• Advances in Computational Design
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• 제4권1호
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• pp.15-32
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• 2019

One of the efficient and useful tools to achieve the optimal design of structures is employing the sensitivity analysis in the finite element model. In the numerical optimization process, often the semi-analytical method is used for estimation of derivatives of the objective function with respect to design variables. Numerical methods for calculation of sensitivities are susceptible to the step size in design parameters perturbation and this is one of the great disadvantages of these methods. This article uses complex variables method to calculate the sensitivity analysis and combine it with discrete sensitivity analysis. Finally, it provides a new method to obtain the sensitivity analysis for linear structures. The use of complex variables method for sensitivity analysis has several advantages compared to other numerical methods. Implementing the finite element to calculate first derivatives of sensitivity using this method has no complexity and only requires the change in finite element meshing in the imaginary axis. This means that the real value of coordinates does not change. Second, this method has the lower dependency on the step size. In this research, the process of sensitivity analysis calculation using a finite element model based on complex variables is explained for linear problems, and some examples that have known analytical solution are solved. Results obtained by using the presented method in comparison with exact solution and also finite difference method indicate the excellent efficiency of the proposed method, and it can predict the sustainable and accurate results with the several different step sizes, despite low dependence on step size.

• 대한기계학회논문집B
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• 제39권1호
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• pp.71-78
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• 2015

본 논문에서는 복합발전시스템을 구성하는 각 단위 구성품의 교체비용이 변화할 때 각 단위 구성품의 용량 및 전체시스템의 경제성이 얼마나 변화하는지를 나타내는 민감도 분석을 수행하는 방법을 제시한다. 민감도 분석에는 복합발전시스템 경제 분석용 툴인 HOMER를 이용한다. 민감도 분석을 통해 교체비용 변화에 대해 민감도가 높은 구성품의 비중이 최소화 되게 설계하거나 예상되는 가격변동을 사전에 고려함으로써 복합발전시스템의 경제성을 최적화할 수 있으며, 민감도가 높은 구성품의 비중을 낮추기 위한 다른 조합의 복합 발전시스템 구성에 대한 정보도 제공할 수 있다. 민감도 분석의 예로서 주택용 부하 모델에 대해 HOMER에서 제공되는 일반적인 데이터를 사용하여 각 구성품 교체비용에 대한 용량 및 경제성 민감도를 정량적으로 분석하였다.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2968-2976
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• 2021

This paper introduces a method to reconstruct the three-dimensional (3D) microstructure of two-phase materials, e.g., porous materials such as highly irradiated nuclear fuel, from two-dimensional (2D) sections via a multi-objective optimization genetic algorithm. The optimization is based on the comparison between the reference and reconstructed 2D sections on specific target properties, i.e., 2D pore number, and mean value and standard deviation of the pore-size distribution. This represents a multi-objective fitness function subject to weaker hypotheses compared to state-of-the-art methods based on n-points correlations, allowing for a broader range of application. The effectiveness of the proposed method is demonstrated on synthetic data and compared with state-of-the-art methods adopting a fitness based on 2D correlations. The method here developed can be used as a cost-effective tool to reconstruct the pore structure in highly irradiated materials using 2D experimental data.

• 전기학회논문지
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• 제66권5호
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• pp.757-764
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• 2017

As the reduction of greenhouse gases(GHGs) emission has become a global issue, the microgrid markets are growing rapidly. With the sudden changes in the market, Korean government suggested a new business model called 'Self-Sufficient Energy Islands'. Its main concern is a stand-alone microgrid composed of Distributed Energy Resources(DERs) such as Renewable Energy Sources(RESs), Energy Storage System(ESS) and Fuel Cell, in order to minimize the emission of GHGs. According to these trend, this paper is written to propose an optimal sizing method of DERs in a stand-alone microgrid by using Genetic Algorithm(GA), one of the representative stochastic methods. It is to minimize the net present cost with the variables, size of RESs and ESS. In the process for optimization, the sunless days are considered as additional constraints. Through the case study analysis, the size of DERs installed in a microgrid system has been computed using the proposed method in MATLAB. And the result of MATLAB is compared with that of HOMER(Hybrid Optimization of Multiple Energy Resources), a well-known energy modeling software.

• Structural Engineering and Mechanics
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• 제56권4호
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• pp.667-694
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• 2015

The suspended dome system is a new structural form that has become popular in the construction of long-span roof structures. Suspended dome is a kind of new pre-stressed space grid structure that has complex mechanical characteristics. In this paper, an optimum topology design algorithm is performed using the enhanced colliding bodies optimization (ECBO) method. The length of the strut, the cable initial strain, the cross-sectional area of the cables and the cross-sectional size of steel elements are adopted as design variables and the minimum volume of each dome is taken as the objective function. The topology optimization on lamella dome is performed by considering the type of the joint connections to determine the optimum number of rings, the optimum number of joints in each ring, the optimum height of crown and tubular sections of these domes. A simple procedure is provided to determine the configuration of the dome. This procedure includes calculating the joint coordinates and steel elements and cables constructions. The design constraints are implemented according to the provision of LRFD-AISC (Load and Resistance Factor Design-American Institute of Steel Constitution). This paper explores the efficiency of lamella dome with pin-joint and rigid-joint connections and compares them to investigate the performance of these domes under wind (according to the ASCE 7-05), dead and snow loading conditions. Then, a suspended dome with pin-joint single-layer reticulated shell and a suspended dome with rigid-joint single-layer reticulated shell are discussed. Optimization is performed via ECBO algorithm to demonstrate the effectiveness and robustness of the ECBO in creating optimal design for suspended domes.

• 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.

• 한국전산구조공학회논문집
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• 제29권6호
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• pp.491-498
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• 2016

리벳이나 볼트가 결합되는 구멍은 항공기, 선박 및 기타 구조물에 사용되는 판재의 응력 집중을 유발한다. 과도한 응력 집중 현상이 지속되면 종래에는 파단이 일어날 수 있으므로 설계 단계에서 응력 집중 현상의 명확한 해석이 중요하다. 이 논문에서는 판재위에 리벳을 배치하는 간단한 최적화 방법이 제시되었다. 첫째로 응력 집중 현상 해석에서 FEM 구조 해석이 얼마나 정확한지 검증하였다. 평판 위에 존재하는 단일 구멍의 반경을 바꿔가며 응력 집중 계수의 변화를 분석하였다. 같은 방법으로 일렬로 존재하는 구멍들 사이에서의 응력 집중 계수를 수치 해석하였다. 각각의 응력 집중 계수를 이론값과 비교하여 정확도를 확인하였다. 마지막으로 두 응력 집중 현상을 독립적으로 적용하는 최적화 방법을 확인 및 검증하였다. 이 결과들은 이론적인 예측과 밀접한 경향성을 보여 앞으로의 리벳 배치 최적화에도 활용될 수 있을 것으로 예상된다.

• 한국기계가공학회지
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• 제12권1호
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• pp.22-27
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• 2013

A shot blasting process is to improve the surface quality of stainless steels. The process is similar to a well-known shot peening that is used to strengthen the surface via the residual stress. In the shot blasting process, it is important to decide many parameters, such as the size, incident angle and velocity of shot balls, to effectively get rid of the iron oxide on the surface of stainless steels. In this study, the simulation of the shot blasting process is carried out by a finite element software, which can help to find out the optimal design parameters to cause the delamination of the iron oxide from the stainless steel substrate. The results obtained are also compared to those of the discrete element method to verify them.

• International Journal of Aerospace System Engineering
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• 제2권2호
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• pp.24-28
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• 2015

Composite materials are highly sensitive to the presence of manufacturing and service-related defects that can reach a critical size during service condition and thereby may affect the safety of the structure. When the structure undergoes some kind of damage, its stiffness reduces, in turn the dynamic responses change. In order to avoid safety issues early detection of damage is necessary. The knowledge of the vibration behavior of a structure is necessary and can be used to determine the existence as well as the location and the extent of damage.

• 대한조선학회논문집
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• 제40권4호
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• pp.1-7
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• 2003

Large Passenger Ferry has been delivered with a tendency of high speed since 1990´s. More than 50 ferries that exceed 25 knots in service speed are operating or under construction these days. Therefore, the hull form development for the large size ferry should be carefully carried out with some design points such as high service speed, severe criteria for stability, and complex design of appendages. This paper reviewed principal particulars and hull form characteristics of a high-speed large passenger ferry. It is also suggested the optimization method of hull form and appendages in point of resistance & propulsion performance. Finally, it is also introduced a high-speed large passenger ferry developed by Samsung Heavy Industries Co., Ltd., the key design points in hull form development.