• 한국환경과학회지
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• 제18권11호
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• pp.1215-1224
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• 2009

This study evaluated the applicability of visible-light-driven N- and S-doped titanium dioxide($TiO_2$) for the control of low-level dimethyl sulfide(DMS) and dimethyl disulfide(DMDS). In addition, a photocatalytic unit(PU)-adsorption hybrid was evaluated in order to examine the removal of DMS and DMDS which exited the PU and a gaseous photocatalytic byproduct($SO_2$) which was generated during the photocatalytic processes. Fourier-Tranform-Infrared(FTIR) spectrum exhibited different surface characteristics among the three-types of catalysts. For the N- and S-doped $TiO_2$ powders, a shift of the absorbance spectrum towards the visible-light region was observed. The absorption edge for both the N- and S-doped $TiO_2$ was shifted to $\lambda$ 720 nm. The N-doped $TiO_2$ was superior to the S-doped $TiO_2$ in regards to DMS degradation. Under low input concentration(IC) conditions(0.039 and 0.027 ppm for DMS and DMDS, respectively), the N-doped $TiO_2$ revealed a high DMS removal efficiency(above 95%), but a gradual decreasing removal efficiency under high IC conditions(7.8 and 5.4 ppm for DMS and DMDS, respectively). Although the hybrid system exhibited a superior characteristic to PU alone regarding the removal efficiencies of both DMS and DMDS, this capability decreased during the course of a photocatalytic process under the high IC conditions. The present study identified the generation of sulfate ion on the catalyst surface and sulfur dioxide(maximum concentrations of 0.0019 and 0.0074 ppm for the photocatalytic processes of DMS and DMDS, respectively) in effluent gas of PU. However, this generation of $TiO_2$ would be an insignificant addition to indoor air quality levels.

• 한국전자파학회논문지
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• 제22권11호
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• pp.1133-1136
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• 2011

본 논문에서는 ISM(산업/과학/의료) 대역(2.4~2.5 GHz)에서 IEEE 802.11b/g 적용을 위한 스트립라인 구조의 코리니어 안테나를 제안하였으며, 이는 동축 코리니어 안테나와 전 방향 평면 마이크로스트립 안테나(OMA)의 단점을 보완한 것이다. 4층 PCB 구조를 이용하여 기존 안테나에 비해 개선된 특성과 제작상의 이점을 가질 수 있었다. 안테나 배열을 위해 안테나 소자들의 외부 도체와 내부 도체를 ${\lambda}$/2 길이로 서로 엇갈리게 연결하여 동위상을 갖는 구조를 가지며, 상대 유전율 4.4, 손실 탄젠트(loss tangent) 0.02인 FR4 epoxy 기판을 이용하여 제작하였다. 최대 이득은 약 4.93 dBi가 측정되었으며, 기존 OMA 구조에 비하여 이득은 약 0.33 dBi 개선된 결과를 얻었다.

• 대한토목학회논문집
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• 제31권1B호
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• pp.13-20
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• 2011

강수량은 시공간적으로 변화하는 수문변량으로서 강수량의 시간적인 특성 또한 강수량의 특성을 정의하는데 매우 중요한 요소이다. 본 연구에서는 극치강수량의 지역빈도해석을 위한 범주화 과정에서 기존의 강수량과 관측소 위치좌표만을 이용한 범주화를 통해 해결할 수 없는 강우 발생의 계절적 변화와 집중에 대한 고려를 반영하기 위하여, 기존의 양적 범주화 과정에 시간적인 영향을 고려할 수 있는 요소로서 극치강수량 발생 시기 통계치를 활용할 수 있는 범주화 과정을 제시하였다. 본 연구에서는 극치강수량의 발생 시기에 대한 정량적인 분석이 가능한 순환통계기법을 이용하여 관측 지점별 시간 통계량을 산정하고, 이를 극치강수량과 결합하여 시 공간적인 특성자료를 생성한 후 수정 K-means 방법을 이용하여 군집화 해석을 수행하였으며, 전국을 다섯 개의 군집으로 분류하였다. 기존의 양적 범주화 결과와의 비교를 통해 발생 시간 통계치를 결합한 범주화 결과가 지형 및 권역을 반영하는 결과를 보임을 확인하였다.

• Earthquakes and Structures
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• 제3권6호
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• pp.821-838
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• 2012

This paper proposes a new three-layer pillar-type hysteretic damper system for residential houses. The proposed vibration control system has braces, upper and lower frames and a damper unit including hysteretic dampers. The proposed vibration control system supplements the weaknesses of the previously proposed post-tensioning vibration control system in the damping efficiency and cumbersomeness of introducing a post-tension. The structural variables employed in the damper design are the stiffness ratio ${\kappa}$, the ductility ratio ${\mu}_a$, and the ratio ${\beta}$ of the damper's shear force to the maximum resistance. The hysteretic dampers are designed so that they exhibit the targeted damping capacity at a specified response amplitude. Element tests of hysteretic dampers are carried out to examine the mechanical property and to compare its restoring-force characteristic with that of the analytical model. Analytical studies using an equivalent linearization method and time-history response analysis are performed to investigate the damping performance of the proposed vibration control system. Free vibration tests using a full-scale model are conducted in order to verify the damping capacity and reliability of the proposed vibration control system. In this paper, the damping capacity of the proposed system is estimated by the logarithmic decrement method for the response amplitudes. The accuracy of the analytical models is evaluated through the comparison of the test results with those of analytical studies.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.640-649
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• 2010

Coarse granular materials such as gravel and crushed stone have been used as an important fill materials to large soil structure of railway, road, dam and so on. Although much studies for general soil materials have been carried out domestically, the studies for coarse materials were insufficient. Particularly, it is the level in which the study for dynamic properties(Elastic modulus and damping ratio) of coarse materials, applies the foreign country literature. This is due to the lack of large equipment for element test. But large soil structures made of coarse granular materials are generally important infrastructures. Therefore, the reliable design parameters for coarse materials should be obtained for safe and economic design, construction and maintenance. Triaxial test is the laboratory test method that is capable of controlling a confining pressure and boundary condition. In this project, we made a multi-purpose large triaxial testing system. This testing system is able to test coarse granular materials with maximum particle diameter of 100mm and support both the load control and displacement control. The load cell is installed inside of triaxial cell and the axial displacement is measured locally in order to control and measure more accurately in the small strain level. The verification test of this testing system was carried out with urethane verification specimens. So, from now on the useful information for coarse granular materials are expected to suggested by performing many tests with various material and condition.

• Design & Manufacturing
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• 제9권3호
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• pp.19-23
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• 2015

Non-pneumatic wheels have been widely used instead of general tube type wheels beause of many reasons, for example, wheel size, price restriction, heavy-duty problem and so on. Almost small size wheels or casters were non-pneumatic type but structural stability was not certified. This paper presents a double structured non-pneumatic wheel, called "smart caster", which consisted with inner and outer wheels connected by chips, and finite element analysis processes were conducted in order to determine important dwsign factors before actual design for mass production. For structural analysis ABAQUS was used under various boundary conditions with incrementally varied loads until 2,000N. Then structural staility was evaluated according to varied loads below ultimate stress. Generally stresses were concentrated at the lower parts of the wheel, and especially contact parts between wheel and ground. In addition, maximum stress appeared at contact parts between the wheel lower part and chips.

• 대한치과보철학회지
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• 제27권2호
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• pp.79-100
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• 1989

The Purpose of this study was to investigate material differences in stress transmission among various artificial teeth and denture base materials. For this study, a two-dimensional finite element model and a two-dimensional photoelastic model of a mandible with complete denture were made. A resin tooth and a porcelain tooth were used as artificial teeth, and a resin base, a metal lined base, and a soft-liner lined base were used as denture bases. An occlusal load was applied and principal stresses generated in the supporting tissues were compared. To test the impact stress transmission, strain gauge attached to the denture base specimens made of the different materials were made in thick and thin groups. Voltage outputs from hitting the specimen with a steel ball were compared. The results were as follows : 1. In FEM, increasing the mucosal thickness reduced the maximum principal stresses in the supporting tissues, but altering the tooth materials and the base materials induced no difference in the stresses. 2. In photoelastic model study, no difference in fringe order among the specimens were observed, but the thick mucosa group and the soft-liner lined group revealed a more uniform distribution of the load. 3. In strain measuring, the impact force transmission was highest in the soft-liner lined group, and was the lowest in the metal lined group(p<0.01). 4. In the thin group using the resin base, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the thick group. In the soft-liner lined group, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the metal lined group. 5. The thick group showed lower impact stress transmission than the thin group(p<0.01).

• Progress in Superconductivity
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• 제4권1호
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• pp.86-89
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• 2002

In this paper, the design of a IMVA single-phase high temperature superconducting(HTS) power transformer with BSCCO-2223 HTS tapes is presented. The rated voltages of each sides of the transformer are 22.9 ㎸ and 6.6 ㎸, respectively The winding of 1MVA HTS transformer is consisted of double pancake type HTS windings, which have advantages of insulation and distribution of high voltage, and are cooled by subcooled liquid nitrogen of 65K. Four HTS tapes were wound in parallel for the windings of low voltage side and the four parallel conductors are transposed. The design of 1MVA HTS transformer, a shell type core made of laminated silicon steel plate is chosen, and the core is separated with the windings by a cryostat with a room temperature bore. The cryostat made of non-magnetic and non-conducting material and a liquid nitrogen sub-cooling system is designed in order to maintain the coolant's temperature of 65K. For electromagnetic analysis of 1MVA HTS transformer, a finite element method of an axis of symmetry is used. The maximum perpendicular component of magnetic flux density of pancake windings is about 0.15T. And through analyzing the magnetic field distribution, an optimal winding arrangement of 1MVA HTS transformer is obtained.

• Journal of Welding and Joining
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• 제28권4호
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• pp.26-32
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• 2010

The purpose of this study is to evaluate the residual stresses at the multi-pass FCA weldment using the finite element analysis (FEA). In order to do it, an H-type specimen was selected as a test specimen. The variable used was in-plane restraint intensity. The temperature distribution at the multi-pass FCA butt weldment was evaluated in accordance with the relevant guidance recommended by the KWJS. The effective conductivity for the weld metal corresponding to each welding pass was introduced to control the maximum temperature below the vaporization temperature of weld metal. The heat flux caused by welding arc was assumed to be applied to the weld metal corresponding to welding pass. With heat transfer analysis results, the distribution of transverse residual stresses was evaluated using the thermo-mechanical analysis and compared with the measured results by XRD and uniaxial strain gage. In thermo-mechanical analysis, the plastic strain resetting at the temperature above melting temperature of $1450^{\circ}C$ was considered and the weld metal and base metal was assumed to be bilinear kinematics hardening continuum. According to the comparison between FEA and experiment, transverse residual stresses at the multi-pass FCA butt weldment obtained by FEA had a good agreement with the measured results, regardless of in-plane rigidity. Based on the results, it was concluded that thermo-mechanical FE analysis based on temperature distribution calculated in accordance with the KWJS’s guidance could be used as a tool to predict the distribution of residual stress of the multi-pass FCA butt weldment.

• 대한기계학회논문집A
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• 제35권7호
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• pp.805-812
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• 2011

손가락형 전극과 압전섬유/에폭시 복합재료(MFC) 압전패치가 분포된 알루미늄 외팔보형의 에너지 회수장치를 설계하여 전기-기계적 특성을 연구하였다. 최대 전력을 얻기 위해서 보와 외부 가진이 공진주파수에서 진동하도록 하였다. ANSYS를 사용하여 해석기법을 개발했으며, 방법의 타당성 검증을 위해서 결과를 실험과 비교하였으며, 두 결과는 잘 일치하였다. 개발된 해석기법을 사용하여 PZT, PVDF, MFC 압전체에 의한 발생전압의 차이를 계산했으며, 압전체의 위치, 보의 치수가 성능에 미치는 영향을 연구하였다. 또한 MFC에 의한 최대 전압발생을 위해서 보의 치수에 대한 최적화가 수행되었으며, 그 결과 최적화된 보에서 1차고유진동수 24.5Hz에서 40.1V의 전압이 발생했으며 이 값은 PZT의 결과와 비슷하다. 그러나 압전섬유형 회수장치는 PZT보다 더 높은 내구수명이 기대되어 유리하다.