• 한국지진공학회논문집
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• 제22권4호
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• pp.253-259
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• 2018

Structure behaviors resulting from an earthquake are experimentally simulated mainly through a shaking table test. As for large-scale structures, however, size effects over a miniature may make it difficult to assess actual behaviors properly. To address this problem, research on the hybrid simulation is being conducted actively. This method is to implement numerical analysis on framework members that affect the general behavior of the structure dominantly through an actual scale experiment and on the rest parts by applying the substructuring technique. However, existing studies on hybrid simulation focus mainly on Slow experimental methods, which are disadvantageous in that it is unable to assess behaviors close to the actual level if material properties change depending on the speed or the influence of inertial force is significant. The present study aims to establish a Real-time hybrid simulation system capable of excitation based on the actual time history and to verify its performance and applicability. The hybrid simulation system built up in this study utilizes the ATS Compensator system, CR integrator, etc. in order to make the target displacement the same with the measured displacement on the basis of MATLAB/Simulink. The target structure was a 2-span bridge and an RC pier to support it was produced as an experimental model in order for the shaking table test and Slow and Real-time hybrid simulations. Behaviors that result from the earthquake of El Centro were examined, and the results were analyzed comparatively. In comparison with the results of the shaking table test, the Real-time hybrid simulation produced more similar maximum displacement and vibration behaviors than the Slow hybrid simulation. Hence, it is thought that the Real-time hybrid simulation proposed in this study can be utilized usefully in seismic capacity assessment of structural systems such as RC pier that are highly non-linear and time-dependent.

• 대한전기학회논문지:전력기술부문A
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• 제52권6호
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• pp.316-324
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• 2003

This paper applied Elite-based Simplex-GA hybrid approach combined with Muptipop-GA (ESGA) to determining the location, size and number of capacitors to improve voltage profile and minimize power losses in unbalanced distribution systems. One of the main obstacles in applying GA to complex problems has been the high computational cost due to their slow convergence rate. To alleviate this difficulty, ESGA approach was developed that combines Elite-based Simplex-GA hybrid approach with Muptipop-GA. The objective function formulated consists of two terms: cost for energy losses and cost related to capacitor purchase and capacitor installation. The cost function associated with capacitor placement is considered as a step function due to banks of standard discrete capacities. Its efficiency was proved through the application in IEEE 13 bus and 34 bus test systems and was compared with several methods using GA.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.307-310
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• 2005

본 연구는 프랑스의 Roxel사와 국과연간의 기술용역 계약을 통하여 추진기관 둔감화 기술과 관련된 연구를 수행한 것이다. 추진제는 연소속도가 7 MPa에서 각각 9.8 mm/s, 21.2 mm/s인 두 종류의 HTPB/AP계 혼합형 추진제를 사용하였고, 둔감 점화기와 하이브리드 연소관을 적용하였다. 2회의 Slow Cook-off(SCO) 시험과 1회의 Fast Cook-off(FCO) 시험을 수행하여 MIL STD 2105C에 규정된 반응 형태를 살펴보았다. SCO의 경우에는 두 종류의 추진제를 시용하였을 때 모두 type IV인 폭연 반응을 나타내었고, FCO의 경우에는 type V의 연소 반응을 나타내었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권9호
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• pp.3885-3906
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• 2020

Hybrid fuzzing which combines fuzzing and concolic execution, has proved its ability to achieve higher code coverage and therefore find more bugs. However, current hybrid fuzzers usually suffer from inefficiency and poor scalability when applied to complex, real-world program testing. We observed that the performance bottleneck is the inefficient cooperation between the fuzzer and concolic executor and the slow symbolic emulation. In this paper, we propose a novel solution named EPfuzzer to improve hybrid fuzzing. EPfuzzer implements two key ideas: 1) only the hardest-to-reach branch will be prioritized for concolic execution to avoid generating uninteresting inputs; and 2) only input bytes relevant to the target branch to be flipped will be symbolized to reduce the overhead of the symbolic emulation. With these optimizations, EPfuzzer can be efficiently targeted to the hardest-to-reach branch. We evaluated EPfuzzer with three sets of programs: five real-world applications and two popular benchmarks (LAVA-M and the Google Fuzzer Test Suite). The evaluation results showed that EPfuzzer was much more efficient and scalable than the state-of-the-art concolic execution engine (QSYM). EPfuzzer was able to find more bugs and achieve better code coverage. In addition, we discovered seven previously unknown security bugs in five real-world programs and reported them to the vendors.

• 한국재료학회지
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• 제31권6호
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• pp.367-374
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• 2021

This paper presents the characteristics of gentamicin-loaded into cetyl trimethyl ammonium intercalated montmorillonite (GtM/CTMA/Mt) as a hybrid composite for a slow-released antibacterial delivery systems. The work describes the successful immobilization of gentamicin into the interlayers of surfactant-modified montmorillonite. Physicochemical characterization of the material is carried out by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The kinetics of the gentamicin release is investigated by in vitro study and analyzed based on UV-Vis spectrometry. In addition, antibacterial study is performed towards Klebsiella pneumoniae Staphylococcus aureus, Escherichia coli, and Streptococcus pyogenes. The results show that the gentamicin loading into CTMA/Mt increases the effectiveness of the antibacterial activity, as shown by the higher inhibition zone for all tested bacteria, compared to gentamicin as a positive control. The kinetics study suggests that the gentamicin release obeys the modified Korsmeyer-Peppas model. The physicochemical study and activity test demonstrate the feasibility of the GtM/CTMA/Mt for practical applications.

• Journal of Electrical Engineering and Technology
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• 제3권2호
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• pp.177-183
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• 2008

The particle swarm optimization(PSO) has been shown to converge rapidly during the initial stages of a global search, but around global optimum, the search process becomes very slow. On the other hand, the genetic algorithm is very sensitive to the initial population. In fact, the random nature of the GA operators makes the algorithm sensitive to initial population. This dependence to the initial population is in such a manner that the algorithm may not converge if the initial population is not well selected. In this paper, we have proposed a new algorithm which combines PSO and GA in such a way that the new algorithm is more effective and efficient and can find the optimal solution more accurately and with less computational time. Optimal location of SVC using this hybrid PSO-GA algorithm is found. We have also found the optimal place of SVC using GA and PSO separately and have compared the results. It has been shown that the new algorithm is more effective and efficient. An IEEE 68 bus test system is used for simulation.

• Smart Structures and Systems
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• 제14권6호
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• pp.1031-1054
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• 2014

Real-time hybrid simulation (RTHS) of a stacked wood shear wall retrofitted with a rate-dependent seismic energy dissipation device (viscous damper) was conducted at the newly constructed Structural Engineering Laboratory at the University of Alabama. This paper describes the implementation process of the RTHS focusing on the controller scheme development. An incremental approach was adopted starting from a controller for the conventional slow pseudodynamic hybrid simulation and evolving to the one applicable for RTHS. Both benchmark-scale and full-scale tests are discussed to provide a roadmap for future RTHS implementation at different laboratories and/or on different structural systems. The developed RTHS controller was applied to study the effect of a rate-dependent energy dissipation device on the seismic performance of a multi-story wood shear wall system. The test specimen, setup, program and results are presented with emphasis given to inter-story drift response. At 100% DBE the RTHS showed that the multi-story shear wall with the damper had 32% less inter-story drift and was noticeably less damaged than its un-damped specimen counterpart.

• 한국해양공학회지
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• 제24권5호
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• pp.67-74
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• 2010

Chromate conversion coating is a coating technique used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, tin, and their alloys to slow corrosion. The process uses various toxic chromium compounds, which may include hexavalent chromium. The industry is developing less toxic alternatives in order to comply with substance restriction legislation, such as RoHS. One alternative is to develop a Cr-free coating solution. In this study, eco-friendly, Cr-free solutions (urethane solution S-700, organic/inorganic solution with Si LRO-317) were used. Test specimens were dried in a drying oven at $190^{\circ}C$ for 3, 5, 7, and 9 minutes. Corrosion resistance was evaluated using a salt spray test for 72 hours. The results show that the optimum corrosion resistance was achieved at $190^{\circ}C$ for five minutes for EGI and three or five minutes for HDGI, respectively. The adhesive properties of the two types of coating solutions were superior regardless of drying time.

• 한국구조물진단유지관리공학회 논문집
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• 제27권6호
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• pp.22-29
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• 2023

재료 및 부재의 내진성능평가 실험 시 재하속도와 수직하중은 성능에 중대한 영향을 미칠 수 있다. 반복 가력 및 하이브리드 실험 시 재하속도는 입력 변위와 출력 변위 사이의 시간 지연현상으로 인해 고속으로 제어하기 어려우며 횡방향 변위에 의해 수직하중을 일정하게 유지하는 것이 어려워 일정한 수직하중이 유지되는 고속 및 실시간 실험은 거의 이루어지지 않았다. 본 연구에서는 면진받침의 속도 의존성과 수직하중의 영향을 조사하기 위해 저속 및 고속 반복 가력 실험과 실시간 하이브리드 실험을 수행하였다. 실험에서 수평 변위와 수직 하중의 실시간 제어를 위해 Adaptive Time Series(ATS) 보정 방법과 State estimator가 포함된 FLB System을 구축하였다. 고속 또는 실시간으로 재하되는 수평 변위 제어 속도와 상부구조물에 의한 수직하중은 면진받침의 강도 및 지진 시 거동에 상당한 영향을 미칠 수 있음을 확인하였으며 내진성능평가를 위한 실험 시 실제와 유사하도록 구현되어야함을 알 수 있었다. 본 연구는 내진성능평가를 위해 구축하고 사용된 시스템의 우수한 성능을 보여주며 정확하고 효율적인 내진성능평가가 가능하도록 하였다.

• 한국산학기술학회논문지
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• 제11권12호
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• pp.4997-5006
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• 2010

플래시 메모리 기반의 SSD는 데스크톱 및 이동형 컴퓨터의 저장 장치를 지원하는 우수한 미디어이다. 플래시 메모리는 비휘발성, 낮은 전력소모, 빠른 데이터 읽기속도 등의 특징으로 데스크톱 및 서버용 데이터베이스의 핵심 저장 요소가 되었다. 하지만, 빠른 읽기 연산에 비하여 상대적으로 느리거나 프리징이 있는 SSD의 쓰기 연산 특성을 고려하여 HDD와 RAID에 기반을 둔 기존의 전통적인 스토리지 관리 기법을 개선할 필요가 있다. 이를 위하여, 본 논문은 전통적인 HDD 미러링에 기반을 둔 헤테로-미러링이라는 새로운 저장 장치 관리 기법을 제안한다. 헤테로-미러링 기반 기법은 SSD에서 발생 가능한 프리징 현상을 피하기 위한 쓰기-부하 밸런싱과 쓰기 지연 연산을 통하여 RAID-1 처리 성능을 개선한다. 테스트 결과 제안한 기법은 쓰기 연산 부하와 프리징 부하를 크게 감소시키고, 기존의 SSD-RAID-1 기법의 성능을 18%, 응답 시간을 38% 개선함을 확인하였다.