• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.11-21
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wav interactions with a system composed of fully submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing between two systems. The fully submerged two systems allow surface and bottom gaps to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of the second kind) that satisfy the Helmholz governing equation in fluid domains. A boundary element program for three fluid domains based on a discrete membrane dynamic model and simple source distribution method is developed. Using this developed computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, gaps, spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters can, if it is properly tuned to the coming waves, have good performances in reflecting the obliquely incident waves over a wide range of wave frequency and headings.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.95-106
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• 1999

A numerical model is represented to calculate the wave fields such as the reflected waves, the transmitted waves and the depth-averaged velocities over submerged breakwaters for the normally incident wave trains of nonlinear mono-chromatic wave and solitary wave. The finite amplitude shallow water equations with the effects of bottom friction are solved numerically in time domain using an explicit dissipative Lax-Wendroff finite difference method. The numerical model is verified by comparisons with the other numerical results and the measured data. It is found that the submerged breakwater may be more useful for protecting the energies of monochromatic waves rather than solitary waves. Finally, the armor stability on submerged breakwater is indirectly analyzed using the hydrodynamic characteristics of flow fields.

• Ocean Science Journal
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• v.41 no.3
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• pp.149-161
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• 2006

The aims of this study are 1) to construct a database using geostatistics and Geographic Information System (GIS), and 2) to derive the spatial relationships between manganese nodule abundance and other geological factors such as metal grade, slope, water depth, topography, and acoustic characteristics of the sub-bottom. Using GIS, it is possible to analyze a large amount of data efficiently, and to maximize the practical application, to increase specialization, and to enhance the accuracy of the analyses. The greater the copper and nickel grade, the higher the rating. The distribution pattern of nickel grade is similar to that of copper grade. The slopes are generally less than $3^{\circ}$ except for seamounts and cliff areas. The rating shows no correlation with slope. The rating is highest for slopes between 2.5 and $3.5^{\circ}$ in block N1 and between 4.0 and $4.5^{\circ}$ in block N3. The topography is classified into five groups: seamount, hill crest, hill slant, hill base or plain, and seafloor basin or valley. The rating proves lowest for seamount and hill crest. Our results show that the rating increases with the water depth in the study area. Nodule abundance dose not show any significant relationship with the thickness of the upper transparent layer in the study area.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.203-207
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• 2008

Prestack depth migration is used to image for complex geological structure such as faults, folds, and subsalt. In this case, it is widely used the surface reflection data as a input data. However, the surface reflection data have intrinsic problems to image the subsalt and the salt flank due to the complex wavefields and multiples which come from overburden. For overcoming the structural defect of the surface reflection data in the imaging, I used the virtual sources in terms of seismic interferometry to image the subsurface and suppress the multiples using the velocity model of the lower part of the virtual sources. The results of the prestack depth migration using virtual source gathers and velocity model below receivers are similar geological interfaces to the results from shot gathers of the conventional ocean bottom seismic survey. And especially artificial interfaces by multiples were suppressed without applying any other data processing to eliminate multiples. This study results by numerical modeling can make a valuable imaging tool when it is applied to satisfied field data for specific condition.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.2
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• pp.143-150
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• 1990

A cooperative Korea-Japan investigation for the demersal fisheries resources of the East China Sea was carried out by using the training ship Oshoro Maru belong to Hokkaido University Japan, during 5-12 November, 1989. The research vessel sampled 24 stations with demersal trawls on the East China Sea continental shelf, and 96 nautical miles of track line were surveyed hydroacoustically. The echo sounder used during the survey was of a scientific type having echo integration capabilities and the computer system was programmed to obtain echo integration data for each depth stratum between the transducer and the bottom. The target strength of fish school(TS per 1kg) was estimated from the relationship between mean volume backscattering strength and catches caught by the demersal trawls. The results obtained can be summarized as follows: 1. Approximately 96 species were identified from survey catches. 2. The mean volume backscattering strength for the layer occupied by bottom trawls at 25 and 100 KHz were-63.9 dB and -67.3 dB, respectively. Then the average catch per unit time of each trawl haul was 58.8 kg/hour. 3. The mean volume backscattering strength for the entire layer between the transducer and the bottom at 25 and 100KHz were -61.9 dB and -67.0 dB, respectively. 4. The mean fish school target strength per unit weight(TS/kg) at 25 and 100 KHz were -23.6 dB/kg and -26.6 dB/kg, respectively.

• 한국해양학회지
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• v.11 no.1
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• pp.18-24
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• 1976

The distribution of tidal currents in Asan Bay was simulated by a numerical experiment. A homogeneous and single layer model with bottom stress taken into account was used. Although the effective configuration of the bay differs significantly between the high tide and the low tkde, its form is assumed to be fixed as a first approximation. The advective term is particularly large because the tidal range of 810cm is large compared to the depth and the changes of velocities occur abruptly. The results of calculations agree fairly well with the observations. For example, the tidal range at Manhoriis amplified 15cm higher and the phase lag is five minutes later than at the mouth of the bay. It also can generally be said that, with the semidiurnal tide at the mouth of the bay, the tidal range is increased toward the inner corner and that tidal currents are found to be large at the deeper part of the bay.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.330-330
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• 2002

The combination of Multi-Beam Echo Sounder swath bathymetry and high-resolution towed Sidescan sonar provides a powerful method of examination about hydrographic survey results. In this paper, we investigate the fast method of 3D bathymetric reconstruction with the Digital Sidescan sonar(Benthos SIS 1500) and Shallow Multi-Beam Echo Sounder(Reson Seabat 8125). The Seabat 8125 is a 455KHz high resolution focused Multibeam echo sounder(MBES) system which measures the relative water depth across a wide swath perpendicular to a vessel's track. The Benthos SIS1500 is a chirp(nominal fq. 200KHz) sonar which map the topographical features & sediment texture of ocean bottom using backscattered amplitude. We generates the very large 3D bathymetric texture mapping model with the Helical System's HHViewer and describes additional benefits of combining MBES and Sidescan Sonar imagery, the removal of geometric distortions in the model and a deterministic sounding noise.

• Special Issue of the Society of Naval Architects of Korea
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• 2006.09a
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• pp.15-22
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• 2006

Global strength check for TLP tendon body can be estimated based on maximum tendon tensions and bending moments, which are resulted in TLP global performance analysis. Final tendon length, especially thread length on Length Adjustment Joint, is easily calculated with water depth at TLP in-place location, TLP lock-off draft and unlocking length of tendon bottom section. And LAJ thread length, which is locked with TLP top tendon connector, should be carefully determined with tendon design and installation tolerances.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.2
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• pp.122-125
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• 2011

In this work, the movement pattern of a floating breakwater is numerically analyzed using Smoothed Particle Hydrodynamic (SPH) method as a Lagrangian scheme. At the seaside, the regular incident waves with varying height and period were considered as the dynamic free surface boundary conditions. The smooth and impermeable beach slope was defined as the bottom boundary condition. The effects of various boundary conditions such as incident wave characteristics, beach slope, and water depth on the movement of the floating body were studied. The numerical results are in good agreement with the available experimental data in the literature The results of the movement of the floating body were used to determine the transmitted wave height at the corresponding boundary conditions.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.165-177
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• 2019

This paper considers corrosion wastage of two ship hull structure members as a part of investigated fuel oil tanks of 25 aging bulk carriers. Taking into account that many factors which influence corrosion wastage of ship hull structures are of uncertain nature, the related corrosion rate ($c_1$) is considered here as a real-valued continuous distribution, assuming that the corrosion wastage starts after 5, 6 or 7 years. In all considered cases, by using available data and applying three basic statistical tests, it is established that between two-parameter continuous distributions, normal, Weibull and logistic distributions are best fitted distributions for the mentioned corrosion rate ($c_1$). Note that the presented statistical, numerical and graphical results concerning two mentioned ship hull structure members allow to compare and discuss the corresponding probabilistic estimates for the corrosion rate ($c_1$).