• 한국수학교육학회지시리즈B:순수및응용수학
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• 제28권1호
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• pp.71-89
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• 2021

We define the constant ratio curves in the isotropic plane and investigate their deflection properties.

• 대한수학회논문집
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• 제35권3호
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• pp.967-977
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• 2020

In this article, we find the necessary and sufficient condition for a proper biharmonic Frenet curve in the Lorentzian Sasakian space forms 𝓜³₁(H) except the case constant curvature -1. Next, we find that for a slant curve in a 3-dimensional Sasakian Lorentzian manifold, its ratio of "geodesic curvature" and "geodesic torsion -1" is a constant. We show that a proper biharmonic Frenet curve is a slant pseudo-helix with 𝜅² - 𝜏² = -1 + 𝜀₁(H + 1)𝜂(B)² in the Lorentzian Sasakian space forms x1D4DC³₁(H) except the case constant curvature -1. As example, we classify proper biharmonic Frenet curves in 3-dimensional Lorentzian Heisenberg space, that is a slant pseudo-helix.

• 한국농공학회지
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• 제45권2호
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• pp.86-95
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• 2003

During this study, constant stress ratio tests with previous compression anisotropic stress history are performed on compacted decomposed granite soil sampled at Iksan, Jeonbuk. Yielding points are determined from stress-strain curves. The shape and characteristics of compression anisotropic yield curves is examined. In addition, the measured value of yielding curve and stress-strain behavior is predicted by Yasufuku's anisotropic constitutive model based on non-associated flow rule. The main results are summarized as follows : 1) Shape of yielding curves shows almost ellipse but asymmetry with respect to stress path during previous consolidation stress. 2) Yasufuku's anisotropic constitutive model is suitable in evaluation of yielding curves on anisotropic consolidated decomposed granite soil. 3) The predicted stress-strain curve shows reasonable agreement to measured behaviours.

• Journal of Advanced Marine Engineering and Technology
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• 제24권2호
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• pp.57-62
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• 2000

The effect of exhaust gas recirculation(EGR) on the characteristics of exhaust gas emissions, and SFC are experimentally investigated by four-cylinder, four-cycle and direct injection marine diesel engine. In order to reduce the soot contents in the recirculated exhaust gas to intake system of the engines, a soot removal system of a cylinderical-type scrubber is specially designed and manufactured for the experimental system. (1) SFC is increased in downward convex curve style with increasing excess air ratio, it is increased with increasing EGR rate at the same excess air ratio. (2) NOx emission is reduced in downward convex curve style with increasing excess air ratio, it is reduced with increasing EGR rate at the same excess air ratio. (3) Soot emission is decreased in downward convex curve style with increasing excess air ratio, it is reduced with increasing EGR rate at the same excess air ratio. (4) CO emission is increased in nearly straight line style with increasing excess air ratio, it is increased with increasing EGR rate at the same excess air ratio. (5) HC emission is not constant tendency with increasing excess air ratio, it is increased with increasing EGR rate at the same excess air ratio.

• 대한기계학회논문집A
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• 제33권10호
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• pp.1158-1162
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• 2009

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26${\mu}m$ thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

• Wind and Structures
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• 제23권6호
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• pp.577-594
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• 2016

In this paper a practical modelling methodology is presented for a series of aero- servo- elastic- coupled numerical analyses of small wind turbine operation, with particular emphasis on variable speed generator modelling in various wind speed conditions. The following characteristics are determined using the available computer tools: the tip speed ratio as a function of the generator constant (under the assumption of constant wind speed), the turbine coefficient of power as a function of the tip speed ratio (the torque curve is modified accordingly and generator speed and power curves are plotted), turbine power curves and coefficient of power curve as functions of the incoming wind speed. The last stage is to determine forces and torques acting on rotor blades and turbine tower for specific incoming wind speeds in order to examine the impact of the stall phenomena on these values (beyond the rated power of the turbine). It is shown that the obtained results demonstrate a valuable guideline for small wind turbines design process.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.417-422
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• 2002

The main purpose of this paper is to determine the dynamic optimal shapes of tapered column with constant volume. The linear, parabolic and sinusoidal tapers with the regular polygon cross-section are considered, whose material volume and span length are always held constant. The ordinary differential equation including the effect of axial load is applied to calculate the natural frequencies. The Runge-Kutta method and Regula-Falsi methods are used to integrate the differential equation and compute the frequencies, respectively. Then the dynamic optimal shape whose lowest natural frequency is highest is determined by reading the critical value of the frequency versus section ratio curve plotted by the frequency data. In the numerical examples, the tapered columns are analysed and the numerical result of this study are shown in table and figures.

• 대한기계학회논문집
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• 제12권1호
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• pp.53-63
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• 1988

본 연구에서는 COA와 COD저항곡선의 기울기가 밀접한 관계가 있다는 점을 고려하여 COD저항곡선을 이용하여 현재까지 거의 연구결과가 없는 Ｔ$_{\delta}$에 의한 불안정균열성장문제를 검토하기로 하고, 이때 필요한 외부하중에 의한 부하 찢어짐계수 Ｔ$_{{\delta}{\app}}$ 의 평가방법에 대해서도 생각해 보기로 한다.한다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1095-1099
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• 2008

Critical state theory involves two state boundary surface. One is Roscoe surface and the other is Hvorslev surface. The shape of these boundary surface was changed because of several parameters : Critical state constant(M), spacing ratio (r) and critical state pore pressure coefficient($\wedge$). As these constants make difference to each model and the way of solution, they may affect the shape of state boundary surface. Specially, spacing ratio (r) is important. On this study, triaxial compression test was performed using remolded weathered mudstone soil and investigated variation of state boundary surface because of spacing ratio. In the results of prediction, critical state point was located highly and the shape of boundary surface was changed more tightly curve as decreasing spacing ratio.

• Journal of Power Electronics
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• 제18권2호
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• pp.640-650
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• 2018

A TRIAC dimmable LED driver with a wide tuning range and a two-stage uniform dimming scheme is proposed in this paper. To solve the restricted dimming range problem caused by the limited conduction ratio of TRIAC dimmers, a conduction ratio compensation technique is introduced, which can increase the output current up to the rated output current when the TRIAC dimmer turns to the maximum conduction ratio. For further optimization, a two-stage uniform dimming diagram with a rapid dimming curve and a slow dimming curve is designed to make the LED driver regulated visually uniform in the whole adjustable range of the TRIAC dimmer. The proposed control chip is fabricated in a TSMC $0.35{\mu}m$ 5V/650V CMOS/LDMOS process, and verified on a 21V/500mA circuit prototype. The test results show that, in the 90V/60Hz~132V/60Hz ac input range, the voltage linear regulation is 2.6%, the power factor is 99.5% and the efficiency is 83%. Moreover, in the dimming mode, the dimming rate is less than 1% when the maximum dimming current is 516mA and the minimum dimming current is only about 5mA.