• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.101-109
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• 1987

The governing differential equations for the free vibration of general arch are derived including the effect of rotary inertia in addition to the usual actions. These differential equations are applied to the sinusoidal arch and the numerical methods are developed to analyze these equations. A trial eigenvalue method and the Runge-Kutta method are used to determine the natural frequencies and to perform the integration of the differential equations, respectively. A detailed studies are made of the lowest three vibration frequencies for hinged arches with the span length equal to 10 m. The effect of the rotary inertia is analyzed. And as the numerical results the frequency versus the rise of arch and the radius of gyration are presented in figures.

• Explosives and Blasting
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• v.42 no.3
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• pp.49-57
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• 2024

Pre-fracturing is the blasting method to weaken the rock mass prior to the main excavation. This study aims to evaluate the effectiveness of pre-fracturing by using half the explosive charge typically employed in conventional blasting designs. Field tests conducted at a quarry in Gapyeong showed that noise levels were reduced by 2.7 dB due to the decreased amount of explosive per blast hole, and vibration levels were controlled to the precision vibration control blasting standard. Rock weakening was confirmed through induced cracks observed on the surface and core samples, and it was noted that the weakening effect of the blasting decreased as the burden increased. The vibrations from conventional blasting were found to be lower than those from pre-fracturing. This was attributed more to the geological conditions, such as joints, rather than the blasting design factors like explosive amount, burden, and the number of free face.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.3
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• pp.37-46
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• 1991

A method is developed for solving the natural frequencies and mode shapes of linearly variable tapered beams. The governing differential equation for the tapered beam is derived. Three kinds of cross sectional shape are considered in differential equation. The Runge-Kutta method and the determinant search method are used to perform the integration of the differential equation and to determine the natural frequencies, respectively. The hinged-hinged, hinged-clamped, damped-clamped and free-damped end constraints are investigated in numerical examples. The lowest four nondimensional natural frequencies are obtained as functions of $d_b/d_a$. ratio. The effects of end constraints and cross sectional shapes on frequencies are analyzed and typical mode shapes are also presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.481-488
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• 2003

A fluid-structure-isolator interaction program was developed in this study. The behavior of liquid regions are simulated by the boundary element method, and then the technique of analyzing the free surface motion in time domain is developed by using the nonlinear free surface boundary condition(NFBC) and the condition of interface between the structure and the fluid. Structure regions are modeled by the finite element method. In order to construct the governing equation of the fluid structure interaction(FSI)problem in time domain, the finite elements for a structure and boundary elements for liquid are coupled using the equilibrium condition, the compatibility condition and NFBC. The isolator is simulated by equation proposedin 3D Basis Me. In order to verify the validity and the applicability of the developed fluid- structure -Isolator interaction program, The horizontal forced vibration analysis was performed. The applicability of the developed method is verified through the artificial seismic analysis of real size liquid storage tank.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.6 no.1
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• pp.1-16
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• 1996

This study was conducted at an automobile assembly line located in Kyonggi-do, Korea from January 16 to February 28, 1995. The purposes of this study were to assess worker exposures to hand-arm vibration and the performance of gloves for reduction of vibration. The exposure to vibration was measured using to the ISO 5349(1986) method. Vibration acceleration and frequency spectra for each tool were determined on-line replicating actual working conditions and analyzed together with exposure time for evaluating individual worker exposure. Eight pneumatic hand tools, 60 workers exposured to hand-arm vibration, and three pairs of gloves were involved in this study. Results are summarized as follows. 1. Dominant frequencies of vibration for all tools(n=8) measured in this study ranged from 250 Hz to 800 Hz. 2. There was no significant correleration between dominant frequencies and free running speed (p>0.05). 3. Total predicted exposure times of using impact, hammer type did not exceed 40 minutes, but metal finish task, using grinder and sander exceeded 40 minutes. Total exposure time affected significantly the frequency-weighted, 4 hr equivalent acceleration. 4. Predicted prevalence and observed exposure period data were compared in workers(n=60), according to ISO 5349. In this results, 23(50.0 %) and 24(48.07 %) persons exceeded the mean latency periods for vibration-induced white finger(VWF) at 10 % (n=46) and 50 % (n=52) standards, respectively. On the basis of ISO equation, mean latent periods for VWF were 3.23, 4.72 years at 10 %, 50 % standards, respectively. 5. Reduction of vibration by gloves was evaluated. Since impact pneumatic tools produced low frequency vibrations, conventional gloves did not provide any protection. Gloves A and C amplify somewhat the signal at frequency below 400 Hz; the attenuation increases progressively by frequency to reach 18 dB ($7.94{\times}10^{-6}m/s^2$) at 1,000 Hz, slightly worsening Glove B did not provide any protection and made the situation slightly worse. However, since they make the hands warm, the occurrence of vibration-induced white fingers may be reduced.

• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.600-606
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• 2007

3D finite element analyses of a corrugated steel web girder and a steel truss web girder are conducted to investigate the static and dynamic behaviour of the hybrid girders. And the analyses results are compared with those by the equivalent beam theory. The equivalent theory is a theory that all section properties of a truss structure are replaced by section properties of a beam including a shear coefficient. When applying the equivalent beam theory, the shear coefficient of the corrugated steel web girder is estimated as the area ratio of flange section to web section and that of the steel truss web girder is calculated by the equation proposed by Abdel. Static deflections and natural frequencies by 3D finite element analyses and those by the equivalent beam theory are in good agreement.

• Journal of Korean Association for Spatial Structures
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• v.9 no.1
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• pp.61-68
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• 2009

This paper is concerned with the investigation of the structural behavior of waffle structure. Parametric variation on waffle floor thickness, main beam depth and column sizes are imposed to study the effects on mode shapes and natural frequencies of waffle structures. Comparisons between FEM models using shell and 3D-solid elements have also been made. The analysis result has shown that the mode frequencies increase with i) increase in main beam depth at level 2 and ii) decrease in waffle slab thickness at level 3. Both 3D and 2D model shown similar mode shapes. Besides, there is a consistent difference in mode frequencies between 3D and 2D model ranging from 25% to 36%.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.177-184
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• 2002

Large amplitude sloshing can occur in contained fluid region due to the seismic ground motion. Also, The pressure by large amplitude sloshing damages the connections between the wall and roof of a fluid container and causes outflow of contained fluid. Therefore, to predict the dynamic behavior accurately, three dimensional analysis with the nonlinear boundary condition must be performed. In this study, the numerical solution procedure is developed using the boundary element method with the Lagrangian particle approach. In order to demonstrate the accuracy and validity of the developed method, the fluid motion for a free oscillation with small amplitude and a forced vibration are analyzed. And the numerical results are compared with the linear theory results and the previous studies with the nonlinear boundary condition.

• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.19-27
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• 2003

This paper presented an experimental modal analysis of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the Rayleigh-Ritz method and compared with the experimental results. Good agreement was obtained between the analytical solution and experimental result. The experimental results in water showed that the mode shapes are not sensitive to the depth of submergence. The natural frequencies were shown to decrease drastically once the perforated plates come in contact with water. However, the natural frequencies decrease with the depth of submergence until a certain depth is reached, and become the asymptotic values beyond this depth of submergence. The depth of submergence did not affect the damping ratio greatly.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.47 no.3
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• pp.86-94
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• 2024

In this study, an attempt was made to approximate the main characteristic values of Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (= BNKT) depending on the content of Fe₂O₃ additives, aiming to approach the values of lead(Pb) piezoelectric ceramic materials (PZT). Specifically, when the piezoelectric coefficient (d₃₃) value of lead(Pb) piezoelectric ceramic material (PZT polycrystalline ceramic powder) is 300[pC/N] or higher, it is applied for hard purposes such as ultrasonic welding machines and cleaning machines, and when it exceeds 330[pC/N], it is applied for soft purposes like piezoelectric sensors. In this study, research and development were conducted for devices with a piezoelectric coefficient (d₃₃) of 300[pC/N] or more for actuators. For this purpose, K⁺ exceeding 0.02 to 0.12 mol% was added to (Na_0.78K_0.22)_0.5Bi_0.5TiO₃ to analyze structural changes due to K⁺ excess, and (Na_0.78K_0.22)_0.5Bi_0.5TiO₃ + 8mol% K₂CO₃ Ti⁴⁺ was substituted with Fe³⁺ to manufacture lead-free piezoelectric materials. As a result, ceramics with Fe³⁺ substitution at x = 0.0075 yielded an average value of d₃₃ = 315[pC/N]. Furthermore, for ceramics with Fe³⁺ substitution at x = 0.0075, the average values of maximum polarization (P_max), residual polarization (P_rem), and coercive field (E_c) were found to be 39.63 μC/cm², 30.45 μC/cm², and 2.50 kV/mm, respectively. The reliable characteristic values obtained from the research results can be applied to linear actuator components (such as the zoom function of mobile cameras, LDM for skin care, etc.) and ultrasonic vibration components.