• Title/Summary/Keyword: Plane Wave

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The most unstable case in plane Poiseuille flow on transition by using pseudospectra method (Pseudospectra를 이용한 평행 평판 사이 유동에서 가장 불안정한 경우)

  • Choi Sangkyu;Chung Myung Kyoon
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.691-694
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    • 2002
  • The most unstable situation of laminar plane Poiseuille flow for transition to turbulence is investigated by using a pseudo-spectral method. A number of various disturbance modes are tested and it is found that the flow is the most unstable when it is disturbed by an oblique wave with an angle of $29.7^{\circ}$.

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PROPERTIES OF ELASTIC SYMBOLS AND CONSTRUCTION OF SOLUTIONS OF THE DIRICHLET PROBLEM

  • Kawashita, Mishio;Soga, Hideo
    • Communications of the Korean Mathematical Society
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    • v.16 no.3
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    • pp.399-404
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    • 2001
  • We examine plane waves of the elastic reduced wave equation in the half-space, and show that linear combinations of them can cover all plane waves on the boundary. The proof is based on the complex analysis for the symbol in the (dual) variable in the normal direction to the boundary.

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Experimental Study on Corrosion Detection of Aluminum Alloy Using Lamb Wave Mixing Technique (램파 혼합 기법을 이용한 알루미늄 합금의 부식 결함 검출에 대한 실험 연구)

  • Choi, Heeung;Lee, Jaesun;Cho, Younho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.11
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    • pp.919-925
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    • 2016
  • In this study, the Lamb wave mixing technique, which is basised on advanced research on the nonlinear bulk wave mixing technique, is applied for corrosion detection. To demonstrate the validity of the Lamb wave mixing technique, an experiment was performed with normal and corroded specimens. Comparison group in an experimentation are selected to mode and frequency with dominant in-plane displacement and out-of-plane displacement of Lamb waves. The results showed that the Lamb wave mixing technique can monitor corrosion defects, and it has a trend similar to that of the conventional Lamb wave technique. It was confirmed that the dominant displacement and mode matching the theory were generated. Flaw detectability is determined depending on displacement ratio instead of using the measurement method and mode selection.

Development of Single Feed Antenna for Integrated Public Network and 5G Network Frequency Dual-band Cover (통합 공공망과 5G 주파수 이중대역 커버용 단일 급전 안테나 개발)

  • Hong, Ji-Hun;Choi, Yoon-Seon;Woo, Jong-Myung
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.18 no.6
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    • pp.233-240
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    • 2019
  • In this paper, due to the development of 5G communication technology, an antenna capable of covering both LTE and 5G bands is currently needed. In addition, we designed and manufactured a single feed antenna for the integrated public network (LTE) and 5G frequency dual band cover to satisfy the frequency bandwidth of more than 10% in each band. The antenna designed by adopting the dipole of the basic dipole antenna in a planar structure is a form in which the radiating element is vertically extended at all of the 700 MHz antennas and folded into a 'ㄷ' shape. In addition, the radiating element of the 700MHz band serves as a reflector of the 3.5GHz band radiating element. As a result, the 700 MHz band -10 dB bandwidth 104 MHz(14.8%) and 3.5 GHz band -10 dB bandwidth 660 MHz(18.8%) were obtained and the radiation pattern characteristic resulted in gains of 8.46 dBi, beam width E-plane 55°, H-plane 81° and 3.5 GHz bands 6.14 dBi, beamwidth E-plane 79°, H-Plane 49°.

Partial H-plane Filter with Periodic Structure (주기 구조를 이용한 Partial H-plane Filter)

  • Kim Dong-Jin;Chung Woo-Sung;Lee Jeong-Hae
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.17 no.8 s.111
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    • pp.746-752
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    • 2006
  • In this paper, a compact partial H-plane filter with periodic structure is proposed. Guided wavelength of periodic structure' is reduced by slow wave effect. Cross-section and length of partial H-plane filter with periodic structure are considerably reduced by 75% and 30%, respectively, as compared with conventional E-plane filter. In addition, spurious responses of the bandpass filter are improved. To design bandpass filter with periodic structure, we have analyzed a periodic structure of partial H-plane waveguide and derived equations of the periodic filter. Measured results are in good agreement with simulated results.

Solution Comparisons of Modified Mild Slope Equation and EFEM Plane-wave Approximation (수정 완경사파랑식과 EFEM 평면파 근사식의 해 비교)

  • Seo, Seung-Nam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.21 no.2
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    • pp.117-126
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    • 2009
  • In order to test the accuracy between the modified mild slope equation (MMSE) without evanescent modes and the plane-wave approximation (PA) of eigenfunction expansion method, various numerical results from both models are presented. In this study, analytical solutions of two models are employed, one based on the MMSE derived by Porter (2003) and the other on the scatterer method of PA by Seo (2008a). Judging from direct comparisons against existing results of rapidly varying topography, the PA model gives better predictions of the wave propagation than the MMSE model.

Propagation of plane waves in an orthotropic magneto-thermodiffusive rotating half-space

  • Sheokand, Suresh Kumar;Kumar, Rajeshm;Kalkal, Kapil Kumar;Deswal, Sunita
    • Structural Engineering and Mechanics
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    • v.72 no.4
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    • pp.455-468
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    • 2019
  • The present article is aimed at studying the reflection phenomena of plane waves in a homogeneous, orthotropic, initially stressed magneto-thermoelastic rotating medium with diffusion. The enuciation is applied to generalized thermoelasticity based on Lord-Shulman theory. There exist four coupled waves, namely, quasi-longitudinal P-wave (qP), quasi-longitudinal thermal wave (qT), quasi-longitudinal mass diffusive wave (qMD) and quasi-transverse wave (qSV) in the medium. The amplitude and energy ratios for these reflected waves are derived and the numerical computations have been carried out with the help of MATLAB programming. The effects of rotation, initial stress, magnetic and diffusion parameters on the amplitude ratios are depicted graphically. The expressions of energy ratios have also been obtained in explicit form and are shown graphically as functions of angle of incidence. It has been verified that during reflection phenomena, the sum of energy ratios is equal to unity at each angle of incidence. Effect of anisotropy is also depicted on velocities of various reflected waves.

Design of Antenna for Intelligent Detection Sensor (지능형 주차검지센서용 안테나 개발)

  • Choi, Yoon-Seon;Hong, Ji-Hun;Woo, Jong-Myung
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.19 no.2
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    • pp.104-109
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    • 2020
  • In this paper, we proposed a miniaturized folded inverted F antenna with ISM-band (center frequency : 447 MHz) for mounting in intelligent parking sensor. First, to mount the antenna in the intelligent parking sensor module (72 mm × 70 mm) with limited size, a folded inverted F antenna was designed at low frequency 447 MHz (wavelength λ : 670 mm) of the ISM-band. As a result, it resonates in the ISM band and obtains suitable characteristic with a -10 dB bandwidth of 13 MHz (2.9%). In addition, the H-plane pattern by the vertical and horizontal elements represents the omni-directional patterns from which the null point is removed, and the E-plane has directivity in a specific direction. Finally, it is suitable as and antenna for vehicle management in parking lots.

Fractional wave propagation in radially vibrating non-classical cylinder

  • Fadodun, Odunayo O.;Layeni, Olawanle P.;Akinola, Adegbola P.
    • Earthquakes and Structures
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    • v.13 no.5
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    • pp.465-471
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    • 2017
  • This work derives a generalized time fractional differential equation governing wave propagation in a radially vibrating non-classical cylindrical medium. The cylinder is made of a transversely isotropic hyperelastic John's material which obeys frequency-dependent power law attenuation. Employing the definition of the conformable fractional derivative, the solution of the obtained generalized time fractional wave equation is expressed in terms of product of Bessel functions in spatial and temporal variables; and the resulting wave is characterized by the presence of peakons, the appearance of which fade in density as the order of fractional derivative approaches 2. It is obtained that the transversely isotropic structure of the material of the cylinder increases the wave speed and introduces an additional term in the wave equation. Further, it is observed that the law relating the non-zero components of the Cauchy stress tensor in the cylinder under consideration generalizes the hypothesis of plane strain in classical elasticity theory. This study reinforces the view that fractional derivative is suitable for modeling anomalous wave propagation in media.

The Ettects of Bottom Friction and Refraction on the Wave Height (마찰과 굴절이 파고에 미치는 영향)

  • 강관원;함경재
    • Water for future
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    • v.17 no.2
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    • pp.113-124
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    • 1984
  • The equations for the wave orthogonals and wave heights are presented along the depth using time as the independent variable, The effect of wave refracion is included. In this paper, a numerical procedure is described for the calculation and two analytical solutions are presneted in case of straight and parallel bottom contours and horizontal bottom in order to check the computed results. The computer outputs are in the form of automatically plotted wave orthogonals and wave heights along the wave path. In practical calculation of wave heights, Samchuckk Pohang, and Hanlim are selected as plane sloping bottoms.

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