# A numerical analysis of several wave energy converter arrays deployed in the Black Sea

### Significance Statement

The interaction of sea waves with floating or bottom-mounted objects in close proximity plays an important role in the analysis of a number of applications. Very Large Floating Structures either supported by a large number of bottom mounted or floating legs, offshore wind turbines, wave energy converter arrays, and columns of tension-leg platforms are typical examples of these applications that waves interactions with multiple bodies take place. The forces acting on these bodies may vary considerably as compared to forces acting on an isolated body because of array configuration, waves direction, number and dimensions of bodies in the selected array, and gap distance between the bodies.

Wave interactions with wave energy converter arrays are considered as a potential area of application considering that the wave energy converter may have complicated geometries than a circular cylinder normally used in several offshore applications. However, most studies on the interaction of waves by wave energy converter arrays have majorly focused on Oscillating Water Column wave energy converter only.

İlkay Özer Erselcan and Abdi Kükner from Istanbul Technical University investigated the effect of the number of wave energy converters in an array on the generation of energy. They analyzed one linear arrangement with two wave energy converters and two square arrays with 4 and 9 wave energy converters in four states experienced in two regions of the Eastern Black Sea coasts of Turkey by implementing a definite gap and wave direction. They also presented a detailed design of a hydraulic power take-off system. Their work is published in Ocean Engineering.

A float is the part of the wave energy converter that interacts with the waves, therefore providing the mechanical force as well as motion that the power take-off system needs in order to produce electricity. For this reason, it is important to know the motions of the float in a bid to compute the amount of electricity that can be produced in a selected sea state. Linear wave theory is majorly used in calculating the oscillatory motions experienced by ships and other sea-going vehicles due to the wave moments and forces acting on the bodies.

In the theory, the fluid is assumed inviscid, incompressible, and irrotational. Therefore, the fluid velocity is represented by the gradient of a scalar function, which is termed as the velocity potential. The wave amplitudes and motion amplitudes, which the body experience, are assumed smaller than the wave lengths and the corresponding body lengths.

The authors realized that the interaction of waves with the wave energy converters exhibit varying behaviors in the various array configurations and became even complicated as the arrays became larger. Their analyses carried out in three different arrays indicated that the hydrodynamic interaction of the waves with the floats led to a drop in the amount of energy produced by all the converters in the arrays. The authors did the analyses with a constant gap between the converters in all arrays and with one incident wave angle.

Erselcan and Kükner proposed that extent of the drop for energy produced as well as the severity of the hydrodynamic interaction of the waves with the bodies ought to be investigated. This should be done by defining different distances between the converters, different incident angles, and by analyzing arrays with varying configurations and with varying number of wave energy convers in the arrays.

### About the author

Abdi Kükner is a Professor of Naval Architecture and Ocean Engineering at Istanbul Technical University (ITU). He received his B.Sc. and M.S. in Shipbuilding and Marine Engineering in 1975 and 1977 from Istanbul Technical University. He also received a M.Sc. degree in Naval Architecture in 1980 from the University of California, Berkeley. Finally, he earned his PhD in Ocean Engineering at Stevens Institute of Technology in 1984. He has been teaching and researching in the Department of Naval Architecture and Ocean Engineering at Istanbul Technical University since 1985.

His research interests include design and building of ships and small crafts, ship hydrodynamics, wave and wind energy, computational fluid mechanics, dynamics of marine structures, and harbour design and management. He served as the Head of Ocean Engineering Department at ITU from 1999 to 2011 and was assigned as the Dean of ITU Maritime Faculty between 2016 and 2017. Moreover, Prof Kükner worked with engineering companies as an engineering consultant.

Furthermore, he participated in several research projects which include the design and optimization of different types of ships, the risk assessment of ports, the investigation of currents in a harbor and real-time simulation of ship maneuvering in Istanbul Strait. He published many peer-reviewed papers in indexed journals and in conferences.

### About the author

Dr İlkay Özer Erselcan is currently employed as a naval architect and ocean engineer in a Turkish naval shipyard. He received his B.S. in Naval Architecture and Marine Engineering in 2004 and completed his SM in Naval Architecture and Marine Engineering at Massachusetts Institute of Technology (MIT) in 2010. He studied seakeeping of ships at MIT and advised by Prof Michael S. Triantafyllou during his studies. He later started to study on the design of point absorber type wave energy converters and further studied on the hydrodynamics of wave energy converter arrays and on the influence of hydrodynamic interactions among wave energy converters in an array.

He completed his studies on wave energy converter arrays in 2017 and received his PhD in Shipbuilding and Ocean Engineering from Istanbul Technical University. He published 5 peer-reviewed papers in the fields of seakeeping of ships and wave energy converters.

### Reference

İlkay Özer Erselcan and Abdi Kükner. A numerical analysis of several wave energy converter arrays deployed in the Black Sea. Ocean Engineering, volume 131 (2017), pages 68–79.