• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.738-740
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• 2003

A lot of R&D on the diagnosis of stator winding insulation for large rotating machines has been carried out since the 1970s. The on-line partial discharge measurement has proved to be an effective technique in the evaluation of the state of stator insulation in high voltage rotating machines. It is well known that if the discharge pulses propagate through the winding conductor, they are attenuated and delayed. In the present study, to investigate the attenuation and the time delay of discharge pulses through the winding conductor, a series of tests were conducted using a model coils and slot. Thus it could be concluded that while the high frequency pulse propagates in radiation or end-winding coupling modes, the low frequency one does in a series mode through the coil conductor.

• Advances in concrete construction
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• v.13 no.3
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• pp.255-264
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• 2022

Vibration is expected to occur in microtubules as tubular heterodimers. They oscillate like electric dipoles. Several research studies have estimated a frequency of vibration using the orthotropic model, a beam or rod like models and shell models, considering the surface forces. The effects of body forces on the dynamics of the microtubules were not yet taken into account. This study seeks to capture the body force effects on the vibration modes generated and on the corresponding frequency for microtubules. An orthotropic elastic shell model for the structural details of microtubules is used for the analysis. The tests are conducted out for microtubules, exposed to electro-magnetic and gravitational forces, the transverse vibration, radial mode vibration, and axial mode of vibration have accomplished. We therefore, evaluate and compare microtubules' frequencies with prior results of vibration frequency without the effects of body force.

• Advances in materials Research
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• v.12 no.4
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• pp.309-330
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• 2023

The humid thermal vibration characteristics of a nonhomogeneous thermopiezoelectric nonlocal plate of polygonal shape are addressed in the purview of generalized nonlocal thermoelasticity. The plate is initially stressed, and the three-dimensional linear elasticity equations are taken to form motion equations. The problem is solved using the Fourier expansion collocation method along the irregular boundary conditions. The numerical results of physical variables have been discussed for the triangle, square, pentagon, and hexagon shapes of the plates and are given as dispersion curves. The amplitude of non-dimensional frequencies is tabulated for the longitudinal and flexural symmetric modes of the thermopiezoelectric plate via moisture and thermal constants. Also, a comparison of numerical results is made with existing literature, and good agreement is reached.

• Geotechnical Engineering
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• v.13 no.1
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• pp.111-122
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• 1997

The calculation of phase velocities in Spectral-Analysis -of-Surface -Waves (SASW) meas urements requires unwrapping phase angles. In case of layered systems with strong stiffness contrast like a pavement system, conventional phase unwrapping algorithm to add in teger multiples of 2n to the principal value of a phase angle may lead to wrong phase volocities. This is because there is difficulty in counting the number of jumps in the phase spectrum especially at the receiver spacing where the measurements are in the transition Bone of defferent modes. A new phase interpretation scheme, called "Impulse Response Fil traction ( IRF) Technique," is proposed, which is based on the separation of wave groups by the filtration of the impulse response determinded between two receivers. The separation of a wave group is based on the impulse response filtered by using information from Gabor spectrogram, which visualizes the propagation of wave groups at the frequency -time space. The filtered impulse response leads to clear interpretation of phase spectrum, which eliminates difficulty in counting number of jumps in the phase spectrum. Verification of the IRF technique was performed by theoretical simulation of the SASW measurement on a pavement system which complicates wave propagation.opagation.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.301-307
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• 2002

The propagation characteristic of an optical waveguide was investigated by measuring with a near-field scanning optical microscope (NSOM) the evanescent field formed at the neighbor of its core-cladding interface. For this purpose, the NSOM system was developed specially as a form of Photon scanning tunneling microscope. The evanescent field distributions of several channel waveguides were measured at the wavelength of 1550 ㎚, and the usefulness of the system was verified by comparing experimental results with simulation results. In particular, the interference phenomena of the guided modes during their propagation along a multimode channel waveguide could be observed directly from the measured evanescent field distribution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.71-81
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• 2008

This paper proposes a spectral element which can represent dynamic responses in high frequency domain such as Lamb waves on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by piezoelectric layer (PZT layer) bonded on a base plate. In the two layer beam model, a PZT layer is assumed to be rigidly bonded on a base beam. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with electro mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are formulated through equations of motions converted into frequency domain. A detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through comparison results with the conventional 2-D FEM and the previously developed spectral elements.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.3
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• pp.209-214
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• 2017

A plane-wave incident upon asymmetric multi-layered dielectric grating as well as symmetric grating structure generates space harmonics. Selected space harmonics among those harmonics can undergo strong resonance scattering variations known as GMR(guided-mode resonance). In this paper, to clarify these effects, the field propagation and dispersion curve inside the grating region are analyzed by using a rigorous equivalent transmission-line theory(RETT) based on eigenvalue problem. The results show that, at the peak of a scattering resonance, the reflected mode is almost identical to a leaky wave that can be supported by the grating structure. Thus, it confirms to be occurred GMR effect associated with the free-resonant character of leaky waves at asymmetric multi-layered dielectric gratings. Quantitative simulation results illustrating the behavior of typical gratings are given, and the special case of normal incidence is discussed for TE and TM modes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.278-281
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• 2012

Numerical studies were performed to investigate the three-dimensional front structure and dynamics features of detonation wave propagating in a circular tube such as Pulse Detonation Engine (PDE). By carrying out a series of parametric study using one step irreversible Arrhenius kinetics model, mechanisms of the three-dimensional front structure were investigated for two-, three-, four and six-cell mode detonations. A comparison with two-dimensional results, the effects of slapping transverse waves in radial direction were confirmed. In the all muti-cell modes, the detonation front structures and smoked-records on the wall are formed by the propagation of transverse waves along the wall in clockwise and counter-clockwise while the slapping move in radial direction. And the strength of reflected waves on the curved wall is changed by the multi-dimensional confinement effect.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3
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• pp.129-139
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• 2008

The purpose of the present work is to derive the reflection and transmission coefficients of $S_0\;and\;A_0$ mode Lamb waves in relation to the geometry of a rectangular notch when the waves propagate across the notch in an elastic plate. Firstly, the excitable modes of the Lamb wave were analyzed with respect to the plate thickness. The scattering phenomena were divided into three independent processes according to the boundary shape of the notch and the direction of the wave propagation. Linear equations for each process were derived with corresponding free or continuous boundary conditions to analyze the scattered waves. By the rule of linear superposition, the waves scattered at each process were summed for each mode. Then the steady-state reflection and transmission coefficients of the scattered waves were determined so that the difference of energy flux between the incident and the scattered waves would remain within 4%.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.90-97
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• 1996

A numerical method for scattering of electromagnetic waves from a periodic strip grating over a grounded dielectric slab is considered for TE and TM polarization cases from the viewpoints of both reflection grating problem and leaky wave antenna problem. The analysis is based on a mode expansion method, floquet's theorem, and the method of moments. Numerical results involving some combinations of geometric parameters are presented in terms of complex propagation constant (kd-$\beta$d diagram), radiation pattern, and relative scattered powers of spectral modes. In particular, the relationship between complex propagatio constnat form the viewpoint of leaky wqve antenna problem and Off-bragg and bragg blazing phenomena from the viewpoint of reflecton graing problem is investigated.