scholarly journals Representative Transmission Coefficient for Evaluating the Wave Attenuation Performance of 3D Floating Breakwaters in Regular and Irregular Waves

2021 ◽  
Vol 9 (4) ◽  
pp. 388
Author(s):  
Huu Phu Nguyen ◽  
Jeong Cheol Park ◽  
Mengmeng Han ◽  
Chien Ming Wang ◽  
Nagi Abdussamie ◽  
...  
Keyword(s):  
Transmission Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Transmitted Wave ◽  
Irregular Waves ◽  
Hydrodynamic Analysis ◽  
Evaluation Approach ◽  
Floating Breakwater ◽  
Floating Breakwaters ◽  
Evaluation Approaches

Wave attenuation performance is the prime consideration when designing any floating breakwater. For a 2D hydrodynamic analysis of a floating breakwater, the wave attenuation performance is evaluated by the transmission coefficient, which is defined as the ratio between the transmitted wave height and the incident wave height. For a 3D breakwater, some researchers still adopted this evaluation approach with the transmitted wave height taken at a surface point, while others used the mean transmission coefficient within a surface area. This paper aims to first examine the rationality of these two evaluation approaches via verified numerical simulations of 3D heave-only floating breakwaters in regular and irregular waves. A new index—a representative transmission coefficient—is then presented for one to easily compare the wave attenuation performances of different 3D floating breakwater designs.

Wave Attenuation Performance of Floating Breakwater Needs to be Evaluated by Using Irregular Waves

2021 ◽  
Author(s):  
Chien Ming Wang ◽  
Huu Phu Nguyen ◽  
Jeong Cheol Park ◽  
Mengmeng Han ◽  
Nagi abdussamie ◽  
...  
Keyword(s):  
Transmission Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Irregular Waves ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Floating Breakwater ◽  
Floating Breakwaters

<p>Floating breakwaters have been used to protect shorelines, marinas, very large floating structures, dockyards, fish farms, harbours and ports from harsh wave environments. A floating breakwater outperforms its bottom-founded counterpart with respect to its environmental friendliness, cost-effectiveness in relatively deep waters or soft seabed conditions, flexibility for expansion and downsizing and its mobility to be towed away. The effectiveness of a floating breakwater design is assessed by its wave attenuation performance that is measured by the wave transmission coefficient (i.e., the ratio of the transmitted wave height to the incident wave height or the ratio of the transmitted wave energy to the incident wave energy). In some current design guidelines for floating breakwaters, the transmission coefficient is estimated based on the assumption that the realistic ocean waves may be represented by regular waves that are characterized by the significant wave period and wave height of the wave spectrum. There is no doubt that the use of regular waves is simple for practicing engineers designing floating breakwaters. However, the validity and accuracy of using regular waves in the evaluation of wave attenuation performance of floating breakwaters have not been thoroughly discussed in the open literature. This study examines the wave transmission coefficients of floating breakwaters by performing hydrodynamic analysis of some large floating breakwaters in ocean waves modelled as regular waves as well as irregular waves described by a wave spectrum such as the Bretschneider spectrum. The formulation of the governing fluid motion and boundary conditions are based on classical linear hydrodynamic theory. The floating breakwater is assumed to take the shape of a long rectangular box modelled by the Mindlin thick plate theory. The finite element – boundary element method was employed to solve the fluid-structure interaction problem. By considering heave-only floating box-type breakwaters of 200m and 500m in length, it is found that the transmission coefficients obtained by using the regular wave model may be smaller (or larger) than that obtained by using the irregular wave model by up to 55% (or 40%). These significant differences in the transmission coefficient estimated by using regular and irregular waves indicate that simplifying assumption of realistic ocean waves as regular waves leads to significant over/underprediction of wave attenuation performance of floating breakwaters. Thus, when designing floating breakwaters, the ocean waves have to be treated as irregular waves modelled by a wave spectrum that best describes the wave condition at the site. This conclusion is expected to motivate a revision of design guidelines for floating breakwaters for better prediction of wave attenuation performance. Also, it is expected to affect how one carries out experiments on floating breakwaters in a wave basin to measure the wave transmission coefficients.</p>

Wave Steepness and Relative Width: Influence on Transmission Coefficient of Horizontal Interlaced, Multilayered, Moored Floating Pipe Breakwater With Five Layers

2011 ◽  
Vol 45 (5) ◽  
pp. 20-27
Author(s):  
Sacchi Rajappa ◽  
Arkal Vittal Hegde ◽  
Subba Rao ◽  
Veena Channegowda
Keyword(s):  
Physical Model ◽  
Transmission Coefficient ◽  
Wave Height ◽  
Incident Wave ◽  
Wave Attenuation ◽  
Transmitted Wave ◽  
Relative Width ◽  
Wave Steepness ◽  
Transmission Characteristics ◽  
Time Period

AbstractThis paper presents the results of a series of physical model scale experiments conducted to determine the transmission characteristics of a horizontal interlaced, multilayered, moored floating pipe breakwater. The studies are conducted on physical breakwater models having five layers of PVC pipes. The wave steepness (Hi/gT2, where Hi is incident wave height, g is acceleration due to gravity, and T is time period) was varied between 0.063 and 0.849, relative width (W/L, where W is width of breakwater and L is the wavelength) was varied between 0.4 and 2.65, and relative spacing (S/D, where S is horizontal centre to centre spacing of pipes and D is the diameter of pipes) was set equal to 2. The transmitted wave height is measured, and the gathered data are analyzed by plotting nondimensional graphs depicting the variation of Kt (transmission coefficient) with Hi/gT2 for values of d/W (d is depth of water) and of Kt with W/L for values of Hi/d. It is observed that Kt decreases as Hi/gT2 increases for the range of d/W between 0.082 and 0.139. It is also observed that Kt decreases with an increase in W/L values for the range of Hi/d from 0.06 to 0.40. The maximum wave attenuation achieved with the present breakwater configuration is 78%.

scholarly journals FLOATING BREAKWATERS AS PUBLIC PLATFORMS – IMPACT ON POSTURAL STABILITY

2018 ◽  
pp. 63
Author(s):  
Elizabeth Freeman ◽  
Kristen Splinter ◽  
Ron Cox
Keyword(s):  
Energy Dissipation ◽  
Degrees Of Freedom ◽  
Wave Attenuation ◽  
Cost Effective ◽  
Irregular Waves ◽  
Main Function ◽  
Wave Flume ◽  
Floating Breakwater ◽  
Safety Considerations ◽  
Floating Breakwaters

Floating Breakwaters are used extensively to provide cost effective protection from wind and vessel waves. Floating breakwaters are commonly multitasked, being used as a point of mooring for vessels or simply an access way to other pontoons in a small boat harbour, as well as their main function as wave dissipators. A floating breakwater does not completely stop the incident wave; rather it partially transmits, partially reflects and partially dissipates the wave energy. Cox et al (2007) completed wave flume testing of a number of floating breakwaters and reported on performance in irregular waves with particular emphasis on wave transmission and reflection, energy dissipation and restraining forces. Motion measurements were limited by the instrumentation. This paper discusses the results from a further series of laboratory experiments on the dynamic motions of an active floating breakwater system. The performance is related to wave attenuation, wave reflection and energy dissipation as well as safety considerations for standing persons based on high resolution measurements of accelerations in all six degrees of freedom.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

scholarly journals LABORATORY SIMULATIONS OF WAVE ATTENUATION BY AN EMERGENT VEGETATION OF ARTIFICIAL PHRAGMITES AUSTRALIS: AN EXPERIMENTAL STUDY OF AN OPEN-CHANNEL WAVE FLUME

2015 ◽  
Vol 23 (4) ◽  
pp. 251-266 ◽  
Author(s):  
Li YIPING ◽  
Desmond Ofosu ANIM ◽  
Ying WANG ◽  
Chunyang TANG ◽  
Wei DU ◽  
...  
Keyword(s):  
Experimental Study ◽  
Phragmites Australis ◽  
Wave Height ◽  
Plant Density ◽  
Wave Attenuation ◽  
Emergent Vegetation ◽  
Irregular Waves ◽  
Shore Protection ◽  
Near Shore ◽  
Wave Conditions

This paper presents a well-controlled laboratory experimental study to evaluate wave attenuation by artificial emergent plants (Phragmites australis) under different wave conditions and plant stem densities. Results showed substantial wave damping under investigated regular and irregular wave conditions and also the different rates of wave height and within canopy wave-induced flows as they travelled through the vegetated field under all tested conditions. The wave height decreased by 6%–25% at the insertion of the vegetation field and towards the downstream at a mean of 0.2 cm and 0.32 cm for regular and irregular waves respectively. The significant wave height along the vegetation field ranged from 0.89–1.76 cm and 0.8–1.28 cm with time mean height of 1.38 cm and 1.11 cm respectively for regular and irregular waves. This patterns as affected by plant density and also location from the leading edge of vegetation is investigated in the study. The wave energy attenuated by plant induced friction was predicted in terms of energy dissipation factor (fe) by Nielsen’s (1992) empirical model. Shear stress as a driving force of particle resuspension and the implication of the wave attenuation on near shore protection from erosion and sedimentation was discussed. The results and findings in this study will advance our understanding of wave attenuation by an emergent vegetation of Phragmites australis, in water system engineering like near shore and bank protection and restoration projects and also be employed for management purposes to reduce resuspension and erosion in shallow lakes.

scholarly journals Parametric Comparison of Rectangular and Circular Pontoons Performance as Floating Breakwater Numerically

2018 ◽  
Vol 25 (s1) ◽  
pp. 94-103 ◽  
Author(s):  
Seyyed Mohammad Reza Tabatabaei ◽  
Hamid Zeraatgar
Keyword(s):  
Cross Sections ◽  
Computer Code ◽  
Diffraction Theory ◽  
Mooring Line ◽  
Numerical Comparison ◽  
Dimensional Parameter ◽  
Hydrodynamic Analysis ◽  
Circular Section ◽  
Floating Breakwater ◽  
Floating Breakwaters

Abstract Rectangular and circular pontoons are one of the most widely cross-sections used as floating breakwaters (FB). Although, there are several articles on comparison of behavior of rectangular and circular floating breakwaters however, the Authors try to show some details of difference between these two types where they have not been addressed before. To do so, transmission coefficient (Ct), as a measure of merit, of similar rectangular and circular sections is numerically compared. A computer code is developed for two-dimensional hydrodynamic analysis of floating breakwater based on diffraction theory in frequency domain in regular waves with any configuration of mooring line. The numerical method is the finite element method and validated by comparing with experimental and numerical results. Three types of rectangular sections are defined equivalent to circular section and a numerical comparison is made between 100 similar sections. The Ct versus wave frequency has been considered in detail and three new points called LMinF, LMaxF and LMaxCt are introduced. It has been shown that LMinF and LMaxF of circular section are greater and LMaxCt is much smaller than equivalent rectangular section. The LMaxCt of both sections are very dependent to new non-dimensional parameter B/D (Breadth/Draft). Although, rectangular sections are more common for floating breakwater, however the results of this study show that possibility of using circular sections must be also considered.

SCRAP TYRE BREAKWATERS IN COASTAL ENGINEERING

1978 ◽  
Vol 1 (16) ◽  
pp. 132 ◽  
Author(s):  
Robert Charles McGregor ◽  
Neil Sinclair Miller
Keyword(s):  
Wave Attenuation ◽  
Coastal Engineering ◽  
Performance Criteria ◽  
Extensive Literature ◽  
Coastal Structures ◽  
Floating Breakwater ◽  
Fixed Structure ◽  
Floating Breakwaters ◽  
State Of Art ◽  
Stimulation Of

The problem of the protection of shorelines and coastal structures from wave action is one of long standing. More recently it has become necessary to examine the feasibility of providing the same sort of wave attenuation for locations further offshore. Where the need for protection is in shallow water, close to the shoreline, bed-based breakwaters are possible and floating breakwaters may only be desirable on the basis of one or more of the following grounds: a) cost, b) requirement for protection being of short duration, c) reduced interference with currents, d) adaptability to changing performance criteria, e) poor foundations. As the water depth becomes larger, the costs of a fixed structure become prohibitive whereas only the anchoring fraction escalates for a floating breakwater. There is an extensive literature extending from 1842 on the floating breakwater concept. Most of the references, however, are postwar following the wartime stimulation of interest in aid of assault landings. Recent sources of state-of-art information are Kowalski (1974) and Adee (1976). The use of scrap automobile tires has been discussed by Candle (1974), Kowalski (1974, 1976) , Noble (1976) and Harms (1978). Candle was proposing what may be called near rigid mats of tires where neighbouring tyres move relatively little with respect to one another, whereas the Noble, Harms and Kowalski designs use the breakwater flexibility. In the Kowalski breakwater**, the tires are formed into groups which are known as modules which allow the breakwater to "breathe" and so dissipate more energy by internal movement as well as making construction easier. Several breakwaters of a fairly simple form have been built using this concept. These have been operational in the U.S.A. for several years and have successfully protected at least one marina through hurricane conditions.

scholarly journals Hydrodynamic Performance of a Multi-Module Three-Cylinder Floating Breakwater System under the Influence of Reefs: A 3D Experimental Study

2021 ◽  
Vol 9 (12) ◽  
pp. 1364
Author(s):  
Jianting Guo ◽  
Yongbin Zhang ◽  
Chunyan Ji ◽  
Xiangqian Bian ◽  
Sheng Xu
Keyword(s):  
Wave Attenuation ◽  
Hydrodynamic Performance ◽  
Theoretical Research ◽  
Practical Significance ◽  
Large Wave ◽  
Motion Responses ◽  
Short Period ◽  
Floating Breakwater ◽  
Mooring Forces ◽  
Floating Breakwaters

As the technical and theoretical research of floating breakwaters is becoming increasingly mature, the floating breakwaters are now being utilized, especially in offshore reefs. Therefore, it is of practical significance to study the hydrodynamic performance of a multi-module floating breakwater system under the influence of reefs. In this study, a 3D model experiment was carried out on a system consisting of eight three-cylinder floating breakwater modules under the influence of reefs. A wave attenuation mesh cage was incorporated at the bottom of the model. The floating breakwater system was slack-moored in its equilibrium position, and each module was connected by elastic connectors. The reefs were modeled on a bathymetric map of existing reefs in the East China Sea. In this experiment, the wave transmission coefficients, motion responses, and mooring forces of the floating breakwater system were measured. The results showed that the three-cylinder floating breakwater in the beam waves (β = 90°) has excellent wave attenuating performance under the influence of reefs, especially for short-period waves. However, under the influence of the reef reflection wave and the shallow water effect, the motion responses in the three main stress directions of the floating breakwater were large, and there was some surge and pitch motion. Under the influence of the aggregation and superposition of reflected waves on both sides of the reefs, the peak mooring forces in the middle position of the floating breakwater system were the largest at large wave height. The three-cylinder floating breakwater exhibited satisfactory hydrodynamic performance under the influence of reefs. It has broad application prospects in offshore reefs.

scholarly journals WAVE SETUP ON VEGETATED BEACH: LABORATORY EXPERIMENTS

2017 ◽  
pp. 4 ◽  
Author(s):  
Yavuz Ozeren ◽  
Daniel Wren ◽  
Weiming Wu
Keyword(s):  
Wave Height ◽  
Wave Breaking ◽  
Wave Attenuation ◽  
Irregular Waves ◽  
Wave Tank ◽  
Wave Setup ◽  
Irregular Wave ◽  
Rigid Vegetation ◽  
Flexible Vegetation ◽  
Vegetation Models

In this study, wave height evolution and wave setup were measured in a laboratory wave tank with a sloping beach covered with rigid and flexible artificial vegetation under regular and irregular wave conditions. The experiments were conducted in a 20.6 m long, 0.69 m wide and 1.22 m deep wave tank at the USDA-ARS National Sedimentation Laboratory, Oxford, MS, USA. Regular and irregular waves were generated using a computer controlled piston type wave generator. A plane wooden beach with a 1:21 slope was constructed at the down-wave end of the wave tank, 11.5 m away from the wave paddle. Rigid vegetation was constructed out of wooden dowels and flexible vegetation was constructed using polyurethane tubes. Both vegetation models were 3.1 mm in diameter and 0.2 m long and had a population density of 3,182 stems/m2. The results were compared with those from experiments on a non-vegetated plane beach. Both rigid and flexible vegetation models reduced the wave height and wave setup substantially, but rigid vegetation typically performed better in reducing wave setup. For some of the experiments, no wave breaking was observed over the vegetated models, indicating that wave attenuation due to vegetation reduced the shoaling rate. For other experiments, wave breaking was observed and wave height attenuation was very small; however, wave setup was still significantly lower than in the plane beach experiments.

Experimental Study on Regular Wave of Transmission Coefficient through a Hollow-Block Mound Breakwater

2012 ◽  
Vol 170-173 ◽  
pp. 2200-2203 ◽  
Author(s):  
Zhi Qi Gao ◽  
Rui Jin Zhang ◽  
Shu Guang Luan ◽  
Dong Wei Fu
Keyword(s):  
Transmission Coefficient ◽  
Wave Height ◽  
Incident Wave ◽  
Marine Biology ◽  
Wave Attenuation ◽  
Wave Period ◽  
Theoretical Research ◽  
Engineering Practice ◽  
Regular Wave ◽  
Hollow Block

Besides wave attenuation, hollow-block mound breakwater acts as artificial reef which could protect the marine biology and repair the marine ecological environment. Transmission coefficient is the main index of breakwater’s wave attenuation effect evaluation. In this paper through the sectional model experiment on the special assembled hollow-block mound breakwater under regular wave, affecting factors (opening size, water depth, wave period, incident wave height) of the transmission coefficient of breakwater were studied. The main factors that influence the wave attenuation of the hollow-block mound breakwater are the opening size of the hollow-block and the depth of the water while the wave period and the wave height of the incident wave have less influence for the wave attenuation of the breakwater. The research results can provide the reference for the following theoretical research and engineering practice.

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