• Title/Summary/Keyword: Numerical wave tank(NWT)

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Dynamic Response Analyses of Fixed Type Substructures for 2.5MW Class Offshore Wind Turbine

  • Song, Chang Yong;Yoo, Jaehoon
    • Journal of Advanced Research in Ocean Engineering
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    • v.3 no.1
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    • pp.15-24
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    • 2017
  • This paper explores a series of numerical simulations of dynamic responses of multi-piles (dolphin) type substructures for 2.5MW class offshore wind turbine. Firstly computational fluid dynamics (CFD) simulation was performed to evaluate wave loads on the dolphin type substructures with the design wave condition for the west-south region of Korea. Numerical wave tank (NWT) based on CFD was adopted to generate numerically a progressive regular wave using a virtual piston type wave maker. It was found that the water-piercing area of piles of the substructure is a key parameter determining the wave load exerted in horizontal direction. In the next the dynamic structural responses of substructure members under the wave load were calculated using finite element analysis (FEA). In the FEA approach, the dynamic structural responses were able to be calculated including a deformable body effect of substructure members when wave load on each member was determined by Morison's formula. The paper numerically identifies dynamic response characteristics of dolphin type substructures for 2.5MW class offshore wind turbine.

A time-domain simulation of an oscillating water column with irregular waves

  • Koo, Weoncheol;Kim, Moo-Hyun
    • Ocean Systems Engineering
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    • v.2 no.2
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    • pp.147-158
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    • 2012
  • A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

Numerical Analysis of Hydrodynamic Forces on a Floating Body in Two-layer Fluids (밀도가 상이한 두 유체층에서 부유체 동유체력 특성의 수치적 해석)

  • Kim, Mi-Geun;Koo, Weon-Cheol
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.3
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    • pp.369-376
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    • 2010
  • In this study, a radiation and a diffraction problems of a floating body in two-layer fluids were solved by the Numerical Wave Tank(NWT) technique in the frequency domain. In two-layer fluids, two different wave modes exist and the hydrodynamic coefficients can be obtained separately for each mode. The two-domain Boundary Element Method(BEM) in the potential fluid using the whole-domain matrix scheme was used to investigate the characteristics of wave forces, added mass and damping coefficients. The effects of the ratio of density and water depth in the lower domain were also evaluated and compared with given references.

Free surface simulation of a two-layer fluid by boundary element method

  • Koo, Weon-Cheol
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.2 no.3
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    • pp.127-131
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    • 2010
  • A two-layer fluid with free surface is simulated in the time domain by a two-dimensional potential-based Numerical Wave Tank (NWT). The developed NWT is based on the boundary element method and a leap-frog time integration scheme. A whole domain scheme including interaction terms between two layers is applied to solve the boundary integral equation. The time histories of surface elevations on both fluid layers in the respective wave modes are verified with analytic results. The amplitude ratios of upper to lower elevation for various density ratios and water depths are also compared.

Numerical Wave Tank Technology for Multipurpose Simulation in Marine Environmental Engineering (해양환경공학의 다목적 시뮬레이션을 위한 수치파랑수조 기술)

  • 박종천
    • Journal of Ocean Engineering and Technology
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    • v.17 no.4
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    • pp.1-7
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    • 2003
  • A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D Numerical Wave Tank(NWT). The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation. The Marker-Density function technique is adopted to implement the fully nonlinear freesurface kinematic condition. The marine environmental situations, i.e., waves, currents, etc., are reproduced by use of multi-segmented wavemakers on the basis of the so-called ″snake-principle″. In this paper, some numerical reproduction techniques for regular, and irregular waves, multi-directional waves, Bull's-eye wave. wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

Development of Multidirectional Nonlinear Numerical Wave Tank by Naoe-FOAM-SJTU Solver

  • Cao, Hong-Jian;Wan, De-Cheng
    • Journal of Advanced Research in Ocean Engineering
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    • v.1 no.1
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    • pp.14-24
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    • 2015
  • A three-dimensional multidirectional nonlinear numerical wave tank (NWT) based on the Navier-Stokes equations and the Finite Volume Method (FVM) is developed by using the two-phase hydrodynamic flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. The free surface is capturing with the Volume Of Fluids (VOF). The directional wave including Stokes wave, solitary wave and nonlinear wave are simulated and verified. The multi-directional waves are also simulated with particular wave spectral such as JONSWAP and wave directional spreading function. The obtained numerical results show the capability of the solver to generate different type of multidirectional nonlinear waves accurately. Meanwhile, it implies that the presented NWT can easily extend to model the wave-structures interactions, which will be great help to the offshore structures design.

Flow Analysis of Two-Dimensional Floating Body with Moon Pool Using a Numerical Wave Tank (수치 파동 수조를 이용한 부유체의 문풀 (Moon Pool) 유동해석)

  • Koo, Weon-Cheol;Lee, Kyoung-Rok
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.2
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    • pp.107-112
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    • 2011
  • The aim of this study is to analyze the hydrodynamic properties of a 2D floating body with moon pool using a 2D fully nonlinear Numerical Wave Tank(NWT). This NWT was developed based on the Boundary Element Method(BEM) with potential theory and fully nonlinear free surface boundary conditions. Free surface elevations in the moon pool were calculated in the time domain for various frequencies of forced body motions. The added-mass and damping coefficients of the heaving body were also obtained. The present numerical results were compared with the analytic and experimental results and their accuracy was verified.

Simplified formulas of heave added mass coefficients at high frequency for various two-dimensional bodies in a finite water depth

  • Koo, Weoncheol;Kim, Jun-Dong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.7 no.1
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    • pp.115-127
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    • 2015
  • The aim of this study is to develop a simplified formula for added mass coefficients of a two-dimensional floating body moving vertically in a finite water depth. Floating bodies with various sectional areas may represent simplified structure sections transformed by Lewis form, and can be used for floating body motion analysis using strip theory or another relevant method. Since the added mass of a floating body varies with wave frequency and water depth, a correction factor is developed to take these effects into account. Using a developed two-dimensional numerical wave tank technique, the reference added masses are calculated for various water depths at high frequency, and used them as basis values to formulate the correction factors. To verify the effectiveness of the developed formulas, the predicted heave added mass coefficients for various wetted body sections and wave frequencies are compared with numerical results from the Numerical Wave Tank (NWT) technique.

Hydrodynamic analysis of a floating body with an open chamber using a 2D fully nonlinear numerical wave tank

  • Uzair, Ahmed Syed;Koo, Weon-Cheol
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.4 no.3
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    • pp.281-290
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    • 2012
  • Hydrodynamic analysis of a surface-piercing body with an open chamber was performed with incident regular waves and forced-heaving body motions. The floating body was simulated in the time domain using a 2D fully nonlinear numerical wave tank (NWT) technique based on potential theory. This paper focuses on the hydrodynamic behavior of the free surfaces inside the chamber for various input conditions, including a two-input system: both incident wave profiles and forced body velocities were implemented in order to calculate the maximum surface elevations for the respective inputs and evaluate their interactions. An appropriate equivalent linear or quadratic viscous damping coefficient, which was selected from experimental data, was employed on the free surface boundary inside the chamber to account for the viscous energy loss on the system. Then a comprehensive parametric study was performed to investigate the nonlinear behavior of the wave-body interaction.

Numerical Analysis of Internal Waves in Two-layer Fluids by a Two-domain Boundary Element Method (Two-domain 경계 요소법을 이용한 해양 내부파의 수치적 재현)

  • Koo, Weon-Cheol;Kim, Mi-Geun
    • Journal of Ocean Engineering and Technology
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    • v.23 no.4
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    • pp.6-11
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    • 2009
  • In this study, the internal waves in two-density layered fluids were analyzed using the Numerical Wave Tank (NWT) technique in the frequency domain. The NWT is based on a two-domain Boundary Element Method with the potential fluids using the whole-domain matrix scheme. From the mathematical solution of the two-domain boundary integral equation, two different wave modes could be classified: a surface wave mode and an internal wave mode, and each mode were shown to have a wave number determined by a respective dispersion relation. The magnitudes of the internal waves against surface waves were investigated for various fluid densities and water depths. The calculated results are compared with available theoretical data.