등류에서의 연성체 고리 진동

Abstract

An improved version of the immersed boundary (IB) method is developed for simulating flexible ring clamped at one point with tension and bending stiffness in a uniform flow. The boundary of the ring consists of a flexible filament with tension and bending stiffness, which can be modeled as a linear spring with spring constant k and initial unstreched length. Penalty method derived from fluid compressibility was used for conservation of area inside the flexible ring. The internal area of the ring is conserved through the penalty method. For the Reynolds number of 100, resonance is observed at specific tension stiffness with fixed bending stiffness and also at specific bending stiffness with fixed tension stiffness in the same manner. The optimal tension and bending coefficient that minimize the drag force of the flexible ring is found. In our simulation we observe bistable states, one stationary and another oscillatory, that coexist over a range of flow velocities. The bistable property of ellipse shape flexible ring different from that of ordinary flapping filament was observed with two flapping motions in same conditions except initial tilting angle whose amplitude is different from each other and not zero.