• 산업기술연구
• /
• 제2권
• /
• pp.53-60
• /
• 1982

A strain gage relief technique was used to determine the magnitude and directions of a virgin principal stresses, but the values measured in the same borehole are always not consistent. This paper has shown the use of the eigen analysis to achieve precise and reliable principal stress from measured values. The best fit stress ellipsoid to the data has been obtained through consideration of direction cosine of each principal stress.

• 제어로봇시스템학회논문지
• /
• 제4권6호
• /
• pp.759-764
• /
• 1998

We propose a novel algorithm capable of recognizing the road lane by image processing. Considering the fact that the direction and location of road lane are maintained similarly in successive images we formulate a function to represent the property. However, as noises play the role of making a lot of similar patterns appear and disappear in the road image, keeping of robustness in the lane detection has been known a difficult work. To overcome this problem, we introduce the following three ideas: 1) design of a function based on an edge direction and magnitude, 2) construction of a recursive filter to estimate the function recursively for successive images, 3) principal axis-based line fitting. These concepts enhance the adaptability to cope with the random environment of traffic scene and eventually lead to the reliable detection of a road lane.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1021-1026
• /
• 2003

The problem of predicting the fracture strength behavior in orthotropic plate with a crack inclined with respect to the principal material axes is analyzed. Both the load to cause fracture and the crack direction of crack growth arc of interest. The theoretical results based on the normal stress ration theory show significant effects of biaxial loading and the fiber orientation on the crack growth angle and the critical stress. The additional term in the asymptotic expansion of the crack tip stress field appears to provide more accurate critical stress prediction.

• 대한안전경영과학회지
• /
• 제14권2호
• /
• pp.35-40
• /
• 2012

The aims of this study are to investigate stereotypes of motion-direction and real motion-directions for seven principal controls in passenger cars, and to compare the stereotypes and real motion-directions for the controls. The stereotypes were obtained by using questionnaire survey, in which 385 subjects participated. The real motion-direction data were gathered for 64 passenger cars including RVs and SUVs. The results showed that while there are dominant motion-directions for head light, door key and door lock controls, dominant motion-directions are not found for other controls investigated in this study. The stereotypes of motion-directions for seven controls obtained in this study were much different from those of the real data. Furthermore, the stereotypes for wiper, head light and high beam controls based on the questionnaire survey were opposite to the real motion-directions.

• 한국지진공학회논문집
• /
• 제11권5호
• /
• pp.33-47
• /
• 2007

실무에서 지진해석법으로 널리 쓰이는 방법은 등가정적해석법과 응답스펙트럼해석법이다. 이 중 등가정적해석법에 의한 밑면전단력은 구조물의 주축을 해석좌표축에 어떻게 배치하는가와 상관없이 일관된 값을 나타낸다. 그러나 응답스펙트럼해석은 해석좌표 축에 구조물의 주축을 다르게 배치하여 해석을 수행하면 밑면전단력이 각기 다르게 발생한다. 이는 엔지니어가 구조물을 설계함에 있어 구조물의 주축을 해석좌표축에 어떻게 설정했는지에 따라 설계부재력이 모두 달라질 수 있음을 뜻한다. 또한 응답스펙트럼해석은 지진을 가한 방향의 직각방향에서 적지 않은 응답이 발생하는 경우가 생긴다. 한방향 해석에 대한 X와 Y축을 따라 분리되는 이러한 양방향 응답은 보정계수 산정시 쓰이는 밑면전단력을 작게 만들며 이는 결과적으로 보정계수를 크게하여 과다설계의 우려가 생긴다. 내진설계시 발생하는 이러한 문제점을 해결하기 위하여 본 논문에서는 수평의 강성 차이에 따라 구조물을 크게 세 가지(양방향 대칭 구조물, 한방향 비대칭구조물, 양방향 비대칭구조물)로 분류하여 각각의 경우에 대하여 간단한 모델을 선정하고 구조물의 주축을 회전시켜가면서 지진해석을 수행하였다. 각 경우의 예제구조물이 가지는 동적특성과 설계부재력을 살펴보았다. 현재 실무에서 적용되는 보정계수 산정법에 의한 설계부재력과 앞선 문제들을 해결하고자 본 논문에서 제안하는 새로운 보정계수 산정법에 의한 설계부재력을 비교하여 제안하는 보정계수 산정법의 효율성을 검토하였다. 그 결과로 새로 제안된 보정계수 산정법에 의하여 설계부재력을 산정하는 것이 내진설계시 엔지니어들이 겪을 수 있는 혼란을 덜어주며 경제적인 부재설계가 가능함을 알 수 있었다.

• 터널과지하공간
• /
• 제15권6호
• /
• pp.391-399
• /
• 2005

본 연구에서는 횡등방성 암반에서 이방성 정도에 따른 응력 차와 3차원 주응력 하의 터널방향, 이방성 정도에 따른 터널 단면에서의 2차원 응력 차를 이론적으로 구하였다. 구해진 응력상황 하의 터널에 대하여 $FLAC^{2D}$를 이용하여 이방성 고려여부에 따른 천단, 측벽, 바닥의 응력 차를 비교${\cdot}$검토하였다. 그 결과 이방성을 무시할 경우 응력 조건에 무관하게 주응력의 크기와 방향이 다르게 나타나며, 이방성 정도가 커질수록 응력차가 증가함을 알 수 있다. 이방성의 방향에 따라 응력 차가 달리 나타나며, 특히 이방성의 방향이 x축으로부터 시계반대방향으로 $45^{\circ}$와 $135^{\circ}$에서 가장 큰 응력 차가 발생함을 확인하였다.

• Geomechanics and Engineering
• /
• 제14권2호
• /
• pp.195-202
• /
• 2018

Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.

• Geomechanics and Engineering
• /
• 제6권2호
• /
• pp.153-172
• /
• 2014

In order to investigate the effect of different perforation angles (the angle between the perforation direction and the maximum horizontal principal stress) on the fracture initiation and propagation during hydraulic fracturing of highly deviated well in oil & gas saturated formation, laboratory experiments of the hydraulic fracturing had been carried out on the basis of non-dimensional similar criteria by using 400^3 $mm^3$ cement cubes. A plane fracture can be produced when the perforations are placed in the direction of the maximum horizontal principal stress. When the perforation angle is $45^{\circ}$, the fractures firstly initiate from the perforations at the upper side of the wellbore, and then turn to the maximum horizontal principal stress direction. When the well deviation angle and perforation angle are both between $45^{\circ}$ and $90^{\circ}$, the fractures hardly initiate from the perforations at the lower side of the wellbore. Well azimuth (the angle between the wellbore axis and the maximum horizontal principal stress) has a little influence on the fracture geometries; however it mainly increases the fracture roughness, fracture continuity and the number of secondary fractures, and also increases the fracture initiation and propagation pressure. Oriented perforating technology should be applied in highly deviated well to obtain a single plane fracture. If the well deviation angle is smaller, the fractures may link up.

• Journal of Mechanical Science and Technology
• /
• 제14권3호
• /
• pp.291-297
• /
• 2000

Modern helicopter rotor blades with non-homogeneous cross sections, composed of anisotropic material, require highly sophisticated structural analysis because of various cross sectional geometry and material properties. They may be subjected by the combined axial, bending, and torsional loading, and the dynamic and static behaviors of rotor blades are seriously influenced by the structural coupling under rotating condition. To simplify the analysis procedure using one dimensional beam model, it is necessary to determine the principal coordinate of the rotor blade. In this study, a method for the determination of the principal coordinate including elastic and shear centers is presented, based upon continuum mechanics. The scheme is verified by comparing the results with confirmed experimental results.

• 대한기계학회논문집A
• /
• 제21권6호
• /
• pp.981-987
• /
• 1997

Modern helicopter rotor blades with non-homogeneous cross section composed of anisotropic material rquire highly sophisticated structural analysis. Variation in cross section geometry makes this task of analysis more complicated. Since rotor blades generally are much longer than their lateral dimensions, one-dimensional models seem feasible, at least from a computational point of view. Therefore determination of the principal coordinate system is very important to remove the structural coupling for one-dimensional beam modelling. In this study, shear center, and principal direction. The method will be verified by comparing the results with confirmed experimental results.