Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

dimensional and dimensionless physical quantities. The familiar shear velocity formed from hydraulic quantities belongs to the group of dynamic velocities. In the present case four independent dimensional basic quantities (particle diameter, mean waterdepth, gravitational acceleration and kinematic viscosity) and two independent dimensionless numbers (the ratio of sediment density measured in water and water density, further the slope of the energy gradient) are used to form 15 potential dynamic velocities and from these four independent velocity rations. The resistance coefficient VjU

t at the boundary of movement — no movement is shown to be a function of these velocity ratios: d , D . an

d U.yo d V V v2ia g

—1/3 By comparing parameters relating to the critical condition, observed by himself and other investigators under a wide variety of hydraulic circumstances, the author concluded that the effect of the last two of the four velocity rations mentioned above is usually negligible in comparison with that of the first two. From Fig. 1 showing the relationship between VJU

. and these two parameters it will be perceived in spite of the considerable scatter of points, in what manner the resistance coefficient and one of the velocity ratios decrease with increasing relative roughness. 4* 51