Abstract
INGINE Inc. developed its own wave energy converter (WEC) named INWAVE and has currently installed three prototype modules in Jeju Island, Korea. This device is an on-shore-type WEC that consists of a buoy, pulleys fixed to the sea-floor and a power take off module (PTO). Three ropes are moored tightly on the bottom of the buoy and connected to the PTO via the pulleys, which are moving back and forth according to the motion of the buoy. Since the device can harness wave energy from all six degrees of movement of the buoy, it is possible to extract energy efficiently even under low energy density conditions provided in the coastal areas. In the PTO module, the ratchet gears convert the reciprocating movement of the rope drum into a uni-directional rotation and determine the transmission of power from the relation of the angular velocities between the rope drum and the generator. In this process, the discontinuity of the power transmission occurs and causes the modeling divergence. Therefore, we introduce the concept of the virtual torsion spring in order to prevent the impact error in the ratchet gear module, thereby completing the PTO modeling. In this paper, we deal with dynamic analysis in the time domain, based on Newtonian mechanics and linear wave theory. We derive the combined dynamics of the buoy and PTO modules via geometric relation between the buoy and mooring ropes, then suggest the ratchet gear mechanism with the virtual torsion spring element to reduce the dynamic errors during the phase transitions. Time domain simulation is carried out under irregular waves that reflect the actual wave states of the installation area, and we evaluate the theoretical performance using the capture width ratio.
Highlights
Since industrialization, the use of fossil fuel energy has increased exponentially
The idea of wave energy has existed for a long time, the commercialization has been slower than other sources of renewable energy
We present the INWAVE modeling including this power take off module (PTO) module based on the Newtonian mechanics and linear wave theory (LWT) [10,11]
Summary
The use of fossil fuel energy has increased exponentially. the awareness and concern for the entirety life on Earth is growing due to side effects, such as global warming. To reduce the proportion of the cable installation cost in the capital expenditure of the WEC, a large-capacity wave energy farm should be built It requires more complete initial verification than other renewable energy sources for commercialization [5]. Since the power production unit price of a diesel generator is higher than that of the mainland, renewable energy sources in the islands are cost competitive. This has been represented in the example of Samsø Island in Denmark [6]. The ratchet gear is a mechanical element that converts the reciprocating motion of the mooring rope into a uni-directional rotation to the generator. We carry out simulations under JONSWAPirregular waves in various wave periods, to demonstrate the characteristics of the device
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