Response of Beams Under the Impact of Freak Waves

Recently the research on freak waves has focused on the formation mechanism as well as the experimental and numerical simulation, however the study of freak waves’ action on marine structures which is often confined to numerical methods is still not much. As beams are often studied as the simplified model of plates for structural safety assessment, in this paper, the response of a beam which is hit by a 2-D freak wave is studied. The freak wave is generated in a numerical wave tank (NWT) which solves the 2-D incompressible Navier-Stokes equations. The freak wave is based on the data of real sea condition in the Sea of Japan. An efficient wave absorbing method which satisfies the mass conservation is applied in the numerical wave tank. The influence of the beam’s motion on the freak wave fluid field is also considered in this paper, as well as different boundary conditions of the beam. It is found that the natural frequency has a great impact on the response of the beam.

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Numerical Investigation of Focused Waves and Their Interaction With a Vertical Cylinder Using REEF3D

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4036206 ◽

2017 ◽

Vol 139 (4) ◽

Cited By ~ 15

Author(s):

Hans Bihs ◽

Mayilvahanan Alagan Chella ◽

Arun Kamath ◽

Øivind Asgeir Arntsen

Keyword(s):

Free Surface ◽

Stokes Equations ◽

Free Surface Flows ◽

Surface Elevation ◽

Numerical Wave Tank ◽

Free Surface Elevation ◽

Wave Tank ◽

Numerical Wave ◽

Focused Wave ◽

The Impact

For the stability of offshore structures, such as offshore wind foundations, extreme wave conditions need to be taken into account. Waves from extreme events are critical from the design perspective. In a numerical wave tank, extreme waves can be modeled using focused waves. Here, linear waves are generated from a wave spectrum. The wave crests of the generated waves coincide at a preselected location and time. Focused wave generation is implemented in the numerical wave tank module of REEF3D, which has been extensively and successfully tested for various wave hydrodynamics and wave–structure interaction problems in particular and for free surface flows in general. The open-source computational fluid dynamics (CFD) code REEF3D solves the three-dimensional Navier–Stokes equations on a staggered Cartesian grid. Higher order numerical schemes are used for time and spatial discretization. For the interface capturing, the level set method is selected. In order to test the generated waves, the time series of the free surface elevation are compared with experimental benchmark cases. The numerically simulated free surface elevation shows good agreement with experimental data. In further computations, the impact of the focused waves on a vertical circular cylinder is investigated. A breaking focused wave is simulated and the associated kinematics is investigated. Free surface flow features during the interaction of nonbreaking focused waves with a cylinder and during the breaking process of a focused wave are also investigated along with the numerically captured free surface.

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The Analysis and Application of Numerical Wave Tank Based on the Viscous Fluid

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 4 ◽

10.1115/omae2010-20922 ◽

2010 ◽

Author(s):

Lei Yue ◽

Zhiguo Zhang ◽

Dakui Feng

Keyword(s):

Three Dimensional ◽

Wave Generation ◽

Green Water ◽

Numerical Wave Tank ◽

Wave Tank ◽

Water On Deck ◽

Impact Forces ◽

Numerical Wave ◽

The Impact ◽

Shipping Water

The so-called numerical wave tank is to use a mathematical model to simulate the process of making waves and interaction between waves and structures. Shipping water occurs when the wave height exceeds the deck level of a floating vessel. A large amount of seawater flows down onto the deck. It damages deck equipment and causes even submergence. The water on deck is called “Green Water”, and it is dangerous for ships. It is of great significance to analyze and simulate wave and green water phenomenon. This paper developed a three-dimensional numerical wave tank and presented VOF method to deal with the movement with free surface, and then simulated process of wave generation numerically. A two-dimensional numerical simulation of the green water phenomenon of a hull placed in regular wave was performed. The process of wave running up and wave deforming were obtained. The results show that the present numerical scheme and methods can be used to simulate process of wave generation and phenomenon of green water on deck, and to predict and analyze the impact forces between waves and structures due to green water.

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Generation of Freak Waves in a Numerical Wave Tank and Its Validation in Wave Flume

Journal of the Society of Naval Architects of Korea ◽

10.3744/snak.2009.46.5.488 ◽

2009 ◽

Vol 46 (5) ◽

pp. 488-497

Author(s):

Seong-Jae Jeong ◽

Seong-Wook Park

Keyword(s):

Numerical Wave Tank ◽

Freak Waves ◽

Wave Tank ◽

Wave Flume ◽

Numerical Wave

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Numerical Modeling of Breaking Waves Over a Reef With a Level-Set Based Numerical Wave Tank

Volume 7: CFD and VIV ◽

10.1115/omae2013-10363 ◽

2013 ◽

Author(s):

Mayilvahanan Alagan Chella ◽

Hans Bihs ◽

Arun Kamath ◽

Michael Muskulus

Keyword(s):

Level Set ◽

Wave Breaking ◽

Stokes Equations ◽

Numerical Results ◽

Navier Stokes ◽

Breaking Wave ◽

Numerical Wave Tank ◽

Wave Tank ◽

Navier Stokes Equations ◽

Numerical Wave

Wave breaking is a highly unsteady, non-linear and extremely turbulent phenomenon. During the wave breaking process, the energy of the wave system is focused close to the crest of the wave and a spatial spread of wave energy occurs. Thus, the description of such a physical phenomenon is highly complex and it requires a deep insight into the breaking wave process. The accurate assessment of breaking wave kinematics is essential for an accurate prediction of hydrodynamic loads on structures. Besides, the understanding of the transformation of waves propagating over an artificial or natural reef is important concerning the coastal processes. The numerical model used in this study is a two-phase model, which solves the flow problem for air and water simultaneously. The Navier-Stokes equations are solved on uniform Cartesian grids in two dimensions. The complex free surface is captured by the level set method. A staggered grid is used for the computation with the velocities defined at the cell edges and the pressure at the cell centres. This avoids unphysical pressure oscillations that can occur due to the coupling of pressure and velocity in the incompressible Navier-Stokes equations. The Ghost Cell Immersed Boundary Method is employed to handle the boundary conditions for complex boundaries. Turbulence modelling is carried out using the k-ω model. Discretization of the convective terms is performed using the 5th order Weighted Essentially Non-Oscillatory (WENO) scheme. In this study, a two-dimensional numerical wave tank is used to simulate waves propagating over steep slopes and wave dissipation. The main objective of the present study is to investigate the wave breaking process over a submerged reef. This is accomplished by examining the wave profile during wave breaking and the breaker indices. Also, the numerical results are compared to data from physical experiments and the numerical results exhibit reasonable agreement with experimental data.

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Analysis of Wave Interaction With Cylinders Using a 3D Numerical Wave Tank

Volume 2: CFD and VIV ◽

10.1115/omae2014-23474 ◽

2014 ◽

Author(s):

Arun Kamath ◽

Hans Bihs ◽

Øivind A. Arntsen

Keyword(s):

Free Surface ◽

Numerical Model ◽

Flow Field ◽

Stokes Equations ◽

Total Force ◽

Numerical Wave Tank ◽

Offshore Structure ◽

Wave Tank ◽

Computational Performance ◽

Numerical Wave

Evaluation of flow around a cylinder placed in waves is a challenging task due to the complex nature of the flow. A good understanding of the flow physics involved here is important as coastal and offshore structures consist of horizontal and vertical cylindrical elements. This paper explores the use of Computational Fluid Dynamics (CFD) to evaluate the flow field around cylindrical structures. A 3D numerical wave tank is employed to study the free surface and fluid velocities around a vertical cylinder placed in waves and the total force acting on the cylinder is evaluated. The numerical results are compared with experimental data. Further, a simple representation of an offshore structure modelled as multiple cylinders in proximity is also simulated in the numerical wave tank. The presence of neighbouring cylinders has an effect on the flow field. This affects the force acting on each of the cylinders in the group. The forces acting on every cylinder in the group are evaluated and the free surface elevation in the flow field is also visualised. The numerical result is compared with the result from an analytical formula. The numerical model uses the Reynolds-Averaged Navier-Stokes equations to evaluate the flow field. The convective terms are discretized using a 5th-order conservative finite difference WENO scheme. Time discretization is carried out using a 3rd-order Runge-Kutta scheme. Pressure discretization is carried out using Chorin’s projection method. The Poisson pressure equation is solved using a pre-conditioned BiCGStab algorithm. A sharp representation of the free surface is obtained using the level set method. Turbulence modeling is carried out using the k-ω model. Computational performance of the numerical model is improved by parallel processing using the MPI library.

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