Studies on the laws for sand transport in bed load by waves, winds and currents

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In this study, theoretical investigations of the laws for sand transport in bed load by waves, winds and currents were made in order to unify the mechanism of sand transport by these actions. The main results are:1) A theory of the dynamical response of sand grains to turbulence was proposed taking into account the virtual mass and uplift forces due to the shear effect. The dynamical response characteristics of sand grains to turbulence in air and water were solved. By this theory, the threshold of sand movement by waves, winds and currents were dynamically formulated and the theoretical results were in good agreement with experimental ones.2) The dynamics of motion of a sand grain as saltation or sliding by waves, winds and currents was established. The characteristics of the sand grain motion were obtained. The influence of the virtual mass force and wave acceleration force were made clear.3) In the saltation the mechanism of collision of a saltating sand grain to the granular bed wa … More s dynamically formulated both in uniform and graded sand. By the theoretical result, the influence of the distribution of graded sand on the transport rate of graded sand in blown sand was well explained with experimental and field data of sand transport.4) By applying the momentum conservation law in a saltation layer, the law for sand transport rates was theoretically formulated in the uniform condition introducing the saltation characteristics. The formulas agree well with experimental data of sand transport.5) In order to extend the law for sand transport rates in the uniform condition to that in the unsteady condition, the governing equations of sand -fluid two-phase systems were derived. By integrating it over the waterdepth from the bottom to the water surface, the conservation equations of sand transport rates were obtained. The equations are one of the generalized expression of sand transport rates and may be extended as the basic theory of sand transport by waves, winds and currents. Less