Optimum Layouts of a Cluster of Heaving Point Absorbers in front of Wall-type Coastal Structures under Regular Wave Attack

Abstract

The present paper aims at determining optimum layouts for a cluster of identical semi-immersed oblate spheroidal heaving Point Absorbers (PAs) in front of a bottom-mounted wall-type structure under the action of regular waves. Optimum layouts correspond to those that for a given incident wave frequency and direction maximize the power absorbed by the cluster and satisfy predefined spatial constraints. The corresponding optimization problem is solved by developing and coupling a Genetic Algorithm (GA) solver with a frequency-based hydrodynamic analysis numerical model. Initially, the efficiency of the developed optimization process is verified by comparing results with the parametric ones of other investigators. Next, various optimization cases for a cluster of five devices under the action of perpendicular to the wall waves are formed and solved. Focus is given on the effect of the incident wave frequency, the available for deploying the devices wall length and of symmetrical layout considerations, on the formation of the optimum layouts and on the power absorbed by the cluster.

When optimization is performed at a frequency smaller than the heave natural frequency of the devices, the PAs within the optimum layouts are placed close to the wall and they form sub-clusters of closely-positioned bodies. Contrary to the above, maximization of the absorbed power at a frequency equal to the devices’ heave natural frequency is realized by placing the PAs at a large perpendicular distance from the wall and without forming any sub-clusters. In the latter case, the optimally-arranged devices show also a much better power absorption ability. The deployment of part of the whole wall length for placing the PAs reduces the power absorbed by the optimally-arranged clusters, compared to the cases, where no wall-length restrictions are taken into account. Finally, the consideration of symmetrical features in the formation of the optimum layouts affects at a small degree the power absorption ability of the PAs clusters.