• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.781-789
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• 2016

Busbar has been used as electric conductor within extra high voltage (EHV) gas insulated switchgear (GIS), which makes EHV GIS higher security, smaller size and lower cost. However, the main fault of GIS is overheating of busbar connection parts, circuit breaker and isolating switch contact parts, which has been already restricting development of GIS to a large extent. In this study, a coupled magneto-flow-thermal analysis is used to investigate the thermal properties of GIS busbar in steady-state. A three-dimensional (3-D) finite element model (FEM) is built to calculate multiphysics fields including electromagnetic field, flow field and thermal field in steady-state. The influences of current on the magnetic flux density, flow velocity and heat distribution has been investigated. Temperature differences of inner wall and outer wall are investigated for busbar tank and conducting rod. Considering the end effect in the busbar, temperature rise difference is compared between end sections and the middle section. In order to obtain better heat dissipation effect, diameters of conductor and tank are optimized based on temperature rise simulation results. Temperature rise tests have been done to validate the 3-D simulation model, which is observed a good correlation with the simulation results. This study provides technical support for optimized structure of the EHV GIS busbar.

• Computers and Concrete
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• 제20권5호
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• pp.605-616
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• 2017

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

• 대한기계학회논문집A
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• 제38권5호
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• pp.567-573
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• 2014

최근에, 의학 분야의 MEMS 기술이 발전하면서 다양한 미세 유체 이송 시스템이 연구되고 있다. 본 논문에서는 기존의 펌프와는 다른, 두 개의 분리된 압전 판을 이용해 위장의 연동 운동을 모방한 마이크로 압전 펌프를 제안한다. 본 펌프는 진행파를 이용해 연동 운동을 일으켜 작동된다. 특히, 압전판에서 인가된 입력 전압에 의해 발생된 변위에 의해 동작된다. 이에 두 판 사이에서 진행파가 일어나며 유체는 진행파에 의해 생성된 압력차에 의해 이동된다. 압전 소자, 탄성체, 유체가 복합된 시스템을 이해하기 위해서 유한 요소 해석을 사용하였다. 챔버의 높이, 세라믹 개수 등의 설계 변수들을 변화시켜 유체의 유량을 확인하였다.

• 대한기계학회논문집A
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• 제35권12호
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• pp.1549-1556
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• 2011

자동차 인스트루먼트 패널에 사용되는 플라스틱의 온도와 시간에 따른 기계적 거동을 알아보기 위해 시편에 대한 인장 및 크리프 시험을 수행하였다. 여러 가지 온도에서의 물성치를 구한 결과 온도에 따라 물성치가 크게 변화함을 알 수 있었다. 4 가지 하중조건하에서의 3 점굽힘 크리프시험을 수행하고 지수법칙의 시간경화식을 적용하여 각종 계수를 구하고 크리프 거동을 간단한 식으로 표현하였다. 유한요소 크리프 해석 결과 하중이 커짐에 따라 수치해석 결과와 실험 결과가 차이가 커지지만 대체적으로 두 결과가 유사한 것을 확인할 수 있었다.

• The Journal of Advanced Prosthodontics
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• 제6권6호
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• pp.456-461
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• 2014

PURPOSE. Translucency and colour stability are two most important aspects for an aesthetic dental restoration. Glass ceramic restorations are popular amongst clinicians because of their superior aesthetic properties. In the last decade, zirconia has generated tremendous interest due to its favorable mechanical and biological properties. However, zirconia lacks the translucency that lithium disilicate materials possess and therefore has limitations in its use, especially in esthetically demanding situations. There has been a great thrust in research towards developing translucent zirconia materials for dental restorations. The objective of the study was to evaluate and compare the transmittance of a translucent variant of zirconia to lithium disilicate. MATERIALS AND METHODS. Two commercially available zirconia materials (conventional and high translucency) and 2 lithium disilicate materials (conventional and high translucency) with standardized dimensions were fabricated. Transmittance values were measured for all samples followed by a microstructural analysis using a finite element scanning electron microscope. One way analysis of variance combined with a Tukey-post hoc test was used to analyze the data obtained (P=.05). RESULTS. High translucency lithium disilicate showed highest transmittance of all materials studied, followed by conventional lithium disilicate, high translucency zirconia and conventional zirconia. The difference between all groups of materials was statistically significant. The transmittance of the different materials correlated to their microstructure analysis. CONCLUSION. Despite manufacturers' efforts to make zirconia significantly more translucent, the transmittance values of these materials still do not match conventional lithium disilicate. More research is required on zirconia towards making the material more translucent for its potential use as esthetic monolithic restoration.

• 한국수자원학회논문집
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• 제31권4호
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• pp.491-501
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• 1998

접근수로의 유황 파악과 안정적인 흐름조건을 만족시키는 여수로 유도벽 설계를 위하여 수치모의를 수행하였다. 복잡한 지형 재현이 용이한 2차원 유한요소모형인 RMA-2를 사용하였으며, 수리모형실험의 결과를 이용하여 모형의 매개변수를 추정하였다. 세부구간과 확장구간으로 나누어서 수치모의를 수행하였으며, 이를 통하여 경계의 영향을 무시할 수 있는 수리모형실험의 상류경계의 위치를 설정하였다. 접근수로 내의 흐름을 안정화시키기 위하여 유도벽의 대안 설계를 하였으며, 이에 대한 수치모의를 통해서 각 대안에 대하여 흐름해석을 하였다. 대안설계에 대한 해석결과, 접근수로 내의 유황이 안정적이며 횡방향 수위편차가 여수로 월류부 전면에서 거의 해소되는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.179-197
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• 2012

This study presents the findings of the structural health monitoring and the real time system identification of one of the first large scale building instrumentations in Turkey for earthquake safety. Within this context, a thorough review of steps in the instrumentation, monitoring is presented and seismic performance evaluation of structures using both nonlinear pushover and nonlinear dynamic time history analysis is carried out. The sensor locations are determined using the optimal sensor placement techniques used in NASA for on orbit modal identification of large space structures. System identification is carried out via the stochastic subspace technique. The results of the study show that under ambient vibrations, stocky buildings can be substantially stiffer than what is predicted by the finite element models due to the presence of a large number of partitioning walls. However, in a severe earthquake, it will not be safe to rely on this resistance due to the fact that once the partitioning walls crack, the bare frame contributes to the lateral stiffness of the building alone. Consequently, the periods obtained from system identification will be closer to those obtained from the FE analysis. A technique to control the validity of the proportional damping assumption is employed that checks the presence of phase difference in displacements of different stories obtained from band pass filtered records and it is confirmed that the "proportional damping assumption" is valid for this structure. Two different techniques are implemented for identifying the influence of the soil structure interaction. The first technique uses the transfer function between the roof and the basement in both directions. The second technique uses a pre-whitening filter on the data obtained from both the basement and the roof. Subsequently the impulse response function is computed from the scaled cross correlation between the input and the output. The overall results showed that the structure will satisfy the life safety performance level in a future earthquake but some soil structure interaction effects should be expected in the North South direction.

• 한국태양에너지학회 논문집
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• 제34권6호
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• pp.67-74
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• 2014

An inverter scroll compressor is used for the air conditioning in cars. Scrolls would be changed from the aluminum material to the magnesium material in order to satisfy the light weight trends of cars. The material changing influences on the scroll dimensions particularly the gap between two scrolls. Since the larger gap declines the performance of the compression, the gap between wraps of scrolls or the gap between wraps of scrolls to the plate of the opposite scroll is regarded as an important design variable. This paper is focused on the effects of the thermal stress due to the materials changing. The temperature difference between the inlet and the outlet is about 60 degrees and the highest operating temperature in the compressor is less than 110 degrees. The level of thermal stresses in the magnesium scroll is less than the result from aluminum one. The trend of the deformation is revealed that the normal directional deformation is 2 times lager than the in-plane directional deformation. Therefore the gap between the top of the wrap to the plate of the opposite scroll become more important than the other gaps. The orbiting scroll deforms larger than the fixed scroll by the thermal stresses. The deformation of the magnesium scroll is about 10% lager than that of the aluminum scroll. This value is similar to the ratio of the coefficients of thermal expansion of two materials. At the initial design stage, the results give many useful guides to engineers to propose gaps between parts.

• 한국전산구조공학회논문집
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• 제24권2호
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• pp.193-200
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• 2011

본 연구를 통해 superlite라 불리는 단열 파우더를 채용한 NO96 멤브레인 타입 LNG선 단열 화물창의 만선항해 시 LNG의 BOR(Boil-Off Rate) 예측모델을 제시하였다. LNGCC(LNG Cargo Containment)의 비정상상태 열전달 FEM모델은 만선항해 시 대기 및 해수 조건을 반영하고 복잡한 화물창 단열구조에 균질화 기법을 적용하여 구축하였다. BOR은 만선항해중 LNGCC 내부로 침입하는 총 열량을 이용하여 평가되었으며, 주요 변수에 따른 BOR의 변화는 파라메트릭 열전달해석을 통하여 분석하였다. 그리고 파라메트릭 BOR 특성해석 결과를 토대로 LNG선의 탱크 크기, 단열층의 두께 그리고 superlite의 열전도율을 함수로 하는 BOR 예측모델을 유도하였다. 비선형 과도 열전달해석을 통해 직접 구한 BOR과의 비교를 통해 유도한 예측모델은 최대 1% 이내의 상대오차를 나타내었다.

• 전기학회논문지
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• 제66권11호
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• pp.1568-1574
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• 2017

This paper studied cogging torque reduction effect for sloping notch applied two notches on stator teeth. We have confirmed accuracy of FEM(Finite Element Method) through comparison previous model using asymmetric notch for experiment and 3D FEM results, and then cogging torque comparison of previous model and sloping notch model. Also the sloping notch model has been modified to step-sloping notch model to consider manufactur. The modification method of sloping notch changed the degree of slope of notch (a)(Notch(a) sloping Deg) and the degree of Slope of notch (b)(Notch(b) Sloping Deg). When Cogging torque is case of minimum, Notch (a) Sloping Deg is $-12[^{\circ}]$ and Notch(b) Sloping Deg $12[^{\circ}]$. In this case, cogging torque was about 23.9[mNm]. Cogging torque of previous model is about 40.8[mNm], so sloping notch model is less than previous model by 41.42[%]. Also, if sloping notch model is changed to step-sloping notch model, cogging torque of step-sloping notch model is about 24.82[mNm], Therefore the difference between the two cogging torque is about 3.85[%], so step-sloping notch model can be applied when considering manufacture.