• Asia pacific journal of information systems
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• 제9권3호
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• pp.75-92
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• 1999

Executive information systems (EIS) developers are faced with an increasingly difficult choice problem in the evaluation and selection of software packages. For many reasons, they frequently must depend on identification and evaluation of features of packages. When EIS software evaluation is regarded as an unstructured or semi-structured group decision making problem, the most appropriate decision-aiding methods are needed to help effective group interaction. This paper examines evaluation criteria of full-featured EIS packages and considers the priority of these criteria using the Analytic Hierarchy Process (AHP). Two exploratory phases are presented. In the first phase, an approach combining the AHP with the linear weighted attribute method is presented to computer qualities of some packages. In the second phase, the decision making group includes EIS developers, users, and vendors to prioritize evaluation criteria.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.78-83
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• 2003

General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthills acoustic analogy and Curls extension of Lighthills. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method permits generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.

• 천문학회보
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• 제36권2호
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• pp.106.2-106.2
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• 2011

The two competing theories of star formation are based on turbulence and ambipoar diffusion. I will first briefly explain the two theories. There have been analytical (or semi-analytic) models, which estimate star formation rates in a turbulent cloud. Most of them are based on the log-normal density PDF (probability density function) of the turbulent cloud without self-gravity. I will first show that the core (star) formation rate can be increased significantly once self-gravity of a turbulence cloud is taken into account. I will then present the evolution of molecular line profiles of HCO+ and C18O toward a dense core that is forming inside a magnetized turbulent molecular cloud. Features of the profiles can be affected more significantly by coupled velocity and abundance structures in the outer region than those in the inner dense part of the core. During the evolution of the core, the asymmetry of line profiles easily changes from blue to red, and vice versa. Finally, I will introduce a method for incorporating ambipolar diffusion in the strong coupling approximation into a multidimensional magnetohydrodynamic code.

• 천문학회보
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• 제41권1호
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• pp.69.2-69.2
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• 2016

We study the environmental dependence of the mass-size relation for the most massive early type galaxies (M>$10^{10.7}M_{\odot}$) in the redshift range 0.10~0.15. The sizes of galaxies are measured by non-parametric method. We find that galaxies more massive than $10^{11.1}M_{\odot}$ show the environmental dependence in the mass-size relation. The galaxies with M>$10^{11.1}M_{\odot}$ located in the densest, cluster like environment have larger sizes and extended surface brightness profiles than their counterparts located in a low dense environment. We also find that the environmental dependence of the mass-size relation is more significant for the brightest cluster galaxies (BCGs) than non-BCGs. We use the semi analytic galaxy formation simulation based on the Millennium 1 Simulation for interpretation. Our result can be explained with a hierarchical growth of the most massive galaxies through dissipation-less merger in dense environment.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.232-237
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• 2003

A new displacement-based transmitting boundary is developed for the transient analysis of dynamics interactions between flexible dam body and reservoir impounding compressible water The mechanical model is derived analytically in time domain from the kernel function, Bessel function, appearing in the convolution integral and corresponding mechanical model is developed that consists of mass, damping and stiffness matrices. The resulting system of, equations uses displacement degrees of freedom. Hence it can be coupled directly with the displacement-based solid finite element model of dam body, linear of nonlinear. The method was applied to the rigid and flexible dam models. The results showed very good agreement : with the semi-analytic frequency domain solutions.

• 한국해안해양공학회지
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• 제13권2호
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• pp.89-99
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• 2001

본 논문에서는 음향 증폭장치로 널리 사용되고 있는 헤름홀츠 공명장치의 원리를 해수교환 방파제에 적용한 문제를 다뤘다. 입사파의 주파수와 공명구조물의 고유주파수가 일치되면, 공진현상으로 입사파는 공명구조물 내에서 크게 증폭된다. 공진현상으로 크게 증폭된 위치에너지는 외해로부터 들어온 공명구조물내의 깨끗한 해수를 도수로를 통하여 항만내로 공급한다. 공급된 해수는 항내의 오염된 해수를 희석·순환시켜 항내 수질개선에 도움을 준다. 선형포텐셜 이론을 가지고 공명구조물내의 파도응답을 정합점근전개법을 사용하여 해석하였다. 해석모델로 수학적 표현이 가능한 반원형 공명구조물을 채택하였다. 공명구조물이 1개가 있는 경우와 여러개가 일정한 간격을 가지고 배열된 경우를 함께 살펴보았다. 해석해의 타당성을 검증하기 위하여 2차원 수조에서 모형실험을 수행하였다. 도수로가 열린 상태가 닫힌 상태에서 공명구조물내의 파고분포와 도수로에서의 유속을 측정하였다.

• 한국해안해양공학회지
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• 제3권4호
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• pp.223-234
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• 1991

본 연구에서는 경계적분 방법을 사용하여 기존에 문제점으로 지적되온 외해 경계조건을 임의의 가상 경계상에 용출점을 분포시키는 기법으로 처리하여 항만 입구의 방파제나 기타 구조물 등에 의하여 발생되는 파랑의 회절효과를 반영하였다. 또한 항내 에너지 손실효과는 부분 반사개념을 사용하여 해석하였다. 본 연구의 수치적 검증은 해석해를 구할 수 있는 직사각형 항만과 여러 반원형 항만에 대한 파랑응답 특성을 비교하였으며 그 결과는 잘 일치하였다. 또한 후포항에 대한 파고분포를 계산하여 수리 모형실험의 결과 및 시간의존 완경사 방정식을 이용한 수치모형의 결과와 비교하여 좋은 결과를 얻었다.

• 대한기계학회논문집A
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• 제33권8호
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• pp.745-752
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• 2009

In robust design, the mean and variance of design performance are frequently used to measure the design performance and its robustness under uncertainties. In this paper, we present the Gauss-type quadrature formula as a rigorous method for mean and variance estimation involving arbitrary input distributions and further extend its use to robust design optimization. One dimensional Gauss-type quadrature formula are constructed from the input probability distributions and utilized in the construction of multidimensional quadrature formula such as the tensor product quadrature (TPQ) formula and the univariate dimension reduction (UDR) method. To improve the efficiency of using it for robust design optimization, a semi-analytic design sensitivity analysis with respect to the statistical moments is proposed. The proposed approach is applied to a simple bench mark problems and robust topology optimization of structures considering various types of uncertainty.

• Nuclear Engineering and Technology
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• 제41권10호
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• pp.1347-1360
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• 2009

A multi-dimensional component for the thermal-hydraulic system analysis code, MARS, was developed for a more realistic three-dimensional analysis of nuclear systems. A three-dimensional and two-fluid model for a two-phase flow in Cartesian and cylindrical coordinates was employed. The governing equations and physical constitutive relationships were extended from those of a one-dimensional version. The numerical solution method adopted a semi-implicit and finite-difference method based on a staggered-grid mesh and a donor-cell scheme. The relevant length scale was very coarse compared to commercial computational fluid dynamics tools. Thus a simple Prandtl's mixing length turbulence model was applied to interpret the turbulent induced momentum and energy diffusivity. Non drag interfacial forces were not considered as in the general nuclear system codes. Several conceptual cases with analytic solutions were chosen and analyzed to assess the fundamental terms. RPI air-water and UPTF 7 tests were simulated and compared to the experimental data. The simulation results for the RPI air-water two-phase flow experiment showed good agreement with the measured void fraction. The simulation results for the UPTF downcomer test 7 were compared to the experiment data and the results from other multi-dimensional system codes for the ECC delivery flow.

• The Journal of the Acoustical Society of Korea
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• 제22권4E호
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• pp.183-196
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• 2003

General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curl's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method penn its generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.