A Methodology for Modeling Lift as a Modulated Process

Abstract

This paper presents a methodology for using a modulated process to model the lift forces induced on circular cylinders by an oscillating flow. The generalization of the existing quasi-steady flow model leads to techniques which apply the Hilbert transform in model evaluation and parameter determination. Analysis of measured lift forces reveals clearly identifiable forms of amplitude and angle modulation, justifying the use of a modulation model. As a demonstration, a method is presented for evaluating the quasi-steady flow model and for determining model parameters using data obtained under both periodic and random flow conditions. Although empirical in nature, modulation models can reproduce critical characteristics of lift forces such as frequency content, amplitude, and zero-crossings. It is suggested that the Hilbert transform can facilitate model development and evaluation beyond the simple quasisteady form. Further, the methodology employed can be used in characterizing any physical process exhibiting amplitude and/or angle modulation.