Vízügyi Közlemények, 1996 (78. évfolyam)
2. füzet - Hankó Zoltán: A hidraulika kismintakísérletek a folyószabályozás szolgálatában
A hidraulikai kismintakísérletek a folyószabályozás szolgálatában 187 megfelelőjét nem teremtettük meg, akkor a modellbeli kimosás/feltöltődés csak a hajlamot jelzi és számszerű értékelésre nem alkalmas. Ezért kellett a görgetett hordalékhozam becslésével is foglalkozni, hogy megkereshessük annak modellbeli megfelelőjét. A számpélda gyakorlatban is használható eredményt hozott. A modellben megfigyelt mederváltozási sebességből következtetni lehet a prototípusban várható mederváltozás sebességére. * * * The role of hydraulic scale model experiments in river training by Dr. Zoltán HANKÓ C.E. The effects of the scale concerns the geometric dimensions (vertical and horizontal dimensions) of the scale-model. The vertical distortion T h of the solid bed scale-model implies the distortion of the hydraulic radius T R as well (Fig. I.). The invariance of the Froude number provides a method for the conversion of the velocity (3), but it can also be used for calculating the channel roughness coefficient. Consideration invariance of the intensity of vortex flow (11) and the ratio of the relative roughness to the relative thickness of the laminar boundary layer (19)-(22) provide possibility for the conversion of the Colenbrook-White formula, thus enabling the calculation of the height distortion T h and the horizontal scale multiplier (20,21). The theoretical considerations are supported by a numerical example (Table I.) Movable-bed models need special additional considerations (Figure 2.). They are aimed at the estimation of the range of particle size of the prototype along with the sediment discharge, using the Laursen constant (23, 27). The use of similarity conditions (the similarity of sediment discharge and the identical character of sediment movement) will enable the determination of the range of particle size and material-density in the model (Table II.). Observations on the sediment movement of the model (erosion-degradation-deposition) allow the drawing of conclusions on the expectable rate of channel changes in the prototype. In the numerical example of Section 6. the rate of channel changes of the model was about three orders of magnitude higher than that of the prototype. The final conclusion was as follows: — Hydraulic scale-models of the solid bed type should be designed for the minimum of the specified discharge range of the study in concern, in order to have Reynolds number with values less than 1000 (as magnified with the hydraulic radius); — The design procedure specifies corresponding horizontal and hydraulic scales. The horizontal scale decreases and the vertical distortion increases as the water movement approaches the "hydraulically smooth" resistance conditions. Although the basic principle of design is that the intensity of vortex flow should be identical, the upper limit of vertical distortion should taken as T h=3; — In addition to those stated above the design of movable-bed hydraulic models requires special considerations. The density of bed-load sediment of the model can exceed that of the water by a few percentages only, but this can be calculated along with the range of the particle size, allowing the estimation of the sediment discharge; — In spite of the above conditions the sediment movement of the model will differ from that of the prototype in three factors:
