• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2953-2959
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• 2021

A new practical modeling of the Norton's power law creep is proposed and implemented to analyze the high temperature behaviors of Alloy 690 SG tube material. In the model, both the stress exponent n and the rate constant B are simply treated as the temperature dependent parameters. Based on the two-step optimization procedure, the temperature function of the rate constant B(T) was determined for the data set of each B value after fixing the stress exponent n value by using the prior optimized function at each temperature. This procedure could significantly reduce the numerical errors when using the power law creep equations. Based on the better description of the steady-state creep rates, the experimental rupture times could also be well predicted by using the Monkman-Grant relationship. Furthermore, the difference in tensile strengths at high temperatures could be very well estimated by assuming the imaginary creep stress related to the given strain rate after correcting the temperature effects on the elastic modulus.

• International Journal of Quality Innovation
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• 제5권1호
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• pp.1-9
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• 2004

The nonhomogeneous poisson process (NHPP) is often used to model repairable systems that are subject to a minimal repair strategy, with negligible repair times. In this situation, the system can be characterized by its intensity function. There have been many NHPP models according to intensity functions. However, the intensity function of system in use can be changed because of repair or its aging. We consider the single change point model as the modification of the power law process. The shape parameter of its intensity function is changed before and after the change point. We detect the presence of the change point using Bayesian methodology. Some numerical results are also presented.

• 생물환경조절학회지
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• 제24권3호
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• pp.135-146
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• 2015

본 연구는 온실에 작용하는 풍하중 산정을 위한 설계 풍속을 결정하는데 필요한 자료를 제공하기 위하여 10m 이하 높이에서의 풍속을 측정하여 풍속고도분포지수를 산정하고 변화를 분석하였다. 고도에 따른 풍속분포함수를 결정하기 위한 풍속고도분포지수를 계산하기 위해서는 $5m{\cdot}s^{-1}$ 이상의 풍속을 사용하는 것이 타당하다고 판단된다. 농촌 개활지인 부안지역의 고도에 따른 풍속변화는 지표면으로부터 풍속이 지수함수로 증가하는 우리나라의 RDC 기준과 일본의 JGHA 기준과 잘 일치하였고 풍속고도분포지수도 0.26으로 기준들에서 제시된 0.25와 거의 동일한 값을 나타내었다. 반면 군위지역의 경우는 풍속고도분포지수가 0.06으로 산정되어 지표면조도가 클수록 풍속고도분포지수가 증가하는 일반적인 변화 경향과는 반대로 나타났다. 이는 타워가 주변지대보다 약 2m 가량 더 높은 위치에 설치되었기 때문에 유선의 급격한 변화에 의한 것으로 판단된다. 따라서 일반적으로 농촌 개활지에 설치되는 온실의 설계를 위해 적용할 풍속고도분포로는 우리나라의 RDC기준과 일본의 JGHA기준에서 제시한 풍속고도분포가 가장 타당한 것으로 사료된다. 부안의 경우 오전 7시 경부터 풍속고도 분포지수가 감소하다가 오후 3시경에 최소가 된 후 다시 증가하여 24시경에 일정해지는 것으로 나타나 시간에 따른 풍속고도분포지수의 일반적인 변화경향과 잘 일치하였다. 부안지역은 형상변수가 1.51로 나타나 간척지인 부안지역의 풍속특성이 제주도 연안지역과 유사한 풍속특성을 가지고 있음을 확인하였다.

• 한국조명전기설비학회지:조명전기설비
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• 제11권6호
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• pp.81-89
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• 1997

In order to achieve the zero voltage regulation of the output voltage, the function control law will be used. In the previous function control law, only the proportional controller is used and the stability of the closed loop system was not analyzed. In this paper, for the realization of the control law, a new method to retrieve the low frequency component of the inductor voltage is proposed and analyzed. The large signal closed loop characteristics are alos analyzed to ensure the stable operation of the system disturbances. By using the function control law in the control system, the effect of the disturbance of the supply voltage is reduced in 93.3% for the direct dusty ration method. Also, in the effect of the disturbance of the load current, the output voltage has a logn recovery-time and is changed proportionally in the direct duty ratio method, but has stable in the function control law. Finally, the analysis shows that the disturbance of the output voltage being due to the supply voltage variation can be eliminated completely and the closed loop output voltage is insensitive to the disturbance of the load current. Therefore, it is proved that by using the function control law, the switching power supply with zero-voltage regulation output voltage can be realized.

• Journal of Power Electronics
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• 제18권5호
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• pp.1380-1397
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• 2018

The synchronous reluctance motor (SynRM) servo-drive system has highly nonlinear uncertainties owing to a convex construction effect. It is difficult for the linear control method to achieve good performance for the SynRM drive system. The nonlinear backstepping control system using upper bound with switching function is proposed to inhibit uncertainty action for controlling the SynRM drive system. However, this method uses a large upper bound with a switching function, which results in a large chattering. In order to reduce this chattering, a nonlinear backstepping control system using an adaptive law is proposed to estimate the lumped uncertainty. Since this method uses an adaptive law, it cannot achiever satisfactory performance. Therefore, a nonlinear backstepping control system using a reformed recurrent Hermite polynomial neural network with an adaptive law and an error estimated law is proposed to estimate the lumped uncertainty and to compensate the estimated error in order to enhance the robustness of the SynRM drive system. Further, the reformed recurrent Hermite polynomial neural network with two learning rates is derived according to an increment type Lyapunov function to speed-up the parameter convergence. Finally, some experimental results and a comparative analysis are presented to verify that the proposed control system has better control performance for controlling SynRM drive systems.

• 한국정밀공학회지
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• 제15권7호
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• pp.91-97
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• 1998

The analysis model is the infinite body consisted of power law creep material containing a rigid inclusion with line crack shape subjected to the arbitrarily directional stress on an infinite boundary. The crack analysis is performed using the complex pseudo-stress function. The strain rate intensity factor is determined in the closed form as new fracture mechanics parmeter which represents the magnitudes of stress and strain rate near the tip in power law creep material.

• Journal of Astronomy and Space Sciences
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• 제14권1호
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• pp.1-17
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• 1997

The results of a restricted numerical simulation for the color gradients within globular clusters have been presented. The standard luminosity function of M3 and Salperter's initial mass functions were used to generate model clusters as a fundamental population. Color gradients with the sample clusters for both King and power law cusp models of surface brightness distributions are discussed in the case of using the standard luminosity function. The dependence of color gradients on several parameters for the simulations with Salpter's initial mass functions, such as slope of initial mass functions, cluster ages, metallicities, concentration parameters of King model, and slopes of power law, are also discussed. No significant radial color gradients are shown to the sample clusters which are regenerated by a random number generation technique with various parameters in both of King and power law cusp models of surface brightness distributions. Dynamical mass segregation and stellar evolution of horizontal branch stars and blue stragglers should be included for the general case of model simulations to show the observed radial color gradients within globular clusters.

• Journal of the Korean Statistical Society
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• 제34권4호
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• pp.331-344
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• 2005

Inference on current data could be more reliable if there exist similar data based on previous studies. Ibrahim and Chen (2000) utilize these data to characterize the power prior. The power prior is constructed by raising the likelihood function of the historical data to the power $a_o$, where $0\;{\le}\;a_o\;{\le}\;1$. The power prior is a useful informative prior in Bayesian inference. However, for model selection or model comparison problems, the propriety of the power prior is one of the critical issues. In this paper, we suggest two joint power priors for the power law process and show that they are proper under some conditions. We demonstrate our results with a real dataset and some simulated datasets.

• 상하수도학회지
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• 제20권2호
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• pp.295-302
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• 2006

Over the past decades, a flocculation and/or sedimentation process have been adopted to remove pollutants from CSOs. It has been learned that major factors affecting settlement of pollutants are the particle size distribution, their settling velocities and their specific gravity. It is, therefore, a good idea to analyze the particle size distribution and settleability of CSOs pollutants in order to develop details in designing a process. Discussed in this study are pollutant characteristics of CSOs such as particle size distribution and settleability of pollutants. The power law function is applied and is found to be an effective and reliable index for expressing the particle size distribution of pollutants in CSOs. Based on the regression analysis it is observed that the derived constants of curves representing settling velocity profile are proportional to the initial concentration of particles and to the ${\beta}$-values of power law distributions.

• Structural Engineering and Mechanics
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• 제69권6호
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• pp.637-649
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• 2019

In the current research paper, a quasi-3D beam theory is developed for free vibration analysis of functionally graded microbeams. The volume fractions of metal and ceramic are assumed to be distributed through a beam thickness by three functions, power function, symmetric power function and sigmoid law distribution. The modified coupled stress theory is used to incorporate size dependency of micobeam. The equation of motion is derived by using Hamilton's principle, however, Navier type solution method is used to obtain frequencies. Numerical results show the effects of the function distribution, power index and material scale parameter on fundamental frequencies of microbeams. This model provides designers with guidance to select the proper distributions and functions.