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[en] Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil-fueled power plants as a countermeasure against the global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power system to capture the energy of ocean waves have been developed. However, suitable turbine type is not normalized yet because of relatively low efficiency of the turbine systems. The purpose of this study is to investigate the performance of a newly developed direct drive hydro turbine (DDT), which will be built in a caisson for wave power plant. Experiment and CFD analysis are conducted to clarify the turbine performance and internal flow characteristics. The results show that the DDT obtains fairly good turbine efficiency in both cases of with wave and no wave conditions. As the turbine performance is influenced considerably by the wave condition, designed point of the turbine should be determined according to the wave condition at an expected installation site. Most of the output power generates at the runner passage of the Stage 2.
[en] The use of field components in local coordinates moving with the material when evaluating terms contributing to electromagnetic power conversion is shown to be necessary for relativistic conservation of power. This enables known ambiguities in the procedure for calculating total electromagnetic forces acting on relativistic systems in nonuniform motion to be resolved with the possibility of new practical applications
[en] In this paper, we elaborate on quite a simple analytical framework for the physically intelligible principle of a ray description of inhomogeneous wavefields on the basis of the generic properties of active and reactive wave power flows. While being very close to traditional geometric optics (GO) in the limit of lossless media, in substantially non-Hermitian systems this approach turns out to be a distinct method capable of keeping up ray trajectories in a real-valued domain. We also demonstrate that the ray method based on power-flow analysis is mostly free from the standard limitations of GO. In this regard, the proper use of the ray-tracing technique can be justified for modelling a wide range of non-regular wave phenomena if wave power transport is under consideration. The paraxial equations are shown to comply with the power-flow formulation, thus finding an extended range of applicability.
[en] The full-scale mock-up of the equatorial launcher was fabricated in basis of the baseline design to investigate the mm-wave propagation properties of the launcher, the manufacturability, the cooling line management, how to assemble the components and so on. The mock-up consists of one of three mm-wave transmission sets and one of eight waveguide lines can deliver the mm-wave power. The mock-up was connected to the ITER compatible transmission line and the 170GHz gyrotron and the high power experiment was carried out. The measured radiation pattern of the beam at the location of 2.5m away from the EL mock-up shows the successful steering capability of 20°∼40°. It was also revealed that the radiated profile at both steering and fixed focusing mirror agreed with the calculation. The result also suggests that some unwanted modes are included in the radiated beam. Transmission of 0.5MW-0.4sec and of 0.12MW-50sec were also demonstrated
[en] A different concept of gyrodevices in the form of a coaxial-waveguide cyclotron autoresonance maser (CARM) is proposed. Embodying the salient features of large cross-sectional area, low guiding magnetic field, and good mode selectivity as compared to the gyrotron and to the conventional CARM, the proposed device is well suited for operation at both high power and ultrahigh gain in the millimeter wave and far infrared regions. Gyrokinetic analysis and nonlinear simulation are given in detail for a coaxial configuration--with outer and inner radii of 1.83 and 0.50 cm--designed to operate in the TE28,16 mode at 335 GHz, yielding a gain of 64 dB on using a 90 keV and 50 A electron beam confined by a 9.35 T magnetic field. Nonlinear simulation demonstrates the possibility of power enhancement via a tapered magnetic field. The competition of the degenerate mode and the excitation of the absolute instability are discussed
[en] A variety of designs of self-rectifying air turbines for wave power conversion have been proposed over the last decade. However, the noise characteristics of the turbines have not been presented so far. In order to clarify the noise characteristics of the turbines, experimental investigations have been performed under steady flow conditions in this study. As a result, it is found that the noise characteristics of impulse-type turbines are superior to those of Wells-type turbines. Moreover, the noise characteristics have been discussed from the viewpoint of the specific noise level, a term used widely in engineering. (Author)
[en] An experiment on EAST is used to study the fast wave rectification by only an actively powered I-port antenna. The plasma potential up to 100 V was found in the region that does not map along the magnetic field line to active I-port antenna. This enhancement correlates with the local fast wave intensity. An increase in the loading resistance and heating efficiency was observed at a low parallel wave number. The higher heating efficiency is seen to cause lower unabsorbed fast wave power in the SOL regions. This can cause a decrease in the fast wave field intensity that reaches plasma facing components and can result in a decrease in the plasma potential and slow wave intensity. (letter)
[en] Ocean surface waves are both random in time and nonlinear. For a linear random model of the sea surface, the average shape of a large crest is found to be the scaled auto-correlation function, as is shown mathematically by Lindgren [Lindgren G. Some properties of a normal process near a local maximum. Ann Math Stat 1970;41:1870-83] and Boccotti [Boccotti P. Some new results on statistical properties of wind waves. Appl Ocean Res 1983;5:134-40]. Using field data from the North Sea, the applicability of this simple result is discussed. Stokes-type corrections up to fifth order are incorporated in an approximate but robust manner, valid at least locally in space and time. Exact second-order wave theory is used to check the accuracy of the approximate Stokes treatment and to clarify the magnitude and character of the second-order contributions. A giant wave, called the New Year wave, recorded at the Draupner platform in the North Sea at 15:20 on 1st January 1995, is examined. In a sea-state with a significant wave height of approximately 12 m, this freak wave, which has a peak elevation of 18.5 m above still water level, was unambiguously recorded. The local asymmetries of this wave are removed using the Stokes model, allowing the probability of occurrence of this remarkable event to be estimated, based on the standard Rayleigh distribution for linear crest amplitude. It is concluded that new physics, not incorporated in standard approaches to offshore engineering design, may have played an important role in the generation of this freak wave. (author)
[en] The mechanism of fast wave minority ion heating is discussed in some detail. The ray tracing algorithm is used to simulate fast wave heating for the plasma of two kinds of ions, and the calculation results of different ratios of two ions' density are obtained