Earticle

연구목적: 연성 플러터는 고풍속대에서 발생되는 공력 불안정 현상으로서, 플러터 발현을 한계풍속 이 하에서 억제하는 것이 장대교량의 계획 및 설계단계에서 가장 신중히 검토되어야 할 사항이다. 장대교 량의 플러터 발현을 억제하기 위해서는 보강거더 단면의 플러터 메커니즘을 분석하여야 한다. 연구방 법: 본 연구에서는 다양한 변장비를 갖는 구형 단면(Rectangular Sections)을 대상으로 복소고유치 해석 (Complex Eigenvalue Analysis) 및 공탄성 에너지 방법(Aeroelastic Engergy Method)을 적용하여 연성 플러터 발현 특성을 검토하였다. 연구결과: 변장비 5인 구형단면은 감쇠비례항에 의한 에너지 성분 (Damping-Driven Energy)이 플러터 발현을 유발하였고, 변장비 8~20의 구형단면은 강성비례항에 의한 에너지 성분(Stiffness-Driven Energy)이 플러터 발현을 유발함을 확인하였다. 결론: 공탄성 에너지 방 법을 적용하여 다양한 변장비를 갖는 구형단면의 플러터 발현 유형을 분석하였고, 이러한 기법을 다양 한 단면형상에 적용하여 플러터 발현유형 분석 및 플러터 안정화 방안을 수립할 수 있을 것이다.

Purpose: Since the coupled flutter instability may lead to the collapse of stiffened girder, its stabilization is the most important issue for the feasibility of long-span bridges. The clarification of coupled flutter mechanism is indispensible for the effective stabilization of the catastrophic oscillation. Method: In this study, the generation mechanism of coupled flutter instability for rectangular sections is examined based on the complex eigenvalue analysis and aeroelastic energy method. Result: It is concluded that the bluff rectangular section with the aspect ratio of 5 (B/D=5) is classified into damping-driven flutter type, and that relatively slender rectangular sections (B/D=8~20) is stiffness-driven flutter type. Conclusion: In this study, the generation mechanism of coupled flutter instability for rectangular sections are investigated based on complex eigenvalue analysis and aeroelastic energy, which could be applied to the further development of coupled flutter stabilizaton of various girder section shapes in long-span bridges.

In the country designated as national treasures and cultural treasures, was built in most of the timber. These traditional wooden structure are state on degradation and deformation caused by deterioration, and it's about time that maintenance and preservation should take a deep interest. However, the current maintenance and preservation are carried out by the previous experience of carpenter, these bring secondary deformation and degradation because did not identify the exact reason, and it is the reality of our maintenance and preservation of cultural assets. Therefore, future maintenance and preservation of traditional wooden buildings should be followed to the scientific and structural approach. So, this study choose unit member where many damages happen to structural members of wooden cultural property, and made 8 specimen of rectangular section of flexural member to understand the structural behavior and phase by reinforce damaged members with synthetic resin. The results of the experiment, the most neutral axes of specimens are located at the opposite of the reinforced part. If the neutral axis moves to the reinforced part, the maximum strength is expected to be improved. And the compression is judged to be effective.

The main material of wooden structures is wood, can be obtained easily in nature and higher strength per unit weight as well as eco-friendly and process of the manufacture has been superb. A weak point is Knots, while, cross grain, vermin by insects, fire and strength degradation due to fatigue and corrosion by deterioration. especially the deterioration of the wooden structure must be accompanied by appropriate conservation measures, because it is most the cultural assets. Conservation of wooden structure as possible, reuse the original repair itself, the consideration of the cultural value of attending to the basic principle is to maintain a archetype. Accordingly, the physical and chemical combined methods using a synthetic resins is emerging. A study on conservation methods using synthetic resins is only a short time. So former studies was the aspect of pure science to conserve, it is not that improvement of capacity using synthetic resins in wooden structures. Therefore, this study will confirm the possibility of usability in practice and an effect of reinforcement in compressive element possessed rectangular section. The results of the experiment, the compressive element with rectangular section rather than the direction of radiation in the direction of tangent reinforcement is more effective and less ratio of reinforcement is more effective. It is also effective on the total length of the element and adequate reinforcement is more efficient than new element.

본 연구에서는 보의 양 단부 모멘트 구속에 의한 최대하중과 현수작용을 알아보기 위해 휨 실험을 통하여 양 단부 지지조건에 따른 각형강관 보의 거동을 분석하였다. 모멘트 구속은 보의 양 단부에 3개의 앵글과 앵커를 이용(하부 플랜지에 1개, 양쪽 웨브에 2개)하여 실현하였다. 보 경간은 3,600 mm이며 콘크리트 벽체는 지지부가 수평방향으로 상대적으로 큰 강성을 발휘하여 현수거동이 발생하게 설계하였다. 실험 결과 현수작용에 의한 앵커의 인장력에 의해 최대하중은 약 55% 증가하며 이를 2차 최대하중이라 한다. 이때의 하중을 2차 최대하중이라 하며 2차 최대하중은 지점부 앵커가 인장력에 충분히 저항할 경우에만 발생한다.

In this study, a behavior of beam with rectangular hollow section (RHS) was investigated through three-point bending test, which was to evaluate the peak load and the catenary action of beam having the moment restraint at both ends. The moment restraint is provided by three angles and three anchor bolts (one in bottom flange and two in web sides) at beam end. The beam span was 3,600mm and the concrete wall for supporting a beam was designed with relatively rigid stiffness to the horizontal direction so as to generate the catenary action of beam. Test results showed that the tensile force of anchor due to catenary action increased the load-carrying capacity by approximately 55%, which is called as the second peak load. This second peak load happens when the anchor at a support fully resists a tensile force.

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as $0^{circ},\;30^{circ},\;45^{circ},\;60^{circ}\;and\;90^{circ}$. The plastic zone expands more at the upper side of the composite beam than at the lower side for $30^{circ},\;45^{circ}\;and\;60^{circ}$ orientation angles. Residual stress components of ${\sigma}_{x}\;and \;{\tau}_{xy}$ are also found in the section of the composite beam.

$Al_2O_3-SiO_2-ZrO_2$ short fiber reinforced aluminium matrix composites have been produced by squeeze casting. The specimens aere evaluated as a function of various mechanical and phisical properties such as hardness and compressive stress, thermal expansion coefficient, and wear resistance. The results were compared those of conventional cast iron(FC25). The characteristics of short fiber in the preform also have been investigated via micro analyzing technique. $Al_2O_3-SiO_2-ZrO_2$<TEX> system showed an excellent war resistence which is the most important characteristic. and is expected to replace cast iron to improve weight and engine performance. Crankshaft damper pulley hub has been produced using <TEX>$Al_2O_3-SiO_2-ZrO_2$<TEX> short fiber reinforced aluminium matrix composite. Bolt axial tension relaxation and thermal cyclic test \yere performed. The products developed descrived above provide a hub aeight reduction of approximately 60% and a crankshaft damper pulley aeight reduct ion of approximately 20%.

건조물문화재의 부식 및 노후화에 대한 보존수리는 원형유지를 기본원칙으로 하며, 수리로 인해 인위적인 훼손을 가하는 과오를 범해서도 안 된다. 따라서 합성수지를 이용한 보존처리방법이 부각되어지고 있다. 본 연구의 목적은 합성수지로 보강한 사각단면 목재의 휨 성능에 관한 연구로서 합성수지의 보강길이, 보강면적비율, 합성수지 재료강도, 보강위치를 변수로 하여 총 11개의 시험체를 제작하여 실험하였다. 이 연구의 결과는 목재의 휨 보강재로 합성수지의 보강효과가 있는 것으로 나타났으며, 사용 가능성을 확인 할 수 있었다.

The basis principle of conservation about deterioration and corrosion of cultural assets building is the archetype maintenance, and should not make a factitious damage mistake by repair. Accordingly, conservation processing method using synthetic resins is embossed. The purpose of this paper is about flexural capacity of rectangular section wood using synthetic resins, the 11 specimens are manufactured and made an experiment about reinforcement length, ratio, material strength, direction of synthetic resins as variable. The results of this paper has shown that flexural reinforcement of wood by synthetic resins are efficient and found the possibility of using.

The twisting and bending extrusion process is developed by the $DEFORM^TM$-3D. Because the rectangular section of the extruded product has the symmetry line of cross-section area, the twisting and the bending of extruded product has not occurred. The product with the rectangular section is applied to the twisting and bending extrusion process through the twisted die surface and eccentricity die section. It is shown that the twisting of extruded product is caused by the twisted die surfaces and the bending of extruded product is causd by the eccentricity between the die section. The results by the analysis show that the twisting angle and the curvature of extruded products increases by the die twisting angle, the eccentricity, but decreases by the die length, and friction condition

목적: 고령의 환자에게 발생한 A2형 이상의 전자간 골절에 대하여 무시멘트형의 직각 단면을 가진 표준형 대퇴 주대(이중 쐐기형)를 이용하여 인공 고관절 반치환술을 시행하고 그 결과를 알아보고자 하였다. 대상 및 방법: 2006년 2월부터 2010년 2월까지 본원에서 수술을 시행하고 2년 이상 추시가 가능하였던 37예의 환자를 대상으로 하였다. 평균 연령은 73.5세(65-88세) 였고 남자환자가 16예 여자 환자가 21예 였다. 수술 시간과 출혈양, 수술 후 보행능력의 회복정도와 방사선학적 결과 그리고 합병증에 대해서 알아 보았다. 결과: 평균 수술 시간은 75.3분(50-185분), 평균 출혈양은 755.5 cc(75-1,400 cc) 였다. 최종 추시 시점에서 27예의 환자(72.9%)에서 수술 전 바델 지수의 80 %를 회복 하였다(72.8±15.1). 합병증은 비구부 미란과 심부 감염이 1예, 대전자의 불유합이 3예 있었고, 인공 관절물의 해리 등의 이유로 재치환을 시행한 예는 없었다. 결론: 무시멘트형 직각 단면을 가진 표준형 대퇴 주대를 이용한 인공 고관절 반치환술은 조기 거동이 가능한 장점이 있어 고령의 환자에게 발생한 A2형 이상의 전자간 골절에 대하여 선택적으로 사용될 수 있는 수술 방법 중 하나로 생각 된다.

Purpose: To evaluate the treatment outcome for Type A2 or above intertrochanteric fractures in elderly patients using cementless bipolar hemiarthroplasties incorporating a standard (tapered, rectangular) stem. Materials and Methods: We retrospectively reviewed the records of 37 patients who had undergone bipolar hemiarthroplasty between February 2006 and February 2010 in our hospital, and who had received follow up evaluation for more than two years after the surgery. The mean patient age was 73.5 years (range 65-88 years),and 16 patients were male and 21 were female. We evaluated the the results of their treatment by analyzing the operation duration, volume of bleeding, measured results for the recovery of walking capability, and any complications and radiologic findings. Results: The mean operation duration was 75.3 minutes(50-185 minutes). The average total volume of bleeding was of 755.5 cc(75-1,400 cc). Upon the final follow-up visit, 27 patients(72.9%) had recovered more than 80% of their pre-injury Barthel index values(72.8±15.1). Complications included one case of deep infection, one case of acetabular erosion, and 3 cases of greater trochanter non-union. There were no cases of revisions due to prosthesis loosening or for other reasons. Conclusion: Cementless bipolar hemiarthroplasty using a tapered, rectangular stem is a viable alternative treatment for type A2 intertrochanteric fractures in elderly patients which supports rapid patient mobilization ability.

The differential equations governing free vibrations of the elastic arches with rectangular hollow section are derived in polar coordinates, in which the effect of rotatory inertia is included. Natural frequencies is computed numerically for circular arches with both clamped ends and both hinged ends. The lowest four natural frequency parameters are reported, with the rotatory inertia, as functions of three non-dimensional system parameters: the breadth ratio, the thickness ratio and the shape ratio.

본 연구에서는 엔진 나셀 화재를 모사하고 이전의 실험결과를 보충하기위해 이차원 둔각물체 주위의 반응유동장에 대하여 수치해석을 수행하였다. Direct numerical simulation (DNS) 기반의 fire dynamic simulator (FDS)를 이용하여 반응유동장의 특성을 조사하였고, 실험결과와의 비교를 통해 화학반응식을 결정하였다. 산화제는 공기를 사용하였고, 연료는 메탄을 사용하였다. 동축류와 대향류 분사 모두의 경우에 화염의 안정성이나 모양은 둔각물체 주위의 와 강도와 크기에 크게 영향을 받았다. 동축류 분사의 경우 계산에 통한 화염소화한계를 결정하였는데 연료유속이 커질수록 공기의 유속 또한 커지는 경향이 있었고, 그 속도들 또한 기존의 실험결과와 잘 일치함을 볼 수 있었다. 유동장 특성에 대한 화학반응의 효과를 고찰하기 위해 반응이 없는 경우를 계산하여 비교하였다. 모든 경우에 비반응 유동장에 비해 반응 유동장의 후류와는 크기도 감소하고 세기도 감소함을 볼 수 있었는데 이는 반응에 의한 후류의 온도증가가 유체의 밀도 및 모멘텀을 감소시켰기 때문으로 판단된다.

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to simulate an engine nacelle fire and to complement the previous experimental results of the bluff body stabilized flames. Fire Dynamic Simulator (FDS) based on the Direct Numerical Simulation (DNS) was employed to clarify the characteristics of reacting flow around bluff body. The overall reaction was considered and the constant for reaction was determined from flame extinction limits of experimental results. The air used atmosphere and the fuel used methane. For both fuel ejection configurations against an oxidizer stream, the flame stability and flame mode were affected mainly by vortex structure near bluff body. In the coflow configuration, air velocity at the flame extinction limit are increased with fuel velocity, which is comparable to the experiment results. Comparing with the isothermal flow field, the reacting flow produces a weak and small recirculation zone, which is result in the reductions of density and momentum due to temperature increase by reaction in the wake zone.

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

In this study, experimental procedures were suggested to investigate the sloshing behavior of a liquid storage tank subjected to inevitably external vibrating conditions. For this purpose. liquid storage tank with rectangular cross section was made of an acrylic resin for the visualization of liquid fluctuation. A specially designed vibrator was used to provide a specified vibrating condition to the liquid storage tank. Extrapolation technique was applied to determine sloshing natural frequency by using various sloshing frequencies at each vibrating displacement and liquid contents at a fixed vibrating frequency. Sloshing mode was also determined from continuous images or liquid fluctuation captured from a video camera. In addition, change in the height of the liquid free surface was measured by using a floating target and a laser displacement sensor. It is found that the suggested method can be applicable to identify the sloshing behavior of liquid storage tank with rectangular cross section.

By using unique experimental techniques and careful construction of the experimental apparatus, the characteristics of the local heat transfer were investigated using the condensing R134a two-phase flow, in horizontal single mini-channels. The circular channels ($D_h=0.493$, 0.691, and 1.067 mm) and rectangular channels ($D_h=0.494$, 0.658, and 0.972 mm) were tested and compared. Tests were performed for a mass flux of 100, 200, 400, and 600 $kg/m^2s$, a heat flux of 5 to 20 $kW/m^2$, and a saturation temperature of $40^{\circ}C$. In this study, effect of heat flux, mass flux, vapor qualities, hydraulic diameter, and channel geometry on flow condensation were investigated and the experimental local condensation heat transfer coefficients are shown. The experimental data of condensation Nusselt number are compared with existing correlations.

다양한 시설의 지하화가 진행되고 있는 현 상황에서 지중구조물 중 도시 기반시설 기능의 상당 부분을 담당하고 있는 지하공동구의 지진 응답에 대한 합리적 평가 필요성이 높아지고 있다. 본 연구에서는 기존에 제안된 국내외 지중구조물 내진평가방법 중 단순화 2차원 프레임 해석모델을 사용한 의사정적 방법의 주요 내용과 차이점을 살펴보고 국내에 시공된 1련 박스형 단면의 지하공동구에 적용하여 지진거동, 특히 횡방향 뒤틀림 변형에 대한 예측 적합성을 검토한다. 이에 덧붙여, 이러한 방법을 적용하여 지중구조물의 지진응답 평가 시 유의할 점을 논의한다.

Various underground facilities are being constructed to improve the urban environment. Therefore, it is more necessary than ever to reasonably evaluate the seismic response of underground utility tunnels, playing a significant part in urban infrastructure. In this study, the major features and differences of two types of existing pseudo-static analysis methods are reviewed. Each method uses a simplified 2D frame model to represent the seismic behavior of underground structures. Applying each method to a one-barrel rectangular utility tunnel in Korea, the suitability in predicting seismic responses, especially the racking deformation of the tunnel, is examined. In addition, several precautions and suggestions are provided in this study against the inattentive application of the methods to seismic evaluation of underground structures.

철근콘크리트 휨 부재의 최대철근비에 대한 설계 규정은 일반적으로 부재 파괴 시 철근이 항복하도록 하여 충분한 연성과 경제성을 보장 하도록 하고 있다. 콘크리트구조기준(2012)에서 최대철근비는 인장 철근의 순인장변형률 항으로 표현되고, 고강도 재료가 사용되는 경우 매우 높은 철근비를 나타낸다. 따라서 이는 콘크리트 타설시 시공성 확보에 어려움을 야기할 수 있다. 이에 반해, 도로교설계기준(한계상태설계)에서는 최대중립축 깊이비가 0.4가 되도록 최대철근비를 규정하고 있다. 이 결과로부터 시공성 및 연성을 확보할 수 있는 최대철근비에 대한 합리적인 모델을 제시하였다.

The design provisions for the maximum steel ratio in reinforced concrete flexural members is normally provided to ensure sufficient ductility and economy by steel yielding at member failure. In the Concrete Structural Design Code (2012), the maximum steel ratio is expressed in terms of a net strain in tensile steel, and leading to very high steel ratio in the case of using high strength materials. Thereby, this may result in difficulty to satisfy a required workability at concrete placing. On the contrary, in the Korean Highway Bridge Design Code (Limit State Design) the maximum steel ratio is given in terms of the maximum neutral axis depth ratio that is 0.4. From these results, a rational model for the maximum steel ratio is suggested so as to satisfy a ductility as well as a workability.

Purpose of this study is to investigate structural behavior of the rectangular hollow column with various transverse reinforcement details. Experimental variables are diameter, arrangement details and lateral spacing of cross tie. A total of 66 column specimens have been prepared and tested under axial compressive load. Test results showed that behaviors of column specimens were different depending on the cross tie details. Specimens with cross tie wrapping longitudinal steel and transverse steel have greater strength and ductility than specimens with cross tie wrapping the longitudinal steel.

단면이 직사각형 형태를 갖는 마이크로채널에서 이론적인 퍼텐셜의 분포변화를 제타퍼텐셜과 수력학적 지름을 변수로 조사하였다. 그리고 종/횡(Height-Width) 비를 1, 1/2, 1/3로 변화시켜서 형태의 변화에 따른 퍼텐셜의 분포변화를 조사하였다. 이를 위하여 Comsol 사의 FEMLAB 3.0을 이용하여 전산 무사를 실시하였다. 그 결과 단면의 수력학적 지름이 감소함에 따라서 높이방향 표면이 퍼텐셜 분포에 미치는 영향이 일정한 영역까지 나타났다. 또한 단면의 중앙을 지나는 가상의 선상에서 퍼텐셜 값은 제타퍼텐셜에 정비례하여 증가하였으며, 퍼텐셜 값은 단면의 종/횡 비가 증가함에 따라서 그 기울기가 증가하였다. 그렇지만 전체적으로 보았을 때, 단면의 종/횡 비가 감소함에 따라서 전기이중층이 표면방향으로 압축되는 형태를 나타내었으며, 이는 제타퍼텐셜의 증가를 가져올 것으로 사료된다.

In this study, we investigated the potential changes in the cross sectional area of the rectangular microchannel with various zeta potentials and hydraulic diameters. We changed height/width ratio as 1, 1/2, and 1/3 and investigated its effect on the potential change. For this research, FEMLAB(Comsol, verson 3.0) was used to investigate the theoretical potential distribution. The potential changes in the cross section shows that right and left surfaces affect to some ranges. For the same area and shape, the potential value is directly proportional to the zeta potential change. With the decrease in the H/W ratio, the electrical double layer is condensed to the side surfaces.