• Journal of Advanced Navigation Technology
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• v.27 no.4
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• pp.469-472
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• 2023

If temperature management is required in factory or environmental monitoring, temperature can be measured by connecting various sensors wired or wirelessly. Surface acoustic wave sensors measure temperature using changes in acoustic waves on the sensor surface according to temperature, and are useful for wireless networks. In this paper, in order to build a wireless temperature measurement system in the 900 MHz frequency band, the temperature characteristics of the passive SAW sensor were measured, and the analysis and removal of multipath reflection wave effect inside the high temperature chamber were conducted. The resonant frequency of the SAW sensor was measured, and radio transmission/reception and multipath reflected wave removal techniques were proposed in the shielded chamber.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1269-1274
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• 2014

Since power and control cables have narrow bandwidth due to their loss at high frequencies, it is difficult to detect the weak fault using conventional reflectometry. It is because the reflected wave caused by the weak fault is overlapped and hidden by the ripple of the strong reflected wave from the end of the cable. This paper proves that the reflected wave from the weak fault can be considered to be linearly superposed on the strong reflected wave from the end of the cable based on the transmission line theory. Then, the weak fault point is experimentally diagnosed using the difference between reflection coefficients before and after the fault generation.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.95-104
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• 2002

The theoretical and analytical studies on dynamic signals(force and acceleration signals) measured at SPT rod are actively made. In this paper, the characteristics of stress wave(force signals) in SPT rod were studied experimentally using model rod system. It was noted that the amplitude ratios of reflected wave over incident wave in different end conditions were well matched with theoretical results. The impedance of soil could be determined if the characteristics of incident and reflected waves could be evaluated quantitatively in situ SPT test. On the other hand, the results of model tests showed that the effect of reflected wave caused by side friction was negligible, and therefore, the analysis model considering only end resistance of sampler could be applicable in dynamic analysis of SPT.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.3
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• pp.123-129
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• 2018

In this study, CFD is used to compare and analyze the flow characteristics using reflected pressure wave during the intersection of two trains in straight tunnel. Two tunnels of different lengths; 600 m and 3,400 m were designed and numerical analysis of the flow characteristics of two tunnels carried out by setting the crossing state of the two trains at a constant velocity of 27 m/s form the center of the tunnel. The simulation model was designed using the actual tunnel and subway dimensions The train motion was achieved by using the moving mesh method. For the numerical analysis, $k-{\omega}$ standard turbulence model and an ideal gas were used to set the flow conditions of three-dimensional, compressible and unsteady state. In the analysis results, it was observed that the inside of the long tunnel without interference of the reflected pressure wave was maintained at a pressure lower than the atmospheric pressure and that the flow direction was determined by the pressure gradient and shear flow. On the other hand, the flow velocity in the short tunnel was faster and the pressure fluctuation was noted to have increased due to the reflected pressure wave, with more vortices formed. In addition, the flow velocity was noted to have changed more irregularly.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.175-185
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• 2001

A numerical model is represented to calculate the reflected waves, the runup of waves and the wave induced velocities on impermeable slopes for the normally incident wave trains of nonlinear monochromatic wave and solitary wave. The finite amplitude shallow water equations with the effects of bottom friction are solved numerically in time domain using an explicit dissipative Lax-Wendroff finite difference method. The numerical model is verified by comparisons with the other numerical results, the measured data and asymptotic results. It is found that the uprushing and downrushing of incident waves may be accurately predicted by the present numerical model. Therefore, the present numerical model can be applicable to swells as well as long waves.

• Journal of Ocean Engineering and Technology
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• v.34 no.4
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• pp.245-252
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• 2020

Wave run-up is an important phenomenon that should be considered in ocean structure design. In this study, the wave run-up of a surface-piercing circular cylinder was calculated in the time domain using the three-dimensional linear and fully nonlinear numerical wave tank (NWT) techniques. The NWT was based on the boundary element method and the mixed Eulerian and Lagrangian method. Stokes second-order waves were applied to evaluate the effect of the nonlinear waves on wave run-up, and an artificial damping zone was adopted to reduce the amount of reflected and re-reflected waves from the sidewall of the NWT. Parametric studies were conducted to determine the effect of wavelength, wave steepness, and the draft of the cylinder on the wave run-up of the cylinder. The maximum wave run-up value occurred at 0°, which was in front of the cylinder, and the minimum value occurred near the circumferential angle of 135°. As the diffraction parameter increased, the wave run-up increased up to 1.7 times the wave height. Furthermore, the wave run-up was 4% higher than the linear wave when the wave steepness was 1/35. In particular, the crest height of the wave run-up increased by 8%.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.169-172
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• 2002

When a plane shockwave reflects ken a concave wall, it is focused at a certain location, resulting in extremely high local pressure and temperature. This focusing is due to a nonlinear phenomenon of shock wave. The focusing phenomenon has been extensively applied to many diverse folds of engineering and medical treatment as well. In the current study, the focusing of shock wave over a reflector is numerically investigated using a CFD method. The Harten-Yee total variation diminishing (TVD) scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The incident shock wave Mach number $M_{s}\;of\;1.1{\~}l.3$ is applied to the parabolic reflectors with several different depths. Detailed focusing characteristics of the shock wave are investigated in terms of peak pressure, gasdynamic and geometrical foci. The results obtained are compared with the previous experimental results. The results obtained show that the peak pressure of shock wave focusing and its location strongly depend on the magnitude of the incident shock wave and depth of parabolic reflector. It is also found that depending up on the depth of parabolic reflector, the weak shock wave focusing process can classified into three distinct patterns : the reflected shock waves do not intersect each other before and after focusing, the reflected shock waves do not intersect each other before focusing, but intersect after focusing, and the reflected shock waves intersect each other before and after focusing. The predicted Schlieren images represent the measured shock wave focusing with a good accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3211-3223
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• 1996

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic of anisotropic material was studied. And the influence of boundary conditions (free or clamped edge) upon the reflection of elastic wave was anlyzed. Also, double exposure holographic interferometer using ruby pulse laser was formed in order to investigate transient waves. Before the elasitc wave was reflected from the edges, the elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1917-1922
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• 2000

The split Hokinson pressure bar(SHPB) test has been used to find the mechanical property of materials at high strain rate. A tensile split Hopkinson pressure bar test system is developed and the threaded tensile specimen and the split collar are placed between elastic bars. When the compressive elastic wave generated by a striker is transferred from the transmit bar to the incident bar, some elastic wave is reflected at the threaded parts of the specimen and the transmit bar. This reflected wave can interfere with the transmitted wave. A proper length of elastic bars and the location of strain gage in these elastic bars are determined to avoid this interference. In order to avoid the interference of elastic wave reflected at the threaded parts of specimen and elastic bar, the length of transmit bar must be longer than that of incident bar. Strain gage in transmit bar must be located as close as possible from the interface of a transmit bar and specimen. In the developed tensile SHPB test system, A12011-T3 and A17075-T6 are tested to get the true stress-strain relation in the range of strain rate at $10^3/sec$