Search

Abstract:  This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients is based on Fourier analysis of the time-history of damped oscillation tests.

Abstract:  The damped horizontal oscillations of a circular cylinder in linearly stratified fluid are studied experimentally. The cylinder is fixed to the lower end of a physical pendulum with variable restoring moment. The impulse response function of the pendulum in time domain is recorded and converted to the frequency response function using Fourier transform. The density stratification is shown to have a strong effect on frequency-dependent hydrodynamic coefficients (added mass and damping). The data obtained are compared with available theoretical predictions. The applicability of a simplicistic method implying approximation of impulse response functions by analytical functions is discussed.