Luca Martinelli, Piero Ruol, Giampaolo Cortellazzo


The design of a mooring system of a Wave Energy Converter is a challenging process that points out several unsolved technical problems, mostly related to the highly non-linear hydrodynamic phenomena occurring when high waves (e.g. 8 m high with 200 m wavelength) propagate in relatively shallow waters (e.g. 20 m). The aim of this note is to point out the relevance of the non-linear response of a WEC anchored in relatively shallow waters (shallow in the “non-linear” sense) in terms of loads applied to the mooring lines. Further, the effects of this cyclic load on the anchors is investigated. Note that to some extent it is like checking the importance of geotechnical and coastal engineers in the design process of the WEC structure and its mooring system (typically carried out by naval architects). The whole mooring design process is first outlined and then it is schematically applied to a specific case, namely a promising Italian device named SeaBreath (www.seabreath.it), in view of a possible deployment in the Adriatic Sea. The main concern of mooring designers is related to resonance effects induced by the second order drift. Therefore specific tests have been carried out in the 36 m long x 1.0 m wide x 1.3 m high wave flume of Padova University. Tests focused on the forces on the mooring lines induced by the sum of two regular waves of similar frequency. The mooring design is still far from complete: the physical model proved the relevance of the aforementioned effects but a numerical investigation (not yet performed) is required to draw final conclusions.


Wave energy converter; mooring design; anchor design

Full Text:



Alcorn, R., Hunter, S., Signorelli, C., Obeyesekera, R., Finnigan, T., and Denniss, T. 2005. Results of the testing of the Energetech wave energy plant at Port Kembla. Energeth Report.

Boake, C.B., Whittaker, T.J.T., Folley, M., and Ellen, H. 2002. Overview and initial operational experience of the LIMPET wave energy plant. Proceedings of the 12th international offshore and polar engineering conference, 586-594.

Curran, R., Stewart, T., and Whittaker, T.J.T. 1997. Design synthesis of oscillating water column wave energy converters: performance matching. Proc.Inst.Mech.Eng.A: J.Power Energy, 211(6), 489-505.http://dx.doi.org/10.1243/0957650981537375

Dizadji, N., and Sajadian, S.E. 2011. Modeling and optimization of the chamber of OWC system. Energy, 36(5), 2360-2366.http://dx.doi.org/10.1016/j.energy.2011.01.010

El Marjani, A., Castro, F., Rodriguez, M.A., and Parra, M.T. 2008. Numerical modelling in wave energy conversion systems. Energy, 33(8), 1246-1253.http://dx.doi.org/10.1016/j.energy.2008.02.018

Falcão, A.F.O., Sabino, M., Whittaker, T., and Lewis, A. 1995. Design of a shoreline wave power pilot plant for the island of pico, azores. Proceedings of the 2nd European Wave Power Conference, Lisbon, Portugal, 87-93.

Falcão, A.F.d.O. 2000. The shoreline OWC wave power plant at the Azores. Proceedings of the 4th European Wave Power Conference, 42-48.

Gouaud, F., Rey, V., Piazzola, J., and Van Hooff, R. 2010. Experimental study of the hydrodynamic performance of an onshore wave power device in the presence of an underwater mound. Coastal Engineering, 57(11-12), 996-1005.http://dx.doi.org/10.1016/j.coastaleng.2010.06.003

Hafsia, Z., Hadj, M.B., Lamloumi, H., and Maalel, K. 2009. Internal inlet for wave generation and absorption treatment. Coastal Engineering, 56(9), 951-959.http://dx.doi.org/10.1016/j.coastaleng.2009.05.001

Heath, T., Whittaker, T.J.T., and Boake, C.B. 2000. The design, construction and operation of the LIMPET wave energy converter (Islay, Scotland). Proceedings of the 4th European Wave Energy Conference, 49-55.

Hirt, C.W., and Nichols, B.D. 1981. Volume of fluid (VOF) method for the dynamics of free boundaries. Journal of Computational Physics, 39(1), 201-225.http://dx.doi.org/10.1016/0021-9991(81)90145-5

Jayashankar, V., Anand, S., Geetha, T., Santhakumar, S., Jagadeesh Kumar, V., Ravindran, M., Setoguchi, T., Takao, M., Toyota, K., and Nagata, S. 2009. A twin unidirectional impulse turbine topology for OWC based wave energy plants. Renewable Energy, 34(3), 692-698.http://dx.doi.org/10.1016/j.renene.2008.05.028

Josset, C., and Clément, A.H. 2007. A time-domain numerical simulator for oscillating water column wave power plants. Renewable Energy, 32(8), 1379-1402.http://dx.doi.org/10.1016/j.renene.2006.04.016

Lin, P., and Liu, P.L.F. 1999. Internal wave-maker for Navier-Stokes equations models. Journal of Waterway, Port, Coastal and Ocean Engineering, 125(4), 207-217.http://dx.doi.org/10.1061/(ASCE)0733-950X(1999)125:4(207)

Lopes, M., Ricci, P., Gato, L., and Falcão, A.F.O. 2007. Experimental and numerical analysis of the oscillating water column inside a surface-piercing vertical cylinder in regular waves. Proceedings of the 7th European Wave and Tidal Energy Conference, Porto, Portugal.

Morris-Thomas, M.T., Irvin, R.J., and Thiagarajan, K.P. 2007. An investigation into the hydrodynamic efficiency of an oscillating water column. Journal of Offshore Mechanics and Arctic Engineering, 129 273.http://dx.doi.org/10.1115/1.2426992

Pereiras, B., Castro, F., El Marjani, A., and Rodriguez, M.A. 2011. An improved radial impulse turbine for OWC. Renewable Energy, 36(5), 1477-1484.http://dx.doi.org/10.1016/j.renene.2010.10.013

Schäffer, H.A., and Klopman, G. 2000. Review of multidirectional active wave absorption methods. Journal of Waterway, Port, Coastal, and Ocean Engineering, 126 88.http://dx.doi.org/10.1061/(ASCE)0733-950X(2000)126:2(88)

Setoguchi, T., Santhakumar, S., Maeda, H., Takao, M., and Kaneko, K. 2001. A review of impulse turbines for wave energy conversion. Renewable Energy, 23(2), 261-292.http://dx.doi.org/10.1016/S0960-1481(00)00175-0

Takao, M., Setoguchi, T., Kinoue, Y., and Kaneko, K. 2007. Wells turbine with end plates for wave energy conversion. Ocean Engineering, 34(11–12), 1790-1795.http://dx.doi.org/10.1016/j.oceaneng.2006.10.009

Thakker, A., Usmani, Z., and Dhanasekaran, T.S. 2004. Effects of turbine damping on performance of an impulse turbine for wave energy conversion under different sea conditions using numerical simulation techniques. Renewable Energy, 29(14), 2133-2151.http://dx.doi.org/10.1016/j.renene.2004.03.015

Thiruvenkatasamy, K., and Neelamani, S. 1997. On the efficiency of wave energy caissons in array. Applied Ocean Research, 19(1), 61-72.http://dx.doi.org/10.1016/S0141-1187(97)00008-4

Troch, P., and De Rouck, J. 1999. An active wave generating–absorbing boundary condition for VOF type numerical model. Coastal Engineering, 38(4), 223-247.http://dx.doi.org/10.1016/S0378-3839(99)00051-4

Wang, D.J., Katory, M., and Li, Y.S. 2002. Analytical and experimental investigation on the hydrodynamic performance of onshore wave-power devices. Ocean Engineering, 29(8), 871-885.http://dx.doi.org/10.1016/S0029-8018(01)00058-0

Washio, Y., Osawa, H., Nagata, Y., Fujii, F., Furuyama, H., and Fujita, T. 2000. The offshore floating type wave power device "Mighty Whale": open sea tests. Proceedings of 10th International Offshore Polar Engineering Conference, Seattle, 2000, 1, 373-380.

Zhang, Y., Zou, Q.-P., Greaves, D. 2012. Air–water two-phase flow modelling of hydrodynamic performance of an oscillating water column device. Renewable Energy, 41, 159-170.http://dx.doi.org/10.1016/j.renene.2011.10.011

DOI: http://dx.doi.org/10.9753/icce.v33.structures.3