Papers by Keyword: Nonuniform Sediment

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Authors: Mohammad J. Aarabi, Mohammad R. Chamani, Amir A. Dehghani, Keyvan Asghari
Abstract: Due to economical and serviceability reasons, local scour must be considered in the design of bridge piers. Although beds of natural rivers consist of nonuniform sediments, but most researches in this subject were carried out with uniform sediments. In nonuniform sediments case, the effect of sheltering of the finer particles by the coarser ones may alter the scour process. In this paper, the time-variation of local scour with nonuniform sediments around a cylinder pier is simulated using SSIIM software. This study shows that the SSIIM is capable of predicting the temporal evolution of local scour in bridge piers with nonuniform sediments.
Authors: Bin Zhang, Xing Nian Liu, Feng Guang Yang
Abstract: Based on a method stochastic processes, two new bedload transport models for the ith size fraction nonuniform sediment are theoretically developed by using a stochastic model of sediment exchange and the probabilistic distribution of fractional bedload transport rates. The relations, proposed recently by Yang, for the probability of fractional incipient motion and for the average velocity of particle motion are introduced to bedload formulas. Plenty of experimental data for the bedload transport rate of uniform sediment are used to determine parameters. Finally, the two models are verified with natural data expressing the transport of nonuniform sediment under full motion in laboratory flume. The result shows that the experimental observations agree well with the predicted fractional bedload transport rates. Comparison of the theory with field data shows that the proposed formula still applies to uniform sediment transportation condition as long as the relevant parameters for uniform sediment are taken into account.
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