• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제5권1호
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• pp.85-100
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• 2001

In this paper we propose a block-type parallel preconditioner for solving large sparse nonsymmetric linear systems, which we expect to be scalable. It is Multi-Color Block SOR preconditioner, combined with direct sparse matrix solver. For the Laplacian matrix the SOR method is known to have a nondeteriorating rate of convergence when used with Multi-Color ordering. Since most of the time is spent on the diagonal inversion, which is done on each processor, we expect it to be a good scalable preconditioner. Finally, due to the blocking effect, it will be effective for ill-conditioned problems. We compared it with four other preconditioners, which are ILU(0)-wavefront ordering, ILU(0)-Multi-Color ordering, SPAI(SParse Approximate Inverse), and SSOR preconditioner. Experiments were conducted for the Finite Difference discretizations of two problems with various meshsizes varying up to 1024 x 1024, and for an ill-conditioned matrix from the shell problem from the Harwell-Boeing collection. CRAY-T3E with 128 nodes was used. MPI library was used for interprocess communications. The results show that Multi-Color Block SOR and ILU(0) with Multi-Color ordering give the best performances for the finite difference matrices and for the shell problem only the Multi-Color Block SOR converges.

• 한국군사과학기술학회지
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• 제1권1호
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• pp.145-153
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• 1998

천음속 날개꼴의 수치최적화 설계에 있어서, 하나의 흐름조건에 의해 설계된 날개꼴의 공력특성은 다른 흐름조건에서 나쁜 특성을 나타낼 수 있다. 따라서, 실용적인 날개꼴의 설계를 위해서 multi-point 수치최적화 설계능력은 필수적인 요소이다. 본 논문에서는 Navier-Stokes 방정식 흐름해석 코드와 feasible direction 최적화 알고리즘을 이용하여 two-point 수치최적화 설계를 수행하였으며, 가중치가 수치최적화 설계에 주는 영향을 분석하고 비교하였다. 그 결과로서 two-point수치최적화 설계된 날개꼴이 두 흐름조건의 주변영역에서 동시에 요구 공력특성을 만족시키며, 가중치가 큰 방향으로 최적화 설계됨을 확인하였다.

• 한국분무공학회지
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• 제15권1호
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• pp.31-37
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• 2010

The aim of this work is to investigate the spray and combustion characteristics of dimethyl-ether (DME) at various injection conditions. The spray characteristics such as spray tip penetration and spray cone angle were experimentally studied from the spray images which obtained from the spray visualization system. Combustion and emissions characteristics were numerically investigated by using KIVA-3V code coupled with Chemkin chemistry solver. From these results, it revealed that DME spray had a shorter spray tip penetration and wider spray cone angle than that of diesel spray due to the low density, low surface tension, and fast evaporation characteristics. At the constant heating value condition, DME fuel showed higher peak combustion pressure and earlier ignition timing, because of high cetane number and superior evaporation characteristics. In addition, the combustion of DME exhausted more $NO_x$ emission and lower HC emission due to the active combustion reaction in the combustion chamber. The result shows that DME had a little soot emission due to its molecular structure characteristics with no direct connection between carbons.

• 한국산학기술학회논문지
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• 제3권1호
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• pp.10-19
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• 2002

본고는 다종, 소규모 회분식 공정 또는 공장을 수학적 프로그래밍 기법으로 최적 설계하는 방법에 대한 것이다. 제안된 일반 회분식 공장문제는 Papageorgaki와 Reklaitis에 의해 혼합정수비선형식(MINLP)으로 수립된 것인데, 최적해답을 보장하며 공장의 확장 등 불확실성을 고려하여 선형화 한 후(MILP) 푸는 방법론이 제시되었다. Bende식 문제분할 방식을 개조하여 몇가지 예제에 대한 풀이를 제시하였다. IBM의 OSL 최적화 패키지를 이용하였고 MILP를 직접 푸는 경우보다 계산시간을 크게 단축할 수 있었다.

• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.169-187
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• 2019

This work presents a practical detailed finite element (FE) approach for the three-dimensional (3D) free-vibration analysis of actual aircraft and spacecraft-type lightweight and thin honeycomb sandwich panels. It consists of calling successively in $MATLAB^{(R)}$, via a developed user-friendly GUI, a detailed 3D meshing tool, a macrocommands language translator and a commercial FE solver($ABAQUS^{(R)}$ or $ANSYS^{(R)}$). In contrary to the common practice of meshing finely the faces and core cells, the proposed meshing tool represents each wall of the actual hexagonal core cells as a single two-dimensional (2D) 4 nodes quadrangularshell element or two 3 nodes triangular ones, while the faces meshes are obtained simply using the nodes at the core-faces interfaces. Moreover, as the same 2D FE interpolation type is used for meshing the core and faces, this leads to an automatic handling of their required FE compatibility relations. This proposed approach is applied to a sample made of very thin glass fiber reinforced polymer woven composite faces and a thin aluminum alloy hexagonal honeycomb core. The unknown or incomplete geometric and materials properties are first collected through direct measurements, reverse engineering techniques and experimental-FE modal analysis-based inverse identification. Then, the free-vibrations of the actual honeycomb sandwich panel are analyzed experimentally under different boundary conditions and numerically using different mesh basic cell shapes. It is found that this approach is accurate for the first few modes used for pre-design purpose.

• International Journal of Contents
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• 제15권2호
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• pp.53-58
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• 2019

The aim of this paper is to discuss how designers lead and direct 'technology-driven society' using their creative communication skill. To this end, it is required for communication designers to take conscious steps to recognize the future direction of their profession. Despite the advancement in technology, there is a human being at the center of all design activities. From a certain point of view, contemporary communication design takes an open-ended exploration of the subject matter, rather than a finished output. The notion of creative leadership may potentially expand more in terms of improving the methodology of today's visual culture. The paper will examine creative leadership that could be proposed by the challenge of discourse upon the upcoming industrial revolution. Today, communication designers are confronted by new leadership opportunities and challenges. Some leading designers seem to focus on brand new media technologies to prepare the 4th industrial revolutions. However, communication design cannot be discussed in the medium but can be understood as a process. Top-down and bottom-up process is always a concerned about the relationship since the focus of leadership has changed. In the top-down process, the leadership has existed between 'designer and client' because designers have played their role as a problem solver. On the other hand, there is a different model of leadership between 'design and technology' based on bottom-up process, which stem from the design authorship. In this regard, the new definition of creative leadership in the $4^{th}$ industrial revolution proposes a designer as a problem-finder based on the relationship between the 'designer and the public'.

• 아태비즈니스연구
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• 제9권4호
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• pp.99-117
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• 2018

This study has investigated Linear Programming (LP) applications to special decision making problems in managerial accounting with the help of spreadsheet Solver tools. It uses scenario approaches to case examples having three products and three resources in make-and-supply business operations, which is applicable to cases having more variables and constraints. Integer Programmings (IP) are applied in order to model situations when products are better valued in integer values or logical constraints are required. Three cases in one-time-only special order decisions include Goal Programming approach, Knapsack problems with 0/1 selections, and fixed-charge 0/1 integer modelling techniques for set-up operation costs. For the decisions in outsourcing problems, opportunity-costs of resources expressed by shadow-prices are considered to determine their precise contributions. It has also shown that the improvement in work-shop operation for an unprofitable product must overcome its 'reduced cost' by the sum of direct manufacturing cost savings and its shadow-price contributions. This paper has demonstrated how various real situations of special decision problem in managerial accounting can be approached without mistakes by using LP's and IP's, and how students both in accounting and management science can acquire LP skills in their education.

• 한국해양공학회지
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• 제33권5호
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• pp.387-393
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• 2019

In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.

• 한국가시화정보학회지
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• 제22권2호
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• pp.44-54
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• 2024

This study investigates the effectiveness of using a plasma actuator for active control of turbulent flow around a finite square cylinder. The primary objective is to analyze the impact of plasma actuators on flow separation and wake region characteristics, which are critical for reducing drag and suppressing vortex-induced vibrations. Direct Numerical Simulation (DNS) was employed to explore the flow dynamics at various operational parameters, including different actuation frequencies and voltages. The proposed methodology employs a neural network trained using the Proximal Policy Optimization (PPO) algorithm to determine optimal control policies for plasma actuators. This network is integrated with a computational fluid dynamics (CFD) solver for real-time control. Results indicate that this deep reinforcement learning (DRL)-based strategy outperforms existing methods in controlling flow, demonstrating robustness and adaptability across various flow conditions, which highlights its potential for practical applications.

• 멤브레인
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• 제20권1호
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• pp.29-39
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• 2010

본 연구는 차세대 에너지원으로 주목 받고 있는 직접메탄올연료전지(Direct Methanol Fuel Cell, DMFC)에 대해 mutiscale 기법을 사용하여 DMFC의 MEA부분에 대한 상세 모델링 및 전산모사를 통한 이론적 고찰을 시도하였다. 본 연구에서 이용한 multiscale 모델링 방법은 공정시스템 공학의 kinetic 중심의 모델링 방법과 전산유체역학(Computational Fluid Dynamics, CFD)의 유동중심의 모델링 방법을 유기적으로 결합하여 모사 중간에 필요한 데이터 교환을 함으로써 정확한 모델링 및 전산모사 결과를 얻었다. CFD 모델링으로 유체 이동현상을 3차원으로 해석하였고, 동시에 복잡한 비선형 대수방정식으로 표현되는 반응속도, 전기화학반응을 DAE (Differential & Algebraic Equation) solver로 계산하였다. 모델은 메탄올의 산화반응과 산소의 환원반응을 중심으로 MEA (Membrane Electorde Assembly)부분에서 물리화학적, 전기적 현상 현상을 규명하고, 반응 메커니즘을 구성하였다. MEA 모델은 3차원 공간에서 변위를 가지는 3차원 모델로 구성하였으며, 정상상태 및 등온공정의 조건하에 수립되었다. 이를 통해 channel을 포함한 MEA 부분에서 발생되는 물리적, 화학적, 전기적 현상을 정확히 예측 할 수 있다. 본 연구를 통해 수행된 결과는 DMFC의 실험계획 및 운전조건을 도출함에 있어 매우 유용한 역할을 할 수 있을 것으로 사료되며, 추가적인 연구를 통해 DMFC의 상용화에 크게 이바지 할 수 있을 것으로 사료된다.