• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.75-86
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• 2013

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

• 한국안전학회지
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• 제17권2호
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• pp.8-15
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• 2002

In order to investigate the vibration characteristics of fluid-structure interaction problem, we modeled two identical rectangular plates coupled with fluid. A commercial computer code, ANSYS was used to perform finite element analysis and FEM solutions were compared with the experimental results to verify the finite element model. As a result, comparison of FEM and experiment showed good agreement, and the transverse vibration modes, in-phase and out-of-Phase, were observed alternately in the fluid-coupled system. The effect of fluid gap size on the fluid-coupled natural frequency were investigated. It was shown that the mode numbers increased, the normalized natural frequencies monotonically increased. And it was also found that an increase of the fluid gap reduced the coupled natural frequencies for the in-phase modes but increased the coupled natural frequencies for the out-of phase modes, and eventually converged to the results of an infinite fluid gap.

• 한국해양공학회지
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• 제34권5호
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• pp.325-333
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• 2020

As regulations concerning ship vibration and noise are becoming stricter, considerable attention is being drawn to prediction technologies for ship vibration and noise. In particular, the resonance and lock-in phenomena caused by vortex-induced vibration (VIV) have become considerably important with increases in the speed and the size of ships and ocean structures, which are known to cause structural problems. This study extends the fluid-structure interaction (FSI) analysis method to predict resonances and lock-in phenomena of high modes and VIV of ship rudders. Numerical stability is secured in underwater conditions by implementing added mass, added damping, and added stiffness by applying the potential theory to structural analysis. An expanded governing equation is developed by implementing displacements and twist angles of high modes. The lock-in velocity range and resonant frequencies of ship rudders obtained using the developed FSI method agree well with the experimental results and the analytic solution. A comparison with local vibration guidelines published by Lloyd's Register shows that predictions of resonances and lock-in phenomena of high modes are necessary in the shipbuilding industry due to the possible risks like fatigue failure.

• 한국철도학회논문집
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• 제16권4호
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• pp.253-261
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• 2013

KTX 열차가 정거장에서 정차 시 측정한 제동 스퀼소음은 저주파에서부터 18,000Hz의 고주파 영역에 걸쳐 관찰되었다. 제동 스퀼소음이 제동디스크/패드의 상호작용에 의한 불안정 진동모드에 의해 발생한다는 가정 하에 유한요소법을 적용하여 하나의 제동디스크와 4개의 제동패드로 구성된 제동 유니트에 대해 유한요소 모델링을 하고 마찰계수, 마찰면에 작용하는 압력, 마찰재와 백플레이트의 탄성계수 등 여러 파라미터의 특성값을 변경해 가면서 제동 유니트의 불안정 진동모드에 미치는 영향을 해석하고 각 파라미터의 영향을 분석하였다. 해석결과에 의하면 불안정 진동모드는 이러한 변수들과 밀접한 관련이 있음을 알 수 있었다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제16권4호
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• pp.347-355
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• 2016

Purpose: With the advance of miniaturization of electronic products, stacked packages of high density semiconductors are commonly used. Potential failure modes and mechanisms of stacked packages are identified. Methods: Failure modes and mechanisms of thin chip stacked packages are determined through the categorization and failure analysis: delamination, non-wet, crack, ESD, EMI and the process related damages. Results: Those failure modes are not easy to find and require excessive amount time and effort for analysis and subsequent improvement. Conclusion: In this study, a method of estimating the failure rate based on the strength measurement is suggested.

• 디자인학연구
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• 제20권2호
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• pp.65-76
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• 2007

The primary purpose of this study was to evolve integrated design process for Experiential Design which is based on the former study, 'The Influence of Cognitive Factors on the Creative Abilities in Design'. Experience is a transformation factor to all of the design processes, which has three phase of problem solving; Input, Process, and Output. We regard Experiential Design is a transforming process from concept to experience, and set up a mode) of Holistic Design Process (HDP), which consists of four domains: Four Causes, Thinking Modes, Sensory Modalities, and Creative Abilities. Revolving Sensory Modalities (SM), Creative Abilities (CA), and Thinking Modes (TM) around Product Design Specification (PDS) through a design process, Design Concepts ripen and mature into Externalization. Each component of Experiential Design (TM, SM, and CA) turns around the PDS. Here, experience is first perceived by the five senses. Then, the knowledge is formed, and the CA works for a problem solving. And TM controls all of these procedures. We regard these are a phenomenon of Experiential Design. The HDP can be helpful to develop valuable solutions and create a good experience.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.668-671
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• 1997

In order to investigate the vibration characteristics of fluid-structure interaction problem, we modeled two identical rectangular plates coupled with bounded fluid. The fixed boundary condition along the plate edges and an ideal fluid were assumed. A commercial computer code, ANSYS was used to perform finite element analysis and FEM solutions were compared with the experimental results to modify the finite element model. As a result, comparison of FEM and experiment showed good agreement, and the transverse vibration modes, in-phase and out of-phase. were observed alternately in the tluid-coupled system. The effects of distance between two rectangular plates and width to length ratio on the fluid-coupled natural frequency were investigated. And it was found that the ormalized natural frequency of the fluid-coupled system monotonically increased with an increase in the number of modes.

• STI Policy Review
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• 제7권1호
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• pp.17-39
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• 2016

Despite the importance of university-industry collaboration, issues pertaining to the characteristics of collaborating firms, their modes of interaction, and the relationship between these modes and outcomes are not well-researched. The impact of country's development on these issues is also unclear. This case study examines Japan and Thailand-respectively representing developed and developing countries-and features the following key findings: 1) the characteristics of firms affect modes, with large Japanese firms being more collaborative with universities, whereas Thai SMEs significantly collaborate more with universities; 2) the relationship between modes in Thai firms is stronger than those of Japanese firms because in Thailand, perhaps due to weak technological capacity, R&D collaboration is conducted alongside university consultancy services; and 3) in Japan, R&D and human resource development collaboration lead to product innovation, whereas different outcomes are expected from different modes in Thailand. Apparently, trivial informal collaborations do have significant impact on innovation.

• 한국과학교육학회지
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• 제20권3호
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• pp.353-363
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• 2000

본 연구에서는 4개 소집단의 학생간 토론 양상을 조사하였다. 소집단 토론 과정에서 나타나는 언어적 상호작용을 녹음 및 녹화한 후, 기록 원고를 작성하고, 분석하였다. 개별 진술, 상호작용 단위, 에피소드 수준의 분류들을 개발하였다. 개별 진술 분석에서 학생들의 이전 성취도와 지식 구성 과정 기여도 사이에는 뚜렷한 관계가 없었다. 상호작용 단위 분석에서는 부분 참여형 상호작용과 대칭적 상호작용이 상대적으로 많이 발견되어 학생간의 상호작용이 부분적이고 피상적인 것으로 나타났다. 또한, 에피소드 분석에서는 제시된 의견의 수용이나 부분적인 정교화 유형이 가장 흔히 나타났고, 변증법적인 대화는 드물었다.

• 로봇학회논문지
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• 제12권3호
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• pp.356-364
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• 2017

This paper presents a force control based on the observer without taking any force or torque measurement from the robot which allows realizing more stable and robust human robot interaction for the developed multi-functional upper limb rehabilitation robot. The robot has four functional training modes which can be classified by the human robot interaction types: passive, active, assistive, and resistive mode. The proposed observer consists of internal disturbance observer and external force observer for distinctive performance evaluation. Since four training modes can be quantitatively identified as impedance variation, position-based impedance control with feedback and feedforward controller was applied to the assistive training mode. The results showed that the proposed sensorless observer estimated cleaner and more accurate force compared to the force sensor and the impedance controller embedded with the proposed observer completed the assistive training mode safely and properly.