• Title, Summary, Keyword: RANS equation

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On the Feasibility of Freak Waves Formation within the Harbor Due to the Presence of Infra-Gravity Waves of Bound Mode Underlying the Ever-Present Swells (Bound Mode의 외중력파에 의한 항내 이상파 생성가능성에 대하여)

  • Cho, Yong Jun;Bae, Jung Hyun
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.31 no.1
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    • pp.17-27
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    • 2019
  • We carry out the numerical simulation to test a hypothesis that freak waves can be triggered by the infragravity waves of bound mode underlying the ever-present swells and its constructive interaction with swells using the Tool Box called the ihFoam that has its roots on the OpenFoam, and Bi-spectrum. Numerical simulation is implemented for the SamChcuk LNG Plant where freak waves have been reported in front of the private wharf during its construction phase due to the uncompleted northern breakwater. Infra-gravity waves of bound mode is generated using the difference wave-wave interaction between the local wind waves of 7 s and a swell of 11.4 s based on the Bi-spectrum. For the sake of comparison, numerical simulation for infra-gravity waves of free mode is also carried out. Numerical results show that stem waves along the private wharf for SamChcuk LNG Plant can be triggered by the infra-gravity waves of bound mode coming from the north, which eventually leads to freak waves when encounters the reflected waves from the south jetty.

Development of Two Dimensional Blade Section with High Efficiency for Marine Propeller (선박 프로펠러용 고효율 2차원 날개단면 개발)

  • Na, Yun-Cheol;Song, In-Haeng;Ahn, Jong-Woo
    • Journal of the Society of Naval Architects of Korea
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    • v.34 no.1
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    • pp.11-23
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    • 1997
  • This paper contains a new approach to blade section design method for marine propellers. The hydrodynamic characteristics of 2-D section are highly influenced by its geometrical parameters i.e., thickness and camber distributions and leading edge radius etc. To consider fully turbulent flow field near 2-D section. the finite volume method with k-${\varepsilon}$ turbulent model which solve Reynolds time averaged Navier-Stokes(RANS) equation is applied. In this study, O-type grid system that can provide many calculation points on blade surface is used. The results were compared with those of the experiment of NACA0012 to confirm the accuracy of the developed codes. The goal of this study is the development of a blade section with high efficiency and low drag. To achieve this, we carried out the tests of lift, drag and cavitation characteristics in cavitation tunnel. The results of experiment were compared with numerical results in order to validate the proposed blades design method. By comparing the numerical results with the experiments, we found that the new blade section, KH28 allows superior performance in efficiency and cavitation avoidance characteristics. We further investigated the blade section design method and an application study of this section, KH28 to apply to the marine propeller. In order to improve the accuracy of numerical results on prediction of lift and drag, we conclude here that the 2-layer boundary model must be used.

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The Effect of Skewness of Nonlinear Waves on the Transmission Rate through a Porous Wave Breaker (파형의 왜도가 투과성 방파제 투과율에 미치는 영향)

  • Cho, Yong Jun;Kang, Yoon Koo
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.29 no.6
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    • pp.369-381
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    • 2017
  • It has been presumed that highly nonlinear skewed waves frequently observed in a surf zone could significantly influence the transmission behaviour via a porous wave breaker due to its larger inertia force than its nonlinear counterparts of zero skewness [Cnoidal waves]. In this study, in order to confirm this perception, a numerical simulation has been implemented for 6 waves the skewness of that range from 1.02 to 1.032. A numerical simulation are based on the Tool Box called as the ihFoam that has its roots on the OpenFoam. Skewed waves are guided by the shoal of 1:30 slope, and the flow in the porous media are analyzed by adding the additional damping term into the RANS (Reynolds Averaged Navier-Stokes equation). Numerical results show that the highly nonlinear skewed waves are of higher transmitted ratio than its counterparts due to its stronger inertia force. In this study, in order to see whether or not the damping at the porous structure has an effect on the wave celerity, we also derived the dispersive relationships of Nonlinear Shallow Water Eq. [NSW] with damping at the porous structure being accounted. The newly derived dispersive relationships shows that the phase lag between the damping friction and the free surface elevation due to waves significantly influence the wave celerity.

Directional Wave Generation in the Navier-Stokes Equations Using the Internal Wave Maker (Navier-Stokes 방정식 모형의 경사지게 입사하는 파랑 내부조파)

  • Ha, Tae-Min;NamGung, Don;Cho, Yong-Sik
    • Journal of Korea Water Resources Association
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    • v.45 no.6
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    • pp.545-555
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    • 2012
  • A numerical modeling has become increasingly popular and more important to the study of water waves with a rapid advancement of computer technology. However, different types of problems are induced during simulating wave motion. One of the key problems is re-reflection to a computation domain at the incident boundary. The internal wave generating-absorbing boundary conditions have been commonly used in numerical wave models to prevent re-reflection. For the Navier-Stokes equations model, the internal wave maker using a mass source function of the continuity equation has been used to generate various types of waves. Nonetheless, almost every numerical experiment is performed in two dimensions and only a few tests have been expanded to three dimensions. More recently, a momentum source function of the Boussinesq equations is applied to generate essentially directional waves in the three dimensional Navier-Stokes equations model. In this study, the internal wave maker using a momentum source function is employed to generate targeted linear waves in the three-dimensional LES model.

A Study on Improvement γ-Reθt Model for Hypersonic Boundary Layer Analysis (극 초음속 경계층 해석을 위한 γ-Reθt모델 개선 연구)

  • Kang, Sunoh;Oh, Sejong;Park, Donghun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.48 no.5
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    • pp.323-334
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    • 2020
  • Since boundary layer transition has a significant impact on the aero-thermodynamic performance of hypersonic flight vehicles, capability of accurate prediction of transition location is essential for design and performance analysis. In this study, γ-Reθt model is improved to predict transition of hypersonic boundary layers and validated. A coefficient in the production term of the intermittency transport equation that affects the transition onset location is constructed and applied as a function of Mach number, wall temperature, and freestream stagnation temperature based on the similarity numerical solution of compressible boundary layer. To take into account a Mach number dependency of transition onset momentum thickness Reynolds number and transition length, additional correlation equations are determined as function of Mach number and applied to Reθc and Flength correlations of the baseline model. The suggested model is implemented to a commercial CFD code in consideration of practical use. Analysis of hypersonic flat plate and circular cone boundary layers is carried out by using the model for validation purpose. An improvement of prediction capability with respect to variation of Mach number and unit Reynolds number is identified from the comparison with experimental data.