• 제목/요약/키워드: transient wave field

검색결과 56건 처리시간 0.041초

Transient wave propagation in piezoelectric hollow spheres subjected to thermal shock and electric excitation

  • Dai, H.L.;Wang, X.
    • Structural Engineering and Mechanics
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    • 제19권4호
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    • pp.441-457
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    • 2005
  • An analytical method is presented to solve the problem of transient wave propagation in a transversely isotropic piezoelectric hollow sphere subjected to thermal shock and electric excitation. Exact expressions for the transient responses of displacements, stresses, electric displacement and electric potentials in the piezoelectric hollow sphere are obtained by means of Hankel transform, Laplace transform, and inverse transforms. Using Hermite non-linear interpolation method solves Volterra integral equation of the second kind involved in the exact expression, which is caused by interaction between thermo-elastic field and thermo-electric field. Thus, an analytical solution for the problem of transient wave propagation in a transversely isotropic piezoelectric hollow sphere is obtained. Finally, some numerical results are carried out, and may be used as a reference to solve other transient coupled problems of thermo-electro-elasticity.

2011년 1월의 동아시아 한랭 아노말리 특성 (Characteristic Features Observed in the East-Asian Cold Anomalies in January 2011)

  • 최우갑;정지연;전종갑
    • 대기
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    • 제23권4호
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    • pp.401-412
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    • 2013
  • East Asia experienced extremely cold weather in January 2011, while the previous December and the following February had normal winter temperature. In this study National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data are used to investigate the characteristic features observed in the meteorological fields such as temperature, sea-level pressure, geopotential height, and wind during this winter period. In January the planetary-wave pattern is dominated by stationary-wave form in the mid-to-high latitude region, while transient waves are significant in the previous month. To understand the planetary-wave features quantitatively, harmonic analyses have been done for the 500-hPa geopotential height field. In the climatological-mean geopotential heights the wave numbers 1, 2, and 3 are dominant during the whole winter. In January 2011 the waves of number 1, 2, and 3 are dominant and stationary as in the climatological-mean field. In December 2010 and February 2011, however, the waves of number 4, 5, and 6 play a major role and show a transient pattern. In addition to the distinctive features in each month the planetary-wave patterns dependent on the latitude are also discussed.

Supersonic and Subsonic Projectile Overtaking Problems in Muzzle Gun Applications

  • Gopalapillai, Rajesh;Nagdewe, Suryakant;Kim, Heuy-Dong;Setoguchi, Toshiaki
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2008년 영문 학술대회
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    • pp.711-722
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    • 2008
  • A projectile when passes through a moving shock wave, experiences drastic changes in the aerodynamic forces as it moves from a high-pressure region to a low pressure region. These sudden changes in the forces are attributed to the wave structures produced by the projectile-flow field interaction, and are responsible for destabilizing the trajectory of the projectile. These flow fields are usually encountered in the vicinity of the launch tube exit of a ballistic range facility, thrusters, retro-rocket firings, silo injections, missile firing ballistics, etc. In earlier works, projectile was assumed in a steady flow field when the computations start and the blast wave maintains a constant strength. However, in real situations, the projectile produces transient effects in the flow field which have a deterministic effect on the overtaking process. In the present work, the overtaking problem encountered in the near-field of muzzle guns is investigated for several projectile Mach numbers. Computations have been carried out using a chimera mesh scheme. The results show that, the unsteady wave structures are completely different from that of the steady flow field where the blast wave maintains a constant strength, and the supersonic and subsonic overtaking conditions cannot be distinguished by identifying the projectile bow shock wave only.

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Experimental Identification of Input Power to the Plate Using the Transient Structural Intensity Map

  • Oey, Agustinus;Ih, Jeong-Guon
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2009년도 추계학술대회 논문집
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    • pp.110-112
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    • 2009
  • Transient acoustic pressure in the near field of an impacted plate carries information that can be utilized for recovering the impact force history. The inverse calculation approach using BEM-based NAH, which is conventionally used for time harmonic excitation, can be applied for reconstructing the transient waves using the principle of Fourier transform and spectral analysis. Then, using the recovered velocity in normal direction of the plate surface, the corresponding structural intensity can be obtained and the identification of input power can be performed. However, several manipulations should be given to overcome numerical artifacts, such as aliasing and erratic oscillation at discontinuity, and to suppress the effect of noise. Experiment using a simply supported plate is presented for demonstration purpose.

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SkyMapper Optical Follow-up of Gravitational Wave Triggers: Overview of Alert Science Data Pipeline (AlertSDP)

  • Chang, Seo-Won
    • 천문학회보
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    • 제46권1호
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    • pp.61.2-61.2
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    • 2021
  • SkyMapper is the largest-aperture optical wide-field telescope in Australia and can be used for transient detection in the Southern sky. Reference images from its Southern Survey cover the sky at δ <+10 deg to a depth of I ~ 20 mag. It has been used for surveys of extragalactic transients such as supernovae, optical counterparts to gravitational-wave (GW) and fast radio bursts. We adopt an ensemble-based machine learning technique and further filtering scheme that provides high completeness ~98% and purity ~91% across a wide magnitude range. Here we present an important use-case of our robotic transient search, which is the follow-up of GW event triggers from LIGO/Virgo. We discuss the facility's performance in the case of the second binary neutron star merger GW190425. In time for the LIGO/Virgo O4 run, we will have deeper reference images for galaxies within out to ~200 Mpc distance, allowing rapid transient detection to i ~ 21 mag.

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결합 적분방정식을 이용한 삼차원 임의형태 도체 구조물의 전자파 지연산란 해석 (Analysis of Transient Scattering from Arbitrarily Shaped Three-Dimensional Conducting Objects Using Combined Field Integral Equation)

  • 정백호
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • 제51권11호
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    • pp.551-558
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    • 2002
  • A time-domain combined field integral equation (CFIE) is presented to obtain the transient scattering response from arbitrarily shaped three-dimensional conducting bodies. This formulation is based on a linear combination of the time-domain electric field integral equation (EFIE) with the magnetic field integral equation (MFIE). The time derivative of the magnetic vector potential in EFIE is approximated using a central finite difference approximation and the scalar potential is averaged over time. The time-domain CFIE approach produces results that are accurate and stable when solving for transient scattering responses from conducting objects. The incident spectrum of the field may contain frequency components, which correspond to the internal resonance of the structure. For the numerical solution, we consider both the explicit and implicit scheme and use two different kinds of Gaussian pulses, which may contain frequencies corresponding to the internal resonance. Numerical results for the EFIE, MFIE, and CFIE are presented and compared with those obtained from the inverse discrete Fourier transform (IDFT) of the frequency-domain CFIE solution.

후드를 이용한 협소 터널 미기압파 감소 효과에 대한 수치적 연구 (Numerical Study of effects on micro-pressure wave reduction by a hood on a narrow tunnel)

  • 윤수환;김병열;구요천;이동호;권혁빈;고태환
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2005년도 추계학술대회 논문집
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    • pp.872-877
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    • 2005
  • The train entry into a tunnel generates a strong compression wave in the tunnel. The high amplitude of compression wave causes high pressure gradients that are responsible for both the aural discomfort of passengers and the impulsive acoustical wave called the miro-pressure wave. This paper provides a numerical study on effects of hood for micro'-'pressure wave reduction. An axisymmetric numerical solver, considering the cross sectional area of Korean Tilting Train eXpress, is used for a transient flow field in the tunnel. Results show that the micro-pressure wave is able to be reduced by a hood. In this results, the maximum reduction of micro--pressure wave is shown at 2L(length), 1.35D(diameter) hood around $56\%$ against the non-hood case.

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적분 방정식을 이용한 도선 산란체 및 안테나의 과도응답 해석 (Analysis of Transient Response from Conducting Wire Scatterer and Antenna Using Integral Equation)

  • 정백호;서정훈;윤희상
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • 제51권11호
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    • pp.559-566
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    • 2002
  • In this paper, we present an accurate and stable method for the solution of the transient electromagnetic response from the conducting wire structures using the time domain integral equation. By using an implicit scheme with the central finite difference approximation for the time domain electric field integral equation, we obtain the transient response from a wire scatterer illuminated by a plane wave and a conducting wire antenna with an impressed voltage source. Also, we consider a wire above a 3-dimensional conducting object. Numerical results are presented, which show the validity of the presented methodology, and compared with a conventional method using backward finite difference approximation.

A.C. 전장이 인가된 광굴절 Bi12SiO20 결정의 2광파 혼합 이득의 시간종속 변화 (Transient Behaviour of Photorefractive $Bi_{12}SiO_{20}$ Crystal: Two Wave Mixing with an External A.C. Field)

  • 곽종훈
    • 한국광학회지
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    • 제4권1호
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    • pp.73-83
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    • 1993
  • 광굴절결정에 구형과 및 저현파형의 외부 전장을 인가할 때 유기되는 공간 전하장의 시간 종속 해를 해석적으로 유도하였다. B$i_{12}$Si$O_{20}$ 결정에 최대 7KV/cm (주파수<1KHz)의 전장을 가하면서 시간 종속적인 2광파 혼합의 이득 변화를 측정하고 이론치와 정량적으로 비교 분석하였다.

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기총 폭발 하중에 대한 모델 수립과 구조 해석에 관한 연구 (A Study on Model Establishment and Structural Analysis for Gun Blast Load)

  • 김대관;한재흥;장재호
    • 한국항공우주학회지
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    • 제33권7호
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    • pp.33-39
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    • 2005
  • 총구로부터 방출되는 폭발파에 대한 수학적 모델(GUNBLAST)을 수립하였으며, 폭발 하중에 대한 구조 응답 해석을 수행하였다. 폭발파는 자유영역 폭발파와 반사 폭발파로 구분되어질 수 있다. 본 연구에서는 스케일 기법을 이용하여 자유영역 폭발파 모델을 수립하였으며, 경사 충격파 이론과 전산유체역학(Computational Fluid Dynamics) 계산을 통하여 반사 충격파를 계산하였다. GUNBLAST는 두 가지의 구조 모델에 적용되었으며 구조 표면으로부터의 총구거리 변화에 따른 폭발파 특성을 파악하기 위하여 평판에 대한 적용을 통하여 균일하중조건과의 비교를 수행하였다. 또한 MSC/NASTRAN을 이용하여 12.7mm 기총을 장착한 비행기 날개 모델의 과도 응답 해석을 수행하였다. 결과적으로 이러한 폭발파는 랜덤진동과 항공기에 탑재된 장비에 고주파의 손상을 일으킬 수 있음을 확인하였다.