• 대한토목학회논문집
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• 제2권3호
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• pp.1-13
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• 1982

원구멍과 타원구멍을 갖는 두 개의 강판(鋼板)에 완전교번하중(完全交番荷重)(completely reversed load, completely alternating load ;같은 크기의 인장(引張) 압축(壓縮)의 반복)을 가할 때 유한요소법(有限要素法)을 써서 강복요소(降伏要素)가 발생하는 단계마다 각 절점(節點)의 변위(變位), 각 요소(要素)의 응력(應力) 및 변형률(變形率), 하중(荷重)의 크기 등을 계산하여 파괴력학적(破壞力學的)인 검토를 행하였다. 이로부터, 강판(鋼板)의 파괴기구(破壞機構)를 밝히는 데에 핵심이 된다고 생각되는 응력확대계수(應力擴大係數)를 계산할 수 있는 토대가 마련되었으며, 흠선단(先端)의 응력집중(應力集中)현상과 소성역(塑性域)의 변화과정이 밝혀졌다. 또, 재하(載荷) 중에 강복(降伏)을 경험한 부분에서는 강하(降荷)때에 영구변형(永久變形)(잔류변형(殘留變形))이 남게 되고 이것이 나머지의 제하(除荷)를 구속(拘束)하여 반대방향의 재하(載荷)의 효과를 일으킴으로서 흠선단(先端)에 가까운 부분에는 인장(引張) 후의 제하(除荷) 때에 심지어 압축재강복(壓縮再降伏)까지, 압축(壓縮) 후의 제하(除荷) 때에는 심지어 인장재강복(引張再降伏)까지 일으키며 이들이 인장(引張) 및 압축(壓縮)의 재하(載荷) 중의 강복(降伏)과 교번(交番)으로 반복됨으로써 흠선단(先端)에 파로(波勞)현상을 초래하게 된다는 사실을 예견할 수 있었다. 아울러 흠이 원구멍일 때와 타원구멍일 때의 계산결과를 비교하여 홈이 예리한 균열에 가까워질수록 빨리 파괴에 달하게 된다는 사실을 확인할 수 있었다.

• 대한토목학회논문집
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• 제32권1A호
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• pp.39-48
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• 2012

본 논문에서는 V형 노치 및 반원형 노치 균열을 갖는 패치보강 적층판의 응력확대계수 산정을 위하여 수치해석적 방법을 사용한다. p-수렴 비등매개변수 모델이 고려되고, 이와 같은 비등매개변수 모델의 결과를 활용한 3차원 가상균열닫힘법에 대한 식이 표현된다. 1차원 로바토 함수로부터 확장된 3차원 계층적 형상함수를 가지고서, 임의의 요소에서의 변위장의 변위-변형률 관계와 3차원 구성방정식이 표현된다. 원형경계의 기하형상을 나태내기 위해 초유한사상기법을 사용한다. 응력집중계수, 응력분포, 자유도, 그리고 무차원 응력확대계수 등의 항목에 대해서, 제안된 모델의 정확도와 단순성이 기존의 결과들과의 비교를 통해 설명된다. 균열 적층판의 폭, 높이, 노치근입부의 반경, V형 노치의 경사각, 균열길이 등의 변화에 따른 응력확대계수가 산정된다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.165-173
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• 1997

The present study investigates heat/mass transfer for flow through perforated plates for application to combustor wall and turbine blade film cooling. The experiments are conducted for hole length to diameter ratios of 0.68 to 1.5, for hole pitch-to-diameter ratios of 1.5 and 3.0, for gap distance between two parallel perforated plates of 1 to 3 hole diameters, and for Reynolds numbers of 60 to 13, 700. Local heat/mass transfer coefficients near and inside the cooling holes are obtained using a naphthalene sublimation technique. Detailed knowledge of the local transfer coefficients is essential to analyze thermal stress in turbine components. The results indicate that the heat/mass transfer coefficients inside the hole surface vary significantly due to flow separation and reattachment. The transfer coefficient near the reattachment point is about four and half times that for a fully developed circular tube flow. The heat/mass transfer coefficient on the leeward surface has the same order as that on the windward surface because of a strong recirculation flow between neighboring jets from the array of holes. For flow through two perforated plate layers, the transfer coefficients on the target surface (windward surface of the second wall) affected by the gap spacing are approximately three to four times higher than that with a single layer.

• 설비공학논문집
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• 제16권9호
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• pp.845-854
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• 2004

The evaporation heat transfer coefficient for R-l34a, R-407C (a mixture of 23wt% R-32, 25 wt% R-125, and 52 wt% R-l34a) and R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the exchanger by four plates of commercial geometry with a corrugated sinusoid shape of a chevron angle of 45 degree. The effects of the mean vapor quality, mass flux, heat flux, and saturation temperature of different refrigerants on the evaporation heat transfer were explored in detail. Similar to the case of a Plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient in the plates is much higher than that in circular pipes. The present data show that the evaporation heat transfer coefficients of all refrigerants increase with the vapor quality. At a higher mass flux h, is higher than for the entire range of the vapor quality. Raising the imposed wall heat flux was found to slightly improve h$_{r}$, while h$_{r}$ is found to be lower at a higher refrigerant saturation temperature. A comparison of the performance of the various refrigerants reveals that R-410A has the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. Based on the present data, empirical correlations of the evaporation heat transfer coefficient were proposed.sed.

• Journal of the Korean Wood Science and Technology
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• 제22권4호
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• pp.26-36
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• 1994

The comparative wood anatomy of 1 species belonging to genus Myrica of Myricaceae, 9 species to genus Populus and 8 species to genus Salix of Salcaceae, occurring in Korea, was described and coded according to IAWA list(Wheeler, 1989). Myrica rubra. of Myricaceae is a typical diffuse-porous wood with numerous vessels per $mm^2$ and its pores are mainly angular in outline. Vessels scalariform perforation plates with a few bars, very small inter vessel pits; axial parenchyma abundant, diffuse or diffuse-in-aggregates which is distinct and easily observed on cross section; rays 1-3 seriate, Kribs' heterogeneous I or II types, frequently contains rhomboidal crystals; Dark pigmented substances included in some rays and axial parenchyma. Salicaceae, a typical diffuse porous wood, has mainly radial pore multiple, large intervessel pits, distinct alternate pits, simple perforation plates, ray-vessel pits with circular large pits, uniseriate rays, marginal parenchyma composed of 1-2 layers. In some species, ray parenchyma contain crystals. Populus and Salix wood can be distinguished from one another by the following characters. Pores of Populus woods almost angular in outline. Uniseriate homogeneous rays slightly higher than Salix and long linear on tangential section. Whereas Salix woods appear the pores almost oval, uniseriate heterogeneous rays, which are smular narrow fusiform on tangential section and lower in height than Populus.

• 한국재료학회지
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• 제3권2호
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• pp.197-204
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• 1993

Plastic기 복합재료의 파괴거동에 미치는 원공크기오 판폭의 영향을 검토하기 위하여 단축인장시험을 행하였다. 점응력파손조건에서의 특성길이 $d_o$는 원공크기 및 판폭에 의존하며, 이를 기초로 파손강도를 예측하기 위한 수정 점응력 파손조건식을 제안하였다. 이 파손조건의 예측값은 실험값과 잘 일치하였다. 파손 강도는 원공선단의 손상비의 증가에 따라 증가하며, 이는 손상영역의 형성으로 인한 응력완화현상으로 설명되어 진다. 또한 불안정 파괴시의 최대균열길이 $a_c$는 특성길이 $d_o$의 약 2배의 값을 나타낸다. 파괴인성에 대응하는 한계에너지해방율 $G_c$의 변화는 원공선단의 손상영역의 증가에 의한 응력완화가 주요한 원인이라고 할 수 있다.

• Steel and Composite Structures
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• 제23권3호
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• pp.363-383
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• 2017

In cold-formed stainless steel lipped channel-sections, use of web openings for service purposes are becoming increasingly popular. Web openings, however, result in the sections becoming more susceptible to web crippling. This paper presents a finite element investigation into the web crippling strength of cold-formed stainless steel lipped channel-sections with circular web openings under the interior-two-flange (ITF) loading condition. The cases of web openings located centred and offset to the bearing plates are considered in this study. In order to take into account the influence of the circular web openings, a parametric study involving 2,220 finite element analyses was performed, covering duplex EN1.4462, austenitic EN1.4404 and ferritic EN1.4003 stainless steel grades. From the results of the parametric study, strength reduction factor equations are proposed. The strengths obtained from reduction factor equations are first compared to the strengths calculated from the equations recently proposed for cold-formed carbon steel lipped channel-sections. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are unconservative for the stainless steel grades by up to 17%. New coefficients for web crippling strength reduction factor equations are then proposed that can be applied to all three stainless steel grades.

• 한국강구조학회 논문집
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• 제23권1호
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• pp.83-97
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• 2011

본 논문에서는 콘크리트 채움 U형 강재보와 철근콘크리트 기둥으로 구성된 접합부의 내진 상세를 개발하였다. 접합부 내진성능을 평가하기 위하여 세 개의 보-기둥 접합부 실험체를 반복주기하중에 대하여 실험하였다. 보춤과 기둥 단면 형상을 실험 변수로 하였다. 합성보의 춤은 슬래브 두께를 포함하여 610mm, 710mm이며, 철근콘크리트 기둥은 사각단면과 원형단면이 사용되었다. 접합부를 보강시키기 위하여 사각단면 기둥과 원형단면 기둥에 각각 대각 철근과 외다이어프램 강판을 사용한 특수 상세가 사용되었다. 실험 결과 실험체는 강도와 변형능력, 에너지 소산에 있어서 우수한 성능을 보여주었다. 변형능력은 특수모멘트골조 기준인 4% 이상의 층간변위각을 발휘하였다.

• 한국농공학회지
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• 제34권1호
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• pp.78-86
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• 1992

This paper aims at investigating the effect of steel ratio and the magnitude of edge-ratio on the mechanical characteristics of reinforced concrete ring sector plate. The influence of steel bars was taken into account by coupling stiffness matrix of the steel bar element with that of the concrete plate element without dealing with separate element of steel bar and by establishing the composite stiffness matrix, which leads to the desirable result which does not increase th number of element could be obtained. Through case studies with 6 cases various steel ratios in ring sector plate supported at four edges and 4 cases with different open angles, the influence of the steel ratio was examined. A numerical analysis to find out the effect of the steel ratio d ue to above mentioned cases was carried out by 4 boundary conditions ; all edges clamped (B.C-1), all edges simply supported (B.C-2), curvilinear two edges clamped and other edges free (B.C-3) and curvilinear two edges simply supported and other edges free(B.C-4). The main results obtained are summarized as follows : 1. The effect of steel ratio on the magnitude of lateral deflection and x-directional bending moment at the center of sector plate and the midpoint of outer and inner curvilinear edges is almost the same up to $30^{\circ}$ of open angle. Beyond $30^{\circ}$ of the angle, the larger the angle, the greater the effect of ratio. 2. In design works using balanced steel ratio, the effect of steel bar can be ignored. But for larger open angles, especially greater than $90^{\circ}$, it proves desirable to consider the effect of steel bar. 3. The effect of the arc length of center circle/straight edge on lateral deflection and bending moment is remarkable in B.C-2. For larger open angle, the effect is also noted except for B.C-3 which turn out hardly affected. 4. The effect of the radius of curvature/straight side length on lateral deflection and x-directional bending moment is noted in B.C-2. As open angle increases, B.C-1 and B.C-3 almost agree and B.C-2 approaches B.C-4.

• 천문학논총
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• 제36권3호
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• pp.65-78
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• 2021

Jagyeokru, an automatic striking water clock described in the Sejong Sillok (Veritable Records of King Sejong) is essentially composed of a water quantity control device and a time-signal device, with the former controlling the amount or the flow rate of water and the latter automatically informing the time based on the former. What connects these two parts is a signal generating device or a power transmission device called the 'Jujeon' system, which includes a copper rod on the float and ball-racked scheduled plates. The copper products excavated under Gongpyeong-dong in Seoul include a lot of broken plate pieces and cylinder-like devices. If some plate pieces are put together, a large square plate with circular holes located in a zigzag can be completed, and at the upper right of it is carved 'the first scheduled plate (一箭).' Cylinder-like devices generally 3.8 cm in diameter are able to release a ball, and have a ginkgo leaf-like screen fixed on the inner axis and a bird-shaped hook of which the leg fixes another axis and the beak attaches to the leaf side. The lateral view of this cylinder-like device appears like a trapezoid and mounts an iron ball. The function of releasing a ball agrees with the description of Borugak Pavilion, where Jagyeokru was installed, written by Kim Don (1385 ~ 1440). The other accounts of Borugak Pavilion's and Heumgyeonggak Pavilion's water clocks describe these copper plates and ball releasing devices as the 'Jujeon' system. According to the description of Borugak Pavilion, a square wooden column has copper plates on the left and right sides the same height as the column, and the left copper plate has 12 drilled holes to keep the time of a 12 double-hours. Meanwhile, the right plate has 25 holes which represent seasonal night 5-hours (Kyeong) and their 5-subhours (Jeom), not 12 hours. There are 11 scheduled plates for seasonal night 5-hours made with copper, which are made to be attached or detached as the season. In accordance with Nujutongui (manual for the operation of the yardstick for the clepsydra), the first scheduled plate for the night is used from the winter solstice (冬至) to 2 days after Daehan (大寒), and from 4 days before Soseol (小雪) to a day before the winter solstice. Besides the first scheduled plate, we confirm discovering a third scheduled plate and a sixth scheduled plate among the excavated copper materials based on the spacing between holes. On the other hand, the width of the scheduled plate is different for these artifacts, measured as 144 mm compared to the description of the Borugak Pavilion, which is recorded as 51 mm. From this perspective, they may be the scheduled plates for the Heumgyeonggak Ongru made in 1438 (or 1554) or for the new Fortress Pavilion installed in Changdeokgung palace completed in 1536 (the 31^st year of the reign of King Jungjong) in the early Joseon dynasty. This study presents the concept of the scheduled plates described in the literature, including their new operating mechanism. In addition, a detailed model of 11 scheduled plates is designed from the records and on the excavated relics. It is expected that this study will aid in efforts to restore and reconstruct the automatic water clocks of the early Joseon dynasty.