Advanced Power Take-off and Conversion System for Submerged Ocean Wave Energy Convertors

Abstract

Today, unmanned undersea vehicles (UUVs) are taking an increased number of U.S. Navy mission roles. These vehicles will most likely be launched within a large distance from its assigned mission area. At times it may be desirable for these vehicles to loiter and await tasking. One of the major limiting factors for these UUV activities is endurance. Currently, UUVs are limited to the range provided by one single battery charge. However, a reliable and renewable power resource to charge the battery trays is a big challenge issue for the U.S. Navy. Which is why the U.S. Navy is interested in developing a renewable seabed power source that will allow UUVs to charge while deployed and remain undetected. UUVs are generally far away from terrestrial power with no power source available to charge a battery. A covert, submerged, renewable power source that utilizes wave energy, wind, solar, temperature differences, etc., to charge a submerged power center is highly desirable. Working with the Navy Science Advisor, we obtained the requirements for a typical UUVs battery, which includes i) the high-charge-rate for two battery trays has about ~11kWh, ii) takes about 7 hours to charge from 0 to 100 percent, iii) the charge voltage is 32VDC, iv) and the power charge station is preferably located on ocean bed, which is typically under 60 meters of ocean water surface.Ocean wave energy offers a renewable resource that is predictable several days in advance and is significantly higher in its energy density comparing to wind and solar energies. But current tactics of harvesting energy from the ocean have a lot of flaws [1] –[7]. Therefore, a new and innovative technology must be invented and developed for a renewable rechargeable submerged ocean generator for U.S. Navy UUVs. One of our proposed submerged ocean wave power generators is shown in the Figure 1(a). The rotating mass can be designed to let all the power take off components be housed in a nondeformed water isolated housing, which solves the water leakage challenge of a submerged WEC. However, no existing power take-off and conversion technology is suitable for this submerged WEC.We have successfully developed a portion of the submerged WEC, the power take-off and conversion system, as shown in Figure 1(b), which can be isolated in a solid shell without motion or deformation interaction with outside seawater. The system can pick up ocean wave energy with submerged buoy which then transfers the vibrational energy absorbed by the buoy to the deep-water generator through a rope-spring system. Centrifugal rotational mass converts wave vibration energy to arbitrary direction rotational energy. During this, a gear system converts low speed rotation to high-speed rotation to the alternator/motor which then converts more rotational energy to electrical energy. In the power-take-off system, three groups of gear systems are uniformly distributed on a circular plate to make a stable and balanced 3D system. Each group of gear systems is ended with two-side gears and one driving gear to make a more stable gear sub-system. In order to reduce friction, ball bearings are used in combination with holding shifts on circular plate. In addition, one-way clutches are used to block resistance from backward rotation of motors. The system has the potential to generate kWs of electrical power underwater. In this presentation, we will discuss i) the innovative design concept and work principle, ii) the mechanical power take-off mechanism, iii) mechanical energy transportation, and iv) the mechanical to electrical power alternators. In this paper/poster, both analytical modeling and experimental studies will be presented. In addition, we are planning to demonstrate the system in the exhibition hall of this conference to let anyone approach and test this system for themselves.