• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 봄 학술발표회 논문집
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• pp.185-191
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• 1997

The study presents the linear dynamic analysis of bridges under vehicular movement to examine the performance characteristics due to the various structural and loading conditions. The road surface roughness and bridge-vehicle interactions are considered. The road surface profiles for the approaching roadway and bridge decks are generated from power spectral density functions for different road roughness conditions. A new filtering method using the wheel trace is proposed to obtain the more rational bridge-vehicle interactions from the randomly generated road surface. The dynamic responses of various bridges designed according to current design practice are examined, in which important structural parameters(such as span length, girder spacing, etc.) are considering systematically. In addition, the traffic conditions of multi-truck traveling either consecutively on the same lane or side-by-side on the adjacent lanes are also evaluated.

• Wind and Structures
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• 제12권3호
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• pp.281-283
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• 2009

Marquardt method is used to estimate the aerodynamic parameters in urban area of Beijing City, China, including displacement length (d), roughness length ($z_0$) and friction velocity (u*) and drag coefficient. The surface drag coefficient defined as the ratio between friction velocity and mean wind speed is 0.125 in our research, which is close to typical urban area value. The averaged d and $z_0$ are 1.2 m and 7.6 m. d and $z_0$ change with direction because of the surface heterogeneity over urban surface and reach their maximum values at S-SW sector, this tendency agrees with the surface rough element distribution around the observation tower.

• 한국지리정보학회지
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• 제1권1호
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• pp.99-108
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• 1998

국지 기상 모형의 지표 특성을 표현하기 위해 토양 구분, 식생 구분, 지표 거칠기 길이, 지표 알베도와 엽면지수가 지면 과정 모수화 내에서 처방되어야 한다. 이 연구에서는 인공위성 관측값으로부터 계절함수로 얻어진 경,위도 1도 및 1도의 엽면지수, 지표거칠기 길이, 눈이 없을 때의 지표 알베도와 상세 격자 NDVI를 지면 과정 모형에 적용하였다. 생물권과 대기권 사이, 지면과 대기 사이의 상호작용에서 이러한 인공위성 자료를 사용한 것과 사용하지 않은 것을 비교함으로써, 열, 에너지 및 수증기 속들, 지면 기온, 바람, 식생 물함유량, 비습, 강수장의 민감도가 조사되었다.

• 한국전자통신학회논문지
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• 제14권2호
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• pp.289-296
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• 2019

최근 스마트폰 카메라 기술의 발달로 고화질의 동영상을 촬영할 수 있다. 이러한 기술을 다양한 방법으로 활용하기 위해 디스플레이 등의 외부 장치로 신호 전송이 가능하여야 한다. 영상신호의 전송 성능은 전송선로의 손실과 배선의 길이에 따라 결정된다. 논문에서는 스마트폰 디자인에 따라 변경되는 배선 길이와 인쇄회로기판 도체 배선 소재 표면 거칠기 진폭에 따른 HDMI 전송선로 설계 기준을 제안하였다. 또한 실제 스마트폰 설계에 제안된 설계 기준을 적용하여 검증하였다. 본 논문을 통해 제안된 설계 기준은 모바일 어플리케이션외 고속신호 전송선로가 포함되는 다양한 응용분야에 확대 적용될 수 있을 것으로 판단된다.

• 대한원격탐사학회지
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• 제27권3호
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• pp.225-234
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• 2011

This study proposes an inversion algorithm to extract the surface parameters, such as surface roughness and soil moisture contents, using multi-frequency SAR data. The study areas include the tidal flats of Jebu Island and the reclaimed lands of Hwaong district on the western coasts of the Korean peninsula. SAR data of three frequencies were accordingly calibrated to provide precise backscattering coefficients through absolute radiometric calibration. The root mean square (RMS) height and the correlation length, which can describe the surface roughness, were extracted from the backscattering coefficients using the inversion of the Integral Equation Method (IEM). The IEM model was appropriately modified to accommodate the environmental conditions of tidal flats. Volumetric soil moisture was also simultaneously extracted from the dielectric constant using the empirical model, which define the relations between volumetric soil moistures and dielectric constants. The results obtained from the proposed algorithm were verified with the in-situ measurements, and we confirmed that multi-frequency SAR observations combined with the surface scattering model for tidal flats can be used to quantitatively retrieve the geophysical surface parameters in tidal flats.

• 소성∙가공
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• 제23권3호
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• pp.159-163
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• 2014

In the current study, the effect of small surface defects in the starting material including roughness, indentations, or scratches, which are perpendicular to the direction of drawing, on the product quality is investigated using the finite element method. An axisymmetric defect is assumed. Such defects are defined by a cylindrical defect area and two tapered regions connecting the defect area to the non-defective area of the material. Various conditions for these initial surface defects are considered, including defect depth, defect slope and defect length. To describe the plastic deformation of the defect in detail during the simulation, local remeshing is applied. Based on the finite element results, defect disappearance maps were generated. It was found that defect disappearance is significantly dependent on the defect depth and the defect length coupled with the defect slope.

• 한국기계가공학회지
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• 제21권4호
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• pp.23-30
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• 2022

Small-scale production is increasing, and the manufacturing industry is gradually changing into a smart manufacturing industry. Therefore, research on securing optimal cutting conditions for factors affecting machining precision during cutting is very important. Therefore, the purpose of this study is to After machining the inner diameter hole of SCM415 steel with a cermet tool on a CNC automatic lathe, the surface roughness, dimensional accuracy, and dimensional straightness are measured according to the feed rate to analyze the machining characteristics and suggest optimal cutting conditions. The test material was cut using a cermet tool for secondary cutting after a round bar with a diameter of 20 mm was mounted on a CNC automatic lathe. The cutting length was fixed at 0.5 mm, and the cutting speed was fixed at 3200 rpm. When the feed rate was changed to 0.05, 0.1, and 0.15 mm/rev, the respective surface roughness during the 15th test was measured. Consequently, The lower the feed rate, the better is the surface roughness. In addition, the optimum cutting conditions for SCM415 steel were observed to be the most ideal cutting conditions than the condition of 0.05 mm/rev at a cutting speed of 3,200 rpm and a feed rate of 0.1 mm/rev.

• 한국환경과학회지
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• 제23권6호
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• pp.1199-1211
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• 2014

The momentum flux and the sensible heat flux were measured with the scintillometers and ultrasonic anemometers at 6 sites of which surface characteristics like roughness length and zero-displacement are different each other. We estimated the momentum flux and the sensible heat flux based on the bulk transfer method with the drag coefficient and the heat transfer coefficient calculated from the temperature and wind speed at two heights. The variation of bulk transfer coefficients showed a remarkable difference depending on the atmospheric stability which is less influenced by the zero-displacement than the roughness length. The estimated sensible heat fluxes were in good agreement with those measured at 3 m, showing 23.7 $Wm^{-2}$ of the root mean square error that is less than 10% of its maximum. Since the estimated momentum flux is not only effected by drag coefficient but also by wind speed square, the determination of wind speed in the bulk transfer method is critical.

• Composites Research
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• 제33권6호
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• pp.371-376
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• 2020

접착강도는 표면처리 기술을 통해 향상시킬 수 있다. 가장 일반적인 방법은 기계적인 결합력을 향상시킬 수 있는 접착 표면의 변화이다. 본 연구는 접착면의 레이저 표면 처리가 기계적 결합력에 미치는 영향과 탄소섬유 강화 복합재료(CFRP)의 접착 결합에 대해 설명한다. 1064 nm의 레이저를 활용하여 표면 조도를 패턴화했다. 레이저 샷의 수, 패턴의 방향, 길이가 CFRP/CFRP 단일 조인트의 접착력에 미치는 영향을 인장 시험을 통해 조사했다. ASTM D5868에 따른 시험을 수행하였으며, 파단 후 손상된 표면을 분석하여 결합 메커니즘을 결정했다. 접착 강도의 증가를 위해서는 CFRP 표면에 최적화된 레이저 샷의 수와 조도 깊이가 구성되어야 한다. 인장방향에서의 전단응력을 고려할 때, 접착층의 파단 경로를 길어지게 하는 45°의 방향의 조도가 접착강도의 증가를 야기했다. 그러나 레이저에 의한 조도의 길이는 접착 강도에 크게 영향을 주지 못했다. 레이저를 이용한 접착면의 표면처리는 기계적 결합 메커니즘을 확보하고 CFRP 접착 조인트의 접착 강도를 향상시키는 적합한 방법이라는 결론을 도출할 수 있다. 레이저 처리를 이용한 이점을 완전히 이용하기 위해서는 최적화된 레이저 공정 변수에 대한 연구가 반드시 필요하다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.961-964
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• 1997

In this paper, grinding characteristics of ultra high speed cylindrical plunge grinding was investigated by use of vitrified CBN wheel. From the experimental result, it was convinced that grinding power is decreased according to the increase of wheel and workpiece speed due to changing of grinding mechanism which decreases depth of cut and length of contact curve according to increment of wheel speed. And also, stock removal reduction of each gram lead to improvement of surface roughness by increasing the wheel speed.