• Structural Engineering and Mechanics
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• 제66권3호
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• pp.329-341
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• 2018

This paper considers the smooth receding contact problem between a homogeneous half-plane and a composite laminate composed of an inhomogeneously coated elastic layer. The inhomogeneity of the elastic modulus of the coating is approximated by an exponential function along the thickness dimension. The three-component structure is pressed together by either a concentrated force or uniform pressures applied at the top surface of the composite laminate. Both semianalytical and finite element analysis are performed to solve for the extent of contact and the contact pressure. In the semianalytical formulation, Fourier integral transformation of governing equations and boundary conditions leads to a singular integral equation of Cauchy-type, which can be numerically integrated by Gauss-Chebyshev quadrature to a desired degree of accuracy. In the finite element modeling, the functionally graded coating is divided into homogeneous sublayers and the shear modulus of each sublayer is assigned at its lower boundary following the predefined exponential variation. In postprocessing, the stresses of any node belonging to sublayer interfaces are averaged over its surrounding elements. The results obtained from the semianalytical analysis are successfully validated against literature results and those of the finite element modeling. Extensive parametric studies suggest the practicability of optimizing the receding contact peak stress and the extent of contact in multilayered structures by the introduction of functionally graded coatings.

• 치과방사선
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• 제29권2호
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• pp.397-405
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• 1999

Purpose: To clarify the usefulness and the limitation of Digora system/sup (R)/ by evaluating the physical characteristics as the quantitative image on Image Plate(Ip). Materials and Methods: Radiograms were taken by Heliodent MD(Siemens Co.. Germany) with the image plate for adult. Cu-step wedge as reference material. and three pieces of dry mandibular bone. Image analysis was performed by single color enhancement. density measurement with histogram. The relationship between the exposure conditions and the distribution of the pixel values of the image. the variation of pixel values of each step of Cu-step wedge at two different area and Cu-equivalent value of three pieces of dry mandibular bone measure by the conversion equation. Results: There was no linear relationship between the exposure condition and the average pixel value of the image. of which the distribution was not even. The pixel value differences between the center portion and the periphery were ranged from 60 to 70 in vertical plane and from 15 to 26 in horizontal plane. Two plot profile formed at two different areas of the Cu-step wedge were different. The measured Cu-equivalent values showed the discrepancy among the times of measurement. Conclusion: As above results. Image Plate(Ip) of Digora system/sup (R)/ showed the limitation as the quantitative image. The physical property of IP was expected to need to be compensated for the quantitative evaluation of the bone or others

• 한국산학기술학회논문지
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• 제14권7호
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• pp.3158-3163
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• 2013

본 연구에서는 회전속도, 브레이크 압력 제어가 가능한 브레이크 다이나모메타를 제작하여 스퀼 소음 실험을 실시하였다. 브레이크 패드는 각각 $34^{\circ}$, $30^{\circ}$, $26^{\circ}$로 가공하여 패드 각도에 따른 스퀼 발생 조건과 음의 기울기 발생에 따른 스퀼 연관성을 연구 하였다. 각도에 따라 특정한 회전속도와 브레이크 압력에서 스퀼이 발생하였으며, 각도에 상관없이 하모닉 성분을 가지는 특정 주파수 소음을 발견하였다. 햄머링 테스트 및 유한요소해석을 통해서 특정 주파수는 In-plane모드 성격을 갖고 있으며, 패드 각도에 둔감한 모드임을 밝혀냈다.

• 비파괴검사학회지
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• 제30권3호
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• pp.181-193
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• 2010

The paper presents an alternative way to classical stereocorrelation. First, 2D image processing of random patterns is described. Sub-pixel displacements are determined using phase analysis. Then distortion evaluation is presented. The distortion is identified without any assumption on the lens model because of the use of a grid technique approach. Last, shape measurement and shape variation is caught by fringe projection. Analysis is based on two pin-hole assumptions for the video-projector and the camera. Then, fringe projection is coupled to in-plane displacement to give rise to 3D measurement set-up. Metrological characterization shows a resolution comparable to classical (stereo) correlation technique ($1/100^{th}$ pixel). Spatial resolution seems to be an advantage of the method, because of the use of temporal phase stepping (shape measurement, 1 pixel) and windowed Fourier transform (in plane displacements measurement, 9 pixels). Two examples are given. First one is the study of skin properties; second one is a study on leather fabric. In both cases, results are convincing, and have been exploited to give mechanical interpretation.

• Geomechanics and Engineering
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• 제30권1호
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• pp.67-73
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• 2022

In this study, the fiber orientation distribution (FOD) is investigated using both micro-CT (computerized tomography) and image analysis of physically cut specimens prepared from Polyvinyl Alcohol (PVA) fiber reinforced cemented Toyoura sand. The micro-CT images of the fiber reinforced cemented sand specimens were visualized in horizontal and vertical sections. Scans were obtained using a frame rate of two frames and an exposure time of 500 milliseconds. The number of images was set to optimize and typically resulted in approximately 3000 images. Then, the angles of the fibers for horizontal sections and in vertical section were calculated using the VGStudio MAX software. The number of fibers intersecting horizontal and vertical sections are counted using these images. A similar approach was used for physically cut specimens. The variation of results of fiber orientation between micro-CT scans and visual count were approximately 4-8%. The micro-CT scans were able to precisely investigate the fiber orientation distribution of fibers in these samples. The results show that 85-90% of the PVA fibers are oriented between ±30° of horizontal, and approximately 95% of fibers have an orientation that lies within ±45° of the horizontal plane. Finally, a comparison of experimental results with the generalized fiber orientation distribution function 𝜌(θ) is presented for isotropic and anisotropic distribution in fiber reinforced cemented Toyoura sand specimens. Experimentally, it can be seen that the average ratio of the number of fibers intersecting the finite area on a vertical plane to number of fibers intersecting the finite area on a horizontal plane (N^V_tot/N^H_tot) cut through a sample varies from 2.08 to 2.12 (an average ratio of 2.10 is obtained in this study). Based up on the analytical predictions, it can be seen that the average N^V_tot/N^H_tot ratio varies from 2.13 to 2.17 for varying n values (an average ratio of 2.15).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1709-1712
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• 2008

The trunk is inclined to the loaded side when carrying an object as one of activities of daily living. As the reaction to this behavior the human body may be inclined to his/her trunk to unloaded side. The present study investigated the biomechanical effects of weight variation for sided load carriage during walking upon joint moments and muscle torques, through the tracker agent and joint driving dynamic analysis. To perform the experiment one male was selected as subject for the study. Gait analysis was performed by using a 3D motion analysis system. Thirty nine 14mm reflective markers, according to the plug-in marker set, were attached to the subject. We used BRG.LifeMOD(Biomechanics Research Group, Inc., USA), for skeletal modeling and inverse and joint driving dynamic simulation during one gait cycle. In walking with a sided load carriage, the subject modeled held the carriage with the right hand, which weighed 0, 5, 10, 15kg, 20kg respectively. The result of this simulation showed that knee and hip in the coronal plane were inclined to the loaded side and loaded side had larger moments as the sided load carriage was increased. On the other hand thoracic and lumbar in the coronal plane had larger negative values as the sided loaded carriage was increased. The thoracic and lumbar in the transverse plane also had larger values as the sided load was increased. And the several muscles of loaded side were increased as increasing sided load. It could be concluded that human body is adopted to side loaded circumstances by showing more biologic force. These results could be very useful in analysis for delivery motion of daily life.

• 한국전산구조공학회논문집
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• 제22권2호
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• pp.189-196
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• 2009

본 논문에서는 적층구조 해석을 위해 부분 선형 층별이론에 의해 정식화된 저매개변수 유한요소 모델을 제안한다. 얇은 직교이방성 문제뿐만 아니라, 두꺼운 식교이방성 적층판 해석을 위해 제안된 모델은 2차원 세분화 기법에 기초를 두고 있다. 즉, 이 모델은 두께방향으로의 면내거동에 대해서는 선형변화로 가정하는 층별분리 이론이 적용되고, 두께방향으로의 면외거동에 대해서는 상수로 가정하는 등가단층이론이 사용된다. 변위장을 정의하기 위해 적분형 르장드르 다항식이 사용된다. 또한 가우스-로바토 적분법을 사용하여, 적층평판의 종래의 가우스적분점이 아닌 절점의 위치에 발생하는 최대응력값을 별도의 외삽법을 사용하지 않고 바로 산출하였다. 제안된 모델의 정당성과 특성은 직교이방성 다층적층판 문제를 사용하여 검증되었으며, 그 결과는 출판된 참고문헌의 값들과 비교되었다. 이 연구에서는 최적의 유한요소 적층모델을 결정하기 위해 응력과 최대처짐을 사용한 수렴성조사가 수행되었다. 또한, 적층 수의 증가에 따른 두께방향으로의 변위와 응력분포의 변화가 조사되었다.

• 한국지반공학회논문집
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• 제16권4호
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• pp.107-116
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• 2000

흙 필터를 대신한 토목섬유의 사용량이 점차 증가하고 있다. 따라서 흙과 결합된 복합체계에 대한 메카니즘 연구가 활발히 진행되고는 있지만 이러한 복합체의 거동은 흙과 사용 필터재의 상호작용으로 인한 여러 가지 영향 인자들 때문에 실제의 필터 설계는 경험적인 방법에 의존하고 있다. 본 연구에서는 흙/부직포 시스템에서 세립자 이동에 의한 폐색 현상을 규명하고자 하였다. 국내의 대표적인 풍화잔적토 지반에 속하는 서울의 신내동과 포이동 지역의 흘을 시료로 이용한 본 실험은 필터재 내에서의 흐름방향에 따라 수평흐름과 수직흐름으로 나누어 실내 시험을 실시하였다. 필터재로서는 현장에서 배수재로 광범위하게 쓰이는 토목섬유를 사용하였다. 흙 모체와 필터가 결합된 복합체의 적합성 여부를 필터재의 흐름에 따라 비교, 분석하고 기존에 제안된 폐색 방지 기준을 적용하여 보았다. 이러한 실험결과를 토대로 하여 수평 흐름시 발생하는 공간적 투수 계수 변화를 예측할 수 있는 모델을 제안하고 실내에서 실시한 모형실험과 이론적 모델예측의 비교를 통하여 투수능 저하 현상의 시각적, 공간적 변화 양상을 파악하였다.

• 한국조경학회지
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• 제27권3호
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• pp.58-68
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• 1999

Purpose of this thesis is to find out the relationship among the amount of change and the visual cognition, and the visual preference which people like and can feel. Through the investigation of relationships between the amount of change, which indicates the degree of visual variation and the visual preference, the amount of change and the visual cognition, and the visual preference and the visual cognition, basic design data will be supplied, which can satisfy users' desire as much as possible in the most economic way. In order to investigate the relationship between the visually produced the amount of change and preferences, graphic simulation, in which variables other than the visual change are controlled, has been proceeded. Graphic factors of the visual change in the cyber exterior space are determined on the point of location (base plane, vertical plane, overhead plane), shape, size and color. As for the relationship between the amount of change and the preference, only the size is effective. since preferences on the location, shape and color are individual preferences, no common trend can be found. Therefore, we cannot say that which shape or color is better, Since the location, shape and color are qualitative change and the size is the quantitative change, the size can be the measurable change quantity. The relationship between the amount of change of size and the degree of preference is found to be inverse U-shape, i.e., as the amount of change of size increases the degree of preference first increases and, after a certain level, decreases. The same result has been obtained in photo simulation.

• 대한기계학회논문집A
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• 제35권8호
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• pp.835-846
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• 2011

최근 보편화 되고 있는 내측개방형절골술 시에 의도하지 않은 경골후방경사각의 변화로 인한 문제점들이 보고되었다. 이를 해결하기 위해 많은 연구들이 진행되어 왔지만 환자의 다양한 경골의 형상 및 절단면의 기울기에 적용될 수 있는 일반적 해석 모델은 아직 제안되지 못하고 있다. 따라서 본 논문에서는 일반적인 케이스에 적용할 수 있는 근위경골절골술의 해석 모델을 제안한다. 이를 위해 내반교정각만을 조정할 수 있는 가상경골축을 정의하고, 이를 통해 절단면과 경골개방축이 내반교정각에 주는 영향을 나타내는 수학적 모델을 제안하고, 기존의 수술적인 변수들간의 상관관계를 명확히 나타내었다. 또한 내반교정각과 경골후방경사각에 추가로, 새로운 각도인 경골뒤틀림각의 존재를 도입함으로써 수술 시 발생하는 모든 기하학적 변수들간의 관계를 완성된 형태로 표현하였다.