• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.52.2-52.2
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• 2014

The Immersion Grating Infrared Spectrometer (IGRINS) is an unprecedentedly minimized infrared cross-dispersed echelle spectrograph with a high-resolution and high-sensitivity optical performance. A silicon immersion grating features the instrument for the first time in this field. IGRINS will cover the entire portion of the wavelength range between 1.45 and $2.45{\mu}m$ accessible from the ground in a single exposure with spectral resolution of 40,000. Individual volume phase holographic (VPH) gratings serve as cross-dispersing elements for separate spectrograph arms covering the H and K bands. On the 2.7m Harlan J. Smith telescope at the McDonald Observatory, the slit size is $1^{\prime\prime}{\times}15^{\prime\prime}$. IGRINS has a $0.27^{\prime\prime}$ pixel-1 plate scale on a $2048{\times}2048$ pixel Teledyne Scientific & Imaging HAWAII-2RG detector with SIDECAR ASIC cryogenic controller. The instrument includes four subsystems; a calibration unit, an input relay optics module, a slit-viewing camera, and nearly identical H and K spectrograph modules. The use of a silicon immersion grating and a compact white pupil design allows the spectrograph collimated beam size to be 25mm, which permits the entire cryogenic system to be contained in a moderately sized rectangular vacuum chamber. The fabrication and assembly of the optical and mechanical hardware components were completed in 2013. In this presentation, we describe the major design characteristics of the instrument and the early performance estimated from the first light commissioning at the McDonald Observatory.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.285-292
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• 2012

Fixed connection is generally used for beam and column connections of concrete structures, but significant damages at the connection due to severe earthquakes have been reported. In order to reduce damages of the connection and improve seismic performance of the connection, several innovative connections have been suggested. One newly proposed connection type allows a rotation of the connection for applications in rotating or rocking beams, columns, and shear walls. Such structural elements would provide a nonlinear lateral force-displacement response since their contact depth developed during rotation is gradually reduced and the stress across the sections of the elements is non-linearly distributed around a contact area, which is called an elastic hinge region in the present study. The purpose of the present study is to define the elastic hinge region or length for the rocking columns, through investigating the cross-sectional stress distribution during their lateral behavior. Performing a finite element analysis (FEA), several parameters are considered including axial load levels (5% and 10% of nominal strength), different boundary conditions (confined-ends and cantilever types), and slenderness ratios (length/depth = 5, 7, 10). The FEA results showed that the elastic hinge length does not directly depend on the parameters considered, but it is governed by a contact depth only. The elastic hinge length started to develop after an opening state and increased non-linearly until a rocking point(pre-rocking). However, the length did not increase any more after the rocking point (post-rocking) and remained as a constant value. Half space model predicting the elastic hinge length is adapted and the results are compared with the numerical results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.612-620
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• 2019

The increasing use of curved beams in buildings, vehicles, ships, and aircraft has results in considerable effort being directed toward developing an accurate method for analyzing the dynamic behavior of such structures. The stability behavior of elastic curved beams has been the subject of a large number of investigations. Solutions of the relevant differential equations have traditionally been obtained by the standard finite difference. These techniques require a great deal of computer time as the number of discrete nodes becomes relatively large under conditions of complex geometry and loading. One of the efficient procedures for the solution of partial differential equations is the method of differential quadrature. The differential quadrature method(DQM) has been applied to a large number of cases to overcome the difficulties of the complex algorithms of programming for the computer, as well as excessive use of storage due to conditions of complex geometry and loading. In this study, the in-plane extensional vibration for asymmetric curved beams with linearly varying cross-section is analyzed using the DQM. Fundamental frequency parameters are calculated for the member with various parameter ratios, boundary conditions, and opening angles. The results are compared with the result by other methods for cases in which they are available. According to the analysis of the solutions, the DQM, used only a limited number of grid points, gives results which agree very well with the exact ones.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.845-856
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• 2020

This study proposes a bridge evaluation system for indivisible permit vehicles such as hydraulic cranes. The permit loads for the bridge evaluation are divided into three categories: routine permit loads, special permit 1 loads, and special permit 2 loads. Routine permit and special permit 1 vehicles are allowed to cross a bridge with normal traffic. For these two permits, the standard lane model in the Korean Highway Bridge Design Code was adopted to consider normal traffic in the same lane. Special permit 2 vehicles are assumed to cross a bridge without other traffic. Structural analyses of two prestressed-beam bridges and two steel box girder bridges were conducted for the proposed permit loads. The rating factors of the four bridges for all permit loads were calculated as sufficiently large values for the moment and shear force so that crossing the bridges can be permitted. A reliability assessment of the bridges was performed to identify the reliability levels for the permit vehicles. It was confirmed that the reliability level of the minimum required strength obtained by the load-resistance factors yields the target reliability index of the design code for the permit vehicles.

• Geomechanics and Engineering
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• v.37 no.6
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• pp.599-614
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• 2024

To evaluate the safety status of deteriorated segments in a submarine shield tunnel during its service life, a seepage model was established based on a cross-sea shield tunnel project. This model was used to study the migration patterns of erosive ions within the shield segments. Based on these laws, the degree of deterioration of the segments was determined. Using the derived analytical solution, the internal forces within the segments were calculated. Lastly, by applying the formula for calculating safety factors, the variation trends in the safety factors of segments with different degrees of deterioration were obtained. The findings demonstrate that corrosive seawater presents the evolution characteristics of continuous seepage from the outside to the inside of the tunnel. The nearby seepage field shows locally concentrated characteristics when there is leakage at the joint, which causes the seepage field's depth and scope to significantly increase. The chlorine ion content decreases gradually with the increase of the distance from the outer surface of the tunnel. The penetration of erosion ions in the segment is facilitated by the presence of water pressure. The ion content of the entire ring segment lining structure is related in the following order: vault < haunch < springing. The difference in the segment's rate of increase in chlorine ion content decreases as service time increases. Based on the analytical solution calculation, the segment's safety factor drops more when the joint leaks than when its intact, and the change rate between the two states exhibits a general downward trend. The safety factor shows a similar change rule at different water depths and continuously decreases at the same segment position as the water depth increases. The three phases of "sudden drop-rise-stability" are represented by a "spoon-shaped" change rule on the safety factor's change curve. The issue of the poor applicability of indicators in earlier studies is resolved by the analytical solution, which only requires determining the loss degree of the segment lining's effective bearing thickness to calculate the safety factor of any cross-section of the shield tunnel. The analytical solution's computation results, however, have some safety margins and are cautious. The process of establishing the evaluation model indicates that the secondary lining made of molded concrete can also have its safety status assessed using the analytical solution. It is very important for the safe operation of the tunnel and the safety of people's property and has a wide range of applications.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.403-414
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• 2004

In the accompanying paper, we proposed a real. time volumetric imaging method using a cross array based on receive dynamic focusing and synthetic aperture focusing along lateral and elevational directions, respetively. But synthetic aperture methods using spherical waves are subject to beam spreading with increasing depth due to the wave diffraction phenomenon. Moreover, since the proposed method uses only one element for each transmission, it has a limited transmit power. To overcome these limitations, we propose a new real. time volumetric imaging method using cross arrays based on synthetic aperture technique with linear wave fronts. In the proposed method, linear wave fronts having different angles on the horizontal plane is transmitted successively from all transmit array elements. On receive, by employing the conventional dynamic focusing and synthetic aperture methods along lateral and elevational directions, respectively, ultrasound waves can be focused effectively at all imaging points. Mathematical analysis and computer simulation results show that the proposed method can provide uniform elevational resolution over a large depth of field. Especially, since the new method can construct a volume image with a limited number of transmit receive events using a full transmit aperture, it is suitable for real-time 3D imaging with high transmit power and volume rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8A
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• pp.950-961
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• 2004

In this paper, we measured and analyzed propagation characteristics in a subway tunnel that is recently increasingly becoming one of the radio communication environments. The measurements are carried out in a subway tunnel with frequency bands of 2.45㎓ and 5.8㎓. The length of tunnel we used for this study is 175m of LOS (Line-of-sight) and 270m of NLOS (Non Line-of-Sight). The subway tunnel is curved and its cross section is horseshoe type. The measurement systems we employ in this study are a narrow-band system and a wide-band system. The narrow-band system is used to get path loss measurement and the wide-band system is used to figure out delay profile measurement. In particular, the wide-band system consists of 1023 length PN sequence generator using a chip rate of 80MHz based on a sliding correlation technique. The omni-directional antennas and directional antennas are used to analyze propagation characteristics for beam type of antenna. The path loss displays only pure path loss of a tunnel environment. The delay profile indicates the mean excess delay and RMS (root mean square) delay spread.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.321-339
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• 2014

This paper concerns the development of a knowledge-based tunnel design system within the framework of artifical neural networks(ANNs). The system is aimed at expediting a routine tunnel design works such as computation of segment lining body forces and stability analysis of selected cross section. A number of sub-modules for computation of segment lining body forces and stability analysis were developed and implemented to the system. It is shown that the ANNs trained with the results of 3D numerical analyses can be generalized with a reasonable accuracy, and that the ANN based tunnel design concept is a robust tool for tunnel design optimization. The details of the system architecture and the ANNs development are discussed in this paper.

• Steel and Composite Structures
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• v.37 no.3
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• pp.353-369
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• 2020

Eight cold-formed thin-walled steel beams were performed to investigate the effect of corrosion damage on the flexural behavior of steel beams. The relationships between failure modes or load-displacement curves and corrosion degree of steel beams were investigated. A series of parametric analysis with more than forty finite element models were also performed with different corrosion degrees, types and locations. The results showed that the reduction of cross-section thickness as well as corrosion pits on the surface would lead to a decline in the stiffness and flexural capacity of steel beams, and gradually intensified with the corrosion degree. The yield load, ultimate load and critical buckling load of the corroded specimen IV-B46-4 decreased by 22.2%, 26% and 45%, respectively. The failure modes of steel beams changed from strength failure to stability failure or brittle fracture with the corrosion degree increasing. In addition, thickness damage and corrosion pits at different locations caused the degradation of flexural capacity, the worst of which was the thickness damage of compression zone. Finally, the method for calculating flexural capacity of corroded cold-formed thin-walled steel beams was also proposed based on experimental investigation and numerical analysis results.

• Steel and Composite Structures
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• v.37 no.3
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• pp.323-339
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• 2020

In steel framed-tube structures (SFTSs), the plastic hinges at beam-ends cannot be adequately improved because of the large cross sections of spandrel beams, which results in the lower ductility and energy dissipation capacities of traditional SFTSs. To address this drawback, high-strength steel fabricated SFTSs with bolted web-connected replaceable shear links (HSFTS-SLs) have been proposed. In this system, shear links use conventional steel and are placed in the middle of the deep spandrel beams to act as energy dissipative components. In this study, 2/3-scaled HSFTS-SL specimens were fabricated, and cyclic loading tests were carried out to study the seismic performance of both specimens. The finite element models (FEMs) of the two specimens were established and the numerical results were compared with the test results. The results showed that the specimens had good ductility and energy dissipation capacities due to the reliable deformation capacities. The specimens presented the expected failure modes. Using a shorter shear link can provide a higher load-carrying capacity and initial elastic lateral stiffness but induces lower ductility and energy dissipation capacity in HSFTS-SLs. The performance of the specimens was comparable to that of the original sub-structure specimens after replacing shear links. Additionally, the expected post-earthquake recoverability and resilience of the structures could be achieved by replacing shear links. The acceptable residual interstory drift that allows for easy replacement of the bolted web-connected shear link was 0.23%. The bolted web-connected shear links had reliable hysteretic responses and deformation capacities. The connection rotation had a notable contribution to total link rotation. The results of the numerical analysis run for the proposed FEMs were consistent with the test results. It showed that the proposed FEMs could be used to investigate the seismic performance of the HSFTS-SL.