• Smart Structures and Systems
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• 제4권5호
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• pp.641-653
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• 2008

This paper proposes a practical and realistic method to establish an optimal lifetime maintenance strategy for deteriorating bridges by considering the life-cycle performance as well as the life-cycle cost. The proposed method offers a set of optimal tradeoff maintenance scenarios among other conflicting objectives, such as minimizing cost and maximizing performance. A genetic algorithm is used to generate a set of maintenance scenarios that is a multi-objective combinatorial optimization problem related to the lifetime performance and the life-cycle cost as separate objective functions. A computer program, which generates optimal maintenance scenarios, was developed based on the proposed method using the life-cycle costs and the performance of bridges. The subordinate relation between bridge members has been considered to decide optimal maintenance sequence and a corresponding algorithm has been implemented into the program. The developed program has been used to present a procedure for finding an optimal maintenance scenario for steel-girder bridges on the Korean National Road. Through this bridge maintenance scenario analysis, it is expected that the developed method and program can be effectively used to allow bridge managers an optimal maintenance strategy satisfying various constraints and requirements.

• 한국시스템다이내믹스연구
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• 제1권2호
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• pp.5-31
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• 2000

The summit meeting of the South North Korean leaders was a turning point in the relationships between the two countries. It was followed by the Red-Cross Meeting, Minister-Level Meeting, economic agreements, which have increased the relationship more colorful in both quantities and qualities. However, the half-century period for separation was too long to overcome all the problems by only one event. The two countries have quite different social systems; one politically strong person is governing the North, while many interest groups are involved in political decision making processes in the South. In short, it would take a long time to settle down all the problems residing between the two countries. A system dynamics model is developed to describe the long term dynamics of the relations between the South and North Koreas. As a first attempt, the model focuses only on the diplomatic meeting issues between the South and North. The model aggregates diplomatic issues into 5 categories; economic issues, security issues, infrastructure, cultural issues, and past problems. It assumes that there would not be any dramatic changes between the two countries. It is a conceptual model composed of around 200 variables, and should not be used as a forecast tool. However, it captures most of the logics discussed in the papers and conferences concerning the South and North Korea relations. Many sensitivity studies and Monte Carlo simulations have shown that the simulation results matches with mental models of experts; that is the model can be used as a learning tool or as a secondary opinion until the data required by the model is collected. In order to analyze the current situation, five scenarios are simulated and analyzed; the functional approach, the conditional approach, the balanced approach, the circumstantial approach, and the strategic approach. The functional approach represents that the South makes efforts in the area where the possibility of agreement is high for the next 10 years. The conditional approach is a scenario where the South impose all difficult issues as conditions for resolving other diplomatic issues. The balanced approach is resolving the five issues with the same priorities, while the circumstantial approach is resolving issues which seem to be resolved easily. Finally, another optimum approach has been seek using the system dynamics model developed. The optimum strategy (it is named as the strategic approach) was strikingly different from other four approaches. The optimum strategy is so complicated that no one could find it with mental model(or by just insights). Considering that the system dynamic model used to find the optimum is a simplifind (maybe over simplified) version of the reality, it is concluded that a well designed system dynamics model would be of great help to resolving the complicated diplomatic problems in any kind.

• 한국강구조학회 논문집
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• 제9권3호통권32호
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• pp.457-465
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• 1997

형상최적화는 단면최적화에 비하여 구조물의 중량과 경비를 줄일 수 있다. 많은 양의 애매한 정보가 최적설계 문제의 제약조건에 존재할 수도 있다. 상대적으로 중요한 퍼지정도를 포함한 여러개의 기준을 묘사하고 다루는 것은 매우 어렵고 때로는 애매하다. 본 논문에서는 ${\alpha}$-절단법에 의한 퍼지 구조계의 다목적 형상최적화에 대한 가중치방법을 제안한다. 본 연구의 알고리즘을 2부재 트러스 구조물에 적응하여 그 결과가 검토되었다. 그 결과는 ${\alpha}$-절단법과 체적과 변위에 관한 가중치에 따른 최적해를 얻음으로써 설계자는 실제에 적합한 하나의 해를 택할 수 있음을 보여준다.

• 한국정밀공학회지
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• 제14권12호
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• pp.24-29
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• 1997

Recently, Genetic Algorithm(GA), which is a stochastic direct search strategy that mimics the process of genetic evolution, is widely adapted into a search procedure for structural optimization. Contrast to traditional optimal design techniques which use design sensitivity analysis results, GA is very simple in their algorithms and there is no need of continuity of functions(or functionals) any more in GA. So, they can be easily applicable to wide area of design optimization problems. Also, owing to multi-point search procedure, they have higher porbability of convergence to global optimum compared to traditional techniques which take one-point search method. The methods consist of three genetics opera- tions named selection, crossover and mutation. In this study, a method of finding the omtimum size and topology of drilling machine is proposed by using the GA, For rapid converge to optimum, elitist survival model,roulette wheel selection with limited candidates, and multi-point shuffle cross-over method are adapted. And pseudo object function, which is the combined form of object function and penalty function, is used to include constraints into fitness function. GA shows good results of weight reducing effect and convergency in optimal design of drilling machine.

• Journal of Microbiology and Biotechnology
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• 제24권6호
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• pp.781-787
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• 2014

2-Ketogluconic acid production by Klebsiella pneumoniae is a pH-dependent process, strictly proceeding under acidic conditions. Unfortunately, cell growth is inhibited by acidic conditions, resulting in low productivity of 2-ketogluconic acid. To overcome this deficiency, a two-stage fermentation strategy was exploited in the current study. During the first stage, the culture was maintained at neutral pH, favoring cell growth. During the second stage, the culture pH was switched to acidic conditions favoring 2-ketogluconic acid accumulation. Culture parameters, including switching time, dissolved oxygen levels, pH, and temperature were optimized for the fed-batch fermentation. Characteristics of glucose dehydrogenase and gluconate dehydrogenase were revealed in vitro, and the optimal pHs of the two enzymes coincided with the optimum culture pH. Under optimum conditions, a total of 186 g/l 2-ketogluconic acid was produced at 26 h, and the conversion ratio was 0.98 mol/mol. This fermentation strategy has successfully overcome the mismatch between optimum parameters required for cell growth and 2-ketogluconic acid accumulation, and this result has the highest productivity and conversion ratio of 2-ketogluconic and produced by microorganism.

• 통상정보연구
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• 제13권3호
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• pp.511-541
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• 2011

본 연구에서는 앞으로 있을 한 중 FTA협상 추진 전략을 중국의 낮은 수준의 FTA 체결 선(先)제의에 대한 우리나라의 최적 대응전략 측면에서 고찰하였다. 국제협상 분석 게임모델 중 비협조게임의 기본 모형인 죄수의 딜레마 게임을 기본 틀로 하여 Putnam의 2단계 게임 론을 활용하여 결론을 도출하였다. 향후 한 중 FTA 추진의 전략적 기본원칙은 정부가 주장하는 높은 관세양허 수준의 포괄적 FTA보다는 비록 경제적 효과가 다소 떨어지더라도 가능한 빠른 시일 내 '중간 수준'의 FTA(포괄적이나 전반적으로 낮은 관세양허 방안)를 시작하는 정책을 추진함이 바람직 할 것으로 결론지었다. 이러한 관점에서 한 중 양국이 상대국으로부터의 수입액 중 일정 비율, 가령 70-80%에 해당하는 품목에 대해 협상개시와 함께 관세를 내리는 조기수확 프로그램(EHP: Early Harvest Program)을 활용하는 전략도 한 방법이 될 것이다.

• 전자공학회논문지CI
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• 제39권1호
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• pp.23-34
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• 2002

본 논문에서는 진화전략을 이용하여 빠르게 학습하는 새로운 구조의 뉴로퍼지 시스템을 제안하고 제안한 시스템의 효용성을 입증하기 위하여 비선형 시스템 동정에 응용한 결과를 설명한다. 뉴로퍼지 시스템의 학습 방법으로는 지금까지 주로 변형된 오류역전파 알고리즘과 최적화 기법인 유전자 알고리즘이 많이 사용되어왔으나, 오류역전파 알고리즘은 학습시간이 많이 걸리며 유전자 알고리즘은 해를 유전형 형태로 표현함으로 인하여 미세한 탐색이 힘든 단점이 있었다. 본 논문에서 사용한 진화전력은 해를 표현형의 개체로 나타내어 실수형태로 진화하기 대문에 미세한 탐색이 가능하며 오류역전파 알고리즘에 비해 지역해에 빠질 가능성이 작고 속도가 빠른 장점이 있다. 제안한 뉴로퍼지 시스템을 비선형 시스템 동정에 적용한 결과 학습속도가 빠르며 학습결과도 우수함을 보았다.

• 대한토목학회논문집
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• 제26권6A호
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• pp.1023-1032
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• 2006

본 논문에서는 기존 교량 유지관리방법의 한계를 극복하고 예방유지관리 체계의 구현을 위하여 새로운 교량 유지관리기법을 제안하였다. 제안된 방법은 생애주기비용뿐만 아니라 생애주기성능을 함께 고려하여 열화되는 교량의 최적 유지관리전략을 수립할 수 있다. 교량의 성능변화는 신뢰성에 기초한 안전도와 상태등급을 세분화한 상태지수에 의해 평가되며, 생애주기 비용은 직접유지관리비용뿐만 아니라 도로이용자비용과 파손비용을 고려하여 추정하였다. 교량수명 동안의 성능 및 비용과 관련된 다중목적 조합 최적화 문제인 교량 유지관리 시나리오 집합의 생성을 위해 유전자알고리즘을 적용하였다. 개발된 방법을 실교량에 적용하여 유지관리전략 수립의 과정과 효과를 고찰하였다. 이러한 결과를 통해, 개발된 방법은 유지관리를 위한 의사결정과정에 효과적으로 활용될 수 있을 것으로 판단된다.

• Journal of Microbiology and Biotechnology
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• 제22권2호
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• pp.220-225
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• 2012

In batch culture for Poly(vinyl alcohol) (PVA)-degrading enzyme (PVAase) production by a mixed culture, higher pH (pH 7.5) was favorable for PVAase production at the prophase of cultivation, but lower pH (pH 7.0) was favorable at the anaphase. This situation was caused by the fact that the optimum pH for different key enzymes [PVA dehydrogenase (PVADH) and oxidized PVA hydrolase (OPH)] production is various. The activity and average specific production rate of PVADH reached the highest values at constant pH 7.5, whereas those of OPH appeared at pH 7.0. A two-stage pH control strategy was therefore developed and compared for its potential in improving PVAase production. By using this strategy, the maximal PVAase activity reached 2.05 U/ml, which increased by 15.2% and 24.2% over the fermentation at constant pH 7.5 and 7.0.

• Smart Structures and Systems
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• 제18권3호
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• pp.569-584
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• 2016

This paper presents a method for stochastic modelling of fatigue crack growth and optimising inspection and maintenance strategy for the structural members of steel bridges. The fatigue crack evolution is considered as a stochastic process with uncertainties, and the Gamma process is adopted to simulate the propagation of fatigue crack in steel bridge members. From the stochastic modelling for fatigue crack growth, the probability of failure caused by fatigue is predicted over the service life of steel bridge members. The remaining fatigue life of steel bridge members is determined by comparing the fatigue crack length with its predetermined threshold. Furthermore, the probability of detection is adopted to consider the uncertainties in detecting fatigue crack by using existing damage detection techniques. A multi-objective optimisation problem is proposed and solved by a genetic algorithm to determine the optimised inspection and maintenance strategy for the fatigue affected steel bridge members. The optimised strategy is achieved by minimizing the life-cycle cost, including the inspection, maintenance and failure costs, and maximizing the service life after necessary intervention. The number of intervention during the service life is also taken into account to investigate the relationship between the service life and the cost for maintenance. The results from numerical examples show that the proposed method can provide a useful approach for cost-effective inspection and maintenance strategy for fatigue affected steel bridges.