• 한국추진공학회지
• /
• 제16권6호
• /
• pp.1-8
• /
• 2012

본 연구에서는 정상초음파의 간섭에 의해 야기되는 프로판/공기 예혼합화염의 사각관내 전파거동 및 구조안정화를 규명하기 위한 실험결과를 제시한다. 전파화염의 이미지는 고속카메라를 이용하여 획득하였으며, 이미지 후처리를 통해 정상초음파 유무에 따른 화염선단의 구조변이와 전파속도를 상세히 관찰하였다. 전파속도는 정상초음파가 교반하는 경우 증가하였으며, 이론당량비에서 벗어남에 따라 초음파의 영향은 보다 크게 발현하였다. 정상초음파에 의한 화학반응과 혼합의 촉진은 화염선단의 형상에 대한 부력의 영향을 압도하여 화염의 구조적 안정화에 기여한다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
• /
• pp.63-69
• /
• 2000

Korea Institute of Geology Mining and Materials(KIGAM) cooperating with Southern Methodist University(SMU) has been operating seismo-acoustic array in Chul-Won area to discriminate man-made explosions from natural earthquakes since at the end of July 1999. In order to characterize propagation parameters of detected seismo-acoustic signal and to associate these signals as a blast event accompanying seismic and acoustic signals simultaneously it is necessary to understand infrasound wave propagation in the atmosphere. Two comparable Effective Sound Velocity Structures(ESVS) in atmosphere were constructed by using empirical model (MSISE90 and HWM93) and by aerological observation data of Korea Meteorological Administration (KMA) at O-San area. Infrasound propagation path computed by empirical model resulted in rare arival of refracted waves on ground less than 200km from source region. On the other hand Propagation paths by KMA more realistic data had various arrivals at near source region and well agreement with analyzed seismo-acoustic signals from Chul-Won data. And infrasound propagation in specific direction was very influenced by horizontal wind component in that direction. Linear travel time curve drawn up by 9 days data of the KMA in autumn season showed 335.6m/s apparent sound velocity in near source region. The propagation characteristics will be used to associate seismo-acoustic signals and to calculate propagation parameters of infrasound wave front.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2003년도 ICCAS
• /
• pp.2072-2077
• /
• 2003

Animal-like robots are serving an important role as a linkage between biology and engineering. So, in this paper, we aim to develop a biomimetic microrobot that mimics the locomotion mechanism of a gastropod. This microrobot has 3 DOF (x, y translation and rotation), and has small size, unlimited traveling range, high resolution and low cost. Its movement can be made using propagation wave that is generated by the controllable sinusoidal voltage source and piezoelectric effects. This soft motion that can be generated by propagation wave and piezoelectric mechanism would be useful for the motion on the slippery surface. So we modeled the propagation wave mechanism including piezoelectric effect and friction on the contact surface, and could know the velocity of the microrobot is dependent on the driving frequency, input voltage peak, propagation wavelength and surface friction coefficient. With these results we design the microrobot, and accomplish its fabrication and experimentation. The development of this microrobot shall be aimed to design an autonomous moving actuator like animal. Also it can be used from micromanipulation system technology to biology and medicine.

• Steel and Composite Structures
• /
• 제31권6호
• /
• pp.641-653
• /
• 2019

In this paper, wave propagation is studied and analyzed in double-layered nanotubes systems via the nonlocal strain gradient theory. To the author's knowledge, the present paper is the first to investigate the wave propagation characteristics of double-layered porous nanotubes systems. It is generally considered that the material properties of nanotubes are related to the porosity and hygro-thermal effects. The governing equations of the double-layered nanotubes systems are derived by using the Hamilton principle. The dispersion relations and displacement fields of wave propagation in the double nanotubes systems which experience three different types of motion are obtained and discussed. The results show that the phase velocities of the double nanotubes systems depend on porosity, humidity change, temperature change, material composition, non-local parameter, strain gradient parameter, interlayer spring, and wave number.

• 설비공학논문집
• /
• 제9권4호
• /
• pp.561-571
• /
• 1997

In this paper, the fundamental equations are developed for the pulsatile laminar flow generated by changing the oscillatory flow with $0{\leq}f{\leq}48Hz$ into a steady one with $0{\leq}Re{\leq}2500$ in a rigid circular pipe. Analytical solutions for the wave propagation factor k, the axial distributions of cross-sectional mean velocity $u_m$ and pressure p are schematically derived and confirmed experimentally. The axial distributions of centerline velocity and pressure were measured by using Pitot-static tubes and strain gauge type pressure transducers, respectively. The cross-sectional mean velocity was calculated from the centerline velocity by applying the parabolic distribution of the laminar flow and it was confirmed by using the ultrasonic flowmeter. It was found that the axial distributions of cross-sectional mean velocity and pressure agree well with theoretical ones and depend only on the Reynolds number Re and angular velocity $\omega$.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1996년도 춘계학술대회 논문집
• /
• pp.714-718
• /
• 1996

The interference phenomenonof a dynamic crack propagation in a inclined DEN(double edge notched) specimen has been investigated by using the dynamic photoelasticity. One crack initiated by static loading is propagated dynamically and experiences a mixed mode condition(interference) as the crack approaches to the inclined edge notch. We use the overdeterministic least-square method to extract dynamic $K_{Id}$ K sub IId/and .sigma. $_{ox}$from the recorded dynamic photoelastic pattern surounding a running crack. The evaluated $K_{Id}$ $K_{IId}$and .sigma. $_{ox}$together with the crack propagation velocity estimate the dynamic crack interference phenomenonenonon

• Steel and Composite Structures
• /
• 제17권6호
• /
• pp.891-906
• /
• 2014

This study aims to present a three dimensional finite element model to investigate the wave propagation in a concrete filled steel tubular column (CFSC) due to transient impact load. Both the concrete and steel are regarded as linear elastic material. The impact load is simulated by a semi sinusoidal impulse. Besides the CFSC models, a concrete column (CC) model is established for comparing under the same loading condition. The propagation characteristics of the transient waves in CFSC are analyzed in detail. The results show that at the intial stage of the wave propagation, the velocity waves in CFSC are almost the same as those in CC before they arrive at the steel tube. When the waves reach the column side, the velocity responses of CFSC are different from those of CC and the difference is more and more obvious as the waves travel down along the column shaft. The travel distance of the wave front in CFSC is farther than that in CC at the same time. For different wave speeds in steel and concrete material, the wave front in CFSC presents an arch shape, the apex of which locates at the center of the column. Differently, the wave front in CC presents a plane surface. Three dimensional effects on top of CFSC are obvious, therefore, the peak value and arrival time of incident wave crests have great difference at different locations in the radial direction. High-frequency waves on the waveforms are observed. The time difference between incident and reflected wave peaks decreases significantly with r/R when r/R < 0.6, however, it almost keeps constant when $r/R{\geq}0.6$. The time duration between incident and reflected waves calculated by 3D FEM is approximately equal to that calculated by 1D wave theory when r/R is about 2/3.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 1999년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall
• /
• pp.91-98
• /
• 1999

In this study a modified ground strain model is developed for an equivalent earthquake load and is applied to the seismic analysis of buried pipelines, The ground strain can be obtained using the ratio of a maximum ground velocity to a wave propagation velocity. To reflect soil conditions and seismic characteristics the wave propagation velocity is evaluated by a proposed dispersion curve based on wave energy distribution. In order to verify the procedures the observed earthquake data and the results of this study are compared. For the application of an equivalent earthquake load to the seismic analysis the buried pipelines are modeled using the beam theory. the results of the analyses are compared with those of a dynamic analysis code and those obtained from the response displacement method. Finally various parametric studies considering different soil conditions and seismic loads are examined.

• Steel and Composite Structures
• /
• 제38권2호
• /
• pp.141-150
• /
• 2021

In the present paper we have investigated the Stoneley wave propagation at the interface of two dissimilar homogeneous nonlocal magneto-thermoelastic media under the effect of hall current applied to multi-dual-phase lag heat transfer. The secular equations of Stoneley waves have been derived by using appropriate boundary conditions. The wave characteristics such as attenuation coefficients, temperature distribution and phase velocity are computed and have been depicted graphically. Effect of nonlocal parameter and hall effect are studied on the attenuation coefficient, phase velocity, temperature distribution change, stress component and displacement component. Also, some particular cases have been discussed from the present study.

• Wind and Structures
• /
• 제35권6호
• /
• pp.395-403
• /
• 2022

The present research is concerned with the study of Stoneley wave propagation at the interface of two dissimilar homogeneous orthotropic magneto-thermoelastic solids with fractional order theory of type GN-III with three phase-lags and combined effect of hall current and rotation. With the help of appropriate boundary conditions the secular equations of Stoneley waves are obtained in the form of determinant. The characteristics of wave such as phase velocity, attenuation coefficient and specific loss are computed numerically. The effect of rotation on the Stoneley wave's phase velocity, attenuation coefficient, specific loss, displacement components, stress components and temperature change has been depicted graphically. Some particular cases are also derived in this problem.