• 한국해양공학회지
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• 제37권2호
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• pp.68-79
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• 2023

Even though submerged breakwater reduces incident wave energy, it redistributes the coastal area's wave-induced current, sediment transport, and morphological change. This study examines the coastal hydrodynamics and the morphological response of a wave-dominated beach with submerged breakwaters installed through field observation and quasi-3D numerical modeling. The pre-and post-storm bathymetry, water level, and offshore wave under storm forcing were collected in Bongpo Beach on the East coast of Korea and used to analyze the coastal hydrodynamic response. Four vertically equidistant layers were used in the numerical simulation, and the wave-induced current was examined using quasi-3D numerical modeling. The shore normal incident wave (east-northeast) generated strong cross-shore and longshore currents toward the hinterland of the submerged breakwater. However, the oblique incident wave (east-southeast) induced the southeastward longshore current and the sedimentation in the northeast area of the beach. The results suggested that the incident wave direction is a significant factor in determining the current and sediment transport patterns in the presence of the submerged breakwaters. Moreover, the quasi-3D numerical modeling is more appropriate for estimating the wave transformation, current, and sediment transport pattern in the coastal area with the submerged breakwater.

• 한국해양공학회지
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• 제37권6호
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• pp.225-237
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• 2023

In this study, numerical simulations for a single fixed truncated circular cylinder in regular waves were conducted to investigate the nonlinear wave run-up under various dampers and wave period conditions. The present study used the volume of fluid (VOF) technique to capture the air-water interface. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation with the k- 𝜖 turbulence model was solved using the commercial computational fluid dynamics (CFD) software STAR-CCM+. First, a systematic spatial convergence study was conducted to assess the performance and precision of the present numerical wave tank. The numerical scheme was validated by comparing the numerical results of wave run-up on a bare truncated cylinder with the experimental results, and a good agreement was achieved. Then, a series of parametric studies were carried out to examine the wave run-up time series around the truncated cylinder with single and dual dampers in terms of the first- and second-order harmonic and mean set-up components. Additionally, the local wave field and the flow velocity vectors adjacent to the cylinder were evaluated. It was confirmed that under short wave conditions, the high position of the damper led to a noticeable increase in the wave run-ups with significant changes in the first- and second-order harmonic components.

• 한국해안·해양공학회논문집
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• 제34권6호
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• pp.177-187
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• 2022

본 연구는 2020년 해양수산부에서 제시한 개정된 천해설계파 추산방법인 바람장을 이용하여 부산항 신항을 대상으로 태풍 내습 시 설계파를 추산하고 파랑 관측자료와의 검증을 통해서 신뢰할 수 있는 천해설계파 산출방법을 제안하였다. 부산항 신항에 영향을 미친 태풍에 대해서 현업에서 일반적으로 많이 사용하고 있는 태풍 바람장과 SWAN 수치모델을 이용하여 태풍파를 추산한 결과 태풍 KONG-REY(1825), MAYSAK(2009)을 제외하고 재현성이 불량한 것으로 나타났다. 특히 부산항 신항에 가장 크게 영향을 미쳤던 태풍 MAEMI(0314)의 경우 최대유의 파고가 파랑 관측치에 비해서 약 35.0% 작게 추산되었다. 이에 바람장을 보정한 방법과 Boussinesq 방정식 수치모델을 이용하는 방법을 각각 적용하여 태풍파 재현성 개선방안을 검토하였다. 검토결과 바람장을 보정한 경우는 바람장 보정전과 동일하게 재현성이 떨어지는 것으로 나타났으나, 바람장 자료와 SWAN 모델 실험결과 그리고 Bou ssinesq 수치모델을 연계하는 방법으로 태풍 MAEMI(0314) 내습 시 태풍파를 추산한 결과 파랑 관측치와 최대유의파고가 유사하게 나타나 재현성이 양호한 것으로 검토되었다.

• 한국해양공학회지
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• 제32권2호
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• pp.123-130
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• 2018

The present study investigated the validity of an equilibrium shoreline empirical formula for real phenomena. Among three types of equilibrium shoreline formulas, Hsu's parabolic type static formula was employed, which is well-known and the most practical for shoreline estimation after coastal or harbor structure construction. The wave data observed at Maengbang beach and the CERC formula on longshore sediment transport were used in the present investigation. A comparison study was only conducted for the case of a shoreline change after the construction of a groyne. Reasonable agreement was seen between the observed wave data and the data obtained under a wave angle spreading function S = 3.5. However, significant changes were observed when S increased. Thus, careful application is required when using Hsu's formula.

• 물과 미래
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• 제10권1호
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• pp.101-117
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• 1977

The statatistical characteristics and spectra of sea waves at Mookho were analysed by several statistical methods. As the results, the following conclusions are obtained: 1. Values of surface elevation of sea wave are better fitted to Gram Charlier distribution than Gaussian distribution. This proves that sea waves have not only characters of irregularity but also non-linearity. 2. Distribution of maxima of surface elevation practically follows the distribution of Cartwright and Longuet-Higgins, also spectral width parameter is found to be increased with the increase of root mean square of surface elevation. 3. Sea wave may have spectrum of broad frequency band, however distributions of wave heights and periods follow the Rayleigh distribution which is derived from the assumption of narrow frequency band. 4. Ratios among mean wave heights from observed data show good agreements with theoretical values from Rayleigh distribution. 5. Spectral density and spectral width parameter increase with increase of wind velocity. And wave period at optimum band gas higher value than significant wave period by about 10 percent.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1989년도 춘계학술대회
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• pp.15-18
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• 1989

This paper presents a new algorithm for P-wave detection in the ECG signal. We detect the peak and valley point using significant point extraction algorithm with 9-point derivative. Because P-wave duration is changed according to heart-rates, we search for the R-peak and calculate the R-R interval time prior to the determination of P-wave duration threshold values in order to actively adapt to the change of P duration. We determine the parameters for P-wave detection and then P-peak, P-onset and P-offset are detected by these parameters. The results obtained from the proposed algorithm have detected successively P-wave almost more than 90%.

• 비파괴검사학회지
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• 제21권4호
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• pp.371-382
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• 2001

The recognition of such natural wave guides as plates, rods, hollow cylinders, multi-layer structures or simply an interface between two materials combined with an increased understanding of the physics and wave mechanics of guided wave propagation has led to a significant increase in the number of guided wave inspection applications being developed each year. Of primary attention Is the ability to inspect partially hidden structures, hard to access areas, and teated or insulated structures. An introduction to some physical consideration of guided waves followed by some sample problem descriptions in pipe, ice detection, fouling detection in the foods industry, aircraft, tar coated structures and acoustic microscopy is presented in this paper. A sample problem in Boundary Element Modeling is also presented to illustrate the move in guided wave analysis beyond detection and location analysis to quantification.

• Structural Engineering and Mechanics
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• 제56권5호
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• pp.767-785
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• 2015

The stochastic finite element method is employed to obtain a stochastic dynamic model of angled beams subjected to impact loads when uncertain material properties are described by random fields. Using the perturbation technique in conjunction with a precise time integration method, a random analysis approach is developed for efficient analysis of random elastic waves. Formulas for the mean, variance and covariance of displacement, strain and stress are introduced. Statistics of displacement and stress waves is analyzed and effects of bend angle and material stochasticity on wave propagation are studied. It is found that the elastic wave correlation in the angled section is the most significant. The mean, variance and covariance of the stress wave amplitude decrease with an increase in bend angle. The standard deviation of the beam material density plays an important role in longitudinal displacement wave covariance.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.335-354
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• 2023

In this study, analysis of wave propagation characteristics for functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates is performed using first-order shear deformation theory (FSDT) and nonlocal strain gradient theory. Uniform distribution (UD) and three types of functionally graded distributions of carbon nanotubes (CNTs) are assumed. The effective mechanical properties of the FG-CNTRC nanoplate are assumed to vary continuously in the thickness direction and are approximated based on the rule of mixture. Also, the governing equations of motion are derived via the extended Hamilton's principle. In numerical examples, the effects of nonlocal parameter, wavenumber, angle of wave propagation, volume fractions, and carbon nanotube distributions on the wave propagation characteristics of the FG-CNTRC nanoplate are studied. As represented in the results, it is clear that the internal length-scale parameter has a remarkable effect on the wave propagation characteristics resulting in significant changes in phase velocity and natural frequency. Furthermore, it is observed that the strain gradient theory yields a higher phase velocity and frequency compared to those obtained by the nonlocal strain gradient theory and classic theory.

• 한국해안·해양공학회논문집
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• 제24권3호
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• pp.179-188
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• 2012

기후변화가 구조물의 안정성에 미치는 영향을 분석하기 위해 여러 수심에서 가상적으로 설계된 직립방파제의 성능을 평가하였다. 성능평가에서는 기후변화영향인 해수면 상승과 파고 증가를 고려한 성능설계법이 사용되었다. 성능설계법의 파랑변형 계산과정에서 많은 시간이 요구되는 문제를 극복하기 위해 범용 SWAN 모형에 인공신경망을 결합하였다. 학습된 인공신경망에 심해유의파고와 심해주파향 그리고 조위가 입력되면 구조물 위치에서 유의파고와 주파향이 신속하게 계산된다. 전반적으로 구조물의 안정성은 기후변화영향으로 감소하였지만 수심에 따라 서로 다른 경향을 보였다. 쇄파대 밖에서는 수심이 증가할수록 해수면 상승의 영향은 감소하고 파고 증가의 영향은 증가하였다. 한편, 쇄파대 내에서는 수심이 감소할수록 파고 증가와 해수면 상승의 영향 모두 감소하였다. 하지만 파고 증가의 영향이 해수면 상승의 영향보다 컸다. 이와 같은 결과를 반영하여 직립방파제의 유지보수 및 보강 대책을 수립해야 할 것이다.