An experimental study of dynamics of towed flexible cylinders

In this paper, some experiments are described which were designed to illustrate the dynamical behaviour of towed flexible cylinders and to test the theory. A silicone rubber cylinder was manufactured such that it was almost neutrally buoyant when immersed in water. The cylinder was terminated by plexiglas end-pieces and was held in horizontal water flow by a length of nylon thread (towrope). Video capturing along with image processing techniques were used to measure the transverse displacement of the cylinder in the horizontal plane. For the cylinder with relatively streamlined nose and tail end pieces, non-flexural (rigid body), as well as flexural instabilities developed as the flow velocity was increased; shortening the towrope was not very effective for stabilizing the system, but a sufficiently blunt tail end piece had a very significant stabilizing effect. The experimental observations are generally in qualitative agreement with the available nonlinear theory. Quantitative comparison of various quantities, e.g the instability thresholds, between experiment and theory, based on the estimated values of some of the theoretical nondimensional parameters, is also fairly good. (C) 2015 Elsevier Ltd. All rights reserved.