Experimental Performance Evaluation of a Hydraulic PTO System for Centipede Wave Energy Converter


Sea-Based Energy Research group, Babol Noshirvani University of Technology


In the past decade, ocean and marine waves like other renewable energy sources attracted attention due to its high energy density. The most important part of a wave energy converter (WEC) is power take-off (PTO) system. In this study, a proper hydraulic power take-off system for centipede WECs has been evaluated and analyzed in experimental scale. Experimental analysis has been done in dry conditions. Important parameters are resistant load of rheostats and the opening percent of the flow control valve. System input is the wave force, which is modeled as an external mechanical force applied to the end of the lever. Resistant load of rheostats is changeable in the range of 9.5 to 55 ohms. In addition, according to the range of valve opening, six positions are selected to study. Results in this research show that, as resistance load increases, output power and efficiency, are enhanced significantly. On the other hand, in all the resistive loads tested, there is a maximum point (2 rev. valve opening) for efficiency, which shows the positive effect of controlling the input flow to the Hydro Motor (HM). The efficiency in this position of the flow control valve opening has enhanced by 40% compared to neighbor situations.


  1. J. Falnes, "A review of wave-energy extraction," Marine structures, vol. 20, no. 4, pp. 185-201, 2007. [DOI:10.1016/j.marstruc.2007.09.001]
  2. I. López, J. Andreu, S. Ceballos, I. M. de Alegría, and I. Kortabarria, "Review of wave energy technologies and the necessary power-equipment," Renewable and sustainable energy reviews, vol. 27, pp. 413-434, 2013. [DOI:10.1016/j.rser.2013.07.009]
  3. M. Den Elzen, A. Admiraal, M. Roelfsema, H. van Soest, A. Hof, and N. Forsell, "Contribution of the G20 economies to the global impact of the Paris agreement climate proposals," Climatic Change, vol. 137, no. 3-4, pp. 655-665, 2016. [DOI:10.1007/s10584-016-1700-7]
  4. R. Alamian, R. Shafaghat, and M. Ghasemi, "Experimental evaluation of attenuator WEC in a laboratory wave tank," (in eng), Journal Of Marine Engineering, Research Paper vol. 14, no. 28, pp. 1-9, 2019.
  5. M. Negahdari, H. Dalayeli, and M. Moghadas, "modelling and analyzing piont absorber WEC for a cylinderical buoy in heave motion," (in persian), 1394.
  6. P. Yoosefi Khiabani, M. A. Abbaszadeh, A. Khorshid, and M. M. Ettefagh, "Investigation of WaveStar Energy Converter Performance in Caspian Sea Using Regular Wave and Froude-Krylov Force," (in persian), Journal Of Marine Engineering, Research Paper vol. 12, no. 23, pp. 45-55, 2016.
  7. [7] R. Waters et al., "Experimental results from sea trials of an offshore wave energy system," Applied Physics Letters, vol. 90, no. 3, p. 034105, 2007. [DOI:10.1063/1.2432168]
  8. H. Sarlak, M. S. Seif, and M. Abbaspour, "Experimental investigation of offshore wave buoy performance," Journal of Marine Engineering, vol. 6, no. 11, pp. 0-0, 2010.
  9. R. Henderson, "Design, simulation, and testing of a novel hydraulic power take-off system for the Pelamis wave energy converter," Renewable energy, vol. 31, no. 2, pp. 271-283, 2006. [DOI:10.1016/j.renene.2005.08.021]
  10. B. Drew, A. Plummer, and N. Sahinkaya, "A review of wave energy converter technology," vol. 223, ed: Sage Publications Sage UK: London, England, 2009, pp. 887-902. [DOI:10.1243/09576509JPE782]
  11. R. Hansen, T. Andersen, H. Pedersen, and A. Hansen, "Control of a 420 kn discrete displacement cylinder drive for the wavestar wave energy converter," in ASME/BATH 2014 Symposium on Fluid Power and Motion Control, 2014: American Society of Mechanical Engineers Digital Collection. [DOI:10.1115/FPMC2014-7833]
  12. H.-N. Nguyen, G. Sabiron, P. Tona, M. M. Kramer, and E. Vidal Sanchez, "Experimental validation of a nonlinear MPC strategy for a wave energy converter prototype," in ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, 2016: American Society of Mechanical Engineers Digital Collection. [DOI:10.1115/OMAE2016-54455]
  13. M. Lopes, J. Hals, R. Gomes, T. Moan, L. Gato, and A. d. O. Falcão, "Experimental and numerical investigation of non-predictive phase-control strategies for a point-absorbing wave energy converter," Ocean Engineering, vol. 36, no. 5, pp. 386-402, 2009. [DOI:10.1016/j.oceaneng.2009.01.015]
  14. M. Kramer, L. Marquis, and P. Frigaard, "Performance evaluation of the wavestar prototype," in Proceedings of the 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, pp. 5-9: Citeseer.
  15. R. Alamian, R. Shafaghat, R. Bayani, and A. H. Amouei, "An experimental evaluation of the effects of sea depth, wave energy converter's draft and position of centre of gravity on the performance of a point absorber wave energy converter," Journal of Marine Engineering & Technology, vol. 16, no. 2, pp. 70-83, 2017. [DOI:10.1080/20464177.2017.1282718]
  16. Hydraulic Motors, Variable Displacement, in HY30-8223/UK, P. Hannifin, Ed., ed. sweden, 2014.