• Journal of the Society of Naval Architects of Korea
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• v.60 no.2
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• pp.120-134
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• 2023

In this study, hydrodynamic characteristics of dam break flow were investigated by a series of experiments. The experiments were performed in a 2-D rectangular flume with obtaining instantaneous images of dam break flow to capture the free surface elevation, and pressure distributions on vertical wall and bottom of the flume. The initial water depth of the dam break flow was changed into 3 different heights, and the gate opening speed was changed during the experiments to study the effect of the gate speed in the dam break flow. Generation of dam break phenomena could be classified into three stages, i.e., very initial, relatively stable, and wall impact stages. The wall impact stage could be separated into 4 generation phases of wall impinge, run-up, overturning, and touchdown phases based on the deformation of the free surface. The free surface elevation were investigated with various initial water depth and compared with the analytic solutions by Ritter (1892). The pressures acting on the vertical wall and bottom were provided for the whole period of dam break flow varying the initial water depth and gate open speed. The measurement results of the dam break flow was compared with the hydrodynamic characteristics of green water phenomena, and it showed that the dam break flow could overestimate the green water loading based on the estimation suggested by Buchner (2002).

• Journal of Ocean Engineering and Technology
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• v.35 no.5
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• pp.382-392
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• 2021

In recent years, floating offshore wind turbines have attracted more attention as a new renewable energy resource while bottom-fixed offshore wind turbines reach their limit of water depth. Various projects have been proposed with the rapid increase in installed floating wind power capacity, but the economic aspect remains as a biggest issue. To figure out sensible approaches for saving costs, a comparison analysis of the levelized cost of electricity (LCOE) between floating and bottom-fixed offshore wind turbines was carried out. The LCOE was reviewed from a social perspective and a cost breakdown and a literature review analysis were used to itemize the costs into its various components in each level of power plant and system integration. The results show that the highest proportion in capital expenditure of a floating offshore wind turbine results in the substructure part, which is the main difference from a bottom-fixed wind turbine. A floating offshore wind turbine was found to have several advantages over a bottom-fixed wind turbine. Although a similarity in operation and maintenance cost structure is revealed, a floating wind turbine still has the benefit of being able to be maintained at a seaport. After emphasizing the cost-reduction advantages of a floating wind turbine, its LCOE outlook is provided to give a brief overview in the following years. Finally, some estimated cost drivers, such as economics of scale, wind turbine rating, a floater with mooring system, and grid connection cost, are outlined as proposals for floating wind LCOE reduction.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.84-93
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• 1987

A beach nourishment method can be used as one of the beach erosion protection methods which may keep coastal environments whithout constructing coastal structures on the HAE UN DAE beach. The beach nourishmens is affected by a natural condition and artificial condition;a natural condition includes conditions of bottom slope, diameter of bottom materials and waves, and artificial conditions include deposit position, method, diameter and quantity of the nourishing sand. It has accomplished to obtain the deposit position and the best diameter of the nourishing sand from a two-dimensional hydraulic model test, which simulates the erosional HAE UN DAE beach. In this study, the protection of the beach erosion can be maximized when the nourishing sand of 3.3mm in diameter, which is about 5.5.times of the bottom materials in diameter, is deposited layerly in front of the breaker zone which has a water depth of 4.6m.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.21-28
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• 2011

The primary purpose of the present study was to investigate the mechanism causing scour around a pipeline placed on the seabed in a shallow water zone. Such submarine pipelines are usually exposed to currents and waves. The present experiments made estimates for each different flow type. The scour width and depth in the equilibrium scour phase were analyzed by non-dimensional parameters. The experiment in this study considered various parameters: pipe diameters, wave periods, wave heights, and current velocities. Using the experimental results, the correlations of scour width, scour depth, and main non-dimensional parameters such as the Fr number and KC number were analyzed. In the case of steady currents, the scour hole was closely related to the bottom velocity, while the scour hole in waves showed a relatively low correlation to the bottom velocity because when exposed to waves the scour hole was restricted according to the movement distance of the water particles during a wave period. However, the scour width under a steady current was not limited because vortex shedding was well developed from having enough time and distance.

• Proceedings of the KSRS Conference
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• v.2
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• pp.692-694
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• 2006

X-SAR images taken on the coastal waters of Hwanghe province in Korea during SIR-C/X-SAR campaign in April and October 1994 are analysed. The SAR images show the peculiar signatures like nail marks, curved long string, and vortex streets patterns and they all seem to be produced by strong interactions between the topography in the coastal waters and tidal currents. The nail mark signatures are located at the same position of small scaled sand banks and the curved line patterns are almost identical to the outer boundary of large sand banks. Based on the tidal record, all the three images are taken at the almost same phase of tidal cycles, which are close to the low tide. It seems that bottom shapes are more strongly appeared on the SAR images when the tidal currents are slow. The front between two different current velocities caused by the flows along the steep boundaries of sandbanks is also the main factors imprinting the bottom features to the sea surface SAR images

• Korean Journal of Remote Sensing
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• v.22 no.5
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• pp.415-419
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• 2006

X-SAR images taken on the coastal waters of Hwanghe province in Korea during SIR-C/X-SAR campaign in April and October 1994 are analysed. The SAR images show the peculiar signatures like nail marks, curved long string, and vortex street patterns and they all seem to be produced by strong interactions between the topography in the coastal waters and tidal currents. The nail mark signatures are located at the same position of small scaled sand banks and the curved line patterns are almost identical to the outer boundary of large sand banks. Based on the tidal records, all the three images are taken at the almost same phase of tidal cycles, which are close to the low tide. It seems that bottom shapes are more strongly appeared on the SAR images when the tidal currents are slow. The front between two different current velocities caused by the flows along the steep boundaries of sandbanks is also the main factors imprinting the bottom features to the sea surface SAR images.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.70-82
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• 1995

A multi-layer simulation program is developed to estimate the ocean current considering sea bottom geometry. The so-called $\sigma$ coordinate system is introduced in vertical direction to describe sea bottom topography more accurately and effectively. Leapfrog scheme combined with Euler backward scheme is used to reduce computation error which may be possibly accumulated in time evolution by Leapfrog scheme alone. In this paper, very simple examples of rectangular basins with various bottom geometries were taken and the effect of sea bottom geometry on vertical structure of the ocean tidal current and its direction were investigated. Through comparisons between the present three dimensional calculation in which bottom topography is directly taken into consideration and the two dimensional calculation in which depth average concept is employed, it was found that magnitude of surface current and its direction could be largely affected by the sea bottom topography, particularly in shallow region with complex bottom shape.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1995.10a
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• pp.75-80
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• 1995

The model for the combined refraction and diffraction of water waves, the so-called mild-slope equation, was first developed by Berkhoff (1972) and has been studied by many coastal engineers because the model is able to consider the combined effect of refraction and diffraction of water waves and eliminate the problem of ray crossing which may happen in the previously developed ray theory. (omitted)

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.115-127
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• 2015

The aim of this study is to develop a simplified formula for added mass coefficients of a two-dimensional floating body moving vertically in a finite water depth. Floating bodies with various sectional areas may represent simplified structure sections transformed by Lewis form, and can be used for floating body motion analysis using strip theory or another relevant method. Since the added mass of a floating body varies with wave frequency and water depth, a correction factor is developed to take these effects into account. Using a developed two-dimensional numerical wave tank technique, the reference added masses are calculated for various water depths at high frequency, and used them as basis values to formulate the correction factors. To verify the effectiveness of the developed formulas, the predicted heave added mass coefficients for various wetted body sections and wave frequencies are compared with numerical results from the Numerical Wave Tank (NWT) technique.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.07a
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• pp.177-178
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• 2015

Sediments play a major role in determining pollution pattern in aquatic systems and reflecting the pollutant deposition. In the present study analysis the depth effect of organic pollutants and heavy metals using slow release biostimulant ball (BSB) in coastal sediment. BSB size fixed at 3cm, depth varied from 0cm to 10cm depth and 1 and 3 month interval period was carried out for the study. The organic pollutants of chemical oxygen demand, total solids and volatile solids were significantly changed at the surface sediment (0cm)in 1 month and 3 month interval time using BSB. In contrast, sediment depth increase upto 10cm the reduction percentage decrease like to control. Vertical distribution of heavy metals are not consistent from the surface layer toward the bottom layers. Heavy metals fractions were significantly changes, the exchangeable fraction was reduced and other organic and residual fractions were stabilized percentage are increased. This finding concluded BSB is effective for reduce organic pollutants, heavy metals stabilization from the contaminated sediment.