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当无法用流速仪实测洪峰流量时,可用比降——面积法进行计算。这一方法的结果与许多具有很大量测误差的量(如水位等)有关;另一些关键的量如满宁(糙度)系数 n,甚至无法直接观测,只能加以估计;最后,河道的冲淤可能使洪峰期间的水力学条件与所观测到的河道条件很不一致。本文采用台劳级数逼近流量公式和众所周知的相关随机变量之和的方差公式,据根误差的统计分析方法,估计了上述各种潜在的误差对流量计算值精度的影响。结果证明所计算的流量的均方误差是各种量测误差的协方差的加权和,而权重与河道的水力学条件和几何结构有关。数学分析结果证实了这样的经验:即当流速水头大于水位差,流场扩散,以及横向流速变化(α)很大时,流量计算值的相对误差迅速增大。另外还表明,准确地估计冲淤情况特别重要。
When unable to measure the peak flow rate meter, the available ratio - area method to calculate. The result of this method is related to many quantities (such as water level) that have a great amount of measurement error; other key quantities such as the Manning (roughness) coefficient n are not even directly observable and can only be estimated; and finally, Scouring and silting may make the hydrodynamic conditions during the flood peak very different from the observed river conditions. In this paper, we use the class of work force to approximate the variance formula of the sum of the flow equation and the well-known correlation random variable. Based on the statistical analysis of the root error, we estimate the influence of the above potential errors on the calculated flow accuracy. The results show that the mean square error of the calculated flow is the weighted sum of the covariances of the various measurement errors, and the weights are related to the hydraulic conditions and geometry of the river. The mathematical analysis confirms the experience that the relative error of the calculated flow rate rapidly increases when the flow head is larger than the water level, the flow field is diffused, and the lateral velocity variation (α) is large. It has also been shown that accurate estimates of erosion and deposition are of particular importance.