7. On the Bottom Friction in an Oscillatory Current

概要

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The frictional coefficient C of an oscillating turbulent flow is estimated on the assumption that the eddy viscosity is proportional to the amplitude of the bottom friction velocity and the height above the bottom. The dependence of C on parameters such as the amplitude of the vertically averaged horizontal velocity, the period of the oscillation, the depth of water, and the roughness length z0(for the case of a rough boundary) or the molecular viscosity υ(for the case of a smooth boundary) is shown graphically by choosing suitable non-dimensional parameters. The frictional coefficient for the case of a laminar oscillatory flow is also discussed.渦動粘性係数を,水底摩擦速度と水底からの高さに比例すると仮定して摩擦係数を計算し,底面が粗および滑らかな場合のそれぞれについて,摩擦係数が流れの振幅,周期,水深に関してどう変るかを適当な無次元量をつかつて図示した.浅海の潮流については,摩擦係数はz0/z(z:水深,z0:粗度長さ)によつてきまり,z0/zのもつともらしい値に対して摩擦係数は2×10-3程度となるが,周期の短かいセイシュなどでは摩擦係数が大きくなる.
1964-05-30