Extreme Wave Generation, Breaking, and Impact Simulations Using Wave Packets in REEF3D

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Hans Bihs ◽  
Arun Kamath ◽  
Mayilvahanan Alagan Chella ◽  
Øivind A. Arntsen
Keyword(s):  
Wave Packets ◽  
Wave Generation ◽  
Wave Forces ◽  
Breaking Wave ◽  
Extreme Wave ◽  
Offshore Structure ◽  
Transient Wave ◽  
Individual Wave ◽  
The Individual ◽  
Impact Simulations

On several occasions, freak waves have been observed in the past, some causing severe damage. In order to model such extreme wave conditions, one possibility is to use focused waves of first- or second-order based on irregular sea-state wave spectra. The wave phase is chosen such that the waves focus at a predetermined location and time, but the individual wave components become steep and start breaking before the focus location for large amplitudes. In this study, transient wave packets are used for extreme wave generation. Extreme waves are generated that are higher and only break at the concentration point using the transient wave packets method implemented in the open-source CFD model REEF3D. Model validation is performed by comparison to experimental results. The generation of wave packets with an 8.3 times shorter focus distance is investigated and the wave is replicated in a shorter domain with a 9% higher crest. The method is further used to generate a steepness induced-breaking wave and calculation of extreme wave forces on an offshore structure is demonstrated.

scholarly journals Extreme Wave Generation, Breaking and Impact Simulations With REEF3D

2017 ◽  
Author(s):  
Hans Bihs ◽  
Arun Kamath ◽  
Mayilvahanan Alagan Chella ◽  
Øivind A. Arntsen
Keyword(s):  
Stokes Equations ◽  
Wave Packets ◽  
Offshore Structures ◽  
Wave Generation ◽  
Three Dimensions ◽  
Immersed Boundary ◽  
Extreme Waves ◽  
Extreme Wave ◽  
Transient Wave ◽  
Numerical Tests

An accurate description of extreme waves is necessary in order to estimate maximum wave forces on offshore structures. On several occasions freak waves have been observed in the past, some causing severe damage. In order to model such extreme wave conditions with a computational fluid dynamics (CFD) model, emphasize needs to be put on the wave generation. One possibility is to use focused waves of first or second order based on irregular sea state wave spectra. For focused waves, the wave phase is chosen, so that the waves focus in a predetermined location at a specified time. Numerical tests have shown, that generating extreme waves based on this method is somewhat limited. The individual wave components are steep enough, that they start to break before the focus location. In the current paper, transient wave packets are used for extreme wave generation. This way, extreme waves can be generated that are higher, but only break at the concentration point. The transient wave packets method is implemented in the open-source CFD software REEF3D. This model uses the level set method for interface capturing. For the hydrodynamics, the Navier-Stokes equations are solved in three dimensions. The code employs a staggered Cartesian mesh, ensuring tight pressure-velocity coupling. Complex geometries are handled with a ghost cell immersed boundary method. High-performance computing is enabled through domain decomposition based parallelization. Convection discretization of the different flow variables is performed with the fifth-order WENO (weighted essentially non-oscillatory) scheme. For the explicit time treatment a third-order Runge-Kutta scheme is selected. In order to validate the extreme wave generation, numerical tests in an empty wave tank are performed and compared with experimental data. Then, the extreme wave breaking on a vertical circular cylinder is investigated.

scholarly journals Frequencies of wave packets of whistler-mode chorus inside its source region: a case study

2008 ◽  
Vol 26 (6) ◽  
pp. 1665-1670 ◽  
Author(s):  
O. Santolik ◽  
E. Macusova ◽  
E. E. Titova ◽  
B. V. Kozelov ◽  
D. A. Gurnett ◽  
...  
Keyword(s):  
Wave Packets ◽  
Source Region ◽  
Central Position ◽  
Backward Wave Oscillator ◽  
Whistler Mode ◽  
Poynting Flux ◽  
Wave Oscillator ◽  
Individual Wave ◽  
Night Side ◽  
The Individual

Abstract. Whistler-mode chorus is a structured wave emission observed in the Earth's magnetosphere in a frequency range from a few hundreds of Hz to several kHz. We investigate wave packets of chorus using high-resolution measurements recorded by the WBD instrument on board the four Cluster spacecraft. A night-side chorus event observed during geomagnetically disturbed conditions is analyzed. We identify lower and upper frequencies for a large number of individual chorus wave packets inside the chorus source region. We investigate how these observations are related to the central position of the chorus source which has been previously estimated from the Poynting flux measurements. We observe typical frequency bandwidths of chorus of approximately 10% of the local electron cyclotron frequency. Observed time scales are around 0.1 s for the individual wave packets. Our results indicate a lower occurrence probability for lower frequencies in the vicinity of the central position of the source compared to measurements recorded closer to the outer boundaries of the source. This is in agreement with recent research based on the backward wave oscillator theory.

Transient Wave Packets: New Application in CFD-Methods

2014 ◽  
Author(s):  
Günther F. Clauss ◽  
Sven Stuppe ◽  
Matthias Dudek
Keyword(s):  
Potential Theory ◽  
Wave Packets ◽  
Model Tests ◽  
Irregular Waves ◽  
Design Stage ◽  
Detailed Knowledge ◽  
Offshore Structure ◽  
Transient Wave ◽  
Space And Time ◽  
Hull Structure

Detailed knowledge of motion and seakeeping behaviour in an early design stage is indispensable in modern layout of marine offshore structures. Therefore, numerical methods are used to calculate the Response Amplitude Operators (RAO), which are generally based on potential theory or the Reynolds-Averaged-Navier-Stokes-Equation (RANSE). Calculations with potential-codes are commonly used, well established and time-saving. Main disadvantages are the neglect of viscous effects and the hull structure above the still water level. By using RANSE-methods, these nonlinear effects can be investigated in detail, but at the price of calculation time and extensive grid generation. To achieve sufficient RAOs in frequency domain, time-consuming and intensive calculations would be necessary with these CFD-methods, using seastate applications with regular or irregular waves only. Therefore, these methods are not convenient for standard motion analysis by now. Transient Wave Packets (TWP) represent an approved method at model tests, revealing the entire RAO for any offshore structure within one single, short test run. Main advantage of this technique is the accurate predictability and short superposition in space and time. Containing all elementary wavelengths of the generated initial wave spectra, the TWP-method could be used in RANSE-methods, implementing all necessary initial conditions to the CFD-solver. To reduce the calculation effort to a minimum in space and time, the superimposed wave train is generated near the investigated offshore structure by using modified, linear wave theory in spatial domain. To present this method by means of a practical example, the motion and sloshing behaviour of an offshore LNG-carrier (LNGC) are investigated in detail. For validation purpose, all results are compared to model tests, conducted in the seakeeping basin at Technische Universität Berlin (TUB), as well as numerical results of the potential theory solver WAMIT.

scholarly journals Characteristics of Breaking Wave Forces on Piles over a Permeable Seabed

2021 ◽  
Vol 9 (5) ◽  
pp. 520
Author(s):  
Zhenyu Liu ◽  
Zhen Guo ◽  
Yuzhe Dou ◽  
Fanyu Zeng
Keyword(s):  
Wave Breaking ◽  
Stokes Equations ◽  
Slope Angle ◽  
Wave Force ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Secondary Wave ◽  
Wave Forces ◽  
Breaking Wave ◽  
Breaking Wave Forces

Most offshore wind turbines are installed in shallow water and exposed to breaking waves. Previous numerical studies focusing on breaking wave forces generally ignored the seabed permeability. In this paper, a numerical model based on Volume-Averaged Reynolds Averaged Navier–Stokes equations (VARANS) is employed to reveal the process of a solitary wave interacting with a rigid pile over a permeable slope. Through applying the Forchheimer saturated drag equation, effects of seabed permeability on fluid motions are simulated. The reliability of the present model is verified by comparisons between experimentally obtained data and the numerical results. Further, 190 cases are simulated and the effects of different parameters on breaking wave forces on the pile are studied systematically. Results indicate that over a permeable seabed, the maximum breaking wave forces can occur not only when waves break just before the pile, but also when a “secondary wave wall” slams against the pile, after wave breaking. With the initial wave height increasing, breaking wave forces will increase, but the growth can decrease as the slope angle and permeability increase. For inclined piles around the wave breaking point, the maximum breaking wave force usually occurs with an inclination angle of α = −22.5° or 0°.

Performance of a Near Shore Oscillating Wave Surge Converter With Variable Flap Configurations in Various Sea Conditions

2021 ◽  
Author(s):  
Landon Sugar ◽  
Faete Filho ◽  
Tarek Abdel-Salam ◽  
Michael Muglia ◽  
Kurabachew Duba
Keyword(s):  
Wave Energy ◽  
Structural Integrity ◽  
Specific Reference ◽  
Wave Forces ◽  
Extreme Wave ◽  
Wide Range ◽  
Near Shore ◽  
Wave States ◽  
Pass Through ◽  
Survival Mode

Abstract Oscillating Wave Surge Converters (OWSCs) are designed to enter survival mode during extreme wave conditions where they forego the opportunity to extract energy to preserve structural integrity. While this is a good tradeoff, it is important that OWSC technology progresses to a point where energy is constantly extracted as long as waves are present. This work addresses the need for an OWSC that can extract wave energy in a wide range of sea conditions while minimizing structural overloading by regulating the fluid-structure interaction. The OWSC being studied here was conceptually designed and patented by researchers at NREL. It consists of a flap face that resembles household blinds, where the flaps can be opened or closed to accommodate the sea conditions. The performance of this variable geometry OWSC in various, shallow wave states was studied in two numerical modeling programs. Of particular interest were the flap’s hydrodynamic coefficients and potential power generation at a specific reference site. This configuration was predicted to mitigate wave forces by allowing some of the wave energy to pass through the device, thus preserving its structural integrity.

Detailed Study on Breaking Wave Interactions With a Jacket Structure Based on Experimental Investigations

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Jithin Jose ◽  
Olga Podrażka ◽  
Ove Tobias Gudmestad ◽  
Witold Cieślikiewicz
Keyword(s):  
Wind Turbines ◽  
Wave Breaking ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Wave Forces ◽  
Breaking Wave ◽  
Offshore Wind Turbines ◽  
Wave Parameters ◽  
Wave Slamming ◽  
Breaking Wave Forces

Wave breaking is one of the major concerns for offshore structures installed in shallow waters. Impulsive breaking wave forces sometimes govern the design of such structures, particularly in areas with a sloping sea bottom. Most of the existing offshore wind turbines were installed in shallow water regions. Among fixed-type support structures for offshore wind turbines, jacket structures have become popular in recent times as the water depth for fixed offshore wind structures increases. However, there are many uncertainties in estimating breaking wave forces on a jacket structure, as only a limited number of past studies have estimated these forces. Present study is based on the WaveSlam experiment carried out in 2013, in which a jacket structure of 1:8 scale was tested for several breaking wave conditions. The total and local wave slamming forces are obtained from the experimental measured forces, using two different filtering methods. The total wave slamming forces are filtered from the measured forces using the empirical mode decomposition (EMD) method, and local slamming forces are obtained by the frequency response function (FRF) method. From these results, the peak slamming forces and slamming coefficients on the jacket members are estimated. The breaking wave forces are found to be dependent on various breaking wave parameters such as breaking wave height, wave period, wave front asymmetry, and wave-breaking positions. These wave parameters are estimated from the wave gauge measurements taken during the experiment. The dependency of the wave slamming forces on these estimated wave parameters is also investigated.

Wave Forces on Cylindrical Members at Offshore Structure

1991 ◽  
Author(s):  
Yuzo Mizuno ◽  
Kazuo Tokikawa ◽  
Mitsunari Hirasawa ◽  
Yutaka Nagai ◽  
Takashi Kadono
Keyword(s):  
Wave Forces ◽  
Offshore Structure

Seismic Analysis of a Double-Hinged Articulated Offshore Tower

2008 ◽  
Author(s):  
Syed Danish Hasan ◽  
Nazrul Islam ◽  
Khalid Moin
Keyword(s):  
Seismic Analysis ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Forces ◽  
Offshore Structure ◽  
Concentrated Mass ◽  
Energy Principle ◽  
Rotational Angle ◽  
Sea Bed ◽  
Time Histories

The response of offshore structures under seismic excitation in deep water conditions is an extremely complex phenomenon. Under such harsh environmental conditions, special offshore structures called articulated structures are feasible owing to reduced structural weight. Whereas, conventional offshore structure requires huge physical dimensions to meet the desired strength and stability criteria, therefore, are uneconomical. Articulated offshore towers are among the compliant offshore structures. These structures consist of a ballast chamber near the bottom hinge and a buoyancy chamber just below the mean sea level, imparting controlled movement against the environmental loads (wave, currents, and wind/earthquake). The present study deals with the seismic compliance of a double-hinged articulated offshore tower to three real earthquakes by solving the governing equations of motion in time domain using Newmark’s-β technique. For this purpose Elcentro 1940, Taft 1952 and Northridge 1994 earthquake time histories are considered. The tower is modeled as an upright flexible pendulum supported to the sea-bed by a mass-less rotational spring of zero stiffness while the top of it rigidly supports a deck in the air (a concentrated mass above water level). The computation of seismic and hydrodynamic loads are performed by dividing the tower into finite elements with masses lumped at the nodes. The earthquake response is carried out by random vibration analysis, in which, seismic excitations are assumed to be a broadband stationary process. Effects of horizontal ground motions are considered in the present study. Monte Carlo simulation technique is used to model long crested random wave forces. Effect of sea-bed shaking on hydrodynamic modeling is considered. The dynamic equation of motion is formulated using Lagrangian approach, which is based on energy principle. Nonlinearities due to variable submergence and buoyancy, added mass associated with the geometrical non-linearities of the system are considered. The results are expressed in the form of time-histories and PSDFs of deck displacement, rotational angle, base and hinge shear, and the bending moment. The outcome of the response establishes that seismic sea environment is an important design consideration for successful performance of hinges, particularly, if these structures are situated in seismically active zones of the world’s ocean.

Experimental investigation on non-breaking wave forces and overtopping at the recurved parapets of vertical breakwaters

2018 ◽  
Vol 141 ◽  
pp. 52-67 ◽  
Author(s):  
L. Martinelli ◽  
P. Ruol ◽  
M. Volpato ◽  
C. Favaretto ◽  
M. Castellino ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Wave Forces ◽  
Breaking Wave ◽  
Breaking Wave Forces
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