PERFORMANCE OF SUBMERGED ACTIVE BREAKWATERS IN A HYDRAULIC MODEL

K.R. Hall, M.P. Fischer

Abstract


A submerged active breakwater consists of a large buoyant cylinder that is held horizontal beneath the free surface of the water, by a spring and damper restraint system. The cylinder will be forced to oscillate in a certain mode, in response to an incident wave train. If properly "tuned", the cylinder can absorb a considerable fraction of the incident wave energy. Utilization of this concept may provide a number of potential benefits including; 1) a no loss to fish habitat; 2) a depth-independent materials cost; 3) a scheme easily adaptable to long term water level changes (such as those which occur naturally in the Great Lakes and those which are anticipated with sea level rise); and 4) the capability of adequately protecting a coastal area while maintaining boat access and water circulation. Knowledge of these devices however, is currently limited to performance in; 1) regular wave trains of narrow frequency bands, 2) zero angle of incidence between the wave crest and the structure, and 3) waves of small amplitude. Research evaluating the performance of submerged active breakwaters was performed in a two-dimensional wave flume in the Queen's University Coastal Engineering Research Laboratory (QUCERL). Both single cylinders and multi-cylinders placed in series were evaluated. Transmission coefficients in the range of 0.3 to 0.7 were measured over a broad range of conditions, indicating the possibility of these devices being used in prototype situations to achieve the benefits described above.

Keywords


hydraulic model; breakwater; submerged breakwater

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