• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.3
• /
• pp.259-266
• /
• 2011

The transient vibration test and synchronized human excitation is performed for low-rise concrete buildings and their identified natural frequency, damping ratio, and mode shape are compared. Form the identified dynamic parameters, it was found that the damping ratio obtained through the synchronized human excitation test is greater than those obtained from the transient vibration test. However, the mode shapes of the first mode are not significantly different regardless of the test method. Further, the stiffness of the interior brick partition considerably affect the stiffness of the entire building such that the first natural mode of rectangular shaped building occurred in the longitudinal direction rather than transverse direction.

• Journal of Korean Association for Spatial Structures
• /
• v.11 no.1
• /
• pp.67-75
• /
• 2011

The present work investigate the effect of sound reinforcement systems on the acoustics of a large dome stadium using a computer simulation. The acoustics of a dome stadium was predicted analyzed by varying room absorption, as well as the configuration of speakers including their directivity, installed height, and numbers. It was found that both D50 and RASTI were improved by increasing room absorption. Larger EDTs were observed according to the increase of room absorption at mid and high frequencies. On the other hand, RT did not show any significant correlation with the changes in room absorption, which might be the effect of a forced linear fitting for non -linear energy decay process. With respect to the speaker configuration, the speech intelligibility of a sound reforcement system installed at higher placed more relied upon their directivity rather than room absorption, Also, lower placing of speakers was found to be effective in decreasing RTs regardless of room absorption.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.6
• /
• pp.1-10
• /
• 2019

The wave motion inside the nozzle is known as one of the major damping elements of the rocket's combustion instability by it's aeroacoustic effects that result from the flow passage through the nozzle throat. These effects can be quantitatively evaluated by the nozzle admittance. In this study, one-dimensional linearized Euler equation was adopted to calculate the nozzle admittance, and trend analysis was performed depending on the nozzle's main design variables. As a result, when nozzle converging part shortens, it is verified that the frequency dependency of the nozzle admittance is decreased due to the widened frequency range with lowered longitudinal nozzle admittance. Also, admittance estimation using the short nozzle theory is not appropriate when the first tangential mode of the pressure perturbation arises.

• Journal of the Korean Geosynthetics Society
• /
• v.10 no.2
• /
• pp.21-28
• /
• 2011

Several theoretical soil nonlinear models to predict damping ratio, which is one of the typical dynamic properties of soils, it is impractical to predict damping ratio. The resonant column and torsional shear test(RC-TS) is used to represent the dynamic behavior of soils from intermediate to medium shear strains. A limitation of RC-TS is measure precise shear strain in large strains and the modified equivalent radius($R_{eq}$) was obtained using both modified hyperbolic model and Ramberg-Osgood model. Bonneville clays were tested using RC-TS test to obtain rotation and torque. The measured rotation and torque were then compared with calculated rotation and torque using curve-fitting method. Then, the nonlinear soil model parameters were obtained and the equivalent radius was calculated using the model parameters.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.6
• /
• pp.794-801
• /
• 2012

Finite Element Method is a strong tool to analyse static and dynamic problem of a structure. FEM is a good method for static problem, but for dynamic problem there are some differences between real phenomena and analyzed phenomena. Therefore some modifications are needed to identify two results. In this paper authors propose a genetic algorithm method 1) to adjust dimensions of plate for identifying natural frequencies, 2) to fit amplitude of FEM Frequency Response Function(FRF) onto it of real FRF. Analysis by raw FEM data gave questions if the results were for the same object. By only adjusting Young's modulus much better accordances were obtained, but limitation existed still. Very good agreements were achieved by shape modification and damping coefficient identification.

• Journal of the Korean Geophysical Society
• /
• v.3 no.3
• /
• pp.193-200
• /
• 2000

The attenuation characteristics($Q^{-1}$) are important factors representing the physical properties of the Earth interiors, and are essential for the quantitative prediction of strong ground-motion. Based on 156 earthquakes including 76 single-station record on the seismic station located Deok-jung Ri, southeastern Korea, we made the simultaneous measurement of P and S wave attenuation($Q_P^{-1}\;and\;Q_S^{-1}$) by means of extended coda-normalization method. Estimated $Q_P^{-1}\;and\;Q_S^{-1}$ decreased from $1{\times}10^{-2}\;and\;9{\times}10^{-3}$ at 1.5 Hz to $6{\times}10^{-4}\;and\;5{\times}10^{-4}$ at 24 Hz, respectively. This can be expressed by $Q_P^{-1}=0.01\;f^{-1.07}\;and\;Q_S^{-1}=0.01\;f^{-1.03}$ which indicate strong frequency dependence.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.16 no.2
• /
• pp.25-33
• /
• 2012

To examine the performance of a thin plate damper attached to coupling beam of bearing wall system, 5 specimens were designed with the variable parameters of the thickness and length of a thin steel plate, which was constructed and tested with a lateral load with up to a 5% drift ratio. The result was that the total amount of the energy dissipation of the specimen with the thin plate damper was greater than that of the standard RC specimen, and the plate buckling and plastic deformation could be seen in steel plate. The shorter the length of the damper, the higher was the lateral resistant force, but there was no apparent increase in the energy dissipation. By comparison of the experiments with the elastic buckling analysis, it was shown that the buckling force from the analysis could properly estimate the maximum value of the linear elastic range.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.5
• /
• pp.27-36
• /
• 2013

Linear stability analysis for combustion instability within a cylindrical port of solid rocket motor has been conducted. The analysis of acoustic energy has been performed by a commercial COMSOL code to obtain the mode function associated to each acoustic mode prior to the calculation of stability alpha. An instability diagnosis based on the linear stability analysis of Culick is performed where special interests have been focused on 5 stability factors(alpha) such as pressure coupling, nozzle damping, particle damping and additionally, flow turning effect and viscous damping to take into account the flow and viscosity effect near the fuel surface. The instability decay characteristics depending on the particle size is also analyzed.

• Journal of Aerospace System Engineering
• /
• v.15 no.1
• /
• pp.7-18
• /
• 2021

A semi-active MR damper landing gear is a damper that generates a fluid damping force and a magnetic field control damping force when the MR fluid passes through annular flow paths. In the case of MR fluid passing through annular flow paths, an incompletely developed flow inevitably occurs, causing an error in calculating damper inner forces including the fluid damping force. This error results in an inaccurate design of damper structural parameters and control gain selection, resulting in deterioration of dynamic characteristics and shock absorption performance of the landing gear. In this paper, we derived a mathematical model of an MR damper landing gear considering additional damping force generated in the entrance region of annular flow paths of the MR damper. If the mathematical modeling derived from this paper is applied to the design and optimization process of an MR damper landing gear, excellent performance of the MR damper landing gear is expected.

• Journal of the Korean Society of Radiology
• /
• v.16 no.7
• /
• pp.927-934
• /
• 2022

This study attempted to find out the degree of agreement between ultrasound image findings along with analysis of attenuation index and scatter distribution index values within tissues through quantitative measurement analysis using liver ultrasound images. From August 2022 to October 2022, liver ultrasound was performed on 45 patients who were suspected of having fatty liver and who received a prescription for liver ultrasound. As a result of the study, as a result of analyzing the agreement between the ultrasound image findings and the tissue attenuation index, the Kappa value was 0.82 (p<0.05), showing a very high agreement between the two examination methods. In addition, as a result of the agreement analysis between the ultrasound image findings and the scatter distribution index in the tissue, the Kappa value was 0.642 (p<0.05), showing high agreement between the two examination methods. At the time of fat liver prediction, the use of liver ultrasound findings and quantitative ultrasonography techniques, such as intra-tissue attenuation index and intra-tissue scatter distribution index, may be helpful in determining the degree of progression of fatty liver patients.