• 소음진동
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• 제7권4호
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• pp.571-578
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• 1997

Recently, many general-purpose packages for fluid-structure interaction problems have been announced. However, they have a lot of limitations to model structures in the fluid-structure interaction problems reasonably. Utilizing general-purpose packages such as MSC/NASTRAN and SYSNOISE, in this paper, a method to slove the radiation scattering problems with some accuracy in the fluid-structure interaction problems was developed. Using a simple model, the results from the presented method here are compared with those from SYSNOISE. The result shows quite a good agreement between the two methods. The problems, which could not be solved by SYSNOISE, were tried to solve with the presented method and results were presented. It was proved that this method could be safely used to solve fluid-structure interaction problems.

• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1731-1741
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• 2005

In this paper, we studied about the effect of the open crack and a tip mass on the dynamic behavior of a cantilever pipe conveying fluid with a moving mass. The equation of motion is derived by using Lagrange's equation and analyzed by numerical method. The cantilever pipe is modelled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influences of the crack, the moving mass, the tip mass and its moment of inertia, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the tip-displacement of the cantilever pipe are analytically clarified.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1161-1169
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• 2007

In this paper, the dynamic stability of a rotating cantilever pipe conveying fluid with a crack is investigated by the numerical method. That is, the influence of the rotating angular velocity, mass ratio and crack severity on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating cantilever pipe are derived by using extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of fracture and always opened during the vibrations. Generally, the critical flow velocity for flutter is proportional to the rotating angular velocity of a pipe. Also, the critical flow velocity and stability maps of the rotating pipe system for the variation each parameter are obtained.

• 전기학회논문지
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• 제56권12호
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• pp.2173-2178
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• 2007

Dynamics of plasma sheath was analyzed using simple ion fluid model with poison equation. Incident ion current, energy, potential distribution and space charge density profile were calculated as a function of time. The effects of initial floating sheath on the evolution of biased sheath were compared with ideal matrix sheath. The effects of finite rising time of pulse bias voltage on the ion current and energy was studied. The influence of surface charging on the evolution of sheath was also investigated

• Interaction and multiscale mechanics
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• 제5권1호
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• pp.27-40
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• 2012

The two-dimensional incompressible flow of a linear viscoelastic fluid we considered in this research has rapidly oscillating initial conditions which contain both the large scale and small scale information. In order to grasp this double-scale phenomenon of the complex flow, a multiscale analysis method is developed based on the mathematical homogenization theory. For the incompressible flow of a linear viscoelastic Maxwell fluid, a well-posed multiscale system, including averaged equations and cell problems, is derived by employing the appropriate multiple scale asymptotic expansions to approximate the velocity, pressure and stress fields. And then, this multiscale system is solved numerically using the pseudospectral algorithm based on a time-splitting semi-implicit influence matrix method. The comparisons between the multiscale solutions and the direct numerical simulations demonstrate that the multiscale model not only captures large scale features accurately, but also reflects kinetic interactions between the large and small scale of the incompressible flow of a linear viscoelastic fluid.

• 한국소음진동공학회논문집
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• 제17권11호
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• pp.1119-1126
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• 2007

In this paper, the dynamic stability of a cracked cantilever pipe conveying fluid with tip mass is investigated. The pipe is modelled by the Euler-Bernoulli beam theory in which rotatory inertia and shear deformation effects are ignored. The equation of motion is derived by the energy expressions using extended Hamilton's Principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influence of the crack severity, the position of crack, the mass ratio, and a tip mass on the stability of a cantilever pipe conveying fluid are studied by the numerical method. Besides, the critical flow velocity and the stability maps of the pipe system as a function of mass ratios($\beta$) for the changing each parameter are obtained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.254-257
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• 2006

In this paper a dynamic behavior(natural frequency) of a cracked cantilever and simply supported pipe conveying fluid is presented. In addition, an analysis of the flutter and buckling instability of a cracked pipe conveying fluid subjected to a follower compressive load is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• 한국기계가공학회지
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• 제10권3호
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• pp.79-86
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• 2011

The dynamic instability and natural frequency of elastically restrained pipe conveying fluid with the attached mass and crack are investigated. The pipe system with a crack is modeled by using extended Hamilton's Principle with consideration of bending energy. The crack on the pipe system is represented by a local flexibility matrix and two undamaged beam segments are connected. In this paper, the influence of attached mass, its position and crack on the dynamic stability of a elastically restrained pipe system is presented. Also, the critical flow velocity for the flutter and divergence due to the variation in the position and stiffness of supported spring is studied. Finally, the critical flow velocities and stability maps of the pipe conveying fluid with the attached mass are obtained by the changing parameters.

• 치위생과학회지
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• 제11권4호
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• pp.339-344
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• 2011

본 연구는 흡연군, 흡연중단군, 비흡연군의 치은열구액 내 MMP-9을 측정하여 흡연과 치은열구액 내 MMP-9의 관계를 조사하고자 2009년부터 9월부터 2010년 7월까지 본 연구에 동의한 332명을 대상으로 기초설문조사와 치면세균막지수, 치주낭측정 등을 실시하고 치은열구액을 상악전치부 치간 사이 채취하여 치은열구액 내 MMP-9의 농도를 측정하여 분석하였다. 그 결과, 1. 연령대에 따른 치은열구액 내 평균 MMP-9의 농도는 10대 7.54ng/ml, 20대 15.98 ng/ml, 30대 28.47ng/ml, 40대 36.78ng/ml, 50대 이상은 45.06ng/ml로 집단간의 차이는 유의하였다(p<0.001). 2. 치은지수에 따른 치은열구액 내 평균 MMP-9의 농도는 0점 16.15ng/ml, 1점 20.97ng/ml, 2점 48.79ng/ml로 치은지수가 증가함에 따라 치은열구액 내 MMP-9의 농도가 증가하는 경향을 보였으나 유의하지는 않았다(p>0.05). 3. CPI에 따른 치은열구액 내 평균 MMP-9의 농도는 0점 14.74ng/ml, 1점 6.57ng/ml, 2점 10.29ng/ml, 3점 29.71ng/ml, 4점 56.52ng/ml였으며 군간 유의한 차이가 있었다(p<0.001). 4. 흡연여부에 따른 치은열구액 내 MMP-9의 평균 농도는 흡연군이 30.86ng/ml, 흡연중단군이 29.82ng/ml, 11.33ng/ml이었으며 연령, 치은지수, CPI을 공변량으로 보정한 전, 후 모두에서 각 군간 유의한 차이를 나타내었다(p<0.001). 흡연, 흡연중단군이 비흡연군에 비해 치은열구액내 MMP-9의 농도가 높은 것으로 나타나 흡연은 치은열구액 내 MMP-9의 농도를 증가시키고 있는 것으로 보이며 MMP-9은 치조골 파괴 및 치주질환에 영향을 미치므로 흡연자에서 치주질환 발생 및 발생가능성이 높을 것으로 사료되었다.

• 한국소음진동공학회논문집
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• 제18권2호
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• pp.177-184
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• 2008

The dynamic stability of elastically restrained cantilever pipe conveying fluid with crack is investigated in this paper. The pipe, which is fixed at one end, is assumed to rest on an intermediate spring support. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by the energy expressions using extended Hamilton's Principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influence of a crack severity and position, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method are studied. Also, the critical flow velocity for the flutter and divergence due to variation in the support location and the stiffness of the spring support is presented. The stability maps of the pipe system are obtained as a function of mass ratios and effect of crack.