• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.88-91
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• 2007

In the shape design optimization of an airfoil, the shape function has been used to find the optimal airfoil shape for given conditions. The parameters determining the airfoil shape are used in the shape design optimization as design variables. However, they usually don't have physical meaning. The PARSEC (Parametric Shapes) function is a recently proposed shape function and its parameters have the physical meaning. In this study the usefulness of the PARSEC is tested for the RAE2822 airfoil in the transonic flow region to reduce the shock strength and the result is compared with Hicks-Henne function. The optimized airfoils reduce the shock strength and they show similar result.

• 한국컴퓨터정보학회논문지
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• 제11권2호
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• pp.35-42
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• 2006

본 논문에서는 Parsec을 이용하여 병렬디지털신호처리용 분산공유메모리 다중처리시스템의 성능 분석을 위한 시뮬레이터를 구현한다. 이 시뮬레이터의 특징은 TMS320C6701 DSP 칩의 DMA 기능과 빠른 접근시간을 가진 지역메모리를 사용하는 시스템의 시뮬레이션에 적합하다는 것이다. 또한 시스템의 성능 매개변수 수정과 하드웨어 구성요소들에 대한 재구성이 쉽기 때문에 다양한 실행 환경에서 시스템의 성능을 분석할 수 있다. 시뮬레이션에서는 DSP 알고리즘에서 널리 사용하는 FET, 2D FET, Matrix Multiplication, Fir Filter를 사용하여 프로세서의 수 데이터 크기, 하드웨어 요소의 변화에 따른 실행 시간을 측정한다. 그리고 그 결과를 비교함으로써 본 논문에서 구현한 시뮬레이터의 성능을 검증한다.

• 한국전산유체공학회지
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• 제17권2호
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• pp.28-34
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• 2012

In this study, the reliability-based design optimization of the airfoil was performed. PARSEC function was used to consider the uncertainty of the aerodynamic shape for the reliability-based shape optimization of airfoils. Among various reliability analysis methods, the moment method was used to compute the probability of failure of the aerodynamic performance. The accuracy of the reliability analysis was compared with other methods and it was found that the moment method predicts the probability of failure accurately. Deterministic and reliability-based optimizations were performed for the shape of the airfoil and it was demonstrated that reliability-based optimum assures the aerodynamic performances under uncertainties of the shape of the airfoil.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.50-54
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• 2010

In this study, reliability-based design optimizations of airfoils were performed. PARSEC function was used to consider the uncertainty of the aerodynamic shape for the reliability-based shape optimization of airfoils. Among aerodynamic performance. The accuracy of the reliability analysis was compared with other method and it was found that the moment method predicts the probability accurately. Deterministic and reliability-based optimizations were performed for shape of the RAE2822 airfoil and it was demonstrated that reliability-based optimizations the aerodynamic performances under uncertainties of the shape of the airfoil.

• 컴퓨터교육학회논문지
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• 제17권1호
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• pp.107-115
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• 2014

본 논문은 다중코어의 성능을 평가하고 분석하기 위해 TILE-Gx36(Gx36) 다중코어 프로세서를 사례로 연구하였다. Gx36의 성능 평가는 비교적 최신 병렬 벤치마크인 PARSEC을 이용하였고, 성능 분석을 돕기 위한 비교 시스템으로 인텔의 Core i7 (i7)과 Atom을 사용하였다. 실험결과 2의 제곱으로 동시에 수행 가능한 스레드를 발생시켰을 때, Gx36은 i7보다 평균 2.73배 낮은 성능을 보였으며, Atom보다는 평균 1.93배 높은 성능을 보였다. Gx36은 비교 프로세서보다 상대적으로 큰 Last-Level Cache(LLC)를 갖고 있음에도 불구하고, 가장 많은 LLC miss를 발생시켰다. 이는 Gx36이 기대치 이하의 성능을 보이는 주된 이유로 판단되며, DDC가 일반적 고성능 컴퓨팅을 위한 캐시구조로 적절하지 않음을 보여준다. 다중코어 시스템의 실측을 통한 성능평가는 향후 다중코어 구조개선 및 올바른 방향 설정을 위한 객관적인 자료를 제공한다.

• 천문학회보
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• 제36권2호
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• pp.56.1-56.1
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• 2011

We investigate the hydrodynamics of gas clouds in the central few hundred parsecs of the Galaxy. Non-axisymmetry (elongation) of the Galactic bulge can form a reservoir of dense molecular clouds at around two hundred parsecs from the center through the X1-X2 orbit transfer, and the star formation that has been sustained for the lifetime of the galaxy can build up a nuclear bulge there. If the nuclear bulge is elongated, this again can transport the gas there down to the central few parsecs region. We perform a series of 3-D hydrodynamic simulations that consider a potential for this "nested bar", cooling/heating, star formation and supernova feedback, and estimate the efficiency of the gas inflow down to the central parsec region.

• 천문학회보
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• 제40권2호
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• pp.36.3-37
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• 2015

4C39.25 (0923+392) is a distant radio loud AGN placed at redshift 0.695. The motivation of our work is peculiar properties 4C39.25. Firstly, it has a conspicuous distinction of jet direction between kilo-parsec scale observation made by VLA (Kollgaard et al. 1990) and the parsec scale observation by VLBA (Kellermann et al. 1998). This might indicate episodic-jet activity which recently turned on. This object currently shows two stationary compact parsec-scale components which are bright jet component on east and less luminous core on west. Also, it is known that there have been superluminal jet components which are flowing from the core toward east, and then merging with the bright jet component (Marscher et al. 1991, Alberdi et al. 2000, Lister et al. 2013). Although 4C39.25 seems to be a blazar-like source having broad emission lines (SDSS) and superluminal motion, its property that jet component is brighter than the core is different from ordinary blazars. Furthermore, it has young radio galaxy-like properties such as non-variation in total flux (Alberdi et al. 1997, 2000, MOJAVE database) and high frequency peak at spectral energy distribution (Orienti et al 2007). Such complex properties led us to make recent observations to reveal precise properties and new changes of the source. We used Korean VLBI Network (KVN) and VLBI Exploration of Radio Astronomy (VERA) Array (KaVA) which provide high-frequency (23GHz and 43GHz) and high spatial resolution (1.2mas and 0.6mas). Therefore, this system is suitable for morphological and physical research on parsec scale structure. We present results for several epochs observed during 2013 to 2014, mainly focusing on morphological changes of 4C39.25 using KaVA images.

• 한국항공우주학회지
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• 제41권7호
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• pp.509-515
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• 2013

본 연구에서 익형 형상 설계를 위해 전역적 다목적 최적화 기법인 적응영역 다목적 유전자 알고리즘 코드를 개발하였다. 저마하수에서 최대 양력과 순항조건에서 최대 양항비를 동시에 만족시키기 위해 목적함수로 양력계수와 양항비를 선정하였으며, 익형 형상 설계를 위해 PARSEC 기법을 이용하였다. 그 결과 참조 익형 대비 나은 공력 특성을 나타내는 2개의 익형이 선택되었으며 최대 양력과 양항비는 첫 번째 익형에 대해 약 4.89%, 5.38% 증가하였으며, 두 번째 익형에 대해 약 7.13%, 4.33% 증가하였다.

• 천문학회보
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• 제41권1호
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• pp.37.1-37.1
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• 2016

Jets of compact radio sources are highly relativistic and Doppler boosted, making studies of their intrinsic properties difficult. Observed brightness temperatures can be used to study the intrinsic physical properties of the relativistic jets. The intrinsic properties of relativistic jets depend on inner jet models. We aimed to observationally test the inner jet models. The very long baseline interferometry (VLBI) cores of compact radio sources are optically thick at a given frequency. The distance of the core from the central engine is inversely proportional to the frequency. Under the equipartition condition between the magnetic field energy and particle energy densities, the absolute distance of the VLBI core can be predicted. We compiled the brightness temperatures of VLBI cores at various radio frequencies of 2, 8, 15, and 86~GHz. The brightness temperatures in the rest frame were investigated in the sub-parsec regions of the compact radio sources. From the vicinity of the central engine, the brightness temperatures increased slowly and then rose with steeper slope, indicating that the Lorentz factor increases along the jet. This implies that the jets are accelerated in the (sub-)parsec regions from the central engine.

• 천문학논총
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• 제30권2호
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• pp.429-432
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• 2015

We present a kinematic study of the parsec-scale radio jet in OJ 287, one of the most studied BL Lac objects, during ${\gamma}$-ray flares, to explore the relation between parsec-scale radio jet activity and ${\gamma}$-ray emission. The 22-GHz light curve of OJ 287 show three obvious flare events around 2011 May, 2011 October, and 2012 March. The second radio flare occurred during the ${\gamma}$-ray flaring period, and the third radio flare seemed to precede the ${\gamma}$-ray flare by one month. One jet component moved outward with respect to the core component with an apparent superluminal speed (~ 11c) from 2010 November to 2011 November. Then it changed direction, moving apparently inward in 2011 November, when the ${\gamma}$-ray flare occurred. The observed apparent inward motion of the jet at 22 GHz could be caused by a new jet component, unresolved at 22 GHz, in the innermost region.