• Journal of Navigation and Port Research
• /
• v.29 no.10 s.106
• /
• pp.853-858
• /
• 2005

Recently, various novel numerical models based on Navier-Stokes equation have been developed for calculating wave motions in the sea with coastal or ocean structures. Among those models, Volume Of Fluid (VOF) method might be the most popular one, and it has been used for numerical simulations of wave motions including complicated phenomena of wave breakings. VOF method, however, needs enormous computation time and large computational storage memories in general, thus it is practically difficult to use this method for calculations in the case of random waves because long and stable computation (e.g for more than 100 significant wave periods) is required to obtain statistically meaningful results. On the other hand if the wave motion is potential motion, Boundary Element Method (BEM), which is a much faster and more accurate method than VOF method, can be effectively used. The aim of this study is to develop a new efficient model applicable to calculations of wave motion and/or wave-structure interactions under random waves. To achieve this, a strictly combined BEM-VOF model has been developed by making the best use of both methods' merits; VOF method is used in a restricted fluid domain around a structure where complicated phenomena of wave breakings may exist, and BEM is used in the other domains far from the disturbance where the wave motion may be assumed to be potential. The verification of the model was performed with numerical results for Stokes' 5th order wave propagation and a random wave propagation.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2005.10a
• /
• pp.153-159
• /
• 2005

Recently, various novel numerical models based on Navier-Stokes equation rave been developed for calculating wave motions in the sea with coastal or ocean structures. Among those models, Volume Of Fluid (VOF) method might be the most popular one, and it has been used for numerical simulations of wave motions including complicated phenomena of wave breakings. VOF method, however, needs enormous computation time and large computational storage memories in general, thus it is practically difficult to use VOF method for calculations in the case of random waves because long and stable computation ( e.g. for more than 100 significant wave periods) is required to obtain statistically meaningful results. On the other hand of the wave motion is potential motion, Boundary Element Method (BEM), which is a much faster and more accurate method than VOF method, am be effectively used. The aim of this study is to develop a new efficient model applicable to calculations of wave motion and/or wave-structure interactions under random waves. To achieve this, a strictly combined BEM-VOF model has been developed by making the best use of both methods' merits; VOF method is used in a restricted fluid domain around a structure where complicated phenomena of wave breakings may exist, and BEM is used in the other domains far from the disturbance where the wave motion may be assumed to be potential. The verification of the model was performed with numerical results for Stokes'5th order wave propagation and a random wave propagation.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.27 no.2
• /
• pp.324-339
• /
• 2021

In this study, we determined the correlation between the wave characteristics and the change in the area of Haeundae Beach, conducted regression analysis between the wave characteristics and the change in beach area, and derived a formula for calculating the change in beach area. The change in beach area was calculated by applying the derived formula to wave observation data corresponding to a period of approximately 10 months, and the formula was subsequently validated by comparing the obtained results with the observed area. It is found that the error associated with the formula for calculating the change in beach area ranges from 1.5 m to 2.7 m based on the average beach width, and the correlation coefficient corresponding to the observed area ranges from 0.91 to 0.94. Furthermore, it is observed that the change in beach area is af ected by the wave direction in the western zone, wave height in the central zone, and wave height and wave period in the eastern zone. These results can contribute to understanding the impact of a coastal improvement project on the beach area fluctuation characteristics of Haeundae Beach and the ef ectiveness of such a coastal improvement project. By applying the aforementioned derived formula to highly accurate wave prediction data, the change in beach area can be calculated and incorporated for predicting significant long-term changes in beach areas. Furthermore, such a prediction can be considered as the basis for making decisions while establishing preemptive countermeasure policies to prevent coastal erosion.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2001.10a
• /
• pp.108-116
• /
• 2001

In this paper, statistical properties of waves in the sea area of Mara-do, Korea are examined based on 1998-1999's wave data from a directional wave buoy which is located in Mara-do. Wave data aquisition rate, monthly maximium, minimum and mean wave heights, frequency of wave direction are summarized. Wave height and period scatter diagrams and n-year return period wave heights are estimated. Wave periods of maximum wave heights are also estimated.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.3
• /
• pp.117-123
• /
• 2016

One of the major characteristics of the swell-like high waves, which occur in the East Sea mostly in winter with large height and long period, is its suddenness associated with the rapid development of high waves from a calm state of sea. To represent such suddenness, in this study, the term sudden high waves is introduced. To propose the criterion of sudden high waves, comparisons were made between the wave measurement data at Gangneung and Wangdolcho for eight years from 2005 and the record of marine accidents and property damage on the coast of Gangwon-do Province and Gyeongsangbuk-do Province during the same period. It was found that most of the accidents occurred when ${\Delta}(H^2L)/{\Delta}t$ was approximately greater than the top 20% or $88.6m^3/hr$, which is therefore proposed as the criterion of sudden high waves. The used variable represents the rate of increase of the wave energy in one wavelength, including not only height and period but also suddenness of high waves.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.40 no.4
• /
• pp.360-366
• /
• 2004

This paper presents a method analyzing the motion of cylindrical buoy moored at 2 points and tensions action on each mooring line under the action of periodic waves. It was found that submersible buoy was more effective than floating one in the severe conditions considering its dynamic motions, wave forces, and mooring line tensions. The wave induced its dynamic responses and mooring line tensions peak when the ratio d/${\lambda}$ of the buoy length d to the waves length ${\lambda}$ was 0.66 due to its natural frequency. The results of this study were in agreement with the existing measurement ones, however, further verifications are needed considering resonance of cylindrical buoy and its displacements to wave height by a series of model tests.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.3 no.2
• /
• pp.92-99
• /
• 1991

A moored body in the sea is subjected to second-order wave forces as well as to linear oscillatory ones. The second-order farces contain slowly-varying components, of which the characteristic frequency can be as low as the natural frequency of horizontal motions of the moored body. As a consequence, the slowly-varying force can excite unexpectedly large horizontal excursion of the body, which may cause a serious damage on the mooring system. In design analysis of Turret-type mooring system which is one of the interesting mooring systems for a floating body. the slowly-varying drift forces and the transient motion of the system during weathervaning are very important. In this paper the slowly-varying drift forces were calculated by using the Quadratic Transfer Function with considering the second order free-wave contributions. Additionaly the transient surge motion of the moored body was simulated with including the roll of the time-memory effect. In this simulation the spring constant of the spread Turret mooring system is updated at every time step for considering the nonlinear effect.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.12 no.4
• /
• pp.190-194
• /
• 2000

Dispersion coefficient influenced by the wave parameters was derived analytically using the vertical velocity distribution based on linear wave theory. It is the depth- and wave period-averaged value and shows larger values in deep water condition than in shallow water condition. It also shows the general pattern of the dispersion coefficient in the oscillatory flows, i.e. it converges the specific value as the wave period is much larger than the vertical mixing time but it approaches zcro as the wave period is much smaller than the vertical mixing time. The dispersion coefficient derived in the condition of the simple assumption have to be modified in order to consider the shallow water condition or the real condition.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.20 no.6
• /
• pp.489-500
• /
• 1987

Annual reproductive cycle of Bluegill, Lepomis macrochirus (RAFINESQUE) were studied in the natural population. Based on these informations, reproductive mechanism of the fish including activation, degeneration and remature were examined under the controlled conditions of temperature and photoperioe. In the natural populations, gonads began to grow with the temperature increase in March ana matured in June, and spawning occurred in July. With the onset of the shorter day-length and the maximum temperature condition in August, the gonads began to degenerate. Resting stage was continued during winter season. In the laboratory-reared population, activation of the gonads was initiated by the complex environmental factors including higher temperature$(>15^{\circ}C)$ and longer photoperiod $(>14L)$. For the maturation, photoperiod of more than 14 hours was critical. Under this condition higher temperature was the only compensative factor. Regeneration of the gonads was induced by higher temperature$(>25^{\circ}C)$ and the shorter photoperiod accelerated the regenerative processes. Even from the resting stage the gonads can be induced to matured stage by the longer photoperiod $(>15L)$. Based on these observations, the reproductive rhythm of this fish is supposed to be artificially controlled.

• Journal of Korea Water Resources Association
• /
• v.46 no.2
• /
• pp.205-218
• /
• 2013

The likelihood of rip current at Haeundae beach according to wave parameters, such as wave height, period, direction, and tidal elevation, was estimated by using numerical simulations with a Boussinesq model, FUNWAVE. To examine the estimation, the rip current occurred on 12th June, 2011 at Haeundae beach was simulated based on observations. For the estimation, the following procedure was carried out. First, extensive numerical simulations of nearshore circulations are performed under various random sea conditions according to the wave parameters. Second, from the numerical results, cross shore components of two-wave-period averaged velocities over the nearshore area were computed, and their seawardly maximum was defined as rip current velocity of the area. Third, using time series of the rip current velocity, we computed the ratio of the simulation time and the time period in which the rip current velocity exceed a threshold velocity for rip-current accidents, and thus the ratio was quantified as the likelihood of rip current at Haeundae beach for the input wave parameters. From the resultant estimations, it was found that the rip current likelihood increases as wave height and period increase, and tidal elevation decreases.