• 지구물리
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• 제6권2호
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• pp.99-105
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• 2003

Rayleigh waves which has more than 70% of the total seismic energy is the principal component of ground roll. Frequency component of a surface wave has a different propagation velocity, that is, phase velocity, which results in a different wavelength called dispersion. Rayleigh wave is one of the most common ways to use the dispersive properties of surface waves. MASW is a seismic method to evaluate shear-wave velocity information of the ground.

• Structural Engineering and Mechanics
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• 제61권4호
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• pp.539-549
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• 2017

In this paper, the wave propagation in an infinite poroelastic cylindrical bone with cavity is studied. An exact closed form solution is presented by employing an analytical procedure. The frequency equation for poroelastic bone is obtained when the boundaries are stress free and is examined numerically. The magnitude of the frequency equation, wave velocity and attenuation coefficient are calculated for poroelastic bone for different values of magnetic field, density and frequency. In wet bone little frequency dispersion was observed, in contrast to the results of earlier studies. Such a model would in particular be useful in large-scale parametric studies of bone mechanical response. Comparison was made with the results obtained in the presence and absence of magnetic field. The results indicate that the effect of magnetic field, density and frequency on wave propagation in poroelastic bone are very pronounced.

• Steel and Composite Structures
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• 제47권1호
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• pp.71-77
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• 2023

This paper presents a study on the wave propagation of functionally graded material (FGM) sandwich nanoplates with soft core resting on a Winkler foundation. The structure is modelled by classical theory. Motion equations are derived by the assumption of nonlocal Eringen theory and energy method. Then, the equations are solved using an exact method for finding phase velocity responses. The effects of Winkler foundation, nonlocal parameters, thickness and mode number on the dispersion of elastic waves are shown. With the increase of spring constant, the speed of wave propagation increases and reaches a uniform state at a higher wave number.

• Structural Engineering and Mechanics
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• 제75권4호
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• pp.435-444
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• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• 전기학회논문지
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• 제57권11호
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• pp.2011-2014
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• 2008

We measured the permittivity and electromagnetic wave propagation velocity of used insulation oil with wide frequency range including ultra-high frequency by time domain reflectometry. The permittivity or propagation velocity is essential for locating discharge faults of oil filled power transformer. We derived 2.21 as a permittivity and $2.03{\times}10^8 m/s$ as a velocity from the measurement of pulse travelling time along a coaxial line filled with used insulation oil or air. The permittivity measurement system we designed shows high measurement accuracy and the convenience for field use.

• 한국분말재료학회지
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• 제17권1호
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• pp.29-35
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• 2010

We produced cylindrical porous TiNi bodies by Self-propagating High-temperature Synthesis (SHS) process, varying the heating schedule prior to ignition of a loose preform compact made from (Ti+Ni) powder mixture. To investigate the effect of the heating schedule on the behaviour of combustion wave propagation and the structure of porous TiNi shape-memory alloy (SMA) body, change of temperature in the compact during SHS process was measured as a function of time and used for determining combustion temperature and combustion wave velocity. Microstructure of produced porous TiNi SMA body was observed and the results were discussed with the combustion characteristics. From the results it was concluded that the final average pore size could be controlled either by the combustion wave velocity or by the average temperature of the preform compact prior to ignition.

• 한국안전학회지
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• 제29권5호
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• pp.1-6
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• 2014

When the fluid energy convert into kinetic energy due to water hammer, the propagation velocity of pressure wave appear. The propagation velocity of pressure wave(1050 m/s) of very fast could be damage to the pipeline system. If the occurrence of water hammer is due to down-pressure, the faster the air exhaust or supply device is needed. it is high Speed Air Valve. In this paper, Each 3.12, 3.13, 3.72, $3.74kg/cm^2$ pipeline pressure were setting, and then executed pressure rapid drop for obtaining a high Speed Air Valve Operating time and pressure change data. the result was that pipe line pressure stabilization time were each 0.98, 1, 1.22, 1.25 sec. In other words, that pressure drop experimental results pipe line pressure was equal to atmospheric pressure without negative pressure After about one second. The study result would be useful to pipe line system stability design because this data could be foresee pressure stabilization time.

• Structural Engineering and Mechanics
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• 제20권4호
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• pp.421-434
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• 2005

In this paper, the finite element method is applied to investigate the effect of the lateral boundary in homogenous soil on the seismic response of a superstructure. Some influencing factors are presented and discussed, and several parameters are identified to be important for conducting soil-structure interaction experiments on shaking tables. Numerical results show that the cross-section width L, thickness H, wave propagation velocity and lateral boundaries of soil layer have certain influences on the computational accuracy. The dimensionless parameter L/H is the most significant one among the influencing factors. In other words, a greater depth of soil layer near the foundation should be considered in shaking table tests as the thickness of the soil layer increases, which can be regarded as a linear relationship approximately. It is also found that the wave propagation velocity in soil layer affects the numerical accuracy and it is suggested to consider a greater depth of the soil layer as the wave propagation velocity increases. A numerical study on a soil-structure experimental model with a rubber ring surrounding the soil on a shaking table is also conducted. It is found the rubber ring has great effect on the soil-structure interaction experiments on shaking table. The experimental precision can be improved by reasonably choosing the elastic parameter and width of the rubber ring.

• 한국전산구조공학회논문집
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• 제20권2호
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• pp.95-103
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• 2007

본 논문에서는 포화된 다공성매체에서 파동의 전파속도와 감쇠를 구할 수 있는 해석적 이론해를 유도하여 제시하였다. 이론해의 유도를 위하여 압축성의 고체입자와 간극수를 고려하는 완전 연계 Field모델을 사용하였다. 완전 포화된 다공성 매체의 해석을 위한 공학적인 접근방법이 채택되었으며, 균질 영역에서 1차원 파동의 전파를 위한 이론해가 유도되었다. 본 논문에서 유도한 이론해는 고체입자의 압축성, 간극수의 압축성, 다공성입자의 변형, 공간의 감쇠(Spatial damping) 등을 고려할 수 있어 매우 다양하게 사용될 수 있다. 또한 다양한 지반체에서 두 가지 종류의 파속(Wavespeed)과 감쇠계수를 계산하는데 이용 가능하다. 본 논문에서 제시한 이론해를 전산코드화하여 파동의 전파속도와 감쇠에 대한 파라미터연구를 수행한 결과는 본 연구의 II부에 제시할 예정이다.

• 지구물리
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• 제9권3호
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• pp.231-240
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• 2006

The crustal structure of the Korean Peninsula was investigated by analyzing phase velocity dispersion data of Rayleigh waves. Earthquakes recorded by three component broad-band velocity seismographs during 1999-2004 in South Korea were used in this study. The fundamental mode Rayleigh waves were extracted from vertical components of seismograms by multiple filter technique and phase match filter method. Phase velocity dispersion curves of the fundamental mode signal pairs for 14 surface wave propagation paths on the great circle in the range 10 to 80 sec were computed by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocity data of Rayleigh wave were inverted. All the result models can be explained by a rather homogeneous crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to about 33 km depth without any distinctive crustal discontinuities and an uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec. Our results turn out to agree well with recent study of Cho et al. (2006 b) based on the analysis of seismic background noises to recover short-period (0.5-20 sec) Rayleigh- and Love-wave group velocity dispersion characteristics.