The Interaction of Nonlinear Waves With the Submerged Caissons of a Gravity Based Structure

2008 ◽  
Author(s):  
Marios Christou ◽  
Jannicke S. Roos ◽  
Chris Swan ◽  
Ove T. Gudmestad
Keyword(s):  
Wave Field ◽  
Incident Wave ◽  
Nonlinear Waves ◽  
Wave Structure ◽  
Boundary Integral ◽  
Numerical Predictions ◽  
Water Region ◽  
Geometric Discontinuities ◽  
The Waves ◽  
Wave Structure Interaction

This paper concerns the numerical description of nonlinear waves propagating over the storage caissons of a gravity based structure. This process produces a steepening of the incident wave-field, which occurs when the waves propagate into the shallower water region above the storage caissons, resulting in the focussing of wave energy. A fully nonlinear Multiple-flux Boundary Element Method (MF-BEM) is applied to simulate this effect. The MF-BEM differs from traditional boundary integral approaches in two important respects: first, a multiple-flux approach is employed to overcome the problem of geometric discontinuities; and, second, no filtering, smoothing, re-gridding or redistribution of the nodes is performed at any stage during the simulations. These two aspects are believed to play an important role in accurately predicting the steepening of the incident wave-field. The numerical predictions are compared to new laboratory observations that examine the extent of this wave-structure interaction and, particularly, the steepening of the incident wave-field.

Wave-Vessel Interactions in Beam Seas

2009 ◽  
Author(s):  
Eirini Spentza ◽  
Chris Swan
Keyword(s):  
Wave Field ◽  
Incident Wave ◽  
Laboratory Data ◽  
Wave Structure ◽  
Wave Pattern ◽  
Scaled Model ◽  
Beam Seas ◽  
Wave Basin ◽  
Wave Slamming ◽  
Speed Of Propagation

This paper concerns the nonlinear interaction of waves with a floating vessel. A detailed experimental study has been undertaken in a 3-D wave basin, using a scaled model tanker subject to a variety of incident wave conditions. The vessel, which is free to move in heave, pitch and roll, has a draft of 14m (at full-scale) and is subject to a range of incident wave periods propagating at right angles to the side shell of the vessel. Measurements undertaken with and without the vessel in place allow the diffracted-radiated wave field to be identified. The laboratory data indicate that the diffracted-radiated wave pattern varies significantly with the incident wave period. Detailed analysis of the experimental results has identified a hitherto unexpected second-order freely propagating wave harmonic generated due to the presence of the vessel. Given its frequency content and its relatively slow speed of propagation, this harmonic leads to a significant steepening of the wave field around the vessel and therefore has an important role to play in terms of the occurrence of wave slamming. Physical insights are provided concerning the latter and the practical implications of the overall wave-structure interactions are considered.

scholarly journals Hydroelastic interaction of nonlinear waves with floating sheets

2021 ◽  
Author(s):  
Vasily Kostikov ◽  
Masoud Hayatdavoodi ◽  
R. Cengiz Ertekin
Keyword(s):  
Wave Field ◽  
Nonlinear Waves ◽  
Wave Reflection ◽  
Numerical Solutions ◽  
Beam Theory ◽  
Wave Structure ◽  
Elastic Plates ◽  
Wide Range ◽  
Local Wave ◽  
Elastic Surfaces

AbstractHydroelastic responses of floating elastic surfaces to incident nonlinear waves of solitary and cnoidal type are studied. There are N number of the deformable surfaces, and these are represented by thin elastic plates of variable properties and different sizes and rigidity. The coupled motion of the elastic surfaces and the fluid are solved simultaneously within the framework of linear beam theory for the structures and the nonlinear Level I Green–Naghdi theory for the fluid. The water surface elevation, deformations of the elastic surfaces, velocity and pressure fields, wave reflection and transmission coefficients are calculated and presented. Results of the model are compared with existing laboratory measurements and other numerical solutions. In the absence of any restriction on the nonlinearity of the wave field, number of surfaces, their sizes and rigidities, a wide range of wave–structure conditions are considered. It is found that wave reflection from an elastic surface changes significantly with the rigidity, and the highest reflection is observed when the plate is rigid (not elastic). It is also found that due to the wave–structure interaction, local wave fields with different length and celerity are formed under the plates. In the case of multiple floating surfaces, it is observed that the spacing between plates has more significant effect on the wave field than their lengths. Also, the presence of relatively smaller floating plates upwave modifies remarkably the deformation and response of the downwave floating surface.

Real-Time-Forecast of Wave-Structure Interaction in Natural Sea States: Influence of the Wave Encounter Angle

2014 ◽  
Author(s):  
Sascha Kosleck
Keyword(s):  
Wave Field ◽  
Transfer Functions ◽  
Wave Structure ◽  
Surface Elevation ◽  
Just In Time ◽  
Sea State ◽  
Structure Interaction ◽  
Model Scale ◽  
Vessel Structure ◽  
Wave Structure Interaction

In an offshore environment the ability to predict the development of a natural wave field can be of significant interest for a wide range of operations, such as for example on/off loading of cargo, installation or heavy lift processes, helicopter landing or even dynamic positioning. Being able to deterministically predict natural sea state just in time also allows for the prediction of wave structure interaction. Hence, not only motions in 6 degrees of freedom, for an arbitrary number of vessels or structures, but also velocities and accelerations at certain points of interest can be derived before they occur. Especially in difficult, slightly unclear weather conditions at the edge of operational limitations additional information on a potential exceedance of operational limits, such as for example wave heights, motions or accelerations, help to differentiate between safe and critical situations. Objective of the work conducted within the last years by Clauss, and Kosleck et al. is the development of a linear, deterministic approach for the just-in-time prediction of an ocean wave field of arbitrary specification. The survey presented within this paper focuses on the forecast of natural sea states and wave induced vessel/structure motions based on information gathered from a series of surface elevation snapshots of the surrounding free water surface. In order to investigate the approach a typical North Sea sea states with an underlying JONSWAP spectrum is generated and investigated at model scale. Simultaneous measurements of the surface elevation at over 450 different positions along the direction of wave propagation enable the artificial generation of surface elevation snapshots, used as input for the prediction method. Furthermore, these measurements also provide the basis for a comparison of calculated predictions and measurements at a huge variety of positions along the tank. The development of algorithms based on frequency domain analyses and the characterization of the sea state using a linear approach, enable the prediction of natural sea states in time and space — inside a well-defined range of validity. Knowing the general motion behaviour (transfer functions) of a structure/vessel together with the wave train to be encountered in the near future, its motion behaviour can subsequently be derived deterministically, taking into account that for the sailing vessel the transfer functions change depending on the actual cruising speed. The motion forecast procedure is compared and validated using measurements of the motion behaviour of an LNG carrier, again at model scale. So far, it has been shown (please see [1]) that the developed linear methods for the prediction of the motion behaviour of a stationary or cruising vessel/structure deliver excellent results for the vessel heading at different speeds but constant heading, namely 180° and 0° (defining head seas and following seas). This paper presents, for the first time, investigations with a vessel at zero speed but changing heading, hence a time varying change of the angle of wave attack.

Time-Domain Simulation of Motions of Large Structures in Nonlinear Waves

2002 ◽  
Author(s):  
Debabrata Sen
Keyword(s):  
Incident Wave ◽  
Time Domain ◽  
Nonlinear Waves ◽  
Large Amplitude ◽  
Time Integration ◽  
Offshore Structures ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Computational Scheme ◽  
Irregular Waves

In this paper, we discuss development of a time-domain motion simulation method for studying the interaction of nonlinear waves with large offshore structures. The computational algorithm follows a simplified numerical wave-tank approach based upon a boundary-integral method and time-integration of boundary conditions. The simplifying approximations include linearization of the interaction hydrodynamic effects (radiation and diffraction) while the incident wave effects are considered in full. The main aim is to develop a method that will consider all important nonlinear effects associated with a large-amplitude incident wave, and yet practical enough to be applied routinely by the industry. In the time-integration of motion equations, numerical instabilities usually arise if difference rules are applied for determining pressures, due to coupling between forces and motions. To avoid this, an algorithm has been developed for the pressure evaluation. The resulting computational scheme is numerically stable for all conditions. The method can incorporate effects of other forces such as Morison forces, forces from mooring lines etc. which can be nonlinear. After providing a description of computational scheme, force and motion results for the interaction of large amplitude regular waves as well as irregular waves with two practical semisubmersible configurations are presented.

scholarly journals A Procedure to Calculate First-Order Wave-Structure Interaction Loads in Wave Farms and Other Multi-Body Structures Subjected to Inhomogeneous Waves

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1761
Author(s):  
José Miguel Rodrigues
Keyword(s):  
Wave Field ◽  
Experimental Studies ◽  
Wave Structure ◽  
Linear Potential ◽  
Interaction Method ◽  
Structure Interaction ◽  
First Order ◽  
Inhomogeneous Waves ◽  
Multi Body ◽  
Wave Structure Interaction

A typical assumption when performing analytical, numerical, and experimental studies in wave–structure interaction in multi-body problems such as for wave farms and very large floating structures is the homogeneity of the wave field. Important interactions between the floating elements are dependent on the direction, amplitude, and phase of the waves acting on each. Then, wave homogeneity is probably unrealistic in near-shore areas where these installations are to be deployed. In the present work, an existing interaction method, which allows the use of standard boundary element diffraction codes for solving the first order wave structure linear potential for each unique geometry in the problem, is shown to be able to account for inhomogeneous sea states across the domain of a multi-body problem requiring only minimal modification to its implementation. A procedure to use the method to include arbitrary incoming undisturbed wave conditions at each body is presented. A verification study was done by using an artificial numerical configuration to mimic an inhomogeneous wave field in a standard diffraction code, which was used as a reference. The results obtained using the interaction-method based procedure are shown to be in excellent agreement with the reference ones. Furthermore, an example of frequency inhomogeneity of the wave field in a wave farm is shown and the effects on the motion amplitudes and absorbed power are presented illustrating the applicability of the procedure.

scholarly journals Investigation of a Stochastic Inverse Method to Estimate an External Force: Applications to a Wave-Structure Interaction

2012 ◽  
Vol 2012 ◽  
pp. 1-25 ◽  
Author(s):  
S. L. Han ◽  
Takeshi Kinoshita
Keyword(s):  
External Force ◽  
Inverse Method ◽  
Inverse Function ◽  
Wave Structure ◽  
Dynamic Responses ◽  
Structure Interaction ◽  
External Forces ◽  
Interaction Problem ◽  
Wave Structure Interaction

The determination of an external force is a very important task for the purpose of control, monitoring, and analysis of damages on structural system. This paper studies a stochastic inverse method that can be used for determining external forces acting on a nonlinear vibrating system. For the purpose of estimation, a stochastic inverse function is formulated to link an unknown external force to an observable quantity. The external force is then estimated from measurements of dynamic responses through the formulated stochastic inverse model. The applicability of the proposed method was verified with numerical examples and laboratory tests concerning the wave-structure interaction problem. The results showed that the proposed method is reliable to estimate the external force acting on a nonlinear system.

scholarly journals MACH-REFLECTION AS A DIFFRACTION PROBLEM

1976 ◽  
Vol 1 (15) ◽  
pp. 45 ◽  
Author(s):  
Udo Berger ◽  
Soren Kohlhase
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Water Waves ◽  
Gas Dynamics ◽  
Mach Reflection ◽  
Diffraction Problem ◽  
Vertical Wall ◽  
Oblique Wave ◽  
Wave Heights ◽  
The Waves

As under oblique wave approach water waves are reflected by a vertical wall, a wave branching effect (stem) develops normal to the reflecting wall. The waves progressing along the wall will steep up. The wave heights increase up to more than twice the incident wave height. The £jtudy has pointed out that this effect, which is usually called MACH-REFLECTION, is not to be taken as an analogy to gas dynamics, but should be interpreted as a diffraction problem.

scholarly journals Efficient Solution of the 3D Laplace Problem for Nonlinear Wave-Structure Interaction

2008 ◽  
Author(s):  
Harry B. Bingham ◽  
Allan P. Engsig-Karup
Keyword(s):  
Nonlinear Wave ◽  
Efficient Solution ◽  
Wave Structure ◽  
Finite Difference Schemes ◽  
Surface Boundary ◽  
Computational Domain ◽  
Problem Size ◽  
Structure Interaction ◽  
Nonlinear Wave Structure ◽  
Wave Structure Interaction

This contribution presents our recent progress on developing an efficient solution for fully nonlinear wave-structure interaction. The approach is to solve directly the three-dimensional (3D) potential flow problem. The time evolution of the wave field is captured by integrating the free-surface boundary conditions using a fourth-order Runge-Kutta scheme. A coordinate-transformation is employed to obtain a time-constant spatial computational domain which is discretized using arbitrary-order finite difference schemes on a grid with one stretching in each coordinate direction. The resultant linear system of equations is solved by the GMRES iterative method, preconditioned using a multigrid solution to the linearized, lowest-order version of the matrix. The computational effort and required memory use are shown to scale linearly with increasing problem size (total number of grid points). Preliminary examples of nonlinear wave interaction with variable bottom bathymetry and simple bottom mounted structures are given.

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