• 한국해양공학회지
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• 제20권6호
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• pp.41-53
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• 2006

This experimental study investigated the flow characteristics for regular waves passing a rectangular floating structure in a two-dimensional wave tank. The particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The phase average was used to extract the mean flow and turbulence property from repeated instantaneous PIV velocity profiles. The mean velocity field represented the vortex generation and evolution on both sides of the structure. The turbulence properties, including the turbulence length scale and the turbulent kinetic energy budget were investigated to characterize the flow interaction between the regular wave and the structure. The results shaw the vortex generated near the structure corners, which are known as the eddy-making damping or viscous damping. However, the vortex induced by the wave is longer than the roll natural period of the structure, which presents the phenomena opposing the roll damping effect; that is, the vortex may increase the roll motion under the wave condition longer than the roll natural period.

• 한국해양공학회지
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• 제22권6호
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• pp.7-12
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• 2008

The present study numerically investigates the effect of the shape of absorbing revetment on wave overtopping rate under regular and irregular incident waves. At first, the numerical model developed by Hur and Choi(2008), which considers the flow through a porous medium with inertial, laminar and turbulent resistance terms, directly simulates Wave-Structure-Sandy seabed interaction and can determine the eddy viscosity with LES turbulent model in 2-Dimensional wave field (LES-WASS-2D), is validated when compared to experimental data. Numerical simulations are then performed to examine the effect of the shape of absorbing revetment and incident wave conditions on wave overtopping rate. The numerical result shows that the wave overtopping rate decreases with the slope gradient of absorbing revetment under both regular and irregular waves. In addition, the effects of mean grain size and porosity of absorbing revetment, incident wave period and crest height on wave overtopping rate are discussed.

• 한국해안·해양공학회논문집
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• 제25권5호
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• pp.267-275
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• 2013

HadGEM2-AO 기후모델의 기후변화 시나리오 자료와 파랑 모델을 이용하여 기후변화에 따른 북서태평양에서의 미래 파랑 기후를 전망하였다. 21세기말 북서태평양에서 연 평균 풍속이 현재보다 낮아질 것으로 전망됨에 따라 연 평균 유의파고도 낮게 전망되었다. 현재 기후에 비해서 21세기 말 연평균 유의파고는 RCP4.5 시나리오의 경우 2~7% 감소하고, RCP8.5의 경우 4~11% 정도 감소하는 것으로 나타났다. 극한파랑의 경우도 유의파고 및 풍속이 현재에 비해서 감소할 것으로 전망되었다. 계절별로 분석한 결과 겨울철의 극한파랑은 연 극한 파랑과 비슷하게 감소하는 경향을 보인 반면, 여름철의 경우 북서태평양에서는 현재보다 증가할 것으로 나타나 미래에는 태풍의 강도가 강화 될 것으로 전망된다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1983년도 제25회 수공학 연구발표회 논문초록집
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• pp.78-79
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• 1983

It is well known that small amplitude wave theory, a first approximation to the complete theoretical description of wave behavior, yields a maximum investment in mathematical endeavor. But, if the wave amplitude is large, the small amplitude considerations are not valid, and finite amplitude wave theory which retains higher-order terms to obtain an accurate representation of the wave motion is numercal theory. The Stream function wave theory, one of the numerical methods, was developed by Dean for use with asymmetric measured wave profiles and with symmetric theoretical wave profiles. Dalrymple later improved the comjputational procedure by adding two Lagrangian constraints so that more efficient convergence of the iterative numerical method to a specified wave heigh and to a zero mean free surface displacement resulted. This paper introduces in details the Dean and Darlymple Stream Function Method in case of the symmetric theoretical wave, because in design purposes, wave height and wave period are given.

• 한국해양공학회지
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• 제12권3호통권29호
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• pp.75-85
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• 1998

A finite difference model for predicting time-dependent, wave-induced nearshore current is studied. The model includes wave refraction, wave-current interaction, bottom friction and wind effect. This model iteratively solved the linear the linear set of conservation of both mass and momentum, which were time averaged (over one wave period) and depth integrated, for mean velocities and free surface displacement. Numerical simulations of nearshore current under oblique wave attack, and for wave and wind induced current on a longshore periodic beach are carried out. Longshore velocities tend to zero in some distances outside the breaker line. And the peak velocity is shifted shoreward at the breaker line. The results represent the general characteristics of the nearshore current induced by wave.

• 한국해안·해양공학회논문집
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• 제31권5호
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• pp.265-277
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• 2019

파랑관측 자료와 실측된 해안선 위치를 활용하여 맹방해안에 형성되는 beach cusp의 일 년에 걸친 대순환과정과 계절별 특성을 포획모드 Edge waves와 beach cusp의 인과 관계를 중심으로 살펴보았다. 맹방표사 계에 출현하는 beach cusp의 시공을 통한 변화 추이를 가늠하기 위해 threshold 상향통과 법으로 특정된 각 beach cusp의 파장과 진폭을 활용하여 정량화하였으며, 스펙트럼 해석의 경우에는 spectral mean sand wave number를 도입하여 정량화하였다. Spectral mean sand wave number의 시계열자료로부터 sand wave의 융합과 분할이 반복되는 주기를 산출하는 경우 beach cusp의 대순환과정은 일 년에 두 번에 걸쳐 진행되는 것으로 보인다. 해빈면적의 경우 해빈 대순환 과정이 완성되는 일 년을 기준으로 $14,142m^2$ 정도 증가하였으며, quadratic 회귀 분석하여 얻은 평균 해안선의 경우 맹방해안 남단과 북단에서는 18 m, 맹방해안 중앙부에서는 2.4 m 내외로 전진하였다. 해빈면적은 2017.11.26부터 2017.12.22 사이에 $30,345m^2$ 내외로 급속하게 증가하였으며, 이렇게 급속한 해빈면적 증가는 상당히 예외적인 것으로 11월 26부터 12월 22일 사이에 맹방해안으로 내습한 파랑의 성격에 기인하는 것으로 판단된다. 전술한 기간은 온화한 장주기 너울이 지배적이며, 대부분의 파랑이 영의 영각에 가깝게 맹방해안으로 내습한다. 이러한 파랑조건은 주 표사 이송모드가 횡단 표사라는 것을 의미하며 자연 해빈의 자기 치유능력이 횡단 표사를 통해 구현된다는 사실을 상기하면 전술한 해빈면적의 급속한 증가는 영의 영각으로 진입하는 파랑의 경계층 streaming에 의해 해안방향으로 회귀되는 표사가 누적되어 발생하는 것으로 판단된다.

• 한국해양공학회지
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• 제21권1호
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• pp.7-17
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• 2007

Based on the Boussinesq wave model, the wave distribution in the Chagui-Do sea area in Jeju was simulated by applying the directional irregular waves at an incident boundary. The time and spatial variations of monthly mean wave height and period were investigated, which aims to provide basic information on optimal sites for wave power generation. The grid size and time interval of the Boussinesq wave model were validated by examining wave distributions around a surface piercing wall, fixed at sea bottom with a constant slope. Except for the summer season, the significant wave height is dominated by wind waves and appears to be relatively high at the north sea of Chagui-Do, which is open to the ocean, while it is remarkably reduced at the rear sea of Chagui-Do because of its blocking effect on incident waves. In the summer, the significant wave height is higher at the south sea, and it is dominated by the swell waves, which is contributed by the strong south-west wind. The magnitude of significant wave height is the largest in the winter and the lowest in the spring. Annual average of the significant wave height is distinctively high at the west sea close to the Chagui-Do coast, due to a steep variation of water depth and corresponding wave focusing effect. The seasonal and spatial distribution of the wave period around Chagui-Do sea reveals very similar characteristics to the significant wave height. It is suggested that the west sea close to the Chagui-Do coast is the mast promising site for wave power generation.

• 대기
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• 제23권4호
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• pp.401-412
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• 2013

East Asia experienced extremely cold weather in January 2011, while the previous December and the following February had normal winter temperature. In this study National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data are used to investigate the characteristic features observed in the meteorological fields such as temperature, sea-level pressure, geopotential height, and wind during this winter period. In January the planetary-wave pattern is dominated by stationary-wave form in the mid-to-high latitude region, while transient waves are significant in the previous month. To understand the planetary-wave features quantitatively, harmonic analyses have been done for the 500-hPa geopotential height field. In the climatological-mean geopotential heights the wave numbers 1, 2, and 3 are dominant during the whole winter. In January 2011 the waves of number 1, 2, and 3 are dominant and stationary as in the climatological-mean field. In December 2010 and February 2011, however, the waves of number 4, 5, and 6 play a major role and show a transient pattern. In addition to the distinctive features in each month the planetary-wave patterns dependent on the latitude are also discussed.

• 한국지리정보학회지
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• 제22권4호
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• pp.197-214
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• 2019

본 연구에서는 Terra/Aqua MODIS LST(Moderate Resolution Imaging Spectroradiometer Land Surface Temperature)의 Daytime, Nighttime 자료와 기상청 기상관측소 86개 지점에 대한 최고, 최저 및 평균기온을 이용하여 두 자료 사이의 상관성을 분석하고, 한파 및 폭염 발생 기간의 특성을 집중적으로 분석하였다. 모든 자료는 2008년부터 2018년까지 총 11년간 일별로 구축하였으며, Pearson 상관계수(Pearson correlation coefficient, R)와 평균제곱근오차(Root Mean Square Error, RMSE)를 이용하여 상관성 분석을 수행하였다. 시계열 분석 결과, 대상 기간 전체에서 기온과 MODIS LST 간의 변동 양상은 유사하였고, 최고 기온과 MODIS 자료의 R 0.9 이상, 평균기온과 최저 기온과는 0.8 이상으로 기온과 MODIS LST 사이의 상관성은 높은 것으로 나타났다. 특히, 최고 기온은 Terra MODIS LST Daytime과 정확도가 제일 높고, 최저 기온은 Terra MODIS LST Nighttime과 상관성이 제일 높은 것으로 분석되었다. 한파 기간에는 Terra/Aqua MODIS 모두 주간 자료보다 야간 자료의 상관성이 더 높은 것으로 분석되었으며, 특히 Terra MODIS LST Nighttime과의 상관성이 좋은 것으로 분석되었다. 폭염 기간에는 Aqua MODIS LST Daytime 자료가 가장 좋은 것으로 분석되었으나, 전체적인 R이 0.5보다 낮아 추후 활용을 위해서는 식생이나 토지이용, 고도 등 다른 요소를 활용한 추가 분석이 필요할 것으로 판단된다.

• International Journal of Ocean System Engineering
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• 제2권1호
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• pp.50-56
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• 2012

This study investigates flow fields and energy dissipation due to regular wave interaction with a perforated vertical breakwater, through velocity data measurement in a two-dimensional wave tank. As the waves propagate through the perforated breakwater, the incoming wave energy is reflected back to the ocean, dissipated due to very turbulent flows near the perforations and inside the chamber, and transmitted through the perforations of the breakwater. This transmitted energy is further reduced due to the presence of the perforated back wall. Hence most of the energy is either reflected or dissipated in the vicinity of the structure, and only a small amount of the incoming wave energy is transmitted through the structure. In this study, particle image velocimetry (PIV) technique was employed to measure two-dimensional instantaneous velocity fields in the vicinity of the structure. Measured velocity data was treated statistically, and used to calculate mean flow fields, turbulence intensity and turbulent kinetic energy. For investigation of the flow pattern, time-averaged mean velocity fields were examined, and discussed using the cross-sections through slot and wall for comparison. Flow fields were obtained and compared for various cases with different regular wave conditions. In addition, turbulent kinetic energy was estimated as an approach to understand energy dissipation near the perforated breakwater. The turbulent kinetic energy was distributed against wave height and wave period to see the dependence on wave conditions.