scholarly journals Slamming Force Contribution due to Plunging Breakers on Circular, Square and Diamond Cylinders

2019 ◽  
Author(s):  
Xin Wang ◽  
Arun Kr Dev ◽  
Longbin Tao ◽  
De Wang Chia ◽  
Yali Zhang
Keyword(s):  
Cross Section ◽  
Wave Breaking ◽  
Extreme Event ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Design Guidelines ◽  
Cylindrical Shape ◽  
Offshore Structure ◽  
Slamming Load

Abstract Plunging breakers, unlike non-breaking waves, impose additional slamming load on the offshore structures. This additional slamming load is considered an extreme event and is one of the most devastating forces that an offshore structure could encounter during its operational lifecycle. Whilst there are design guidelines for offshore structures pertaining to breaking waves, however it is limited to only cylindrical shape. The amount of slamming load contribution by the plunging jet is also dependent on the cross section geometries of the offshore structures. Different geometries would give rise to different air entrainment phenomenon during wave breaking and therefore affecting the slamming load contributions. In this research, JONSWAP spectrum was used to create plunging breakers via the focusing method at Newcastle University’s Wind Wave and Current tank. The crux of this research is to investigate the wave-breaking impact load on cylindrical structures with different cross section geometries commonly used in the offshore industry.

An Assessment of Load and Response for Horizontal Slamming Loads From Model Scale Experiments

2018 ◽  
Author(s):  
Martin Storheim ◽  
Gunnar Lian
Keyword(s):  
Structural Response ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Load Level ◽  
Material Behavior ◽  
Wave Impact ◽  
Large Variability ◽  
Slamming Load ◽  
Reasonable Approach ◽  
Wave Slamming

Steep breaking waves can result in high impact loads on offshore structures, and several model test campaigns have been conducted to assess the effect of horizontal wave slamming. High loads have been measured, and they can be challenging to withstand without significant deformation. For wave slamming problems it is common to estimate the characteristic slamming load and assume that this will give an equivalent characteristic response. One challenge related to the slamming load is that it has a large variability in load level, the duration of the load and the shape of the overall load pulse. This variability can have a large impact on the estimated response to the characteristic load, causing a similar or larger variability in response. Due to the sensitivity to the structural response, it may be difficult to interpret large amounts of such data to arrive at a relevant design load without making overly conservative assumptions. This paper investigates the sensitivity of the structural response to assumptions made in the material modelling and how the short term variability is affected if we instead of load use response indicators such as plastic strain and max deformation to arrive at a characteristic load. For this purpose, a simplified dynamic response model is created, and the recorded wave impact events can then be evaluated based on the predicted structural response from the simplified model. It was found that the structural response is sensitive to the structural configuration. The assumed material behavior and hydro-elastoplastic effects were identified to greatly affect the structural response. A reasonable approach to arrive at the q-annual response seems to be to first estimate the q-annual extreme slamming load, and then run the structural analysis on several of the measured slamming time series with the estimated q-annual extreme pressure.

High-fidelity simulations of bubble, droplet and spray formation in breaking waves

2016 ◽  
Vol 792 ◽  
pp. 307-327 ◽  
Author(s):  
Zhaoyuan Wang ◽  
Jianming Yang ◽  
Frederick Stern
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Power Law ◽  
Wave Breaking ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Small Scale ◽  
High Fidelity ◽  
Spray Formation ◽  
High Fidelity Simulations

High-fidelity simulations of wave breaking processes are performed with a focus on the small-scale structures of breaking waves, such as bubble/droplet size distributions. Very large grids (up to 12 billion grid points) are used in order to resolve the bubbles/droplets in breaking waves at the scale of hundreds of micrometres. Wave breaking processes and spanwise three-dimensional interface structures are identified. It is speculated that the Görtler type centrifugal instability is likely more relevant to the plunging wave breaking instabilities. Detailed air entrainment and spray formation processes are shown. The bubble size distribution shows power-law scaling with two different slopes which are separated by the Hinze scale. The droplet size distribution also shows power-law scaling. The computational results compare well with the available experimental and computational data in the literature. Computational difficulties and challenges for large grid simulations are addressed.

A Coupled VOF-Eulerian Multiphase CFD Model to Simulate Breaking Wave Impacts on Offshore Structures

2016 ◽  
Author(s):  
Pietro D. Tomaselli ◽  
Erik Damgaard Christensen
Keyword(s):  
Wave Breaking ◽  
Bubble Column ◽  
Vertical Cylinder ◽  
Air Entrainment ◽  
Offshore Structures ◽  
Laboratory Scale ◽  
Breaking Wave ◽  
Cfd Model ◽  
Bubble Plume ◽  
Wave Induced

Breaking wave-induced loads on offshore structures can be extremely severe. The air entrainment mechanism during the breaking process plays a not well-known role in the exerted forces. This paper present a CFD solver, developed in the Open-FOAM environment, capable of simulating the wave breaking-induced air entrainment. Firstly the model was validated against a bubble column flow. Then it was employed to compute the inline force exerted by a spilling breaking wave on a vertical cylinder in a 3D domain at a laboratory scale. Results showed that the entrained bubbles affected the magnitude of the force partially. Further analyses on the interaction of the bubble plume with the flow around the cylinder are needed.

Estimating Loads From Breaking Waves Using Operational Modal Analysis

2020 ◽  
Author(s):  
Michael Vigsø ◽  
Christos Georgakis
Keyword(s):  
Modal Analysis ◽  
Wave Breaking ◽  
Dynamic Properties ◽  
Structural Response ◽  
Wave Theory ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Operational Modal Analysis ◽  
Wave Flume ◽  
Load Effects

Abstract Load effects from breaking waves on offshore structures may be a driving point for the design. It is hence important to assess the likelihood of occurrence along the magnitude of the loads in the event of an impact. Traditionally, loads are predicted using wave theory combined with a load model such as the Morison. This paper features an alternative approach in determining the loads from wave breaking. It is demonstrated how the structural response can be used for (indirectly) estimating the magnitude of the loads caused by wave breaking. The theory is applied to an experimental setup in a wave flume, where a flexible model is subjected to loads from breaking waves. The dynamic properties are mapped using operational modal analysis and it is consequently shown that the loads can be identified using the vibration measurements.

A CFD Investigation on the Effect of the Air Entrainment in Breaking Wave Impacts on a Mono-Pile

2017 ◽  
Author(s):  
Pietro D. Tomaselli ◽  
Erik Damgaard Christensen
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Breaking Wave ◽  
Line Force ◽  
Entrainment Process ◽  
The Impact

In impacts of breaking waves on offshore structures, it is still not well-known how the air entrainment phenomenon affects the exerted loads. In this paper, a developed CFD solver capable of simulating the air entrainment process was employed to reproduce an experimental investigation on the impact of a spilling wave against a circular cylinder. The exerted in-line force was computed with and without the inclusion of dispersed bubbles. Results showed that the magnitude of the computed force was affected when the entrainment of bubbles was simulated.

scholarly journals Remote Sensing Observations of Dominant Breaking Waves in Intermediate to Deep Water from a Lighthouse During Storm Conditions

2021 ◽  
Author(s):  
Caio Eadi Stringari ◽  
Jean-François Filipot ◽  
Fabien Leckler ◽  
Rui Duarte
Keyword(s):  
Remote Sensing ◽  
Deep Water ◽  
Wave Breaking ◽  
Rogue Waves ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Video Data ◽  
Occurrence Rate ◽  
Winter Storms ◽  
Technical Issues

Wave breaking is one of the most important yet poorly understood water wave phenomena. It is via wave breaking that waves dissipate most of their energy and the occurrence of wave breaking directly influences several environmental processes, from ocean-atmosphere gas exchanges to beach morphodynamics. Large breaking waves also represent a major threat for navigation and for the survivability of offshore structures. This paper provides a systematic search for intermediate to deep water breaking waves with particular focus on the elusive occurrence of plunging breakers. Using modern remote sensing and deep learning techniques, we identify and track the evolution of over four thousand unique wave breaking events using video data collected from La Jument lighthouse during ten North Atlantic winter storms. Out of all identified breaking waves (Nb=4683), ≈22% were dominant breaking waves, that is, waves that have speeds within [0.77cp, 1.43cp], where cp is the peak wave speed. Correlations between the occurrence rate of dominant breaking waves (that is, waves per area and time per peak wave period) and wave steepness and wave age were observed. As expected, the number of identified plunging waves was small and six waves of all detected breaking waves, or 0.13%, could undoubtedly be considered as plunging waves. Two waves were also identified as unusually large, or rogue waves. Although afflicted by several technical issues, the data presented here provides a good indication that the probability of occurrence of plunging waves should be better incorporated into the design of offshore structures, particularly the ones that aim to harvest energy in offshore environments.

Period tripling and energy dissipation of breaking standing waves

1998 ◽  
Vol 369 ◽  
pp. 273-299 ◽  
Author(s):  
LEI JIANG ◽  
MARC PERLIN ◽  
WILLIAM W. SCHULTZ
Keyword(s):  
Wave Breaking ◽  
Standing Waves ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Wave Dissipation ◽  
Wave Resonance ◽  
Support Force ◽  
Sharp Crest ◽  
Steep Wave

We examine the dynamics of two-dimensional steep and breaking standing waves generated by Faraday-wave resonance. Jiang et al. (1996) found a steep wave with a double-peaked crest in experiments and a sharp-crested steep wave in computations. Both waveforms are strongly asymmetric in time and feature large superharmonics. We show experimentally that increasing the forcing amplitude further leads to breaking waves in three recurrent modes (period tripling): sharp crest with breaking, dimpled or flat crest with breaking, and round crest without breaking. Interesting steep waveforms and period-tripled breaking are related directly to the nonlinear interaction between the fundamental mode and the second temporal harmonic. Unfortunately, these higher-amplitude phenomena cannot be numerically modelled since the computations fail for breaking or nearly breaking waves. Based on the periodicity of Faraday waves, we directly estimate the dissipation due to wave breaking by integrating the support force as a function of the container displacement. We find that the breaking events (spray, air entrainment, and plunging) approximately double the wave dissipation.

scholarly journals A two-phase flow model for three-dimensional breaking waves over complex topography

2015 ◽  
Vol 471 (2180) ◽  
pp. 20150101 ◽  
Author(s):  
Zhihua Xie
Keyword(s):  
Wave Breaking ◽  
Flow Model ◽  
Two Phase Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Phase Flow ◽  
Complex Topography ◽  
Two Phase

A two-phase flow model has been developed to study three-dimensional breaking waves over complex topography, including the wave pre-breaking, overturning and post-breaking processes. The large-eddy simulation approach has been adopted in this study, where the model is based on the filtered Navier–Stokes equations with the Smagorinsky sub-grid model being used for the unresolved scales of turbulence. The governing equations have been discretized using the finite volume method, with the PISO algorithm being employed for the pressure–velocity coupling. The air–water interface has been captured using a volume of fluid method and the partial cell treatment has been implemented to deal with complex topography in the Cartesian grid. The model is first validated against available analytical solutions and experimental data for solitary wave propagation over constant water depth and three-dimensional breaking waves over a plane slope, respectively. Furthermore, the model is used to study three-dimensional overturning waves over three different bed topographies, with three-dimensional wave profiles and surface velocities being presented and discussed. The overturning jet, air entrainment and splash-up during wave breaking have been captured by the two-phase flow model, which demonstrates the capability of the model to simulate free surface flow and wave breaking problems over complex topography.

scholarly journals Deep neural networks for active wave breaking classification

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caio Eadi Stringari ◽  
Pedro Veras Guimarães ◽  
Jean-François Filipot ◽  
Fabien Leckler ◽  
Rui Duarte
Keyword(s):  
Machine Learning ◽  
Wave Breaking ◽  
Present Method ◽  
Breaking Waves ◽  
Future Research ◽  
Accuracy Score ◽  
Offshore Structure ◽  
Management Tools ◽  
Active Wave ◽  
Ocean Properties

AbstractWave breaking is an important process for energy dissipation in the open ocean and coastal seas. It drives beach morphodynamics, controls air-sea interactions, determines when ship and offshore structure operations can occur safely, and influences on the retrieval of ocean properties from satellites. Still, wave breaking lacks a proper physical understanding mainly due to scarce observational field data. Consequently, new methods and data are required to improve our current understanding of this process. In this paper we present a novel machine learning method to detect active wave breaking, that is, waves that are actively generating visible bubble entrainment in video imagery data. The present method is based on classical machine learning and deep learning techniques and is made freely available to the community alongside this publication. The results indicate that our best performing model had a balanced classification accuracy score of $$\approx$$ ≈ 90% when classifying active wave breaking in the test dataset. An example of a direct application of the method includes a statistical description of geometrical and kinematic properties of breaking waves. We expect that the present method and the associated dataset will be crucial for future research related to wave breaking in several areas of research, which include but are not limited to: improving operational forecast models, developing risk assessment and coastal management tools, and refining the retrieval of remotely sensed ocean properties.

PHYSICAL INTERPRETATION OF WAVE BREAKING CRITERIA

2017 ◽  
Author(s):  
Sergey Kuznetsov ◽  
Sergey Kuznetsov ◽  
Yana Saprykina ◽  
Yana Saprykina ◽  
Boris Divinskiy ◽  
...  
Keyword(s):  
Nonlinear Wave ◽  
Wave Breaking ◽  
Second Harmonic ◽  
Vertical Axis ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Spectral Structure ◽  
Similarity Parameter ◽  
Nonlinear Harmonics ◽  
The Waves

On the base of experimental data it was revealed that type of wave breaking depends on wave asymmetry against the vertical axis at wave breaking point. The asymmetry of waves is defined by spectral structure of waves: by the ratio between amplitudes of first and second nonlinear harmonics and by phase shift between them. The relative position of nonlinear harmonics is defined by a stage of nonlinear wave transformation and the direction of energy transfer between the first and second harmonics. The value of amplitude of the second nonlinear harmonic in comparing with first harmonic is significantly more in waves, breaking by spilling type, than in waves breaking by plunging type. The waves, breaking by plunging type, have the crest of second harmonic shifted forward to one of the first harmonic, so the waves have "saw-tooth" shape asymmetrical to vertical axis. In the waves, breaking by spilling type, the crests of harmonic coincides and these waves are symmetric against the vertical axis. It was found that limit height of breaking waves in empirical criteria depends on type of wave breaking, spectral peak period and a relation between wave energy of main and second nonlinear wave harmonics. It also depends on surf similarity parameter defining conditions of nonlinear wave transformations above inclined bottom.

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