• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.30 no.2
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• pp.153-162
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• 2012

In this paper, we propose a new shape similarity measure for M:N polygon pairs regardless of different object cardinalities in the pairs. The proposed method compares the projections of two shape functions onto Zernike polynomial basis functions, where the shape functions were obtained from each overall region of objects, thus not being affected by the cardinalities of object pairs. Moments with low-order basis functions describe global shape properties and those with high-order basis functions describe local shape properties. Therefore several moments up to a certain order where the original shapes were similarly reconstructed can efficiently describe the shape properties thus be used for shape comparison. The proposed method was applied for the building objects in the New address digital map and a car navigation map of Seoul area. Comparing to an overlapping ratio method, the proposed method's similarity is more robust to object cardinality.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.40-47
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• 2021

This study investigates the influence of hooked-end steel fiber volume fraction and aspect ratio on the mechanical properties, such as compressive and flexural performance, of concrete with specified compressive strength of 30MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were selected. The flexural tests of steel fiber reinforced concrete (SFRC) prismatic specimens were conducted according to EN 14651. The compressive performance of SFRC with different volume fractions (0.25, 0.50 and 0.75%) were evaluated through standard compressive strength test method (KS F 2405). Experimental results indicated that the flexural strength, flexural toughness, fracture energy of concrete were improved as steel fiber volume fraction increases but there is no unique relationship between steel fiber volume fraction and compressive performance. The flexural and compressive properties of concrete incorporating hooked-end steel fiber with aspect ratio of 64 and 80 are a little better than those of SFRC with aspect ratio of 67. For each SFRC mixture used in the study, the residual flexural tensile strength ratio defined in Model Code 2010 was more than the limit value to be able to substitute rebar or welded mesh in structural members with the fiber reinforcement.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.22-27
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• 2010

본 논문은 유한체적법에 근거한 CFD 분석기법을 이용하여 증기 이젝터의 성능에 대하여 구동노즐의 기하학적 형상에 따른 영향을 조사하였다. 구동노즐의 직경비를 변화시키고 또한 직경비를 일정하게하고 구동 노즐의 위치를 변화시키면서 최적의 조건을 조사하였다. 연구 결과 이젝터의 성능은 구동노즐의 직경과 노즐의 출구 위치에 의해 좌우됨을 확인하였다. 일정 노즐 면적비에 대하여 노즐 목 직경이 감소함에 따라 혼입율이 증가하는 것을 확인하였고 일정 노즐 목 직경에 대하여 면적비의 증가는 혼입율의 감소의 원인이 된다는 것을 확인할 수 있었다. 또한 혼입율은 노즐의 출구 위치에 따라 영향을 받는다는 것도 확인하였다. 혼입율은 노즐 출구의 위치가 이젝터의 상류로 이동할수록 증가하고 그 위치는 이젝터의 일정단면적부 직경(D)에 대하여 0.4D일 때 최적의 성능을 보였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.2
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• pp.163-174
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• 2009

The large underground structure under earthquake is affected more by soil dynamic characteristic and volume of structure than by structural dynamic characteristic itself. Therefore, it is the purpose of research that the aseismic analysis for caverns including various aseismic analysis factors (rock quality-Q value, soil dynamic characteristic, shape ratio $&$ volume, underground structural dynamic characteristic, and aseismic level) are applied by using the numerical analysis program (SAUS; seismic analysis of underground structures). The result of research is stated that maximum strain, maximum moment, and maximum shear are not sensitive with respect to shape ratio. However those values are sensitive with respect to Q value, volume of underground structure and aseismic level. Based on the results of this research, the assessment for the influence factors of aseismic analysis for large underground structure could be possible.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.255-262
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• 2020

In modern passive sonar systems, a towed array sensor is used to minimize the effects of own ship noise and to get a higher SNR. The thin and long towed array sensor can be guided in a non-linear form according to the maneuvering of tow-ship. If this change of the array shape is not considered, the performance of beamformer may deteriorate. In order to properly beamform the elements in the array, an accurate estimate of the array shape is required. Various techniques exist for estimating the shape of the linear array. In the case of a method using a heading sensor, the estimation performance may be degraded due to the effect of heading sensor noise. As means of removing this potential error, weighted polynomial fitting technique for estimating array shape is developed here. In order to evaluate the performance of proposed method, we conducted computer simulation. From the experiments, it was confirmed that the proposed method is more robust to noise than the conventional method.

• Journal of the Korean Geotechnical Society
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• v.37 no.3
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• pp.31-41
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• 2021

A dozer is a construction machinery used to move soil mass along large open tracts of land. Soil thrust generated on the soil-track interface determines the performance of the dozer; to improve the tractive performance of the dozer, the outer surface of the continuous-track is designed to protrude with grousers. In this study, we calculated soil thrust of the dozer equipped with grousers with various shape ratios, and evaluated the optimal grouser shape ratio considering ground conditions. Grouser generated additional soil thrust on the side of the continuous-track (e.g., side soil thrust) and converted the shearing surface (e.g., from soil-track interface to soil-soil interface), increasing the soil thrust of dozer by about 1.3 to 1.6 times. The effect of grouser's shape ratio on the soil thrust of dozer differed with the relative density of the ground. As the shape ratios of grouser increased, soil thrust of dozer decreased at the relative density of 40% and increased at the relative density of 80%. Based on these results, it can be concluded that the shape ratio of grouser severely affects the dozer's performance; thus, careful consideration of the optimal shape ratio of grouser is of great importance in the mechanical design, evaluation, and optimization of the undercarriage of dozers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1105-1114
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• 2010

Ice shapes accumulated on the aircraft surfaces are categorized into rime and glaze ice, which are highly dependent on various parameters such as ambient temperature, liquid water contents (LWC), mean volumetric droplet diameter and freestream velocity. In this study, quantitative analyses on the ice accretion have been attempted in a systematical manner and the key findings are as follows. First, the increase of freestream velocity can cause tremendous change in the ice accumulation such as the growth of ice accretion area, ice heading direction and maximum thickness of ice horn. Second, LWC is found to be linearly proportional to the ice accretion area. Third, the effects of ambient temperature on incoming water mass seem to be relatively small in comparison with LWC and freestream velocity. Finally, it was shown that MVD has only a little influence on ice shapes. However, it may increase the ice accretion area by increasing the droplet impacting range.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.515-525
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• 2007

In this investigation, results of laboratory tests on four reinforced concrete flat plate interior connections with elongated rectangular column support which has been used widely in tall residential buildings are presented. The purpose of this study is to evaluate an effect of column aspect ratio (${\beta}_c={c_1}/{c_2}$=side length ratio of column section in the direction of lateral loading $(c_1)$ to the direction of perpendicular to $c_1$) on the hysteretic behavior under earthquake type loading. The aspect ratio of column section was taken as $0.5{\sim}3\;(c_1/c_2=1/2,\;1/1,\;2/1,\;3/1)$ and the column perimeter was held constant at 1200mm in order to achieve nominal vertical shear strength $(V_c)$ uniformly. Other design parameters such as flexural reinforcement ratio $(\rho)$ of the slab and concrete strength$(f_{ck})$ was kept constant as ${\rho}=1.0%$ and $f_{ck}=40MPa$, respectively. Gravity shear load $(V_g)$ was applied by 30 percent of nominal vertical shear strength $(0.3V_o)$ of the specimen. Experimental observations on punching failure pattern, peak lateral-load and story drift ratio at punching failure, stiffness degradation and energy dissipation in the hysteresis loop, and steel and concrete strain distributions near the column support were examined and discussed in accordance with different column aspect ratio. Eccentric shear stress model of ACI 318-05 was evaluated with experimental results. A fraction of transferring moment by shear and flexure in the design code was analyzed based on the test results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.51-58
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• 2006

The spray characteristics of liquid jet injected into subsonic cross-flow were investigated experimentally. Spray trajectories were captured using CCD camera. Droplet sizes were measured using PDPA and Image Express. The nozzle diameter was 0.5 mm, and its length-to-diameter ratios (L/D) ran$4.11{\times}10^6$ged from 1.0 to 6.0. Experimental results indicate that the breakup point is delayed by increasing gas momentum ratio and the penetration length is decreased by increasing Weber number. At low injection angle(${\theta}$ < $90^{\circ}$), Weber number is dominant parameter for trajectories, but at high injection angle(${\theta}$ > $90^{\circ}$), L/D is dominant parameter for trajectories rather than Weber number.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.354-359
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• 2013

일반적으로 건축물의 설계시 풍동 실험을 통한 풍환경의 평가를 수행하고 있으며, 이는 환경 영향 평가법에서 정한 건축 사업 시행 시 수반되어야 할 자연환경, 생활환경 그리고 사회경제환경의 영향 평가의 일환으로 실시되고 있다. 그러나, 풍동 실험의 경우 여러 가지 현실적 제약조건으로 설계와 실험의 피드백 (Feedback)이 원활하지 못하며, 특히 대상 건축물이 공장과 같이 대기 오염원이 되는 경우 실험은 더욱 어려운 형편이다. 이에 대한 보완책으로 전산 유체 역학을 이용한 건축물의 풍압 해석에 의한 풍하중 추정이나 인접 지형-지물의 영향을 고려한 건축물 주위의 풍환경 평가가 있다. 전산 모사에 의해 풍동 실험의 미비점을 보완하고, 보다 상세한 정보를 확보함으로써 건축물의 구조적 안전성의 증대와 환경 피해 감소를 기할 수 있다. 그러나 복잡한 지형-지물이나 건축물 주위의 풍환경에 대한 전산 모사는 주로 두 가지의 기술적 어려움을 수반하게 되다. 그 중 하나는 고정 경계면을 이루는 형상의 복잡성으로 인해 기존에 많이 이용하고 있는 Body-fitted 격자계를 이용하는 경우, 격자 생성 과정이 매우 복잡하고 어려울 뿐 만 아니라 생성된 격자가 주로 비정렬 (unstructured) 특성을 갖게 되어 수치해석 과정의 효율을 저하시키는 요인이 되며, 격자의 형상도 수치해석의 수렴성을 저하시키는 예가 많다. 다른 어려움으로 풍환경은 전형적인 난류 유동장으로서 난류의 전산 해석은 아직도 해결하지 못한 부분이 많다는 점이다. 이에 본 논문에서는 복잡한 지형-지물이나 건축물의 풍하중과 풍환경의 전산 모사 기술 확보를 위하여 수행중인 연구의 일환으로 물체 형상의 기하학적 복잡성의 극복을 위한 가상경계법 (Immersed Boundary Method)과 난류 유동장의 물리적 엄밀성을 높이기 위한 다와동 모사 (Large Eddy Simulation)을 이용한 물체 형상과 무관한 유동장 해석 기술 개발에 대하여 다루고자 한다. 먼저 최근에 유동 해석에 이용되는 방법인 가상경계법(IBM)은 물체를 포함한 전체 전산 영역을 직교 좌표계에 의해 이산화하고, 유동장내 존재하는 물체의 표면에서의 점착 조건을 만족시키기 위하여 지배 방정식에 적절한 외력을 추가로 고려하는 방법이다. 본 연구에서는 가상경계법을 이용하여 경계층에 위치한 건물 형상의 각진 물체 주위 사이에 형성되는 공동 내부의 비정상 유속 및 압력에 대한 전산 해석을 수행하고, 풍상측 전면에 형성되는 경계층에 의한 영향을 분석하였다.