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 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>

Experimental Study of Wave Force Distribution on a Monopile Structure

2018 ◽  
Author(s):  
Malene H. Vested ◽  
Stefan Carstensen ◽  
Erik Damgaard Christensen
Keyword(s):  
Experimental Studies ◽  
Cost Effective ◽  
Wave Force ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Force Distribution ◽  
Wave Forces ◽  
Total Force ◽  
Wave Flume ◽  
Effective Manner

As the demand for offshore wind energy continues to grow, the strive to understand the wave forces acting on the substructure of the wind turbines continues. In regard to wind turbine design, it is vital to consider not only the total wave force, but also the local wave forces. Local forces are particularly important for the design of secondary structures as e.g. mooring platforms. Typically, however, experimental studies mainly concern total forces or idealized local forces. We present here a rather simple way to measure local forces along a model monopile. The study is conducted in a wave flume of 28 m in length, in which waves are generated by a piston-type wave maker at a water depth of 0.515 m and shoal onto a bed of slope 1:25. A model monopile is installed and subjected to forcing from a series of both regular and irregular waves. In the experimental set-up, the model monopile is fixed at the bottom and the top and consists of seven independent cylindrical sections. The cylindrical sections are connected by force transducers which measure local shear, and so the associated local forces may be determined. The measured local forces are compared to the force distribution given by Morisons equation combined with linear theory and Wheeler stretching, which is a force estimate commonly used in the industry. This study shows that the total force is rather well captured by Morison’s equation. The force distribution estimated from Morison’s equation, however, shows larger discrepancies from the measured forces. This encourages for further measurements. In this study, we show that it is possible to measure force distribution on a model monopile in a simple and cost-effective manner. The aim is here to demonstrate the method and we will later present a larger body of work associated with the outcome of the measurements.

Hydrodynamic Performance of a Novel Free Surface Pitching Breakwater

2014 ◽  
Author(s):  
Vengatesan Venugopal ◽  
Stefan Zlatev
Keyword(s):  
Body Shape ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Scale Model ◽  
Reflected Waves ◽  
Irregular Wave ◽  
Wave Flume ◽  
Floating Breakwater ◽  
Wave Heights ◽  
Transmission Ct

A new concept floating breakwater was developed and tested to evaluate its hydrodynamic performance in this paper. This innovative floating breakwater has a rocking body shape which could also be used as a wave power device. A scale model was tested in a wave flume under regular and irregular wave conditions for various combinations of wave frequencies and wave heights. The breakwater has been tested for three immersion depths of 0.05 m, 0.09 m and 0.13 m from still water level. The measured transmitted and reflected waves were used to evaluate the coefficients of transmission (CT), reflection (CR) and dissipation (CL). The results illustrated that the breakwater model performed at its best when submerged at 0.13m, as this immersion depth produced lower coefficients of transmission (CT), lower reflection coefficients (CR) and higher energy dissipation (CL) coefficients. The comparison between regular and irregular waves produced similar ranges of transmission, reflection and energy coefficients.

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.

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.

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.

APPLICATION OF ACOUSTIC METHODS IN RESEARCHES OF THE BOTTOM SEDIMENT DYNAMICS

2018 ◽  
Author(s):  
Б. Дивинский ◽  
B. Divinskiy ◽  
И. Грюне ◽  
I. Gryune ◽  
Р. Косьян ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
Sediment Concentration ◽  
Irregular Waves ◽  
Single Frequency ◽  
Contactless Measurement ◽  
Measurement Means ◽  
Uniform Field ◽  
Wave Flume ◽  
Acoustic Methods ◽  
Back Scattering

Acoustic methods belong to contactless measurement means, possess high spatial and time resolution. Thus, the use of multifrequency allows directly profile both concentration and granulometric structure of the suspended substances. In 2008 in the Big Wave Flume (Hanover, Germany) by efforts of the Russian and German scientists there have been carried out the experiment on studying the bottom material suspension laws under the influence of irregular waves. The Aquascat 1000 acoustic back scattering sensor (ABS) manufactured by British company Aquatec (www.aquatecsubsea.com), equipped by a three-frequency transmitter with frequencies 1,0, 2,0 and 3,84 MHz, has been set on distance of 0,75 m from the bottom and 111 m from wave generator at the total depth of 3,2 m. Several dozen series of measurements at various parameters of surface waves have been carried out. The general picture of suspension is so that the external dynamic influence (currents, wave movements, turbulence, gravitation forces) creates a non-uniform field (gradient) of the suspended particles and in most cases due to this the average size of particles undergoes to the spatial-time variations. For this reason while defining the mass concentration of suspended sediment, using the single frequency transmitter there is necessity for numerous definition of the suspension granulometric structure what by isn’t always possible. If two and more frequencies are used the observed results comparison can give the information on average diameters of particles and on that basis the calculation of suspended sediment concentration is possibleLet's emphasize the basic advantages of back scattering acoustic gauges usage: – Obtaining the particles sizes and concentration distribution profiles is possible; – The initial granulometric structure of bottom sediments can be unknown (at use of several frequencies). The following can be referred to some lacks of the device: – The system should be calibrated in laboratory conditions; – In a positive feedback conditions the iterative computing process can converge to zero or to infinity. In this case experiments with a variation of carrier frequencies chosen for the analysis allow partially solve the problem (say experiments with different frequencies pairs, as 2/1 of MHz or 4/2 MHz).

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