Abstract
For most of the ocean currents, such as the Kuroshio at east Taiwan, the Gulf Stream at east Florida and the Agulhas Current at southeast Africa, the depth of the seabed is generally deeper than one hundred meters, some waters of which can even reach one thousand meters. In such deep waters, the design of the turbine, as well as the anchoring system shall have special features so that existing ocean engineering technologies can be applied and the engineering cost can be lowered. Thus, as regards design, in addition to the analysis of the interaction between turbine and current, priority shall also be given to the design of the anchoring system of the turbine. To address the concerns, the authors propose an ocean turbine featured as follows: (1) it can be anchored in deep waters with a single cable; (2) it can generate high power in a current of moderate flow speed while producing low drag; (3) it can be self-balanced against current disturbance; (4) it is shrouded to enhance power efficiency; (5) the dynamic variations due to the interaction between the turbine and current are small. All of these features are confirmed with the computational results, leading to a detailed design of the turbine structure. If the easy-to-install high-efficiency shrouded turbines, having the capability to self-balance and requiring minimum maintenance effort, are successfully developed, the power supply pressure in Taiwan can be greatly alleviated. The Kuroshio was chosen as the typical current for the present dynamic analysis because, firstly, the flow characteristics of Kuroshio are similar to those of other large-scale currents mentioned above, and secondly, the data of Kuroshio are highly available to us so that a thorough analysis can be done.
Highlights
According to Kawai [1], Kuroshio is a branch of the North Pacific Gyre, the segment of which between Taiwan and Japan is named Kuroshio, wherein kuro and shio refer to “black” and “tidal current”, respectively
The results revealed [23] that, in wake regions, the flow speed decreased along the streamlines (Figure 4), with the flow in the central region moving most slowly
To yield more insight into the influence of phase angle, we modeled force loads carried by the turbine system with two rotors operating at different phase angles
Summary
According to Kawai [1], Kuroshio is a branch of the North Pacific Gyre, the segment of which between Taiwan and Japan is named Kuroshio, wherein kuro and shio refer to “black” and “tidal current”, respectively. Kuroshio, known as the Geostrophic Current, is influenced by coriolis force and the sea surface elevation difference, indicating that the momentum of Kuroshio must be sufficiently large to maintain equilibrium at least among gravitational, coriolis and inertial forces, which accounts for the fact that the flow rate becomes larger as the gulf stream flows more northward [2]. The Kuroshio flowing in proximity through the region east of Taiwan is approximately 100 km in the E-W direction and 400 km in the N-S direction [2], the water from the south and the east injecting into which to assist Kuroshio in overcoming the friction force caused by the seabed, internal turbulence and atmospheric circulation. In the region east of Taiwan, under the complex influence of said forces, the Kuroshio accelerates northward toward Ryukyu along a path tens of kilometers in length, which thereafter slows down, with the overall flow rate remaining constant
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