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Yasuyuki Nishi,Hiromichi Koga,Terumi Inagaki 한국유체기계학회 2023 International journal of fluid machinery and syste Vol.16 No.1
In this study, a multi-objective optimization design method, combining a design of experiments, single-phase flow analysis, response surface method and a multi-objective optimization method was developed to optimize the collection device shape of an axial flow hydraulic turbine with a collection device to achieve high power and low axial thrust. In addition, the effectiveness of this design method was validated through verification experiments in an open channel with shallow water depth and multiphase flow analysis considering a free surface, and the differences from the single-phase flow analysis results were also discussed. As a result, the optimized collection device obtained by this design method showed the same axial thrust coefficient and improved power coefficient compared with the original collection device in the single-phase flow analysis. In the open channel, the power coefficient of the optimized collection device was significantly higher than that of the original collection device, but unlike the results of the single-phase flow analysis, the axial thrust coefficient of the diffuser was significantly increased, resulting in a significant increase in total axial thrust coefficient.
Yasuyuki Nishi,Nozomi Mori,Terumi Inagaki 한국유체기계학회 2023 International journal of fluid machinery and syste Vol.16 No.1
In this study, we created an optimization design method for a rotor of propeller-type wind turbine that combined design of experiments, response surface method, and optimization method with the blade element momentum theory. This design method was applied to a small propeller-type wind turbine. We then examined the performance of an obtained rotor using a three-dimensional computational fluid dynamics analysis and a wind tunnel experiment and examined the relationship between local torque and pressure distribution on the blade surface to investigate the mechanism to improve power output. Our findings showed that the experimental value of power coefficient of optimized rotor designed with our design method was approximately 6.9% higher than that of an original rotor designed with the blade element momentum theory only. This was because the optimized rotor had similar pressure difference between the pressure surface and the suction surface to that of the original rotor as the separation at the leading edge side were decreased on the tip side, and because its local torque increased as the pressure difference increased due to a longer chord length. Thus, the effectiveness of our design method was demonstrated
A Method for Distinguishing the Two Candidate Elliptic Curves in the Complex Multiplication Method
Yasuyuki Nogami,Mayumi Obara,Yoshitaka Morikawa 한국전자통신연구원 2006 ETRI Journal Vol.28 No.6
In this paper, we particularly deal with no Fp-rational two-torsion elliptic curves, where Fp is the prime field of the characteristic p. First we introduce a shift productbased polynomial transform. Then, we show that the parities of (#E − 1)/2 and (#E΄− 1)/2 are reciprocal to each other, where #E and #E΄ are the orders of the two candidate curves obtained at the last step of complex multiplication (CM)-based algorithm. Based on this property, we propose a method to check the parity by using the shift product-based polynomial transform. For a 160 bits prime number as the characteristic, the proposed method carries out the parity check 25 or more times faster than the conventional checking method when 4 divides the characteristic minus 1. Finally, this paper shows that the proposed method can make CM-based algorithm that looks up a table of precomputed class polynomials more than 10 percent faster.
Determining Basis Conversion Matrix without Gauss Period Normal Basis
Yasuyuki Nogami,Erika Yanagi,Masami Hagio,Yoshitaka Morikawa 대한전자공학회 2009 ITC-CSCC :International Technical Conference on Ci Vol.2009 No.7
This paper proposes a more efficient basis conversion matrix calculation method than a method using GNB (Gauss period Normal Basis). The method is not using GNB, thus it is possible to calculate a basis conversion matrix when GNB does not exist.