• Wind and Structures
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• 제23권2호
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• pp.157-169
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• 2016

The structural integrity of tube bundles represents a major concern when dealing with high risk industries, such as nuclear steam generators, where the rupture of a tube or tubes will lead to the undesired mixing of the primary and secondary fluids. Flow-induced vibration is one of the major concerns that could compromise the structural integrity. The vibration is caused by fluid flow excitation. While there are several excitation mechanisms that could contribute to these vibrations, fluidelastic instability is generally regarded as the most severe. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. The tubes are therefore stiffened by means of supports to avoid these vibrations. To accommodate the thermal expansion of the tube, as well as to facilitate the installation of these tube bundles, clearances are allowed between the tubes and their supports. Progressive tube wear and chemical cleaning gradually increases the clearances between the tubes and their supports, which can lead to more frequent and severe tube/support impact and rubbing. These increased impacts can lead to tube damage due to fatigue and/or wear at the support locations. This paper presents simulations of a loosely supported multi-span U-bend tube subjected to turbulence and fluidelastic instability forces. The mathematical model for the loosely-supported tubes and the fluidelastic instability model is presented. The model is then utilized to simulate the nonlinear response of a U-bend tube with flat bar supports subjected to cross-flow. The effect of the support clearance as well as the support offset are investigated. Special attention is given to the tube/support interaction parameters that affect wear, such as impact and normal work rate.

• 한국소음진동공학회논문집
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• 제16권9호
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• pp.904-911
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• 2006

A modified energy method for the fretting wear of the steam generator tube is proposed to calculate the wear-out depth between the nuclear steam generator tube and its support. Estimation of fretting-wear damage typically requires a non-linear dynamic analysis with the information of the gap velocity and the flow density around the tube. This analysis is very complex and time consuming. The basic concept of the energy method is that the volume wear rate due to the fretting-wear phenomena Is related to work rate which is time rate of the product of normal contact force and sliding distance. The wearing motion is due to dynamic interaction between vibrating tube and its support structure, such as tube support plate and anti-vibration bar. It can be assumed that the absorbed work rate would come from turbulent flow energy around the vibrating tube. This study also numerically obtains the wear-out depth with various wear topologies. A new dissection method is applied to the multi-span tubes to represent the vibrational mode. It turns out that both the secondary side density and the normal gap velocity are important parameters for the fretting-wear phenomena of the steam generator tube.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.154-161
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• 2000

As a mass flow controller is widely used in many manufacturing processes for controlling a mass flow rate of gas with accuracy of 1%, several investigators have tried to describe the heat transfer phenomena in a sensor tube of an MFC. They suggested a few analytic solutions and numerical models based on simple assumptions, which are physically unrealistic. In the present work, the heat transfer phenomena in the sensor tube of the MFC are studied by using both experimental and numerical methods. The numerical model is introduced to estimate the temperature profile in the sensor tube as well as in the gas stream. In the numerical model, the conjugate heat transfer problem comprising the tube wall and the gas stream is analyzed to fully understand the heat transfer interaction between the sensor tube and the fluid stream using a single domain approach. This numerical model is further verified by experimental investigation. In order to describe the transport of heat energy in both the flow region and the sensor tube, the Nusselt number at the interface between the tube wall and the gas stream as well as heatlines is presented from the numerical solution.

• Steel and Composite Structures
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• 제13권3호
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• pp.277-293
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• 2012

The interaction between steel tube and concrete core is the key design considerations for concrete-filled steel tube columns. In a concrete-filled steel tube (CFST) column, the steel tube provides confinement to the concrete core which permits the composite action among the steel tube and the concrete. Due to construction faults and plastic shrinkage of concrete, the debonding separation at the steel-concrete interface weakens the confinement effect, and hence affects the behaviour and bearing capacity of the composite member. This study investigates the axial loading behavior of the concrete filled circular steel tube columns with debonding separation. A three-dimensional nonlinear finite element model of CFST composite columns with introduced debonding gap was developed. The results from the finite element analysis captured successfully the experimental behaviours. The calibrated finite element models were then utilized to assess the influence of concrete strength, steel yield stress and the steel-concrete ratio on the debonding behaviour. The findings indicate a likely significant drop in the load carrying capacity with the increase of the size of the debonding gap. A design formula is proposed to reduce the load carrying capacity with the presence of debonding separation.

• Steel and Composite Structures
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• 제38권6호
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• pp.739-749
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• 2021

This paper introduces an improved design equation to evaluate the resisting capacity of circular reinforced concrete (RC) columns partially strengthened with outer steel tube. When RC column members are required to be strengthened according to the change in the loadings considered and/or the deterioration progress in columns, wrapping up RC column with steel circular tube, which takes the form of concrete filled steel tube (CFST), has been popularly considered because of its structural advantage induced from the confinement effect. However, the relatively high construction cost of steel tube is restricting its use to the required region, while deriving the shape of a partial CFST column. To evaluate the resisting capacity of a partial CFST column, numerical analyses need to be performed, and a numerical model proposed in the previous study for the numerical analysis of full CFST columns is used to conduct parametric studies for the introduction of a design equation. The bond-slip effect developed along the interface between the in-filled concrete and the exterior steel tube is taken into consideration and the validity of the numerical model has been established through correlation studies between experimental data and numerical results for partial CFST circular columns. Moreover, parametric studies make it possible to introduce a design equation for determining the optimum length of outer steel tube which produces partial CFST circular columns.

• 한국콘텐츠학회논문지
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• 제22권8호
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• pp.1-13
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• 2022

본 연구는 유튜브 정치동영상 이용자들을 대상으로 선택적 노출과 정치적 성향, 정치적 관심도의 태도극화에 대한 상호작용효과를 살펴보았다. 주요 결과를 제시하면 다음과 같다. 먼저 연구문제 1, 연구문제 2와 관련하여 유튜브 정치동영상 이용자들의 선택적 노출과 정치적 성향에 대한 태도극화, 선택적 노출과 정치적 관심도에 대한 태도극화를 살펴본 결과, 선택적 노출에서 동일하게 태도극화 '나'에 대한 주 효과가 발견되었다. 그러므로 유튜브 이용자들의 정치동영상에 대한 선택적 노출이 높아질수록 유튜브 이용자 자신의 태도극화가 강화되는 것으로 나타났다. 연구문제 3과 관련하여 유튜브 정치동영상 이용자들의 정치적 성향과 정치적 관심도에 대한 태도극화를 살펴본 결과, 정치적 성향과 정치적 관심도의 태도극화 '나' 에 대한 상호작용효과가 발견되었다. 따라서 진보적 성향이나 보수적 성향 모두 정치적 관심이 높을 때, 유튜브 이용자 자신의 태도극화도 강화되는 것으로 나타났다.

• 디지털융복합연구
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• 제19권2호
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• pp.457-462
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• 2021

최근 동영상을 통해 이용자가 자유롭게 참여하고 정보를 공유할 수 있어 쌍방향 소통이 가능한 유튜브가 대표적인 미디어 플랫폼으로 자리 잡고 있다. 유튜브를 활용한 마케팅이 기업 차원에서도 긍정적인 효과를 나타내고 있어 그 영향력에 대한 관심도 증가하였다. 이에 본 연구는 유튜브 뷰티콘텐츠 이용자의 준사회적 상호작용이 행동의도에 미치는 영향을 연구하고 그 결과를 효율적 마케팅 전략 수립의 기초자료로 제공하고자 한다. 본 연구 결과에 따르면 준사회적 상호작용은 행동의도에 유의미한 정(+)의 영향을 미치는 것으로 나타났다. 이에 이용자의 특성에 따른 실효성 있는 준사회적 상호작용 확대 방안을 연구하여야 할 것으로 사료된다.

• 설비공학논문집
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• 제24권3호
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• pp.265-270
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• 2012

A finned tube type heat exchange module has been proposed for a multi-burner water tube boiler. Fin density and length increase in streamwise direction to equalize the evaporation for each module, which makes it difficult to apply conventional bulk design procedure. The design program has been improved by updating data for every row of tubes along the flow. A numerical simulation has been also conducted to evaluate the effect of inlet conditions and validated with experiment. The heat transfer of the first row has been underpredicted by the conventional Zhukauskas correlation, since the acceleration of the flow due to the blockage is not fully inflected. The fin tip temperature is also underpredicted by Bessel solution, because of the interaction with neighboring fins.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.528-533
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• 2007

A finned tube type heat transfer module has been proposed for a multi-burner water tube boiler. Fins change their geometry along the streamwise direction to maximize the performance, which makes it difficult to apply conventional bulk analysis. The design program has been improved by updating data for every row of tubes along the flow. A numerical simulation has been also performed to evaluate the effect of inlet conditions and validated with experiment. The heat transfer of the first row has been underpredicted by the conventional Zhukauskas correlation, where the acceleration of the flow due to the blockage is not fully inflected. The fin tip temperature is also underpredicted by Bessel solution, because of the interaction with neighboring fins.

• 한국멀티미디어학회논문지
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• 제23권12호
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• pp.1576-1585
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• 2020

The purpose of this study is to design and apply YouTube ecosystem using digital curation to improve the interaction of untact class. The untact digital instructional model for building the YouTube ecosystem is composed of four modules: domain, tutor, student, and interface, and the role of each module is described. As an application example, the team project "Development and Operation of Instructional Assistant YouTube" is performed in the Introduction to Media Software class. The learning experience is described in terms of professor, peer tutors, and learners, and learning outcomes are presented through surveys.