While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponen...While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponents such as 1/6 and 1/7 are generally applied. However, exponent of power law is an index representing bed resistance related with relative roughness and furthermore influences the shapes of vertical velocity distribution. The purpose of this study is to investigate characteristics of vertical velocity distribution of the natural rivers by testing and optimizing previous methods used for determination of power law exponent with vertical velocity distribution data collected with ADCPs during the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient has been calculated from the equation of Limerinos. And using theoretical and empirical formulae, and representing relationships between bed resistance and power law exponent, it has been evaluated whether the exponents suggested by these equations appropriately reproduce vertical velocity distribution of actual rivers. As a result, it has been confirmed that there is an increasing trend of power law exponent as bed resistance increases. Therefore, in order to correctly predict vertical velocity distribution in the natural rivers, it is necessary to use an exponent that reflects flow conditions at the field.展开更多
Power-law distributions and other skew distributions,observed in various models and real systems,are considered.A model,describing evolving systems with increasing number of elements,is considered to study the distrib...Power-law distributions and other skew distributions,observed in various models and real systems,are considered.A model,describing evolving systems with increasing number of elements,is considered to study the distribution over element sizes.Stationary power-law distributions are found.Certain non-stationary skew distributions are obtained and analyzed,based on exact solutions and numerical simulations.展开更多
随着电力系统通信自动化技术的发展,各种信息采集系统得到广泛应用,这为分析电网故障的时空特性提供了有利条件。以H省电网500 k V输电网为例,探讨了5年间500 k V输电线路故障在较长时间段上的行为特性。首先在输电线路故障时间序列层面...随着电力系统通信自动化技术的发展,各种信息采集系统得到广泛应用,这为分析电网故障的时空特性提供了有利条件。以H省电网500 k V输电网为例,探讨了5年间500 k V输电线路故障在较长时间段上的行为特性。首先在输电线路故障时间序列层面上,统计分析输电线路故障发生的时间(单位:天)与同一时间点故障累计频次和累计概率之间的相互关系,采用Kolmogorov-Smirnov(K-S)法检验其分布的正态性,并根据R/S时序分析法计算出H省电网500 k V输电网5年间输电线路故障基于时序的Hurst指数,从而判断其在时间序列上具有长程相关性。然后,在空间层面上,统计分析5年期间H省电网每条500 k V输电线路故障次数与其发生频次和累计概率的关系,得出输电线路故障在空间上符合幂律分布特征。研究电网故障的时空分布特性为电网的风险管理和风险预测提供了辅助决策的依据。展开更多
文摘While log law is an equation theoretically derived for near-bed region, in most cases, power law has been researched by experimental methods. Thus, many consider it as an empirical equation and fixed power law exponents such as 1/6 and 1/7 are generally applied. However, exponent of power law is an index representing bed resistance related with relative roughness and furthermore influences the shapes of vertical velocity distribution. The purpose of this study is to investigate characteristics of vertical velocity distribution of the natural rivers by testing and optimizing previous methods used for determination of power law exponent with vertical velocity distribution data collected with ADCPs during the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient has been calculated from the equation of Limerinos. And using theoretical and empirical formulae, and representing relationships between bed resistance and power law exponent, it has been evaluated whether the exponents suggested by these equations appropriately reproduce vertical velocity distribution of actual rivers. As a result, it has been confirmed that there is an increasing trend of power law exponent as bed resistance increases. Therefore, in order to correctly predict vertical velocity distribution in the natural rivers, it is necessary to use an exponent that reflects flow conditions at the field.
文摘Power-law distributions and other skew distributions,observed in various models and real systems,are considered.A model,describing evolving systems with increasing number of elements,is considered to study the distribution over element sizes.Stationary power-law distributions are found.Certain non-stationary skew distributions are obtained and analyzed,based on exact solutions and numerical simulations.
文摘随着电力系统通信自动化技术的发展,各种信息采集系统得到广泛应用,这为分析电网故障的时空特性提供了有利条件。以H省电网500 k V输电网为例,探讨了5年间500 k V输电线路故障在较长时间段上的行为特性。首先在输电线路故障时间序列层面上,统计分析输电线路故障发生的时间(单位:天)与同一时间点故障累计频次和累计概率之间的相互关系,采用Kolmogorov-Smirnov(K-S)法检验其分布的正态性,并根据R/S时序分析法计算出H省电网500 k V输电网5年间输电线路故障基于时序的Hurst指数,从而判断其在时间序列上具有长程相关性。然后,在空间层面上,统计分析5年期间H省电网每条500 k V输电线路故障次数与其发生频次和累计概率的关系,得出输电线路故障在空间上符合幂律分布特征。研究电网故障的时空分布特性为电网的风险管理和风险预测提供了辅助决策的依据。
