Abstract

Mechanical aspects of ocean current energy capture are considered with emphasizing a difference between mechanical problems in capture of current and wind energy. Because of this difference, underwater power stations have to be built as anchored frames, oscillating wings have a higher effectiveness than rotating blade, and biofouling becomes the most important problem of maintenance.

Introduction

The environmental challenge and global energy needs have changed the relation of technology paths for energy production over the past two decades. Renewable sources of energy with little environmental impact have started to attract the attention of both scientists and governments. Flow energy is the cleanest and most renewable source for electric power generation, although it requires large areas for collection. Hydropower is the oldest and very effective renewable energy technology. The density of hydraulic energy (the energy quantity per area unite of flow cross-section) in the flow within hydraulic power stations is much greater than in wind or currents. It occurs because dams have been constructed to increase this density near electric power stations; but the dam construction leads to environmental issues, including flooding of lands, impact on the water quality and the fish population. Thus, other paths of flow energy capture have also been considered.

Impressive successes in capturing renewable energy were attained by using wind energy. Experience in airplane propeller design served as the basis for the development of devices to transform wind energy into the energy of a rotating device. The wind plants can be built near customers, and neither energy transfer, nor maintenance of these plants and power nets is a problem. In the near future, the significant efforts must be made1 to improve the efficiency of these plants and reduce their negative environmental factor (such as noise).

However, an essential issue in the capture of wind energy is the relatively small density of this energy. For a wind of 10 MPH, 1 m2 of the flow cross-section cannot give more than 85W of power, but losses reduce a real limit to less than 50W/m2. The density of ocean current energy is not much higher than wind energy because the currents are slow. Average speeds of the open-ocean surface currents remain below 0.5 m/s. Exceptions to this are found in the western boundary currents, such as the Gulf Stream; their velocities in some places rise up to 1-2 m/s. Nevertheless, the currents are not intermittent, and they are seasonally stable. Therefore, the ocean energy capture becomes quite attractive.

The significant physical similarity between flows of air and water (between winds and currents) encourages to urges a direct transfer of the knowledge gained in a successful experience of wind energy capture to an attempt to capture the energy of ocean currents. In our opinion, it looks like an intention to cross the ocean in a car, and we are going to explain how the problem of ocean current energy capture relates to ocean engineering. It is very important to emphasize the specific issues involved in a capture of ocean current energy.

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