• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.3
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• pp.181-187
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• 2009

To estimate the status and volume of artificial reefs(ARs) deployed at the sea bottom in fishing grounds, this study assessed the initial volume of ARs, the cubic volume of AR groups, and the porosity of each AR using image data collected during a survey using a multi-beam echo sounder(MBES) and a side scan sonar(SSS). These results were compared with data collected during diver surveys and used to develop a new method and prediction formulas for countermeasures, facility volume, and efficient use of volume for deployed ARs(cubic concrete). The field survey results for nine ARs deployed in the Busan Sea region were calculated, and the average value of coefficient k(indicating the efficient use of volume ratio) among ARs was 0.753, and the correlation between coefficient k and year(Yr) of deployment was calculated as k=0.0023Yr+0.725. The relationship between these two factors was poor. In years following the deployment of artificial reefs, coefficient k and year of deployment were not correlated, in spite of the hardening ground due to subsidence and the reduced distance between ARs. Consequently, it is reasonable to suppose that coefficient k was defined by bottom surface conditions and initial deployment conditions.

• Journal of the Korean Geotechnical Society
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• v.31 no.6
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• pp.27-44
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• 2015

An analytical solution of dynamic responses for seabed in finite and infinite thicknesses including shallow has been developed under flow and partial standing wave with arbitrary reflection ration coexisting field at a constant water depth condition. In the analytical solution, a field was simply transited to a coexisting field of progressive wave and flow when reflection ratio was 0 and to a coexisting field of fully standing wave and flow when reflection ratio was 1. Based on the Biot's consolidation theory, the seabed was assumed as a porous elastic media with the assumptions that pore fluid is compressible and Darcy law governs the flow. The developed analytical solution was compared with the existing results and was verified. Using the analytical solution the deformation, pore pressure, effective and shear stresses were examined under various given values of reflection ratio, flow velocity, incident wave's period and seabed thickness. From this study, it was confirmed that the dynamic response of seabed was quite different depending on consideration of flow, which causes changing period and length of incident and reflection waves. It was also confirmed that dynamic response significantly depends on the magnitude of reflection ratio.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.2
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• pp.118-134
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• 2015

An analytical solution of dynamic responses for seabed in shallow, finite and infinite thicknesses has been developed under flow and standing wave coexisting field at a constant water depth condition. To do this, based on the Biot's consolidation theory, the seabed is assumed as a porous elastic media with the assumptions that pore fluid is compressible and Darcy law governs the flow. The developed analytical solution is compared with the previous results and is verified. Using the analytical solution the deformation, pore pressure, effective and shear stresses of seabed are examined under various given values of flow velocity, incident wave period and seabed thickness. From this study, it is confirmed that the seabed response is quite different depending on consideration of flow, which causes changing period and length of incident and reflection waves.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.295-304
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• 2012

This study proposed a two-dimensional horizontal numerical model based on the nonlinear shallow water wave equations to simulate tsunami propagation and coastal inundation. We numerically investigated the possible impacts of tsunami caused by the triple interlocked Tokai, Tonankai and Nankai Earthquakes on the Jeju coastal areas, using the proposed model. The simultaneous Tokai, Tonankai and Nankai Earthquakes were created a virtual tsunami model of an M9.0 earthquake. In numerical analysis, a grid nesting method for the local grid refinement in shallow coastal regions was employed to sufficiently reproduce the shoaling effects. The numerical model was carefully validated through comparisons with the data collected during the tsunami events by 2011 East Japan Earthquake and 1983 central East Sea Earthquake (Nihonkai Chubu Earthquake). Tsunami propagation triggered by the combined Tokai, Tonanakai and Nankai, Earthquakes was simulated for 10 hours to sufficiently consider the effects of tsunami in the coastal areas of Jeju Island. The numerical results revealed that water level fluctuation in tsunami propagation is greatly influenced by water-depth change, refraction, diffraction and reflection. In addition, the maximum tsunami height numerically estimated in the coastal areas of Jeju Island was about 1.6 m at Sagye port.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.277-286
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• 2012

In the numerical simulation of wave fields using a multi-phase flow model that considers simultaneous flows of materials with different states such as gas, liquid and solid, there is need of an accurate representation of the interface separating the fluids. We adopted an algebraic interface capturing method called tangent of hyperbola for interface-capturing(THINC) method for the capture of the free-surface in computations of multi-phase flow simulations instead of geometrical-type methods such a volume of fluid(VOF) method. The THINC method uses a hyperbolic tangent functions to represent the surface, and compute the numerical flux for the fluid fraction functions. One of the remarkable advantages of THINC method is its easy applicability to incorporate various numerical codes based on Navier-Stokes solver because it does not require the extra geometric reconstruction needed in most of VOF-type methods. Several tests were carried out in order to investigate the advection of interfaces and to verify the applicability of the THINC method to wave fields based on the one-field model for immiscible two-phase flows (TWOPM). The numerical results revealed that the THINC method is able to track the interface between air and water separating the fluids although its algorithm is fairly simple.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.4
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• pp.262-272
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• 2020

A large number of studies on wave breaking have been carried out, and many experimental data have been documented. Moreover, on the basis of various experimental data set, many empirical or semi-empirical formulas based primarily on regression analysis have been proposed to quantitatively estimate wave breaking for engineering applications. However, wave breaking has an inherent variability, which imply that a linear statistical approach such as linear regression analysis might be inadequate. This study presents an alternative nonlinear method using an neural network, one of the machine learning methods, to estimate breaking wave height and breaking depth. The neural network is modeled using Tensorflow, a machine learning open source platform distributed by Google. The neural network is trained by randomly selecting the collected experimental data, and the trained neural network is evaluated using data not used for learning process. The results for wave breaking height and depth predicted by fully trained neural network are more accurate than those obtained by existing empirical formulas. These results show that neural network is an useful tool for the prediction of wave breaking.

• Journal of Bio-Environment Control
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• v.3 no.1
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• pp.20-27
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• 1994

This study was conducted to improve marketing value and productivity of cucumber which was cultivated with primary scaffold stem type (Mannungcheongjang) and lateral stem type (Sayeup). The results are summarized as follows ; 1. Investigation of fruit setting characteristics to improve cucumber training type was resulted that the fruit-thinning was effective 3 nodes in Mannung- cheongjang and 4 nodes in Sayeup, because of defected yield potential and marketing value. 2. In the matter of early growing stage after training and cucumber quality at different treatment, cucumber weight at flowering curved cucumber and growth analysis of Mannungcheongjang were good in order of horizontal>vertical>slant training. And those of Sayeup were good in order of horizontal >slant> vertical training. 3. Aspect of light reception of cucumber plant in the level of plant height and accumulated leaf area index, vertical and horizontal training are better than slant in Mannungcheongjang, and there is order of horizontal >vertical >slant training in Sayeup. 4. Horizontal training in Mannungcheongjang was superior to any other case In view of cucumber number, productivity, and marketing rate. Therefore, this training was suggest ed of best method in cucumber cultivation.

• Korean Journal of Environmental Agriculture
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• v.12 no.3
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• pp.239-246
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• 1993

In order to clarify the possible contamination of rice straw used as a crude feed for livestock, Korean native cattle and cow, by pesticides, the samples collected from 21 sites in Korea were analyzed by a multiresidue method for 10 pesticides with GLC to obtain the following results. 1. Detection limits were 0.001ppm in butachlor, 0.002ppm in chlorpyrifos, 0.003ppm in BPMC, pirimiphos-methyl and diazinon, 0.004ppm in fenitrothion, 0.005ppm in phenthoate, 0.009ppm in IBP, 0.015ppm in carbofuran, and 0.03ppm in carbaryl. 2. In recovery tests, 73-101% of the pesticides applied were recovered, the recovery being low in carbofuran and chlorpyrifos. 3. Butachlor, 2-chloroacetanilide herbicide, and BPMC, carbaryl, and carbofuran, carbamate insecticides, were not detected in any sample. 4. In organophosphorus insecticides, the amounts of fenitrothion in sample No. 1, 2, 4, 5, 7, 12, 20 and 21 were in the range of 0.01-0.05ppm, those of phenthoate detected in sample No. 10 and 12 were 0.4 and 0.17ppm, respectively, and those of IBP in all samples, with the exception of sample No. 7, 12, 16, 17, 20, and 21, were in the range of 0.01-0.20ppm. The residues of chlorpyrifos, diazinon, and pirimiphos-methyl were not detected.

• Journal of Food Hygiene and Safety
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• v.33 no.5
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• pp.412-415
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• 2018

The objective of this study was to establish a quantitative count method of Vibrio vulnificus cells. Plate count method is often used to count the number of V. vulnificus cells using thiosulfate citrate bile salts sucrose (TCBS) agar plate. However, this method is unsuitable for counting V. vulnificus cells due to growth inhibition and cell injuries in TCBS medium. In this study, we suggested a most probable number-polymerase chain reaction (MPN-PCR) method using alkaline peptone water medium for the quantification of V. vulnificus. This MPN-PCR method showed 2 log higher cell number than TCBS agar plate method. Similar results were also found in the control using, Luria-Bertani agar containing 2% NaCl. Thus, this MPN-PCR method can be used a sensitive method for quantitative count of viable V. vulnificus cells in fish and shellfish samples.

• Journal of Life Science
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• v.14 no.2
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• pp.331-338
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• 2004

Growth and sexual differentiation of the seaweed Porphyra pseudolinearis Ueda have been investigated monthly in the intertidal zone of the East Sea, Korea. Young blades of P. pseudolinearis appeared at the beginning of October. Carp os pores were released at the end of November immediately after carposporangia formation. Then the thalli of P. pseudolinearis were extinguished at the end of March. Young thalli were budded through the stages of conchocelis and conchospore. Thalli showed lanceolate type in shape, cordate type in holdfast, absence of microscopic spinulate process and sexual generation. Ratios of length to width in female thalli ranged from 5.6 to 7.4 at the maturation in December and slightly decreased 3.3 to 4.8 in January and 4.9 to 7.3 in December while the ratios of male thalli ranged from 4.2 to 4.8 in January. On October 12, average five individuals were obsered in a quadrate (30 cm ${\times}$ 30 cm), 238$\pm$18 individuals for the maturation stage in December and then it was reduced to 150 individuals in February and 15 individuals in March. Average sex ratios for female, male and vegetative thalli were 31.3% 46.9% and 21.9% respectively in early December, the beginning time of sex maturation. The sex ratio of female and male thalli in December 17, changed to 69.4%, 30.6% respectively.