• Earthquakes and Structures
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• v.13 no.2
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• pp.103-118
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• 2017

In vertical seismic isolation (VSI), a building is partitioned intentionally by vertical layers into two dynamically different substructures for seismic response reduction. Initially, a 1-story frame was partitioned into two substructures, interconnected by viscous and visco-elastic links, and seismic responses of the original and the vertically isolated structures (VIS) were obtained, considering a large number of stiffness and mass ratios of substructures with respect to the original structure. Color contour graphs were defined for presentation and investigation of large amounts of output results. Dynamic characteristics of the isolated structures were studied by considering the non-classical damping of the system, and then the effects of viscous and visco-elastic link parameters on the modal damping ratios were discussed. On this basis, three states of mass isolation, interactional state, and control mass were differentiated. Response history analyses were performed by Runge-Kutta numerical method. In these analyses, interaction of isolation ratios and link parameters, on response control of VIS was studied and the appropriate ranges for link parameters as well as the optimal ranges for isolation ratios were suggested. Results show that by using the VSI technique, seismic response reduction up to 50% in flexible substructure and even more in stiff substructure is achievable.

• Current Optics and Photonics
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• v.5 no.4
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• pp.444-449
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• 2021

A photonic crystal coupled-cavity waveguide created on silicon-on-insulator is designed to act as a refractive-index-sensing device at midinfrared wavelengths around 4 ㎛. To realize high sensitivity, effort is made to engineer the structural parameters to obtain strong modal confinement, which can enhance the interaction between the resonance modes and the analyzed sample. By adjusting some parameters, including the shape of the cavity, the width of the coupling cavity, and the size of the surrounding dielectric columns, a high-sensitivity refractive-index sensor based on the optimized photonic crystal coupled-cavity waveguide is proposed, and a sensitivity of approximately 2620 nm/RIU obtained. When an analyte is measured in the range of 1.0-1.4, the sensor can always maintain a high sensitivity of greater than 2400 nm/RIU. This work demonstrates the viability of high-sensitivity photonic crystal waveguide devices in the midinfrared band.

• The Journal of the Petrological Society of Korea
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• v.21 no.1
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• pp.13-30
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• 2012

Phlogopite and kaersutite, showing distinctively different textural characteristics compared to the common phenocrysts, are observed in alkali basalt from Jeju Island. They occur as large crystals (2-10 mm) in host basalts, whereas fine-grained phlogopite and kaersutite occur in ultramafic mantle xenoliths and mafic gabbroic xenoliths, respectively, as an interstitial and microvein phases, or in corona textures (<1 mm). This textural characteristics of fine-grained grains clearly indicates secondary in origin. Phlogopite contains high $TiO_2$(4.1-6.9 wt%) and F(2.8-4.6 wt%) and relatively high mg#[=100Mg/(Mg+$Fe^t$) in mols, where $Fe^t$ is total iron](88-80), whereas kaersutite has high $TiO_2$(5.6-6.11 wt%) and much lower mg#s(68-64). Our textural observations and the geochemical character of these hydrous minerals suggest that they were unrelated to each other and mica formation happened early in the upper mantle before the mantle xenoliths had been trapped. In contrast, kaersutite formation has happened later, probably during the late stage of crystallization as intracrustal processes. The presence of phlogopite and kaersutitic amphibole is a direct evidence for K-, Ti-, F- and $H_2O$-bearing fluid/melt percolation in the lithosphere beneath Jeju Island, indicating that they are product of interaction between host rock/peridotite/fluid-melt. Thus, the upper mantle/lower crust beneath Jeju Island are metasomatized to various extents, characterized by a change in major metasomatic hydrous minerals from phlogopite to amphibole with decreasing depth.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.305-313
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• 2017

In this paper, sound absorption of thin elastic plates installed in a rigid duct is discussed using an analytic method. The number of plates can be one or two, and each plate might have micro-perforation. Vibration of the plates and sound pressure fields inside the duct and air cavity are expressed in terms of an infinite series of modal functions. Under the plane wave assumption, a low frequency approximation is derived by including the first few plate modes. It is found that the sound absorption coefficient of the plates without micro-perforation shows sharp peaks at resonance frequencies, and due to the interaction between the plates and air cavity, the resonance frequencies move as the cavity depth changes. For the case of micro-perforated plates, it is found that the sound absorption is mainly affected by the perforation ratio. When the perforation ratio is order of few percent, the sound absorption is almost independent of plate vibration.

• Wind and Structures
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• v.26 no.5
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• pp.267-277
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• 2018

Numerical simulations are performed of a long flexible cylinder undergoing vortex-induced vibration at a Reynolds number of 500. The cylinder is pinned at both ends, having an aspect ratio of 100 (cylinder length to cylinder diameter) and a mass ratio of 4.2 (structural mass to displaced fluid mass). Temporal and spatial information on the cross-flow (CF) and in-line (IL) vibrations is extracted. High modal vibrations up to the $6^{th}$ in the CF direction and the $11^{th}$ in the IL direction are observed. Both the CF and IL vibrations feature a multi-mode mixed pattern. Mode competition is observed. The $2^{nd}$ mode with a low frequency dominates the IL vibration and its existence is attributed to a wave group propagating back and forth along the span. Distributions of fluid force coefficients are correlated to those of the CF and IL vibrations along the span. Histograms of the x'-y motion phase difference are evaluated from the total simulation time and a complete vibration cycle representing the standing or travelling wave pattern. Correlations between the phase difference and the vibrations are discussed. Vortex structures behind the cylinder show an interwoven near-wake pattern when the standing wave pattern dominates, but an oblique near-wake pattern when the travelling wave pattern prevails.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.4
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• pp.274-282
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• 2014

Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.447-454
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• 2007

본 논문에서는 사용자의 가상환경 내의 위치 정보에 대한 감각을 향상시키는 방법론으로서 햅틱 피드백(haptic feedback)과 사운드 피드백(sound feedback)의 모달리티를 활용한 그리드(grid)를 제안한다. 제안된 그리드는 사용자의 3차원 공간 내의 움직임(explorative procedure)에 추가적인 비 시각적인(non-visual) 위치정보 피드백을 부여하는데 그 목적을 두고 있다. 햅틱 모달리티를 활용한 3차원 그리드는 SensAble사의 PHANTOM(R) Omni$^{TM}$ 를 활용하여 설계되었으며, 사운드 모달리티를 활용한 경우 저주파 배경음의 주파수 특성(frequency characteristics of sound source)을 사용자 손의 공간 좌표값에 근거하여 재생 시의 표본 추출 비율(sampling rate)를 연속적으로 바꾸는 방식으로 설계되었다. 이러한 공간 그리드는 두 모달리티 각각의 독립적인 제시 및 동시 제시/제거를 통해 평가되었으며, 동시 제시의 경우 두 모달리티간의 어긋남(cross-modal asynchrony)이 없도록 설계되어 사용자의 공간 작업 시 모달리티간의 조화 (manipulating congruency)를 확보할 수 있도록 하였다. 실험을 통해 얻어진 결과는 그것의 통계적 유의미성을 분석하기 위해 다원변량분석과 사후검증(Turkey. HSD)을 거쳐 해석이 되었다. 공간 내 특정 좌표 선택을 기준으로 하는 그리드의 사용자 평과 결과, 3차원 내의 움직임에 대해 햅틱 및 사운드 피드백의 비 시각적 피드백은 사용자의 공간 작업의 오차를 줄여 주고 있음이 확인되었다. 특히 시각적인 정보만으로 확인하기 어려운 Z축 상의 움직임은 그리드의 도움으로 그 오차정도가 50% 이상 줄어 드는 것으로 확인되었다(F=19.82, p<0.01). 이러한 시각적 정보를 보존하는 햅틱, 사운드 피드백 방식을 HCI의 중요한 요소인 사용성과 유용성과 연관시켜 MMHCI(multimodal human-computer interaction) 방법론으로의 적용 가능성을 검토해 본다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1265-1271
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• 2011

In this study, the safety of a rack structure was evaluated through seismic analysis considering fluid-structure interactions using a finite-element model. The rack structure was immersed under water, so it was influenced by the water. The fluid-structure interaction can be specified in terms of the hydrodynamic effect, which is defined as the added mass per unit length. Modal analysis and seismic analysis using the Floor Response Spectrum (FRS) were carried out under Operating Basis Earthquake (OBE) and Safe Shutdown Earthquake (SSE) conditions. The analytical maximum displacements of the rack structure were 0.29 and 0.36 mm under OBE and SSE conditions, respectively. The maximum stresses were 17.9 MPa under OBE conditions and 19.6 MPa under SSE conditions; these results corresponded to 23 % and 14% of the yield strength of the applied material, respectively.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.38-46
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• 2020

The purpose is to evaluate the structural characteristics of 750 mm diameter injection spiral blades under various operating conditions. A fiber-glass reinforced polypropylene material was employed to the injection blades, and mechanical tests on two kinds of glass-reinforced polypropylene were performed to evaluate the mechanical properties and to select a suitable candidate material. Also, three kinds of spiral blade geometries were studied to observe the influence of fixing rods between blades. For this, structural analyses were conducted to understand the role of fixing rods under a range of rotating speed. In addition, modal analysis was performed to confirm the resonance in the operating speed range. One-way fluid-structure interaction (FSI) analysis was carried out to know its mechanical integrity under dangerous wind speed conditions. Through this work, the structural characteristics of the proposed spiral blade geometries were studied under various operating conditions, and the requirements of mechanical properties of blades were determined.

• Earthquakes and Structures
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• v.18 no.3
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• pp.367-377
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• 2020

Incremental dynamic analysis (IDA) widely uses for the collapse risk assessment procedures of buildings. In this study, an IDA-based collapse risk assessment methodology is proposed, which employs a novel approach for detecting the near-collapse (NC) limit state. The proposed approach uses the modal pushover analysis results to calculate the maximum inter-story drift ratio of the structure. This value, which is used as the upper-bound limit in the IDA process, depends on the structural characteristics and global seismic responses of the structure. In this paper, steel midrise intermediate moment resisting frames (IMRFs) have selected as case studies, and their collapse risk parameters are evaluated by the suggested methodology. The composite action of a concrete floor slab and steel beams, and the interaction between the infill walls and the frames could change the collapse mechanism of the structure. In this study, the influences of the metal deck floor and autoclaved aerated concrete (AAC) masonry infill walls with uniform distribution are investigated on the seismic collapse risk of the IMRFs using the proposed methodology. The results demonstrate that the suggested modified IDA method can accurately discover the near-collapse limit state. Also, this method leads to much fewer steps and lower calculation costs rather than the current IDA method. Moreover, the results show that the concrete slab and the AAC infill walls can change the collapse parameters of the structure and should be considered in the analytical modeling and the collapse assessment process of the steel mid-rise intermediate moment resisting frames.