• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.582-589
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• 2006

Shear wane velocity is important property for grasping the dynamic characteristics of material. It is has been used in various fields such as non-destructive testings of structures, seismic analysis of geotechnical structures and maintenance of concrete structure, and etc. Usually, shear wave velocities of rock cores and concrete cylinders are determined by free-free resonance tests, Shear wave measurement in free-free resonance tests is not straightforward, as compared with rod wave and flexural wane measurements. In This study, a new technique using resonance features of flexural and shear waves were proposed in which the nodal points for the fundamental mode of flexural waves were employed to generate and measure the shear waves with the flexural waves minimized. The real measurements for aluminum cylinders proved validity and reliability of the proposed algorithm. In addition to the proposed algorithm, the effects of material properties on elastic-wave velocities in resonance measurements were also studied. In summary, a new framework of the resonance measurements for shear-wave velocity determination was established, based on the results of this thesis.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.353-360
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• 1998

Dynamic measurements are used rather sparingly to determine the elastic moduli of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are : 1) elastic moduli can be consistently determined by laboratory seismic testing. 2) nonlear deformation characteristic of rock cores was tentatively proposed with variation in elastic modulus with strain.

• Journal of the Korean Society of Tobacco Science
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• v.29 no.2
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• pp.146-151
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• 2007

Gas phase and particulate phase radicals in mainstream cigarette smoke were determined Electron Spin Resonance(ESR) spectroscopy. The free radicals in particulate phase have been investigated by benzene extract of Cambridge Filter Pad containing the smoke condensate. Spin trapping method in conjunction with ESR was used to investigate free radicals in the gas phase of cigarette smoke. Several analytical experiments were conducted in order to determine the optimal conditions for maximum signal intensities and reproducibility of results. All the tests were optimized and normalized using the University of Kentucky 2R4F reference cigarette. The optimal conditions were 0.6 mL for analysis volume of ESR, $4{\sim}5\;mL$ for collection volume of spin-adducts, and PBN for quantification of free radicals in gas phase. The radical levels of Kentucky 2R4F cigarettes were found $2.18{\times}10^{14}\;spins/cig.$ and $2.10{\times}10^{15}\;spins/cig.$ in gas phase.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.460-470
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• 2015

In general ships and FPSOs, roll damping is very small and consequently roll motion is very large at the roll resonance frequency. Proper evaluation of the roll damping coefficient at the resonance frequency is an important task in the study of roll motion and usually it is done by the analysis of free roll decay tests. The relative decrement method based on energy relation has been used mainly for the evaluation of roll damping coefficient from the roll decay test so far. As another method, the logarithmic decrement method based on equivalent linear decay assumption can be used for the same purpose and it is relatively simple. In this paper, both of the relative decrement method and the logarithmic decrement method are used for the evaluation of roll damping coefficient including quadratic damping from the free roll decay tests, and their results are cross-checked for verifying the obtained damping coefficients. Through applications to a box-type floating body equiped with bilge keels, it is shown that the two methods give almost the same damping coefficients in a practical view point and the cross-check of their results is to be a good tool to prevent a possible error. And also the quantitative effects of the bilge keels on the roll damping of box-type floating body are shown and discussed.

• The Journal of Engineering Geology
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• v.24 no.3
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• pp.363-372
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• 2014

Granite rock is reported to have three orthogonal anistoropic planes i.e., rift, grain induced by microcrack characteristics and mineral arrangement. We investigated the influence of thus fabric anisotropy in granite on elastic wave properties using free-free resonance test to obtain unconstrained compression wave velocity, shear velocity, Poisson ratio and damping ratio. As a result, Rod wave velocity is more dependent on anisotropy of granite due to microcrack distribution than shear wave velocity. In addition, anisotropy of Poisson ratio and damping ratio is also observed with respect to three anisotropic planes.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.95-100
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• 1999

Dynamic measurements are used rather sparingly to determine the elastic modull of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are: 1) elastic modull can be consistently determined by laboratory seismic testing. 2) nonlinear deformation characteristics of rock cores was tentatively proposed with variation in elastic modulus with strain.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.75-80
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• 1998

Dynamic measurements are used rather sparingly to determine the elastic moduli of rock cores and modulus values are not much utilized in design practices. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 time) than those determined statically. This paper presents results from dynamic and static tests on rock cores. One of the findings is that both moduli determined by statically and dynamically on a solid rock core agrees well at the same-strain. At different strain levels, the ratio between dynamic and static modult widely varies depending upon micro-cracks and discontinuites of rock cores.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.9
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• pp.707-714
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• 2016

This paper describes analysis results of vibration characteristics and modal test for a small-scale quad-rotor drone. The rotor arm has a slender body with a propeller and motor at its tip. Rotor system generates excitation for an unbalanced mass. Therefore, the drone platform is involved in the possibility of resonance. For advance identification of the possibility of resonance, confirmation of eigen-mode being closest to the propeller operation range is necessary. Material properties of CFRP tubes used for the rotor arm were acquired by finding the natural frequency based on Rayleigh method. A simplified quad-rotor FE model consisting of rotor arm assembly with tip mass was built to perform numerical analysis, and a free-free boundary condition was applied to provide flight status. Modal tests for the actual platform with impact hammer instrument were performed to verify analysis results. Separation margin from hazardous eigen-mode was checked on the propeller operation range.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.122-132
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• 2000

A simplified modeling approach of forced vibration for occupied car seats was demonstrated by using a mathematical model presented in 'Free Vibration of Car seat and Mannequin System' nonlinear and linear equations of motions were rederived for forced vibration and the transfer function was used to calculate the frequency response function. The experimental apparatus were set up and hydraulic shaker was used to obtain the system responses. Through the tests mannequin's head had a lot of problems and the responses with a head and without a head were measured. To explore the effects of linear dampings and friction moments at the joints linear analyses were performed. New sets of linear spring and damping coefficients and torsional dampings at the joints were calculated through parameter study to match up with experimental results. Good agreement between experimental and simulation frequency response estimates were obtained both in terms of locations of resonances and system deflection shapes at resonance indicating that this is a feasible method of modeling seated occupants.

• Earthquakes and Structures
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• v.14 no.6
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• pp.567-576
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• 2018

This manuscript introduces a new damping device which is composed of a water tank and a pendulum. The new damping device can be tuned to multiple frequencies. In addition, it has a higher energy dissipation capacity when compared with the conventional Tuned Liquid Dampers (TLDs). In order to evaluate the efficiency of this new damping device a series of free vibration and forced vibration tests were conducted on a scaled down single-story one-bay steel frame. Two different configurations were studied for the mass of the pendulum that included a completely and a partially submerged mass. It was observed that the completely submerged configuration led to 44% higher damping ratio when compared with the conventional TLD. In addition, the completely submerged configuration reduced the peak displacement response of the structure 1.6 times more than the conventional TLD. The peak acceleration response of the structure equipped with the new damping device was reduced twice more than the conventional TLD. It was also found that, when the excitation frequency is lower than the resonance frequency, the conventional TLD performs better than the partially submerged configuration of the new damping device.