A transfer function method of modeling systems with frequency-dependent coefficients

Abstract

The fluid forces that act on a floating body conventionally are represented in the frequency domain by frequency-dependent coefficients, the added mass, and damping. This paper describes a method of characterizing these forces in the time domain by a rational transfer function, an equivalent dynamic system that can be appended to the dry body dynamics. The technique is illustrated by an application to the roll motion of a flatbottomed barge; a low-order transfer function represents the infinite-order fluid dynamic system with acceptable accuracy. The influence of the frequency-dependent coefficients oh the overall system dynamics is discussed, and it is shown that multiple roll resonance peaks are possible.