非定常流中の運動体に働く流体力と落体の運動

概要

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A new method to compute the hydrodynamic force acting on a moving body with velocity w in unsteady flow with velocity u has been studied. Firstly, the hydrodynamic force acting on a moving body with velocity u in a flow with the same velocity u has been formulated. Secondly, the hydrodynamic force acting on a moving body with velocity w-u in a static flow field has been formulated. Thirdly, based on linear superposition principle, these two hydrodynamic forces are superposed and combined with gravitational force and buoyancy, and the equation of motion of a moving body in gravitational and viscous unsteady flow field has been formulated as a differential equation. Solving the differential equation under regularly reciprocating current condition by difference scheme, supposing that the sinking body is sphere, the following facts have been revealed; (1) Regularly and vertically reciprocating fluid movement reduces the terminal speed of a free sinking body. (2) Suppose plankton regularly and reciprocally moves up and down by itself, its movement reduces the terminal sinking speed substantially. These results have never been derived from neither conventional Stokes' law approach nor Newton's law approach.
2013-07-15