Stability of array configurations under the action of deviatoric mean drift forces

Monochromatic waves incident on an array of structures give rise to nonlinear mean drift forces acting on the structures within the array. These drift forces are not purely in the direction of wave propagation, but have a significant component perpendicular to the wave propagation. If the structures are not rigidly connected but, say, individually moored to the bottom, these deviatoric drift forces can, in contrast to effect of the linear time-periodic exciting forces, cause a change of the spatial configuration of the array. This can lead to possible collisions between the structures, or lead to excitation or mooring forces that are significantly different than those for which the structures were designed. Using computational simulations and theoretical analysis, we study the equilibrium spatial configurations of arrays of axisymmetric bodies under the action of inter-body mean drift forces in monochromatic waves. We discuss the stability of equilibrium configurations with respect to deviations in body positions, and we address the effect of the equilibrium type on the mean drift force in the direction of wave propagation. We study this problem within the potential flow theory, employing the multiple scattering framework to obtain the non-linear, second-order mean drift force from the first-order linear potential. This study can be relevant for the design of floating wind farms, wave energy converter arrays, as well as harbor operations.