• Structural Engineering and Mechanics
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• 제57권2호
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• pp.327-355
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• 2016

A new analytical derivation of the elastodynamic point load solutions for an isotropic multi-layered half-space is presented by means of the precise integration method (PIM) and the approach of dual vector. The time-harmonic external load is prescribed either on the external boundary or in the interior of the solid medium. Starting with the axisymmetric governing motion equations in a cylindrical coordinate system, a second order ordinary differential matrix equation can be gained by making use of the Hankel integral transform. Employing the technique of dual vector, the second order ordinary differential matrix equation can be simplified into a first-order one. The approach of PIM is implemented to obtain the solutions of the ordinary differential matrix equation in the Hankel integral transform domain. The PIM is a highly accurate algorithm to solve sets of first-order ordinary differential equations and any desired accuracy of the dynamic point load solutions can be achieved. The numerical simulation is based on algebraic matrix operation. As a result, the computational effort is reduced to a great extent and the computation is unconditionally stable. Selected numerical trials are given to validate the accuracy and applicability of the proposed approach. More examples are discussed to portray the dependence of the load-displacement response on the isotropic parameters of the multi-layered media, the depth of external load and the frequency of excitation.

• Journal of Welding and Joining
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• 제15권4호
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• pp.99-108
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• 1997

Analytical model for the temperature distribution and the cooling rate of weld in dual beam laser welding is presented for investigating the possibility of controling the cooling rate. The model is based on the solutions to the problem of heat flow due to the distributed and line heat sources for preheating and welding respectively in plates with finite thickness. The effects of beam power, beam distribution parameter, interbeam distance, and welding speed on the resulting temperature distribution and cooling rate are presented. The cooling rates of dual beam laser weld at the weld centerline under the investigated conditions are reduced to as one third of those of welds which were produced by single beam laser. And it appeared that the cooling rate of dual beam laser weld is strongly dependent on the process parameters of preheating laser beam power and welding speed.

• 한국군사과학기술학회지
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• 제4권2호
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• pp.112-121
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• 2001

From the beginning of 1990s, the leading countries, especially United States, are trying to develop dual-use technology which can be used for both military and commercial purpose, and to improve the efficiency of management system in logistics and procurements. Considering the global trends, Department of Defence has been seeking for solutions as to how to reform military specifications, and launched specification unification projects. As a result of the project, a series of dual-use standards for hardwares are being developed in the form of Korea Industrial Standards(KS standards). However, there are many of foreign standards, which are not readily interpretable by users, referenced in the standards. In this study, needs for the conversion of referenced foreign standards to KS standards are reviewed and the appropriate approaches as to the conversion are suggested.

• 한국경영과학회지
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• 제14권1호
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• pp.16-26
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• 1989

The terminal layout problem is fundamental in may centralized computer networks, which is generated formulated as the capaciated minimum spanning tree problem (CMSTP). We present an implementation of the dual-based procedure to solve the CMSTP. Dual ascent procedure generates a good feasible solutions to the dual of the linear programming relaxation of CMSTP. A feasible primal solution to CMSTP can then be constructed based on this dual solution. This procedure can be used either as a stand-alone heuristic or, else, it can be incorporated into a branch and bound algorithm. A numerical result is given with quite favorable results.

• 대한기계학회논문집B
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• 제23권2호
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• pp.243-253
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• 1999

The dual reciprocity boundary element method (DRBEM) is used to solve the Graetz problem of laminar flow inside circular duct. In this method the domain integral tenn of boundary integral equation resulting from source term of governing equation is transformed into equivalent boundary-only integrals by using the radial basis interpolation function, and therefore complicate domain discretization procedure Is completely removed. Velocity profile is obtained by solving the momentum equation first and then, using this velocities as Input data, energy equation Is solved to get the temperature profile by advancing from duct entrance through the axial direction marching scheme. DRBEM solution is tested for the uniform temperature and heat flux boundary condition cases. Local Nusselt number, mixed mean temperature and temperature profile inside duct at each dimensionless axial location are obtained and compared with exact solutions for the accuracy test Solutions arc in good agreement at the entry region as well as fully developed region of circular duct, and their accuracy are verified from error analysis.

• 정보학연구
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• 제3권2호
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• pp.73-85
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• 2000

본 논문에서는 여러가지 상이한 메세지를 전송하는 정보통신 네트워크의 효율적인 해법을 개발하였다. 이 문제는 네트워크 이론에서의 전형적인 다품종 네트워크로의 전환이 가능하다. 이러한 문제는 문제의 크기에 따라 계산의 복잡도가 지수적으로 증가하는 대표적인 NP-완전문제이다. 본 논문에서 개발된 해법은 전통적인 라그랑지 이완법을 보완한 것으로 다음과 같이 구성된다. 우선 우수한 초기 실현가능해(good initial feasible solution)를 얻을 수 있는 휴리스틱 방법을 개발하고 초기 실현가능해가 얻어지면 이를 이용하여 초기 쌍대변수(이완된 제약식에 붙게되는 라그랑지 승수)를 추정한다. 대개의 경우 쌍대 변수를 임의로 0으로 설정하고 해법을 수행하는데, 이 경우 쌍대 최적해와의 차이가 많이 나게되므로 비효율이 발생할 수 있다. 쌍대 최적해를 얻은 후 원문제의 실현가능조건을 위배하는 경우에는 재할당 방법(re-allocation method)를 통해 원문제의 실현가능조건을 충족하도록 한다. 해법의 성능(효율성) 테스트 결과 저자들이 개발한 해법이 수행속도 면에서 상업용 팩키지와 기존의 효율적인 해법들에 비하여 매우 우수하다는 결과를 얻을 수 있었다. 또한 본 해법은 최적해를 보장하지 않지만 최적해와의 차이가 평균 2% 미만의 근사 최적해를 얻을 수 있었다.

• 한국전산유체공학회지
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• 제9권4호
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• pp.1-6
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• 2004

This study investigates the transition of flows in a natural convection problem with periodic wall temperatures of the form, T/sub L/=T₁＋δ Tsinκχ and T/sub L/=T₂＋δ Tsinκχ .The fluid considered is air with P/sub γ/=0.7. In the conduction-dominated regime with a small Rayleigh number, two large cells are formed over one wave length, for all wave numbers. When k≤1.8, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length, and several kinds of transition phenomena, such as 2→3→4, 4→3→2, and 2→4 eddy flow, occur with increase( or decrease) of the Rayleigh number. Dual solutions are found above a critical Rayleigh number, and an anomalous bifurcation is observed.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1996년도 춘계공동학술대회논문집; 공군사관학교, 청주; 26-27 Apr. 1996
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• pp.530-533
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• 1996

This paper deals with finding an initial solution and modifying search direction by the centrering force in the predictor-corrector method which is a variant of the primal-dual barrier method. These methods were tested with NETLIB problems. Initial solutions which are located close to the center of the feasible set lower the number of iterations, as they enlarge the step length. Three heuristic methods to find such initial solution are suggested. The new methods reduce the average number of iterations by 52% to at most, compared with the old method assigning 1 to initial valurs. Solutions can move closer to the central path fast by enlarging the centering force in early steps. It enlarge the step length, so reduces the number of iterations. The more effective this method is the closer the initial solution is to the boundary of the feasible set.

• 대한기계학회논문집B
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• 제25권6호
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• pp.804-810
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• 2001

Transition of flows in natural convection in a horizontal cylindrical annulus is investigated for the fluid with Pr=0.2. The unsteady streamfunction-vorticity equation is solved with finite difference method. As Rayleigh number is increased, the steady crescent-shaped eddy flow bifurcates to a time-periodic flow with like-rotating eddies. After the first Hopf bifurcation, however, a reverse transition from oscillatory to a steady flow occurs by the flow pattern variation. Hysteresis phenomenon occurs between the solution branches of up-scan and down-scan stages, and dual solutions with one steady and one oscillatory flow are found. Overall Nusselt of the flows at the flows at the down-scan stage is greater than that at the up-scan stage.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1000-1002
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• 2017

본 연구에서는 내재적 이중시간 전진기법을 이용한 비정상 Navier-Stokes 코드를 개발하였다. 내재적 이중시간 전진기법은 가상시간에 대한 새로운 잔류항을 도입하는 개념으로 비정상 잔류항에 실시간 미분항을 더한 잔류항을 가상시간으로 푸는 기법이다. 비정상 코드 검증 방법으로 Stokes 2nd 문제인 '주기성 하모닉 진동을 하는 평판 위의 층류 유동'을 해석하였다. 계산된 속도분포와 마찰계수를 방정식 이론적 해와 비교한 결과 매우 근접한 수치해를 얻을 수 있었다.