• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2049_2050
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• 2009

본 연구에서는 수소 연료전지의 엔드플레이트와 외부 연결 부분의 금속을 진동시험기를 이용하여 접촉저항을 측정하였다. 수소 연료전지의 집접판에서의 전류밀도의 변화와 온도 분포의 변화를 비교해 볼 수 있었으며, 접촉저항을 측정 할 수 있었다. 진동시험기는 5~50 Hz의 범위까지 설계하였으며 진동에 대한 접촉저항의 변화도 확인 할 수 있었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.341-348
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• 2001

In this study, nonlinear vibration analysis of the cylindrical orthotropic porous thin plate under V-shaped tension distribution with wire impact damping is considered. We make dynamic model of the plate under the tension using commercial FEM code and reduce the number of its degrees of freedom using dynamic condensation. The dynamic model of wire is obtained as lumped mass model from string equation. And then we analyze the nonlinear vibration of the plate including the impact phenomenon between the plate and the wire using the reduced mass and stiffness matrices of the plate and lumped model of the wire. The contact phenomenon between them can be described by impact contact elements composed of contact stiffness coefficients from Hertzian contact theory and contact damping coefficients from restitution coefficient between them. And we discussed the results of nonlinear vibration analysis for variations of their design parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.651-656
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• 2004

This paper presents the application of Differential Transformation to the bucking load and the vibration problem of the rectangular plate loaded by varying in-plane stress. Numerical calculations are carried out and compared with previously published results to validate the results of the resent method. The results obtained by this method agree well with those reported in the Devious works. The results obtained by the present method are presented for various non-uniform loads.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.227-238
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• 1988

The curved structures in space, such as multi-level inter-changes, ramped structures, and circular curved structures etc., are modelled as helically curved members with constant helix angle in this study. Equilibrium equations are derived, considering the geometrical properties and initial curvatures of helix. Modal equations of the simply supported helically curved members which can calculate the normalized natural frequencies are derived from these equations by assuming the modal shape function. These equations are used to calculate the normalized natural frequencies of the simply supported helically curved members and verify the distribution of the natural frequencies of them.

• Computational Structural Engineering
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• v.7 no.2
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• pp.77-87
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• 1994

Vibrational analysis of slab tracks for HSR(High Speed Rail) is performed in order to find dynamic characteristics and to control noise and vibration for the tracks. Wheel-rail interactive force is included in the analysis by modelling the vehicle and track as an unsprung mass and elastically-supported-double-beam respectively, and both are assumed to be connected by the Hertzian spring. From this study, it has been found that vibration in the track and the force transmitted to the infrastructure could be reduced by controlling elasticity, mass and stiffness of the track supporting system appropriately.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.380-385
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• 1996

우리나라와 같이 강진의 발생이 거의 없는 지역에서, 가까운 장래에 예상되는 지진동 파형을 추정하는 기법으로서는 설계응답스펙트럼에 위상정보를 가미하는 모의지진동에 의한 작성방법을 흔히 사용하고 있으며, 이에 사용되는 위상스펙트럼의 특성을 랜덤으로 가정하는 경우가 대부분이다. 그러나 본 논문에서는 우리들이 일반적으로 랜덤으로 취급하는 위상스펙트럼에도 지진의 특성이 반영되어 있을 것이라는 가정하에 위상차분의 특성과 포락파형의 상관관계를 도출하고 위상차분을 고려한 모의지진동 작성방법을 제안하였다. 지진파형의 포락곡선을 확률분포로 사용하여 계산한 위상차분스펙트럼의 형상은 지진파형의 포락곡선과 거의 유사함을 확인하였고, 지금까지는 랜덤으로 취급한 위상스펙트럼에 물리적인 의미를 부여하는 계기가 되었다. 그러므로 앞으로 한반도에서 지진관측자료가 축적되어 한반도에서의 특징적인 위상차분스펙트럼이 정의된다면 우리나라의 지형조건이 고려된 진일보된 설계지진동을 작성할 수 있을 것이다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.8
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• pp.639-647
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• 2002

The nonlinear vibration of the thin perforated plate is analyzed in consideration of the V-shaped tension distribution and the effect of wire impact damping. The reduced order FEM model of the tension plate is obtained from dynamic condensation for the mass and stiffness matrices. Tension wire is modeled using the lumped parameter method to effectively describe its contact interactions with the plate. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. From the evaluation of the computational accuracy and computation time for the deduced impact stiffness and damping coefficient, we determined proper values for the simulation works, accounting for the computational accuracy as well as the computational efficiency. Finally we discussed the results of nonlinear nitration analysis for variations of their design parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1378-1386
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• 2002

In the present study, velocity profile and wall shear stress distributions of developing turbulent oscillatory flows in an oscillator connected to straight duct located in exit region of a curved duct was investigated experimentally. The experimental study for air flows was conducted to measure axial velocity profiles, shear stress distributions by using the Laser Doppler Velocimetry(LDV) system with the data acquisition and processing system of Rotating Machinery Resolver(R.M.R) and PHASE software. The results obtained from experimental studies are summarized as follows. The critical Reynolds number for a change from transitional oscillatory flow to turbulent flow was about 7500, in the 60region of dimensionless axial position which was considered as a fully developed flow region. The turbulent oscillatory flow, velocity profiles of the inflow period in the entrance region were gradually developed, but those of the outflow period were not changed nearly. Velocity profiles of inflow and outflow were shown as a symmetric form in a fully developed flow region. The wall shear stress distributions of turbulent oscillatory flow increase rapidly as the flow proceeds to downstream and flow was in good agreement with the theoretically.

• The KSFM Journal of Fluid Machinery
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• v.4 no.4 s.13
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• pp.37-42
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• 2001

In the present study, flow characteristics of turbulent oscillatory flow in an oscillator connected to square-sectional $180^{\circ}$ curved duct are investigated experimentally. In order to investigate wall shear stress and pressure distributions, the experimental studies for air flows we conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisitions and the processing system. The wall shear stress at bend angle of the $150^{\circ}$ and pressure distribution of the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) by $10^{\circ}$ intervals of the duct are measured. The results obtained from the experiment are summarized as follows : wall shear stress values in the inner wall we larger than those in an outer wall, except for the phase angle (${\omega}t/{\pi}/6$) of 3, because of the intensity of secondary flow. The pressure distributions are the largest in accelerating and decelerating regions at the bend angle(${\phi}$) of $90^{\circ}$ and pressure difference of inner and outer walls is the largest before and after the ${\phi}=90^{\circ}$.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.245-251
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• 1994

The charateristics of switching between two modes in a ring dye laser has been analyzed by the Monte-Carlo computer simulation. The effect of including pump fluctuations in the first-passage-time (FPT) distributions was compared with the distribution with the quantum fluctuation. The results show the same tendency in both cases, such as steep increases from 0 to peak an exponential decrease in long time range. However the introduction of pumping fluctuation is turned out to shorten the mean FPT. The variation of the mean FPT is examined for the various fluctuationrelated parameters. The mean FPT is lengthened when pump parameter a is increased while it is shorted when Q. $\GAMMA$ are decreased. eased.