• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.148-148
• /
• 2011

Riemann 문제는 천수방정식과 같은 쌍곡선형 방정식과 단일한 도약에 의해 불연속인 어떤 점의 좌 우에서 상수인 자료로 구성되는 초기치 문제로서 그 해법은 Godunov 방법과 같이 정확해에 의하면 정확 Riemann 해법, 근사 기법에 의하면 근사 Riemann 해법으로 불린다. 지금까지 이용되는 근사 Riemann 해법으로는 1981년에 P. L. Roe가 제안한 Roe의 선형화 기법과 1983년에 A. Harten, P. D. Lax, 그리고 B. van Leer가 제안한 HLL 기법의 수정 기법들이다. 최대 및 최소 파속만 고려하는 것으로 알려진 HLL 기법은 1988년에 B. Einfeldt의 제안에 의해 두 파속의 결정에서 Roe의 선형화 기법에 따른 고유치와 비교하는 것으로 수정되었다(HLLE 기법). 또한, 1994년에 E. F. Toro 등은 접촉파를 고려하기 위해 선형화된 지배방정식의 정확해로부터 중앙 파속을 고려하는 기법을 제안하였고, 이를 HLLC 기법으로 불렀다. 2002년에 T. Linde는 중앙 파속을 평가하기 위해 일반화된(수학적) 엔트로피 함수를 도입하였으며, van Leer는 이를 HLLL 기법으로 불렀다. 이 기법에서는 접촉파의 평가를 위해 보존변수에 대한 일반화된 엔트로피 함수로부터 중앙 파속이 유도되며, 이것과 특성 속도의 비교를 통해 최대 및 최소 파속이 결정된다. 따라서 이 기법에서는 모든 파속이 초기치로부터 결정되므로 HLLE 기법과 달리 Roe의 선형화 기법과 완전히 결별되고 HLLC 기법과 달리 정확해에 의존되지 않는 점에서 HLLL 기법은 모태인 HLL 기법의 온전한 계승으로 볼 수 있다. HLLL 기법은 여러 분야에 적용된 바 있으나, 수공학 분야에 적용된 사례는 알려진 바 없다. 이는 천수방정식에 대한 (물리적) 엔트로피 함수가 명확하지 않기 때문인 것으로 보인다. 이 연구에서는 보존변수로부터 정의되는 총 에너지를 일반화된 엔트로피 함수로 간주하여 모형을 구성하고, 정확해가 알려진 1차원 문제에 대해 적용성을 검토하였다. 정확해가 알려진 경우에 대해 모의한 결과, 1차 정도 수치해의 한계에도 불구하고, HLLL 기법의 결과는 대체로 정확해와 잘 일치하였으며 그 외의 HLL-형 기법의 그것에 비해 우수한 것으로 나타났다. 특히, 물이 빠져 바닥이 드러나는 상태에 대한 접촉 파속의 추정에서 Riemann 불변량을 이용하는 HLLC 기법에 비해 물이 빠지는 전선을 더 정확하게 포착하는 HLLL 기법의 결과는 매우 고무적이었다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.19 no.2
• /
• pp.10-19
• /
• 1995

Heat trnasfer for absorbing and emitting media in laminar layer along the cylinders has been analyzed. Governing equation are transformed to local nonsimilarity equations by the dimensional analysis. The effects of the Stark number, Prandtl number, Optical radius and wall emissivity are mainly investigated. For the formal solution a numerical integration is performed and the results are compared with those obtained by P-1 and P-3 approximation. The results show that boundary layers consist of conduction-convection-radiation layer near the wall and convection-radiation layer far from the wall. As the Stark number of wall emissivity increases the local radiative heat flux is increased. The Pradtl number or curvature variations do not affect the radiative heat flux from the wall, but The Prandtl number or wall emissivity variations affect the conduction heat flux. Consequently the total heat flux from the wall are affected by the Prandtl number or wall emissivity variation.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.1 no.2
• /
• pp.33-38
• /
• 2008

The baseline wander of ECG makes difficult to detect P-, Q-, R- and S-wave. This paper presents and compares two method to remove the baseline wander of ECG using slope traceing waves. For the first method that had been proposed already[1], the ascending slope tracing method is used to eliminate baseline wander. And the second method employs the contour of the approximated S-wave to remove baseline wander. These two methods are common to use the slope tracing wave. However, the first one is to get difference signals between the ascending tracing waves and ECG signals, and the other is to remove baseline wander using the contour of the approximated S-wave obtained from descending slope waves. To evaluate these methods, we apply to MIT/BIH database.

• The Korean Journal of Applied Statistics
• /
• v.2 no.1
• /
• pp.48-53
• /
• 1989

In contrast to the customary approximations based on standard normal percentage points, direct approximations involve simple functions of parameters (such as degrees of freedom and tail area of the t distributions). This article used techniques of exploratory data analysis following Hoaglin to develop direct approximations for percentage points in the commonly used portions of upper tail of the t distribution with small to moderate numbers of degrees of freedom. These approximations are convenient to use and they compare favorably in accuracy with the popular approximations based on standard normal percentage points such as Peiser's. They can be used as an initial value generator in algorithms for getting more accurate percentage points.

• Journal of the Korean Chemical Society
• /
• v.42 no.4
• /
• pp.432-442
• /
• 1998

Since the definition of pH, $pH=-Ioga_H$ is based on a single ion activity, pH values can not be determined with measurement itself, but require an approximation method. They are derived from EMF measurement of a liquid junction free cell using hydrogen and Ag/AgCl electrodes. Primary standard materials with certified pH values can be obtained with this approximation method. Standard buffer solutions are used to calibrate pH meters. Thus the accuracy of the pH values of standard buffer solutions limits the reliability of measured pH values can be obtained with this approximation method. Standard buffer solution are used to calibrate pH meters. Thus the accuracy of the pH values of standard buffer solutions limits the reliability of measured pH values of sample solutions. To certify the pH values, we have established the system for the primary standard measurement and certified the pH of buffer solutions in the range of 1.6∼12.5 pH unit within uncertainty of ${\pm}0.005$ pH unit.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.4 no.3
• /
• pp.223-230
• /
• 1999

A conventional sliding mode control approach is often impractical or difficult when it is applied to high order process b because the number of tuning parameters in the sliding mode controller increases with the order of the plant. C Camacho(l996) proposed a design method of a fixed structure sliding mode controller based on a first order plus dead t time approximation to the higher-order process. But, his method has such problems as chattering, over‘shoot, and c command following due to the Taylor the approximation en‘ors for the time delay term of the first order model. In this p paper, a new design technique for a sliding mode controller based on the modified Taylor approximation considered a w weight is developed to improve the Camacho's problems.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.10 no.1
• /
• pp.13-22
• /
• 2000

본 논문에서는 Skipjack의 변환규칙 A와 같은 반복적인 구조에 대한 차분 특성 및 선형 근사식의 확률의 상한 값을 제시하고 이를 증명한다. 즉 라운드 함수에 대한 확률의 최대 값이 p이면 15라운드 후에 p4이 됨을 보인다. 따라서 본 논문에서 고려한 구조는 현재까지 DC 및 LC에 대한 안전성을 증명할 수 있는 구조인 Feistel 구조 및 MISTY 구조와 더불어 블록 암호의 설계 방법에 대한 다양성을 제공한다.

• Geotechnical Engineering
• /
• v.13 no.1
• /
• pp.101-110
• /
• 1997

This paper presents a two dimensional p-version static infinite element for analyzing $1/r^n$ displacement decay type problems in unbounded media. The proposed element is developed by using shape functions based on approximate expressions of an analytical solution. Numerical results are presented for an opening in a homogeneous elastic infinite medium and a rigid footing rested on a homogeneous elastic half-space. The numerical results show the effectiveness of the proposed infinite element.

• The Journal of the Acoustical Society of Korea
• /
• v.18 no.3
• /
• pp.73-78
• /
• 1999

The paper describes a theoretical study on the flexural vibration of an elastic flat bar with periodically nonuniform material properties. The approximate solution of the natura1 frequency and mode shape has been obtained using the perturbation technique for sinusoidal modulation of the flexural rigidify and mass density. The numerical solution obtained by using the finite element method verifies the trend of the approximate solution. It appears that distributed vibrations exist in the low modes, and this approach can be extended to the vibration analysis of the p1ate in the flat panel speaker.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.12C
• /
• pp.1150-1156
• /
• 2006

In this paper we derive some lower bounds on the linear complexity and upper bounds on the 1-error linear complexity over $F_p$ of M-ary Sidel'nikov sequences of period $p^m-1$ when $M\geq3$ and $p\equiv{\pm}1$ mod M. In particular, we exactly compute the 1-error linear complexity of ternary Sidel'nikov sequences when $p^m-1$ and $m\geq4$. Based on these bounds we present the asymptotic behavior of the normalized linear complexity and the normalized 1-error linear complexity with respect to the period.