• Journal of Magnetics
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• 제20권3호
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• pp.258-264
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• 2015

In this paper, an adequate B-H curve extrapolation method is proposed and its reliability is verified through experiments. A method is developed to estimate the magnetic saturation induction from the density of the lamination core and electrical resistivity. The magnetic saturation induction of electrical steels measured using a vibration sample magnetometer are compared with the analytical results to validate the accuracy of the proposed estimation method. It is found that the predicted error in the magnetic saturation induction of the electrical steels are approximately 1.2% when the proposed method is used. The performance of interior permanent magnet synchronous motors that applies the proposed method are evaluated via 2D nonlinear finite element analysis and through experiments. Based on the obtained results, the extrapolated B-H curves from the estimated saturation induction can be used for various analyses in saturation region.

• 한국해양공학회지
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• 제14권3호
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• pp.41-45
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• 2000

In solving the unsteady potential flow problem of the ship in waves with the panel method, in general one can consider the basic flow as the free stream or double body solution. For the double body solution, the body boundary condition has the 2nd derivatives of the velocity potential. Low order panel methods are known to suffer from the significant error in the 2nd derivatives computed at the body surface. This paper analyzes the numerical error in the 2nd derivatives for a 2-D cylinder and a 3-D sphere problem, and an extrapolation method to obtain the correct derivatives on the body surface is suggested.

• 대한기계학회논문집B
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• 제31권7호
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• pp.620-627
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• 2007

In this paper, we adapt a modified internal energy non-equilibrium first-order extrapolation thermal boundary condition to the thermal lattice Boltzmann model (TLBM). This model is the double populations approach to simulate hydrodynamic and thermal fields. The bounce-back boundary condition which is a traditional boundary condition of lattice Boltzmann method has only a first order in numerical accuracy at the boundary and numerical instability. A non-equilibrium first-order extrapolation boundary condition has been verified to be of better numerical stability than the bounce-back boundary condition and this boundary condition is proved to be of second-order accuracy for the flat boundaries. The two-dimensional natural convection flow in a square cavity with Pr=0.71 and various Rayleigh numbers are simulated. The results are found to be in good agreement with those of previous studies.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.279-286
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• 2009

Improving over a previous study [1], this paper provides a Monte Carlo method for the heat conduction analysis of problems with complicated geometry (such as a pebble with dispersed fuel particles). The method is based on the theoretical results of asymptotic analysis of neutron transport equation. The improved method uses an appropriate boundary layer correction (with extrapolation thickness) and a scaling factor, rendering the problem more diffusive and thus obtaining a heat conduction solution. Monte Carlo results are obtained for the randomly distributed fuel particles of a pebble, providing realistic temperature distributions (showing the kernel and graphite-matrix temperatures distinctly). The volumetric analytic solution commonly used in the literature is shown to predict lower temperatures than those of the Monte Carlo results provided in this paper.

• 한국해양공학회지
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• 제34권6호
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• pp.387-393
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• 2020

Frictional resistance comprises more than 60% of the total resistance for most merchant ships. Active and passive devices have been used to reduce frictional resistance, but the most effective and practical device is an air lubrication system. Such systems have been applied in several ships, and their effects have been verified in sea trials. On the other hand, there are some differences between the results predicted in model tests and those measured in sea trials. In this study, numerical analyses were carried out for a model and a full-scale ship. A new extrapolation method was proposed to improve the estimation of the full-scale resistance of a ship with an air lubrication system. The volume of fluid (VOF) method was considered for the numerical models of the air layer. The numerical method was validated by comparing the experimental data on the air layer pattern and the total resistance.

• 한국차세대컴퓨팅학회논문지
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• 제13권4호
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• pp.29-39
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• 2017

다양한 전자전 상황에서 단위 위협체에 대하여 전자전 모델링과 시뮬레이션을 수행할 수 있는 통합 전자전 시뮬레이터의 개발 필요성이 대두되고 있다. 본 논문에서는 전자전 상황에서 전자정보 수집신호의 변수를 기반으로 전자파 신호를 발산하는 레이더 위협을 역추정하기 위한 시뮬레이션 시스템의 구성요소를 분석하고, 역추정 모델을 점진적으로 유지할 수 있는 방법을 제안한다. 또한, 실험을 통하여 점진적 역추정 모델 갱신 기법의 유효성 및 개별 역추정 결과의 통합 기법을 평가한다. 개별 역추정 모델의 생성을 위하여 의사결정트리, 베이지안 분류기, 인공신경망 및 유클리디안 거리 측정방식과 코사인 유사도 측정방식을 활용하는 군집화 알고리즘을 이용하였다. 첫 번째 실험에서 레이더 위협체에 대한 역추정 모델을 구축하기 위한 위협 예제의 크기를 점진적으로 증가시키면 역추정 모델의 정확도는 향상되었으며, 이러한 과정이 반복되면 역추정 모델에 대한 정확도는 일정한 값으로 수렴하였다. 두 번째 실험에서는 개별 역추정 모델의 결과를 통합하기 위하여 투표, 가중투표 및 뎀스터-쉐이퍼 알고리즘을 이용하였으며, 역추정 모델의 통합 결과는 뎀스터-쉐이퍼 알고리즘에 의한 역추정 정확도가 가장 좋은 성능을 보였다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.99-106
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• 2005

Performance of first, second and third order accurate methods for calculation of in viscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe's scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2007년도 한국음성과학회 공동학술대회 발표논문집
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• pp.315-318
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• 2007

This paper proposes the methods to enhance the speech quality of source controlled variable bit-rate coder based on the waveform interpolation. The methods are to estimate and generate the parameters that are not transmitted from encoder to decoder by the repetition and extrapolation schemes. For the performance evaluation, the PESQ(Perceptual Evaluation of Speech Quality) scores are measured. The experimental results shows that our proposed method outperforms the conventional source controlled variable bit-rate coder. Especially, the performance of the extrapolation method is better than that of the repetition method.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.229-232
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• 2007

고체 추진제 연소 현상을 해석할 때 요구되는 이동 경계면에 대한 수치 기법을 연구하였다. Eulerian 좌표계에서는 Ghost-Cell Extrapolation 기법을 적용하였고, Non-Eulerian 좌표계에서는 Lagrangian 기법을 적용하여 이동 경계면을 해석하였다. 도관 내 일차원 자유 피스톤 운동을 이 수치 기법으로 해석하여 이론 결과 값과 비교 검증하였다.

• Wind and Structures
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• 제31권5호
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• pp.419-430
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• 2020

Weibull distribution is a conspicuous distribution known for its accuracy and its usage for wind energy analysis. The two and three parameter Weibull distributions are adopted in this study to fit wind speed data. The daily mean wind speed data of Ennore, Tamil Nadu, India has been used to validate the procedure. The parameters are estimated using maximum likelihood method, least square method and moment method. Four statistical tests namely Root mean square error, R2 test, Kolmogorov-Smirnov test and Anderson-Darling test are employed to inspect the fitness of Weibull probability density functions. The value of shape factor, scale factor, wind speed and wind power are determined at a height of 100m using extrapolation of numerical equations. Also, the value of capacity factor is calculated mathematically. This study provides a way to evaluate feasible locations for wind energy assessment, which can be used at any windy site throughout the world.