• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.145-150
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• 2007

The spacer grid set is a component in the nuclear fuel assembly. The set supports the fuel rods saftely. Therefore, the spacer gl1d set should have sufficient strength for the external impact forces. The fretting wear occurs between the spring of the fuel rod and the spacer grid due to tile flow-induced vibration. The conceptual design of the spacer grid set is performed based on the Independence Axiom of axiomatic design. Two functional requirements are defined and corresponding design parameters are selected. The overall flow of the design is defined according to the application of axiomatic design. The design for the impact load is carried out by using nonlinear dynamic analysis to determine the length of the dimple. Topology optimization is carried out to determine a new configuration of the spring. The fretting wear is reduced by shape optimization using the homology theory. In the design to reduce the fretting wear, the deformed shape of the spring should be the same as that of the fuel rod. This condition is transformed to a function and considered as a constraint in the shape optimization process. The fretting wear is expected to be reduced due to the homology constraint. The objective function is minimizing the maximum stress to allow a slight plastic deformation. Shape optimization results are confirmed through nonlinear static analysis because the contact area becomes wider.

• 한국전산구조공학회논문집
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• 제25권3호
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• pp.185-194
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• 2012

이 연구는 회전관성과 전단변형을 동시에 고려한 변단면 Timoshenko 보의 자유진동에 관한 연구이다. 변단면 보의 단면은 폭이 포물선 함수로 변화하는 변화폭 직사각형 단면으로 채택하였다. 이러한 보의 자유진동을 지배하는 수직변위에 대한 4계 상미분방정식을 유도하였다. 이 상미분방정식을 수치해석하여 고유진동수와 진동형을 산출하였다. 수치해석 예에서는 회전-회전, 회전-고정, 고정-고정 지점을 고려하였다. 진동형은 변위의 진동형뿐만 아니라 합응력의 진동형도 산출하여 그림에 나타내었다. 휨 회전각과 전단변형에 의한 수직변위 및 전단면 회전각의 구성비율을 산정하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.523-526
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• 2010

볼트 몸체의 특정부위를 팽창시켜 결합된 상대물과의 압착을 통해 풀림이 방지되는 볼트를 개발하였다. 볼트 풀림현상은 볼트가 사용되는 분야에서 많은 문제점을 일으켜왔다. 이를 해결하기 위하여 현재 여러 종류의 풀림방지 장치가 개발되어 사용되고 있지만 완벽한 풀림방지기능을 갖는 것은 개발되지 못했다. 이와 같은 문제로 볼트가 적용된 구조물들은 진동, 충격 등의 외부 하중에 의해 풀림이 발생되었고 이를 유지보수하기 위하여 일정 기간마다 다시 조여주어야만 했다. 본 연구는 볼트 내부 형상, 화약량, 공이뭉치를 설계인자로 하여 볼트 몸체 특정부위의 팽창을 조절할 수 있는 기술을 확보하였으며 팽창률에 따른 풀림방지 성능이 선형 비례한다는 것을 확인하였다. 따라서 현장에서 사용될 때 요구되는 풀림 방지기능을 팽창률 제어를 통해 만족시킬 수 있는 풀림방지 볼트를 개발하게 되었다.

• Wind and Structures
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• 제10권3호
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• pp.233-247
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• 2007

The insertion of steel braces has become a common technique to limit the deformability of steel framed buildings subjected to wind loads. However, when this technique is inadequate to keep floor accelerations within acceptable levels of human comfort, dampers placed in series with the steel braces can be adopted. To check the effectiveness of braces equipped with viscoelastic (VEDs) or friction dampers (FRDs), a numerical investigation is carried out focusing attention on a three-bay fifteen-storey steel framed building with K-braces. More precisely, three alternative structural solutions are examined for the purpose of controlling wind-induced vibrations: the insertion of additional diagonal braces; the insertion of additional diagonal braces equipped with dampers; the insertion of both additional diagonal braces and dampers supported by the existing K-braces. Additional braces and dampers are designed according to a simplified procedure based on a proportional stiffness criterion. A dynamic analysis is carried out in the time domain using a step-by-step initial-stress-like iterative procedure. Along-wind loads are considered at each storey assuming the time histories of the wind velocity, for a return period $T_r=5$ years, according to an equivalent wind spectrum technique. The behaviour of the structural members, except dampers, is assumed linear elastic. A VED and an FRD are idealized by a six-element generalized model and a bilinear (rigid-plastic) model, respectively. The results show that the structure with damped additional braces can be considered, among those examined, the most effective to control vibrations due to wind, particularly the floor accelerations. Moreover, once the stiffness of the additional braces is selected, the VEDs are slightly more efficient than the FRDs, because they, unlike the FRDs, dissipate energy also for small amplitude vibrations.

• 대한기계학회논문집A
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• 제34권11호
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• pp.1733-1740
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• 2010

대형 드럼세탁기의 낙하 충격에 대한 포장재의 동적 거동 분석을 수행하였다. 해석에는 충격 해석에 널리 쓰이고 있는 LS-DYNA를 사용하였으며, 자유 낙하 시의 충격 가속도와 유효 응력, 그리고 고속 카메라를 통한 포장재 압축 변형 비교를 통해 해석 결과의 신뢰성을 검증하였다. 완충 특성 및 포장재 구조 에 대한 파라미터 분석을 통해 기존 포장 구조에 대한 설계 개선안을 도출하였으며, 유통 시험을 통해 유효성을 검증하였다. 본 연구에서 사용한 해석 기법 및 분석 방법 등을 통해, 향후 드럼 세탁기의 완충 성능 및 재료비 개선에 효과적으로 기여할 수 있을 것으로 기대된다.

• 한국항공우주학회지
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• 제37권2호
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• pp.201-208
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• 2009

최근 화석 연료가 고갈됨에 따라 대체 에너지 개발 연구가 활발히 진행되고 있다. 여러 대체 에너지들 중 풍력 발전시스템은 바람의 에너지를 전기적 에너지로 바꾸어 주는 시스템으로 매우 친환경적이기 때문에 다양하게 연구되고 있다. 따라서 본 연구에서 500W급 소형 풍력 발전용 블레이드의 개발을 통해 외국에 비하여 상대적으로 풍속이 낮은 국내와 같은 지역에 적용할 수 있는 블레이드 설계를 수행하였다. 본 논문에서는 피로수명을 고려한 고효율 경량화 블레이드의 공력설계 및 구조설계 방법이 제안되었으며, 구조해석으로 선형 정적해석, 좌굴해석, 진동모드해석이 수행되었다. 이론적 해석 결과를 입증하기 위하여 구조 시험 및 공력 성능 시험 결과 비교적 잘 일치하며 설계 요구 조건을 만족함을 확인하였다.

• 한국재료학회지
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• 제27권12호
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• pp.652-657
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• 2017

The use of continuous welded rail is increasing because of its many advantages, including vibration reduction, enhanced driving stability, and maintenance cost savings. In this work, two different types of continuous welded rails were examined to determine the influence of repeated wheel-rail contact on the crystal structure, microstructure and mechanical properties of the rails. The crystal structure was determined by x-ray diffraction, and the microstructure was examined using optical microscopy and scanning electron microscopy. Tensile and microhardness tests were conducted to examine the mechanical behaviors of prepared specimens taken from different positions in the cross section of both newly manufactured rail and worn rail. Analysis revealed that both the new and worn rail had a mixed microstructure consisting of ferrite and pearlite. The specimens from the top position of each rail exhibited decreased lamella spacing of the pearlite and increased yield strength, ultimate tensile strength and hardness, as compared with those from other positions of the rail. It is thought that the enhanced mechanical property on the top position of the worn rail might be explained by a mixed effect resulting from a directional microstructure, the decreased lamella spacing of pearlite, and work hardening by the repeated wheel-rail contact stress.

• 한국정밀공학회지
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• 제25권6호
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• pp.47-54
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• 2008

Fitting process carried out in the automobile transmission assembly line is classified into three classes; heat fitting, press fitting, and their combined fitting. Heat fitting is a method that heats gear to a suitable range under the tempering temperature and squeezes it toward the outer diameter of shaft. Its stress depends on the yield strength of gear. Press fitting is a method that generally squeezes gear toward that of shaft at room temperature by a press. Another method heats warmly gear and safely squeezes it toward that of shaft. Warm shrink fitting process for the automobile transmission part is now gradually increased, but the parts (shaft/gear) assembled by this process produced dimensional changes in both the outer diameter and profile of the gear. So that it may cause noise and vibration between gears. In order to solve these problems, we need an analysis of warm shrink fitting process, in which design parameters are involved; contact pressure according to fitting interference between outer diameter of shaft and inner diameter of gear, fitting temperature, and profile tolerance of gear. In this study, an closed form equation to predict contact pressure and fitting load was proposed in order to develop an optimization technique of the warm shrink fitting process and verified its reliability through the experimental results measured in the field and FEM, that is, thermal-structural coupled field analysis. Actual loads measured in the field was in good agreements with the results obtained by the theoretical and finite element analysis.

• Steel and Composite Structures
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• 제36권1호
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• pp.1-16
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• 2020

In steel-concrete composite beams, to improve the cracking resistance of the concrete slab in the hogging moment region, a new type of connector in the interface, named uplift-restricted and slip-permitted screw-type (URSP-S) connector has been proposed. This paper focuses on the behavior of steel-concrete composite beams with URSP-S connectors. A total of three beam specimens including a simply supported beam with URSP-S connectors and two continuous composite beams with different connectors arrangements were designed and tested. More specifically, one continuous composite beam was equipped with URSP-S connectors in negative moment region and traditional shear studs in other regions. For comparison, the other one was designed with only traditional shear studs. The failure modes, crack evolution process, ultimate capacities, strain responses at different locations as well as the interface slip of the three tested specimens were measured and evaluated in-depth. Based on the experimental study, the research findings indicate that the larger slip deformation is allowed while using URSP-S connectors. Meanwhile, the tensile stress reduces and the cracking resistance of the concrete slab improves accordingly. In addition, the overall stiffness and strength of the composite beam become slightly lower than those of the composite beam using traditional shear studs. Moreover, the arrangement suggestion of URSP-S connectors in the composite beam is discussed in this paper for its practical design and application.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.