• 대한조선학회논문집
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• 제55권4호
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• pp.321-329
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• 2018

Resonance phenomena occurs at large vertical pump which is operating to cool down the hot steam using sea water in the power plant. To avoid the resonance, the natural frequency needs to be isolated about 20% from motor operating speed. Yet, excessive vibration occurs especially at low tide. At first, natural frequency of the whole pump system and each part is calculated using ANSYS. As it is revealed in the previous journal papers that only circular pipe part is related to resonance, the FSI technique is applied for free vibration analysis. The natural frequency is reduced to 60% (compared to that) of the frequency measured in air as it is similar to other published results. And the frequency obtained by finite element analysis is almost same to that obtained from modal test. Based on the accurate finite element model and analysis, design change is tried to avoid the resonance by changing the thickness of pipe and base supporting plate. In stead of doing optimization process, design sensitivity is computed and used to find such designs to avoid resonance.

• 한국해양학회지
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• 제30권5호
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• pp.512-521
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• 1995

표면혼합층의 단기(2시간~24시간)변화를 조사하기 위하여 대한해협의 한 정점에 서 1983년 10월 12일에서 10월 14일까지 48시간 동안 주로 1시간 간격으로 해양과 기 상에 대한 관측을 실시하였다. 표면혼합층의 깊이와 수온을 시간당 변동률이 평균적으 로 각각 5.2 m/hour, 0.2$^{\circ}C$/hour로 해표면에서의 바람 응력, 부력속과의 상관관계가 매우 적다. 표면 혼합층은 표면혼합층의 수온와 염분이 높을 때 깊고, 낮을 때 얕다. 한편, 표면혼합층 수온의 급격한 하강 또는 상승이 관측되었다. 인공위성 자료와 XBT 자료 분석에 의하면 표면혼합층 수온의 급격한 상승은 고온의 해수의 이류에 의한 일 어남을 알 수 있었다. 위의 결과들은 해류가 비교적 강하고 해수물성이 서로 다른 수 괴가 존재하는 가을철 대한해협에서는 해수의 이류가 표면혼합층의 단기변화에 크게 영향을 준다는 것을 나타낸다.

• Journal of Mechanical Science and Technology
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• 제18권11호
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• pp.1909-1915
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• 2004

The hermetic rotary compressor is one of the most important components of an air conditioning system since it has a great effect on both the performance and the noise and vibration of the system. Noise and vibration occurs due to gas pulsation during the compression process and to unbalanced dynamic force. In order to reduce noise and vibration, it is necessary to identify their sources and transmission path and effectively control them. Many approaches have been tried in order to identify the noise transmission path of a compressor. However, identification has proven to be difficult since the characteristics of compressor noise are complicated due to the interaction of the compressor parts and gas pulsation. In this study, the statistical energy analysis has been used to trace the energy flow in the compressor and to identify the transmission paths from the noise source to the exterior sound field.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.192-195
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• 2004

Products of gridded surface wind and windstress vectors over the world ocean have been constructed by satellite scatterometer data with highly temporal and spatial resolutions. Even if the ADEOS-II/SeaWinds has supplied surface wind data only for short duration in Apr. to Oct. 2003 to us, it permits us to construct a product with higher resolution together with the Qscat/SeaWinds. In addition to our basic product with its resolution of $1^{\circ}\times1^{\circ}$ in space and daily in time, we try to construct products with $1/2^{\circ}\times1/2^{\circ}$ and semi- and quarter-daily resolution. These products are validated by inter-comparison with in-situ data (TAO and NDBC buoys), and also compared with numerical weather prediction(NWP) ones (NCEP reanalysis). Result reveals that our product has higher reliability in the study area than the NCEP's. For the open ocean regions in the middle and high latitudes where there are no in-situ data, we find that there are clear differences between them. Especially in the southern westerly region of 400-600S, the' wind-stress magnitudes by the NCEP are significantly larger than the others, suggesting that they are overestimated. We also calculate wind-stress curl field that is an important factor for ocean dynamics and focus its spatial character in the northwestern Pacific around Japan. Positive curl areas are found to cover from southwest to northeast in our focus region and almost correspond to the Kuroshio path. It is suggested that the vorticity field in the lower atmosphere is related to the upper oceanic one, and thus an aspect of air-sea interaction process.

• 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.

• 한국해양학회지:바다
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• 제22권3호
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• pp.57-68
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• 2017

이어도 종합해양과학기지(IORS, Ieodo Ocean Research Station) 주변 해역은 시 공간적으로 해양 환경 변화가 심하여, 해양-대기교환 과정을 비롯하여 해양 생태계와 기후 변화 연구에 필수적인 해수면온도(SST, Sea surface temperature) 자료의 지속적인 측정이 요구되는 해역이다. 본 연구에서는 이어도 종합해양과학기지에 열적외선 센서를 이용하여 해수면온도 연속 관측이 가능한 시스템을 구축하였다. 자동 대기 보정 및 해양 조건에 따른 방사율 계산이 가능한 해수면온도 추출 알고리즘을 개발하였고, 현장측정 해수면온도 자료와의 비교 및 검증을 통해 정확도를 평가하였다. 2015년 5월 17일부터 26일, 그리고 2016년 7월 15일부터 18일까지 기지에 체류하는 동안 열적외선 관측 시스템으로 측정된 해수면온도와 기지 부착 CT (Conductivity-Temperature) 및 튜브 부착 수온 센서들을 이용하여 현장에서 측정된 해수면온도 시계열을 비교하여 상호상관계수0.72-0.85, 평균제곱근 편차 $0.37-0.90^{\circ}C$의 정확도를 얻었다. 이 시스템은 이어도 종합해양과학기지뿐만 아니라 신안 가거초 및 옹진 소청초 등의 다른 종합해양과학기지에도 쉽게 구축이 가능한 시스템으로써 향후 발사될 인공위성의 해수면온도 산출알고리즘 개발의 테스트사이트나 검보정사이트로 활용될 수 있을 것으로 기대할 수 있다.

• 한국지구과학회지
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• 제43권6호
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• pp.712-736
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• 2022

To understand the characteristics of low-level clouds (CLs), environmental variables are composited on each CL using individual surface observations and six-hourly upper-air meteorologies around the globe. Individual CLs has its own distinct environmental conditions. Over the eastern subtropical and western North Pacific Ocean in JJA, stratocumulus (CL5) has a colder sea surface temperature (SST), stronger and lower inversion, and more low-level cloud amount (LCA) than the climatology whereas cumulus (CL12) has the opposite characteristics. Over the eastern subtropical Pacific, CL5 and CL12 are influenced by cold and warm advection within the PBL, respectively but have similar cold advection over the western North Pacific. This indicates that the fundamental physical process distinguishing CL5 and CL12 is not the horizontal temperature advection but the interaction with the underlying sea surface, i.e., the deepening-decoupling of PBL and the positive feedback between shortwave radiation and SST. Over the western North Pacific during JJA, sky-obscuring fog (CL11), no low-level cloud (CL0), and fair weather stratus (CL6) are associated with anomalous warm advection, surface-based inversion, mean upward flow, and moist mid-troposphere with the strongest anomalies for CL11 followed by CL0. Over the western North Pacific during DJF, bad weather stratus (CL7) occurs in the warm front of the extratropical cyclone with anomalous upward flow while cumulonimbus (CL39) occurs on the rear side of the cold front with anomalous downward flow. Over the tropical oceans, CL7 has strong positive (negative) anomalies of temperature in the upper troposphere (PBL), relative humidity, and surface wind speed in association with the mesoscale convective system while CL12 has the opposite anomalies and CL39 is in between.

• 대기
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• 제26권1호
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• pp.35-45
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• 2016

Initialization of the global seasonal forecast system is as much important as the quality of the embedded climate model for the climate prediction in sub-seasonal time scale. Recent studies have emphasized the important role of soil moisture initialization, suggesting a significant increase in the prediction skill particularly in the mid-latitude land area where the influence of sea surface temperature in the tropics is less crucial and the potential predictability is supplemented by land-atmosphere interaction. This study developed a new soil moisture initialization method applicable to the KMA operational seasonal forecasting system. The method includes first the long-term integration of the offline land surface model driven by observed atmospheric forcing and precipitation. This soil moisture reanalysis is given for the initial state in the ensemble seasonal forecasts through a simple anomaly initialization technique to avoid the simulation drift caused by the systematic model bias. To evaluate the impact of the soil moisture initialization, two sets of long-term, 10-member ensemble experiment runs have been conducted for 1996~2009. As a result, the soil moisture initialization improves the prediction skill of surface air temperature significantly at the zero to one month forecast lead (up to ~60 days forecast lead), although the skill increase in precipitation is less significant. This study suggests that improvements of the prediction in the sub-seasonal timescale require the improvement in the quality of initial data as well as the adequate treatment of the model systematic bias.

• Journal of Ship and Ocean Technology
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• 제12권1호
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• pp.16-27
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• 2008

The interaction between advancing ships and the waves generated by them plays important roles in wave resistances and ship motions. Wave breaking phenomena near the ship bow at different speeds are investigated both numerically and experimentally. Numerical simulations of free surface profiles near the fore bodies of ships are performed and visualized to grasp the general trend or the mechanism of wave breaking phenomena from moderate waves rather than concentrating on local chaotic irregularities as ship speeds increase. Navier-Stokes equations are differentiated based on the finite difference method. The Marker and Cell (MAC) Method and Marker-Density Method are employed, and they are compared for the description of free surface conditions associated with the governing equations. Extra effort has been directed toward the realization of extremely complex free surface conditions at wave breaking. For this purpose, the air-water interface is treated with marker density, which is used for two layer flows of fluids with different properties. Adaptation schemes and refinement of the numerical grid system are also used at local complex flows to improve the accuracy of the solutions. In addition to numerical simulations, various model tests are performed in a ship model towing tank. The results are compared with numerical calculations for verification and for realizing better, more efficient research performance. It is expected that the present research results regarding wave breaking and the geometry of the fore body of ship will facilitate better hull form design productivity at the preliminary ship design stage, especially in the case of small and fast ship design. Also, the obtained knowledge on the impact due to the interaction of breaking waves and an advancing hull surface is expected to be applicable to investigation of the ship bow slamming problem as a specific application.

• 한국지구과학회지
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• 제42권5호
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• pp.536-555
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• 2021

해상풍은 해양의 표층 해류 및 순환, 혼합층, 열속의 변화를 주도하며 해양-대기 상호작용을 이해할 수 있는 중요한 변수이다. 인공위성의 발달에 따라 산란계 관측 자료를 기반으로 산출한 해상풍은 여러 목적으로 광범위하게 사용되어 왔다. 한반도 연안과 같은 복잡한 해양 환경에서 산란계 관측 해상풍은 해양 및 대기 현상 이해에 중요한 요소이다. 따라서 위성 해상풍의 정확도 검증 결과가 다양한 활용을 위하여 중요하게 활용될 수 있다. 본 연구에서는 대표적인 산란계인 MetOp-A/B (METeorological OPerational satellite-A/B)에 탑재된 ASCAT (Advanced SCATterometer) 해상풍 자료를 한반도 주변의 16개 지점에서 2020년 1월부터 12월까지 실측된 해양기상부이 해상풍 자료와 비교하여 해상풍의 정확도를 검증하였다. 해수면으로부터 4-5 m 고도에서 관측된 부이 바람은 LKB (Liu-Katsaros-Businger) 모델을 활용하여 10 m의 중립 바람으로 변환하였다. 일치점 생산 과정 결과 MetOp-A와 MetOp-B에 대하여 5,544개와 10,051개의 일치점을 만들었다. 각 위성 해상풍 풍속의 평균제곱근오차는 1.36 m s^-1와 1.28 m s^-1, 편차는 0.44 m s^-1와 0.65 m s^-1로 나타났다. 산란계의 풍향은 MetOp-A와 MetOp-B에서 각각 -8.03°와 -6.97°의 음의 편차와 32.46°와 36.06°의 평균제곱근오차를 보였다. 이러한 오차들은 해양-대기 경계층 내의 성층과 역학과 관련된 것으로 추정된다. 한반도 주변 해역에서 산란계 해상풍은 특히 풍속이 약한 구간에서 실측 풍속보다 과대추정되었다. 또한 연안으로부터의 거리가 가까워질수록 오차가 증폭되는 특성이 나타났다. 본 연구 결과는 산란계 해상풍 자료를 이용하는 해양-대기 상호작용 및 태풍 연구와 같은 한반도 연안 해역의 예측 모델 발전에 기여할 수 있을 것으로 기대된다.