• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.69-84
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• 2020

Natural shoreline repeats its re-treatment and advance in response to the endlessly varying sea-conditions, and once severely eroded under stormy weather conditions, natural beaches are gradually recovered via a boundary layer streaming when swells are prevailing after storms cease. Our understanding of the boundary layer streaming over surf-zone often falls short despite its great engineering value, and here it should be noted that the most sediments available along the shore are supplied over the surf-zone. In this rationale, numerical simulation was implemented to investigate the hydraulic characteristics of boundary layer streaming over the surf zone in this study. In doing so, comprehensive numerical models made of Spatially filtered Navier-Stokes Eq., LES (Large Eddy Simulation), Dynamic Smagorinsky turbulence closure were used, and the effects of turbulence closure such as Dynamic Smagorinsky in LES and k-ε on the numerically simulated flow field were also investigated. Numerical results show that due to the intrinsic limits of k-ε turbulence model, numerically simulated flow velocity near the bottom based on k-ε model and wall function are over-predicted than the one using Dynamic Smagorinsky in LES. It is also shown that flow velocities near the bottom are faster than the one above the bottom which are relatively free from the presence of the bottom, complying the typical boundary layer streaming by Longuet-Higgins (1957), the spatial scope where boundary layer streaming are occurring is extended well into the surf zone as incoming waves are getting longer. These tendencies are plausible considering that it is the bottom friction that triggers a boundary layer streaming, and longer waves start to feel the bottom much faster than shorter waves.

• Proceedings of the Korea Water Resources Association Conference
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• 2001.05b
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• pp.1212-1217
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• 2001

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.1
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• pp.16-30
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• 1997

Application of digital filter to the wave analysis is studied using the observed data by wave gauge. Sea wave data obtained from wave gauge always include long wave frequency components. In order to estimate the sea wave parameters, we must re-analyzed wave data by using a digital filter and the concept of mean sea level correction method. By the wave by wave analysis and spectral methods, sea wave parameters on the basis of wave data obtained by the conventional method and digital filter are compared. The best-fitted design filter determined by the necessary conditions of frequency responses, can be obtained by calculating various transfer functions. Thus, to get the best the digital filter design, both Butterworth filter and Savitzky-Golay filter of digital filter are used in the frequency and time domain, respectively. Three cases of observation wave data are calculated by applying digital filter. The components of different frequency bands in the surf zone are coexisted in three cases. The wave data for wind wave components is computed using the digital filter the surf zone and off-surf zone, and based on the filtered data, wave parameters are calculated by the spectral analysis and wave by wave analysis methods, respectively. As a results, when sea wave data observed by wave gauge are analyzed, the Savitzky-Golay method is recommended which can well appear cut-off frequency by experimental choosing filter length in the time domain. The better mean sea level correction method is the Butterworth filter in the frequency domain.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.498-504
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• 2016

In this study, to predict the effect of beach nourishment at Haeundae Beach, the waves and wave-induced currents were compared before and after beach nourishment using the XBEACH model. Representative wave conditions were determined for the data observed during 2014 (KHOA). Then, the Hs,max and Hs,1/10 values, and their prevalent directions, were used in the numerical modeling input data. A variable grid system was used for the $5km{\times}2.5km$ model areas, and irregular waves based on the JONSWAP spectrum were given as incident wave conditions. In the summer season, eastward wave-induced currents were developed along the beach by the incident wave direction. Before the beach nourishment, the maximum speed around the surf zone was 1.2-1.5 m/s in the central zone of the beach, whereas the maximum speed increased to 1.4-1.6 m/s at the same areas when the currents toward Mipo Harbor were blocked as an effect of the groins after the beach nourishment. In the winter season, westward wave-induced currents were developed along the beach by the incident wave direction. After the beach nourishment, the maximum current speed increased slightly around the surf zone in the central area of the beach, and the littoral current speed decreased at the submerged breakwaters located at Dongbaek Island. As a result, after the beach nourishment, the maximum wave-induced currents increased about 10% in the surf zone of the central area of the beach.

• Water Engineering Research
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• v.1 no.3
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• pp.187-197
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• 2000

This paper describes an adaptive quadtree-based 2DH wave-current interaction model which is able to predict wave breaking, shoaling, refraction, diffraction, wave-current interaction, set-up and set-down, mixing processes (turbulent diffusion), bottom frictional effects, and movement of the land-water interface at the shoreline. The wave period-and depth-averaged governing equations are discretised explictly by means of an Adams-Bashforth second-order finite difference technaique on adaptive hierarchical staggered quadtree grids. Grid adaptation is achieved through seeding points distributed according to flow criteria(e.g. local current gradients). Results are presented for nearshore circulation at a sinusoidal beach. Enrichment permits refined modelling of important localised flow features.

• 한국해양학회지
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• v.23 no.2
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• pp.53-61
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• 1988

A capacitance wavestaff system was devised, which is suitable for the wave measurement near to surf zone. Laboratory tests show that the performance of the wavestaff is not significantly affected by the sea water characteristics such as temperature and salinity, and output signals of the wavestaff are linearly proportional to sea surface elevations. The major error source of the wavestaff system is the improper setting of the wavestaff in field experiment.

• 한국해양학회지
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• v.30 no.6
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• pp.523-528
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• 1995

The mysids, Archaeomysis kokuboi and Acanthomysis sp., clearly exhibited the diel patterns of interspecific horizontal migration in the surf zone at a sandy shore in Yongil Bay, eastern Korea. Shoreward migration of Acanthomysis sp. at sunset resulted in the presence of significantly high numbers of mysids after dark at the bottom of 1 m depth. At first light, Acanthomysis sp. moved back to deeper water of>1 m depth in conjunction with a reverse migration by A. kokuboi. In the afternoon, A. kokuboi moved to offshore, then these species remained there. Although A. kokuboi has been considered an intertidal species in the exposed beaches with strong wave action, this is not the case in a sandy beach of Yongil Bay. We suggest that evidence for behavioral adaptation comes from the response of k. kokuboi to the sheltered beaches with weak wave action. The habitat shifts presumably provide this species with high availability of food materials in the surf zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.151-158
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• 1990

Various factors may contribute on the mixing processes in the surf zone formed by irregular waves. The turbulence motion driven by wave breaking may be one of the major causes, the effect due to spatial variation on current velocity be a secondary one, and the additional process may result from the irregular superposition of radiation stresses or wave breaking dissipation incurred by random breaking waves in a broadened surf zone. In the present study a numerical model of spectral waves and induced currents was developed using a superposition technique with ${\kappa}-{\varepsilon}$ closure for mixing process and applied to a field situation of longshore current generated by spectral waves on a uniform beach. It was found from the application that the surf-zone mixing processes formed by irregular waves can be well described by using ${\kappa}-{\varepsilon}$ equations if the source of ${\kappa}$ is properly represented. The nonlinear energy transfer was also found to have some influence on the velocity profile of longshore current particularly in very shallow water region near coast.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.766-772
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• 2016

The composition of the diet of juvenile barbel steeds, Hemibarbus labeo was studied using 67 specimens collected in August, 2004 from the surf zone of the Nakdong river estuary. The fish examined ranged from 5.1 to 9.7 cm in standard length (SL). Hemibarbus labeo was found to be carnivorous and consumed mainly amphipods, with teleosts, polychaetes, and shrimps following. They showed size-related changes in diet. Small individuals (< 6.4 cm SL) mainly consumed amphipods. As fish size increased, the portion of amphipods consumed decreased, while a reverse trend was evident for teleosts. It was also observed that Hemibarbus labeo consumed more amphipods and polychaetes during the day, while fish served as their main prey during the night.

• Korean Journal of Ichthyology
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• v.13 no.1
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• pp.32-39
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• 2001

Surf-zone fishes in Daechon Beach, situated at the mouth of Cheonsu Bay, Korea, were collected by a beach seine during the spring and neap tides in August 1999. Short-term variation in species composition was analyzed based on tidal range, tidal level, and time of day. Of 24 species identified, juvenile pelagic fishes predominated in the number of individuals captured. Wilcoxon signed-rank test revealed that the number of individuals was significantly higher during the spring tide than during the neap tide. During the spring tide the fishes were more abundant at the low level than at the high level, while during the neap tide there was no significant difference. The mean density of pelagic fishes did not show significant differences between high and low tides. Demersal fishes were caught mainly in the water below the low level of the neap tide.