• Journal of Navigation and Port Research
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• v.27 no.4
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• pp.455-463
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• 2003

Time series of suspended sediment concentration, surface elevation and velocity were measured and analysed to investigate the role of waves and the predominance of infra-gravity wave component for sediment suspension phenomena in the surf zone. For the investigation in detail, we adopted the cross spectral analysis method between suspended sediment concentration and the characteristic values of wave, and ensemble average analysis method about long-period wave component, which is dominant to sediment suspension in the measurement point. The obtained results are summarized as follows: 1)The relationship between suspended sediment concentration and the characteristic values of wave is stronger for the long-period standing wave components(about 60s and 30s where the nodal point of the first mode and the anti-nodal point of the second mode are located at the measurement point, respectively) than the long wave components(about 100s), which have the most energetic power, 2) and also, it is cleared that suspended sediment concentration is increased in the case of the phase, the velocity components of the first mode long-period standing wave(60sec) were accelerated toward on-shore direction, that is, the water surface in offshore side is higher than on-shore side.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.286-297
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• 2018

In the present study, wave measurements at KOGA-W01 were analyzed and then the numerical wind waves simulations have been conducted to investigate the characteristics of wind waves in the Yellow sea. According to the present analysis, even though the location of the wave stations are close to the coastal region, the deep water waves are prevailed due to the short fetch length. Chun and Ahn's (2017a, b) numerical model has been extended to the Yellow Sea in this study. The effects of tide and tidal currents should be included in the model to accommodate the distinctive effect of large tidal range and tidal current in the Yellow Sea. The wave hindcasting results were compared with the wave measurements collected KOGA-W01 and Kyeockpo. The comparison shows the reasonable agreements between wave hindcastings and measured data, however the model significantly underestimate the wave period of swell waves from the south due to the narrow computational domain. Despite the poorly prediction in the significant wave period of swell waves which usually have small wave heights, the estimation of the extreme wave height and corresponding wave period shows good agreement with the measurement data.

• Journal of Ocean Engineering and Technology
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• v.16 no.2
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• pp.21-26
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• 2002

In this study, the characteristics of long period waves are analyzed by field observation at Sokcho harbor on the eastern coast of Korea. firstly. the pressure data obtained from field observation are transformed into water surface elevations and the wave by wave analysis is applied to the observed wave data. also, we select long period waves by setting up the range 30-200sec, and suggest the relationship between ordinary waves and long period waves using the concept of the significant wave height. and, we examine the effects oft he long period waves on the rate of the harbor operation. The observation results demonstrate that the long period waves with heights of 1.2-14.6cm and periods of 35.8-162sec exist at Sokcho harbor. also, we found the rates of harbor operation based on long period waves are 61.8%-99.5% lower than the usual rates of 93.8%-100%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.873-883
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• 2014

This study proposed an estimation method of allowable wave height for loading and unloading of the ship considering ship motion that is affected by ship sizes, mooring conditions, wave periods and directions. The method was examined validity by comparison with wave field data at pier $8^{th}$ in Pohang new harbor. The wave field data obtained with wave height of 0.10~0.75m and wave period of 7~13s in ship sizes of 800~35,000ton when a downtimes have occurred. On the other hand, the results of allowable wave height for loading and unloading of the ship in this method have obtained with wave heights of 0.19~0.50m and wave periods of 8~12s for ship sizes of 5,000, 10,000 and 30,000ton. Thus this method well reproduced the field data respond to various a ship sizes and wave periods. And the results of this method tended to decrease in 16~62% when have considered long wave, and it is decreased in 0~46% when didn't consider long wave than design standards in case of the ship sizes of 5,000~30,000ton, wave period of 12s and wave angle of $75^{\circ}C$. The allowable wave heights for loading and unloading of the ship proposed by design standards are didn't respond to various the ship sizes and wave periods, and we have found that the design standards has overestimated on smaller than 10,000ton.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.147-150
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• 1998

천해에서의 음파전달은 심해와 비교하여 복잡하고 경계면의 영향을 많이 받으며 서해에서 하계의 평균 수온자료로 잔향음을 계산한 결과 해저면 잔향음(reverberation)이 가장 우세한 것으로 나타났다. 특히 서해에서는 하계에 내부파에 의한 강한 수온약층의 생성이 관측되었으며, 이런 현상은 음파전달에 많은 영향을 줄 것으로 예측된다. 내부파를 조석에 의한 장주기와 단주기로 구분하여 적용한 결과 고주파 음원을 사용할 경우 장주기 내부파에 의한 수온약층의 수식변동에 따른 잔향음은 최대 13dB까지 차이가 났으며 단주기 내부파의 경우 수온약층의 하강한 경우 수온약층이 상승한 경우보다 근거리에서 전달손실 변화가 작았다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.141-146
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• 2003

Time seres of suspended sediment concentration, surface elevation and velocity were measured and analysed to investigate the role of waves and the predominance of infra-gravity wave component for sediment suspension phenomena in the surf zone. For the investigation in detail, we adopted the cross spectral analysis method between sediment concentration and the characteristic values of wave, and ensemble average analysis method about long-period wave component, which is dominant to sediment suspension in the measurement point. The obtained results are summarized as follows: 1) The relationship between sediment concentration and the characteristic values of wave is stronger for the long-period standing wave components(about 60s and 30s) than the long wave components(about 100s), which have the most energetic power, 2) and also, it is cleared that sediment concentration is increased in the case of the phase, the velocity components of the first mode long-period standing wave(60sec) were accelerated toward on-shore direction, that is, the water surface in offshore side is higher than on-shore side.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.801-808
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• 2004

In this paper, we proposed the grating parallel plate waveguide structure for converting a linearly polarized wave to a circularly polarized wave. For the design of the polarizer, the moment method and Floquet's theorem are applied under two assumptions that the incident wave is a plane wave and the structure is infinitely periodic. In order for the more precise design, we performed the near-field analysis for the finite polarizer structure using MATLAB. By comparing with the measured results obtained by the near-field arrangement, we verified the correctness of our near-field analysis. By taking the ideal assumptions considered in the initial design procedure into account, newly designed modified dimensions for the polarizer was suggested which give improved performance.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.6
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• pp.443-456
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• 1992

For a linear double shelf bottom topography as in the Yellow Sea, the dispersion relation of coastally trapped waves is derived for the general case Including high-frequency and short waves and for the case of low-frequency and long waves. With linear bottom topography, the governing equation is Bessel's equation for the latter case but Hummer's equation for the former case. Hypergeometric Functions, which are the solutions of Hummer's equation, are derived and converted to various special functions for the limiting cases. On a double shelf topography, the divergence effects of horizontal flow are important for the wave dynamics, irrespective of cross-shelf dimensions, while on a single shelf they are usually neglected when the cross-shelf dimension is much smaller than the Rossby deformation radius. The divergence effect allows the existence of Kelvin wave and reduces the phase speeds of continental shelf waves. Finally, the frictionless eigenfunctions are proved to be orthogonal.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1992.08a
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• pp.28-28
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• 1992

우리 나라 주요항만의 해면 부진동 현상은 일반적인 파랑 보다 주기가 긴 수분 - 수십분의 주기를 갖는 항만고유의 자유진동으로서 폭풍해일 또는 지진 해일과 밀접한 관계가 있으며 장주기파의 Energy 가 항만내에 크게 영향을 미치는 것을 고려 할때 항만건설, 유지를 위한 설계, 선박의 계류, 묘박지의 정온도, 해난사고 및 화재 방지상 대단히 중요시 되어야 할 요소이다.(중략)

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.3-14
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• 1990

For a moored body on the sea surface, incident waves with narrow-banded spectra excite the body oscillations of short and long periods. Since the period of slow oscillations can be as long as the natural period of the moored body in horizontal modes, resonance can occur and resulting large motions may cause significant strains in mooring cables. By using the perturbation method of multiple scales, the large slow motion can be analyzed without solving any second-order potentials explicitly. To the leading order, the flows associated with the fast and slow motions interact only parametrically and thus they can be studied separately. It is found that the slow motion strongly depends on the mooring stiffness. In particular, if the moring stiffness is considerably weak compared to the body inertia, the slow motion is highly amplified near resonance. It is also shown that the slow motion is associated with the generation of long waves.