In order to improve the performance of Darrieus turbine, the pitch angles of the blades are varied and tested in a low-speed wind tunnel. First, the pitch angles of the blades are varied with an interval of 15 degrees, to evaluate the possibility of the improvement. The tested tip-speed ratio is ranged from 0.5 to 2.8, which covers the peak of the power, and the generated torque is measured by a torque meter. However, none of the blades exceed the performance of zero-pitched blade. Then, the pitch angles of the blades are varied but with an interval of 2 degrees. As a result, it is found that the blades with pitch angle of 4 and 6 degrees give the highest torque, especially in a tip-speed ratio over 1. By changing the pitch angle of the blade from 0 to 6 degrees, the peak value of the power coefficients is improved by more than 30 percent.
An ocean current is an attractive renewable energy source for a country surrounded by sea, like Japan. In the ocean currents, a tidal current can reach to a speed above five meters per second, which has an equivalent energy with a wind of typhoon, nearly 47 meters per second. Moreover, the occurrence of a tidal current is highly periodical and easily predicted. A tidal current changes its flow direction by 180 degrees with regular intervals. The Darrieus-type water turbine is suitable for such situation because of its independency to a current direction, as well as simplicity. Actually, the Darrieus turbine is adopted in the demonstration of power generation from a tidal current at Kanmon Strait (Hiraki, et. al. 2010).
There are some drawbacks for the Darrieus-type turbine. One of them is the lower efficiency of the power generation, as compared to the horizontal-axis turbines. This is one of the reason why the Darrieus turbine is not commonly used in real situations. The attachment of a device that collects a current into the turbine is an option to enhance the efficiency (Hiraki, et. al. 2013). The incapability of self-starting is also a known problem for a turbine that uses a lift force, which is also true for Darriues turbine.
The authors have developed a counter-rotating type hydroelectric unit where tandem runners counter-rotate inner and outer armatures in a peculiar generator, and the unit has penetrated into the market in the small/micro hydropower. The unit has promising advantages such as the rotational torque is counter-balanced itself between the front and the rear runners, namely the inner and the outer armatures. Such technology has been provided for the tidal power unit moored to the seabed with one cable. Tidal stream is abundant and clean energy resource whose power is predictable and sustainable. To generate power effectively from the stream, the unit must effectively work in response to change of the flow direction not only in day cycle but also in unsteady condition with turbulent fluctuation. This paper discusses the effects of the flow direction on the output of the tandem propellers by commercial Computational Fluid Dynamics (CFD) code.
The renewable energy market is growing rapidly and is expected to increase by 2.7 times between 2010 and 2035 (Ellabban, 2014), to cope with the warming global environment. Ocean energy has higher conversion efficiency in comparison with solar and thermal energy, energy density is high, and it is clean energy without depletion. Many types of energy conversion have been proposed to capture the energy available in the ocean (Antonio, 2010). Typical type is to convert the kinetic energy of the tide flow through a horizontal or vertical axis turbine. The horizontal axis tidal turbine is the most progressive and commercially feasible (Laws and Epps, 2016).
Kanemoto, et al (2010) have proposed the use of counter rotating mechanism and applied these units for marine, wind power and hydroelectric power generation. Usui, et al (2013) have proposed a mooring type tidal stream power unit with a cable and a mounting type unit, and then discussed the performances and the hydrodynamic force. Wei, et al (2015) analyzed the influence of blade pitch angle and the axial distance between the tandem propellers on performance of the counter-rotating tidal stream power unit in a wind tunnel. Huang, et al (2015) employed a multi-objective numerical method coupled with a response surface method and genetic algorithm to optimize the pitch angle of the front blade of a counter-rotating type tidal stream power unit.
Kanemoto, Toshiaki (Kyushu Institute of Technology) | Lee, Nak-Joong (Kyushu Institute of Technology) | Heo, Man-Woong (Kyushu Institute of Technology) | Huang, Bin (Kyushu Institute of Technology) | Nakanishi, Yuji (Kanagawa University) | Funami, Yuki (Kanagawa University)
The energy from a tidal stream is abundant and renewable resource whose power is predictable and sustainable. To generate power effectively from the stream a unique counter rotating type tidal stream power unit, whose tandem rotors drive inner and outer armatures in a generator, has been provided by the authors. At the tidal power station located in narrow straits, the unit needs to be reoriented so that useful output power can be obtained from both flood and ebbing tides.
In this paper, the counter rotating tandem rotor turbine was designed for operation in a bidirectional tidal stream and the performance was analyzed. The maximum output power is somewhat lower than that of the rotors designed exclusively for a unidirectional stream. The relative flow has a positive angle of attack at the leading edge and discharges from the trailing edge along the blade camber. The angular momentum change, namely the rotor work, is seen to always be accompanied with a shock loss at the leading edge.
Currently, interest in renewable energy sources is growing worldwide. Among these sources, ocean energy is seen as one of the promising resources that can solve the energy supply depletion problem and cope with the warming global environment due to carbon dioxide emissions from the combustion of fossil fuels. To capture the energy available from the ocean, many methods of energy conversion have been proposed (Antonio, 201 0). One of these methods converts the kinetic energy in a tidal stream via a horizontal or vertical axis turbine. The unit does not adversely affect the surrounding marine environment significantly and is environmentally friendly. For most tidal turbines, the horizontal axis tidal turbine is the most advanced and commercially feasible (Laws and Epps, 2016). The operating principles of such a turbine are similar to wind turbines and it is possible to utilize the design methodology and benefit from advanced technologies in the wind industry (Ng, 2013; Ben Elghali, 2007).
A counter-rotating type horizontal-axis tidal stream power unit has a number of attractive features, for instance, cavitation can be suppressed well owing to decrease the individual rotational speed in keeping the relative rotational speed same as the single propeller speed. A cavitation model based on a homogeneous multiphase flow method implemented in the Reynolds-Averaged Navier-Stokes (RANS) solver CFX14.0 was employed to carry out the cavitation simulations on a counter-rotating type horizontal-axis counter-rotating type impellers in a tidal stream power unit. The cavitation performance curve at a relative high tip speed ratio was obtained, and additional observations were made with regards to cavity size and shape as well as cavitation breakdown behavior.
This paper presents a digital resolved acceleration control method for coordinated motion control of an underwater vehicle equipped with manipulators. Using this method, in spite of large position and attitude errors of the underwater vehicle, good control performances of the end-tips of the manipulators to follow a pre-planned trajectory can be achieved. In this work, theoretical work of the proposed method is described. Then, the effectiveness of the proposed method is demonstrated through experimental work using a 3-link dual-arm underwater robot in actual underwater environment. KEY WORDS: Underwater vehicle; manipulator; UVMS; resolved acceleration; control.
Kanemoto, Toshiaki (Kyushu Institute of Technology) | Galal, Ahmed Mohamed (Kyushu Institute of Technology) | Ikeda, Galal (Kyushu Institute of Technology) | Mitarai, Hiromi (Kyushu Institute of Technology) | Kubo, Koichi (Kyushu Institute of Technology)
The authors have proposed the superior wind turbine generator, which is composed of the tandem wind rotors and the double rotational armature type generator without the conventional stator. It was verified experimentally at the previous two ISOPE conferences that the output of this new type is higher than the conventional wind turbine and is kept constant in the rated operating mode without using the brake and/or the pitch control mechanisms. Continuously, in this paper, the double rotational armature type doubly fed induction generator was prepared and its characteristics were clarified. Besides, the effects of the front blade profile and the wind rotor arrangements on the turbine performances were discussed experimentally in accompany with the flow conditions. INTRODUCTION Growing energy demand and environmental global warming have re-evoked human interest in Renewable Energy. Wind energy is a clean and home grown resource of electric power generation, which has been positively/effectively utilized to cope with the warming global environment. Although propeller wind turbines are so effective, but the conventional turbines may have some weak points such as that the large-sized wind rotor does not operate at the weak wind, the power generation of the small-sized wind rotor is low, and it is necessary to be equipped with the brake and/or the pitch control mechanisms, to suppress the abnormal rotation and the generated overload at the stronger wind, and to keep good quality of the electric power. To overcome the above weak points, the authors have invented the superior wind turbine generator, which was presented at the 15th , and the 16th ISOPE Conferences (Kanemoto et al., 2005) and (Ahmed Mohamed Galal et al., 2006) respectively. This unit was called the “Intelligent Wind Turbine Generator” by the authors, as the rotational speeds of the tandem wind rotors are adjusted pretty well in cooperation with the two armatures of the generator in response to the wind speed.
To cope with the warming global environment, the hydropower should occupy the attention of the electric power generation system as clean and cool energy sources. In such a situation, the tidal current has scarcely been utilized for the power generation. The authors have proposed and developed a new type of generator with counter-rotating rotors instead of the usual mechanism. This paper discusses the effects of the blade profiles on the hydraulic performances. As a result, the design materials for the solidity of the axial flow runners suitable for the given water circumstances are induced from above discussions. INTRODUCTION To cope with the warming global environment, the hydropower should occupy the attention of the electric power generation system as clean and cool energy sources. In such a situation, the tidal current has scarcely been utilized for the power generation, for instance, the Kanmon Straits in Japan has about 54 MW hydraulic energy. It may be appropriate to apply the high specific speed hydraulic turbine for the tidal power generation. It is also desirable to make the machine compact size and simple composition, but the usual generator may reject such desires. That is, it is necessary, for getting sufficiently the electric power, to make the rotor diameter large or equip with the accelerator such as a gear-box, because the electric power is in proportion to the rotational speed in the magnetic field. Therefore, the authors have proposed and developed a new type of generator with counter-rotating rotors instead of the usual mechanism, which can make the generator diameter small on account of relatively double the rotational speed. Moreover, it is extremely easy to board on the floating buoy moored already in the strait, because the inertia moment of the rotor rotation is counter-balanced successfully (Kanemoto and Tanaka, 2001; Tanaka and Kanemoto, 2004; Kanemoto and Osono, 2004).
Kashiwabara, Toshinori (Kochi National College of Technology) | Nakajima, Nobuo (Kochi National College of Technology) | Kanemoto, Toshiaki (Kyushu Institute of Technology) | Nakanishi, Yuji (Kanagawa University)