• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.12-17
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• 2006

Longitudinal static stability and steady aerodynamic characteristics of wings flying over nonplanar ground surfaces (rail and channel) are investigated using the boundary-element method. For a channel with it's fence higher than the wing height, the lift and the nose-down pitching moment increase as the gap between the wingtip and the fence decreases. For a rail with it's width wider than the wing span, the lift and the nose-down pitching moment increase as the rail height decreases. Longitudinal static stability of a single wing flying over nonplanar surfaces is worse than the case of the flat ground. In case of tandem wings, longitudinal static stability of the wings flying over the channel is better than the case of the flat ground. It is believed that the present results can be applied to the conceptual design of high-speed ground transporters.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.360-365
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• 2005

본 논문에서는 콘크리트 표면 균열 영상에서 균열을 효율적으로 추출하기 위한 화상처리 기법과 ART1 기반 RBF 네트워크를 제안하여 균열의 방향성을 인식한다. 본 논문에서 사용된 화상처리 기법으로는 균열 영상의 빛을 보정하기 위한 모폴로지 기법인 채움(Closing)연산을 적용하고 Sobel 마스크를 적용하여 균열 영상의 에지를 추출한 후 반복 이진화를 적용하여 균열 영상을 이진화한다. 이진화 된 영상에 두 차례에 걸쳐 잡음제거를 수행하여 콘크리트 표면 균열 영상으로부터 균열을 추출한다. 본 논문에서는 추출된 균열을 ART1 기반 RBF 네트워크에 적용하여 균열의 방향성(횡방향, 종방향, $-45^{\circ}$방향, $45^{\circ}$방향)을 자동으로 인식할 수 있는 방법을 제안한다. 제안된 ART1 기반 RBF 네트워크는 입력층과 중간층으로의 학습은 ART1을 적용하고 중간층과 출력층 간의 학습은 Delta 학습 방법을 적용한다. 실제 콘크리트 균열 영상을 적용하여 실험한 결과, 콘크리트 표면 균열 영상에서 효율적으로 균열을 추출할 수 있었고 제안된 ART1 기반 RBF 네트워크가 추출된 균열의 방향성 인식에 효율적인 것을 확인하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.169-178
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• 2008

Compressive flanges of steel box girder is designed based on the ultimate strength behavior of sub-panel which is enclosed with longitudinal stiffeners and transverse stiffeners on appropriate safety factor. However, it is rational that the ultimate strength is calculated considering the various factors such as number and stiffness of longitudinal stiffener, spacing of transverse stiffener, initial deformation and residual stress distribution. In this study, an analysis program based on Folded Plate theory is developed considering the geometric effects and the material nonlinearity. The analysis program is applicated to the steel box girder bridges which is really constructed in domestic.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.67-71
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• 2014

Intravascular optical coherence tomography (OCT) enables imaging of the three-dimensional (3D) microstructure of a blood vessel wall. While 3D vascular visualization provides detailed information of the vessel wall and intraluminal structures, a longitudinal imaging pitch that is several times bigger than the imaging resolution of the system has limited true high-resolution 3D imaging. In this paper we demonstrate high-speed intravascular OCT in vivo, acquiring images at a rate of 350 frames per second. A 47-mm-long rabbit aorta was imaged in 3.7 seconds, after a short flush with contrast agent. The longitudinal imaging pitch was 34 micrometers, comparable to the transverse imaging resolution of the system. Three-dimensional volume rendering showed greatly enhanced visualization of tissue microstructure and stent struts, relative to what is provided by conventional intravascular imaging speeds.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.675-687
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• 2019

In recent years, the needs for double deck-tunnels have increased in large cities due to the increase in traffic volume and high land compensation costs. In Korea, a network type tunnel which is smaller than general road tunnels and crosses another tunnel underground is planned. In the shield tunnel joints between the existing shield tunnel and the box-type enlargement section, a partial steel-concrete joint is proposed where the bending moment is large instead of the existing full-section steel joint. In order to analysis the enlargement section of the shield tunnel diverged section to reflect the three-dimensional effect, the two-dimensional analysis model is considered to consider the column effect and the stiffness effect of the longitudinal member. A two-dimensional analysis method is proposed to reflect the stiffness of the longitudinal member and the column effect of the longitudinal point by considering the rigidity of the longitudinal member as the elastic spring point of the connecting part in the lateral model. As a result of the analysis of the model using the longitudinal member, it was considered that the structural safety of the partial steel-concrete joint can be secured by reducing the bending moment of the joint and the box member by introducing the longitudinal member having the stiffness equal to or greater than a certain value.

• Computational Structural Engineering
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• v.8 no.1
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• pp.137-146
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• 1995

Structural stress under shock or impact load is varied with the lapse of time and the structural stress is called stress wave. Propagating longitudinal stress wave is studied in a 2-dimensional plate. A finite element program for elastic stress wave propagation is developed in order to investigate the shape of stress field at time increment. The longitudinal stress wave is generated by unit step function. According to the finite element analysis results, the longitudinal stress wave propagates to the similar direction of impact load and the front of stress wave propagates with the same speed as analytic solution and the shape of stress field is similar to that of analytic solution. The shear wave is occurred after the longitudinal stress wave and declined at an angle of 45 degrees compared with longitudinal stress wave and the speed of shear wave is about a half of the longitudinal stress wave. The intensity of shear wave is larger than that of longitudinal stress wave.

• Journal of Korea Water Resources Association
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• v.35 no.2
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• pp.195-201
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• 2002

In this study, an equation is proposed to estimate the limit velocity for lateral stable bed in a curved channel stream. The stable bed on lateral direction is satisfied when there is no more deformation occurs on the transverse bed slope and non-scouring condition in a bend. A theoretical equation for limit velocity is derived using a transverse bed slope model. So, the limit velocity has its theoretical background in the equilibrium of two forces, lateral shear force at the bed due to longitudinal flow and the corresponding lateral bed shear force. To verify the equation, data from four natural river channels were used. There is good agreement between the calculated values using this equation and the measured values. The corrections in equation was found to be correlated with the averaged particle Froude number.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1296-1300
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• 2015

Ganglion cysts are commonly observed cystic tumor in association with the joints and tendons of the appendicular skeleton. In this paper we propose a method to extract ganglion cysts from ultrasound images with intelligent image processing. The method consists of fuzzy stretching preprocessing to enhance the contrast between related organs and 8-directional contour tracking to model the boundaries of the cysts and labelling procedure to compute the size of cysts. In experiment, we verified that the proposed method extracts ganglion cysts accurately from ultrasound images.

• Korean Journal of Optics and Photonics
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• v.8 no.5
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• pp.415-419
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• 1997

A novel fiber optic sensor is demonstrated using a FBG in PM(Polarization-Maintaining) fiber. Gratings have been written in a Bow-Tie type fiber using the phase mask. The operation of the sensor simply involves monitoring back-reflected Bragg wavelengths from the grating. Since PM fiber has two principal semi-axes with two indices of refraction, two Bragg wavelengths were observed. We have observed the position of Bragg wavelengths for PM FBG shifted simultaneously by either applying the longitudinal strain or temperature change. The wavelength sensitivity of 1.2pm/$\mu$$\varepsilon$ about a longitudinal strain and the wavelength sensitivity of 11.4pm/$^{\circ}C$ about a temperature have been experimentally achieved. The wavelength sensitivity of both longitudinal strain and temperature are approximately same with the reported values for the single mode FBG. On the other hand, the change of separation between Bragg wavelengths was observed by the applying transverse stress. We observed that the separation between two Bragg wavelengths is proportional to the applied transverse stress. The wavelength sensitivity of 14.6 pm/N about a transverse stress has been achieved. We have demonstrated PM FBG sensors can measure the transverse stress independently from the effects of temperature.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.970-975
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• 2005

측면웨어(side weir)는 본류의 수위가 한계수위 이상으로 상승할 경우 본류로부터 저류지나 분수로(distributary channel)로 흐름을 전환하기 위하여 사용하는 수공구조물이다. 최근 들어 치수와 관련된 계획에서 본류의 홍수량 중 일부를 저류지나 홍수 우회수로로 전환시키는 시설에 대한 관심이 높아지고 있다. 측면웨어가 하천에 설치되는 경우, 측면웨어 부근 표층부의 흐름은 측면웨어의 영향을 크게 받으며, 수의바닥이나 측면웨어에서 떨어진 지점의 흐름은 측면웨어의 영향을 작게 받는 등 측면웨어 주변부는 3차원적인 흐름특성을 보인다. 또한 측면웨어를 월류하는 흐름이 일반 웨어와 같이 웨어 마루부에 대하여 직각방향으로 흐르지 않고 본류의 유속에 따라 비스듬하게 흐르게 된다. 이러한 흐름특성으로 인해 측면웨어를 통과하는 유량은 본류의 하폭, 본류의 흐름특성, 측면웨어의 길이 및 설치위치 등에 따라 각기 다르게 산정되는 것으로 알려져 있다. 본 연구에서는 기존 측면웨에에 관한 연구를 정리하고 상용 프로그램인 FLOW-3D를 이용하여 측면웨어가 설치된 경우의 흐름을 해석하였다. 해석결과는 기존 실험연구에 바탕을 둔 이론식과 비교하였다. 계산격자는 구조물 부근의 흐름이 급변하는 곳은 격자크기를 작게, 흐름의 변화가 완만한 곳은 격자크기를 크게 하였다. 경계조건으로 상류는 유량, 하류는 수위경계를 입력하였다. 본 수치모의결과와 이론식을 이용하여 산정한 월류량을 비교한 결과 약 $10-30\% 내외의 오차가 발생하는 것으로 나타났다. 본류의 흐름은 웨어의 길이가 짧을수록 상$\cdot$하류단의 수위차가 작아지며 유속의 경우 웨어길이가 길고, 높이가 낮을수록 빨라진다. 측면웨어 주변부 흐름의 경우, 웨어의 길이가 짧을수록 방류강도가 강하고 횡방향의 수면변위가 급하게 형성되고 있음을 알 수 있다 또한, 웨어의 길이가 상대적으로 길어질 경우에는 3차원적 흐름특성에 의하여 유속의 분포가 다양하여 이론식과 결과의 오차가 점점 더 커짐을 알 수 있다. 본 연구는 사각형수로에 측면웨어가 설치된 경우, 월류량과 수리학적 거동을 해석할 때 수치모형실험이 수리모형실험과 더불어 유용한 해석도구로 이용될 수 있음을 보인 깃으로 이후 관련 구조물의 설계와 해석 시 참고자료로 이용 가능할 것으로 판단된다.