• 대한치과의사협회지
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• 제47권7호
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• pp.444-454
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• 2009

The purpose of this study was to compare the shaping abilities of LightSpeed, ProTaper-Universal, and hybrid technique using S-series of ProTaper-Universal and LigthSpeed. The 72 simulated root canals of J-shape were used and classified as flowing 3 groups according to the instrumentation methods; Group P of 24 canal blocks were prepared with ProTaper-Universal, Group L was prepared with LightSpeed, and Group H was prepared with hybrid technique (initial shaping with ProTaper-Universal SI and S2 and apical shaping with LightSpeed from #25 to #50). A second-year resident of Endodontic department prepared the resin block canals to apical size #50 (F5 in Group P). The time lapses for instrumentation and the reduction of root canal curvature after shaping were measured. The pre- and post-instrumented root canals were scanned and superimposed to evaluate and calculate the increased canal width and apical centering ratio. The results were as followings: Group Land H showed significant less instrumentation time than Group P (p < 0.05). The ProTaper system showed greater reduction of root canal curvature and working length diminishment than other methods (p < 0.05). LightSpeed system showed best canal curvature preserving characteristics. The Group P had greater instrumented widths at all levels examined (p < 0.05). Group L and Group H showed lower centering ratio (ability to preserve the canal center; the lower ratio means the better canal center preservation) than Group P (p < 0.05). Group H had the lowest centering ratio at the 1 mm level.

• 한국지진공학회논문집
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• 제7권4호
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• pp.51-61
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• 2003

본 연구는 철근콘크리트 교각에 대한 새로운 내진설계법을 개발하기 위한 연구의 일환으로서, 축력과 함께 반복 횡하증을 받는 철근콘크리트 교각의 곡률연성도와 변위연성도의 상관관계를 분석하고 연성도 상관관계식을 제시함을 목적으로 한다. 이를 위하여, 반복하중을 받는 철근콘크리트 기둥의 횡하중-변위 포락곡선 실험결과를 비교적 정확하게 예측하며, 특히 변형능력 및 연성도에 대하여는 실험결과에 비하여 안전측의 결과를 제공하는 비선형해석 프로그램(NARCC)를 이용하였다. 해석의 대상 교각으로는, 단면지름, 형상비, 콘크리트 강도, 축방향철근 항복강도, 심부구속철근 항복강도, 축방향철근비, 축력비, 심부구속철근비 등을 주요변수로 하여, 총 7,200개의 철근콘크리트 나선철근 기둥 모델을 채택하였으며, 세 가지 항복변위의 기준을 적용하여 총 21,600개의 해석결과자료를 대상으로 상관관계를 분석하여 형상비를 주요변수로 한 곡률연성도와 변위연성도의 상관관계식을 제안하였다.

• 대한기계학회논문집
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• 제11권3호
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• pp.444-453
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• 1987

본 연구에서는 난류구조에 대한 유선곡률의 영향을 명확히 반영하는 적절한 곡률수정 2-방정식모델을 개발하고자 한다. 이 연구에서 제안된 모델의 타당성은 다 음의 2차원 재순환유동에 대한 실험결과와 계산결과의 비교를 통해서 입증될 것이다. (1) Moss와 Bake에 의하여 맥동열선 풍속계로 측정된 두꺼운 수직벽주위의 유동` (2) 레이저 도플러 속도계로 Fraser와 Siddig에 의해 측정된 얇은 수직벽유동` (3)맥동열 선 풍속계로 Eaton이 실험한 후면벽유동` (4)맥동열선 풍속계로 Moss와 Baker가 측정 한 전면벽유동. 새로운 곡률수정 2-방정식모델은 2장에서 설명되고 있으며, 3장에서 는 경계조건과 수치계산 과정이 간단이 기술되어 있다. 그 뒤에 4장에는 계산결과와 실험치에대한 비교검토가 설명되어 있고 마지막으로 5장에서는 본 연구에 대한 결론을 맺고 있다.

• Computers and Concrete
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• 제6권6호
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• pp.451-472
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• 2009

Based on a numerical method to analyse the full-range behaviour of prestressed concrete beams with unbonded tendons, parametric studies are carried out to investigate the influence of 11 parameters on the curvature ductility of unbonded prestressed concrete (UPC) beams. It is found that, among various parameters studied, the depth to prestressing tendons, depth to non-prestressed tension steel, partial prestressing ratio, yield strength of non-prestressed tension steel and concrete compressive strength have substantial effects on the curvature ductility. Although the curvature ductility of UPC beams is affected by a large number of factors, rather simple equations can be formulated for reasonably accurate estimation of curvature ductility. Conversion factors are introduced to cope with the difference in partial safety factors, shapes of equivalent stress blocks and the equations to predict the ultimate tendon stress in BS8110, EC2 and ACI318. The same equations can also be used to provide conservative estimates of ductility of UPC beams with compression steel.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.17-20
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• 2005

Moment-curvature relation of RC pier is influenced greatly in occurrence form of crack and difference is happened according to consideration existence and nonexistence of tension stiffening effect. However, studies considering these is very insufficient misgovernment. Also, it is sometimes unavoidable lap splice of axial reinforcement in plastic hinge region of RC piers. However, specific design standard about lap splice of axial reinforcement is unprepared real condition and study about effect that lap splice of axial reinforcement get in occurrence form of crack is insufficient misgovernment. Therefore, in this paper, experiments are performed with hollow RC piers that do lap splice of axial reinforcement by main variable. And this study present analytical method about moment-curvature relation of hollow RC pier that consider tension stiffening effect and analyze effect that lap splice of axial reinforcement gets in occurrence form of crack. Analytic method of moment-curvature relation of RC pier that present in this study shows very similar motion with experiment result and crack interval of RC pier is suffering dominate impact in the augmented reinforcement amount by lap splice and average crack interval decreases as lap splice ratio increases.

• 대한기계학회논문집B
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• 제26권6호
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• pp.842-849
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• 2002

The present study showed that a quantitative analogy of the fully developed laminar flows inorthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio could be established. In order to clarify the similarity of the two flows, the dimensionless parameters $K_{LR}$ =Re/√Ro and Rossby number Ro= $w_{m}$/$\Omega$d in a rotating strait duct were used as a set corresponding to Dean number $K_{LC}$ =Re/√λand curvature ratio λ=R/d in a stationary curved duct. Under the condition that the value of Rossby number and curvature ratio was large enough, the flow field satisfied the ‘asymptotic invariance property’: there were strong quantitative similarities between the two flows such as friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of $K_{LR}$ and $K_{LC}$ .

• Structural Engineering and Mechanics
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• 제12권5호
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• pp.459-474
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• 2001

The complete moment-curvature curves of doubly reinforced concrete beams made of normal- or high-strength concrete have been evaluated using a newly developed analytical method that takes into account the stress-path dependence of the constitutive properties of the materials. From the moment-curvature curves and the strain distribution results obtained, the post-peak behavior and flexural ductility of doubly reinforced normal- and high-strength concrete beam sections are studied. It is found that the major factors affecting the flexural ductility of reinforced concrete beam sections are the tension steel ratio, compression steel ratio and concrete grade. Generally, the flexural ductility decreases as the amount of tension reinforcement increases, but increases as the amount of compression reinforcement increases. However, the effect of the concrete grade on flexural ductility is fairly complicated, as will be explained in the paper. Quantitative analysis of such effects has been carried out and a formula for direct evaluation of the flexural ductility of doubly reinforced concrete sections developed. The formula should be useful for the ductility design of doubly reinforced normal- and high-strength concrete beams.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.673-682
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• 1997

이 논문에서는 회전관성과 전단변형이 변화곡률 아치의 고유진동수에 미치는 영향을 분석하였다. 임의의 변화곡률을 갖는 등단면 아치의 자유진동을 지배하는 미분방정식을 유도하였으며, 유도된 미분방정식에 회전-회전, 회전-고정 및 고정-고정의 단부조건을 갖는 포물선, 원호 및 타원 아치를 적용하여 수치해석하였다. 해석결과로서 무차원 변수인 아치높이 지간길이비 및 세장비 변화에 따론 최저차 4개의 무차원 고유진동수를 산출하였다.

• 대한기계학회논문집B
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• 제22권11호
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• 대한기계학회논문집B
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• 제38권10호
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• pp.797-805
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• 2014

본 연구의 목적은 해수 흡입구를 고려한 초공동 수중운동체 캐비테이터의 항력과 양력특성 및 해수 흡입유로의 입구에서 압력손실에 대해 예측하는 것이다. 흡입구 직경과 유로에서의 속도, 흡입구의 곡률반경 및 캐비테이터의 받음각이 미치는 영향에 대해 유동해석을 수행하였다. 연구 결과 직경비가 커지면, 항력계수와 압력손실계수가 감소하며, 속도비가 증가할 때 항력계수와 양력계수는 감소하고 압력손실계수는 증가한다. 해수 흡입구에 곡률을 주면 항력계수와 양력계수에는 영향을 미치지 않지만, 압력손실계수가 크게 감소한다. 캐비테이터의 받음각은 항력계수와 압력손실계수에 미소한 영향만을 주나, 양력계수를 크게 변화시킨다. 초공동 수중운동체 설계 시 본 연구 결과를 반영할 수 있다.