• 대한기계학회논문집B
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• 제27권1호
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• pp.117-124
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• 2003

Thermal design fur satellite propulsion system has been performed. Overall design requirements and the constitution for propulsion system is described. To meet the thermal design requirements, both a primary and a redundant heater circuit, each with two thermostats placed in series, will protect each hydrazine-wetted components, even if one heater circuit fails to operate. Heater power is turned off if any one of these thermostats is opened at its higher setpoint. Thus, even if one thermostat is failed closed, the second thermostat will turn off the heater. All such components shall be insulated with MLI. Propulsion heater sizing based on the constant worst cold case condition is conducted through thermal analysis. All heaters selected fur propulsion components operate to prevent propellant freezing satisfying the thermal requirements for the propulsion subsystem over the worst case average voltage, i.e. 25 volts.

• ETRI Journal
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• 제29권1호
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• pp.50-58
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• 2007

Robust adaptive beamforming based on worst-case performance optimization is investigated in this paper. It improves robustness against steering vector mismatches by the approach of diagonal loading. A closed-form solution to optimal loading is derived after some approximations. Besides reducing the computational complexity, it shows how different factors affect the optimal loading. Based on this solution, a performance analysis of the beamformer is carried out. As a consequence, approximated closed-form expressions of the source-of-interest power estimation and the output signalto-interference-plus-noise ratio are presented in order to predict its performance. Numerical examples show that the proposed closed-form expressions are very close to their actual values.

• 대한전기학회논문지:시스템및제어부문D
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• 제53권7호
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• pp.501-508
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• 2004

In this paper, a coordinated scheduling algorithm is proposed to reduce end-to-end delay in distributed control of systems. For the algorithm, the analysis of practical end-to-end delay in the worst case is performed priory with considering implementation of the systems. The end-to-end delay is composed of the delay caused by multi-task scheduling of operating systems, the delay caused by network communications, and the delay caused by asynchronous timing between operating systems and network communications. Through some simulation tests based on CAN(Controller Area Network), the proposed worst case end-to-end delay analysis is validated. Through the simulation tests, it is also shown that a real-time distributed control system designed to existing worst case delay cannot guarantee end-to-end time constraints. With the analysis, a coordinated scheduling algorithm is proposed here. The coordinated scheduling algorithm is focused on the reduction of the delay caused by asynchronous timing between operating systems and network communications. Online deadline assignment strategy is proposed for the scheduling. The performance enhancement of the distributed control systems by the scheduling algorithm is shown through simulation tests.

• Journal of Computing Science and Engineering
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• 제7권4호
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• pp.285-299
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• 2013

To enable hard real-time systems to take advantage of multicore processors, it is crucial to obtain the worst-case execution time (WCET) for programs running on multicore processors. However, this is challenging and complicated due to the inter-thread interferences from the shared resources in a multicore processor. Recent research used the combined cache conflict graph (CCCG) to model and compute the worst-case inter-thread interferences on a shared L2 cache in a multicore processor, which is called the CCCG-based approach in this paper. Although it can compute the WCET safely and accurately, its computational complexity is exponential and prohibitive for a large number of cores. In this paper, we propose three counter-based approaches to significantly reduce the complexity of the multicore WCET analysis, while achieving absolute safety with tightness close to the CCCG-based approach. The basic counter-based approach simply counts the worst-case number of cache line blocks mapped to a cache set of a shared L2 cache from all the concurrent threads, and compares it with the associativity of the cache set to compute the worst-case cache behavior. The enhanced counter-based approach uses techniques to enhance the accuracy of calculating the counters. The hybrid counter-based approach combines the enhanced counter-based approach and the CCCG-based approach to further improve the tightness of analysis without significantly increasing the complexity. Our experiments on a 4-core processor indicate that the enhanced counter-based approach overestimates the WCET by 14% on average compared to the CCCG-based approach, while its averaged running time is less than 1/380 that of the CCCG-based approach. The hybrid approach reduces the overestimation to only 2.65%, while its running time is less than 1/150 that of the CCCG-based approach on average.

• 전자공학회논문지A
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• 제29A권3호
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• pp.33-40
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• 1992

In this paper, We designed a 2-stage amplifier for transponder of satellite with dual GaAs FETs NE13783, and performed the worst-case analysis for circuit qualification in the space environment. The bandwidth of amplifier was chosen 11.7-12.2 GHz which is the down link frequency band for domestic Ku-band satellite communication, and the alumina substrate with 25 mil of thickness. The design and optimization of amplifier was achieved by the commercial CAD program TOUCHSTONE and the measurement was performed through the automatic network analyzer.

• Journal of Computing Science and Engineering
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• 제9권4호
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• pp.177-189
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• 2015

High-performance processors using Non-Uniform Cache Architecture (NUCA) are increasingly used to deal with the growing wire delays in multicore/manycore processors. Due to the convergence of high-performance computing with embedded computing, NUCA caches are expected to benefit high-end embedded systems as well. However, for real-time systems that use multicore processors with NUCA caches, it is crucial to bound worst-case execution time (WCET) accurately and safely. In this paper, we developed a WCET analysis approach by considering the effect of static NUCA caches on WCET. We compared the WCET in real-time applications with different topologies of static NUCA caches. Our experimental results demonstrated that the static NUCA cache could improve the worst-case performance of realtime applications using multicore processor compared to the cache with uniform access time.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.77-82
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• 2001

Thermal design for KOMPSAT-2 propulsion system has been performed. Overall design requirements and the constitution for propulsion system is described. To meet the thermal design requirements, both a primary and a redundant heater circuit, each with two thermostats placed in series, will protect each hydrazine-wetted components, even if one heater circuit fails to operate. Heater power is turned off if any one of these thermostats is opened at its higher setpoint. Thus, even if one thermostat is failed closed, the second thermostat will turn off the heater. All such components shall be insulated with MLI. Propulsion heater sizing based on the constant worst cold case condition is conducted through thermal analysis. All heaters selected for propulsion components operate to prevent propellant freezing satisfying the thermal requirements for the propulsion subsystem over the worst case average voltage, i.e. 25 volts.

• 대한토목학회논문집
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• 제31권5D호
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• pp.727-737
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• 2011

본 연구에서는 효율적인 철도사고관리 및 복구작업을 위한 임시복구 시나리오를 개발하였다. 문헌조사 및 전문가 설문조사 결과를 통하여 임시복구 Worst Case 선정시기준이 되는 고려항목과 임시복구 시나리오 수립에 필요한 중요항목(event)을 도출하였으며, 임시복구가 가장 힘든 Worst Case로는 터널구간에서 발생하는 철도사고가 선정되었다. 이는 신속한 임시복구를 위해 좁은 공간에서 체계적이고 효율적인 복구절차를 갖추고 숙련된 복구요원 양성이 필요한 것으로 분석되었다. 또한, 본 연구에서는 통계학적 분석기법을 이용하여 임시복구 시나리오 수립 시 중요항목(event)간 중요도(우선순위)를 선정한 결과 임시복구유형중 시설물 붕괴를 가장 우선적으로 복구하고 선로매몰, 차량탈선 순으로 처리함이 복구시간을 단축할 수 있는 것으로 분석되었다. 이는 복구에 많은 시간이 소요되는 순으로 임시복구가 이루어져야 함을 나타낸다. 임시복구 시나리오는 임시복구 Worst Case, 임시복구유형별 중요항목(event)을 종합하여 표준운영절차(안) 11개를 제안하였다. 이를 활용하여 철도사고 DB관리 및 신속한 사고복구를 통해 정시성을 확보하여 열차지연시간을 최소화하는데 크게 기여할 것이다.

• 화약ㆍ발파
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• 제37권3호
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• pp.13-24
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• 2019

본 논문은 명시적 유한요소 해석을 이용하여 군함이나 수상함 아래의 수중에서 어뢰가 폭발할 때의 파편들의 거동을 조사하기 위하여 작성되었다. 본 연구에서는 LS-DYNA에서 라그랑주-오일러 (ALE) 접근법이라 불리는 유체-구조물 상호작용(FSI) 기법을 적용하여 어뢰파편과 선체의 응답을 관찰하였다. 오일러 모델은 공기, 물, 폭약으로 구성되며, 라그랑주 모델은 파편과 선체로 이루어져 있다. 본 모델링의 핵심은 최악파편이 어뢰로부터 가까운 곳(4.5 m)에 위치한 선체에 파공을 일으킬 수 있는지 여부를 파악하는 데 있다. 시뮬레이션은 별도의 두 단계로 수행되었다. 첫 번째의 예비해석에서는 팽창하는 어뢰의 외피가 찢어지는 데 폭약에너지의 30%가 소모된다는 가정 하에 수중폭발 시의 파편속도에 대해 잘 알려져 있는 실험결과를 토대로 최악파편의 초기속도를 결정하였다. 두 번째의 총괄해석에서는 최악파편이 선체에 부딪치기 직전에 보일 것으로 예상되는 파편의 종단속도를 찾고자 하였다. 그 결과, 주어진 조건 하에서 최악파편의 초기속도는 매우 빠른 것으로 나타났다(400 및 1000 m/s). 하지만 충돌이 발생할 때의 파편과 선체 간의 속도차이는 불과 4 m/s 정도로 매우 작았다. 이 결과는 물에 의한 큰 항력의 영향도 있지만 선체에 부여한 비파괴 조건도 영향을 끼쳤을 것으로 보인다. 하지만 적어도 본 논문에서 가정한 해석조건 하에서는 최악파편의 느린 상대속도로 인하여 선체에 파공이 발생하기는 어려운 것으로 나타났다.

• 한국대기환경학회지
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• 제15권2호
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• pp.151-158
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• 1999

Offsite consequences resulting form worst-case scenarios involving release of toxic substances in the Yochon area were estimated using the ALOHA(Areal Locations of Hazardous Atmospheres) model. Eight toxic substances, including NH3, were considered; five were toxic gases and three were toxic liquids at ambient temperature. For toxic gases, the entire quantity was assumed to be released at a constant rate during a 10-minute period. For toxic liquids, the entire quantity stored in the tank was assumed to be spilled and spread and spread instantaneously to form a pool with a depth of 1cm, and then evaporated over some period of time. Except for phosgene and toluene 2,4-diisocyanate, for which concentration levels corresponding to human health effects are very low, average distances of the area at risk of adverse health effects for a 1- tom release were predicted to be $2.3{\pm}1.1 km$ for the worst-case meteorological conditions and $0.93{\pm}0.69km$ under typical meteorological conditions of the Yochon are. Because a large number of people were predicted to be affected in the current analysis, refined analyses considering both realistic accident scenarios and topographic effects were warranted.