算法对电力系统进行分区,并基于皮尔逊相关系数定义频率相似度指标确定区域频率的最优测量节点。其次,由于测量所得的频率变化率(rate of change of frequency, RoCoF)曲线中包含大量的振荡分量,提出一种基于摇摆方程的数值积分方法估计区域及系统全局惯量。最后,在DIgSILENT/PowerFactory中建立改进IEEE10机39节点系统以验证所提方法的有效性。仿真结果表明,该方法适用于不同场景下含风电系统的等效惯量估计。展开更多
We investigate computationally the attenuation and reflection of Terahertz （THz） wave using targets coated with plasmas. The simulators are the Wentzel-Kramer-Brillouin （WKB） method and finite-difference timedoma...We investigate computationally the attenuation and reflection of Terahertz （THz） wave using targets coated with plasmas. The simulators are the Wentzel-Kramer-Brillouin （WKB） method and finite-difference timedomain （FDTD） method. The relation between the frequency of the incident electromagnetic （EM） wave and the attenuation caused by unmagnitized plasma is analyzed. The results demonstrate that the amount of absorbed power is a decreasing function of the EM wave frequency and the plasma collision frequency. For THz band incident wave, the attenuation that is caused by plasma is small when the plasma has common density and the collision frequency. This conclusion has fine applying foreground for plasma anti stealth.展开更多
FM-to-AM(frequency modulation-to-amplitude modulation)conversion caused by nonuniform spectral transmission of broadband beam is harmful to high-power laser facility.Smoothing by spectral dispersion(SSD)beam is a spec...FM-to-AM(frequency modulation-to-amplitude modulation)conversion caused by nonuniform spectral transmission of broadband beam is harmful to high-power laser facility.Smoothing by spectral dispersion(SSD)beam is a special broadband beam for its monochromatic feature at the given time and space on the near field.The traditional method which uses the optical spectral transfer function as filters cannot accurately describe its AM characteristics.This paper presents the theoretical analysis of the etalon effect for SSD beam.With a low-order approximation,the analytic model of the temporal shape of SSD beam is obtained for the first time,which gives the detailed AM characteristics at local and integral aspects,such as the variation of ripples width and amplitude in general situation.We also analyze the FM-to-AM conversion on the focal plane;in the focusing process,the lens simply acts as an integrator to smooth the AM of SSD beam.Because AM control is necessary for the near field to avoid optics damage and for the far field to ensure an optimal interaction of laser-target,our investigations could provide some important phenomena and rules for pulse shape control.展开更多
Prediction of seismic attenuation and dispersion that are inherently sensitive to hydraulic and elastic properties of the medium of interest in the presence of mesoscopic fractures and pores,is of great interest in th...Prediction of seismic attenuation and dispersion that are inherently sensitive to hydraulic and elastic properties of the medium of interest in the presence of mesoscopic fractures and pores,is of great interest in the characterization of fractured formations.This has been very difficult,however,considering that stress interactions between fractures and pores,related to their spatial distributions,tend to play a crucial role on affecting overall dynamic elastic properties that are largely unexplored.We thus choose to quantitatively investigate frequency-dependent P-wave characteristics in fractured porous rocks at the scale of a representative sample using a numerical scale-up procedure via performing finite element modelling.Based on 2-D numerical quasi-static experiments,effects of fracture and fluid properties on energy dissipation in response to wave-induced fluid flow at the mesoscopic scale are quantified via solving Biot's equations of consolidation.We show that numerical results are sensitive to some key characteristics of probed synthetic rocks containing unconnected and connected fractures,demonstrating that connectivity,aperture and inclination of fractures as well as fracture infills exhibit strong impacts on the two manifestations of WIFF mechanisms in the connected scenario,and on resulting total wave attenuation and phase velocity.This,in turn,illustrates the importance of these two WIFF mechanisms in fractured rocks and thus,a deeper understanding of them may eventually allow for a better characterization of fracture systems using seismic methods.Moreover,this presented work combines rock physics predictions with seismic numerical simulations in frequency domain to illustrate the sensitivity of seismic signatures on the monitoring of an idealized geologic CO_(2) sequestration in fractured reservoirs.The simulation demonstrates that these two WIFF mechanisms can strongly modify seismic records and hence,indicating that incorporating the two energy dissipation mechanisms in the geophysical interpret展开更多
文摘随着电力系统中新能源机组渗透率的快速提高,系统惯量水平下降将威胁系统频率稳定性,惯量的空间分布特征也将更加凸显,频率响应的分散性将不能被忽略。针对以上问题,提出一种考虑频率响应分散性及系统分区的含风电电力系统等效惯量估计方法。首先,为降低频率响应分散性对估计精度的影响,基于谱聚类算法对电力系统进行分区,并基于皮尔逊相关系数定义频率相似度指标确定区域频率的最优测量节点。其次,由于测量所得的频率变化率(rate of change of frequency, RoCoF)曲线中包含大量的振荡分量,提出一种基于摇摆方程的数值积分方法估计区域及系统全局惯量。最后,在DIgSILENT/PowerFactory中建立改进IEEE10机39节点系统以验证所提方法的有效性。仿真结果表明,该方法适用于不同场景下含风电系统的等效惯量估计。
基金the National Natural Science Foundation of China (60771017)the China Postdoctoral ScienceFoundation (20060390272)
文摘We investigate computationally the attenuation and reflection of Terahertz （THz） wave using targets coated with plasmas. The simulators are the Wentzel-Kramer-Brillouin （WKB） method and finite-difference timedomain （FDTD） method. The relation between the frequency of the incident electromagnetic （EM） wave and the attenuation caused by unmagnitized plasma is analyzed. The results demonstrate that the amount of absorbed power is a decreasing function of the EM wave frequency and the plasma collision frequency. For THz band incident wave, the attenuation that is caused by plasma is small when the plasma has common density and the collision frequency. This conclusion has fine applying foreground for plasma anti stealth.
基金supported by the National Natural Science Foundation of China(No.11404306)the Presidential Foundation of the China Academy of Engineering Physics(No.YZJJLX2016008)
文摘FM-to-AM(frequency modulation-to-amplitude modulation)conversion caused by nonuniform spectral transmission of broadband beam is harmful to high-power laser facility.Smoothing by spectral dispersion(SSD)beam is a special broadband beam for its monochromatic feature at the given time and space on the near field.The traditional method which uses the optical spectral transfer function as filters cannot accurately describe its AM characteristics.This paper presents the theoretical analysis of the etalon effect for SSD beam.With a low-order approximation,the analytic model of the temporal shape of SSD beam is obtained for the first time,which gives the detailed AM characteristics at local and integral aspects,such as the variation of ripples width and amplitude in general situation.We also analyze the FM-to-AM conversion on the focal plane;in the focusing process,the lens simply acts as an integrator to smooth the AM of SSD beam.Because AM control is necessary for the near field to avoid optics damage and for the far field to ensure an optimal interaction of laser-target,our investigations could provide some important phenomena and rules for pulse shape control.
文摘Prediction of seismic attenuation and dispersion that are inherently sensitive to hydraulic and elastic properties of the medium of interest in the presence of mesoscopic fractures and pores,is of great interest in the characterization of fractured formations.This has been very difficult,however,considering that stress interactions between fractures and pores,related to their spatial distributions,tend to play a crucial role on affecting overall dynamic elastic properties that are largely unexplored.We thus choose to quantitatively investigate frequency-dependent P-wave characteristics in fractured porous rocks at the scale of a representative sample using a numerical scale-up procedure via performing finite element modelling.Based on 2-D numerical quasi-static experiments,effects of fracture and fluid properties on energy dissipation in response to wave-induced fluid flow at the mesoscopic scale are quantified via solving Biot's equations of consolidation.We show that numerical results are sensitive to some key characteristics of probed synthetic rocks containing unconnected and connected fractures,demonstrating that connectivity,aperture and inclination of fractures as well as fracture infills exhibit strong impacts on the two manifestations of WIFF mechanisms in the connected scenario,and on resulting total wave attenuation and phase velocity.This,in turn,illustrates the importance of these two WIFF mechanisms in fractured rocks and thus,a deeper understanding of them may eventually allow for a better characterization of fracture systems using seismic methods.Moreover,this presented work combines rock physics predictions with seismic numerical simulations in frequency domain to illustrate the sensitivity of seismic signatures on the monitoring of an idealized geologic CO_(2) sequestration in fractured reservoirs.The simulation demonstrates that these two WIFF mechanisms can strongly modify seismic records and hence,indicating that incorporating the two energy dissipation mechanisms in the geophysical interpret
