• 한국해양공학회지
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• 제15권3호
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• pp.43-48
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• 2001

In this paper, the real-time prediction of high temperature creep strength and creep for nickel-based superalloy Udimet 720 (high-temperature and high-pressure gas turbine engine materials) was performed on round-bar type specimens under pure load at the temperatures of 538, 649 and 704$^{\circ}C$. The predictive equation of ISM creep has better reliability than that of LMP and LMP-ISM, and its reliability is getting better for long time creep prediction ($10^3~10^5$h).

• 전력전자학회논문지
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• 제17권3호
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• pp.213-221
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• 2012

In a PWM inverter-fed IPMSM (Interior Permanent Magnet Synchronous Motor) drive, a dead time is inserted to prevent a breakdown of switching device caused by the short-circuit of DC link. This distorts the inverter output voltage resulting in a current distortion and torque ripple. In addition to the dead time, nonlinearity exists in switching devices of the PWM inverter, which is generally dependent on operating conditions such as the temperature, DC link voltage, and current. The voltage disturbance caused by the dead time and inverter nonlinearity directly influences on the inverter output performance, and it is known to be more severe at low speed. In this paper, a new compensation scheme for the dead time and inverter nonlinearity under the parameter variation is proposed for a PWM inverter-fed IPMSM drive. The overall system is implemented using DSP TMS320F28335 and the validity of the proposed algorithm is verified through the simulation and experiments.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.136-140
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• 2002

High temperature fatigue crack growth behavior of P92 and STS 316L steel were investigated under four load conditions using CT type specimens. Loading and unloading times for the low wave forms were combinations of 1 sec. and 50 sec., which were two symmetric wave forms and two unsymmetric wave forms. Their behaviors are characterized using ΔK parameter. In STS 316L, Crack growth rate generally increases as frequency decreases. However, sensitivity of the loading rate to crack growth rate was fecund to be far greater than that of the unloading time. It is because as loading time increases, creep occurs at crack tip causing the crack growth rate to increase. However creep does not occur at the crack tip even if the unloading time is increased. In P92 steel, crack growth rate showed same behavior as in STS 316L. But the increase in loading or unloading time made almost no difference in crack growth rate, suggesting that no significant creep occurs in P92 steel even though loading time increases. After conducting high temperature tensile tests and comparing high temperature fatigue crack growth rates under various wave forms, it was proved that P92 steel has not only good high temperature properties but also improved, better high temperature fatigue properties than STS 316L.

• 한국환경과학회지
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• 제26권10호
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• pp.1125-1133
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• 2017

In this study a method for filling in missing data of river water temperature using a pre-constructed mathematical relationship between air and water temperatures is presented. A regression between water temperatures at individual stations and ambient air temperatures at nearby weather stations can provide a practical method for representing missing water temperature data for an entire region. Air and water temperature data that were collected from two test sites (one coastal and, one inland) were individually fitted to a nonlinear regression model. To consider seasonal hysteresis effects, separate functions were fitted to the data in the rising and falling limbs. A single-criterion, multi-parameter optimization technique was used to determine the optimal parameter sets. This method minimizes the differences between the time series of the measured and estimated data. The constructed air-water temperature relationship was subsequently applied to represent missing water temperature data. It was found that the RMSEs(MBEs) were in the range of $1.843-1.976^{\circ}C(-0.329-0.201^{\circ}C)$ and the coefficient of determination were in the range of 0.92-0.96. The results demonstrate that the predicted water temperatures using the regression equations were reasonably accurate.

• 상하수도학회지
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• 제10권2호
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• pp.88-103
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• 1996

The objective of this study is to develop stochastic and deterministic models which could be used to synthesize water application time series. Adaptive models using mulitivariate ARIMA(Transfer Function Model) are developed for daily urban water use forecasting. The model considers several variables on which water demands is dependent. The dynamic response of water demands to several factors(e.g. weekday, average temperature, minimum temperature, maximum temperature, humidity, cloudiness, rainfall) are characterized in the model by transfer functions. Daily water use data of Kumi city in 1992 are employed for model parameter estimation. Meteorological data of Seonsan station are utilized to input variables because Kumi has no records about the meteorological factor data.To determine the main factors influencing water use, autocorrelogram and cross correlogram analysis are performed. Through the identification, parameter estimation, and diagnostic checking of tentative model, final transfer function models by each month are established. The simulation output by transfer function models are compared to a historical data and shows the good agreement.

• Structural Engineering and Mechanics
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• 제74권3호
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• pp.341-350
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• 2020

The present investigation is concerned with two dimensional deformation in a non local thermoelastic solid with two temperatures due to time harmonic sources. The nonlocal thermoelastic solid is homogeneous with the effect of two temperature parameters. Fourier transforms are used to solve the problem. The bounding surface is subjected to concentrated and distributed sources. The analytical expressions of displacement, stress components and conductive temperature are obtained in the transformed domain. Numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of nonlocal parameter and frequency on the components of displacements, stresses and conductive temperature. Some special cases are also deduced from the present investigation.

• 대한기계학회논문집
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• 제17권1호
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• pp.131-140
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• 1993

본 연구에서는 A17075의 활성화에너지의 각 변수 의존성을 온도 보상시간과 Zener-Hollomon 개변수를 써러 조사하고 가장 신빙성이 있는 Miller에 의한 현상론적 크리프식을 조사 연구하였다.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.147-154
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• 2002

The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K$\_$IC/) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating the 7c consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimate K$\_$IC/, using the K$\_$IC/ versus excess temperature (i.e., T-FATT) correlation that is available in the literature for CrMoV rotor steel.

• 대한기계학회논문집
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• 제17권6호
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• pp.1321-1329
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• 1993

본 연구에서는 이들보다 매우 간단한 IS법, 즉 초기 변형률법(ISM: initial strain method)에 의한 크리프 수명예측식을 고안하여, 현재 화력발전용 고압 로터강 에 사용되고 있는 1%Cr-Mo-V강과 발전소 효율향상을 위해 최근 국내최초로 개발된 12% Cr강에 대하여 도출하였고, 이 도출식이 앞에서 언급한 여러 파라메트에 의한 결과와 비교 평가하여 장시간 강도 및 수명예측식으로 사용될 수 있음을 입증하였다.

• 한국유기농업학회지
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• 제25권4호
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• pp.861-873
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• 2017

The present study was conducted to investigate the developmental characteristics of Propylea japonica Thunberg (Coleoptera : Coccinellidae), a predator of aphids under laboratory conditions. The development times of the egg and immature stages of Propylea japonica were investigated at ten constant temperatures(15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, 35 and $38{\pm}1^{\circ}C$; 14L:10D; $60{\pm}5%$ RH). Development time was longest at $17.5^{\circ}C$. The developmental periods of P. japonica from the time of egg oviposited to adult emergence was 36.9 days at $17.5^{\circ}C$, and it decreased ash temperature increasing. Threshold temperature of development and degree days of the P. japonica from egg to adult were $11.9^{\circ}C$ and 196.0 respectively. The Briere 2 and Lactin 2 modes were best fitted for all development stages. The distribution of completion of each development stage was explain relatively well that 2-parameter, 3-parameter and Logistic model except egg and pupal stage.