• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.399-402
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• 2009

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. According to standard acoustic-test procedures, acoustic-pressure signals are measured. Quantitative acoustic properties of sound absorption coefficient are evaluated and thereby, the acoustic damping capacity of the resonator is characterized. Helmholtz resonator on spring-damper system use were understanding for acoustic damping. The length of orifice and the volume of cavity of resonator are selected as design parameters for tuning of the resonator. Acoustic- damping capacity of the resonator increases with its cavity volume. And orifice length as increases with acoustic damping capacity was decreased.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.83-90
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• 2006

In active vibration control of building, controller design considering both control input saturation of controller and parameter uncertainties of building is needed. In our previous research, we proposed a robust saturation controller which guarantees robust stability and control performance of the uncertain linear time-invariant system in the presence of control input saturation. In this paper, the availability of the robust saturation controller for the building with an active mass damper (AMD) system is verified through experimental tests. Experimental tests are carried oui using a two-story building model with a hydraulic-type AMD.

• Geophysics and Geophysical Exploration
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• v.1 no.3
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• pp.155-160
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• 1998

EM tomography technique has been developed. The algorithm used the extended Born approximations for forward modeling and reconstructed a conductivity image by a smoothness constraint least squares inversion method. Observed data, the vertical components of secondary magnetic fields, were simulated with the 3-D integral equation code. The results showed that the location of anomalous body could be imaged very well, but conductivity of the body was lower than real one and the vertical resolution was much higher than the horizontal resolution.

• Computational Structural Engineering
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• v.11 no.1
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• pp.38-45
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• 1998

최근 국내외에서 활발히 개발되고 있는 지진격리 시스템은 원자력 발전소, 교량, 중요한 공공건물 등의 지진피해를 최소화하기 이하여 널리 적용되고 있다. 그리고 다른 방법에 비하여 경제성 및 효율성이 우수하기 때문에 관련 연구 및 응용이 활발히 진행되고 있다. 이에 따라 국내외에서 격리시스템의 비선형성과 구조물의 불연속성을 고려한 지진격리 구조물의 해석을 통한 거동을 규명하는 연구가 과거 수년간 활발히 진행되어 왔다. 당사(금호건설)는 상부하중 지지능력과 감쇠능력이 우수한 지진격리장치를 개발하였으며 지진격리장치를 설치한 교량의 지진해석을 수행하여 본 지진격리 시스템의 이론적 성능을 파악하였다. 본 수치해석은 CrayC94에 탑재된 비선형 해석에 뛰어난 것으로 알려진 ABAQU를 이용하였다. 본 지진격리 시스템은 적층고무받침(Laminated Rubber Bearing)과 PTFE 미끄럼받침으로 구성되어 있으며, 적층고무받침은 주로 복원력을 제공하며 PTFE 미끄럼받침은 상부하중을 지지하며 마찰감쇠를 제공하여 에너지를 소산하는 역할을 한다. 본 수치해석에서는 선형스프링과 마찰요소를 이용하여 각각을 모형화하였다. 개발된 지진격리 시스템이 주로 사용될 상판자중이 무거운 다경간 연속 PC Box Girder교를 모델교량으로 선택하여 해석을 수행하였으며 수치해석에 사용된 격리시스템의 사전에 수행된 동특성 실험결과를 활용하였다. 이러한 해석을 통하여 이론적 효율성을 파악할 수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.108-115
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• 1995

An efficient model for the dynamic analysis of caisson breakwaters under impulsive wave loadings is presented. The caisson structure is. regarded as a rigid body, and the rubble mound foundation is idealized as virtual added masses, springs, and dampers using the elastic half-space theory. The frequency-dependent hydrodynamic added mass and damping coefficients are considered by using the time memory functions and added mass at infinite frequency. To simulate the permanent sliding phenomenon of the caisson, the horizontal spring is modeled as a nonlinear spring with plastic behaviors. Comparisons with experimental results show that the present model gives fairly good results. Sensitivity analysis is performed for the relevant parameters affecting the dynamic responses of a caisson breakwater. Numerical experiments are also carried out to investigate the applicability to the prediction of permanent sliding distance and critical weight of the caisson.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.6
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• pp.482-493
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• 2016

The identification of modal damping of a segmented hull model with torsional response is difficult task due to the coupling of modal response. This is because the 1st and 2nd torsional vibration modes are closely spaced in frequency domain leading to the situation that the modal decomposition is difficult to achieve by simple band-pass filter. Present study applied several different modal decomposition methods to derive the damping ratio of different modes. The modal decomposition methods considered in this study are simple band-pass filter, Hilbert vibration decomposition, Wavelet transform and proper orthogonal decomposition. Coupled free decay signal obtained from the torsional hammering test on a segmented hull model was processed with four different methods and the derived damping ratios were compared with each other. Discussions also have been made on the pros and cons of the different methodologies.

• Journal of Korea Water Resources Association
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• v.43 no.4
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• pp.383-391
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• 2010

The groundwater recharge was assessed by using both SWAT and HELP models in Bocheong-cheon watershed. The SWAT model is a comprehensive surface and subsurface model, but it lacks the physical basis for simulating a soil water percolation process. The HELP model which has a drawback in simulating subsurface lateral flow and groundwater flow component can simulate soil water percolation process by considering the unsaturated flow effect of soil layers. The SWAT model has been successfully applied for estimating groundwater recharge in a number of watersheds in Korea, while the application of HELP model has been very limited. The subsurface lateral flow parameter was proposed in order to consider the subsurface lateral flow effect in HELP model and the groundwater recharge was simulated by the modified exponential decay weighting function in HELP model. The simulation results indicate that the recharge of HELP model significantly depends on the values of lateral flow parameter. The recharge errors between SWAT and HELP are the smallest when the lateral flow parameter is about 0.6 and the recharge rates between two models are shown to be reasonably comparable for daily, monthly, and yearly time scales. The HELP model is useful for estimating groundwater recharge at watershed scale because the model structure and input parameters of HELP model are simpler than that of SWAT model. The accuracy of assessing the groundwater recharge might be improved by the concurrent application of SWAT model and HELP model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5A
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• pp.887-899
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• 2006

The aim of this study is to investigate a correlation between fundamental data on aerodynamic characteristics of bridge girder cross-sections, such as aerodynamic force coefficients and flutter derivatives, and their aerodynamic behaviour. The section model tests were carried out in three stages. In the first stage, seven deck configurations were studied, namely; Six 2-edge girders and one box girder. In this stage, changes in aerodynamic force coefficients due to geometrical shape of girders, incidence angle of flow, wind directions and turbulence intensities were studied by static section model tests. In the second stage, the dynamic section model tests were carried out to investigate the relativity of static coefficients to dynamic responses. And finally, the two-dimensional (lift-torsion) aerodynamic derivatives of three bridge deck configurations were investigated by dynamic section model tests. The aerodynamic derivatives can be best described as a representation of the aerodynamic damping and the aerodynamic stiffness provided by the wind for a given deck geometry. The method employed here to extract these unsteady aerodynamic properties is known as the initial displacement technique. It involves the measurement of the decay in amplitude with time of an initial displacement of the deck in heave and torsion, for various wind speeds, in smooth flow. It is suggested that the proposed aerodynamic force coefficients and flutter derivatives of bridge girder sections will be potentially useful for the aeroelastic analysis and buffeting analysis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.40-50
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• 1994

For an accurate prediction of the temperature field induced by heated water discharged into a shallow crossflow, a two-dimensional near-field numerical model is developed. It is based on a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate are added to those of a 2-equation turbulence model which cannot give the information of the thermal time scale ratio. Vertical diffusion is also considered by including buoyancy production and turbulence heat flux terms. The developed model is applied to a steady flow in an open channel with simple geometry and the results are compared with existing experimental data and those of the already established 2-equation turbulence model. Numerical results of the model agree with the experimental data better than those of the 2-equation model. The present model also simulates quite adequately the physical characteristics of thermal discharge in the jet entrainment and stable regions.