Non-Linear Wave Run-Up Along the Side of Sailing Ships Causing Green Water on Deck: Experiments and Deterministic Calculations

2020 ◽  
Author(s):  
Sanne van Essen ◽  
Henry Bandringa ◽  
Joop Helder ◽  
Bas Buchner
Keyword(s):  
Green Water ◽  
Linear Wave ◽  
Extreme Wave ◽  
Drift Speed ◽  
Highly Nonlinear ◽  
Small Wave ◽  
Non Linear ◽  
Run Up ◽  
Sailing Ship ◽  
Different Levels

Abstract Experiments with a flat plate in oblique waves at different speeds, wave conditions, headings and drift speed were done to evaluate non-linear wave run-up along a sailing ship. Both the incoming and diffracted part of the run-up were highly nonlinear in all test conditions. The run-up was larger at 135 than at 150 deg heading, the influence of speed was small, wave steepness increased run-up up to the point of breaking and a drift speed decreased the run-up. Most of the observed differences were larger than the seed and basin variability. (Semi-) linear diffraction methods are not sufficient to predict the highest runup crests, but applying them to screen for critical events could be further studied. CFD is able to accurately predict the nonlinear run-up in such selected events. Combining different levels of tools seems the most efficient way to predict extreme wave events such as green water due to run-up.

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.

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 Non-Linear Decay Motion of an Oscillatory Plate

2005 ◽  
Author(s):  
K. Abdolmaleki ◽  
K. P. Thiagarajan ◽  
J. J. Monaghan
Keyword(s):  
Free Surface ◽  
Water Jet ◽  
The Body ◽  
Green Water ◽  
Water Impact ◽  
Non Linear ◽  
Run Up ◽  
The Impact ◽  
System Characteristics ◽  
Linear Decay

We study the non-linear decay motion of a 2D plate experimentally and analytically. The plate was hinged to the bottom of a wave flume and was positioned at a certain initial angle. The restoring force on the plate was derived from two horizontal pre-tensioned springs. To maintain the system characteristics linear, the springs were selected to allow a maximum 18 degrees of rotation for the plate. The position, velocity and the acceleration of the plate were retrieved from the load cells attached to the springs. The plate was released from its initial position at t = 0 and allowed to oscillate. The free-surface elevation was captured using a high frame per second (200 fps) digital camera. In addition, two wave probes on either side of the plate were installed. It was observed that the high stiffness of the springs produced a mild impact to the water that caused a relatively large water run-up and water jet. This event, consequently, made the decay motion very non-linear. A formulation based on the linear theory was developed to help with the understanding and interpreting the physics of the problem. The presented experiment aims to benchmark various numerical techniques such as Smoothed Particle Hydrodynamics (SPH) that intend to simulate free-surface and water impact problems. Although the setup did not model a green water incident, most of the features in the problem, like initial water impact, run up and water jet resemble the physics of green water. In the designed experiment, not only body 3D effects were minimum, but also the system characteristics were linear. Moreover, in contrast to the dam break experiments, perfect initial conditions were achieved. Therefore, the effects of the flow nonlinearities such as the plate impact to the water, water run up-down and water jet were studied without interference of the body nonlinearities. The impact of these effects on the damping and the added mass were highlighted.

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

scholarly journals Excitation Forces Estimation for Non-linear Wave Energy Converters: A Neural Network Approach

2020 ◽  
Vol 53 (2) ◽  
pp. 12334-12339
Author(s):  
M. Bonfanti ◽  
F. Carapellese ◽  
S.A. Sirigu ◽  
G. Bracco ◽  
G. Mattiazzo
Keyword(s):  
Neural Network ◽  
Wave Energy ◽  
Linear Wave ◽  
Network Approach ◽  
Neural Network Approach ◽  
Wave Energy Converters ◽  
Non Linear ◽  
Energy Converters

Concrete Modeling for Extreme Wave Slam Events

2017 ◽  
Author(s):  
Kasper Wåsjø ◽  
Terje P. Stavang ◽  
Tore H. Søreide
Keyword(s):  
Time Domain ◽  
Linear Time ◽  
Limit State ◽  
Material Model ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Capacity Control ◽  
Extreme Wave ◽  
Conventional Design ◽  
Non Linear

Experience from model tests has initiated a growing attention towards extreme wave slam as a critical load situation for offshore large volume structures. Most of the problem is related to the local slam pressure, which may go up to several MPa’s for 100-year and 10 000-year waves. The paper deals with modeling techniques for marine concrete structures under extreme slam loading from waves where dynamic effects together with material softening play a major role for the response. Different analysis approaches for ultimate limit state (ULS) and accidental limit state (ALS) controls are discussed in view of reliability philosophy as basis for conventional design approach. The present paper is devoted to the local impact scenario and the alternative approaches for response and capacity control involving non-linear time domain analyses. Conventional design schemes as based on linear elastic models for response calculation together with code specified capacity control often come out more conservative than non-linear approach. The paper demonstrates by case studies how softening of the structure in general reduces the response in terms of section forces. A key issue when going from conventional linear approaches into non-linear techniques is to still keep an acceptable reliability level on the capacity control. Load and material factors are normally based on structures with limited non-linearity where linear response modeling is representative. Implementing non-linear material model in time domain analysis has a major challenge in limiting the sensitivity in response and capacity calculation. The paper demonstrates the way material model of concrete affects the section forces to go into local capacity control, and concludes on needed sensitivity analyses. Practical approaches on the concrete slam problem together with resulting utilizations from the control are demonstrated. The full non-linear technique by response and capacity control in one analysis is also handled, using average material parameters and justifying safety factors for the effect of implementing characteristic lower strength of concrete in the capacity. The paper ends up in a recommendation on non-linear time domain analysis procedure for typically slam problems. A discussion is also given on applicable design codes with attention to non-linear analysis.

scholarly journals Non-linear wave data assimilation with an ANN-type wind-wave model and Ensemble Kalman Filter (EnKF)

2010 ◽  
Vol 34 (8) ◽  
pp. 1984-1999 ◽  
Author(s):  
Ahmadreza Zamani ◽  
Ahmadreza Azimian ◽  
Arnold Heemink ◽  
Dimitri Solomatine
Keyword(s):  
Kalman Filter ◽  
Data Assimilation ◽  
Ensemble Kalman Filter ◽  
Wind Wave ◽  
Wave Model ◽  
Linear Wave ◽  
Wave Data ◽  
Non Linear
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