Incipient motion is the critical condition at which bed particles begin to move. Existing relationships for incipient motion prediction do not consider the effect of seepage. Incipient motion design of an alluvial channel affected from seepage requires the information about five basic parameters, i.e., particle size d, water depth y, energy slope Sf, seepage velocity vs and average velocity u. As the process is extremely complex, getting deterministic or analytical form of process phenomena is too difficult. Data mining technique, which is particularly useful in modeling processes about which adequate knowledge of the physics is limited, is presented here as a tool complimentary to model the incipient motion condition of alluvial channel at seepage. This article describes the radial basis function (RBF) network to predict the seepage velocity vs and average velocity u based on experimental data of incipient condition. The prediction capability of model has been found satisfactory and methodology to use the model is also presented. It has been found that model predicts the phenomena very well. With the help of the RBF network, design curves have been presented for designing the alluvial channel when it is affected by seepage. and Návrh aluviálneho kanála s ohľadom na iniciáciu pohybu dna koryta, ovplyvneného priesakom vyžaduje informáciu o piatich základných parametroch: veľkosti častice d, hĺbke vody y, sklone čiary energie Sf, rýchlosti priesaku vs a priemernej rýchlosti prúdenia u. Pretože proces je extrémne zložitý, získať deterministickú alebo analytickú formu riešenia je ťažké. Príspevok opisuje získavanie údajov (data mining technique), bežne používané pri modelovaní. Opisuje aj sieť tzv. ''radial basis function (RBF)'' na prognózu rýchlosti priesaku vs a priemernej rýchlosti u; výpočet je založený na experimentálnych hodnotách v štádiu začínajúceho sa pohybu častíc v koryte. Bola konštatovaná dobrá schopnosť modelu prognózovať začínajúci pohyb; je uvedená tiež metodológia používania modelu. Bolo zistené, že model predpovedá uvedené javy veľmi dobre. Je tu opísaný návrh aluviálneho kanála ovplyvneného priesakom pomocou návrhových kriviek vytvorených pomocou siete RBF.
The paper describes results of validation of authors' recently proposed formulae for sediment transport and bed friction in the upper plane bed regime using laboratory experiments in a pressurized pipe. Flows of mixture of water and fine to medium ballotini (d50 = 0.18 mm) were observed in a rectangular pipe (51 x 51 mm) with a deposit at the bottom of the pipe. A comparison of test results with transport-formula predictions shows a satisfactory match confirming a good prediction ability of the proposed transport formula at high bed shear. A prediction ability of the friction formulae appears to be less convincing but still reasonable. A joint use of the formulae for transport and friction predicts the delivered concentration of transported sediment within the accuracy range of ± 40 per cent for flows in which transported sediments strongly affect the bed friction, i.e. for flows with delivered concentration of sediment higher than say 3 per cent.
Intense collisional transport of bimodal sediment mixture in open-channel turbulent flow with water as carrying liquid is studied. The study focusses on steep inclined flows transporting solids of spherical shape and differing in either size or mass. A process of vertical sorting (segregation) of the two different solids fractions during the transport is analyzed and modelled. A segregation model is presented which is based on the kinetic theory of granular flows and builds on the Larcher-Jenkins segregation model for dry bimodal mixtures. Main modifications of the original model are the carrying medium (water instead of air) and a presence of a non-uniform distribution of sediment across the flow depth. Testing of the modified model reveals that the model is applicable to flow inclination slopes from 20 to 30 degrees approximately, making it appropriate for debris flow conditions. Changing the slope outside the specified range leads to numerical instability of the solution. A use of the bimodal mixture model is restricted to the grain size ratio 1.4 and no restriction is found for the grain mass ratio in a realistic range applicable to natural conditions. The model reveals trends in the vertical sorting under variable conditions showing that the sorting is more intense if flow is steeper and/or the difference in size or mass is bigger between the two sediment fractions in a bimodal mixture.