• 한국해양공학회지
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• 제23권6호
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• pp.124-130
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• 2009

This study presents a finite element simulation of elastic waves for detecting anti-symmetric damages in an adhesively-bonded single lap joint. Plane strain elements were used for modeling adherents (aluminum) and adhesives (epoxy). Three types of damage were introduced: thickness reduction, elasticity deterioration, and voids in the adhesive layers, and two excitation and reception arrangements (ER1 and ER2) were used to investigate the detectability of the damage. The simulation showed that symmetrically located damage, such as a thickness reduction, can be detected by one excitation and one reception arrangement (ER1) and anti-symmetric damages, such as elasticity deterioration and voids, can be detected by modified two-point elastic wave excitation (ER2). Compared with the ER1 arrangement, the ER2 arrangement does not require a baseline signal for damage detection; hence, an efficient method of anti-symmetric damage detection in an adhesively-bonded single lap joint is proposed.

• Structural Engineering and Mechanics
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• 제58권2호
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• pp.347-378
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• 2016

Within the scope of the plane-strain state, by utilizing the three-dimensional linearized theory of elastic waves in initially stressed piezoelectric and elastic materials, Lamb wave propagation and the influence of the initial stresses on this propagation in a sandwich plate with pre-stressed piezoelectric face and pre-stressed metal elastic core layers are investigated. Dispersion equations are derived for the extensional and flexural Lamb waves and, as a result of numerical solution to these equations, the corresponding dispersion curves for the first (fundamental) and second modes are constructed. Concrete numerical results are obtained for the cases where the face layers' materials are PZT-2 or PZT-6B, but the material of the middle layer is Steel (St) or Aluminum (Al). Sandwich plates PZT-2/St/PZT-2, PZT-2/Al/PZT-2, PZT-6B/St/PZT-6B and PZT-6B/Al/PZT-6B are examined and the influence of the problem parameters such as piezoelectric and dielectric constants, layer thickness ratios and third order elastic constants of the St and Al on the effects of the initial stresses on the wave propagation velocity is studied.

• 한국음향학회지
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• 제7권4호
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• pp.117-126
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• 1988

산란된 파동의 형태는 그 산란체의 기하학적 형상 및 위치에 따라 변한다. 본 논문에서는 매질 내에 임피던스를 가지는 무한 실린더가 있는 경우 평면 입사파에 대한 산란된 파동을 유도하였고 그 결과로부터 산란된 파동의 방향성을 나타내는 지표로서 전방 산란파의 peak 값에 대해 산란파의 크기가 반으로 떨어지는 각도를 구하였다. 이 각도를 검토해 본 결과 입사파의 주파수 및 거리에 따라 그 각의 변화가 뚜렷함을 볼 수 있었다. 따라서 매질 내에 어떠한 산란체가 있는 경우 이 각도가 산란체의 위치 및 형상을 추정하는데 유용하게 적용될 수 있을 것이라 생각된다.

• Journal of Electrical Engineering and Technology
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• 제7권3호
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• pp.389-395
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• 2012

In this paper, we analyzed the frequency spectrum of the electromagnetic waves radiated by an electric discharge as a basic study to develop an on-line diagnostic technique for power equipment installed inside closed-switchboards. In order to simulate local and series arc discharges caused by an electric field concentration and poor connections, three types of electrode systems were fabricated, consisting of needle and plane electrodes and an arc generator meeting the specifications of UL 1699. The experiment was carried out in an electromagnetic anechoic chamber, and the measurement system consisted of a PD free transformer, a loop antenna with a frequency bandwidth of 150 kHz-30 MHz, an ultra log periodic antenna with a frequency bandwidth of 30 MHz-2 GHz, and an EMI test receiver with a frequency bandwidth of 3 Hz-3 GHz. According to the experimental results, the frequency spectra of the electrical discharges were widely distributed across a range of 150 kHz-400 MHz, depending on the defects, while commonly found between 150 kHz and 10 MHz. Therefore, considering the ambient noise and antenna characteristics, the best frequency bandwidth for a measurement system to monitor abnormal conditions by detecting electromagnetic waves in closedswitchboards is 150 kHz-10 MHz.

• 한국지구과학회지
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• 제41권4호
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• pp.344-355
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• 2020

Tropical cyclone scale vortices and associated Rossby waves were investigated numerically using high-resolution barotropic models on the global domain. The equations of the barotropic model were discretized using the spectral transform method with the spherical harmonics function as orthogonal basis. The initial condition of the vortex was specified as an axisymmetric flow in the gradient wind balance, and four types of basic zonal states were employed. Vortex tracks showed similar patterns as those on the beta-plane but exhibited more eastward displacement as they moved northward. The zonal-mean flow appeared to control not only the west-east translation but also the meridional translation of the vortex. Such a meridional influence was revealed to be associated with the beta gyre and the Rossby wave, which are formed around the vortex due to the beta effect. In the case of the basic zonal state of climatological mean, the meridional translation speed reached the maximum value when the vortex underwent recurving.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.451-457
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• 2000

In many dynamic problems such as foundation vibrations ultrasonic nondestructive evaluation and blasting analysts are confronted with the problem of wave propagation in an infinite or semi-infinite media. In order to simulate this situation by a finite analytical model provisions must be made to absorb the stress waves arriving at the boundary. Absorbing boundaries are mathematical artifacts used to prevent wave reflections at the boundaries of discrete models for infinite media under dynamic loads. An analytical study is carried out to examine the effectiveness of Lysmer-Kuhlemeyer model one of the most widely used absorbing boundaries. Validity of the absorbing boundary conditions suggested by Lymer-Kuhlemeyer is examined by adopting the solution of Ewing et al. to the problem of plane waves from a harmonic normal force on the surface of an elastic half-space. The Ewing's problem is than numerically simulated using the finite element method on a semi-circular mesh with and without absorbing boundaries which are represented by viscous dashpots. The absorption ratios are calculated by comparing the displacements at the absorbing boundaries to those at the free field without absorbing boudaries.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1986년도 하계학술대회논문집
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• pp.591-594
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• 1986

An asymptotic solution of electro-magnetic waves diffracted by a dielectric wedge of the angle larger than $180^{\circ}$ is obtained in case of the incidence of a E-polarized plane wave. Based on the dual integral equation in the spectral domain, physical optics approximation is supplemented by correction currents distributed along the interfaces. Those currents are expanded in a series of Bessel functions, known as Neumann's expansion of which fractional order is chosen to satisfy the static edge condition as the limiting value of dynamic case. Numerical results of edge diffraction patterns and field patterns are presented for some typical cases.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.308-313
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• 2015

This paper describes a technique for complete identification of a two-dimensional scattering object and multiple objects immersed in air using microwaves where the scatterers are assumed to be a homogenous dielectric medium. The employed technique consists of initially retrieving the shape and position of the scattering object using a linear sampling method and then determining the electric permittivity and conductivity of the scatterer using adjoint sensitivity analysis. Incident waves are assumed to be TM (Transverse Magnetic) plane waves. This inversion algorithm results in high computational speed and efficiency, and it can be generalized for any scatterer structure. Also, this method is robust with respect to noise. The numerical results clearly show that this hybrid approach provides accurate reconstructions of various objects.

• Advances in aircraft and spacecraft science
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• 제4권6호
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• pp.711-727
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• 2017

This article is concerned with a two-dimensional problem of micropolar generalized thermoelasticity for a half-space whose surface is traction-free and the conductive temperature at the surface of the half-space is known. Theory of two-temperature generalized thermoelasticity with phase lags using the normal mode analysis is used to solve the present problem. The formulas of conductive and mechanical temperatures, displacement, micro-rotation, stresses and couple stresses are obtained. The considered quantities are illustrated graphically and their behaviors are discussed with suitable comparisons. The present results are compared with those obtained according to one temperature theory. It is concluded that both conductive heat wave and thermodynamical heat wave should be separated. The two-temperature theory describes the behavior of particles of elastic body more real than one-temperature theory.

• 소음진동
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• 제7권1호
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• pp.153-159
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• 1997

In a stiffened plate reinforced on one of its sides by beam type stiffeners, the asymmetry about the plate mid-plane induces coupling between flexural wave and longitudinal wave. In this research interactions between flexural and longitudinal wave motion are analyzed in a stiffened plate which is reinforced only in one direction. The plate is modelled as a beam to which offset spring-mounted masses are attached at regular intervals. Propagation constants of the coupled waves and corresponding characteristic waves are derived by using periodic structure theory, and a computer code is developed. Also, sample calculations are carried out and the results are discussed.