• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.27-31
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• 2013

The structure of a variable liquid column oscillator(VLCO) is analogous to that of the tuned liquid column damper used to suppress oscillatory motion in large structures like tall buildings and cargo ships. The VLCO is a system for absorbing the high kinetic energy of the accelerated motions of multiple floating bodies using an air-spring effect produced the installation of inner air chambers. Thus, a VLCO can improve the energy efficiency of the activating object type of wave energy converters made by the Pelamis Company. In this research, an experiment was performed in two cases: with the top valves closed and open. The floating bodies were connected by hinges. The effect of the internal flow was estimated by comparing the results for the closed and open valves.

• Applied Microscopy
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• v.30 no.2
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• pp.233-240
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• 2000

Aspects of structural differentiation of the free -floating hydrophyte, Spirodela polyrhira, has been investigated. The hydrophyte exhibited highly reduced structures having only fronds, connective stalks, and roots as a mature plant. The fronds were major photosynthetic and vegetatively reproducing organ during the growth. Daughter fronds which developed early in the mother frond were also chlorenchymatous, but they remained within foliage sheaths of the mother frond before separation from connecting stalks. Although the stalks and roots originated from the same meristematic region of the frond, they exhibited the distinct polarity showing former lateral growth and latter axial growth. Air chambers were formed only in the fronds and roots. Cellular components were scattered throughout the diffuse cytoplasm in most of the actively growing stalk cells. Root cells protected by the root cap demonstrated relatively complex organization, showing dense cytoplasm with Golgi, rER, mitochondria, and chloroplasts in the cortical cells. Cells in the root cap were highly vacuolated within the peripheral cytoplasm. Such reduction and differentiation of the plant body in Spirodela polyrhiza most effectively contributes to the better adaptation of smaller plants to superficial aquatic environments, while also enabling the rapid growth.

• Journal of the Korea Organic Resources Recycling Association
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• v.26 no.3
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• pp.33-37
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• 2018

In order to recycle sewage dredging soil, we analyzed particle size distribution and organic content of dredged sewage sediments. Based on this, it was determined that particles with relatively low organic content of 1.0 mm or more could be recycled as fine aggregate. Although it was inorganic at the size of 5 mm or more, it contained a number of foreign substances other than fine aggregate, which were needed to be removed with a sieve. Since there are volatile suspended solids between 1.0 and 5.0 mm size, they were removed by means of flotation. Fine aggregate was obtained from dredging soil by screening followed with flotation method, and the proportion of fine aggregate obtained in this study was around 38 %.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.5
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• pp.649-653
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• 1999

A magnetic fluid separation technology was confirmed to be very effective to remove the suspended solids (SS) from aquacultural recirculating water, In this study, the effects of operating variables on the characteristics of SS removal were investigated through the test runs using magnetite of 2 $\mu$m mean diameter as magnetic powder. Magnetic flocculation here formed by adsorbing fine magnetites on the surface of suspended solid was observed. The strength of magnet was of significance in determining the SS removal efficiency as well as the capacity of the equipment. In addition, the SS removal efficiency decreased with an increase in the superficial liquid velocity, but the effect became negligible when the mass ratio of magnetite to the suspended solids was higher than 1.0.

• Journal of Power System Engineering
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• v.20 no.3
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• pp.5-10
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• 2016

The structure of the variable liquid column oscillator(VLCO) is analogous to that of the tuned liquid column damper used to suppress oscillatory motion in large structures like tall buildings and cargo ships. VLCO is using the technology which absorbs high potential energy made by process of accelerated motions effect of air spring by installation of inner air chamber. So, the application of VLCO can improve the efficiency of energy than that of wave energy converters made in Pelamis Company. In this research, experiments were performed for the models which have two different liquid column sizes. In order to find out the biggest motion response, two major conditions are taken into account. Two conditions are to open(or close) the valves and to differentiate the height of the liquid column.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.109-117
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• 2022

There has been an increasing number of studies on photovoltaic energy generation system in an offshore site with the largest energy generation efficiency, as increasing the researches and developments of renewable energies for use of offshore space and resources to replace existing fossil fuels and resolve environmental challenges. For installation and operation of floating photovoltaic systems in an offshore site with harsher environmental conditions, a stiffness of structural members comprising the total system must be reinforced to inland water spaces as dams, reservoirs etc., which have relatively weak condition. However, there are various limitations for the reinforcement of structural stiffness of the system, including producible size, total mass of the system, economic efficiency, etc. Thus, in this study, a floating breakwater is considered for reducing wave loads on the system and minimizing the reinforcement of the structural members. Wave reduction performances of floating breakwaters are evaluated, considering size and distance to the system. The wave loads on the system are evaluated using the higher-order boundary element method (HOBEM), considering the multi-body effect of buoys. Stresses on structural members are assessed by coupled analyses using the finite element method (FEM), considering the wave loads and hydrodynamic characteristics. As the maximum stresses on each of the cases are reviewed and compared, the effect of floating breakwater for floating photovoltaic system is checked, and it is confirmed that the size of breakwater has a significant effect on structural responses of the system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1353-1362
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• 2014

In recent years, numerous environmental problems associated with the excessive use of fossil fuel are taking place. For an alternative energy resource, the importance of renewable energy and the demands of facilities to generate renewable energy are continuously rising. To satisfy such demands, a large number of photovoltaic energy generation structures are constructed and planned with large scale. However, because these facility zones are mostly constructed on land, some troubles are occurred such as rising of construction cost due to the cost of land use, environmental devastation, etc. To solve such problems, the floating type photovoltaic energy generation system using FRP members have been developed in Korea. FRP members are recently available in civil engineering applications due to many advantages such as high strength, corrosion resistance, light weight, etc. and they are suitable to fabricate the floating structures because of their material properties. In this study, the analytical and experimental investigations to evaluate the structural performance of floating PV generation structure and SMC FRP vertical member which is used to fabricate the structure were conducted. The static and dynamic performances of floating PV generation structure are evaluated through the FE analysis and the experiment, respectively. Moreover, the structural safety evaluation and buckling analysis of SMC FRP vertical compression member are also conducted by the FE analysis, and the structural behavior of SMC FRP member under compression and pullout is investigated by the experiments. From this study, it was found that the structural system composed of pultruded FRP and SMC FRP members are safe enough to resist externally applied loads.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.119-127
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• 2013

Recently, several researches on the development of new economical foundation types have been performed to support floating structures as many offshore structures have been constructed. This study focused on the evaluation of bearing capacity of group suction piles, which are connected by a concrete pile cap. The offshore floating structures are mainly subjected to horizontal loading, so the horizontal bearing capacities of the group suction piles were analyzed by performing 3-dimensional finite element analyses. The group suction piles are expected to behave as a rigid pile due to its shallow embedded depth. Therefore, the detailed soil modeling was necessary to simulate the bearing behavior of soils under low confining pressure. The modulus and the strength of soils were modelled to increase with effective confining pressure in soils. For the parametric study, the center-to-center spacing between piles was varied and two soil types of clay and sands were applied. The analyses results showed that the yielding load of the group pile increased with the increase of the pile spacing and the yielding load of the group piles with 5D spacing was about 3 times larger than that of the single pile with free rotation.

• Journal of the Korean Geosynthetics Society
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• v.14 no.1
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• pp.1-10
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• 2015

Recently, several researches on the development of new economical anchor systems have been performed to support floating structures. This study focused on the group suction piles, which connect mid-sized suction piles instead of a single suction pile with large-diameter. The group suction pile shows the complex bearing behavior with translation and rotation, so it is difficult to apply conventional design methods. Therefore, the numerical modeling technique was developed to evaluate the horizontal bearing capacity of the group suction piles in clay. The technique models suction piles as beam elements and soil reaction as non-linear springs. To analyze the applicability of the modeling, the horizontal load-movement curves of the proposed modeling were compared with those of three-dimensional finite element analyses. The comparison showed that the modeling underestimates the capacity and overestimate the displacement corresponding to the maximum capacity. Therefore, the correction factors for the horizontal soil resistance was proposed to match the bearing capacity from the three-dimensional finite element analyses.