• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.6 no.6
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• pp.32-41
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• 1992

In this paper, an advanced Pulse Width Modulation Inverter strategy for driving a variable-speed induction motor is introduced. A switching pattern making use of the near-proportionality of voltage and frequency in AC machines operating with constant flux was computed. At low magnitudes and ow frequencies of the fundamental, many more harmonics are eliminated than at high magnitudes and frequencies. In order to keep the inverter switching frequency constant over the output frequency range, the chopping frequency is diminished as the frequency of the fundamental increases. Using these modulation strategy, the harmonics components of PWM inverter are efficiently eliminated.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.26-33
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• 2002

This study was undertaken to obtain the fundamental knowledges on the weld deflects and it's realtime monitoring method. The paper describes the results of high speed photography, acoustic emission (AE) detection and plasma light emission (LE) measurements during $CO_2$ laser welding of STS 304 stainless steel and A5083 aluminum alloy in different welding condition. The characteristic frequencies of plasma and keyhole fluctuations at different welding speed and shield gases were measured and compared with the results of Fourier analyses of temporal AE and LE spectra, and they had considerably good agreement with keyhole and plasma fluctuation. Namely, the low frequency peaks of AE and LE shifted to higher frequency range with the welding speed increase, and leer the argon shield gas it was higher than that in helium and nitrogen gases. The low frequencies dominating in fluctuation spectra of LE probably reflect keyhole opening instability. It is possible to monitor the weld bead deflects by analyzing the acoustic and/or plasma light emission signals.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1274-1274
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• 2001

An anharmonicity is a fundamental quantity shaping the potential for stretching OH vibration in phenol and its derivatives. The phenomenon is examined both by experimental and theoretical methods. FT-IR and NIR spectra of series of phenols derivatives were measured in the range of fundamental and first two Overtones of $_{s}(OH)$ Vibrations in $CCl_4$ solutions. The electronic influence of substituents on the analyzed frequencies is discussed and correlated with $pK_{a}$ parameters. Ab initio MP2/6-31G(d,p) and B3LYP/6-31G(g,p) calculations of the potential for proton movement in OH group were performed. Equilibrium structures were also determined. The frequencies of fundamental and overtones were calculated by Numerov-type procedure. The results of calculations are compared with the experimental data. The best linear correlations were obtained for the results of MP2/6-31G(d,p) calculations. It was shown that some structural parameters are especially sensitive on substitution. The linear correlations were found between those parameters and spectroscopic data. The results of calculation are compared with available crystallographic data.

• The Journal of the Acoustical Society of Korea
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• v.19 no.8
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• pp.22-25
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• 2000

In this paper, we examine the characteristic of samulnori by the sound analysis techniques. Four instruments of samulnori are constituted with the dual principle of the negative and positive (the male and female) which mean the harmony of each instruments high and low sounds. These sounds are covered the audible whole sounds. Since the fundamental frequencies of jing and janggu sounds are similar to the fundamental frequencies of male and female speech respectively, we feel the affection when we hear the sounds of jing and janggu. Additionally, since human feels the sound not only by ears, but also by the vibration to the skin, the put jing and janggu have the remarkable characteristic of the vibration.

• Current Optics and Photonics
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• v.1 no.4
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• pp.278-283
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• 2017

We theoretically study the dynamics of water tetramer in intense femtosecond laser pulses with different frequencies. The simulations are carried out by incorporating the molecular dynamics method non-adiabatically into the time-dependent local-density approximation (TDLDA-MD). Three typical scenarios of water tetramer including the normal vibration with enlarged OH bonds, free OH bonds breaking and the pure Coulomb explosion are presented by investigating the electronic and ionic dynamics. The result indicates that the ionization is enhanced and the corresponding fragmentation effect as well as the damping of the dipole moment are found more notably when increasing the laser frequency especially when the frequency falls in the resonant region of the absorption spectra. The study of the level depletion reveals that the ratio of the emission amount from different levels can be controlled by changing the laser frequency referring to the Keldysh parameter.

• The Journal of the Acoustical Society of Korea
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• v.27 no.4
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• pp.171-177
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• 2008

In this paper, we have measured the fundamental properties of chime stone for Pyeongyeong. The properties are measured by wave propagation in the stone without destroying the stones, the measured properties are the chime stone density, natural frequencies of extensional wave and bending wave, and Young's modulus which is calculated by the measured properties. To find a value for Young's modulus, the fundamental frequencies which are obtained through spectrum analysis of extensional wave and bending wave are used. We calculated Young's modulus of chime stone by theoretical study and measurement on extensional wave and bending wave of the beam. As a result, we obtained Young's modulus by the fundamental frequencies of extensional wave and bending wave which deviation is within 2%.

• Smart Structures and Systems
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• v.25 no.4
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• pp.501-514
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• 2020

This article presents a comprehensive model to investigate a free vibration and resonance frequencies of nanostructure perforated beam element as nano-resonator. Nano-scale size dependency of regular square perforated beam is considered by using nonlocal differential form of Eringen constitutive equation. Equivalent mass, inertia, bending and shear rigidities of perforated beam structure are developed. Kinematic displacement assumptions of both Timoshenko and Euler-Bernoulli are assumed to consider thick and thin beams, respectively. So, this model considers the effect of shear on natural frequencies of perforated nanobeams. Equations of motion for local and nonlocal elastic beam are derived. After that, analytical solutions of frequency equations are deduced as function of nonlocal and perforation parameters. The proposed model is validated and verified with previous works. Parametric studies are performed to illustrate the influence of a long-range atomic interaction, hole perforation size, number of rows of holes and boundary conditions on fundamental frequencies of perforated nanobeams. The proposed model is supportive in designing and production of nanobeam resonator used in nanoelectromechanical systems NEMS.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.125-130
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• 2003

The aim of this paper is to investigate the dynamic characteristics of ancient stone bridges in Korea and to find the factors influencing their natural frequencies. For this end, on-site free vibration tests were performed for 18 stone arch bridges and one ancient ice storage composed of 4 arches. Test results revealed that the vertical fundamental frequencies were in the range of 10Hz to 45Hz. The damping ratios estimated from the records of free vibration tests showed a wide variety of values, that is, from 0.02 to 0.134. It has been known that the natural frequencies of stone arch bridges are mainly governed by their arch spans. Test results reveal that the presence of spandrel walls and the use of mortar for joints are also important factors influencing the natural frequencies of stone arch bridges.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.1
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• pp.57-65
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• 1992

The main purpose of this paper is to present both the natural frequencies and mode shapes of tapered beams under tensile axial force. The differential equation governing planar free vibration for tapered beams under tensile axial force is derived as nondimensional form. The three kinds of cross sectional shape are considered in differential equation. The Runge-Kutta method and 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, clamped-clamped and constraints are applied in numerical examples. The lowest four nondimensional natural frequencies are reported as the function of nondimensional tensile axial force. The fundamental natural frequencies are presented when section ratios and nondimensional axial forces are varied. The effects of cross sectional shapes are reported and some typical mode shapes are also presented.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.109-115
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• 2023

In this paper, frequencies of zigzag structure of carbon nanotubes isinvestigated based on Donnell shell theory. These tubes are wrapped with the ring supports in the axial direction. The fundamental frequency curves displayed in article show the dependence of vibrations attributes to zigzag single walled carbon nanotubes. Various zigzag indices are introduced against the variation of length to predict the vibration. Also, the influence of ring supports is sketched with proposed structure for frequency analysis. The frequencies of zigzag tube decreases as the length increases. It is observed that the frequencies decreases with ring support and have higher frequencies without ring. The problem is formulated using Partial Differential Equation. Three expressions of modal deformation displacement functions is used for the elimination of temporal variation to form the solution in the eigen from. For the stability of present study the results are compared with experimentally and numerically in the open text.