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Title: Experimental Investigation of Cylindrical Floating Breakwater Performance with different mooring configurations

item OZEREN, YAVUZ - University Of Mississippi
item Wren, Daniel
item ALTINAKAR, MUSTAFA - University Of Mississippi
item WORK, PAUL - University Of Mississippi

Submitted to: Journal of Waterway, Port, Coastal and Ocean Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2011
Publication Date: 3/4/2011
Citation: Ozeren, Y., Wren, D.G., Altinakar, M., Work, P.A. 2011. Experimental investigation of cylindrical floating breakwater performance with different mooring configurations. Journal of Waterway, Port, Coastal and Ocean Engineering. doi:10.1061/(ASCE)WW.1943-5460.0000090.

Interpretive Summary: The earth levees commonly used for irrigation reservoirs are subjected to significant embankment erosion due to wind-generated waves. Large seasonal fluctuations in water level make vegetative bank protection impractical, and other stabilization methods, such as the use of stone or discarded tires, are not acceptable due to ecological or economic concerns. Floating wave barriers represent and economical alternative that can provide substantial protection from waves if designed properly. Here, detailed laboratory testing of cylindrical floating wave barriers with different mooring types is described. It was found that mooring with piles provided the best restraint type. The depth of the wave barrier was also found to be critical, with about 75% of the breakwater beneath the water providing the best performance. The results of this study help to better define the reaction of floating wave barriers to waves, which aids in creating designs that use the least amount of material possible—thus allowing for low cost deployment.

Technical Abstract: Floating breakwaters are typically used on limited-fetch water bodies, such as lakes, reservoirs, and bays, where wavelengths are relatively short. They are also often preferred for sites with large water level changes. Common uses are to protect small marinas or for shoreline erosion control. While the wave-structure interaction and wave transmission problems can be simulated numerically, laboratory data are often collected to validate model results. In spite of the large amount of work on floating breakwaters, there is still a lack of knowledge on the performance of simple cylinders as floating breakwaters for low-cost bank protection. Here a laboratory investigation of the hydrodynamic interaction of short waves such as are found in small reservoirs with floating breakwaters is described. The breakwater models considered here feature single cylindrical cross-sections or combinations of cylinders joined together with different mooring configurations. A wave flume with a flap-type wave generator and a progressive wave absorber were designed, constructed, and used to investigate the wave transmission characteristics of multiple floating breakwater configurations for regular waves in deep and transitional water depths. When the breakwater models were fixed, the reflection was high compared to the partially restrained models, indicating that the efficiency was strongly dependent on draft and freeboard. For partially restrained models, dissipation had an important role on wave attenuation; therefore, the dynamic response of the breakwater strongly affected its efficiency. For the measured range of waves, zd/d=0.7 was the best of the tested draft ratios for the pile-restrained model It was also observed that horizontal restraint is superior to vertical restraint in terms of improving breakwater efficiency.