Wave transformation by a perforated free surface semicircular breakwater in irregular waves

2012 ◽  
pp. 207-210
Author(s):  
H The ◽  
V Venugopal
Keyword(s):  
Free Surface ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Semicircular Breakwater

Optimization of Hydraulic Efficiency of a Free Surface Semicircular Breakwater Using Wave Screens

2015 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal
Keyword(s):  
Free Surface ◽  
Wave Climate ◽  
Wave Transmission ◽  
Hydrodynamic Performance ◽  
Wave Transformation ◽  
Random Waves ◽  
Wave Flume ◽  
Wave Measurements ◽  
Test Models ◽  
Semicircular Breakwater

A free surface semicircular breakwater (SCB) with rectangular perforations has been developed to serve as a wave defence structure. Hydrodynamic performance of the breakwaters of various perforations has been thoroughly investigated through wave measurements in a wave flume under random waves. The SCBs were experimentally confirmed to be good anti-reflection wave structures; however, the level of wave transmission at the leeside of the SCBs was rather high particularly when immersed in limited depth and confronted by waves of longer period. This study aims at optimizing the hydraulic characteristics of the SCB by extending its draft by means of wave screens. Three test configurations have been identified in this study, namely (1) the SCB with front screen, (2) the SCB with rear screen, and (3) the SCB with double screens. For each wave screen, three porosities (i.e. 25, 40 and 50%) have been considered in the experiments. The models of shallow immersion depths have been tested in random waves of different characteristics in a wave flume. Wave transformation at different locations upstream and downstream of the test models has been recorded by wave probes. The hydraulic performance of the breakwater are quantified by the coefficients of wave transmission, reflection and energy dissipation, and the wave climate in the vicinity of the breakwater are presented in the form of a ratio relative to the incident wave height. The optimum design of SCB supplemented by truncated wave screen(s) is proposed at the end of the study.

scholarly journals PERFORMANCE ANALYSIS OF COMPOSITE SEMICIRCULAR BREAKWATERS OF DIFFERENT CONFIGURATIONS AND POROSITIES

2012 ◽  
Vol 1 (33) ◽  
pp. 38 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal ◽  
Tom Bruce
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Performance Analysis ◽  
Physical Modelling ◽  
High Energy ◽  
Immersion Depth ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Semicircular Breakwater ◽  
High Energy Dissipation

The perforated free surface semicircular breakwater developed by Teh et al. (2010) was experimentally proven to be an effective anti-reflection structure with high energy dissipation ability. However, the performance characteristics of the breakwater deteriorated with a decrease in the immersion depth and an increase in wavelength. To enhance the performance of the breakwater with limited immersion depth, wave screens of different configurations and porosities were introduced below the free surface semicircular caisson. The hydrodynamic characteristics of these composite breakwaters were investigated in irregular waves using physical modelling. Comparisons of the experimental results showed that the semicircular caisson with a double screen of 25% porosity was a better breakwater configuration compared to that with a single screen. The extension of wave screen was also found to be particularly helpful in attenuating longer waves.

Oblique Irregular Waves Load on Semicircular Breakwater

2005 ◽  
Vol 47 (4) ◽  
pp. 183-204 ◽  
Author(s):  
Ning-Chuan Zhang ◽  
Li-Qin Wang ◽  
Yu-Xiu Yu
Keyword(s):  
Irregular Waves ◽  
Semicircular Breakwater

scholarly journals Estimation of Irregular Wave Runup on Intermediate and Reflective Beaches Using a Phase-Resolving Numerical Model

2020 ◽  
Vol 8 (12) ◽  
pp. 993
Author(s):  
Jonas Pinault ◽  
Denis Morichon ◽  
Volker Roeber
Keyword(s):  
Time Series ◽  
Best Practices ◽  
Numerical Models ◽  
Laboratory Data ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Model Parameters ◽  
Wave Runup ◽  
Data Set ◽  
Promising Alternative

Accurate wave runup estimations are of great interest for coastal risk assessment and engineering design. Phase-resolving depth-integrated numerical models offer a promising alternative to commonly used empirical formulae at relatively low computational cost. Several operational models are currently freely available and have been extensively used in recent years for the computation of nearshore wave transformations and runup. However, recommendations for best practices on how to correctly utilize these models in computations of runup processes are still sparse. In this work, the Boussinesq-type model BOSZ is applied to calculate runup from irregular waves on intermediate and reflective beaches. The results are compared to an extensive laboratory data set of LiDAR measurements from wave transformation and shoreline elevation oscillations. The physical processes within the surf and swash zones such as the transfer from gravity to infragravity energy and dissipation are accurately accounted for. In addition, time series of the shoreline oscillations are well captured by the model. Comparisons of statistical values such as R2% show relative errors of less than 6%. The sensitivity of the results to various model parameters is investigated to allow for recommendations of best practices for modeling runup with phase-resolving depth-integrated models. While the breaking index is not found to be a key parameter for the examined cases, the grid size and the threshold depth, at which the runup is computed, are found to have significant influence on the results. The use of a time series, which includes both amplitude and phase information, is required for an accurate modeling of swash processes, as shown by computations with different sets of random waves, displaying a high variability and decreasing the agreement between the experiment and the model results substantially. The infragravity swash SIG is found to be sensitive to the initial phase distribution, likely because it is related to the short wave envelope.

Numerical Simulations of Regular and Irregular Wave Forces on a Horizontal Semi-Submerged Cylinder

2017 ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai ◽  
Sopheak Seng
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Simulations ◽  
Stokes Equations ◽  
Wave Length ◽  
Wave Structure ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Submerged Cylinder

Two-dimensional (2D) numerical simulations have been performed using OpenFOAM (an open source CFD software package [1]) and waves2Foam (an OpenFOAM based add-on library for wave generations and absorption [2]) to investigate free surface waves past one fixed horizontally semi-submerged cylinder. The 2-D simulations are carried out by solving Navier-Stokes equations which are discretized based on finite volume method (FVM). Volume of Fluid (VOF) method is employed to capture the free surface in the numerical wave tank. Validation studies have been performed by comparing the numerical results of Stokes first-order wave past a semi-submerged circular cylinder with the published experimental data at different incident wave properties. The numerical results are in good agreement with the experimental data. Subsequently, regular and irregular waves past semi-submerged cylinder at different wave heights and the wave lengths are computed numerically to investigate the effect of the wave height and wave length on wave-structure interaction. The numerical results for irregular waves are compared with those induced by regular waves.

scholarly journals HYDRODYNAMIC PERFORMANCE OF A FREE SURFACE SEMICIRCULAR PERFORATED BREAKWATER

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal ◽  
Tom Bruce
Keyword(s):  
Free Surface ◽  
Wave Attenuation ◽  
Hydrodynamic Performance ◽  
Wave Transformation ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Irregular Wave ◽  
Energy Dissipater ◽  
Horizontal Wave ◽  
Perforated Breakwater

The increasing importance of the sustainability challenge in coastal engineering has led to the development of free surface breakwaters of various configurations. In this study, the hydrodynamic characteristics of a perforated semicircular free surface breakwater (SCB) are investigated for irregular wave conditions. The hydrodynamic performance of the breakwater is evaluated in the form of transmission, reflection and energy dissipation coefficients, which are then presented as a function of the relative submergence depth (D/d) and the relative breakwater width (B/Lp), where D = the depth of immersion, d = the water depth, B = the breakwater width and Lp = the wavelength corresponding to the peak wave period. It is found that the wave attenuation ability of the SCB model improves with the increase of D/d and B/Lp. The SCB performs better as an energy dissipater than as a wave reflector. Based on the analysis of measured data, some empirical equations are proposed to predict the performance of the breakwater under varying submergence depths. The behaviour of wave transformation around and within the breakwater’s chamber is discussed. Also, the measured horizontal wave forces acting on the SCB are reported.

A Physical Model of Wind Waves in the Coastal Zone

2008 ◽  
Author(s):  
Yana Saprykina ◽  
Natalia Andreeva ◽  
Sergey Kuznetsov ◽  
Zhivelina Cherneva ◽  
C. Guedes Soares
Keyword(s):  
Time Series ◽  
Coastal Zone ◽  
Wind Waves ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Free Surface Elevation ◽  
Space And Time ◽  
Initial Stage ◽  
Instantaneous Values ◽  
The Waves

The variability of the amplitude-frequency structure of wind waves in space and time during their transformation in the coastal zone are considered. Wave time series, measured synchronously in 15 points along the wave propagation, obtained at field and laboratory experiments, were used for the analysis. Free surface elevation time series were represented as a sum of first and second harmonics with amplitudes slowly varying in time (or envelopes of the waves of corresponding frequency bands). Relative changes of these amplitudes in space and time were studied also. It was revealed, that at the initial stage of the wave transformation, the changes of amplitudes of the first and the second harmonics are similar and amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. At this stage the variability of parameters of individual irregular waves can be explained by Stokes theory. Nearer to the coast the instantaneous values of the amplitudes of the first and the second harmonics varies in time chaotically and is not possible to construct a simple model of the variability of the parameters of individual irregular waves. The main reason for this effect is the backward energy transfer from the second to the first harmonics of the waves during nearly resonant non-linear triad interactions.

Offshore Breakwaters for LNG and Bulk Terminals: A Design Methodology for Determining Breakwater Layout

2020 ◽  
Author(s):  
Khali Youssef ◽  
Ghassan El Chahal ◽  
Nadjib Saadali
Keyword(s):  
Design Methodology ◽  
Capital Expenditure ◽  
Facility Layout ◽  
Transformation Process ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Mild Slope Equation ◽  
Protection Area ◽  
Wave Conditions ◽  
Gas Market

Abstract Over the last decades LNG and bulk terminals have been constructed in many countries. Many of these terminals have been located in sheltered sites without significant influence of swell and wind seas. As the worldwide gas market continues to grow supplying domestic, industrial and power plant projects, there is a continuous interest in new LNG terminals. With the growing gas demand LNG terminals are planned at exposed sites where the need of a breakwater is important for the ability of the facility to maintain operations and to ensure survivability of the terminal infrastructure. Studies are carried out for LNG terminal concept with the main focus on the need for a breakwater protecting the facility which will have significant impact on the CAPEX (Capital Expenditure). The mooring layout of the FSU/FSRU and LNG carrier whether perpendicular or parallel to the breakwater in addition to the planned operations determine the protection area behind the breakwater. The objective of this study is to establish design curves relating the different environmental and terminal parameters such as wave conditions, berthing facility layout, protection area and breakwater layout. These curves are derived based on the results of numerical simulations for wave transformation process of offshore waves propagating inside the terminal area. More than 700 cases are carried out in this study considering a range of wave periods, breakwater lengths, breakwater type (caisson and rubble mound), facility area dimensions and two incoming waves direction, i.e perpendicular and oblique. The simulations are carried out using the software REFONDE which is based on resolving the mild slope equation for irregular waves. The results of the study are presented in the form of curves and generalized to be used by terminal developers, designers and contractors for general guidance in future projects. Up to the authors’ knowledge, such curves for the design of marine terminals are not available at present. From this overview, a design methodology is developed to determine breakwater layouts during the early planning phase of project considering wave conditions, facility layout and terminal operations.

scholarly journals Free Surface Reconstruction for Phase Accurate Irregular Wave Generation

2018 ◽  
Vol 6 (3) ◽  
pp. 105 ◽  
Author(s):  
Ankit Aggarwal ◽  
Csaba Pákozdi ◽  
Hans Bihs ◽  
Dag Myrhaug ◽  
Mayilvahanan Alagan Chella
Keyword(s):  
Free Surface ◽  
Surface Reconstruction ◽  
Deep Water ◽  
Time Domain ◽  
Present Approach ◽  
Surface Elevation ◽  
Irregular Waves ◽  
Free Surface Elevation ◽  
Irregular Wave ◽  
The Time Domain

The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a computational fluid dynamics (CFD) based model to validate and investigate a non-iterative free surface reconstruction technique for irregular waves. In the current approach, the free surface is reconstructed by spectrally composing the irregular wave train as a summation of the harmonic components coupled with the Dirichlet inlet boundary condition. The verification is performed by comparing the numerically reconstructed free surface elevation with theoretical input waves. The applicability of the present approach to generate irregular waves by reconstructing the free surface is investigated for different coastal and marine engineering problems. A numerical analysis is performed to validate the free surface reconstruction approach to generate breaking irregular waves over a submerged bar. The wave amplitudes, wave frequencies and wave phases are modelled with good accuracy in the time-domain during the higher-order energy transfers and complex processes like wave shoaling, wave breaking and wave decomposition. The present approach to generate irregular waves is also employed to model steep irregular waves in deep water. The free surface reconstruction method is able to simulate the irregular free surface profiles in deep water with low root mean square errors and high correlation coefficients. Furthermore, the irregular wave forces on a monopile are investigated in the time-domain. The amplitudes and phases of the force signal under irregular waves generated by using the current technique are modelled accurately in the time-domain. The proposed approach to numerically reproduce the free surface elevation in the time-domain provides promising and accurate results for all the benchmark cases.

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