【摘要】 以往进行河床变化計算时,常对水流做一些近似的假定,再計算不恆定的泥沙冲淤运动.实际上河床变化必引起水流特性的改变,后者改变又引起冲淤变化,二者相互影响,在上游来水量变化很大时尤其如此.本文同时考虑了水流和河床变形的不恆定現象,推导了等寬渠道中一維的、以悬移貭为主的微分方程組.做了四种不同的簡化后可得五种情形.前三种为以往未采用过的方程組,可用三族特征縐求解.后二种为以往假設过的,分別保存两族和一族特征线.在討論了五种情形的近似性后建議采用第二种,并討論了計算方法.在附录Ⅰ中推导了間断传播速度,藉以說明特征綫的物理意义.附录Ⅱ中說明非等寬渠道的計算方法,以便实际应用.更多还原

【Abstract】 In previous investigations on the methods of computing the change of river bed due to sedimentation, the bed and water surface configurations were computed separately and the conventional back water equations were used. Since the bed changing process and the flow unsteadiness are two co-existing and mutually interfering phenomena, the assumptions necessarily introduced error. A method of computation was suggested in this paper, which takes care of the unsteady effects of the flow. For channels of constant width and flow carrying essentially suspended load, equations of continuity[Eq.（3） to（5）] and one-dimensional equation of motion[Eq.（6）] were presented. After the elimination of c through the use of Velikanoff’s equation of silt transportation, a system of 3 equations for 3 unknowns u, h, z were obtained[Eq.（9）]. 4 additional systems of equations[Eqs.（10）,（11）,（12）,（13）] based on different assumptions were also given, making up 5 cases. It may be mentioned that only Eqs.（12） and（13） have been used in previous investigations. All 5 sets of differential equations can be solved by the method of characteristics, the characteristic equations being Eqs.（20）,（21）;（24）,（25）;（26）,（27）;（28）,（29）;（30）,（31） respectively. The values λ=dx/dt are given by the intersections of the curves F₁, G₁; F₂, G₂; F₃, G₃; F₄, G₄; F₅, G₅, as shown in Fig. 2. It can be seen that due to the simplifying assumptions made, the 4th and the 5th sets of equations have only 2 and 1 group of characteristic curves respectively. The authors recommend the use of Eqs.（24） and（25） in actual computation. In Fig. 4 curves were drawn for rapid determination of the λ’s. It can be seen that for values of the parameters Ku/pω and u²/gh usually encountered in sedimentation problems the three roots are all real. Illustrative example was given. In Appendix Ⅰ, the transportation of sediments by surges was discussed, further clarifying the physical meaning of the λ’s. Equations for channels of variable width were presented in Appendix Ⅱ, and a method of solution was suggested, thus paving the way to practical application.更多还原