• Title, Summary, Keyword: Incident wave

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A Study on the Numerical Calculation for Wind Waves During the Passage of Typhoon 'Memi' (태풍 '매미' 내습시 파랑선정에 관한 기초적 연구)

  • LEE GYONG-SEON;KIM HONG-JIN;YOON HAN-SAM;RYU CHEONG-RO
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.229-234
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    • 2004
  • A Typhoon wave is generated by wind fields during the Passage of Typhoon. Transporting wind field makes wind wave and swell in the open sea, and then, those wave components are transported in the shallow water. Typhoon waves in the shallow water is generated by Typhoon wind field and incident wave. Bisides, Incident waves to the shallow water are deformated by topographic conditions. This paper estimated the analysis of the Typhoon waves by wind fields and incident waves according to wave action balance equation model. As the result of wave numerical experiment, wave field during the passage of Typhoon 'Memi' in the shallow water is strongly effect by wind fields. Wave action balance equaion can be partially used for Typhoon wave simulations.

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Spatial Distribution of Wave Overtopping along Vertical Structure due to Obliquely Incident Waves (경사입사파에 의한 직립구조물에서 월파의 공간적 분포)

  • Kim, Young-Taek;Lee, Jong-In;Cho, Yong-Sik
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.23 no.6
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    • pp.414-421
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    • 2011
  • In determination of the crest height of a vertical structure against attacking of obliquely incident waves, most of existing studies have suggested to use the overtopping reduction factor due to incident angles. However, they have not considered the amplification of wave heights and the spatial distribution of wave overtopping. In this study, a spatial distribution of overtopping due to the amplification of wave heights along a vertical structure is investigated experimentally. It is recommended that the crest height can be determined by the same manner as that for normally incident waves up to 3 significant wave lengths from the one end of the structure. However, the rest part of the structure can be done by employing the overtopping reduction factor with considering the amplification of wave heights and the spatial distribution of wave overtopping.

Effect of the Shape of Absorbing Revetment on Wave Overtopping Rate (소파호안의 형상이 월파량에 미치는 영향)

  • Hur, Dong-Soo;Choi, Dong-Seok;Choi, Sun-Ho
    • Journal of Ocean Engineering and Technology
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    • v.22 no.6
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    • pp.7-12
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    • 2008
  • The present study numerically investigates the effect of the shape of absorbing revetment on wave overtopping rate under regular and irregular incident waves. At first, the numerical model developed by Hur and Choi(2008), which considers the flow through a porous medium with inertial, laminar and turbulent resistance terms, directly simulates Wave-Structure-Sandy seabed interaction and can determine the eddy viscosity with LES turbulent model in 2-Dimensional wave field (LES-WASS-2D), is validated when compared to experimental data. Numerical simulations are then performed to examine the effect of the shape of absorbing revetment and incident wave conditions on wave overtopping rate. The numerical result shows that the wave overtopping rate decreases with the slope gradient of absorbing revetment under both regular and irregular waves. In addition, the effects of mean grain size and porosity of absorbing revetment, incident wave period and crest height on wave overtopping rate are discussed.

High-Frequency Bistatic Scattering from a Corrugated Sediment Surface

  • Cho, Hong-Sang;La, Hyoung-Sul;Yoon, Kwan-Seob;Na, Jung-Yul;Kim, Bong-Chae
    • The Journal of the Acoustical Society of Korea
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    • v.25 no.2E
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    • pp.60-68
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    • 2006
  • High-frequency bistatic scattering measurements from a corrugated surface were made in an acoustic water tank. First the azimuthal scattering pattern was measured from an artificially corrugated surface which has varying impedance. The corrugated surface was installed both transverse to the direction of incident wave and longitudinal to the direction of incident wave. The angle between the corrugated surface and the direction of the incident wave was about $45^{\circ}$. Second, the scattering strengths were measured from the flat sediment and the corrugated sediment. A critical angle of about $37^{\circ}$ was calculated in the acoustic water tank. The measurements were made at three fixed grazing angles: $33^{\circ}$ (lower than critical angle), $37^{\circ}$ (critical angle), and $41^{\circ}$ (higher than critical angle). The scattering angle and the grazing angle are equal in each measurement. Frequencies were from 50 kHz to 100 kHz with an increment of 1 kHz. The corrugated sediment was made transverse to the direction of the incident wave. The first measurement indicates that the scattering patterns depend on the relations between the corrugated surface and the direction of the incident wave. In the second measurement, the data measured from the flat sediment were compared to the APL-UW model and to the NRL model. The NRL model's output shows more favorable comparisons than the APL-UW model. In case of the corrugated sediment, the model and the measured data are different because the models used an isotropic wave spectrum of sediment roughness in the scattering calculations. The isotropic wave spectrum consists of $w_2$ and ${\gamma}_2$. These constants derived from sediment names or bulk size. The model which used the constants didn't consider the effect of a corrugated surface. In order to consider a corrugated surface, the constants were varied in the APL-UW model.

The Boundary Element Analysis of Waves coming with Oblique Angle to a Submerged Breakwater (잠제에 경사로 입사하는 파랑의 경계요소 해석)

  • Kim, Nam Hyeong;Woo, Su Min
    • Journal of The Korean Society of Civil Engineers
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    • v.32 no.5B
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    • pp.295-300
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    • 2012
  • Reflection coefficients of wave due to the types of a submerged breakwater on the inclined incident wave are numerically computed by using boundary element method. The analysis method is based on the wave pressure function with the continuity in the analytical region including fluid and structures. When compared with the existing results on the inclined incident wave, the results of this study show good agreement. It is found that both maximum and minimum values of the reflection coefficient are appeared frequently, as the width of a submerged breakwater becomes wider, and the reflection coefficient increase, as the wave period is longer. In addition, the effect on the reflection coefficient due to the change of submerged breakwater hight is lager than that due to the change of submerged breakwater width. The results indicate that dissipating characteristics of wave due to the types of a submerged breakwater own high dependability regarding the change of inclined incident waves. Therefore, the results of this study is estimated to be applied as an accurate numerical analysis referring to inclined incident waves in real sea.

Realization of acoustic scattering holography (산란 음향 홀로그래피의 구현 방법론)

  • 이상협;김양한
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.640-644
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    • 2003
  • There are many difficulties to get the scattered field generated by obstacle which has arbitrary shape or irregular surface impedance by using analytic solution or numerical methods. In this study, we propose experimental method of acoustic scattering holography that can predict the far-field scattered field based on nearfield measurements. In particular we can get the scattered fields of each wave-number components of incident fields. We express the relationship of wave-number components between incident fields and scattered fields using scattering matrix which is transfer matrix of wave-number components. Lastly, we prove the relation between wave-number components of incident and scattered field by experiments. The errors which are caused by measurements and decomposition methods are also analyzed.

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A study on the wave forces acting on the multiple plils of oceanic circular cylinder (해양원주 구조물에 작용하는 파력에 관한 연구)

  • 오세욱;문병형;이승휘
    • Journal of Ocean Engineering and Technology
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    • v.1 no.2
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    • pp.28-38
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    • 1987
  • Experimental studies are conducted for the wave forces acting on the vertically mounted circular piles in the waves. Two-three-cylinder arrays are equally spaced and the spacings(S/D) as well as the incident angles of various waves are changed to study their separate effects on the wave forces. The numerical results based on the diffraction theory are in good agreement with the experimental results, and the diffraction theory well predicts the trend of the wave forces when the spacings and the incident angles are changed.

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Nonlinear Response Characteristics of the ISSC TLP in Time Domain (시간영역에서 ISSC TLP의 비선형 응답 특성)

  • Lee, Chang-Ho
    • Journal of Ocean Engineering and Technology
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    • v.20 no.5
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    • pp.30-35
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    • 2006
  • In tire presence of incident waves with different frequencies, there are second order sum and difference frequency wave exciting forces due to the nonlinearity of tire incident waves. Although the magnitude of these nonlinear wave forces are small, they act on TLPs at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency waveexciting forces occurring close to tire natural frequencies of TLPs often give greater contributions to high and law frequency resonant responses. Nonlinear motion responses and tension variations in the time domain are analyzed by solving the motion equations with nonlinear wave exciting forces using tire numerical analysismethod. The numerical results of time domain analysis for the nonlinear wave exciting forces on the ISSC TLP in regular waves are compared with the numerical and experimental ones of frequency domain analysis. The results of this comparison confirmed tire validity of the proposed approach.

Realization of Acoustic Scattering Holography (산란 음향 홀로그래피의 구현 방법론)

  • 김양한
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.14 no.11
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    • pp.1101-1106
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    • 2004
  • There are many difficulties to get the scattered field generated by obstacle which has arbitrary shape or irregular surface impedance by using analytic solution or numerical methods. In this study, we propose a method of which makes acoustic scattering holography that can predict the far-field scattered field based on nearfield measurements. This method provides the scattered fields of each wave-number components of incident fields. We express the relationship of wave-number components between incident fields and scattered fields using scattering matrix which is transfer matrix of wave-number components. Lastly, we prove the relation between wave-number components of incident and scattered field by experiments. The errors which are caused by measurements and decomposition methods are also analyzed.

Experimental study on compression wave propagating in a sudden reduction duct (급축소관을 전파하는 압축파에 관한 실험적 연구)

  • Kim, Hui-Dong;Matsuo, Kazuyasu
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.9
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    • pp.1139-1148
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    • 1997
  • Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.