• 한국정밀공학회지
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• 제12권11호
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• pp.98-109
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• 1995

An investigation was performed to study the inner damage of laminated composite plates subjected to out-of-plane load. During the investigation, inpact velocity and equivalent static load relationship was derived. Reddy's higher-order shear deformation theory(HSDT) and Hashin's failure criteria were used to determine inner stresses and damaged area. And impact testing was carried out on laminated composite plates by air gun type impact testing machine. The CFRP specimens were composed of [ .+-. 45 .deg. ]$_{4}$and [ .+-. 45 .deg. /0 .deg. /90 .deg. ]$_{2}$ stacking sequences with 0.75$^{t}$ * 26$^{w}$ * 100$^{l}$ (mm) dimension. After impact testing. As a result, a relationship holds between damaged area and impact energy, and a matrix cracking was caused by the interlaminar shear stress in the middle ply and was caused by the inplane transverse stress in the bottom ply.

• 한국운동역학회지
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• 제12권2호
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• pp.259-278
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• 2002

본 연구에서는 볼 구질의 변화에 따른 스윙 동작의 운동학적인 변인을 3차원적으로 비교 분석하여 스윙 동작의 운동역학적인 원리를 제시하며, 볼 구질이 다른 스윙 동작의 차이점을 밝히는 데 목적이 있으며, 프로골퍼로 경력 3년 이상의 남자 선수 7명을 대상으로 스트레이트 성공, 페이드 성공과 실패로 구분하여 골프 스윙의 운동학적 변인들을 과학적으로 제시하기 위해 비교 분석한 결과 다음과 같은 결론을 얻었다. 페이드 성공시에는 임팩트를 지나서도 계속 손목의 각도가 근소한 차이로 줄어드는 것으로 나타났고 실패시에는 각 프레임의 각도가 규칙적으로 변하지 않게 나타났다. 이는 스트레이트 성공과 페이드 성공에 대한 손목각도의 차이가 영향을 미치는 것으로 나타나 다른 요인과 손목각도와의 관계를 분석하는 것이 필요하다고 하겠다. 페이드 실패의 경우는 임팩트시의 몸통 비틀림각도가 성공때 보다 작아지면서 클럽헤드가 오픈되지 못한 것으로 나타났다. 골프스윙의 형태의 변화로 인하여 어깨관절의 회전력을 더 많이 사용하여 파워을 증진시키기 위한 동작이며, 골프 스윙에서 어깨회전 운동은 축을 중심으로 회전하기 때문에 어깨회전각도의 차이는 없는 것으로 나타났다. 스트레이트 성공시 보다 페이드 성공시에 고관절의 회전각도가 점진적으로 일정하게 각이 커졌다. 이는 고관절의 회전을 더 크게 하여 지연히팅을 보다 자연스럽게 한 것으로 나타났다. 페이드 볼 구사시 임팩트 존에서 클럽의 페이스가 닫히는 것과 팔의 자연스러운 롤링 동작을 억제시키는 것으로 나타났다. 본 연구에서는 구질 변화에 따른 골프 스윙 동작을 스트레이트 성공, 페이드 성공과 실패시로 구분하여 운동학적 변인들을 3차원 동작 분석을 통하여 경기력 향사에 도움이 되고자 하였으며 앞으로 많은 연구자들이 각 종목에 있어서 경기력 향상을 위한 역학적인 분석이 계속 진행되어져야 할 것이다.

• 논리연구
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• 제8권2호
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• pp.3-32
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• 2005

수론(Number theory)과 수학 전반에 걸쳐 무모순성을 확립하고자 한 힐버트의 합리주의적 열망은 무모순성을 주장하는 진술 자체가 그 체계 내에서 결정 불가능한 진술이라는 괴델의 두 번째 정리에 의해 좌절된다. 수학의 어떤 문제에서도 수학자가 "Ignorabimus!" (우리는 모른다!) 해서는 안된다는 힐버트의 낙관 또한 수학에서 증명도 반증도 안되는 결정불가능한 진술의 존재로 인하여 무너진다. 힐버트 프로그램은 일체의 모호함을 배제하고 기호와 기호열에 대한 기계적 연산에 기초하기 때문에 그 충격도 그만큼 클 수밖에 없다. 이 프로그램의 좌절은 그래서 무엇보다도 형식화의 한계를 분명히 보여준다. 이제 수학에서는 통사론적인 증명가능성의 개념이 의미론적인 참의 개념보다 우위를 갖게 되었다. 그리고 그가 제안한 알고리듬(기계적 절차)의 개념은 프로그래밍 언어의 출현에 직접 기여하였다. 그래서 우리는 그의 기획이 비록 좌절했지만 위대한 실패라고 믿고 싶다.

• Steel and Composite Structures
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• 제34권1호
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• pp.17-34
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• 2020

This paper investigates the flexural behavior of concrete beams reinforced longitudinally with either steel bars, molded glass-fiber reinforced polymer (GFRP) grating mesh or pultruded glass-fiber reinforced polymer (GFRP) grating mesh, under four-point bending. The variables included in this study were the type of concrete (normal weight concrete, perlite concrete and vermiculite concrete), type of the longitudinal reinforcement (steel bars, molded and pultruded GFRP grating mesh) and the longitudinal reinforcement ratio (between 0.007 and 0.035). The influences of these variables on the load-midspan deflection curves, bending stiffness, energy absorption and failure modes were investigated. A total of fifteen beams with a cross-sectional dimension of 160 mm × 210 mm and an overall length of 2400 mm were cast and divided into three groups. The first group was constructed with normal weight concrete and served as a reference concrete. The second and third groups were constructed with perlite concrete and vermiculite concrete, respectively. An innovative type of stirrup was used as shear reinforcement for all beams. The results showed that the ultimate load of the beams reinforced with pultruded GFRP grating mesh ranged between 19% and 38% higher than the ultimate load of the beams reinforced with steel bars. The bending stiffness of all beams was influenced by the longitudinal reinforcement ratio rather than the type of concrete. Failure occurred within the pure bending region which means that the innovative stirrups showed a significant resistance to shear failure. Good agreement between the experimental and the analytical ultimate load was obtained.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.939-952
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• 2016

A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of $15{\times}19{\times}6cm$ and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

• Journal of Biomedical and Translational Research
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• 제19권4호
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• pp.79-85
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• 2018

Echocardiography is one of the most useful diagnostic techniques for differentiating heart disease as well as mitral valve lesion. Forty client-owned small breed dogs (weight, 2.3-13.2 kg) aged between 8-17 years with myxomatous mitral valve degeneration (MMVD) were included in the present study. The diagnosis of MMVD in dogs was made based on the clinical signs, chest radiography data, and echocardiographic findings. Echocardiographic examinations were conducted in accordance with recommended standards for dogs. M-mode, Doppler, and 2D echocardiography were performed in left and right lateral recumbency. 2D echocardiography was used to measure LA and Ao diameter from 2D short axis at the level of the aortic valve. In the comparison of conventional echocardiography indices in dogs with different stages of heart failure with MMVD, significant differences were observed in E/A ratio (p=0.005), EDV (p<0.001), EDVI (p<0.001), E-peak velocity (p= 0.001), ESV (p=0.028), ESVI (p=0.004), LA (p<0.001), LA/Ao Ratio (p<0.001), LVIDd (p<0.001), LVIDd/Ao Ratio (p<0.001), LVIDs (p=0.036), LVIDs/Ao Ratio (p=0.002), and MR Velocity (p=0.026). In addition, distinct correlations were found in EDV (r=0.712), LA/Ao ration (r=0.830), LVIDd (r=0.724), and LVIDd/Ao ratio (r=0.759). This study found that known conventional echocardiographic indices, including EDV, LA/Ao ratio, LVIDd dimension, and LVIDd/Ao ratio correlated with the severity of MMVD in point of significant differences and distinct correlations.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.11-20
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• 2019

The biaxial failure mechanism of transversally bedding concrete layers was numerically simulated using a sophisticated two-dimensional discrete element method (DEM) implemented in the particle flow code (PFC2D). This numerical modelling code was first calibrated by uniaxial compression and Brazilian testing results to ensure the conformity of the simulated numerical model's response. Secondly, 21 rectangular models with dimension of $54mm{\times}108mm$ were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$ while the angle of second layer, with high mechanical properties, related to loading direction was $90^{\circ}$, $105^{\circ}$, $120^{\circ}$, $135^{\circ}$, $150^{\circ}$, $160^{\circ}$ and $180^{\circ}$. Is to be note that the angle between bedding layer was $90^{\circ}$ in all bedding configurations. Also, three different pairs of the thickness were chosen in models, i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that in all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Numbers of shear cracks are constant by increasing the bedding thickness. It's to be noted that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

• Smart Structures and Systems
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• 제23권1호
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• pp.81-90
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• 2019

The shear behavior of soil-concrete interface is mainly affected by the surface roughness of the two contact surfaces. The present research emphasizes on investigating the effect of roughness of soil-concrete interface on the interface shear behavior in two-layered laboratory testing samples. In these specially prepared samples, clay silt layer with density of $2027kg/m^3$ was selected to be in contact a concrete layer for simplifying the laboratory testing. The particle size testing and direct shear tests are performed to determine the appropriate particles sizes and their shear strength properties such as cohesion and friction angle. Then, the surface undulations in form of teeth are provided on the surfaces of both concrete and soil layers in different testing carried out on these mixed specimens. The soil-concrete samples are prepared in form of cubes of 10*10*30 cm. in dimension. The undulations (inter-surface roughness) are provided in form of one tooth or two teeth having angles $15^{\circ}$ and $30^{\circ}$, respectively. Several direct shear tests were carried out under four different normal loads of 80, 150, 300 and 500 KPa with a constant displacement rate of 0.02 mm/min. These testing results show that the shear failure mechanism is affected by the tooth number, the roughness angle and the applied normal stress on the sample. The teeth are sheared from the base under low normal load while the oblique cracks may lead to a failure under a higher normal load. As the number of teeth increase the shear strength of the sample also increases. When the tooth roughness angle increases a wider portion of the tooth base will be failed which means the shear strength of the sample is increased.

• 한국융합학회논문지
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• 제13권3호
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• pp.23-31
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• 2022

본 연구는 H해운사에서 제공받은 Starcool사의 실제 냉동 컨테이너 운영데이터를 분석하였다. H사의 현장 전문가와 인터뷰를 통해 4가지 고장 알람 중 Critical 및 Fatal Alarm만 고장으로 정의하였고, 냉동 컨테이너 특성상 모든 변수를 사용하는 것은 비용측면에서 비효율을 초래하는 것을 확인하였다. 이에 본 연구는 특성 중요도 및 PCA 기법을 통한 냉동 컨테이너 고장 탐지 방법을 제시한다. 모델의 성능 향상을 위해 XGBoost, LGBoost 등과 같은 트리계열 모델을 통해 변수 중요도(Feature Importance)를 기반으로 변수 선택(Feature selcetion)을 하고 선택되지 않은 변수는 PCA를 사용하여 전체 변수의 차원을 축소시켜 각 모델별로 지도학습을 수행한다. 부스팅 기반의 XGBoost, LGBoost 기법은 본 연구에서 제안하는 모델의 결과가 62개의 모든 변수를 사용한 지도 학습의 결과보다 재현율(Recall)이 각각 0.36, 0.39씩 향상되는 되는 결과를 보였다.

• Composites Research
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• 제20권5호
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• pp.26-33
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• 2007

본 논문에서는 풀아웃 하중과 전단하중을 받는 복합재 샌드위치 인써트 조인트의 강도 특성을 실험으로 연구하였다. 샌드위치의 면재는 탄소 평직, 심재는 노멕스 하니콤, 접착제는 FM73을 사용하여 동시성형으로 제작하였다. 코어의 높이와 밀도, 면재의 두께, 하중의 형태를 달리하여 10종류, 총 75개의 인써트 조인트에 대한 실험을 수행하였다. 실험 결과, 풀아웃 하중에서는 코어의 높이와 밀도가 모두 파손하중에 영향을 미치지만 밀도의 영향이 상대적으로 더 크게 나타났다. 전단하중의 경우 면재의 두께가 파손하중에 결정적인 영향을 미치는 반면, 코어의 높이는 큰 영향을 미치지 않는 것으로 나타났다. 동일한 치수의 조인트에서도, 포팅된 쎌의 수에 따라 파손하중은 달라지며, 특히 풀아웃 하중에서 그러한 특성이 현저하게 나타났다.