Vízügyi Közlemények, 1980 (62. évfolyam)
2. füzet - Stelczer Károly: A hordalék mozgása. II. rész. Virtuális haladási sebesség meghatározása
A görgetett hordalék mozgása 185 вала требуется T -74,72 часа. Минимальное и максимальное времена соответственно равны /"„,,„ = 41,086 и Г тах = 412,19 часов. Расхождения с виду очень значительные. В течении 1976 года 53 дня велись наблюдения за движением меченых частиц. Наиболее быстрый камышек прошел расстояние 1580 м а наименее быстрый 115 м. С использованием соотношения (16) выполнены контрольные вычисления. Результаты оказались удовлетворительными. * * * Bed load movement, l'art II. Detenu iualioii of the virtual traveling velocity by Dr. Stelczer, Civ. Engr. In order to explore the regularities of bed load transport the author lias performed radioactive tracer measurements in the field. (See Vol. 1980. No. 1 of the present journal for part I. of the paper.) Bv processing the results obtained he succeeded in deriving a relationship between the bottom velocity vs of flow, and the virtual travelling velocity Vhv of the bed load, as given l>y Eq. (15). The field data yielded the bi-variate relationships of Eqs. (12) (14) for three size fractions (Fig. 8). In practice the virtual travelling velocity of bed load is of prime interest and thus it is suggested to rearrange Eq. (15) into the form of Eq. (Hi) as folows 1 fhv = — (Vt - Vre). (ni/SCC) b This relationship is considered valid in alluvial streams for the bed load fraction 0.005 to 0.05 m (occasionally 0.1 in) moving over a hydraulically rough bottom. In this expression the factor b depends on channel conditions. For practical compulations I lie value of the factor b should be taken as 2.'Ю and 60 for „soft" and „hard" channel conditions, respectively. In Eq. (16) one of the dependent variables is the momentary value of the bottom velocity vt of flow. This implies that Eq. (16) is applicable also to the case of unsteady flow conditions (Fig. 9). The other dependent variable involved is the critical bottom velocity vtc of the bed load. The variations in the critical condition are described expediently by Eq. (5). In the case of mixed fractions the partical size is introduced with the value dm or Using the field data of the author and other researchers it lias been concluded that the values of .r and у in Eq. (5) are 0.36 and 0.14. respectively, while the factor a assumes the value 1.65 for „soft" and 1.85 for "hard" channel conditions. The relationship given by Eq. (5) desribes substantially the incipient stage of the critical condition, rather than the critical condition itself. In the concluding Part 4 of the paper the author has presented numerical examples to illustrate the practical application of Eq. (16) for calculating the virtual travelling velocity of bed load. In the first example the problem is to find the time during which the mixedfraction bed load of Dm 0.04 m diameter travels a distance of 200 m, if the bottom' velocity of flow is «r = 0.90 m/sec, the depth is h — 2.50 m and the bottom condition is classified as "soil". In the first step of calculation the minium, mean and maximum values of the critical bottom velocity are found using Eq. (8), yielding i>rc min = 0.589 m/sec. In order lo find the mean value, the uni-dimensional normal distribution of (7 = 0.06 m/sec standard deviation is calculated. In Part I. of the paper the author has established that velocity range pertaining to the normal distribution of <r = ().()(> m/sec standard deviation is 0.28 m/sec, and thus the critical flow velocity, and the maximum critical bottom velocity are obtained as o f c 0.729 m/sec and vtc max = 0.869 m/sec. The virtual travelling velocity is calculated in the second step using Eq. (16). The value thereof is obtained as i> hv = 0.00074.45 m/sec, so that the lime needed lor travelling the distance of 200 m is T 74.72 hours on the average. The shortest and
