• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1595-1611
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• 1994

In this paper, the numerical wave propagation properties of the finite difference-time domain(FD-TD) method is investigated as a discrete model describing electromagnetic(EM) wave propagation phenomena. The leap-frog approximation of Maxwell's curl equations in time-space simulates EM wave propagation in terms of the numerical characteristic and the domain of dependence. A geometrical interpretation of the FD-TD numerical procedure is presented. The numerical dispersion error due to the leap-frog approximation and its dependence on the stability factor are illustrated. The FD-TD method using the leap-frog approximation is inherently a descriptive model. Thus, not only any physical picture about EM wave propagation phenomena can be drawn through this model, but also physical or engineering parameters in the frequency domain can be extracted from descriptive results. E-plane filter characteristics in the WR-28 rectangular waveguide and reflection property of an inductive iris in the WR-90 rectangluar waveguide extracted from simulation of the FD-TD model is included.

• Structural Engineering and Mechanics
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• v.58 no.2
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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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.6
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• pp.1592-1601
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• 1998

The growing use of unlicensed wireless systems has spurred interest in the 2.4 Ghz ISM band. In order to facilitate the efficient design of such systems, understandings of the propserties of radio wave propagation in buildings is necessary. Many authors have reported about statistical propagation models based on the extensive measurements in buildings. However, measurement based statistical analysis will not be enough for the optimum deployment of the communication systems in the specific building. Aviding expensive measurements in the individual buildings prior to installation, or adjustments afterwards, theoretical prediction models have been developed to predict the path loss and delay spread from the building floor plane. Predictions shows good agreements with measurements except for a few environments which was surrounded by heavy scatterers.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.1
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• pp.1-9
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• 1992

Eigen Function Expansion Method(EFEM) and Plane Wave Approximation are employed to study the propagation of linear water waves over trenches. The properties of trapped waves due to depth and ambient current discontinuities and the effect of evanescent modes on wave propagations are investigated. Special attention is paid to the trapped waves, and not only 3-D plots but also B-D plots of wave propagation are presented.

• Earthquakes and Structures
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• v.9 no.4
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• pp.753-766
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• 2015

An investigation has been carried out for the propagation of torsional surface waves in an inhomogeneous prestressed layer over an inhomogeneous half space when the upper boundary plane is assumed to be rigid. The inhomogeneity in density, initial stress (tensile and compressional) and rigidity are taken as an arbitrary function of depth, where as for the elastic half space, the inhomogeneity in density and rigidity is hyperbolic function of depth. In the absence of heterogeneities of medium, the results obtained are in agreement with the same results obtained by other relevant researchers. Numerically, it is observed that the velocity of torsional wave changes remarkably with the presence of inhomogeneity parameter of the layer. Curves are compared with the corresponding curve of standard classical elastic case. The results may be useful to understand the nature of seismic wave propagation in geophysical applications.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.277-280
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• 2001

General source location method that use an arrival time differences among sensors is restricted to the composite material and the complex-shaped material. In this study, a bundle-type acoustic sensor composed of 6 pinducers was utilized to determine wave propagation direction and then to estimate source location of the unidirectional GFRP. For the purpose of the study, slowness curve for the material was obtained and made an assumption that the incident waves on pinducers are propagated as a plane wave. According to the results, measured propagation directions of the wave were coincide with theoretical background, however, it was a hassle to determine the source location exactly. But, it is expected that bundle-type sensor gives more accurate results for zone location than generally used acoustic sensors.

• Structural Engineering and Mechanics
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• v.74 no.6
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• pp.809-819
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• 2020

For the first time, the influence of in-plane magnetic field on wave propagation of Graphene Nano-Platelets (GNPs) polymer composite nanoplates is investigated here. The impact of three- parameter Kerr foundation is also considered. There are two different reinforcement distribution patterns (i.e. uniformly and non-uniformly) while the material properties of the nanoplate are estimated through the Halpin-Tsai model and a rule of mixture. To consider the size-dependent behavior of the structure, Eringen Nonlocal Differential Model (ENDM) is utilized. The equations of wave motion derived based on a higher-order shear deformation refined theory through Hamilton's principle and an analytical technique depending on Taylor series utilized to find the wave frequency as well as phase velocity of the GNPs reinforced nanoplates. A parametric investigation is performed to determine the influence of essential phenomena, such as the nonlocality, GNPs conditions, Kerr foundation parameters, and wave number on the both longitudinal and flexural wave characteristics of GNPs reinforced nanoplates.

• Structural Engineering and Mechanics
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• v.25 no.5
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• pp.597-611
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• 2007

Many works have been done in classical theory of thermoelasticity in materials with memory by researchers like Nunziato, Chen and Gurtine and many others. No work is located in generalized thermoelasticity regarding materials with memory till date. The present paper deals with the wave propagation in materials with memory in generalized thermoelasticity. Plane progressive waves and Rayleigh waves have been discussed in details. In the classical theory of heat conduction it was observed that heat propagates with infinite speed. This paradox has been removed in the present discussion. The set of governing equations has been developed in the present analysis. The results of wave velocity and attenuation coefficient corresponding to low and high frequency have been obtained. For thermal wave the results show appreciable differences with those in the usual thermoelasticity theory.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.