Distribution of damping device on riser pipe in sheared currents

This study investigates a method for suppressing the vortex-induced vibration (VIV) of a riser pipe using a mathematical model of beam vibration and numerical computation. The proposed method uses damping devices that partially cover the riser pipe such that the integral measuring the overlap of the drag distribution with the eigenfunction squared is maximized. By considering the isolines of reduced velocity and vertical profiles of magnitude factor of lift force, we specified a mode that would grow most prominently if no damping device is used. We regard this mode as the one that ought to be intensively damped, thereby configuring an added damping distribution function according to the approximate maximization of the overlap integral. We applied this method to a riser pipe in linearly sheared flows and found that the appropriate specification of the damped mode can suppress the VIV to the same degree as the entire coverage, although this effect varies with the strength of the flow velocity shear. It follows that the proposed method is useful for suppressing the VIV with a small number of damping devices attached.