• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1513-1519
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• 2013

A genetic algorithm (GA) is an optimization technique based on natural evolution theory to find the global optimal solution. Unlike the gradient-based method, it can design nanoscale structures in the electric field because it does not require sensitivity calculation. This research intends to design a nanoaperture with an unprecedented shape by the topology optimization scheme based on the GA and ON/OFF method in the visible frequency range. This research mainly aims to maximize the transmission rate at a measuring area located 10nm under the exit plane and to minimize the electric distribution at other locations. The finite element analysis (FEA) and optimization process are performed by using the commercial package COMSOL combined with the Matlab programming. The final results of the optimized model are analyzed by a comparison of the electric field intensity and the spot size of near field with those of the initial model.

• Korean Journal of Optics and Photonics
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• v.11 no.4
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• pp.246-249
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• 2000

The null lens is designed for testing the elliptical (conic constant>O) mirror which is the third mirror of the off-axis Three Mirror Anastigmat (TMA) designed as a high resolution camera for remote sensing. The mixed type design is proposed as a new design type which has a small annular flat mirror, but has as twice sensitivity as the autostigmatic type design. It is also shown that the null lens of the Mixed type is better than that of the autostigmatic type in terms of the sensitivity of the wavefront distortion which is given as the magnitude of optical path difference with respect to the change of each surface parameters such as the radius of curvature, thickness of lenses and tested mirror.

• Computational Structural Engineering
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• v.8 no.1
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• pp.85-94
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• 1995

The optimum design of the cylindrical shell under external pressure loading is considered. The design variable is a skin thickness of the unstiffened parallel middle body shell. Overall buckling strength and direct stress and displacements constraints are considered in the design problem The optimum design is achieved with one of the standard nonlinear constrained optimization technique. A method for calculating the sensitivity coefficients is developed using the direct differentiation.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.835-837
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• 2002

This paper presents a shape optimization algorithm of electromagnetic devices using the design sensitivity analysis with FEM. The design sensitivity and adjoint variable formulas are derived for the 3D FEM with edge element. This algorithm is applied to 3D electro-magnet pole shape optimization problem to make a uniform flux density at the target region.

• Computational Structural Engineering
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• v.7 no.3
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• pp.46-57
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• 1994

구조최적화 분야는 작게 보면 구조공학의 한 분야에 불과하지만 그것이 지향하는 목표가 보다 근원적이고 원대한 것일 뿐만 아니라, 설계 자체가 복잡하고 다양한 선택과 결정의 과정인 터에, 세부대상이나 접근방법에 따라 여러가지 부 영역을 포괄하는 방대한 연구 영역을 이루고 있다. 크게 대상으로 보아 단면, 기하, 또는 형상과 위상 최적화 등으로 나눌 수 있고, 보다 상급과제로 그들을 통합하는 배치최적화 등이 있다. 다른 한편으로 방법이나 도구로써 각종 수치계산 알고리즘 및 민감도해석과 함께 CAD나 EXPERT SYSTEMS 등을 활용하는 방법 등이 활발히 연구되고 있는 바, 여기서는 구조시스템이 하나의 대규모 공학시스템이라는 본질적 측면에 입각, 복잡한 대형구조시스템의 최적화를 위한 기본이론과 방법을 다루어 보고자 한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.99-104
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• 2008

This study performed robust design optimization of fighter wing planform, considering uncertainty based on neural network model. To construct uncertainty model, aerodynamic performance and their sensitivity were evaluated by 3-dimensional Euler equations and adjoint variable method at experimental points selected from central composite design. In addition, because a neural network model has the advantage of capturing non-linear characteristic, it was possible to predict sensitivity of the aerodynamic performance efficiently and accurately . From the results of robust design optimization, it could be confirmed that the robustness of the objective function and constraints were improved if the variation of uncertainty and sigma level were increased.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.319-332
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• 2004

Due to their high strength to weight ratios and excellent durability, fiber reinforced polymer(FRP) is widely used in construction industries. In this paper, a shape optimum design of FRP bridge decks haying pultruded cellular cross-section is presented. In the problem formulation, an objective function is selected to minimize the volumes. The cross-sectional dimensions and material properties of the deck of FRP bridges are used as the design variables. On the other hand, deflection limits in the design code, material failure criteria, buckling load, minimum height, and stress are selected as the design constraints to enhance the structural performance of FRP decks. In order to efficiently treat the optimization process, the cross-sectional shape of bridge decks is assumed to be a tube shape. The optimization process utilizes an improved Genetic Algorithms incorporating indexing technique. For the structural analysis using a three-dimensional finite element, a commercial package(ABAQUS) is used. Using a computer program coded for this study, an example problem is solved and the results are presented with sensitivity analysis. The bridge consists of a deck width of 12.14m and is supported by five 40m long steel girders spaced at 2.5m. The bridge is designed to carry a standard DB-24 truck loading according to the Standard Specifications for Highway Bridges in Korea. Based on the optimum design, viable cross-sectional dimensions for FRP decks, suitable for pultrusion process are proposed.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.130-138
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• 2007

A coupled variational equation for fluid-structure interaction (FSI) problems is derived from a steady state Navier-Stokes equation for incompressible Newtonian fluid and an equilibrium equation for geometrically nonlinear structures. For a fully coupled FSI formulation, between fluid and structures, a traction continuity condition is considered at interfaces where a no-slip condition is imposed. Under total Lagrange formulation in the structural domain, finite rotations are well described by using the second Piola-Kirchhoff stress and Green-Lagrange strain tensors. An adjoint shape design sensitivity analysis (DSA) method based on material derivative approach is applied to the FSI problem to develop a shape design optimization method. Demonstrating some numerical examples, the accuracy and efficiency of the developed DSA method is verified in comparison with finite difference sensitivity. Also, for the FSI problems, a shape design optimization is performed to obtain a maximal stiffness structure satisfying an allowable volume constraint.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.79-86
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• 2000

In this study, a method of optimal blank design using the sensitivity analysis has been proposed. To get sensitivity a well-known commercial code PAM-STAMP has been used. In order to verify this method, formings of square cup, clover shaped cup and L shaped cup have been chosen as the examples. With the predicted optimal blank both computer simulation and experiment are performed. Excellent agreements are recognized between the numerical results and the target contour shapes. Through the investigation, the proposed systematic method of optimal blank design is found to be effective in the design of the deep drawing process.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1675-1678
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• 2008

어류는 민감하기 때문에 최적화된 어도를 설계하는 것은 매우 어려운 일이다. 이와 같은 문제를 해결하기 위해서, 관찰, 수리모형시험과 같은 방법을 이용한 연구가 주를 이루어 왔다. 최근 들어 어도에 대한 기본 지식의 축적과 CFD 프로그램이 발전함에 따라 수치모의를 이용해 최적 어도를 설계하고자 하는 노력이 활발해 지고 있다. 본 연구에서는 최적 어도 설계를 도모하기 위해서 어류의 휴식을 위해 설치되는 풀(pool) 내의 흐름해석을 수행하였다. 군남홍수조절지를 대상으로 설계도면을 분석하여 3차원으로 변환하여 구조물형상을 구축하였으며, FLOW-3D 모형을 이용하여 흐름을 해석하였다. 휴식 풀 내의 흐름을 모의한 결과 어도 내 월류 수심이 10cm 일 경우, 휴식 풀 내 유속은 풀 내 유입어도의 노치와 잠공부분에서 최대 유속이 0.4m/s로 나타났고, 국부적으로 집중된 유속에 의해 풀 내 순환류가 발생하나, 유속의 범위가 최대 0.15m/s를 넘지 않는 것으로 모의되었다.