• Title, Summary, Keyword: Incident wave

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Propagation Characteristics of Compression Waves Reflected from the Open End of a Duct

  • Kim, Heuy-Dong;Lee, Dong-Hoon;H. Kashimura;T. Setoguchi
    • Journal of Mechanical Science and Technology
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    • v.17 no.5
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    • pp.718-725
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    • 2003
  • The present study addresses the distortion of the compression wave reflected from an open end of a shock tube. An experiment is carried out using the simple shock tube with an open end Computational work is also performed to represent the experimented flows. The second-order Total Variation Diminishing scheme is employed to numerically solve the unsteady, axisy-mmetric, inviscid, compressible governing equations. Both the experimented and predicted results are in good agreement. The generation and development mechanisms of the compression wave, which Is reflected from the open end of the shock tube, are obtained in detail from the present computations. The effect of size of the baffle plate at the open-end that causes the reflection of the incident expansion wave is found negligible. A good correlation is obtained for transition of the reflected compression wave to a shock wave inside the tube. The present data show that for a given wave length of the incident expansion wave the transition of the reflected compression wave to a shock wave can be predicted with good accuracy.

Characteristics of Wave-induced Currents using the SWASH Model in Haeundae Beach (SWASH 모형을 이용한 해운대 해수욕장의 해빈류 특성)

  • Kang, Min Ho;Kim, Jin Seok;Park, Jung Kyu;Lee, Jong Sup
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.27 no.6
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    • pp.382-390
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    • 2015
  • To simulate a complicated hydrodynamic phenomena in the surf zone, the SWASH model is used in Haeundae Beach. The SWASH model is well known as a model competing with the Boussinesq-type model in terms of near shore waves and wave-induced currents modelling. This study is aimed to the detailed analysis of seasonal waves and wave-induced current simulation in Haeundae Beach, where the representative seasonal wave conditions was obtained from hourly measured wave data in 2014 by Korea Hydrographic and Oceanographic Administration( KHOA). Incident wave conditions were given as irregular waves by JONSWAP spectrum. The calculated seasonal wave-induced current patterns were compared with the field observation data. In summer season, a dominant longshore current toward the east of the beach appears due to the effect of incident waves from the South and the bottom bathymetry, then some rip currents occurs at the central part of the beach. In the winter season, ESE incident waves generates a strong westward longshore currents. However, a weak eastward longshore currents appears at the restricted east side areas of the beach.

Optimal Design for Maximum Transmittance of Electromagnetic Wave through Foam Core Sandwich Structures Using Genetic Algorism (유전자 알고리즘을 이용한 폼코어 샌드위치 구조물의 전파 투과성 최적화에 관한 연구)

  • 신현수;전흥재;박근식
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.183-186
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    • 2001
  • In this paper, the analytical model to understand the propagation of electromagnetic waves in the foam core sandwich structures was proposed. Using the analytical model, efforts were made to find the optimal stacking sequence of composite skins for maximum transmittance of electromagnetic wave. Numerical analyses of unidirectional composites and foam as a function of incident angle were performed. From the results of analysis, the general tendencies of transmittance of electromagnetic wave through composites and foam were obtained. Based on the general tendencies, optimal stacking sequences of composite skins for the maximum transmittance of electromagnetic wave were found with certain ranges of incident angle using genetic algorithm(GA).

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Numerical Analysis of the Three-Dimensional Nonlinear Waves Caused by Breaking Waves around a Floating Offshore Structure (부유식 해양구조물 주위의 쇄파현상을 동반한 3차원 비선형성 파의 수치해석)

  • 박종천;관전수명
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.62-73
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    • 1996
  • Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

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Characteristics of Equilibrium Beach Profile under Random Waves (불규칙파랑 효과를 고려한 평형단면의 특성)

  • Lee, Cheol-Eung;Choi, Han-Kyu;Han, Chun-Ho
    • Journal of Industrial Technology
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    • v.16
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    • pp.83-95
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    • 1996
  • The equilibrium beach profiles with the effects of random waves and nonuniform grain size in the surf zone are derived from the Thornton and Guza(1983)'s energy dissipation model. The derived beach profiles are the functions of the breaking wave strength, the frequency of the incident wave, and the wave induced-energy dissipation at breaking point. It is not confirmed that the equilibrium beach profiles are better agreement with the measured profiles than the classical profiles. However, the characteristic of the changes of the beach profiles with respect to the breaking wave stgrngth and the frequency of the incident wave can be analyzed which has not been studied by the classical model.

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Numerical simulation of the free surface around a circular column in regular waves using modified marker-density method

  • Yang, In-Jun;Lee, Young-Gill;Jeong, Kwang-Leol
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.7 no.3
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    • pp.610-625
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    • 2015
  • In this paper the wave run-up around a circular column in regular waves is numerically calculated to investigate the applicability of the Modified Marker-Density (MMD) method to prediction of wave run-up around an offshore platform. The MMD method is one of the methods to define the highly nonlinear free surface. The governing equations are the Navier-Stokes equations and the continuity equation which are computed in Cartesian grid system. To validate incident waves generated by numerical simulation, those are compared with the solutions of the Stokes $5^{th}$ order wave theory. The wave run-up simulations are performed varying the steepness and period of incident waves as referred experimental data. The numerical results are compared to the experimental data and the results show good agreements.

Effect of Tube Area on the Impulse Wave Discharged from the Exit of Tube (관출구로부터 방출되는 펄스파에 미치는 관단면적의 영향)

  • Shin, Hyun-Dong;Lee, Young-Ki;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • pp.544-549
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    • 2003
  • When a shock wave arrives at an open end of tube, an impulse wave is discharged from the tube exit and causes serious noise and vibration problems. In the current study, the effect of the cross-sectional area of tube on the impulse wave is numerically investigated using a CFD method. The Harten-Yee's total variation diminishing(TVD) scheme is used to solve the axisymmetric, two-dimensional, unsteady, compressible Euler equations. With three different cross-sectional areas of tube, the Mach number of the incident shock wave $M_{s}$ is varied between 1.01 and 1.5. The results obtained show that the directivity and magnitude of impulse wave strongly depend upon the Mach number of incident shock wave and are influenced by the tube area. It is also known that the tube cross-sectional area significantly affects the magnitude of impulse wave at or near the tube axis.

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A Computational Study of the Impulsive Wave Discharged from a Circular Tube (원형관으로부터 방출되는 펄스파에 대한 수치해석적 연구)

  • Lee, Young-Ki;Kweon, Yong-Hun;Kim, Heuy-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.7
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    • pp.850-856
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    • 2004
  • When a shock wave arrives at the open end of a tube, an impulsive wave is discharged from the tube exit and causes serious noise and vibration problems. In the current study, the effect of the cross-sectional area of a circular tube on the impulsive wave is investigated using computational methods. Marten-Yee's TVD scheme was employed to solve axisymmetric, unsteady, compressible Euler equations. With a change in the cross-sectional area of the tube, the Mach number of an incident shock wave is varied between 1.01 and 1.50. The results obtained show that the magnitude of the impulsive wave strongly depends upon the Mach number of the incident shock wave and the cross-sectional area of the tube. It is also found that for a given cross-sectional area of the tube, the impulse wave has strong directivity to the tube axis.

Pseudo 3D FEM analysis for wave passage effect on the response spectrum of a building built on soft soil layer

  • Kim, Yong-Seok
    • Earthquakes and Structures
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    • v.8 no.5
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    • pp.1241-1254
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    • 2015
  • Spatially variable ground motions can be significant on the seismic response of a structure due to the incoherency of the incident wave. Incoherence of the incident wave is resulted from wave passage and wave scattering. In this study, wave passage effect on the response spectrum of a building structure built on a soft soil layer was investigated utilizing a finite element program of P3DASS (Pseudo 3-dimensional Dynamic Analysis of a Structure-soil System). P3DASS was developed for the axisymmetric problem in the cylindrical coordinate, but it is modified to apply anti-symmetric input earthquake motions. Study results were compared with the experimental results to verify the reliability of P3DASS program for the shear wave velocity of 250 m/s and the apparent shear wave velocities of 2000-3500 m/s. Studied transfer functions of input motions between surface mat foundation and free ground surface were well-agreed to the experimental ones with a small difference in all frequency ranges, showing some reductions of the transfer function in the high frequency range. Also wave passage effect on the elastic response spectrum reduced the elastic seismic response of a SDOF system somewhat in the short period range.

A Nonlinear Response Analysis of Tension Leg Platforms in Irregular Waves (불규칙파중의 인장계류식 해양구조물의 비선형 응답 해석)

  • Lee, Chang-Ho;Gu, Ja-Sam;Jo, Hyo-Je;Hong, Bong-Gi
    • Journal of Ocean Engineering and Technology
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    • v.12 no.2
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    • pp.33-42
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    • 1998
  • In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

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