• Title/Summary/Keyword: Wave focusing

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Nonlinear Focusing Wave Group on Current (흐름의 영향을 받는 파랑 그룹의 비선형 집중)

  • Touboul, Julien;Pelinovsky, Efim;Kharif, Christian
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.19 no.3
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    • pp.222-227
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    • 2007
  • Formation of freak waves is studied in deep water from transient wave packets propagating on current. Those waves are obtained by means of dispersive focusing. This process is investigated by solving both linear and nonlinear equations. The role of nonlinearity is emphasized in this interaction.

Effect of Wave Focusing Structures in Combined Waves and a Current (파랑과 흐름의 혼합하에서 파랑집적구조물의 영향)

  • Lee, J.W.;Cheung, K.F.
    • Journal of Korean Port Research
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    • v.8 no.2
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    • pp.67-77
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    • 1994
  • A time-domain numerical model is developed to examine the performance of a wave energy focusing structure in combined waves and a current. With the current assumed to be slow and the structure fully submerged, the wave-current interaction problem is reduced to a wave scattering problem in a uniform current. The diffraction of incident waves around a narrow berm is considered. The shape of the berm is defined by a parabola, imitating that of an optical reflector. The energy focus is achieved by reflecting the incident waves through a predetermined focal point. Through the numerical simulations, the numerical model is shown to be effective in modeling the wave-current interaction problem, and the current speed and direction are shown to affect significantly the location, amplitude and sharpness of the focus.

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Effects of Wave Focusing Device on Performance of OWC Chamber (OWC형 파력발전 공기실의 파랑집중장치의 효과에 대한 수치적인 연구)

  • Liu, Zhen;Hyun, Beom-Soo;Hong, Key-Yong;Jin, Ji-Yuan
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.13 no.1
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    • pp.12-17
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    • 2010
  • Oscillating Water Column (OWC) device has been widely employed in the wave energy conversion. Wave Focusing Device (WFD) is proposed to be helpful for improving the operating performance of OWC chamber. In the present paper, a Numerical Wave Tank (NWT) using two-phase VOF model is utilized to simulate the generation and propagation of incident regular waves, water column oscillation inside the chamber. The NWT consists of the continuity equation, Reynolds-averaged Navier-Stokes equations and two-phase VOF functions. The standard k- turbulence model, the finite volume method, NITA-PISO algorithm and dynamic mesh technique are employed. Effects of WFD on the operating performance of OWC chamber are investigated numerically.

Nonlinear Time Reversal Focusing and Detection of Fatigue Crack

  • Jeong, Hyun-Jo;Barnard, Dan
    • Journal of the Korean Society for Nondestructive Testing
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    • v.32 no.4
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    • pp.355-361
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    • 2012
  • This paper presents an experimental study on the detection and location of nonlinear scattering source due to the presence of fatigue crack in a laboratory specimen. The proposed technique is based on a combination of nonlinear elastic wave spectroscopy(NEWS) and time reversal(TR) focusing approach. In order to focus on the nonlinear scattering position due to the fatigue crack, we employed only one transmitting transducer and one receiving transducer, taking advantage of long duration of reception signal that includes multiple linear scattering such as mode conversion and boundary reflections. NEWS technique was then used as a pre-treatment of TR for spatial focusing of reemitted second harmonic signal. The robustness of this approach was demonstrated on a cracked specimen and the nonlinear TR focusing behavior is observed on the crack interface from which the second harmonic signal was originated.

A Study of the Characteristics and Mechanism of Giant wave Appearance (대양에서의 거대파랑 출현 특성과 기구에 관한 연구)

  • Shin Seung-Ho;Hong Keyyong
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2005.10a
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    • pp.147-152
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    • 2005
  • 선형파 이론에 의한 파랑스펙트럼 분포에 의해서는 30m 크기의 파랑은 현실적으로 거의 발생 불가능하다고 인식되어 왔다. 그러나 최근의 위성 영상을 이용한 조사에 의해 3주간의 기간 통안 25m 이상의 거대파가 10개 이상 관측됨에 따라 실해역에서 빈번히 마주칠 수 있는 현상임이 입증되었으며 이에 따라 지금까지 이유 불명으로 치부되어 왔던 많은 해양 재난이 거대파에 의해 발생했던 것으로 추정되고 있다. 거대파의 발생원인은 파군 형성과 관련한 파고분포 특성의 변화, 전파하는 파군의 비선형 공명간섭 통이 제기되고 있으나, 그 출현의 복잡성과 자료의 부족 등으로 아직 명확하게 해명되지 못하고 있다. 본 연구에서는 실해역에서 발생하는 거대파의 특성 및 선형 및 비선형이론에 근거한 거대파 발생 기구를 고찰하고 비선형 파랑전파를 모사할 수 있는 수치모형을 개발하였다.

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Numerical Computations on Extreme Wave Loads on a Vertical Cylinder Considering Hydroelastic Response (유탄성 응답을 고려한 수직 실린더에 작용하는 극한 파랑 충격력 수치해석)

  • Kyoung, Jo-Hyun;Hong, Sa-Young;Kim, Byoung-Wan
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • v.1
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    • pp.195-201
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    • 2006
  • The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as freak wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

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Numerical Computations on Hydroelastic Response of a Vertical Cylinder in Extreme Wave Loads (유탄성 응답을 고려한 수직 실린더에 작용하는 극한파의 파랑하중 수치해석)

  • Hong, Sa-Young;Kim, Byoung-Wan;Kyoung, Jo-Hyun
    • Journal of Navigation and Port Research
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    • v.31 no.1 s.117
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    • pp.21-27
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    • 2007
  • The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as extreme wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

Ultrasound-guided Exact Focusing of Extracorporeal Shock Wave Therapy for the Calcific Tendinitis of Gluteus Medius - A Case Report - (중둔건 석회화 건염의 초음파 유도하 정확한 조준에 의한 체외충격파치료 -증례 보고-)

  • Moon, Sang Ho;Lee, Song;Kim, Kwang Hai;Jeong, Jongpil;Hong, Seong Won
    • The Journal of Korean Orthopaedic Ultrasound Society
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    • v.5 no.2
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    • pp.94-98
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    • 2012
  • Calcific tendinitis is characterized by inflammation around calcium hydroxyapatite crystal deposits. Minimally invasive extracorporeal shock wave therapy (ESWT) has been postulated to be an effective treatment option for treating calcific tendinitis. In clinical practice, shock waves usually are aimed at the painful area after palpation and not focused. It has been known that exact fluoroscopic focusing of ESWT at the calcific deposit for treatment of calcifying tendinopathy is highly effective. Ultrasound is a simple, inexpensive and radiation-free diagnostic tool that has been used to demonstrate tendinopathy including calcific tendinitis. However, focusing of shock wave under ultrasound is less well established. We present a patient in whom large calcific tendinitis of gluteus medius was completely resolved by exact focusing of ESWT by ultrasound with literature review.

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Investigating the Spatial Focusing Performance of Time Reversal Lamb Waves on a Plate through the Finite Element Method (유한요소법을 통한 판에서 시간반전 램파의 공간집속성능 규명)

  • Choi, Jeong-Hee;Lee, Hae-Sung;Park, Hyun-Woo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.21 no.12
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    • pp.1120-1131
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    • 2011
  • Researches using time reversal acoustics(TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of a plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric(PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

Investigating the Spatial Focusing Performance of Time Reversal Lamb waves for Impact Localization on a Plate (판의 충격위치 추정을 위한 시간반전 램파의 공간모임성능 규명)

  • Park, Hyun-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.418-429
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    • 2011
  • Researches using time reversal acoustics (TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of the plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric (PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

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