Wave energy extraction using decommissioned ships

Abstract

About 200–400 large merchant ships are decommissioned and scrapped every year. In addition, the US Navy decommissions tens of naval vessels every year. In 2002/2003, the average cost of custody for a ship to be decommissioned was $25,000 per year, and $2.5 million to scrap it. The US Navy budget to scrap naval vessels in 2002 was $33.4 million. Now apparently the Navy sinks naval vessels by bombs and torpedos. Scrapping can cause pollution, health hazards, accidents and threat to the ecosystem. Can a “polluting” ship about to be scrapped be used to generate clean wave energy? Maybe! It is possible to place the ship (unmanned) in about 50 m of water where deep-water swells may have an average wave period of 6–15 s. The ship would be “tuned” to have large motion response, particularly in heave and pitch. In short waves, the ship could serve as a platform for secondary energy absorption. The idea is to tune the ship to have rigid body resonance, or close to it, and resist that motion to absorb power. A hydraulic ramp connected to an accumulator feeding a hydraulic motor that generates power is one possibility. Several other energy extraction mechanisms such as turbines connected to oscillating water columns are possible devices. These concepts together with a few preliminary numerical analyses are presented and discussed.

Keywords:

• renewable energy
• wave energy
• decommissioned ships
• wave energy extraction system
• ocean wave energy device

Acknowledgements

This study was undertaken at the Ship and Offshore Research Institute (The Lloyd's Register Educational Trust Research Centre of Excellence) of Pusan National University, Busan, Korea. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant no.: K20903002030-11E0100-04610). The Lloyd's Register Educational Trust funds education, training and research programmes in transportation, science, engineering, technology and the safety of life, worldwide for the benefit of all.