• Computers and Concrete
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• 제21권6호
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• pp.727-739
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• 2018

Crack is the most common typical feature of concrete deterioration, so routine monitoring and health assessment become essential for identifying failures and to set up an appropriate rehabilitation strategy in order to extend the service life of concrete structures. At present, image segmentation algorithms have been applied to crack analysis based on inspection images of concrete structures. The results of crack segmentation offering crack information, including length, width, and area is helpful to assist inspectors in surface inspection of concrete structures. This study proposed an algorithm of image segmentation enhancement, named morphological segmentation based on edge detection-II (MSED-II), to concrete crack segmentation. Several concrete pavement and building surfaces were imaged as the study materials. In addition, morphological operations followed by cross-curvature evaluation (CCE), an image segmentation technique of linear patterns, were also tested to evaluate their performance in concrete crack segmentation. The result indicates that MSED-II compared to CCE can lead to better quality of concrete crack segmentation. The least area, length, and width measurement errors of the concrete cracks are 5.68%, 0.23%, and 0.00%, respectively, that proves MSED-II effective for automatic measurement of concrete cracks.

• 한국지진공학회논문집
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• 제23권1호
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• pp.31-42
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• 2019

In this study, the results of an analytical investigation on the seismic behavior of two residential 4-story bearing wall buildings with pilotis, each of which has symmetric or unsymmetric wall arrangement at their piloti level, are presented. The dynamic characteristics and lateral resistance of the piloti buildings were investigated through linear elastic and nonlinear static analyses. According to the results, the analytical natural period of vibration of the piloti buildings were significantly shorter than the fundamental period calculated in accordance with KBC 2016. In the initial elastic behavior, the walls resisting in-plane shear contributed to the lateral stiffness and strength, while the contribution of columns resisting flexural moments in double curvature was limited. However, after the shear cracking and yielding of the walls occurred, the columns significantly contributed to the residual strength and ductility. Based on those investigations, design recommendations of low-rise bearing wall buildings with piloti configuration are given.

• Earthquakes and Structures
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• 제16권1호
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• pp.41-54
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• 2019

Reinforced Concrete (RC) shear walls are widely used in Nuclear power plants as effective lateral force resisting elements of the structure and these may experience nonlinear behavior for higher earthquake demand. Short shear walls of aspect ratio less than 1.5 generally experience combined shear flexure interaction. This paper presents the results of the displacement-controlled experiments performed on six RC short shear walls with varying aspect ratios (1, 1.25 and 1.5) for monotonic and reversed quasi-static cyclic loading. Simulation of the shear walls is then carried out by Finite element modeling and also by macro modeling considering the coupled shear and flexure behaviour. The shear response is estimated by softened truss theory using the concrete model given by Vecchio and Collins (1994) with a modification in softening part of the model and flexure response is estimated using moment curvature relationship. The accuracy of modeling is validated by comparing the simulated response with experimental one. Moreover, based on the experimental work a multi-linear hysteretic model is proposed for short shear walls. Finally ultimate load, drift, ductility, stiffness reduction and failure pattern of the shear walls are studied in details and hysteretic energy dissipation along with damage index are evaluated.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.57-74
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• 2021

The thermal eigenvalue responses of the graded sandwich shell structure are evaluated numerically under the variable thermal loadings considering the temperature-dependent properties. The polynomial type rule-based sandwich panel model is derived using higher-order type kinematics considering the shear deformation in the framework of the equivalent single-layer theory. The frequency values are computed through an own home-made computer code (MATLAB environment) prepared using the finite element type higher-order formulation. The sandwich face-sheets and the metal core are discretized via isoparametric quadrilateral Lagrangian element. The model convergence is checked by solving the similar type published numerical examples in the open domain and extended for the comparison of natural frequencies to have the final confirmation of the model accuracy. Also, the influence of each variable structural parameter, i.e. the curvature ratios, core-face thickness ratios, end-support conditions, the power-law indices and sandwich types (symmetrical and unsymmetrical) on the thermal frequencies of FG sandwich curved shell panel model. The solutions are helping to bring out the necessary influence of one or more parameters on the frequencies. The effects of individual and the combined parameters as well as the temperature profiles (uniform, linear and nonlinear) are examined through several numerical examples, which affect the structural strength/stiffness values. The present study may help in designing the future graded structures which are under the influence of the variable temperature loading.

• 한국동물위생학회지
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• 제46권1호
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• pp.81-85
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• 2023

This case report is about hemolymph nodes found in a dairy cow whose function is still not fully elucidated. A 4-month Holstein cow presented severe respiratory symptoms and hematochezia for a while with respiratory acidosis and metabolic alkalosis. Coccidiosis was diagnosed and treated immediately, but the cow died from respiratory acidosis and metabolic alkalosis. At necropsy, no abnormal appearance in thoracic and peritoneal organs was observed, but hemolymph nodes were observed being multifocally stuck on omasum serosa and the subcutaneous fascia of abdominal region, and the larger dark red lymph nodes were found along the omasum great curvature. Microscopically, lymphoid depletion and lymphadenitis in the lymph nodes were examined to point systemic infection, and in the hemolymph node, multifocally demarcated pale lesions with macrophage infiltration and fibrin deposition nearby subcapsular sinus. In subcapsular sinus of the hemolymph node, rod to linear gram-negative bacteria were found. Through this study, we might conclude that the hemolymph node is involved in pathogen phagocytosis.

• Advances in aircraft and spacecraft science
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• 제11권1호
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• pp.55-81
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• 2024

This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.511-514
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• 1997

The objective of this study is to propose a finite element based design of the dental implant replacing unction and shape of natural teeth. For this, geometric actors were varied to investigate stress distribution of the alveolar bone around dental implant. In this study, the results were obtained based on the theory of linear elastic, with geometrically axisymmetric assumption. Geometric actors determining implant shape are ranged as 0.2mm-0.6mm, 0.04mm-0.1mm, 0.46mm-0.84mm or height of thread, radius of curvature of thread, and pitch, respectively. The stresses in the alveolar bone caused by biting force playa major role in determining implant stability. Especially, the stress concentration in the cortical bone causes bone resorption and finally makes the implant unstable. Therefore, the stress distributions were investigated on the side of the alveolar bone focusing on the area of cortical bone. The maximum von Mises stress was found to increase up to 6% as the height of thread increases, while its value was to decrease to 19% when the radius of curvature increase within the assigned ranges. For the variation of pitch, the larger size of pitch results in greater maximum von Mises stress when the length of the implant under consideration is fixed. The existence of the neck below the shoulder did not affect the stress distribution in the region of alveolar bone. However, the stresses on the side of the implant near the neck were found to be different by 20% approximately. Therefore, the neck can provide the stability of the implant against continuing biting movement. As a conclusion, the finite element based study shows a potential in designing the dental implant systematically.

• 대한토목학회논문집
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• 제43권6호
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• pp.793-799
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• 2023

본 연구는 도시철도역의 입지특성, 역사의 구조, 형태, 이용객 수 등을 반영한 도시철도역사의 유형을 분류하고 역사 유형별 이용자들의 환승이동 동선의 불편정도, 환승정보 수 및 연계성, 환승 이동편의시설의 설치 수, 이용자 간의 상충성, 환승안내정보 표지등에 대해 분석하였다. 자료 분석결과 도시철도이용자들이 환승할 때 가장 불편을 주는 요소들은 환승동선의 길이와 굴곡도, 환승 통로의 보행밀도와 상충자 수, 이동편의시설 설치 유무, 환승안내 문자의 크기나 높이 등으로 나타났다. 이들 환승 불편요소들을 객관화, 지수화하고 도시철도역의 환승 편의성을 측정할 수 있는 평가 지표로 제시하였다. 또한, 각 평가지표별 서비스 수준을 측정할 수 있는 평가척도를 개발하였다. 각 지표별 평가척도는 현장조사를 통해 도출된 자료들의 최대 및 최소값을 기준으로 직선 보간법을 적용하여 6단계를 제시하였다. 다만, 편의성 평가지표별 중요도와 가중치을 하나로 묶은 환승편의성 종합평가는 추후 연구을 통해 정립되어야 할 것으로 판단된다.

• 한국인터넷방송통신학회논문지
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• 제15권4호
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• pp.185-190
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• 2015

본 논문에서는 5세대 이동통신 시스템에 적용하기 위한 V-밴드 내 57-65GHz 대역에서의 앤티포달 핀라인(antipodal finline) 도파관 변환기의 특성을 분석하고, 변환기를 설계하였다. 특히, 핀라인 테이퍼 형태를 설계하기 위해 선형 테이퍼에 곡률변수를 통해 곡률을 추가시켜 스플라인(spline) 테이퍼를 구하는 방식을 제안하였다. 이 방식을 통해 최적화에 부적절한 영역을 최적화 영역에서 제외함으로써 보다 효율적으로 최적화를 할 수 있었다. 앤티포달 핀라인 변환기의 반사손실과 삽입손실은 핀라인 테이퍼 형태에 가장 크게 좌우되었다. 핀라인 변환기 구조에서 발생되는 공진은 변환기의 성능을 저해하는 가장 큰 적이었으며 반원 모양의 패치(patch)를 사용하여 완화시켰다. 설계한 앤티포달 핀라인 변환기는 사용하고자 하는 대역(57-65GHz)에서 반사손실은 -24.2dB이하이고 삽입손실은 -0.24dB 이하로서 매우 양호한 특성을 나타냈다.

• 대한전자공학회논문지SP
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• 제44권2호
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• pp.144-152
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• 2007

본 논문에서는 멀티 레이저 라인 조사 방법을 이용한 능동적 비젼(Active Vision)의 방법으로 비등속 이동물체의 표면을 효율적으로 모델링 하는 방법을 제안한다. 레이저 라인을 물체에 조사하고 레이저가 조사된 방향과 각도를 달리한 방향에서 이를 관찰하면 레이저 라인이 표면의 굴곡에 따라 휘어지는 현상을 관찰할 수 있다. 이를 삼각기법(triangulation method)을 이용하여 분석하면 물체의 표면 3차원 정보 획득이 가능하다. 기존에 대표적 구조화 조명기법인 단일 라인(single stripe) 기법과 단일 프레임(single frame) 기법의 장단점과 제안하는 멀티 라인 기법의 장점을 설명하고 정밀도를 높이기 위한 레이저 라인의 효율적 배치에 대하여 설명한다. 강인한 레이저 라인의 추출을 위하여, 레이저 라인 피크 검출기법과 색 분석을 통해 얻은 레이저 반응도를 함께 이용하는 방법을 소개하였고, 효과적인 레이저 라인의 라벨링 기법을 새로 제안하였다. 개별 3차원 복원 표면을 전체영상으로 표현하기 위하여 동기화 정보 획득에 영상 간 특징점 매칭을 활용한 영상 정합 기법을 접목하였다. 3차원 표면 모델링 기술을 최종적으로 컨테이너 표면 데미지 검사에 활용하여 제안 3D 모델링 기술의 우수성을 확인하였다.