典型断面渠道正常水深计算

Calculation of water normal depth in channels with common shapes

明渠正常水深的计算是排灌渠道设计中的一项重要工作.通过对典型渠道断面引入包含渠道糙率、底坡、断面几何要素和流量的一组量纲为一的参数,将目前文献中正常水深的显式计算公式进行量纲为一化的统一表达,使其更具有通用性并且方便进行相对误差评价;指出每种典型渠道断面量纲为一的参数在实际工程中的常用取值范围,在此范围内对各量纲为一的显式计算公式进行相对误差评价,作出相对误差全局分布图,比较各显式公式的最大相对误差和全局相对误差,并比较公式的简捷性,据此优选出梯形、圆形、弧底梯形、普通城门洞形、马蹄形等5种断面正常水深简捷、精度高、适用范围广的显式计算公式;应用最优一致逼近原理,提出标准城门洞形断面正常水深分段表示的显式计算公式.相对误差分析表明:推荐出的6种典型渠道断面正常水深的显式计算公式的最大相对误差均小于1%,可为典型断面排灌渠道的设计及水力计算提供有效的计算方法.

Water normal depth calculation is an important task in the design of an open channel for drainage and irrigation. First, dimensionless variables including channel roughness coefficient, bed slope, geometric parameters, and discharge were introduced for each common section. In order to obtain general equations and evaluate their accuracy, the explicit equations available for water normal depth were expressed by those dimensionless variables. Then, the real ranges of those variables were specified for each common section in applications, the relative errors in the explicit equations that involve the variables were analyzed in the ranges. Also, the global relative error distribution diagrams were plotted to compare the maximum relative error and the global one. According to these analyses, the most appropriate equations, which can explicitly calculate the water normal depth in the channels with five types of common section, were spotted. Finally, based on the best approximations algorithm a new piecewise explicit equation was proposed for the water normal depth in a standard castle-gate section. It was shown that the maximum relative errors in all the recommended equations are less than 1% for the water normal depth in six types of common section. The results in the paper have provided an effective method for designing channels with six types of common section and carrying out hydraulic calculations.