• Geomechanics and Engineering
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• 제35권2호
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• pp.149-163
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• 2023

This paper presents stability evaluation of unlined tunnels with semi-circular arch and straight sides (SASS) driven in non-homogeneous and anisotropic undrained clay. Numerical analysis has been conducted based on lower bound finite element limit analysis with second order cone programming under plane strain condition. The solutions will be used for the assessment of stability of unlined semi-circular arch tunnels and tunnels in which semi-circular roof is supported over rectangular/square sections. The stability charts have been generated in terms of a non-dimensional factor considering linear variation in undrained anisotropic strength for normally consolidated and lightly over consolidated clay with depth, and constant undrained anisotropic strength for heavily over-consolidated clay across the depth. The effect of normalized surcharge pressure on ground surface, non-homogeneity and anisotropy of clay, tunnel cover to width ratio and height to width ratio of tunnel on the stability factor and associated zone of shear failure at yielding have been examined and discussed. The geometry of tunnel in terms of shape and size, and non-homogeneity and anisotropy in undrained strength of clay has been observed to influence significantly the stability of unlined SASS tunnels.

• Structural Engineering and Mechanics
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• 제57권3호
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• pp.543-567
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• 2016

This study attempts to address the buckling and free vibration characteristics of an isotropic cylindrical panel subjected to non-uniform temperature rise using numerical approach. Finite element analysis has been used in the present study. The approach involves three parts, in the first part non-uniform temperature field is obtained using heat transfer analysis, in the second part, the stress field is computed under the thermal load using static condition and, the last part, the buckling and pre-stressed modal analysis are carried out to compute critical buckling temperature as well as natural frequencies and associated mode shapes. In the present study, the effect of non-uniform temperature field, heat sink temperatures and in-plane boundary constraints are considered. The relation between buckling temperature under uniform and non-uniform temperature fields has been established. Results revealed that decrease (Case (ii)) type temperature variation field influences the fundamental buckling mode shape significantly. Further, it is observed that natural frequencies under free vibration state, decreases as temperature increases. However, the reduction is significantly higher for the lowest natural frequency. It is also found that, with an increase in temperature, nodal and anti-nodal positions of free vibration mode shapes is shifting towards the location where the intensity of the heat source is high and structural stiffness is low.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• KIEAE Journal
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• 제9권5호
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• pp.105-113
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• 2009

Daylighting provides the opportunity for both energy savings and improved visual comfort. An accurate estimation of the amount of daylight entering a building is the key step for daylight designing. This research aims to assess comparative daylighting performance of four different configurations of fenestration in case of unilateral windows and their variation under clear and overcast sky conditions. The selected window openings in this study were single punched, double punched, multiple punched and clerestory, and the area was same for each type of window. The experiment was designed for an office space using 1/10 scale model. Daylighting performance was evaluated by measuring the illuminance on work-plane height using Agilent data logger and photometric sensor Li-Cor. Thecomputer program ECOTECT was also used to simulate the pattern of interior illuminance distribution. Clerestory window showed the best performance in term of both illuminance level and distribution in the experiment. Multiple punched window provided more uniform illuminance distribution than single punched window. Lowest daylighting performance in the experiment was shown by double punched window.

• 대한기계학회논문집B
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• 제32권9호
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• pp.683-694
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• 2008

The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs.

• 플랜트 저널
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• 제12권3호
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• pp.32-38
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• 2016

본 연구에서는 해안 복잡지형에 2열 배치된 풍력단지 운영사례를 분석하여 후류에 의한 풍력발전기의 영향을 분석하여 풍속의 변화 그리고 난류강도의 변화를 분석하였다. 주풍향 대비 인접 풍력발전기와 이격거리가 날개직경(rotor diameter,RD) 90m 기준 4RD인 경우 후류에 의해 풍속감소 및 난류강도의 증가로 인한 발전량의 감소를 확인 할 수 있었다. 특히 후류에의한 급격한 순간풍향의 변화시, 풍력발전기의 불시정지로 발전량이 현저히 감소되었고 이를 보완하기 위하여 요브레이크를 설비를 보강 함으로써 불시정지 빈도를 감소하고 발전량을 제고하는데 효과가 있음을 확인할 수 있었다.

• 한국ITS학회 논문지
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• 제4권1호
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• pp.89-95
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• 2005

본 논문에서는 GSM/GPS/DCS/US-PCS 핸드 셋을 위한 4중 대역 안테나를 제안한다. 제안되어진 안테나는 핸드 셋의 제한된 내부 공간에 집적하기 위하여 저자세로 설계되어 지고 ,다중대역을 위해 $\lambda$/4 길이를 갖는 세 개의 방사점으로 구성된다. 또한 안테나의 크기 변화 없이 넓은 대역폭을 얻기 위하여 방사체 아래의 접지면을 제거하였고, GPS/DCS/US-PCS 대역의 편리한 임피던스 매칭을 위하여 방사체 중앙에 슬릿을 추가하였다. 제안되어진 안테나는 전 대역에서 VSWR 3:1 대역폭을 만족하고, anechoic chamber (10m$\times$6m$\times$4m)내의 측정 결과 전 대역에서 최대 이득은 -2.19 dB 에서 2.09 dB이다

• 한국해양공학회지
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• 제18권3호
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• pp.8-12
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• 2004

The anchor is laid on the seabed, and the main engine is working against incident environmental loads in a typhoon. As the main engine is broken Mum in the storm, the anchor chain is cut and the vessel drifts. Although a ship is moored by two-point mooring lines to maintain her position, it has crashed into a rock because of a typhoon, resulting in a possible accidental oil spillage. In this paper, we studied maintenance of a ship's position, which is analyzed based on the slow motion maneuvering equations considering wave, current, and wind. To estimate wave loads, the direct integration method is employed. The current forces are calculated, using MMG (Mathematical Modeling Group). Th two-point mooring forces are quasi-statistically evaluated, using the catenary equation. Th coefficients of wind forces are modeled from Isherwood's empirical data, and the variation of wind speed is estimated by wind spectrum. The nonlinear motions of a two-point moored ship are simulated, considering wave, current, and wind load, in specific domain of time.

• 전력전자학회논문지
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• 제8권5호
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• pp.418-426
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• 2003

컴퓨터 모니터를 통해 안구망막의 형태와 두께를 보기 위해서 레이저의 경로차를 이용하는 SLO 장비가 사용되고 있다. 이러한 방법으로 망막의 선명한 3차원 영상을 보기 위해서는 레이저 광경로 시스템의 정확한 동기제어가 필요하다. 이 영상을 얼기 위해서는 평면주사를 하는데 있어서 정밀동기제어가 매우 중요하다. 본 논문에서는 안구의 3차원 영상을 만들기 위해 고속 동기제어를 구현한다. 또한 고속 제어시 부하 관성에 의해 발생하는 위치 응답의 오차를 보상하기 위해서 기존 PI(Proportional-Integral) 제어기에 데드비트 외란 관측기를 추가한다. 제안된 제어시스템은 고속 제어시 발생하는 토크 변화에 강인하고 정밀한 시스템이 된다. 이상의 제안된 시스템의 안정성과 유용함이 컴퓨터 시뮬레이션과 실험을 통하여 확인되었다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.807-812
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• 2008

The various attempts is made to solve the energy and environment problems. In addition, people interested in their life quality want the more eco-friendly living space. So we suggested that the earth-sheltered house could be one of the eco-friendly and low energy consuming houses to meet the social interest. And we also made data for design of the earth-sheltered house to be applicable to climate of Korea. In this study, a simulation was performed to estimate a boundary temperature according to earth sheltering thickness at the earth-sheltered part(exterior wall) in the case of earth sheltering on the plane ground not using a sloped site. And we analyzed the reduction of a thermal load by using this boundary temperature. We also compared a case of earth sheltering at the vertical wall with a case of earth sheltering at the roof to know the thermal reduction effect of a case of earth sheltering at the vertical wall.