• 한국수자원학회논문집
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• 제33권3호
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• pp.289-298
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• 2000

본 연구에서는 대구광역시에 위치하고 있는 서변 펌프가압장에서 발생되는 수격압을 최소화하기 위해 사용되는 감압밸브와 공기밸브의 최적 위치결정과 감압밸브의 최적 열림정도를 도모하였다. 가압장에서 발생하는 펌프의 급정지에 기인한 수격현상은 특성선방법을 이용하여 모의를 하였다. 최적화 방법은 강력한 탐색능력을 가지고 있으며 특히 비선형 문제를 해결하는데 탁월한 성능을 가지고 있는 유전자 알고리즘을 이용하여 실시하였다. 유전자 알고리즘의 계산결과는 감압밸브의 열림시간을 적게 할수록 최고 압력수두의 완화에 효과적이고, 열림시간을 크게 할수록 최대부압의 완화에 효과적임을 알 수 있었다. 본 연구는 특성선방법을 기반으로 하는 관망부속물들의 해석이 유전자 알고리즘과 결합되어 관로내 관로부속물의 최적설계에 도움을 줄 수 있음을 보여준다.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.547-560
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• 2022

By presetting various reinforcement diameters in topology optimization with the discrete model finite element analysis, an algorithm of bidirectional evolutionary structural optimization of multi-level reinforcement diameter is presented to obtain the optimal reinforcement topologies which describe the degree of stress of different parts. The results of a comparative study on different reinforcement feasible domain demonstrate that the more angle types of reinforcement are arranged in the initial domain, the higher utilization rate of reinforcement of the optimal topology becomes. According to the nonlinear finite element analysis of some deep beam examples, the ones designed with the optimization results have a certain advantage in ultimate bearing capacity, although their failure modes are greatly affected by the reinforcement feasible domain. Furthermore, the bearing capacity can be improved when constructional reinforcements are added in the subsequent design. However the adding would change the relative magnitude of the bearing capacity between the normal and inclined section, or the relative magnitude between the flexural and shear capacity within the inclined section, which affects the failure modes of components. Meanwhile, the adding would reduce the deformation capacity of the components as well. It is suggested that the inclined reinforcement and the constructional reinforcement should be added properly to ensure a desired ductile failure mode for components.

• 한국전산구조공학회논문집
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• 제36권6호
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• pp.399-405
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• 2023

본 연구에서는 철근콘크리트 모멘트골조의 보-힌지 붕괴 기구를 유도하기 위한 유전자알고리즘 기반의 최적내진설계기법을 제시한다. 제안하는 기법은 두 가지의 목적함수을 사용한다. 첫 번째는 구조물의 비용을 최소화하는 것이고, 두 번째는 구조물의 에너지소산능력을 최대화하는 것이다. 제약조건은 기둥과 보의 강도조건, 기둥-보 휨강도비 최소 조건, 기둥의 소성힌지 발생 방지조건 등이 사용된다. 부재의 강도 평가를 위해 선형정적해석이 수행되고, 에너지소산능력과 소성힌지 발생여부를 평가하기 위해 비선형정적해석이 수행된다. 제안하는 기법은 4층 예제 구조물에 적용되었으며, 보-힌지 붕괴 기구를 유도하는 설계안이 얻어지는 것을 확인하였다. 획득된 설계안의 기둥-보 휨강도비를 분석한 결과, 그 값은 기존 내진 기준에서 제시하는 값보다 큰 것으로 나타났다. 보-힌지 붕괴 모드를 유도하기 위해서는 보다 더 강화된 전략이 필요하다.

• Journal of Microbiology and Biotechnology
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• 제19권4호
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• pp.378-386
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• 2009

A sequential optimization strategy, based on statistical experimental designs, is employed to enhance the production of alkaline protease by a Bacillus pseudofirmus local isolate. To screen the bioprocess parameters significantly influencing the alkaline protease activity, a 2-level Plackett-Burman design was applied. Among 15 variables tested, the pH, peptone, and incubation time were selected based on their high positive significant effect on the protease activity. A near-optimum medium formulation was then obtained that increased the protease yield by more than 5-fold. Thereafter, the response surface methodology(RSM) was adopted to acquire the best process conditions among the selected variables, where a 3-level Box-Behnken design was utilized to create a polynomial quadratic model correlating the relationship between the three variables and the protease activity. The optimal combination of the major medium constituents for alkaline protease production, evaluated using the nonlinear optimization algorithm of EXCEL-Solver, was as follows: pH of 9.5, 2% peptone, and incubation time of 60 h. The predicted optimum alkaline protease activity was 3,213 U/ml/min, which was 6.4 times the activity with the basal medium.

• 대한전자공학회논문지
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• 제11권6호
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• pp.38-43
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• 1974

임의의 전원임피이던스와 임의의 부하임피이던스 사이에 삽입할 때 입력반사계수가 가급적 넓은 주파수범위에서 최소가 되는 임피이던스 정합용 불균일선로 섹션을 설계하는 문제를 고찰하였다. 고려대상의 불균일선로는 수학적으로는 특수한 종류에 속하는 것이나 실제적으로는 완만하게 변하는 거의 모든 전송선로를 포괄할 수 있다. 입력반사 계수의 계산에서는 선로의 ABCD 파라미터의 테일러 급수전관식을 이용하였다. 그리고 설계문제를 비선형 구속조건을 가진 비선형 프로그래밍 문제로서 수식화하였으며 이것을 수차적비구속 최소법(Sequential Unconstrained Minimigation Technique)과 Fletcher-Powell 방법을 병용하여 풀었다. 결과적으로 이제까지 광대역 임피이던시 정합편 전송선제로서 발표된 가장 우수한 것보다 훨씬 특성이 개선된 것을 얻을 수 있었다.

• 한국자동차공학회논문집
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• 제14권6호
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• pp.143-150
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• 2006

In this paper, a new bushing model for vehicle dynamics analysis using Bouc-Wen hysteretic model is proposed. Bushing components of a vehicle suspension system are tested to capture the nonlinear behavior of rubber bushing elements using the MTS 3-axes rubber test machine. The results of the tests are used to define parameters in Bouc-Wen bushing model, which was employed to represent the hysteretic characteristics of the bushing. Bushing parameters are obtained by using genetic algorithms and sensitivity analysis of parameters are also carried out. ADAMS program was used for the identification process and VisualDOC program was employed to find the optimal parameters. A half-car simulation was carried out to show the usefulness of the developed bushing model.

• 한국해양공학회지
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• 제17권5호
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• pp.1-10
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• 2003

When a body with slant angle behind its shoulder is moving at a high speed, the turbulent motion around the afterbody is generally associated with the flow separation, and determines the normal component of the drag. By changing the slant angle of the afterbody, the drag coefficients can be changed, drastically. Understanding and controlling the turbulent separated flows has significant importance for the design of optimal configuration of the moving bodies. In this paper, a new Large Eddy Simulation technique has been developed to investigate turbulent vortical motions around the afterbodies, using slant angle. By understanding the structure of the turbulent flow around the body, the new configuration of afterbodies is designed to reduce the drag of body, and the nonlinear effects, due to the interaction between the body configuration and the turbulent separated flows, are investigated by use of the developed LES technique.

• 대한기계학회논문집A
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• 제37권4호
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• pp.475-481
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• 2013

직접구동형 서보밸브의 제어시스템은 비선형적이며 밸브스풀에 미치는 유체력의 영향은 매우 크고 부하압력의 크기에 좌우된다. 제어시스템의 설계요구조건을 만족시키기 위해, 제약직접탐색방법인 유전자 알고리즘과 콤플렉스법을 적절히 활용하여 진상-지상제어기 및 미분피드백제어기의 최적 상수값을 탐색하였다. 최적 제어기 상수값을 대입하여 제어시스템을 시뮬레이션한 결과 설계요구조건을 만족하였다.

• Earthquakes and Structures
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• 제11권4호
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• pp.701-721
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• 2016

Base isolation is a well-established passive strategy for seismic response control of buildings. In this paper, an efficient framework is proposed for reliability-based design optimization (RBDO) of isolated buildings subjected to uncertain earthquakes. The framework uses reduced function evaluations method, as an efficient tool for structural reliability analysis, and an efficient optimization algorithm for optimal structural design. The probability of failure is calculated considering excessive base displacement, superstructure inter-storey drifts, member stress ratios and absolute accelerations of floors of the isolated building as failure events. The behavior of rubber bearing isolators is modeled using nonlinear hysteretic model and the variability of future earthquakes is modeled by applying a probabilistic approach. The effects of pulse component of stochastic near-fault ground motions, fixity-factor of semi-rigid beam-to-column connections, values of isolator parameters, earthquake magnitude and epicentral distance on the performance and safety of semi-rigidly connected base-isolated steel framed buildings are studied. Suitable RBDO examples are solved to illustrate the results of investigations.

• 대한기계학회논문집A
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• 제27권6호
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• pp.864-870
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• 2003

In recent engineering, the designer has become more and more dependent on the computer simulations such as FEM(Finite Element Method) and BEM(Boundary Element Method). In order to optimize such implicit models more efficiently and reliably, the meta -modeling technique has been developed for solving such a complex problems combined with the DACE(Design and Analysis of Computer Experiments). It is widely used for exploring the engineer's design space and for building approximation models in order to facilitate an effective solution of multi-objective and multi-disciplinary optimization problems. Optimization of a train suspension is performed according to the minimization of forty -six responses that represent ten ride comforts, twelve derailment quotients, twelve unloading ratios, and twelve stabilities by using the Kriging model of a train suspension. After each Kriging model is constructed, multi -objective optimal solutions are achieved by using a nonlinear programming method called SQP(Sequential Quadratic Programming).