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.

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.

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

2004 ◽  
Author(s):  
C. Guedes Soares ◽  
R. Pascoal ◽  
E. M. Anta˜o ◽  
A. J. Voogt ◽  
B. Buchner
Keyword(s):  
Impact Load ◽  
Second Order ◽  
Experimental Program ◽  
Ship Motions ◽  
Linear Wave ◽  
Wave Steepness ◽  
Wave Impact ◽  
Non Linear ◽  
Local Wave ◽  
The Impact

This work aims at characterizing the probability of wave impact and expected impact load on the bow geometry of an FPSO. 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 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 is derived for that type of bow. The proposed model for determining the probability of impact load is based on combining both models. The analytical nature 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 non-linear wave crests and the ship motions. The ship motions can be determined based on a linear response to the non-linear waves considered.

scholarly journals Boussinesq Model and CFD Simulations of Non-Linear Wave Diffraction by a Floating Vertical Cylinder

2020 ◽  
Vol 8 (8) ◽  
pp. 575
Author(s):  
Sarat Chandra Mohapatra ◽  
Hafizul Islam ◽  
C. Guedes Soares
Keyword(s):  
Wave Diffraction ◽  
Perturbation Technique ◽  
Harmonic Wave ◽  
Vertical Cylinder ◽  
Numerical Data ◽  
Second Order ◽  
Wave Number ◽  
Linear Wave ◽  
Cfd Simulations ◽  
Boussinesq Model

A mathematical model for the problem of wave diffraction by a floating fixed truncated vertical cylinder is formulated based on Boussinesq equations (BEs). Using Bessel functions in the velocity potentials, the mathematical problem is solved for second-order wave amplitudes by applying a perturbation technique and matching conditions. On the other hand, computational fluid dynamics (CFD) simulation results of normalized free surface elevations and wave heights are compared against experimental fluid data (EFD) and numerical data available in the literature. In order to check the fidelity and accuracy of the Boussinesq model (BM), the results of the second-order super-harmonic wave amplitude around the vertical cylinder are compared with CFD results. The comparison shows a good level of agreement between Boussinesq, CFD, EFD, and numerical data. In addition, wave forces and moments acting on the cylinder and the pressure distribution around the vertical cylinder are analyzed from CFD simulations. Based on analytical solutions, the effects of radius, wave number, water depth, and depth parameters at specific elevations on the second-order sub-harmonic wave amplitudes are analyzed.

Flexible Riser Response Induced by Springing of an FPSO Hull

2007 ◽  
Author(s):  
Jelena Vidic-Perunovic ◽  
Niels J. Risho̸j Nielsen ◽  
Haiwen Zhang
Keyword(s):  
High Frequency ◽  
Wave Spectrum ◽  
Analytical Form ◽  
Second Order ◽  
Wave Frequency ◽  
Natural Vibration Frequency ◽  
Linear Wave ◽  
Flexible Riser ◽  
Excitation Wave ◽  
Non Linear

The hydrodynamic analysis of the flexible riser for offshore application is usually limited to the first order wave frequency motions of the floating vessel that holds the riser top end. In this paper effort is made to investigate the influence of non-linear second order springing deflection of the production vessel hull on flexible riser response. The system selected in this study consists of a free-hanging flexible riser configuration attached to an FPSO. Due to resonance between the excitation wave frequency and the natural vibration frequency of the hull, second order flexible vertical motions of the FPSO increase. This may influence the riser loads, presumably the tension force. Vertical motions including the second order high frequency contribution are assigned to the flexible riser at a point of attachment to the vessel. To account for the environmental loading, irregular sea is applied, characterized by modified linear wave spectrum. Second order excitation wave spectrum is truncated by use of WAFO routines for random second order wave simulation and an analytical form of the spectrum that accounts for the non-linear wave effects is proposed. Several environmental conditions are examined in order to consolidate the tendency in riser behaviour. The significance of the high-frequency quadratic terms in the loads along the flexible riser is discussed.

Lagrangian approach to non-linear wave interactions in a warm plasma

1971 ◽  
Vol 6 (1) ◽  
pp. 53-72 ◽  
Author(s):  
J. J. Galloway ◽  
H. Kim
Keyword(s):  
Linear Equations ◽  
Wave Interaction ◽  
Lagrangian Approach ◽  
Linear Wave ◽  
Coupling Coefficients ◽  
Direct Expansion ◽  
Wave Interactions ◽  
Electrostatic Waves ◽  
Non Linear ◽  
Warm Plasma

In this paper, the coupled-mode equations and coupling coefficients for three-wave interaction are derived by a Lagrangian approach for a general medium. A derivation of the Low Lagrangian for a warm plasma is then given, which avoids certain problems associated with the original analysis. An application of the Lagrangian method is made to interaction between collinearly-propagating electrostatic waves, and a coupling coefficient is derived which agrees with a previous result obtained by direct expansion of the non-linear equations. The paper serves primarily to present and demonstrate a conceptually useful and efficient theoretical approach to non-linear wave interactions.

Non-Linear Wave Runup Along the Side of Ships Causing Green Water Problems: Experiments and First CFD Calculations

2014 ◽  
Author(s):  
Bas Buchner ◽  
Joris van den Berg ◽  
Joop Helder ◽  
Tim Bunnik
Keyword(s):  
Irregular Waves ◽  
Green Water ◽  
Linear Wave ◽  
Wave Direction ◽  
Wave Runup ◽  
Complex Processes ◽  
Non Linear ◽  
Run Up ◽  
Spilling Breakers ◽  
Water Problems

Large relative wave motions along the side of a ship can lead to green water on the deck. With a simplified test setup of a thin plate under an angle with the wave direction (to separate non-linear wave run up from motion effects), the non-linear wave reflection along the side of ships is studied in the present paper. These pilot tests with regular and irregular waves gave new insight in the process of non-linear wave run up with plunging and spilling breakers close to the plate. The complex processes observed made clear that linear or second order models will not be able to predict this behavior accurately. Previously [1] it was concluded that CFD methods that allow wave breaking are necessary for a prediction of these important effects. In the present paper a first pilot study is presented with an improved Volume of Fluid (VoF) Method. It is concluded that the method is in principle able to present these relative wave motions, but that a finer gridding is necessary to study the detailed flows.

scholarly journals Non-linear wave interaction in a plasma column

1979 ◽  
Vol 46 (6) ◽  
pp. 577-594 ◽  
Author(s):  
J.-M. LARSEN† ◽  
F. W. CRAWFORD
Keyword(s):  
Plasma Column ◽  
Wave Interaction ◽  
Linear Wave ◽  
Non Linear

Non-Linear Calculation of Tailored Wave Trains for Experimental Investigation of Extreme Structure Behaviour

2004 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Janou Hennig ◽  
Christian E. Schmittner ◽  
Walter L. Ku¨hnlein
Keyword(s):  
Experimental Investigation ◽  
Wave Propagation ◽  
Wave Structure ◽  
Linear Wave ◽  
Advantages And Disadvantages ◽  
Non Linear ◽  
Linear Wave Propagation ◽  
Precise Prediction ◽  
Wave Trains ◽  
Wave Models

The experimental investigation of extreme wave/structure interaction scenarios puts high demands on wave generation and calculation. This paper presents different approaches for modelling non-linear wave propagation. Results of numerical simulations from two different numerical wave tanks are compared to models tests. A further approach uses analytical wave models which are combined with empirical terms to allow a fast and precise prediction of non-linear wave propagation for day-to-day use. All approaches can be used either separately or in combination — depending on their particular purpose. As an application, different special wave scenarios — both academic and realistic — are generated and validated by measurements. The advantages and disadvantages of the presented methods are discussed in detail with regard to their appropriate use for investigations of extreme structure behaviour.

Sign in / Sign up

Export Citation Format

Share Document