• International Journal of Naval Architecture and Ocean Engineering
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• 제6권3호
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• pp.685-699
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• 2014

In this study, the dynamic responses of a riser under the combined excitation of internal waves and background currents are studied. A modified Taylor-Goldstein equation is used to calculate the internal waves vertical structures when background currents exist. By imposing rigid-lid boundary condition, the equation is solved by Thompson-Haskell method. Based on the principle of virtual work, a nonlinear differential equation for riser motions is established combined with the modified Morison formula. Using Newmark-${\beta}$ method, the motion equation is solved in time domain. It is observed that the internal waves without currents exhibit dominated effect on dynamic response of a riser in the first two modes. With the effects of the background currents, the motion displacements of the riser will increase significantly in both cases that wave goes along and against the currents. This phenomenon is most obviously observed at the motions in the first mode.

• 한국연안방재학회지
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• 제4권1호
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• pp.7-19
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• 2017

In this study, waves and currents observed by acoustic AWAC, VECTOR and Aquadopp Profiler in Anmok coastal waters were analysed to account for the variability of wave and current and to understand the mechanism of sediment transport generated by wave-induced current in the surf-zone. The monthly variation of wave and residual currents were analysed and processed with long-term observed AWAC data at station W1, located at the water depth of about 18m measured during from February 2015 to September 2016. Wave-induced currents were also analysed with intensive field measurements such as wave, current, suspended sediment, and bathymetry data observed at the surf-zone during in winter and summer. The statistical result of wave data shows that high waves coming from NNE and NE in winter (DEC-FEB) are dominant due to strong winds from NE. But in the other season waves coming from NE and ENE are prevalent due to the seasonal winds from E and SE. The residual currents with southeastern direction parallel to the shoreline are dominant throughout a year except in winter showing in opposite direction. The speed of ebb-dominant southeastern residual currents decreasing from surface to the bottom is strong in summer and fall but weak in winter and spring. By analysing wave-induced current, we found that cross-shore current were generated by swell waves mainly in winter with incoming wave direction about $45^{\circ}$ normal to the shoreline. Depending on the direction of incoming waves, longshore currents in the surf-zone were separated to southeastern and northwestern flows in winter and summer respectively. The variation of observed currents near crescentic bars in the surf-zone shows different direction of longshore and cross-shore currents depending on incoming waves implying to the reason of beach erosion generating the beach cusp and sandbar migration during high waves at Anmok.

• 한국해안·해양공학회논문집
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• 제27권6호
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• pp.382-390
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• 2015

본 연구에서는 SWASH 모형을 이용하여 계절별 이상파랑에 의한 해운대 해수욕장에서 불규칙파의 파랑 변형 및 해빈류 특성을 분석하였다. 개경계에서 불규칙파는 JONSWAP 스펙트럼을 적용하였다. 입사파 조건은 국립해양조사원에서 제공하는 2014년 파랑관측자료를 바탕으로 계절별 대표파를 선정하였다. SWASH에 의한 계절별 해빈류 계산결과는 현장조사 결과와 비교 검토하였다. 하계의 경우 S 계열의 파랑이 지배적이며 동백섬측에서 미포측으로 연안류가 지배적으로 발생하였고 해운대 해수욕장 중앙부근에서는 이안류가 발생하였다. 동계의 경우 ESE 계열의 파랑이 지배적이며 해운대 해수욕장 중앙부근에서 각각 동백섬측과 미포측으로 향하는 연안류가 발생하였다.

• Ocean Systems Engineering
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• 제7권3호
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• pp.275-298
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• 2017

This paper provides a practical stochastic method by which the maximum equilibrium scour depth below a pipeline exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (1996). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases for random waves alone are also suggested.

• Ocean Systems Engineering
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• 제6권2호
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• pp.161-189
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• 2016

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around a vertical pile exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (2002). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases on mild slopes are also suggested.

• Korean Journal of Hydrosciences
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• 제1권
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• pp.73-97
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• 1990

A literature review is made on the numerical models of wave-induced currents. The major processes of the flow system are wave breaking, bottom friction of combined wave-current flow and mixing processes primarily caused by wave breaking as well as the flow fields of waves and currents themselves. The survey is given to each item with great emphasis on numerical implication as well as physical mechanism. As noted is the importance in recent investigations, a brief treatment is also given on the currents driven by random or spectral waves.

• The Korean Journal of Physiology
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• 제27권2호
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• pp.115-122
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• 1993

There is evidence that noradrenaline enhances spontaneous contractions dose-dependently in guinea-pig antral circular muscle. To investigate the mechanism of this excitatory action, slow waves and membrane currents were recorded using conventional microelectrode techniques in muscle strips and the whole cell patch clamp technique in isolated gastric myocytes. On recording slow waves, noradrenaline $(10^{-5}\;M)$ induced the hyperpolarization of the membrane potential, although the shape of the slow waves became tall and steep. Also, spike potentiaIs occurred at the peaks of slow waves. These changes were completely reversed by administration of phentolamine $(10^{-5}\;M),\;an\;{\alpha}-adrenoceptor$ blocker. Noradrenaline-induced hyperpolarization was blocked by apamin $(10^{-7}\;M)$, a blocker of a class of $Ca^{2+}\;-dependent\;K^+$ channels. To investigate the mechanisms for these effects, we performed whole cell patch clamp experiments. Norndrenaline increased voltage-dependent $Ca^{2+}$ currents in the whole range of test potentials. Noradrenaline also increased $Ca^{2+}\;-dependent\;K^+$\;currents, and this effects was abolished by apamin. These results suggest that the increase in amplitude and the generation of spike potentials on slow waves was caused by the activation of voltage-dependent $Ca^{2+}$ channel via adrenoceptors, and hyperpolarization of the membrane potential was mediated by activation of apamin-sensitive $Ca^{2+}\;-dependent\;K^+\;channels$.

• 한국해안해양공학회지
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• 제3권1호
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• pp.54-64
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• 1991

현지해안의 표사이동량을 정확히 예측하기 위해서는, 표사이동의 주외력요소(agitation force)인 다방향불규칙 파랑의 천수변형 특성 및 그들에 의해서 발생하는 표사수송 흐름으로서의 해빈류에 대해서 충분히 파악해 둘 필요가 있다. 그러나, 현재 제안되어져 있는 연안류 및 이안류를 포함하는 해빈류 model은 대부분 규칙파 이론에 근거를 두고 파랑특성을 표현하고 있기 때문에 파랑의 불규칙성 및 방향분산성을 고려한 해빈류에 대한 연구는 극히 제한되어져 있다. 본 연구는 다방향불규칙 파랑에 의한 연안유속의 산정에 관한 기초적 연구로서, 주로 파별해석법에 의한 수치계산법을 제안함과 동시에 그들의 수치해석결과를 평면수리실험과 비교함으로써 그 타당성을 검토하였다.

• 한국연안방재학회지
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• 제4권spc호
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• pp.245-253
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• 2017

In this study, surface currents measured by small lagrangian GPS drifters (Aquadrifter) in Anmok coastal waters were analysed to account for the variability of nearshore surface current and wave-induced current to understand sediment transport mechanism near the crescentic bars in the surf-zone and near Kangneung breakwater and submerged breakwater in Anmok. The 8 times lagrangian drifter experiments were conducted mostly during in 2nd, 3rd, 4th intensive measurements in winter, summer, and spring seasons with long-term wave observation at the station W1. The analysed surface currents near the breakwaters in Anmok show that wave-induced currents at the middle of the submerged breakwater were separated and flowed toward the shoreline but offshore currents were dominant through the channels between the breakwaters. The longshore currents near the shoreline were flowed to the northwest (southeast) depending on the incoming waves from ENE (NNE). The surface nearshore offshore currents were generated mostly by waves and winds in case of high and low wave energy environments. Using the small-size lagrangian surface drifter experiments, we successfully measured longshore and offshore wave-induced currents in the surf-zone and near submerged breakwater close to Kangneung breakwater. The drifter experiment results show the availability of direct observation of nearshore surface currents to understand the mechanism of sediment transport analysing observed wave-induced current and ebb-current in the surf-zone generated by incoming waves and local winds.

• 한국수자원학회논문집
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• 제46권3호
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• pp.245-252
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• 2013

본 연구에서는 다양한 외부흐름에 대한 평탄한 지형을 통과하는 파랑의 반사율을 해석적으로 계산하였다. 수심이 일정한 지형에 외부흐름을 작은 구간의 계단형으로 단순화하였다. 계산에 필요한 적절한 구간의 수와 소멸파 성분의 개수를 제안하였다. 아울러, 외부흐름의 변화와 다양한 양상에 따른 반사율의 특징을 서술하였다.