Second Order Wave Diffraction Around a Fixed Ship-Shaped Body in Unidirectional Steep Waves

2006 ◽  
Vol 128 (2) ◽  
pp. 89-99 ◽  
Author(s):  
J. Zang ◽  
R. Gibson ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
C. Swan
Keyword(s):  
Free Surface ◽  
Wave Diffraction ◽  
Scattering Problem ◽  
Wave Interaction ◽  
Wave Structure ◽  
Second Order ◽  
Wave Impact ◽  
Focused Wave ◽  
Run Up ◽  
Steep Waves

The objective of this research, part of the EU FP5 REBASDO Program, is to examine the effects of second order wave diffraction in wave run-up around the bow of a vessel (FPSO) in random seas. In this work, the nonlinear wave scattering problem is solved by employing a quadratic boundary element method. A computer program, DIFFRACT, has been developed and recently extended to deal with unidirectional and directional bichromatic input wave systems, calculating second order wave diffraction loads and free surface elevation under regular waves and focused wave groups. The second order wave interaction with a vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and experimental measurements conducted at Imperial College shows excellent agreement. The second order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.

Non-Linear Wave Diffraction Around a Moored Ship

2004 ◽  
Author(s):  
J. Zang ◽  
R. Gibson ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
C. Swan
Keyword(s):  
Wave Diffraction ◽  
Scattering Problem ◽  
Wave Interaction ◽  
Wave Structure ◽  
Second Order ◽  
Linear Wave ◽  
Wave Impact ◽  
Non Linear ◽  
Focused Wave ◽  
Run Up

The objective of this research, part of the FP5 REBASDO Programme, is to examine the effects of directional wave spreading on the nonlinear hydrodynamic loads and the wave run-up around the bow of a floating vessel (FPSO) in random seas. In this work, the non-linear wave scattering problem is solved by employing a quadratic boundary element method. An existing scheme (DIFFRACT developed in Oxford) has been extended to deal with uni-directional and directional bi-chromatic input wave systems, calculating second-order wave diffraction under regular waves and focused wave groups. The second order wave interaction with a floating vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and the experimental measurements conducted at Imperial College shows excellent agreement. The second-order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.

On the Validity and Sensitivity of CFD Simulations for a Deterministic Breaking Wave Impact on a Semi Submersible

2018 ◽  
Author(s):  
Henry Bandringa ◽  
Joop A. Helder
Keyword(s):  
Free Surface ◽  
Absorbing Boundary Conditions ◽  
Implicit Time ◽  
Breaking Wave ◽  
Computational Domain ◽  
Wave Impact ◽  
Time Step ◽  
Cfd Simulations ◽  
Detailed Model ◽  
Run Up

To assess the integrity and safety of structures offshore, prediction of run-up, green water, and impact loads needs to be made during the structure’s design. For predicting these highly non-linear phenomena, most of the offshore industry relies on detailed model testing. In the last couple of years however, CFD simulations have shown more and more promising results in predicting these events, see for instance [1]–[4]. To obtain confidence in the accuracy of CFD simulations in the challenging field of extreme wave impacts, a proper validation of such CFD tools is essential. In this paper two CFD tools are considered for the simulation of a deterministic breaking wave impact on a fixed semi submersible, resulting in flow phenomena like wave run-up, horizontal wave impact and deck impacts. Hereby, one of the CFD tools applies an unstructured gridding approach and implicit free-surface reconstruction, and uses an implicit time integration with a fixed time step. The other CFD tool explicitly reconstructs the free surface on a structured grid and integrates the free surface explicitly in time, using a variable time step. The presented simulations use a compact computational domain with wave absorbing boundary conditions and local grid refinement to reduce CPU time. Besides a typical verification and validation of the results, for one of the CFD tools a sensitivity study is performed in which the influence of small variations in the incoming breaking wave on the overall results is assessed. Such an analysis should provide the industry more insight in the to-be-expected sensitivity (and hence uncertainty) of CFD simulations for these type of applications. Experiments carried out by MARIN are used to validate all the presented simulation results.

Numerical Study of Air Gap Response and Wave Impact Load on a Moored Semi-Submersible Platform in Predetermined Irregular Wave Train

2010 ◽  
Author(s):  
Xiufeng Liang ◽  
Jianmin Yang ◽  
Longfei Xiao ◽  
Xin Li ◽  
Jun Li
Keyword(s):  
Impact Load ◽  
Numerical Study ◽  
Wave Train ◽  
Air Gap ◽  
Navier Stokes ◽  
Design Stage ◽  
Wave Impact ◽  
Irregular Wave ◽  
Run Up ◽  
Steep Waves

The importance of understanding air gap response and potential deck impact is well-known in the design stage of semi-submersible platform. The highly non-linear nature of wave elevation around large structures in steep waves makes it difficult to accurately predict wave field under the deck and wave run up along the columns. Present engineering tools for the prediction of air gap response generally based on simplified models. Even the models accounting for nonlinear wave diffraction is not free of uncertainties. A method adopted here couples a Navier-Stokes solver, VOF technique capturing violent free surface and DNV/Seasam predicting motions of moored semi-submersible platform. Air gap response at different locations of the hull was evaluated in predetermined irregular wave train. Wave run up was also measured by wave probes near the columns. Load cells were mounted under the deck of the platform to trace potential deck impact. The predetermined irregular wave train was simulated in a numerical wave tank and verified against physical tank results. Analysis of the air gap response, wave run up and impact loads on the semi-submersible platform were conducted.

Numerical Investigation of Regular Waves Interaction With Two Fixed Cylinders in Tandem Arrangement

2018 ◽  
Author(s):  
Zhenghao Liu ◽  
Decheng Wan ◽  
Changhong Hu
Keyword(s):  
Free Surface ◽  
Surface Deformation ◽  
Wave Interaction ◽  
Wave Structure ◽  
Surface Elevation ◽  
Wave Radiation ◽  
Wave Forces ◽  
Tandem Arrangement ◽  
Interaction Of Waves ◽  
Tandem Cylinders

The interaction of waves with fixed or floating structures involves complex wave radiation, wave diffraction and free surface deformation. In this work, the interaction of waves with a pair of cylinders in tandem arrangement is investigated using a numerical wave tank. The numerical simulation is first validated by comparing numerical results and experimental data for regular wave interaction with a single cylinder. Wave interaction with tandem cylinders is investigated for different center-to-center distances between the cylinders. All the numerical simulations are carried out by the in-house CFD solver naoe-FOAM-SJTU which is developed on the open source platform OpenFOAM. The incompressible unsteady Reynolds averaged Navier-Stokes (URANS) equations are adopted as the governing equations. The volume of fluid (VOF) method is applied to capture the free surface. The surface elevation around the cylinders is probed by a series of wave gauges and analyzed using transfer function. The wave forces of upstream and downstream cylinder are discussed in detail. The wave forces experienced by the tandem cylinders is highly influenced by the distance between the cylinders. The local surface elevation and the scattered wave field around the cylinders are also investigated. The results show that the present CFD solver can be an alternative tool to deal with wave-structure interactions.

An Approach to Calculate the Probability of Wave Impact on an FPSO Bow

2006 ◽  
Vol 129 (2) ◽  
pp. 73-80 ◽  
Author(s):  
C. Guedes Soares ◽  
R. Pascoal ◽  
E. M. Antão ◽  
A. J. Voogt ◽  
B. Buchner
Keyword(s):  
Free Surface ◽  
Vertical Velocity ◽  
Second Order ◽  
Surface Velocity ◽  
Experimental Program ◽  
Ship Motions ◽  
Wave Steepness ◽  
Wave Impact ◽  
Local Wave ◽  
The Impact

This work aims at characterizing the probability of wave impact and determining the position of impact on an FPSO (floating production storage and offloading platform) bow geometry. In order to determine the instants when impact occurs, an experimental program was performed on a specific bow shape. The bow was instrumented with pressure transducers and the test program, also making use of video recordings, was designed such that it was possible to determine the correlation between undisturbed wave shape and the impact pressure time traces. It has been found that the wave impact at the bow is highly correlated with the local wave steepness, which for very high waves has at least second-order effects. A comparison between the probability distributions of local wave steepness of the experimental undisturbed wave time trace and numerical simulations of second-order wave theory is provided and it confirmed that the latter is very adequate for calculations. The experimental results were further used to determine how the probability of impact varies with free surface vertical velocity. It was found that the significant wave height of the sea state itself does not have significant influence on the result and a regression model was derived for the bow type in the experiments. The proposed model for determining the probability of having an impact is based on combining distributions, adjusted a priori to the numerically generated second-order free surface vertical velocity, and the experimental probability of impact of a known certain seastate and free surface velocity. The analytical description makes it fast and easy to expand to other cases of interest and some example calculations are shown to demonstrate the relative ease of the procedure proposed. The position of the impact is determined by the nonlinear wave crests and the ship motions. The ship motions can be determined based on a linear response to the nonlinear waves considered.

Numerical Investigation of Tsunami-Like Solitary Wave Interaction with a Seawall

2017 ◽  
Vol 11 (01) ◽  
pp. 1740006 ◽  
Author(s):  
Changbo Jiang ◽  
Xiaojian Liu ◽  
Yu Yao ◽  
Bin Deng ◽  
Jie Chen
Keyword(s):  
Free Surface ◽  
Solitary Waves ◽  
Stokes Equations ◽  
Dynamic Pressure ◽  
Laboratory Data ◽  
Three Dimensional ◽  
Wave Interaction ◽  
Surface Velocity ◽  
Wave Impact ◽  
Two Phase

Seawall is a most commonly used structure in coastal areas to protect the landscape and coastal facilities. The studies of interactions between the tsunami-like solitary waves and the seawalls are relatively rare in the literature. In this study, a three-dimensional numerical model based on OpenFOAM® was developed to investigate the tsunami-like solitary waves propagating over a rectangular seawall. The Navier–Stokes equations for two-phase incompressible flow, combining with methods of [Formula: see text] for turbulence closure and Volume of Fluid (VOF) for tracking the free surface, were solved. Laboratory experiments were performed to measure some of the hydrodynamic feature associated with solitary waves. The model was then validated by the laboratory data, and good agreements were found for free surface, velocity and dynamic pressure around the seawall. Finally, a series of numerical experiments were conducted to analyze the evolution of both wave and flow fields, the overtopping discharge as well as wave pressure (force) around the seawall, special attention is given to the effects of seawall crest width. Our findings will help to improve the understanding in the occurrences of tsunami-induced damages in the vicinity of seawall such as wave impact and local scouring.

scholarly journals Importance of second-order wave generation for focused wave group run-up and overtopping

2014 ◽  
Vol 94 ◽  
pp. 63-79 ◽  
Author(s):  
Jana Orszaghova ◽  
Paul H. Taylor ◽  
Alistair G.L. Borthwick ◽  
Alison C. Raby
Keyword(s):  
Wave Generation ◽  
Second Order ◽  
Wave Group ◽  
Focused Wave ◽  
Run Up ◽  
Focused Wave Group

Time-Domain Simulation of Second-Order Wave Diffraction in Irregular Wave

2012 ◽  
Author(s):  
Gang Xu ◽  
A. M. S. Hamouda
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Wave Diffraction ◽  
Second Order ◽  
Stokes Wave ◽  
Surface Boundary ◽  
Time Domain Simulation ◽  
Zone Method ◽  
Body Interaction ◽  
Irregular Wave

A time-domain second-order method is presented to simulate three-dimensional (3D) wave-body interaction. In the approach, Taylor series expansions are applied to the free surface boundary conditions, and Stokes perturbation procedure is then used to establish corresponding boundary value problem at first-order and second-order on the time-independent surfaces. A Boundary Element Method (BEM), based on Rankine source, is used to calculate wave field at each time step. Multi-Transmitting Formula coupled with Damping Zone method (MTF+DZ) is employed as radiation condition to minimize the wave reflection. A stable Integral form of Free surface Boundary Condition (IFBC) is used to update velocity potential on the free surface. The present method is applied to compute the second-order Stokes wave diffraction of bottom-mounted circular cylinder first, and then to compute the irregular second-order Stokes wave diffraction of truncated cylinder in infinite water depth with three wave components. It is shown that long time simulation can be done with stability, and the model can be used to time-domain simulation of nonlinear irregular wave-body interaction.

The Drift on Top of Waves

2013 ◽  
Author(s):  
Anne Katrine Bratland
Keyword(s):  
Free Surface ◽  
Second Order ◽  
Wave Direction ◽  
Extra Term ◽  
Steep Waves

Wave particles move in circles, and for steep waves they also move with a drift in the wave direction. This drift can be found by second order Stokes theory. In this document it is questioned if Stokes’ theory gives reliable drift on the free surface, or if an extra term should be introduced in the equations. The CFD program COMFLOW is used to show that classic Stokes theory may be insufficient for calculating drift on the free surface.

A Moving Boundary Finite Element Method for Fully Nonlinear Wave Simulations

1997 ◽  
Vol 41 (03) ◽  
pp. 181-194 ◽  
Author(s):  
D. M. Greaves ◽  
A. G. L. Borthwick ◽  
G. X. Wu ◽  
R. Eatock Taylor
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Free Surface ◽  
Moving Boundary ◽  
Wave Interaction ◽  
Circular Cylinders ◽  
Time Step ◽  
Steep Waves ◽  
The Time Domain ◽  
Element Method

The interaction of steep waves with surface ships and submarines may be simulated efficiently using a moving boundary finite element method. Here, unstructured hierarchical meshes are generated by triangularizing an underlying quadtree grid which adapts at each time step to follow the free surface. A potential flow theory finite element solver, developed by Wu & Eatock Taylor (1994,1995), is used to solve the two-dimensional nonlinear free surface problem in the time domain. Numerical results are presented for the following cases: standing waves in a rectangular tank; standing wave interaction with a fixed surface piercing rectangular body; and wave interaction with fixed submerged horizontal circular cylinders in a rectangular container. The results show encouraging agreement with analytical and alternative numerical schemes.

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