An Experimental Study of Effects of Water Depth on Wave Scattering and Motion Responses of a Moored Floating Breakwater in Regular Waves

2011 ◽  
Author(s):  
Zhenhua Huang ◽  
Wenbin Zhang
Keyword(s):  
Water Depth ◽  
Measurement Unit ◽  
Regular Waves ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Wave Flume ◽  
Motion Responses ◽  
Floating Breakwater ◽  
Series Of Experiments ◽  
Floating Breakwaters

Due to the mobility and low costs, floating breakwaters have been frequently considered as alternatives for protecting marinas and harbors from wave attacks. Main advantages of using floating breakwaters include (i) the exchange of water between a harbor and ocean, and (ii) an adjustable elevation varying with tidal levels. When floating breakwaters are used in shallow water environments (during low tides), the presence of seabed may affect the dynamics of the floating breakwaters. In the present study, a series of experiments were carried out in a wave flume of 1.5m wide and 45m long to study the effects of water depth on the performance of a moored floating breakwater. An inertial measurement unit mounted on the breakwater measures the motion responses. The wave reflection and transmission coefficients and the responses of the breakwater to regular waves are presented for four difference water depths.

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>

scholarly journals TRANSMISSION OF REGULAR WAVES PAST FLOATING PLATES

1974 ◽  
Vol 1 (14) ◽  
pp. 112
Author(s):  
Uygur Sendil ◽  
W.H. Graf
Keyword(s):  
Water Depth ◽  
Wave Length ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Linear Wave ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Wave Flume ◽  
Wave Heights ◽  
Incident Waves

Theoretical solutions for the transmission beyond and reflection of waves from fixed and floating plates are based upon linear wave theory, as put forth by John (1949), and Stoker (1957), according to which the flow is irrotational, the fluid is incompressible and frictionless, and the waves are of small amplitude. The resulting theoretical relations are rather complicated, and furthermore, it is assumed that the water depth is very small in comparison to the wave length. Wave transmissions beyond floating horizontal plates are studied in a laboratory wave flume. Regular (harmonic) waves of different heights and periods are generated. The experiments are carried out over a range of wave heights from 0.21 to 8.17 cm (0.007 to 0.268 ft), and wave periods from 0.60 to 4.00 seconds in water depth of 15.2, 30.5, and 45.7 cm (0.5, 1.0 and 1.5 ft). Floating plates of 61, 91 and 122 cm (2, 3 and 4 ft) long were used. From the analyses of regular waves it was found that: (1) the transmission coefficients, H /H , obtained from the experiments are usually less than those obtained from the theory. This is due to the energy dissipation by the plate, which is not considered in the theory. (2) John's (1949) theory predicts the transmission coefficients, H /H , reasonably well for a floating plywood plate, moored to the bottom and under the action of non-breaking incident waves of finite amplitude. (3) a floating plate is less effective in damping the incident waves than a fixed plate of the same length.

scholarly journals FLOATING BREAKWATER RESPONSE TO WAVE ACTION

1988 ◽  
Vol 1 (21) ◽  
pp. 162 ◽  
Author(s):  
Michael Isaacson ◽  
Ronald Byres
Keyword(s):  
Numerical Model ◽  
Experimental Testing ◽  
Diffraction Theory ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Floating Breakwater ◽  
Mooring Forces ◽  
Wave Drift Forces ◽  
Floating Breakwaters ◽  
Incident Waves

The present paper describes a study carried out to investigate floating breakwater behavior in waves. Components of the study include a field survey of floating breakwaters in British Columbia, Canada, the development of a numerical model of breakwater behavior and the experimental testing of a particular breakwater design. The numerical model has been developed to provide breakwater motions, transmission coefficients and mooring forces. The model combines linear diffraction theory for obliquely incident waves, a mooring analysis, the inclusion of viscous damping coefficients obtained from experimental or field data, and the inclusion of drag and wave drift forces for use in the static analysis of the moorings. The experiments were carried out with normally incident regular waves of different heights and periods. Preliminary results indicate that the numerical model should prove to be a useful tool in floating breakwater design.

Wave Transmission over the Low-Crested Sand Container Breakwaters

2015 ◽  
Vol 802 ◽  
pp. 57-62
Author(s):  
Hee Min Teh
Keyword(s):  
Shallow Water ◽  
Transmission Coefficient ◽  
Water Depth ◽  
Wave Transmission ◽  
Experimental Result ◽  
Regular Waves ◽  
Wave Flume ◽  
Test Models ◽  
Wave Transmission Coefficient ◽  
Transmission Ability

Breakwaters made of sand container is one of the most economical options for wave protection at coastal areas. These breakwaters have been adopted with mixed success at several locations in Malaysia. Nevertheless, the performance of these structure has not been properly studied and documented to date. This study is undertaken to study the wave transmission ability of the submerged sand container breakwater with respect to its width and height as well as the water depth. A number of experiments have been conducted in a wave flume to quantify the wave transmission coefficient of the test models of different layouts when exposed to regular waves. The experimental result has shown that the breakwater is effective in arresting the shorter period waves, particularly in shallow water. The height of the breakwater has to be increased in order to arrest the longer period waves.

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.

Hydrodynamic characteristics of moored floating pipe breakwaters in random waves

2003 ◽  
Vol 217 (2) ◽  
pp. 95-110 ◽  
Author(s):  
V Sundar ◽  
R Sundaravadivelu ◽  
S Purushotham
Keyword(s):  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Random Waves ◽  
Mooring Lines ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Motion Responses ◽  
Analysis Of Results ◽  
Mooring Forces ◽  
Set Up

The hydrodynamic performance characteristics of a floating pipe breakwater (FPBW) model (row of pipes separated by a distance equivalent to the pipe diameter) moored to the flume floor with slack moorings has been investigated in random waves through an experimental programme. The tests have been conducted on three models each with pipes of different diameter. The average reflection and transmission coefficients are evaluated from measurements and reported as a function of relative breakwater width. The motion responses, as well as the variations in the forces on the seaside and lee side mooring lines, are also presented. In addition, statistical analysis has been carried out to prove that the heave and surge motions, as well as the peak mooring forces, follow the Raleigh distribution. The details of the models, set-up, experimental procedure and analysis of results are presented and discussed.

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.

scholarly journals STUDI KARAKTERISKTIK GELOMBANG PADA FLOATING BREAKWATER TIPE TERPANCANG DAN TAMBAT

2021 ◽  
Vol 12 (1) ◽  
pp. 39-52
Author(s):  
Sujantoko Sujantoko ◽  
Wisnu Wardhana ◽  
Eko Budi Djatmiko ◽  
Haryo Dwito Armono ◽  
Wahyu Suryo Putro ◽  
...  
Keyword(s):  
Reflection Coefficient ◽  
Physical Model ◽  
Transmission Coefficient ◽  
Water Depth ◽  
Wave Energy ◽  
Ocean Engineering ◽  
Wave Flume ◽  
Floating Breakwater ◽  
Type 3 ◽  
Transmission And Reflection

Floating breakwater (PGT) is designed to be applied as a wave barrier to reduce beach abrasion and wave energy so that waves coming to the beach have their energy reduced. Compared to conventional breakwater structures, PGT structures are more advantageous if the area to be protected from impact waves has a large enough depth. This structure is more flexible because the elevation follows the tides, so this structure can be used as a wharf at the same time. It is also free from the scouring and sedimentation that often occurs on the feet of conventional breakwater structures. This study aims to attenuate and reflect waves from various PGT configurations of piling and mooring types, by testing the physical model of PGT in the wave flume laboratory of the Department of Ocean Engineering ITS, at a water depth of 80 cm, a wave height of 3.5-5.5 cm, a wave period of 0.5-2 seconds, and the angle of the mooring rope (45o, 60o, 90o). PGT is arranged in a variety of longitudinal and transverse directions to the coast. Based on the experiment, it is known that the effect of configuration and width on the PGT structure on wave transmission and reflection is influenced by the mooring angle. Configuration 3 with the largest width can give the best transmission coefficient Kt = 0.797 at 45o mooring angle and reflection coefficient Kr = 0.572 at 90o mooring angle. In type 3 fixed-configuration gives the greatest value Kt = 0.431-0.623 and Kr = 0.053-0.997 compared to other configurations. Because in configurations 1 and 2 the back of the structure is not supported by piles, so a swing occurs which generates waves. While the effect of the slope of the wave, Kt will increase as the number of waves slopes decreases, conversely the value of Kt decreases with the increase in the slope of the wave.Keywords: Floating breakwater, piling, tethered,  mooring 

Modelling of a circular-section floating breakwater

1995 ◽  
Vol 22 (4) ◽  
pp. 714-722 ◽  
Author(s):  
Michael Isaacson ◽  
Neal Whiteside ◽  
Robert Gardiner ◽  
Duncan Hay
Keyword(s):  
Three Dimensional ◽  
Circular Cross Section ◽  
Diffraction Theory ◽  
Mooring Line ◽  
Coastal Structures ◽  
Regular Waves ◽  
Rectangular Section ◽  
Circular Section ◽  
Floating Breakwater ◽  
Floating Breakwaters

The physical and numerical modelling of a circular cross-section floating breakwater subjected to normal and obliquely incident regular waves is described. The transmission coefficient, breakwater motions, and mooring line forces were measured in two- and three-dimensional laboratory tests for a range of wave conditions and breakwater parameters. The experimental results are compared with results of a numerical model based on linear two-dimensional wave diffraction theory. The performance of the breakwater is summarized and compared with that of a rectangular-section breakwater. Possible modifications to improve the breakwater's performance characteristics are considered. Key words: coastal structures, floating breakwaters, hydrodynamics, moorings, waves.

Hydrodynamic Characteristics of Submerged Impermeable and Seaside Perforated Semicircular Breakwaters

2002 ◽  
Author(s):  
Govindasamy Dhinakaran ◽  
Vallam Sundar ◽  
Renganathan Sundaravadivelu ◽  
Kai-Uwe Graw
Keyword(s):  
Surface Area ◽  
Water Depth ◽  
Hydrodynamic Characteristics ◽  
Transmission Characteristics ◽  
Regular Waves ◽  
Scattering Parameter ◽  
Reflection And Transmission ◽  
Total Height ◽  
Semicircular Breakwater

The semicircular breakwater (SBW) is one of the varieties of breakwaters, which has emerged recently. The world’s first semicircular breakwater has been constructed at Miyazaki port in Japan. The dynamic pressures due to regular waves exerted on a SBW with 7% of its seaside surface area with perforations were measured. The variations of dimensionless pressures for three different water depth (hw) to total height of the model (ht), ratios are presented and discussed in this paper. In addition, the reflection and transmission characteristics of the perforated SBW as a function of scattering parameter, ka is reported. The results on the above stated variables for a seaside perforated SBW are compared with the results for an impermeable SBW.

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