• 대한기계학회논문집A
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• 제20권10호
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• pp.3048-3057
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• 1996

Analysis model containing two inclined surface cracks on semi-infinite elastic body is established and analyzed on the basis of linear fracture mechanics to examine mutual interference of two surface cracks. Muskhelishvili's complex stress functions are introduced and a set of singular integral equations is obtained for a dislocation density function. The stress intensity factors at crack tip are obtained by using the Gerasoulis'method. When two surface cracks are parallel and have the same length, the values of $K_1$and $\Delta K_11$(variation of $K_11$) for crack 1 and crack 2 decrease by the mutual interference of two surface cracks as the distance between the two surface cracks shortens. The effect of mutual interference is remarkable in high friction coefficient. In case that two surface cracks are parallel, the values of $K_1$and $\Delta K_11$for crack 2 decrease as the length ratio ot crack 2 to crack 1 becomes small. As the crack inclination angle rises, the value of $K_1$ and the mutual interference of $K_1$for crack 2 increase and the value of$\Delta K_11$ for crack 1 becomes smaller than that for crack 2.

• 대한토목학회논문집
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• 제14권6호
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• pp.1385-1394
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• 1994

밀도효과(密度效果)를 고려한 물의 유동(流動)에 관한 3차원(次元) 수치모형(數値模型)을 수립하여, 정상수역(靜上水域)으로의 표면온배수(表面溫排水) 확산문제(擴散問題)를 해석하였다. 수립된 수치모형(數値模型)은 수심방향에 대해 정규화(正規化)한 좌표(座標)(${\sigma}$-coordinate)에서 무차원화(無次元化)된 식들을 사용하며, 시간(時間) 적분방법(積分方法)으로는 반음해법(半陰解法)을 사용하여 계산시간의 효율성(效率性)을 도모하였다. 온배수확산(溫排水擴散) 수리실험결과(水理實驗結果)와의 비교를 통하여 모형의 신뢰성(信賴性)을 검토하였으며, 온배수(溫排水) 확산(擴散)(밀도류(密度流)) 계산시 연직확산계수(鉛直擴散係數)와 성층효과(成層效果)를 고려하기 위해 사용되는 안정함수(安定函數)의 여러 형태에 대한 계산결과를 비교하였다. 수립된 모형은 수리실험자료(水理實驗資料)와 일치하는 양호한 계산결과를 보였다. 온배수 확산 모의시 연직(鉛直) 확산계수(擴散係數)의 공간적(空間的) 분포(分布)를 고려해야함을 확인할 수 있었으며, 표면온배수 확산을 정확히 모의하기 위해서는 기존에 널리 사용되는 안정함수(安定函數)가 수정될 필요가 있었다.

• Structural Engineering and Mechanics
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• 제58권1호
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• pp.59-91
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• 2016

Laminated composite shells are commonly used in various engineering applications including aerospace and marine structures. In this paper, using semi-analytical finite strip method, the buckling behavior of laminated composite deep as well as thick shells of revolution under follower forces which remain normal to the shell is investigated. The stiffness caused by pressure is calculated for the follower forces subjected to external fibers in thick shells. The shell is divided into several closed strips with alignment of their nodal lines in the circumferential direction. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness-shear flexibility. Displacements and rotations in the middle surface of shell are approximated by combining polynomial functions in the meridional direction as well as truncated Fourier series with an appropriate number of harmonic terms in the circumferential direction. The load stiffness matrix which accounts for variation of loads direction will be derived for each strip of the shell. Assembling of these matrices results in global load stiffness matrix which may be un-symmetric. Upon forming linear elastic stiffness matrix called constitutive stiffness matrix, geometric stiffness matrix and load stiffness matrix, the required elements for the second step analysis which is an eigenvalue problem are provided. In this study, different parameter effects are investigated including shell geometry, material properties, and different boundary conditions. Afterwards, the outcomes are compared with other researches. By considering the results of this article, it can be concluded that the deformation-dependent pressure assumption can entail to decrease the calculated buckling load in shells. This characteristic is studied for different examples.

• Ocean Systems Engineering
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• 제3권1호
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• pp.35-53
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• 2013

In this study, a hybrid floating structure with cylinder was introduced to reduce the hydrodynamic motions of the pontoon type. The hybrid floating structure is composed of cylinders and semi-opened side sections to penetrate the wave impact energy. In order to exactly investigate the hydrodynamic motions and structural behavior of the hybrid floating structure under the wave loadings, integrated analysis of hydrodynamic and structural behavior were carried out on the hybrid floating structure. Firstly, the hydrodynamic analyses were performed on the hybrid and pontoon models. Then, the wave-induced hydrodynamic pressures resulting from hydrodynamic analysis were directly mapped to the structural analysis model. And, finally, the structural analyses were carried out on the hybrid and pontoon models. As a result of this study, it was learned that the hybrid model of this study was showed to have more favorable hydrodynamic motions than the pontoon model. The surge motion was indicated even smaller motion at all over wave periods from 4.0 to 10.0 sec, and the heave and pitch motions indicated smaller motions beyond its wave period of 6.5 sec. However, the hybrid model was shown more unfavorable structural behavior than the pontoon model. High concentrated stress occurred at the bottom slab of the bow and stern part where the cylinder wall was connected to the bottom slab. Also, the hybrid model behaved with the elastic body motion due to weak stiffness of floating body and caused a large stress variation at the pure slab section between the cylinder walls. Hence, in order to overcome these problems, some alternatives which could be easily obtained from the simple modification of structural details were proposed.

• 대기
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• 제25권4호
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• pp.707-718
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• 2015

This study investigates the characteristics of turbulent fluxes observed at Ieodo Ocean Research Station (IORS) in autumn 2014. The 10 Hz IORS data is quality controlled and calculated to be the 30 minutes turbulent fluxes. The quality control consists of five steps: a weather check, Vickers and Mahrt (VM) sequential check, VM parallel check, flag check, and direction check. Since the IORS is an open-sea station with no orographic influence, there are no significant diurnal variations for the turbulent fluxes and 10 m wind speed. According to stabilities, the unstable and semi-unstable states appear more than 28% and 70% in autumn, respectively and they have strong winds of over $10m\;s^{-1}$. In addition, the turbulent fluxes increase with increasing wind speed. In particular, the latent heat flux and its deviations are clearly shown because the latent heat flux is influenced by the change of both the sea surface roughness and wave height induced by the wind. To demonstrate the changes of the turbulent fluxes before and after typhoon, Vongpong (1419), which is the most intense typhoon affecting the Korean Peninsula in 2014, is considered. The turbulent flux fluctuates in accordance with the location of Vongpong. The turbulent fluxes have a large (small) variation when Vongpong approaches (retreats) at the IORS. The overall results represent that the IORS data helps us understand physical processes related to air-sea interaction by providing the valuable and reliable observed data.

• 한국해양환경ㆍ에너지학회지
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• 제18권2호
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• pp.74-80
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• 2015

통영 연안 양식장 주변 해역에서의 환경특성을 조사하기 위해 2013년 7월부터 12월까지 통영 주변 10개 정점에서 해수와 퇴적물 내의 pH, 용존산소(DO), 용존무기질소(DIN), 용존무기인(DIP), 화학적산소요구량(COD), 산휘발성물질(AVS)에 대해 분석하였다. 양식장 주변 해수의 수질항목들은 계절별에 따른 경향성을 나타내었으며, 퇴적물 속 COD와 AVS를 분석한 결과 수질항목과는 달리 어장으로부터의 거리에 따라 농도가 감소하는 경향을 나타내었다. 이는 본 조사지역에서 반폐쇄성 만에 위치하고 있는 어장 활동에 의해 오염된 유기퇴적물이 비교적 빠른 유속으로 인해 주변 해역으로 분산된 것으로 예측된다.

• Ocean Science Journal
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• 제42권2호
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• pp.103-116
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• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• 한국강구조학회 논문집
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• 제10권2호통권35호
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• pp.221-232
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• 1998

본 연구에서는 지진 등과 같이 소성변형의 범위가 큰 Low-Cycle-Fatigue 범주에서 구조물의 응력변동을 중심으로 사용되는 기존의 피로곡선인 S-N선도 보다 실질적으로 간단하게 측정하여 분석할 수 있는 소성회전각에 의한 피로곡선을 제시하였다. 이는 소성힌지가 생성되는 곳의 소성변형율과 구조물의 소성회전각이 서로 정비례를 이루는 상관관계임을 입증하여, 실험을 통하여 밝혀진 소성변형율의 피로곡선의 기울기와 소성회전각의 기울기가 서로 같은 값을 가짐을 보여 주었다. 이론은 Manson과 Coffin의 변형을 피로곡선을 도입하였고, 실험은 ECCS 주관하에 실시하였으며, 수치해석을 통하여 소성힌지 부위의 위치와 정확한 소성변형율을 산정할 수 있었다.

• 천문학회보
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• 제36권2호
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• pp.141.1-141.1
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• 2011

New CCD BVR light curves of BD And are presented. Our light curves with nearly equal depths for both primary and secondary eclipses show well-defined photometric waves outside eclipse for all of BVR bandpasses. The orbital period is greatly revised as $0.^d92580519$ which is twice longer than that known previously. Sixteen timings from our observations and thirteen ones from the SuperWASP measurements were calculated. All available timings over 76 years, including ours, were analyzed to figure out the dynamical behavior of the system. It was found that the recent CCD O-C residuals varied in a cyclical way with a period of $9.^y18$ and a semi-amplitude of $0.^d0046$. The secondary period of $9.^y18$ is the most shortest one among those which have been ever found in the short period RS CVn binary stars. The periodic variation most likely arises from the light-travel time effect due to a low-mass ($m_3{\sim}0.88\;M_{\odot}$) tertiary companion moving in an orbit with an large eccentricity ($e_3$=0.70) and a low inclination ($i_3{\sim}28^{\circ}$). The Applegate mechanism could not operate properly in both components because the model parameters require too much large luminosity changes of ${\Delta}L/L_{p,s}$ > 10. The new light curves were synthesized using the 2003 version of Wilson-Divinney code. It was found useful to model two huge spots on the surface of the hotter star and a third-light in order to minimize the residuals from the observations. Astronomical basic parameters were deduced from our photometric solution.

• 한국전자파학회논문지
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• 제13권6호
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• pp.538-545
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• 2002

OFDM 통신 시스템에서는 피크전력 대 평균전력비(Peak to Average Power Ratio, PAPR)가 커짐에 따라 전력증폭기에서 비선형 왜곡이 발생되므로 이를 포함한 전송 성능평가가 중요하다. 본 논문에서는 전력증폭기에서 비선형 왜곡이 있는 OFDM 시스템의 성능을 평가하는 새로운 혼합 분석기법을 제안한다. 즉, 제안된 혼합 분석기법은 시뮬레이션을 이용하여 먼저 PAPR의 확률밀도함수와 비선형 잡음의 분산과 평균을 구하고, 이를 이용하여 해석적(analytical) 방법으로 전체 BER을 구하는 방법이다. QPSK 또는 16-QAM 변조방식의 OFDM 시스템에서, 반도체전력증폭기(Solid-State-Power Amplifier, SSPA)의 등가모델을 적용하고, PAPR을 파라미터로 사용하여 IBO 크기에 따른 BER을 분석한다. 제안 방법이 기존의 Monte-Carlo 시뮬레이션에 의한 BER과 거의 동일한 분석 결과를 보이고, 기존 방법보다 BER곡선을 얻는데 필요한 시간이 상당히 감소됨을 보인다