• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.114-117
• /
• 2010

에너지자원(석유, 천연가스, 전기) 이송과 정보전달(해저광케이블)을 위한 다양한 형태의 해저 매설관이 해저면에 설치되어 운영이 되고 있다. 이들 매설관은 지진 또는 해저사면의 유실과 같은 자연재해로 인해 파괴되는 일들이 빈번하게 발생되고 있다. 그 외 태풍 등에 의해 발생되는 파랑하중에 의해서도 이들 매설관이 종종 파괴되는 일이 발생되기도 한다. 태풍 등에 의한 파랑하중은 해저지반에 과다한 과잉간극수압을 발생시켜 지반 액상화를 유발 세굴을 발생시키는데 이로 인해 매설관 하부에는 과도한 인장응력이 유발되어 매설관의 파괴 문제가 야기된다. 만약 석유수송 해저매설관이 파괴되면 경제적?산업적 측면에서 직접적인 피해 이외에도 해양환경에 미치는 영향은 매우 크다고 볼 수 있다. 따라서 파랑하중에 의한 해저매설관 주변 지반의 거동 분석 및 안정성 평가에 관한 연구가 요구된다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.29 no.4
• /
• pp.206-216
• /
• 2017

The temporal distribution of the turbulence kinetic energy (TKE) and the vertical component of Reynolds stresses ($-{\bar{u^{\prime}w^{\prime}}}$) was measured during one wave period under high wave energy conditions. The wave data were obtained at Hujeong Beach in the east coast of Korea at January 14~18 of 2017 when an extratropical cyclone was developed in the East Sea. Among the whole thousands of waves measured during the period, hundreds of regular waves that had with similar pattern were selected for the analysis in order to give three representing mean wave patterns using the ensemble average technique. The turbulence properties were then estimated based on the selected wave data. It is interesting to find out that $-{\bar{u^{\prime}w^{\prime}}}$ has one clear peak near the time of flow reversal while TKE has two peaks at the corresponding times of maximum cross-shore velocity magnitudes. The distinguished pattern of Reynolds stress indicates that vertical fluxes of such properties as suspended sediments may be enhanced at the time when the horizontal flow direction is reversed to disturb the flows, supporting the turbulence convection process proposed by Nielsen (1992). The characteristic patterns of turbulence properties are examined using the CADMAS-SURF Reynolds-Averaged Navier-Stokes (RANS) model. Although the model can reasonably simulate the distribution of TKE pattern, it fails to produce the $-{\bar{u^{\prime}w^{\prime}}}$ peak at the time of flow reversal, which indicates that the application of RANS model is limited in the prediction of some turbulence properties such as Reynolds stresses.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.12 no.3
• /
• pp.188-196
• /
• 2009

This study conducted numerical simulations to analyze the wave characteristics(distribution) depending on the directional changes of waves in the Nakdong river estuary by using SWAN(Simulating WAves Nearshore) model. The results from the tests are summarized as below. The wave height rates are generally highly distributed with the incident waves from the S, SSE, SSW, SE, SW in sequence. When the waves from the S, SSW, SSE directions are predominant, the bigger waves were observed in front of sandbars. According to the results of the wave steepness against the wave direction, at the east coast of Gadeok island(northwest of Nakdong estuary), where has mild seabed slopes, the wave height rates distribute in the range of 0.4~0.6; the wave height rates over the west coastal region of Dadeapo(southeast of Nakdong estuary) are 0.5~0.6. The wave height rate tends to be rapidly decreased over the east region of Nakdong river estuary rather than its west region.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.17 no.2
• /
• pp.146-152
• /
• 2014

Design procedure of WEC (wave energy converter) using the heaving motion of a floating cylinder-type buoy coupled with LEG (linear electric generator) system is introduced. It is seen that the maximum power can actually be obtained at the optimal conditions ($c_{PTO}=b_T$, ${\omega}={\omega}_N$). Then, based on the developed theory, several design strategies are proposed to further enhance the maximum PTO (power take off), which includes the intentional mismatching with the heave natural frequency, which is 15% higher value than the peak frequency of input velocity spectrum. By using the intentional mismatching strategy, the generated power is actually increased and the corresponding draft as well as the required PTO damping value is significantly reduced, which is a big advantage in manufacturing the WEC with practical LEG (linear electric generator) system.

• Journal of Korea Water Resources Association
• /
• v.38 no.6 s.155
• /
• pp.429-438
• /
• 2005

In this study, a couple of ordinary differential equations which can describe random waves are derived from the Boussinesq equations. Incident random waves are generated by using the TMA(TEXEL storm, MARSEN, ARSLOE) shallow-water spectrum. The governing equations are integrated with the 4-th order Runge-Kutta method. By using newly derived wave equations, nonlinear energy interaction of propagating waves in constant depth is studied. The characteristics of random waves propagate over a sinusoidally varying topography lying on a sloping beach are also investigated numerically. Transmission and reflection of random waves are considerably affected by nonlinearity.

• Journal of Korea Water Resources Association
• /
• v.32 no.6
• /
• pp.675-683
• /
• 1999

The reflection coefficients of monochromatic waves propagating over a shelf with varying dimensions are theoretically calculated. The diffraction of waves by an abrupt depth change is formulated by the eigenfunction expansion method. Not only propagating mode but also evanescent modes are considered in formulation. The role of evanescent modes in reflection coefficients is investigated in detail. Water waves are obliquely as well as normally incident to the region. The obtained reflection coefficients are verified by checking conservation of wave energy.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.2
• /
• pp.30-37
• /
• 2000

The roll damping characteristics of the three models of a 3ton class fishing vessel, that is the bare hull, hull with bilge keels, and hull with bilge keels and a central wing are investigated by the free roll tests in head waves in a towing tank with the variations of the forward speed, initial angle and OG. The wave length variations are also included. The experimental results are compared with the numerical results of mathematical modellings by the energy method for these three models and the energy dissipation patterns are also compared. The roll damping speed increases, the effect of the waves on the roll damping of the models with the additional devices is negligible due to the much increased damping caused by the lift increase.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.7 no.1
• /
• pp.47-55
• /
• 2004

In this paper, The statistical properties of ocean waves in the sea area of Hong-do, Korea are examined based on 1998-2002's wave data from a directional wave buoy. Wave data aquisition rate, 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. Large amplitude wave characteristics during the typhoon Prapiroon in 2000, Rusa in 2002 are also examined.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.1 no.1
• /
• pp.29-38
• /
• 1998

This paper summarizes the results of the investigations performed by the authors for a number of years on the performance of oil fences in currents and waves. The leakage inception velocity of currents, the wave-exciting motion of fences and the deformation of the fence skirt due to currents are investigated. The results show that improvement of the fence performance is necessary in order to utilize the oil fences as an effective containing device for spilt oils in ocean environments. As an approach toward improving the fence effectiveness, tandem fences in currents are investigated. It was found that an appropriate deployment of tandem fences of identical configuration could significantly improve the oil containment capability.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.5 no.2
• /
• pp.19-27
• /
• 2002

This paper deals with the experimental investigation on the hydrodynamic behavior of the submerged artificial seabed system in regular waves. This system can function as a basis of seaweed forest which will cultivate coastal fishing ground and enhance coastal productivity. The experiment was conducted with the submerged rectangular plates of different length and depth in 2-D wave flume of KRISO/KORDI. The wave exciting forces, mooring line tension and 2-D motion response are measured and analyzed to figure out the design strategy.