• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.154-160
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• 1998

This study describes a theoretical and experimental investigation of gas wave propagation in the pipe system. Most calculations of compressible flows in the pipe have been based on the method of characteristics. This technique has propensity to truncate waves and is difficult to apply to non-perfect gas. A method that describes the application of a two-step Lax-Wendroff acheme to solution of the unsteady one-dimentional flow in the pipe was developed. Theoretical calculations using both the method of characteristics and the two-step Lax-Wendroff method are presented including a realistic model for heat transfer and friction processes. In the present work, account is taken of the nonlinear behavior. For sections of parallel pipe, an one dimensional unsteady homentropic analysis is employed, and a numerical solution is obtained with the aid of a digital computer, using the method of characteristics and two-step Lax-Wendroff method. This analysis is then combined with boundary models, based on a quasi-steady flow approach, to give a complete treatment of the flow behavior in the pipe system.

• Structural Engineering and Mechanics
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• 제57권3호
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• pp.441-456
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• 2016

This work reports wave propagation in the nanocomposite cylinders that reinforced by straight single-walled carbon nanotubes based on a mesh-free method. Moving least square shape functions have been used for approximation of displacement field in weak form of motion equation. The straight carbon nanotubes (CNTs) are assumed to be oriented in specific or random directions or locally aggregated into some clusters. In this simulation, an axisymmetric model is used and also the volume fractions of the CNTs and clusters are assumed to be functionally graded along the thickness. So, material properties of the carbon nanotube reinforced composite cylinders are variable and estimated based on the Eshelby-Mori-Tanaka approach. The effects of orientation, aggregation and volume fractions of the functionally graded clusters and CNTs on dynamic behavior of nanocomposite cylinders are studied. This study results show that orientation and aggregation of CNTs have significant effects on the effective stiffness and dynamic behaviors.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권3호
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• pp.239-245
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• 2017

As a new technical approach, wave energy converter by using vertical motion of water in the multiple water chambers were developed to realize actual wave power generation as eco-environmental renewable energy. And practical use of wave energy converter was actually to require the following conditions: (1) setting up of the relevant device and its application to wave power generation in case that severe wave loading is avoided; (2) workability in installation and maintenance operations; (3) high energy conversion potential; and (4) low cost. In this system, neither the wall(s) of the chambers nor the energy conversion device(s) are exposed to the impulsive load due to water wave. Also since this system is profitable when set along the jetty or along a long floating body, installation and maintenance are done without difficulty and the cost is reduced. In this paper, we describe the system which consists of a float, a shaft connected with another shaft, a rack and pinion arrangement, a ratchet mechanism, and rotary type generator(s). Then, we present the dynamics model for evaluating the output electric power, and the results of numerical calculation including the effect of the phase shift of up/down motion of the water in the array of water chambers aligned along the direction of wave propagation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1338-1342
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• 2006

This paper presents the theoretical approach to describe the wave propagation in the waveguide with varying cross-section. The waveguides considered in this paper are stepped-rod, tapered-rod, and stepped rod with a tapered section at the middle of wave-transmission. The wave transmission ratio for displacement, stress, and power was calculated for these three rods. The distribution of the stress and displacement along the stepped rod with a tapered section was calculated and compared with the results obtained by FEM analysis.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.1-19
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• 2018

The present work shows many aspects concerning the use of a numerical wave-based methodology for the computation of the structural response of periodic structures, focusing on cylinders. Taking into account the periodicity of the system, the Bloch-Floquet theorem can be applied leading to an eigenvalue problem, whose solutions are the waves propagation constants and wavemodes of the periodic structure. Two different approaches are presented, instead, for computing the forced response of stiffened structures. The first one, dealing with a Wave Finite Element (WFE) methodology, proved to drastically reduce the problem size in terms of degrees of freedom, with respect to more mature techniques such as the classic FEM. The other approach presented enables the use of the previous technique even when the whole structure can not be considered as periodic. This is the case when two waveguides are connected through one or more joints and/or different waveguides are connected each other. Any approach presented can deal with deterministic excitations and responses in any point. The results show a good agreement with FEM full models. The drastic reduction of DoF (degrees of freedom) is evident, even more when the number of repetitive substructures is high and the substructures itself is modelled in order to get the lowest number of DoF at the boundaries.

• 지질공학
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• 제12권3호
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• pp.273-284
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• 2002

화강암의 응력하에서의 손상발달특성을 연구하기 위해 국내의 조립, 중립, 세립 화강암 시료를 채취하였으며, 일축압축에 의한 손상 전과 후에 탄성파속도시험, 투수성시험이 시료의 물리적 특성을 파악하기 위해 수행되었고, 시료의 단면에 발생된 크랙의 육안관찰을 용이하게 하기 위하여 셀롤로즈 아세테이트 필름 복제법이 사용되었다. 그리고 아세테이트필 상의 크랙을 좀더 명확하게 촬영하기 위해, 암시야조명을 이용한 근접촬영법이 적용되었다. 개인용 컴퓨터와 그래픽 프로그램을 이용하여 크랙을 확대 후 스케치하여 측정함으로써 시료단면에 발생한 크랙을 입도 별로 비교 분석하였다. 손상이 발생한 후, 조립·중립화강암이 세립화강암에 비해 상대적으로 더 낮은 탄성파속도, 더 높은 투수성을 가졌으며, 더 많은 크랙 발생을 보였다.

• 비파괴검사학회지
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• 제29권4호
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• pp.269-282
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• 2009

This paper presents a novel approach for Lamb wave based structural health monitoring(SHM) in honeycomb aluminum panels. In this study, a suite of three signal processing algorithms are employed to improve the damage detection capability. The signal processing algorithms used include wavelet attenuation, correlation coefficients of power density spectra, and triangulation of reflected waves. Piezoelectric transducers are utilized as both sensors and actuators for Lamb wave propagation. These SHM algorithms are built into a MatLab interface that integrates and automates the hardware and software operations and displays the results for each algorithm to the analyst for side by side comparison. The effectiveness of each of these signal processing algorithms for SHM in honeycomb aluminum panels under a variety of damage conditions is then demonstrated.

• Structural Engineering and Mechanics
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• 제67권2호
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• pp.175-183
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• 2018

This research deals with the wave dispersion analysis of functionally graded double-layered nanobeam systems (FG-DNBSs) considering the piezoelectric effect based on nonlocal strain gradient theory. The nanobeam is modeled via Euler-Bernoulli beam theory. Material properties are considered to change gradually along the nanobeams' thickness on the basis of the rule of mixture. By implementing a Hamiltonian approach, the Euler-Lagrange equations of piezoelectric FG-DNBSs are obtained. Furthermore, applying an analytical solution, the dispersion relations of smart FG-DNBSs are derived by solving an eigenvalue problem. The effects of various parameters such as nonlocality, length scale parameter, interlayer stiffness, applied electric voltage, relative motions and gradient index on the wave dispersion characteristics of nanoscale beam have been investigated. Also, validity of reported results is proven in the framework of a diagram showing the convergence of this model's curve with that of a previous published attempt.

• Structural Engineering and Mechanics
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• 제68권6호
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• pp.701-711
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• 2018

Herein, the thermo-magneto-elastic wave dispersion answers of functionally graded (FG) double-nanobeam systems (DNBSs) are surveyed implementing a nonlocal strain gradient theory (NSGT). The kinematic relations are derived employing the classical beam theory. Also, scale influences are covered precisely in the framework of NSGT. Moreover, Mori-Tanaka homogenization model is introduced in order to obtain the effective material properties of FG nanobeams. Meanwhile, effects of external forces such as thermal and Lorentz forces are included in this research. Also, based upon the Hamilton's principle, the Euler-Lagrange equations are developed; afterwards, these equations are incorporated with those of NSGT to reach the nonlocal governing equations of FG-DNBSs. Furthermore, according to an analytical approach, the governing equations are solved to obtain the wave frequencies and phase velocities of FG-DNBSs. At the end, some illustrations are rendered to clarify the influences of a wide range of involved parameters.

• Coupled systems mechanics
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• 제12권4호
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• pp.337-364
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• 2023

The Rayleigh wave propagation is considered in the structure of the functionally graded piezoelectric material (FGPM) layer over the elastic substrate. The elastic substrate loosely bonds the layer through a corrugated interface, whereas its upper boundary is also corrugated but stress-free. Additionally, the solutions for the FGPM layer and substrate are derived using the fundamental variable separable approach to convert the partial differential equation to an ordinary differential equation. The results with boundary conditions lead to dispersion relations for the electrically open and electrically short cases in the determinant form. The outcomes have been numerically analyzed using a specific model. The findings were presented in the form of graphs, which were created using Mathematica 7. Graphs are plotted for variations in wavenumber and phase velocity. The outcomes may help measure interface defects and design Surface Acoustic Wave (SAW) devices.