• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.2
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• pp.86-97
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• 2005

Accurate estimation of the wave-induced pore water pressure in the seabed is key factor in studying the stability of the seabed in the vicinity of coastal structure. Most of the existing numerical models for wave structure seabed interaction have been linked through applying hybrid numerical technique which is analysis method separating the wave field and seabed regime. Therefore, it is necessary to develope a numerical model f3r simulating accurately wave$\cdot$structure$\cdot$ seabed interaction under wave loadings by the single domain approach for wave field and seabed regime together. In this study, direct numerical simulation is newly proposed. In this model, modeled fluid drag has been used to detect the hydraulic properties according to the varied geometrical shape inside the porous media by considering the turbulence resistance as well as laminar resistance. Contrary to hybrid numerical technique, direct numerical simulation avoids the explicit formulation of the boundary conditions at the fluid/porous media interface. A good agreement has been obtained by the comparison between existed experimental results by hydraulic model test and direct numerical simulation results far wave $\cdot$structure$\cdot$seabed interaction. Therefore, the newly proposed numerical model is a powerful tool for estimating the nonlinear dynamic responses among a structure, its seabed foundation and water waves.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.257-273
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• 2013

Top tensioned riser (TTR) is often used in a floating oil/gas production system deployed in deep water for oil/gas transport. This study focuses on the extension of the existing numerical code, known as CABLE3D, to allow for static and dynamic simulation of a TTR connected to a floating structure through a tensioner system or buoyancy can, and restrained by riser guides at different elevations. A tensioner system usually consists of three to six cylindrical tensioners. Although the stiffness of individual tensioner is assumed to be linear, the resultant stiffness of a tensioner system may be nonlinear. The vertical friction between a TTR and the hull at its riser guide is neglected assuming rollers are installed there. Near the water surface, a TTR is forced to move horizontally due to the motion of the upper deck of a floating structure as well as related riser guides. The extended CABLE3D is then integrated into a numerical code, known as COUPLE, for the simulation of the dynamic interaction among the hull of a floating structure, such as spar or TLP, its mooring system and riser system under the impact of wind, current and waves. To demonstrate the application of the extended CABLE3D and its integration with COUPLE, the numerical simulation is made for a truss spar under the impact of Hurricane "Ike". The mooring system of the spar consists of nine mooring lines and the riser system consists of six TTRs and two steel catenary risers (SCRs).

• Journal of Ocean Engineering and Technology
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• v.31 no.1
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• pp.47-59
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• 2017

This study conducted numerical simulations using LES-WASS-3D ver. 2.0 to analyze the seawater intrusion characteristics of the incident waves in a coastal aquifer. LES-WASS-3D directly analyzed the nonlinear interaction between the seawater and freshwater in a coastal aquifer, as well as the wave-current interaction in the coastal area. First, the LES-WASS-3D results were compared with the existing experimental results for the mean water level under wave action in the coastal aquifer and seawater penetration into the coastal aquifer. The mean water level, shape and position of the seawater-freshwater interface, and intrusion distance were well implemented in the results. This confirmed the validity and effectiveness of LES-WASS-3D. The overall seawater penetration distance increases in the coastal aquifer as a result of wave set-up and run-up in the swash zone caused by continuous wave actions, and it increases with the wave height and period. Furthermore, a numerical verification was performed by comparing the suggested existing structure and newly suggested curtain wall as a measure against seawater penetration. An existing underground dam showed a better effect with increased height. Additionally, the suggested curtain wall had a better effect when the embedded depth was increased.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.160-176
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• 2017

The interaction of focused wave groups with a vertical wall is investigated based on the second order potential theory. The NewWave theory, which represents the most probable surface elevation under a large crest, is adopted. The analytical solutions of the surface elevation, velocity potential and wave force exerted on the vertical wall are derived, up to the second order. Then, a parametric study is made on the interaction between nonlinear focused wave groups and a vertical wall by considering the effects of angles of incidence, wave steepness, focal positions, water depth, frequency bandwidth and the peak lifting factor. Results show that the wave force on the vertical wall for obliquely-incident wave groups is larger than that for normally-incident waves. The normalized peak crest of wave forces reduces with the increase of wave steepness. With the increase of the distance of focal positions from the vertical wall, the peak crest of surface elevation, although fluctuates, decreases gradually. Both the normalized peak crest and adjacent crest and trough of wave forces become larger for shallower water depth. For focused wave groups reflected by a vertical wall, the frequency bandwidth has little effects on the peak crest of wave elevation or forces, but the adjacent crest and trough become smaller for larger frequency bandwidth. There is no significant change of the peak crest and adjacent trough of surface elevation and wave forces for variation of the peak lifting factor. However, the adjacent crest increases with the increase of the peak lifting factor.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.3
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• pp.129-145
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• 2019

For the design of composite breakwater as representative one of the coastal and harbor structures, it has been widely discussed by the researchers about the relation between the behavior of excess-pore-water pressure inside the rubble mound and seabed caused by the wave load and its structural failure. Recently, the researchers have tried to verify its relation through the numerical simulation technique. The above researches through numerical simulation have been mostly applied by the linear and nonlinear analytic methods, but there have been no researches through the numerical simulation by the strongly nonlinear mutiphase flow analytical method considering wave-breaking phenomena by VOF method and turbulence model by LES method yet. In the preceding research of this study, olaFlow model based on the mutiphase flow analytical method was applied to the nonlinear interaction analysis of regular wave-composite breakwater-seabed. Also, the same numerical techniques as preceding research are utilized for the analysis of irregular wave-composite breakwater-seabed in this study. Through this paper, it is investigated about the horizontal wave pressures, the time variations of excess-pore-water pressure and their frequency spectra, mean flow velocities, mean vorticities, mean turbulent kinetic energies and etc. around the caisson, rubble mound of the composite breakwater and seabed according to the changes of significant wave height and period. From these results, it was found that maximum nondimensional excess-pore water pressure, mean turbulent kinetic energy and mean vorticity come to be large equally on the horizontal plane in front of rubble mound, circulation of inflow around still water level and outflow around seabed is formed in front of rubble caisson.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5B
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• pp.473-482
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• 2009

This study numerically discusses wave forces acting on a vertical wall such as breakwaters or revetments, subjected to incident undular or turbulent bores. Due to the complex hydrodynamics of bore, its wave forces have been predicted, mainly through laboratory experiments. Numerical simulations in this paper were carried out by CADMAS-SURF(CDIT, 2001), which is based on Navier-Stokes momentum equations and VOF method (Hirt and Nichols, 1981) for tracking free water surface. Its original source code was also partly revised to generate bore in the numerical water channel. Numerical raw data computed by CADMAS-SURF included great strong spike phenomena that show the abrupt jumps of wave loads. To resolve this undesired noise of raw data, the band-pass filter with the frequency of 5Hz was utilized. The filtered results showed reasonable agreements with the experimental results performed by Matsutomi (1991) and Ramsden (1996). It was confirmed that CADMASSURF can be applied to the design of coastal structures against tsunami bores. In addition, the transformation process and propagation speed of bores in the same 2-d water channel were discussed by the variations of water level for time and space. The numerical results indicated that the propagation speed of bore was changed due to the nonlinear interactions between negative and reflected waves.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.95-109
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• 2008

We numerically analyzed the nonlinear shoaling, a plunging breaker and its accompanying energetic suspension of sediment at a bed, and a redistribution of suspended sediments by a down rush of preceding waves and the following plunger using SPH with a Gaussian kernel function, Lagrangian Dynamic Smagorinsky model (LDS), Van Rijn's pick up function. In that process, we came to the conclusion that the conventional model for the tractive force at a bottom like a quadratic law can not accurately describe the rapidly accelerating flow over a swash zone, and propose new methodology to accurately estimate the bottom tractive force. Using newly proposed wave model in this study, we can successfully duplicate severely deformed water surface profile, free falling water particles, a queuing splash after the landing of water particles on the free surface and a wave finger due to the structured vortex on a rear side of wave crest (Narayanaswamy and Dalrymple, 2002), a circulation of suspended sediments over a swash zone, net transfer of sediments clouds suspended over a swash zone toward the offshore, which so far have been regarded very difficult features to mimic in the computational fluid mechanics.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.287-296
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• 2020

The wave-impact load on offshore structures can be divided into green-water and wave-slamming impact loads. These wave impact loads are known to have strong nonlinear characteristics. Although the wave impact loads are dealt with in the current classification rules in the shipping industry, their strong nonlinear characteristics are not considered in detail. Therefore, to investigate these characteristics, wave-impact loads induced by a breaking wave on a circular cylinder were analyzed. A model test was carried out to measure the wave-impact loads due to breaking waves in a two-dimensional (2D) wave tank. To generate a breaking wave, the focusing wave method was applied. A series of 2D tank tests under a horizontal wave impact was carried out to investigate the structural responses of the cylindrical structure, which were obtained from the measured model test data. According to the results, we proposed a structural damage-estimation procedure of an offshore tubular member due to a wave impact load. Furthermore, a recommended wave-impact load is suggested that considers the minimum required thickness of each member. From the experimental results, we found that the required minimum thickness is dependent on the impact pressure located in a three-dimensional space on the surface of a tubular member.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.4
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• pp.13-27
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• 1988

Two version of the TUMMAC(Tokyo University Modified Marker-And-Cell) method, i.e., $TUMMAC-IV_{vm1}$ and TUMMAC-VI are applied to two water-wave problems. The ship wave of a Series 60 model($C_B=0.6$) and of the fore-body of a HSVA tanker model are simulated by the $TUMMAC-IV_{vm1}$ method are the results are compared with the experimental results. From the comparison with the experimental data it is ascertained that the $TUMMAC-IV_{vm1}$ method is useful for the analysis of the realized by the TUMMAC-VI method is useful for the analysis of the characteristics of nonlinear ship waves. Three-dimensional wave breaking is realized by the TUMMAC-VI method in the simulation of a flow about a vertical rectangular cylinder. From the results of this simulation, it is shown that the TUMMAC-VI method is very available for the simulation of 3-dimensional wave breaking phenomena.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.601-609
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• 2022

Jack-up drilling rigs are mobile offshore platforms widely used in the offshore oil and gas exploration industry. These are independent, three-legged, self-elevating units with a cantilevered drilling facility for drilling and production. A typical jack-up rig includes a triangular hull, a tower derrick, a cantilever, a jackcase, living quarters and legs which comprise three-chord, open-truss, X-braced structure with a spudcan. Generally, jack-up rigs can only operate in water depths ranging from 130m to 170m. Recently, there has been an increasing demand for jack-up rigs for operating at deeper water levels and harsher environmental conditions such as waves, currents and wind loads. All static and dynamic loads are supported through legs in the jack-up mode. The most important issue by society is to secure the safety of the leg structure against collision that causes large instantaneous impact energy. In this study, nonlinear FE -analysis and verification of the requirement against collision for 35MJ recommended by DNV was performed using LS-Dyna software. The colliding ship used a 7,500ton of shore supply vessel, and five scenarios of collisions were selected. From the results, all conditions do not satisfy the class requirement of 35MJ. The loading conditions associated with chord collision are reasonable collision energy of 15M and brace collisions are 6MJ. Therefore, it can be confirmed that the identical collision criteria by DNV need to be modified based on collision scenarios and colliding members.