• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.1-18
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• 2014

Heave plates have been widely used to enhance viscous damping and thus reduces the heave response of Spar platforms. Single heave plate attached to the keel of the Spar has been reported in literature (Tao and Cai 2004). The effect of double heave plates on hydrodynamic response in random waves has been investigated in this study. The influence of relative spacing $L_d/D_d$ ($D_d$-the diameter of the heave plate) on the hydrodynamic response in random waves has been simulated in wave basin experiments and numerical model. The experimental investigation has been carried out using 1:100 scale model of Spar with double heave plates in random waves for different relative spacing and varying wave period. The influence of relative spacing between the heave plates on the motion responses of Spar are evaluated and presented. Numerical investigation has been carried out to investigate effect of relative spacing on hydrodynamic characteristics such as heave added mass and hydrodynamic responses. The measured results were compared with those obtained from numerical simulation and found to be in good agreement. Experimental and numerical simulation shows that the damping coefficient and added mass does not increase for relative spacing of 0.4 and the effect greater than relative spacing on significant heave response is insignificant.

• Journal of Environmental Health Sciences
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• v.28 no.2
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• pp.23-39
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• 2002

This study focuses on the structure of geographical conditions, the riverbed, the meterological and atmospheric examination, the ecological environment, the food chain and the ecosystem, in order to establish a basic plan for preparing a natural learning area of environmental ecosystem in Bukchun and its surroundings, Gyeongju. The results could be summarized as follows. Bukchun is a first grade which extends 6km along the road from Bomun bridge to the junction of Hyungsangang. The basin area is 7.10$\textrm{km}^2$ and the slope is 1/200~1/300. Gyeongju has good atmospheric conditions, i.e. SO$_2$0.011 ~0.017ppm, CO 0.8~ 1.5ppm, NO$_2$0.013~0.019ppm, $O_3$0.013~0.020ppm, TSP 85~142$\mu\textrm{g}$/㎥, PM-10 47~90$\mu\textrm{g}$/㎥ and Pb 0.057 ~0.129$\mu\textrm{g}$/㎥, which is below the annual and daily averages, and is little lower than those of Pohang and Ulsan. The ecosystem of Bukchun is based on the structure of the food chain, which includes birds such as the grey and white herons at the top of the food chain. This study also considers the development of the river's in terms of culture, environment and ecology concept.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.296-299
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• 2003

In this paper, an underwater acoustic digital transceiver is designed and implemented by a multiple DSPs system. We have designed a QPSK transmitter based on look-up table and 13-symbols Barker code is used for frame synchronization. Channel distortions are compensated by a wide-band beamformer based on FIR filter and an adaptive equalize. with RLS algorithm. Uniform linear array (ULA) with four elements is used for the spartial signal processing. 1/2 convolutional code and Viterbi decoder are implemented to overcome time-varying multi-path fading. Also, we show experimental results in the underwater anechoic basin at KRISO/KORDl and Goseong, Donghae and Soyang lake of Kangwon-do.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.2
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• pp.197-206
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• 2013

Recently, climate change causes climatic anomaly such as global warming, the typhoon and severe rain storm etc. and it brings damage frequently. Climate change and global warming are prevalent all over the world in this century and many researchers including hydrologists have studied on the climate change. In this study, Seonakdong river watershed in the Nakdong river basin was selected as a study area. Real-time monitoring system was used to draw the rating curves, which has 0.78 to 0.96 of $R^2$. To predict runoff change in Seonakdong river watershed caused by climate change, the change in hydrologic runoff were predicted using the watershed model, SWAT. As a result, the runoff from the Seonakdong river watershed was increased by up to 45 % in summer. Because of the non-point sources from the farmland and the urban area, the water quality will be affected by the climate change. In this study, the operating plan of the water gates in Seonakdong river will be suggested by considering the characteristics of the watershed runoff due to the climate change. The optimal watergate opening plan will solve the water pollution problems in the reservoir-like river.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.212-225
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• 2015

In order to preserve the quality of fresh water in the artificial lake after the reclamation of an intertidal flat at the mouth of a river, we suggest two novel methods of water purification by using tidal potential energy and an enclosed permeable embankment called an utsuro (Akai et al., 1990) in the reclaimed region. One method uses an inflatable bag on the seabed within an utsuro, while the other uses a moored floating barge out of a dyke. Each case employs a subsea pipe to allow flow between the inside and outside of the utsuro. The change in water level in the utsuro, which is pushed through the pipe by the potential energy outside, caused circulation in the artificial lake. In this paper, we analyzed the inflatable bag and floating barge motion as well as the pipe flow characteristics and drafts as given by a harmonic sea level, and compared the theoretical value with an experimental value with a simple small model basin. The numerical calculation based on theory showed good agreement with experimental values.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.208-215
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• 2001

An experimental method to investigate the dynamic charasteristics of buoys in extreme environmental condition is established. Because the buoy model requires a resonable size for accurate experiment, the test condition in model basin that satisfies the similarity law is hardly met with capability of test facilities. It is suggested that the linear wave component that is unable to satisy similarity is separated with others. The model experiment can be carried out with mitigated condition for the linear wave components while others including wave drift, current and wind are keeping the similarities. Then the result is extrapolated to give the dynamic behavior of buoys in extreme condition because linear wave component is soley responsible to oscillatory buoy motion and other environmental components are applied as a initial tension. the similarity for current and wind conditions is viewed as equivalence of restoring forces. the validity of proposed method is examined with different types of standard ocean buoys and it indicates that the linearity of measured characteristics is assured with a limitation of resonable distance between test and estimated wave conditions.

• Journal of Ecology and Environment
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• v.43 no.2
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• pp.129-160
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• 2019

Background: Characterizing and describing soils and land use and make a suggestion for sustainable utilization of land resources in the Ethiopian Rift valley flat plain areas of Lake Chamo Sub-Basin (CSB) are essential. Objectives: To (1) characterize soils of experimental area according to World Reference Base Legend and assess the nature and extent of salinity problems; (2) characterize land use systems and their role in soil properties; and (3) identify best land use practices used for both environmental management and improve agricultural productivity. Methods: Twelve randomly collected soil samples were prepared from the above land uses into 120 composites and analyzed. Results: Organic carbon (OC) and total nitrogen (TN) were varied along different land uses and depleted from the surface soils. The soil units include Chernozems (41.67%), Kastanozems (25%), Solonchaks (16.67%), and Cambisols (16.67%). The identified land uses are annual crops (AA), perennial crops (PA), and natural forest (NF). Generally, organic carbon, total nitrogen, percentage base saturation (PBS), exchangeable (potassium, calcium, and magnesium), available phosphorus (P₂O₅), manganese, copper, and iron contents were decreased in cultivated soils. Soil salinity problem was observed in annuals. Annuals have less nutrient content compared to perennials in irrigated agriculture while it is greater in annuals under rainfed. Clay, total nitrogen, available phosphorus, and available potassium (K₂O) contents were correlated positively and highly significantly with organic carbon and electrical conductivity. Conclusion: Management practices that improve soil quality should be integrated with leguminous crops when the land is used for annual crops production.

• Journal of Korea Water Resources Association
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• v.40 no.4
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• pp.287-297
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• 2007

The procedures for identifying channel network are suggested by exploring the scaling property between the local slope and the contributing area, given that the area threshold criterion is an indispensable complement to the slope-area threshold criterion. Through the use of the above procedures and the field data, the basin slopes illustrate the trends of large scatters in space for the geomorphologic/topographic factors. According to the scaling regimes of them both the forms of landscape can be classified as topographic divergence and convergence. The presentation of the procedures proposed in this study is implemented in the case study on Seolma experimental catchment in Korea. As a result the dynamic behaviors of basin are confirmed, and thus the dynamics of channel head advance and channel network are shown to represent better than the method using the topographic chart manually.

• Journal of Korea Water Resources Association
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• v.42 no.1
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• pp.75-92
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• 2009

The development of the method for flood runoff analysis representing Korean mountain basins have been one of big concerns for Korean hydrologists for several decades. Several traditional methods dealing with unit hydrograph have been restricted to be used in Korea basins, because of its drawbacks due to its originality from other countries and the uncertainties of control parameters as well as its linearity assumption between rainfall and runoff relationship. In this paper, several geomorphological similarity relationships for Korean mountain basins was developed by using the experimental data over 40 Korean basins. Then those were applied directly to geomorphological unit hydrograph theory to meet Korean geomorphological unit hydrograph. The developed method was applied to Andong Dam basin. The results show the applicability and simplicity of the developed Korean geomorphological unit hydrograph generally for Korean mountain basins in future. It might be needed for more validations and applications of this method over Korean regions.

• Earthquakes and Structures
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• v.6 no.2
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• pp.163-179
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• 2014

Dynamic test with scaled model of a group of intake towers was performed to study the dynamic interaction between water and towers. The test model consists of intake tower or towers, massless foundation near the towers and part of water to simulate the dynamic interaction of tower-water-foundation system. Models with a single tower and 4 towers were tested to find the different influences of the water on the tower dynamic properties, seismic responses as well as dynamic water-tower interaction. It is found that the water has little influence on the resonant frequency in the direction perpendicular to flow due to the normal force transfer role of the water in the contraction joints between towers. By the same effect of the water, maximum accelerations in the same direction on 4 towers tend to close to each other as the water level increased from low to normal level. Moreover, the acceleration responses of the single tower model are larger than the group of towers model in both directions in general. Within 30m from the surface of water, hydrodynamic pressures were quite close for a single tower and group of towers model at two water levels. For points deeper than 30m, the pressures increased about 40 to 55% for the group of towers model than the single tower model at both water levels. In respect to the pressures at different towers, two mid towers experienced higher than two side towers, the deeper, the larger the difference. And the inside hydrodynamic pressures are more dependent on ground motions than the outside.