• 대한기계학회논문집A
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• 제26권6호
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• pp.1194-1202
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• 2002

A study on the topology optimization of a multi-spectral camera for space-use is presented. The optimization is carried out under self-weight and polishing pressure loading. A multi-spectral camera for space-use experiences degradation of optical image in the space, which can not be detected on the optical test bench on the earth. An optical surface deformation of a primary mirror, which is a principal component of the camera system, is an important factor affecting the optical performance of the whole camera system. In this study, topology optimization of the primary mirror of the camera is presented. As an objective function, a measure of Strehl ratio is used. Total mass of the primary mirror is given as a constraint to the optimization problem. The sensitivities of the objective function and constraint are calculated by direct differentiation method. Optimization procedure is carried out by an optimality criteria method. For the light-weight primary mirror design, a three dimensional model is treated. As a preliminary example, topology optimization considering a self-weight loading is treated. In the second example, the polishing pressure is also included as a loading in the topology optimization of the mirror. Results of the optimized design topology for the mirror with various mass constraints are presented.

• 한국지반신소재학회논문집
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• 제14권1호
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• pp.33-41
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• 2015

본 연구에서는 관중혼합처리공법 개발을 위해 혼합토의 공학적 특성 평가에 관한 실내실험(유동성, 단위중량, 일축압축강도 및 블리딩 시험)을 수행하였다. 실험 결과 흐름 및 블리딩 특성은 함수비에 비례하여 증가하는 것으로 나타났다. 단위중량과 일축압축강도는 함수비 증가에 따라 감소하는 것으로 나타났다. 각 주행 장비별 접지압과 혼합토의 지지력을 비교한 결과 벨트 컨베이어, 백호우, 도저 등의 장비가 즉시 진입 가능한 것으로 검토되었다. 결과적으로 고화재를 사용한 관중혼합처리공법에서 적용 가능한 함수비 영역은 80~200%로 평가되었다. 또한, 본 연구 결과로부터 설계 차트를 개발하여 제시하였다.

• 한국태양에너지학회 논문집
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• 제26권2호
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• pp.19-25
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• 2006

Methane hydrate, non-polluting new energy resource, satisfies requirement and considered as a precious resource that can prevent the global warming. Fortunately, there are abundant resources of methane hydrate distribute in the earth widely. Therefore, developing the techniques that can utilize these gases effectively is highly desired. The work in this paper here is to develop a skill which can transport and store methane hydrate. As a first step, the equilibrium experiment was carried out by increasing temperatures in the cell at fixed pressures. The influence of gas consumption rates under variable degree of subcooling, stirring and water injection has been investigated formation to clarify kinetic characteristics of the hydrate. The results of present investigation showed that the enhancements of the hydrate formation in terms of the gas/water ratio are closely related to operational pressure, temperature, degrees of subcooling, and water injection.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1012-1017
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• 2010

Sewer Pipes are not being managed for twenty years after laying. So, The life span of sewer pipes is on the decrease. For solve the life span decrease of sewer pipes, correct checking of questions and measure preparation are necessary through investigation in sewer pipes. This research investigated on the state of sewer pipes in the housing and industrial sites through CCTV(closed-circuit television) and device of digitalized strain investigation. And, a result is as follows. A results of PE, PVC, GRP, CSP investigations were found of pipe-transformation state by earth pressure and external load.

• 한국철도학회논문집
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• 제9권3호
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• pp.305-312
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• 2006

Gravel ballasted tracks are used as a basic structure for the domestic railway tracks. However, such kind of tracks has few disadvantages with service life of the structure, such as rapid deterioration of the tracks. Due to this reason, there is a need to develop low maintenance track to improve the service life of the conventional line tracks. CMP paved tacks are one of the kind of concrete tracks those were manufactured by using the prepacked concrete techniques. The purpose to develop paved tracks is to reduce the maintenance cost. The most important controlling factors to design the paved tracks are surrounding environmental condition and repeated train loading. In this study, in order to investigate the deformation characteristics such as displacement, earth pressure, strain ratio, and crack along the repeated loading cycle, cyclic loading test through real scale model was carried out.

• 한국지반공학회논문집
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• 제19권2호
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• pp.255-265
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• 2003

본 연구에서는 해마다 여름철 호우기에 집중적으로 발생되는 철도노반 유실 현장의 신속한 복구를 위하여 사용되는 지오백의 공학적 특성을 평가하기 위해, 일련의 실내시험을 수행하였다. 먼저 본 복구시스템에 사용되는 지오백의 최적 크기는 일반적인 철도노반 유실 현장 상황을 고려하여 44cm$\times$66cm로 제안하였으며, 최적 채움도는 일련의 정적하중재하시험 결과 80%가 적합한 것으로 나타났다. 한편 본 연구에서는 일련의 축소모형실험을 통해 정적 및 동적 하중 재하시 지오백축조노반의 공학적 거동 특성 및 토압 분포특성을 평가하였다.

• Geomechanics and Engineering
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• 제13권6호
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• pp.1027-1044
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• 2017

Membrane penetration is the most important factor influencing the measurement of volume change for triaxial consolidated-drained shear test for coarse-grained soil. The effective pressure p, average particle size $d_{50}$, thickness $t_m$ and elastic modulus $E_m$ of membrane, contact area between membrane and soil $A_m$ as well as the initial void ratio e are the major factors influencing membrane penetration. According to the membrane deformation model given by Kramer and Sivaneswaran, an analytical solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law. The basic equations from theory of plates and shells and the elastic mechanics are employed during the derivation. To verify the presented solution, isotropic consolidation tests of a coarse-grained soil are performed by using the method of embedding different diameter of iron rods in the triaxial samples, and volume changes due to membrane penetration are obtained. The predictions from presented solution and previous analytical solutions are compared with the test results. It is found that the prediction from presented analytical solution agrees well with the test results.

• Geomechanics and Engineering
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• 제36권3호
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• pp.247-258
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• 2024

Tailings are waste materials of mining operations, consisting of a mixture of clay, silt, sand with a high content of unrecoverable metals, process water, and chemical reagents. They are usually discharged as slurry into the storage area retained by dams or earth embankments. Poor knowledge of the hydro-mechanical behaviour of tailings has often resulted in a high rate of failures in which static liquefaction has been widely recognized as one of the major causes of dam collapse. Many studies have dealt with the static liquefaction of coarse soils in saturated conditions. This research provides an extension to the case of silty tailings in unsaturated conditions. The static liquefaction resistance was evaluated in terms of stress-strain behavior by means of monotonic triaxial tests. Its dependency on the preparation method, the volumetric water content, the void ratio, and the degree of saturation was studied and compared with literature data. The static liquefaction response was proved to be dependent mainly on the preparation technique and degree of saturation that, in turn, controls the excess of pore pressure whose leading role is investigated by means of the relationship between the -B Skempton parameter and the degree of saturation. A preliminary interpretation of the static liquefaction response of Stava tailings is also provided within the Critical State framework.

• Current Photovoltaic Research
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• 제3권3호
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• pp.75-79
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• 2015

Recently, $Cu_2ZnSn(S_xSe_{1-x})_4$ (CZTSSe) has been received a tremendous attraction as light absorber material in thin film solar cells (TFSCs), because of its earth abundance, inexpensive and non-toxic constituents and versatile material characteristics. Kesterite CZTSSe thin films were synthesized by sulfo-selenization of sputtered Cu/Sn/Zn stacked metallic precursors. The sulfo-selenization of Cu/Sn/Zn stacked metallic precursor thin films has been carried out in a graphite box using rapid thermal annealing (RTA) technique. Annealing process was done under sulfur and selenium vapor pressure using Ar gas at $520^{\circ}C$ for 10 min. The effect of tuning Se/(S+Se) precursor composition ratio on the properties of CZTSSe films has been investigated. The XRD, Raman, FE-SEM and XRF results indicate that the properties of sulfo-selenized CZTSSe thin films strongly depends on the Se/(S+Se) composition ratio. In particular, the CZTSSe TFSCs with Se/(S+Se) = 0.37 exhibits the best power conversion efficiency of 4.83% with $V_{oc}$ of 467 mV, $J_{sc}$ of $18.962mA/cm^2$ and FF of 54%. The systematic changes observed with increasing Se/(S+Se) ratio have been discussed in detail.

• 한국환경과학회지
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• 제27권1호
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• pp.11-25
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• 2018

Both the propagation velocity and the direction of atmospheric waves are important factors for analyzing and forecasting meteo-tsunami. In this study, a total of 14 events of meteo-tsunami over 11 years (2006-2016) are selected through analyzing sea-level data observed from tidal stations along the west coast of the Korean peninsula. The propagation velocity and direction are calculated by tracing the atmospheric disturbance of each meteo-tsunami event predicted by the WRF model. Then, the Froude number is calculated using the propagation velocity of atmospheric waves and oceanic long waves from bathymetry data. To derive the critical condition for the occurrence of meteo-tsunami, supervised learning using a logistic regression algorithm is conducted. It is concluded that the threshold distance of meteo-tsunami occurrence, from a propagation direction, can be calculated by the amplitude of air-pressure tendency and the resonance factor, which are found using the Froude number. According to the critical condition, the distance increases logarithmically with the ratio of the amplitude of air-pressure tendency and the square of the resonance factor, and meteo-tsunami do not occur when the ratio is less than 5.11 hPa/10 min.