• Ocean Systems Engineering
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• 제12권3호
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• pp.359-384
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• 2022

We develop in this work a new well-balanced preserving-positivity path-conservative central-upwind scheme for Saint-Venant-Exner (SVE) model. The SVE system (SVEs) under some considerations, is a nonconservative hyperbolic system of nonlinear partial differential equations. This model is widely used in coastal engineering to simulate the interaction of fluid flow with sediment beds. It is well known that SVEs requires a robust treatment of nonconservative terms. Some efficient numerical schemes have been proposed to overcome the difficulties related to these terms. However, the main drawbacks of these schemes are what follows: (i) Lack of robustness, (ii) Generation of non-physical diffusions, (iii) Presence of instabilities within numerical solutions. This collection of drawbacks weakens the efficiency of most numerical methods proposed in the literature. To overcome these drawbacks a reformulation of the central-upwind scheme for SVEs (CU-SVEs for short) in a path-conservative version is presented in this work. We first develop a finite-volume method of the first order and then extend it to the second order via the averaging essentially non oscillatory (AENO) framework. Our numerical approach is shown to be well-balanced positivity-preserving and shock-capturing. The resulting scheme could be seen as a predictor-corrector method. The accuracy and robustness of the proposed scheme are assessed through a carefully selected suite of tests.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1993년도 춘계학술대회논문집; 한국과학연구소, 21 May 1993
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• pp.107-112
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• 1993

The effect of the applied direction and magnitude of loads on the stability and natural frequency of flexible rotors is analyzed, when the rotors are subject to nonconservative torque and force. The stability criterion derived from the energy and variational principle is discussed and a general Galerkin's method which utilizes admissible functions is employed for numerical analysis. Illustrative examples are treated to demonstrate the analytical developments.

• 대한토목학회논문집
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• 제14권4호
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• pp.867-874
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• 1994

유량이 매우 작은 갈수기(渴水期)에 자연하천으로 방류된 비보존성 오염물질의 이동 및 화학적, 생화학적 변환과정의 복잡성을 구명하기 위해서 이송, 확산, 변환 그리고 하천수로에 존재하는 저장대(貯藏帶)에서 오염물질의 저장 및 교환과정을 규정하는 한 쌍의 방정식으로 이루어진 수학적 모형을 개발하고 이의 해를 수치해석적인 방법에 의해 구하였다. "저장-변환 모형"이라 명명된 본 수화적 모형은 갈수기(渴水期) 하천에서의 비보존성 오염물질의 혼합 및 변환 메카니즘의 비정규분포적인 특성을 보다 정확하게 예측할 수 있도록 개발되었다. 모형의 모의결과, 농도-시간곡선의 전체적인 형태, 첨두농도, 그리고 첨두농도에 도달하는 시간 등에 있어서 저장-변환 모형이 종래의 1차원 확산모형보다 실측자료에 더욱 정확하게 일치한다는 사실이 밝혀졌다. 본 연구에서 개발된 저장-변환 모형은 웅덩이-급여울 연속구조로 이루어진 하천에서의 오염물질의 이동 및 변환거동을 예측하는 모형으로서 1차원 확산모형에 비해 월등히 개선된 모형으로 밝혀졌다.

• 한국수자원학회논문집
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• 제34권4호
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• pp.289-301
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• 2001

비보존성 오염물질의 종확산에 관한 단계분리 유한차분 모형을 낙동강에 적용하여, 1991년에 발생한 페놀누출 사고에 따른 종확산 모의계산을 수행하였다. Preissmann의 4점 음해법에 근거한 부정류 계산모형으로부터 산정된 계산결과를 종확산 모형의 입력자료로 사용하였다. 종확산계수의 산정을 위한 경험식 및 1차 반응의 감쇠계수에 따른 종확산 계산결과의 민감도를 분석하였다. 하류 지점에서의 첨두농도 발생 시각은 사용된 종확산계수 식에 따라 상당히 달라짐을 알 수 있었다. 또한 농도 분포형은 감쇠계수에 따라 변하지 않는 반면, 농도값은 감쇠계수에 상당히 좌우되는 것으로 나타났다. 최적화 기법을 사용하여 흐름 모형 및 종확산 모형을 보정하였으며, 낙동강에 위치한 주요 취수지점들에 대한 첨두농도 발생시각을 모의하여 제시하였다.

• 대한기계학회논문집A
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• 제21권9호
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• pp.1385-1391
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• 1997

An analysis is presented on the stability of an elastic cantilever column subjected to a concentrated follower force as to the influence of the elastic restraint and a tip mass at the free end. The elastic restraint is formed by the rotatory springs. For this purpose, the governing equations and boundary conditions are derived by using Hamilton's principle, and the critical flutter loads and frequencies are obtained from the numerical evaluation of the eigenvalue functions of the considered system.

• 대한기계학회논문집
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• 제7권1호
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• pp.52-63
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• 1983

The purpose of the study is to find development of contact area, contact pressure and friction forces occurring at joints or connection areas inbetween structural members or mechanical parts. The problem has a pair of difficulties intrinsically; a constraint of displacement due to contact, and presence of work term by nonconservative friction force in the variational principle of the problem. Because of these difficulties, the variational principle remains in the form of inequality. It is resolved by penalty method and perturbation method making the inequality to an equality which is proper for computational purposes. A contact problem without friction is solved to find contact area and contact pressure, which are to be used as data for the analysis of the friction problem using perturbed variational principle. For numerical experiments, a Hertz problem, a rigid punch problem, and the latter one with friction effects are solved using $Q_2$-finite elements.

• 소음진동
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• 제7권3호
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• pp.439-447
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• 1997

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower forces are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant, the initial impact forces acting at the end of the model are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, power density spectrum, and Poincare maps. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, direction control constant, and viscous damping, etc., are analysed. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• Earthquakes and Structures
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• 제10권4호
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• pp.965-988
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• 2016

This paper investigates the seismic behavior of reinforced concrete shear wall buildings with multiple underground stories. A base-case where the buildings are modeled with a fixed condition at ground level is adopted, and then the number of basements is incrementally increased to evaluate changes in performance. Two subsurface site conditions, corresponding to very dense sands and medium dense sands, are used for the analysis. In addition, three ground shaking levels are used in the study. Results of the study indicated that while the common design practice of cropping the structure at the ground surface leads to conservative estimation of the base shear for taller and less rigid structures; it results in unpredicted and nonconservative trends for shorter and stiffer structures.

• Structural Engineering and Mechanics
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• 제64권6권
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• pp.723-730
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• 2017

This paper studies on dynamic and stability behavior of a clamped-elastically restrained nanobeam under the action of a nonconservative force with an emphasis on the influence of surface properties on divergence and flutter instability. Using the Euler-Bernoulli beam theory incorporating surface effects, a governing equation for a clamped-elastically restrained nanobeam is derived according to Hamilton's principle. The characteristic equation is obtained explicitly and the force-frequency interaction curves are displayed to show the influence of the surface effects, spring stiffness of the elastic restraint end on critical loads including divergence and flutter loads. Divergence and flutter instability transition is analyzed. Euler buckling and stability of Beck's column are some special cases of the present at macroscale.

• 대한수학회지
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• 제54권1호
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• pp.141-175
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• 2017

We present a high-resolution van Leer-type numerical scheme for the isentropic model of fluid flows in a nozzle with variable cross-section. Basically, the scheme is an improvement of the Godunov-type scheme. The scheme is shown to be well-balanced, as it can capture exactly equilibrium states. Numerical tests are conducted which include comparisons between the van Leer-type scheme and the Godunov-type scheme. It is shown that the van Leer-type scheme achieves a very good accuracy for initial data belong to both supersonic and supersonic regions, and the exact solution eventually possesses a resonant phenomenon.