• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.31 no.5
• /
• pp.294-304
• /
• 2019

This study evaluates the variation characteristics of wave fields (transmission ratio, wave height, time-averaged velocity and time-averaged turbulent kinetic energy) for two-dimensional low-crested structure by olaFlow model based on the two-phases flow numerically. In addition, the present numerical results are verified by comparing with the existing experimental results. The time-averaged velocity, one of various numerical results is formed counterclockwise circulating cell on the front of structure and is occurred strong uni-directional flow on onshore side. It is shown that these are closely related to the factors such as overtopping, etc.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.2
• /
• pp.122-134
• /
• 2020

On the many coasts of South Korea, including the eastern side, it has been recently increasing the coastal disaster such as the severe coastal erosion and road damage swept away by the wave. As one of the alternatives to prevent the coastal disaster, it has been widely studied the coastal disaster reduction method by the Low-Crested Structure (LCS) in the many countries including several European countries. In this study, the olaFLow model is used to simulate the permeable LCS and wave field of the LCS through the three-dimensional irregular waves numerical analysis on the basis of the previous research. From the numerical analysis, it is evaluated the H_rms, nearshore current and time-averaged turbulent kinetic energy. In addition, the pattern of nearshore current and spatial distribution of time-averaged turbulent kinetic energy are compared with the case of submerged breakwater under the irregular wave fields. As one of significant results, it is confirmed that the pattern of nearshore current is different with the case of submerged breakwater.

• Journal of the Society of Naval Architects of Korea
• /
• v.38 no.2
• /
• pp.1-9
• /
• 2001

Based on the linear potential theory with the side wall reflection. the directional spectrum waves are numerically simulated by a source distribution method and these together with long-crested irregular waves are also generated at the towing tank of Pusan National University by considering the transfer function of the wave maker obtained from the regular waves. In the numerical simulation, the characteristics of the directional spreading function are investigated by changing the breadth of the wave-maker unit. the width of the towing tank and the wave period. In the experimental generation, the statistical properties and the power spectrums of the long-crested irregular and directional waves are compared along the towing tank length. The directional spreading functions are also investigated at various positions in the tank.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.1113-1117
• /
• 2005

보 상류의 유속 및 수심과 같은 흐름 조건은 보, 하천 형상, 그리고 하류 흐름 특성에 의해 좌우된다. 본 연구에서는 하류 조건에 따라 보 상류의 흐름 특성에 미치는 영향을 검토하였다. 이를 위해 구형단면의 수로에 하천설계지침(2002)에 따라 보를 제작하여 설치하였으며 보에서의 임계수심 및 이에 따른 유량의 변화를 파악하였으며 실험결과를 기존 문헌과 비교$\cdot$분석하였다. 또한 자유 월류로 빠른 유속을 지닌 흐름이 수로의 마찰저항과 하류 배수효과에 의해 에너지 소멸로 나타나는 도수현상을 관측하여 발생특성을 파악하였다. 도수의 발생조건은 Posey와 Hsing(1938)에 제시한 결과와 유사한 결과를 보였으며 하류영향에 따른 도수 발생 위치는 하류단 수위와 일정한 관계를 갖고 있으나 유량과는 선형적인 관계를 보이지 않는 것을 알 수 있었다. 또한 임계수심 설정에 대해 Knap(1960)이 제시한 산정식과 비교한 결과 유량이 작은 경우 거의 일치하는 결과를 보였으나 유량이 증가할수록 오차가 커졌다. 임계수심 전$\cdot$후의 유량계수를 살펴본 결과 하류 조건에 의해 임계수심을 넘으면 유량계수가 자유 월류 시보다 약 $2\%\~6.5\%의 감소를 나타냈으며 공급유량이 $0.05m^3/s$ 일 경우 유량계수의 차이가 가장 큰 것을 알 수 있다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.660-663
• /
• 2008

방수로는 본류의 첨두홍수량을 분담하여 대상 지역의 홍수피해가능성을 줄이기 위해서 도입되는 구조적 홍수방어대책의 하나로 특히 도시화로 인하여 기존 하천 유역의 저류 능력이 감소하여 홍수 시 유출량이 증가함에 따라 방수로의 필요성은 점차 늘어나고 있다. 외국의 경우에는 이미 대표적인 구조적 홍수방어대책으로 활용되어 그 효과가 이미 확인되어 있다. 방수로로 분담되는 유량은 일반적으로 방수로 유입부에 설치되어 있는 횡월류위어의 월류량을 정확히 산정함으로써 알 수 있다. 따라서 방수로의 홍수방어능력을 알기위해서는 이러한 유입부 횡월류위어의 월류량을 정확히 평가하는 것이 중요하다. 횡월류위어의 형태는 여러 가지가 있지만 가장 기본적인 형태로 예연위어 형태와 광정위어 형태가 있다. 본 연구에서는 그 중에서 광정횡월류위어(broad-crested side weir)을 대상으로 실제 하도와 유사한 흐름 조건을 가지도록 상대적으로 작은 횡월류위어길이(L)와 본류 폭(B) 비(L/B)를 가지는 실험 수로를 이용하여 광정횡월류위어에 대한 실험을 수행한 후 유량 계수를 산정하여 본류 흐름 조건 및 횡월류위어 제원 변화에 따른 영향을 검토하였다. 광정횡월류위어에서의 유량계수도 기본적으로 예연횡월류위어와 동일한 방식을 이용하여 검토할 수 있으며, 동일한 주요 영향 변수를 포함하지만, 위어 폭 W가 횡월류위어의 월류 유량과 본류 유황에 영향을 미치게 된다. 따라서 본 연구에서는 광정횡월류위어의 특성에 따른 산정된 유량계수의 변화에 초점을 두어 분석을 수행하였다.

• Journal of Ocean Engineering and Technology
• /
• v.7 no.2
• /
• pp.114-120
• /
• 1993

Responses of marine vehicles and ocean structures in a seaway can be predicted by applying the probabilistic approach. When we consider a linear system, the responses in a random seaway can be evaluated through spectral analysis in the frequency domain. But when we treat nonlinear system in irregular waves, it is necessary to get time history of waves. In the previous study we introduced one-directional waves (long crested waves)as wave environment and carried out calculations and experiments in the waves. But the real sea in which marine vehicles and structures are operated has multi-directional waves (short crested waves). It is important to get a simulated random sea and analyse dynamic problems in the sea. We need entire sample function or probabillty density function to infer statistical value of random process. However if the process are ergodic process, we can get statistical values by analysis of one sample function. In this paper, we developed the simulation technique of multi-directional waves and proved that the time history given by this method keep ergodic characteristics by the statistical analysis.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.3
• /
• pp.212-219
• /
• 2005

Real sea waves in a towing wave basin have been generated using random periodic motion of the segmented wave makers and the wave reflections of sidewalls. Theoretically, the real sea waves can be described by the superposition of many random oblique waves. This paper introduces numerical real sea wave generation in a rectangular wave basin using spectral method that uses a superposition of orthogonal functions which have to satisfy the Laplace equation. Oblique regular waves, long crested irregular waves and real sea waves were simulated and met the requirement of sidewall wave reflection and wave absorption. MLM (Maximum Likelihood Method) and Spatial Fourier Transform were used in order to obtain propagated wave direction characteristics. The estimated results proved the usefulness of the method and the performances showed reasonable directional patterns comparing with generating patterns.

• Journal of Ocean Engineering and Technology
• /
• v.37 no.1
• /
• pp.20-30
• /
• 2023

Modeling a nonlinear ocean wave is one of the primary concerns in ocean engineering and naval architecture to perform an accurate numerical study of wave-structure interactions. The high-order spectral (HOS) method, which can simulate nonlinear waves accurately and efficiently, was investigated to see its capability for nonlinear wave generation. An open-source (distributed under the terms of GPLv3) project named "HOS-ocean" was used in the present study. A parametric study on the "HOS-ocean" was performed with three-hour simulations of long-crested ocean waves. The considered sea conditions ranged from sea state 3 to sea state 7. One hundred simulations with fixed computational parameters but different random seeds were conducted to obtain representative results. The influences of HOS computational parameters were investigated using spectral analysis and the distribution of wave crests. The probability distributions of the wave crest were compared with the Rayleigh (first-order), Forristall (second-order), and Huang (empirical formula) distributions. The results verified that the HOS method could simulate the nonlinearity of ocean waves. A set of HOS computational parameters was suggested for the long-crested irregular wave simulation in sea states 3 to 7.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.31 no.3
• /
• pp.180-198
• /
• 2019

In recent years, countries like Europe and Japan have been involved in many researches on the Low-Crested Structure (LCS) which is the method to protect beach erosion and it is regarded as an alternative to the submerged breakwaters, and compiled its results and released the design manual. In the past, studies on LCS have focused on two-dimensional wave transmission and calculating required weight of armor units, and these were mainly examined and discussed based on experiments. In this study, three-dimensional numerical analysis is performed on permeable LCS. The open-source CFD code olaFlow based on the Navier-Stokes momentum equations is applied to the numerical analysis, which is a strongly nonlinear analysis method that enables breaking and turbulence analysis. As a result, the distribution characteristics of the LCS such as water level, water flow, and turbulent kinetic energy were examined and discussed, then they were carefully compared and examined in the case of submerged breakwaters. The study results indicate that there is a difference between the flow patterns of longshore current near the shoreline, the spatial distribution of longshore and on-offshore directions of mean turbulent kinetic energy in case of submerged breakwaters and LCS. It is predicted that the difference in these results leads to the difference in sand movement.

• 한국기계연구소 소보
• /
• s.9
• /
• pp.193-208
• /
• 1982

Flap type wave-maker, wave absorber, motion measuring equipment and related instruments were newly installed at Ship Experimental Towing Tank, Ship Research Station, KIMM. The model tests in regular head and following waves were successfully carried out and the motion and wave loads in regular and long crested irregular waves were calculated for a container ship model which was adopted as the hull form for the comparative calculations of the ITTC Seakeeping Committee. The results of model tests show good agreement with calculated results and the latter are generally in good agreement with the results of the comparative calculations.