Free vibration of clusters of cylinders in liquid-filled channels

This paper presents two methods for the calculation of the virtual masses of clusters of parallel cylinders in liquid contained by an outer channel. The first method is based on classical potential flow theory, and its applicability is limited to circular cylinders in circular cylindrical channels; the second, using fluid finite elements, may be applied to more general geometries. Illustrative examples compare the two methods, the classical one being shown to be computationally more efficient—whenever applicable. The eigenvalues and modal shapes are calculated for clusters in still fluid, in channels of circular and rectangular cross-section, showing the effect of proximity on the natural frequencies. Some distinctive patterns in the coupled motions of the cylinders are seen to occur, some not intuitively evident. The effect of viscous hydrodynamic coupling is also discussed.