• Smart Structures and Systems
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• v.20 no.3
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• pp.329-342
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• 2017

In this paper, the dispersion characteristics of elastic waves propagation in sandwich nano-beams with functionally graded (FG) face-sheets reinforced with carbon nanotubes (CNTs) is investigated based on various high order shear deformation beam theories (HOSDBTs) as well as nonlocal strain gradient theory (NSGT). In order to align CNTs as symmetric and asymmetric in top and bottom face-sheets with respect to neutral geometric axis of the sandwich nano-beam, various patterns are employed in this analysis. The sandwich nano-beam resting on Pasternak foundation is subjected to thermal, magnetic and electrical fields. In order to involve small scale parameter in governing equations, the NSGT is employed for this analysis. The governing equations of motion are derived using Hamilton's principle based on various HSDBTs. Then the governing equations are solved using analytical method. A detailed parametric study is conducted to study the effects of length scale parameter, different HSDBTs, the nonlocal parameter, various aligning of CNTs in thickness direction of face-sheets, different volume fraction of CNTs, foundation stiffness, applied voltage, magnetic intensity field and temperature change on the wave propagation characteristics of sandwich nano-beam. Also cut-off frequency and phase velocity are investigated in detail. According to results obtained, UU and VA patterns have the same cut-off frequency value but AV pattern has the lower value with respect to them.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.6
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• pp.748-754
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order modes should be considered to widen the frequency range. Munjal has suggested the method for analyzing the acoustic properties of simple expansion chamber with taking into consideration of higher order mode of inlet/outlet. But his method cannot predict the acoustic properties exactly when the dimensions of inlet/outlet and expansion chamber have not integer multiples. In this paper the new method was suggested to overcome the shortcomings of Munjal's method The predictions by this method were also compared with those by the finite element method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.4
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• pp.329-339
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• 1995

To clarify the surface drift velocity in gravity waves. experimental data measured in a two-dimensional wave flume were compared with theoretical values predicted by the Stokes 2nd- and 5th- order theories as well as by the conduction solution or Longuet-Hinggins (1953). Relative water depth and wave height ranged 0.040.13. For a closed flume condition, Stokes 2nd-order theory gives lower values than the experimental data, and the differences increase as both relative water depth and wave height increase. Based on the observed data of the surface drift velocities, a modified Parabolic model of the return current velocity Profile has been suggested, which is Proved to fit better to the existing experimental data of mass transport velocity profiles in a closed wave flume than the models of Longuet-Hinggins (1953) and Stokes wave theories do.

• Advances in nano research
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• v.16 no.5
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• pp.489-500
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• 2024

This paper studies the free vibration analysis of the piezo-magneto-thermo-elastic FG nanobeam submerged in a fluid environment. The problem governed by the partial differential equations is determined by refined higher-order State Space Strain Gradient Theory (SSSGT). Hamilton's principle is applied to discretize the differential equation and transform it into a coupled Euler-Lagrange equation. Furthermore, the equations are solved analytically using Navier's solution technique to form stiffness, damping, and mass matrices. Also, the effects of nonlocal ceramic and metal parts over various parameters such as temperature, Magnetic potential and electric voltage on the free vibration are interpreted graphically. A comparison with existing published findings is performed to showcase the precision of the results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.4
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• pp.138-146
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• 2012

This research is to analyze the wave propagation characteristics of anisotropic materials subjected to the low-velocity impact. For this purpose, a higher-order finite element program is used to simulate the dynamic behaviors according to the changes of material property, stacking sequence and dimension etc.. Materials for simulation are composed of $[0^{\circ}]_{10s}$, $[45^{\circ}/-45^{\circ}]_{5s}$ and $[90^{\circ}]_{10s}$ stacking sequences. Finally, the results of this simulation are compared with those of wave propagation theory and then the impact responses and wave propagation phenomena are investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.5
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• pp.819-830
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• 2016

Hydrodynamic characteristics of wave propagation through density stratification have not been identified in details. So this study conducted a numerical simulation using LES-WASS-3D ver. 2.0 for analysis of density current due to water temperature and salinity in order to analyze hydraulic characteristics under wave action in a two-layer density stratified fluid. For the validity and effectiveness of numerical wave tank used, it was compared and analyzed with the experiment to show waveform based on $3^{rd}$-order Stoke wave theory at the internal of a density stratification. Using the results obtained from numerical simulation, the surface and internal wave heights are reduced as the wave propagates in a two-layer density stratified water. And the surface or internal wave attenuation became more serious as the vorticities were increased by the velocity difference of wave propagation due to the upper-lower density difference around the interface of a density stratification. As well, the surface and internal wave attenuations became more serious with higher density difference and depth ratio between upper and lower layers when the wave propagates through a density stratification.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• 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.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.56.3-56.3
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• 2018

The present study formulates the theory of spontaneously emitted electromagnetic fluctuations in magnetized plasmas containing particles with an anisotropic suparthermal (bi-Kappa) velocity distribution function. The formalism is general applying for an arbitrary wave vector orientation and wave polarization, and for any wave-frequency range. As specific applications, the high-frequency electromagnetic fluctuations emitted in the upper-hybrid and multiple harmonic electron cyclotron frequency range are evaluated. The fluctuations for low-frequency are also applied, which include the kinetic $Alfv\acute{e}n$, fast magnetosonic/whistler, kinetic slow mode, ion Bernstein cyclotron modes, and higher-order modes. The model predictions are confirmed by a comparison with particle-in-cell simulations. The study describes how energetic particles described by kappa velocity distribution functions influence the spectrum of high and low frequency fluctuations in magnetized plasmas. The new formalism provides quantitative analysis of naturally occurring electromagnetic fluctuations, and contribute to an understanding of the electromagnetic fluctuations observed in space plasmas, where kappa-distributed particles are ubiquitous.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1829-1831
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• 2001

A novel multi-section power divider configuration is proposed to obtain wide-band frequency performance up to microwave frequency region. Design procedures for the proposed microwave broadband power divider are composed of a planar multi-section three-ports hybrid and a waveguide transformer design procedures. The multi-section power divider is based on design theory of the optimum quarter-wave transformer. Furthermore, in order to obtain the broadband isolation performance between the two adjacent output ports, the odd mode equivalent circuit should be matched by using the lossy element such as resistor. The derived design formula for calculating these odd mode matching elements is based on the singly terminated filter design theory. The waveguide transformer section is designed to suppress the propagation of the higher order modes such as waveguide modes due to employing the metallic electric wall. Simulation and experiment show excellent performance of multi section power divider.