• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.531-535
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• 2008

Present study examines the detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. Numerical approaches used in the previous studies of detonation wave propagation were extended to the present study with OpenMP parallelization for multicore SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• Advances in aircraft and spacecraft science
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• v.7 no.3
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• pp.187-202
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• 2020

The exhaust nozzle serves back pressure of Pulse detonation combustor, so combustion chamber gets sufficient pressure for propulsion. In this context recent researches are focused on influence of nozzle effect on single cycle detonation wave propagation and propulsion performance of PDE. The effects of various nozzles like convergent-divergent nozzle, convergent nozzle, divergent nozzle and without nozzle at exit section of detonation tubes were computationally investigated to seek the desired propulsion performance. Further the effect of divergent nozzle length and half angle on detonation wave structure was analyzed. The simulations have been done using Ansys 14 Fluent platform. The LES turbulence model was used to simulate the combustion wave reacting flows in combustor with standard wall function. From these numerical simulations among four acquaint nozzles the highest thrust augmentation could be attained in divergent nozzle geometry and detonation wave propagation velocity eventually reaches to 1830 m/s, which is near about C-J velocity. Smaller the divergent nozzle half angle has a significant effect on faster detonation wave propagation.

• Korean Management Science Review
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• v.18 no.1
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• pp.41-54
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• 2001

In this paper, we proposed a method to determine optimal wave source for mobile telephone communication. The approach is based on wave propagation simulation. Given a wave source we can determine wave propagation effects on every surfaces of wave simulation environment. The effect is evaluated as a cost function while the source’s position x, y, z work as variables for a parameter optimization. Wave propagated 3 dimensional space generates reflected waves whenever it hits boundary surface, it receives multiple waves which are reflected from various boundary surfacers in space. Three algorithms being implemented in this paper are based on a raytracing theory. If we get 3 dimensional geometry input as well as wave sources, we can compute wave propagation effects all over the boundary surfaces. In this paper, we present a new approach to compute wave propagation. First approach is tracing wave from a source. Source is modeled as a sphere casting vectors into various directions. This approach has limit in computing necessary wave propagation effects on all terrain surfaces. The second approach proposed is tracing wave backwards : tracing from a wave receiver to a wave source. For this approach we need to allocate a wave receiver on every terrain surfaces modeled, which requires enormous amount of computing time. But the second approach is useful for indoor wave propagation simulation. The last approach proposed in this paper is tracing sound by geometric computation. We allow direct, 1-relfe tion, and 2-reflection propagation. This approach allow us to save in computation time while achieving reasonable results. but due to the reflection limitaion, this approach works best in outdoor environment.

• Steel and Composite Structures
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• v.32 no.2
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• pp.213-223
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• 2019

For the first time, longitudinal and transverse wave propagation of triclinic nanobeam is investigated via a size-dependent shear deformation theory including stretching effect. Furthermore, the influence of initial stress is studied. To consider the size-dependent effects, the nonlocal strain gradient theory is used in which two small scale parameters predict the behavior of wave propagation more accurately. The Hamiltonian principle is adopted to obtain the governing equations of wave motion, then an analytic technique is applied to solve the problem. It is demonstrated that the wave characteristics of the nanobeam rely on the wave number, nonlocal parameter, strain gradient parameter, initial stress, and elastic foundation. From this paper, it is concluded that the results of wave dispersion in isotropic and anisotropic nanobeams are almost the same in the presented case study. So, in this case, triclinic nanobeam can be approximated with isotropic model.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.227-236
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• 1997

Quantitative analysis and imaging of elastic wave propagation are very important for the materials evaluation as well as flaw detection. The elastic wave propagation in an anisotropic media is more complex, and analysis and imaging become essential for flaw detection and materials evaluation. In the anisotropic media, the wave velocity is dependent on the propagation direction. In addition, the direction of group velocity is different from that of phase velocity, the direction of energy flow is not same as the propagation direction of wavefront (beam skewing effect). Especially, this effect becomes critical for the large anisotropic media such as fiber composite materials, and the results using elastic waves for those materials have to be analyzed considering the wave propagation mechanism. Since the analytical approach for the wave propagation in the anisotropic materials is limited, the numerical analysis such as finite difference method (FDM) have been used for these case. Therefore, 2-dimensional FDM program for the elastic wave propagation is developed, and wave propagation in anisotropic media are simulated.

• Structural Engineering and Mechanics
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• v.88 no.4
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• pp.335-354
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• 2023

In this study, analysis of wave propagation characteristics for functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates is performed using first-order shear deformation theory (FSDT) and nonlocal strain gradient theory. Uniform distribution (UD) and three types of functionally graded distributions of carbon nanotubes (CNTs) are assumed. The effective mechanical properties of the FG-CNTRC nanoplate are assumed to vary continuously in the thickness direction and are approximated based on the rule of mixture. Also, the governing equations of motion are derived via the extended Hamilton's principle. In numerical examples, the effects of nonlocal parameter, wavenumber, angle of wave propagation, volume fractions, and carbon nanotube distributions on the wave propagation characteristics of the FG-CNTRC nanoplate are studied. As represented in the results, it is clear that the internal length-scale parameter has a remarkable effect on the wave propagation characteristics resulting in significant changes in phase velocity and natural frequency. Furthermore, it is observed that the strain gradient theory yields a higher phase velocity and frequency compared to those obtained by the nonlocal strain gradient theory and classic theory.

• Structural Engineering and Mechanics
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• v.61 no.4
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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.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2072-2077
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• 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.

• Geomechanics and Engineering
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• v.31 no.6
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• pp.615-622
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• 2022

In this paper, considering the temperature dependence of material physical parameters as well as the effects of thermal effect and shear deformation, we have conducted an in-depth study on the wave propagation of functionally graded (FG) materials circular plate in thermal environment based on the physical neutral surface concept. The dynamic governing equations of functionally graded plates are established, and the dispersion relation of wave propagation is derived. The influence of different temperature fields on the propagation characteristics of flexural waves in FG circular plates is discussed in detail. It can be found that the phase velocity and group velocity of wave propagation in the plate decrease with the increase of temperature.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.367-370
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• 2007

Present study examines detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. A parametric study was carried out for a various regimes of detonation waves from weakly unstable to highly unstable detonation waves. Numerical approaches that used in the previous study of numerical requirements of the simulation of detonation wave propagations in 2D and 3D channel were used also for the present study with OpenMP parallization for multi-core SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.