• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.103-110
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• 2010

In this study, the possibility of seismic response control of semi-active tuned mass damper (TMD) for spatial structures has been investigated. To this end, an arch structure was used as an example structure because it has primary characteristics of spatial structures and it is a comparatively simple structure. A TMD and semi-active TMD were applied to the example arch structure and the seismic control performance of them were evaluated based on the numerical simulation. In order to regulate the damping force of the semi-active TMD, groundhook control algorithm, which is widely used for semi-active control, was used. El Centro (1940) and Northridge (1994) earthquakes and harmonic ground motion were used for performance evaluation of passive TMD and semi-active TMD. Based on the analytical results, the passive TMD could effectively reduce the seismic responses of the arch structure and it has been shown that the semi-active TMD more effectively decreased the dynamic responses of the arch structure compared to the passive TMD with respect to all the excitations used in this study.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.165-178
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• 2000

The simplified model for 3-dimensional analysis of vehicle-bridge interactions is presented in this study. By using the analysis model which includes the eccentricity of axle loads and the effect of the torsional forces acting on the bridge, the more accurate analysis results of the behavior of the bridge can be obtained. The equations of kinetic energy, potential energy and damping energy are expressed by degrees of freedom of the vehicle and the bridge. And then by applying Lagrange's equations of motion, the equations of motion of the vehicle and the bridge are obtained. By deriving the equations of forces acting on the bridge considering the vehicle-bridge vertical interactions and also by identifying the position of vehicle as time goes by, mass matrix, stiffness matrix, damping matrix and load vector of vehicle-bridge system are constructed in accordance with the position of vehicles. Then using Newmark's β-method(average acceleration), the equations of motion for the total vehicle bridge system are solved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1061-1069
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• 2010

In this study, a simplified axisymmetric model is proposed for the problem of compressible internal flow past a microgap. Using numerical and experimental methods, the phenomena of choked flows are observed; these flows are induced by the acceleration of subsonic flows past the narrow cross-section of an annular shape made by a microgap. The relation between mass flow rate and differential pressure is obtained, and by comparing the result with experimental results, the reliability of the numerical results is discussed. The generation of a supersonic jet flow and its diffraction are visualized by performing the numerical analysis of axisymmetric compressible Navier-Stokes equations. This investigation greatly extends the physical understanding of the axisymmetric compressible flow, which has a wide range of engineering applications, e.g., in the case of valves in automotive power systems.

• Journal of the Korean Ceramic Society
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• v.37 no.11
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• pp.1084-1090
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• 2000

(Bi$_2$O$_2$)$^{2+}$층 사이에 두 개의 Ta-O 팔면체로 연결된 Bi 계의 층상 페로브스카이트 구조인 SrBi$_2$Ta$_2$O$_{9}$ (SBT) 박막을 XPS를 이용하여 깊이별 화학 상태 변화를 분석하였다. 아르곤 이온으로 SBT 박막을 식각하면, SBT 박막의 각 구성물들은 가속 Ar$^{+}$ 이온의 에너지에 따라 변화한다. SBT 각 구성물 중 Sr 3d의 화학 상태는 Ar$^{+}$ 이온의 에너지변화에 따라 근소하게 변화한다. 반면에, Ta 4f와 Bi 4f의 화학 상태 변화는 인가되는 Ar$^{+}$ 이온 에너지에 확실하게 의존한다. 특히, Bi 4f는 Sr과 Ta에 비해 낮은 Ar$^{+}$ 이온 에너지에서도 Bi-O의 화학 상태가 금속 Bi 화학 상태로 현저하게 변화한다. 이러한 SBT 박막의 화학 상태 변화는 산호 원자의 선택적인 식각 때문에 발생하며 선택적인 식각은 SBT 박막 내에서 각 구성물과 산소간의 질량 차이와 각 구성물의 열적 안정성에 의존함을 알 수 있다.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.129-134
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• 1994

A Laser Cutter is designed for the precise fabrications in the shipyards recently. The cutter is a gantry type one with specified functions of movability and strength in order to satisfy the workability. The gantry frame should move with a certain velocity in a relatively short time for the proper cutting of the object materials. The gantry is fitted with ball screw and the acceleration field is formed by actuating this ball screw. The relative displacement should be within the allowable design criteria to make sure the precise cutting of the materials by the laser. In this paper, modal and structural analysis for a Laser Cutter which is commonly used in the shipyards, is carried out to check the design criteria of the system. The system is modeled by placing the proper shell and soils finite elements and fictitious mass properties to represent the real one. The way how to extract the loading conditions based on the given velocity criteria of the system is presented. Static structural analysis is performed and the results came out as expected. Modal analysis for finding eigen-values and mode shapes of the system is performed and it is shown that the time dependent dynamic analysis is unnecessary for this system for its operating circumstances.

• Korean Journal of Ecology and Environment
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• v.56 no.4
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• pp.281-302
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• 2023

Carbon is not only an essential element for life but also a key player in climate change. The radiocarbon (¹⁴C) analysis using accelerator mass spectrometry (AMS) is a powerful tool not only to understand the carbon cycle but also to track pollutants derived from fossil carbon, which have a distinct radiocarbon isotope ratio (Δ¹⁴C). Many studies have reported Δ¹⁴C of carbon compounds in streams, rivers, rain, snow, throughfall, fine particulate matter (PM_2.5), and wastewater treatment plant effluents in South Korea, which are reviewed in this manuscript. In summary, (1) stream and river carbon in South Korea are largely derived from the chemical weathering of soils and rocks, and organic compounds in plants and soils, strongly influenced by precipitation, wastewater treatment effluents, agricultural land use, soil water, and groundwater. (2) Unprecedentedly high Δ¹⁴C of precipitation during winter has been reported, which can directly and indirectly influence stream and river carbon. Although we cannot exclude the possibility of local contamination sources of high Δ¹⁴C, the results suggest that stream dissolved organic carbon could be older than previously thought, warranting future studies. (3) The ¹⁴C analysis has also been applied to quantify the sources of forest throughfall and PM_2.5, providing new insights. The ¹⁴C data on a variety of ecosystems will be valuable not only to track the pollutants derived from fossil carbon but also to improve our understanding of climate change and provide solutions.

• Progress in Medical Physics
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• v.20 no.4
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• pp.308-316
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• 2009

To achieve the accurate evaluation of given absorbed dose from output dose of linear accelerator photon beam through investigate the characteristics of LiF:Mg,Cu,P TLD powder. This experimental TL phosphor is performed with a commercial LiF:Mg,Cu,P powder (Supplied by PTW) and TL reader (LTM, France). The TLD was exposed to 6 MV X rays of linear accelerator photon beam with range 15 to 800 cGy in blind dose at two hospitals. The dose evaluation of TLD was through the experimental algorithms which were dose dependency, dose rate dependency, fading and powder weight dependency. The glow curve has shown the three peaks which are 110, 183 and 232 degrees of heating temperature and the main dosimetric peak showed highest TL response at 232 high temperature. In this experiments, the LiF:Mg,Cu,P phosphor has shown the 2.5 eV of electron trap energy with a second order. This experiments guided the dose evaluation accuracy is within 1% +2.58% of discrepancy. The TLD powder of LiF:Mg,Cu,P was analyzed to dosimetric characterists of electron captured energy and order by glow shape, and dose-TL response curve guided the accuracy within 1.0+2.58% of output dose discrepancy.

• Journal of Korean Society of Steel Construction
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• v.16 no.3 s.70
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• pp.305-314
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• 2004

Many residential buildings and mixed-use (i.e., residential and commercial) buildings that are currently under construction in the country mainly consist of building clusters rather than single structures. Recent trends show single buildings that actually consist of two houses. The lower part of the building consists of a single dwelling space. However, the upper part of the building is split into two dwellings, considering the aspects of commercialism and appearance, such as ventilation and lighting. These tall and complex buildings not only have low mass and damping. They also depend on wind loads for their structural stability and serviceability, due to the interaction between the building groups and the wind. In architectural design, however, the interaction effects among neighboring houses within a building group have yet to be identified. In addition, it is difficult to predict these interaction effects. In this regard, this thesis aims to model patterns of architecture, which consist of two houses that are existing or under construction. Current structures are investigated by comparing their wind-reduced response interaction effects, based on the measured distance between two buildings, and the acceleration response through the wind tunnel test. The results of this study are expected to provide basic data for wind-induced response interaction effects of building groups. Furthermore, the outcomes are also intended to be used as data for more rational and economical structure design.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.487-496
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• 2010

The structural damping ratios for seismic design of nuclear power plant structures are specified in Regulatory guide 1.61 of the United States NRC for RC structures of 4%(OBE) and 7%(SSE), and for steel structures of 3%(OBE) and 4%(SSE), but not for steel-plate concrete (SC) structures that have been developed recently. The objective of this study is to investigate the damping ratios of SC structures by identifying the relative differences in the damping ratios between RC and SC structures. An experimental study was performed on four specimens, RC-S, RC-M, SC-S and SC-M, where S stands for shear-governed and M for moment-governed. The conducted method was free vibration testing by rupturing a brittle steel plate that linked the actuator and the mass center. The test results were analyzed to determine fundamental frequencies and damping ratios at various load levels. By examining the relative differences in damping ratios of four specimens, it is proposed for SC structures to use the same damping ratio of 4% as RC one at OBE, but 1% less damping ratio than RC one resulting in 6% at SSE.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.2
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• pp.164-171
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• 2002

In this study, a mass-spring model is used to dynamically describe and calculate the shape and movement of a mid-water trawl system. This mathematical model theorizes that the factors constituting the system are the material points and the external forces such as hydrodynamic load, gravity, and buoyancy act on these material points. In addition, it surmises that these material points are connected to each other by springs, the springs do not have any mass, and the internal force acts on these springs. The non-linear differential equations are implicitly integrated with time for guaranteeing a stable solution. The dynamic simulation by the mass-spring model shows the status of the gear such as fishing gear depth, distance between doors, shape of the gear, and tension of each line. It depends on the parameters such as towing force, warp length, force of a sinker, buoyancy of a float, type of door and netting materials. The validity of the model is verified by comparing simulation motions of a trawl system obtained from computed values to those from an actual experiment.