• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.375-376
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• 2006

Turbulent structure of a boundary-layer over a flat plate coated with micro riblet film(MRF) has been investigated experimentally. The turbulent structure was visualized using a dynamic particle image velocimetry (Dynamic PIV) system. We identified the vortex structures from 2-D velocity field data by applying the complex eigenvalue definition. The velocity field images acquired by using the complex eigenvalue definition showed the whole 2-D vortex structures clearly. In addition, the spatial distributions of small-scale vortices as well as large-scale vortices were obtained with high accuracy. The difference of vortex structures between the MRF coated flat plate and the smooth flat plate was analysed in detail. With varying upstream flow speed, the characteristics of vortex structure over the MRF coated flate plate was compared with those over the smooth flat plate.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2252-2254
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• 2002

The Reactor internal structures which consist of many complex components are subjected to flow-induced vibration due to high temperature and pressure in Reactor coolant system. The above flow-induced vibration causes degradation of structural integrity of the Reactor and may result in loosing mechanical binding component which might impact other equipment and component or cause flow blockage. It is important to analyze reactor noise signal for the early detection of potential problem or failure in order to diagnosis reactor integrity in the point of view of safety and plant economics. Detailed composition of diagnostic system reactor internal structures using neutron noise(RIDS).

• Wind and Structures
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• v.3 no.2
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• pp.97-115
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• 2000

The technique of proper orthogonal decomposition is potentially useful in specifying the fluctuating surface pressure field around structures. However there has been a degree of controversy over whether or not the calculated modes have physical meanings. This paper addresses this issue through consideration of the results of full scale experiments, and through an analytical investigation. It is concluded that the lower, most energetic modes are likely to reflect different fluctuating flow mechanisms, although no mode is likely to be associated with just one flow mechanism or vice versa. The higher, less energetic modes are likely to represent interactions between different flow mechanisms, and to be significantly affected by the number of measurement points and measurement errors. The paper concludes with a brief description of the application of POD to the problem of building ventilation, and the calculation of cladding pressures.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2166-2168
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• 2001

Reactor Noise is defined as the fluctuations of measured instrumentation signals during full-power operation of reactor which have informations on reactor system dynamics such as neutron kinetics. The Reactor internal structures which consist of many complex components are subjected to flow-induced vibration due to high temperature and pressure in reactor coolant system. The above flow-induced vibration causes degradation of structural integrity of the reactor and may result in loosing mechanical binding component which might impact other equipment and component or cause flow blockage. It is important to analyze reactor noise signal for the early detection of potential problem or failure in order to diagnosis reactor integrity in the point of view of safety and plant economics. Detailed design of hardware diagnostic system reactor internal structures using neutron noise(RIDS).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.949-953
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• 2004

In this paper, Power Flow Boundary Element Method(PFBEM) is studied as the numerical method for the vibration and sound predictions of complex structures in medium-to-high frequency ranges. NASPFA, the sound analysis software based on PFBEM, is developed and is used for the vibro-acoustic analysis. And also the developed software is used for the prediction of interior and exterior sound fields of vibrating structures and for the analysis of the multi-domain problems. To verify the accuracy, NASPFA is applied to the prediction of the energy distribution in the simple structures, and its results are compared with exact PFA solutions. And various practical vehicle systems are modeled and the distributions of the acoustical energy density are successfully predicted.

• The Journal of the Acoustical Society of Korea
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• v.21 no.4E
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• pp.164-169
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.8
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• pp.303-313
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• 2001

The identification of power flow in dynamically loaded structures Is essential in the analysis of structure-borne noise. However there are no general purpose tools to estimate powers flow. To make matters worse. It is very difficult to measure it. The power flow can be formulated in terms of balance forces(ELFORCE) at each element and velocities at the associated node obtained with MSC/NASTHAN. In this paper the procedure which is consist of the computations of the balance forces of al1 elements and the velocities at all nodes using MSC/NASTRAN. The calculations of the power f1ow at each element using PCL(PATRAN Command Language) and the Preparation of post -processes is set UP.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.11 s.242
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• pp.1189-1198
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• 2005

Direct numerical simulations were performed to investigate the physics of a spatially developing turbulent boundary layer flow subjected to spanwise oscillating electromagnetic forces in the near wall region. A fully implicit fractional step method was employed to simulate the flow. The mean flow properties and the Reynolds stresses were obtained to analyze the near-wall turbulent structure. It is found that skin friction and turbulent kinetic energy can be reduced by the electromagnetic forces. The decrease in production is responsible fur the reduction of turbulent kinetic energy. Instantaneous flow visualization techniques were used to observe the response of streamwise vortices and streak structures to spanwise oscillating forces. The near-wall vortical structures are affected by spanwise oscillating electromagnetic forces. Following the stopping of the electromagnetic force, the flow eventually relaxes back to a two-dimensional equilibrium boundary layer.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.75-78
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• 2004

Traditionally aluminum alloy have been used in manufacturing of aircraft structures, and semi-monocoque structural concept have been mainly applied in structural design of fuselage and wing. However, recently monocoque structural concept is applied in many small-size aircraft structures manufactured with composite materials. In such case appling monocoque structural concept, in initial conceptual design stage on wing, it is not easy to analyze shear flow using classical shear flow analytical method because composite skin structure can support span-wise tension/compression stress as well as sectional shear stress. In this study, an extended shear-flow analytical method to apply to composite monocoque structural concept was developed through extending the classical shear-flow analytical method.

• The Journal of the Acoustical Society of Korea
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• v.21 no.4
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• pp.164-164
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.