Estimating the stability of a bed protection of a weir-mounted tidal turbine

Coastal infrastructure, such as bridges and storm surge barriers with weirs, provides an attractive location for harvesting renewable energy using tidal turbines. Often stone layers are applied downstream of coastal infrastructure to protect the sea bed from erosion. However, little is known about the potential effect of tidal energy extraction on the stability of this granular bed protection. This paper describes a study of the flow conditions influencing the stability of the bed protection downstream of a weir-mounted tidal turbine, using hydrodynamic data of an experimental test. The analysis indicates that the flow recirculation zone downstream of a weir may become shorter and flatter due to the presence of a horizontal-axis turbine. As a result, energetic turbulence eddies can transport more horizontal momentum towards the bed – hence the reason a heavier bed protection may be required for granular beds downstream of weirs when a turbine is installed. This information is essential when designing safe bed protections for coastal infrastructure with tidal turbines.

Physical Modeling of Spatial and Temporal Development of Local Scour at the Downstream of Bed Protection for Low Froude Number

Local scour at the downstream of the river bed protection is one of the most important parameters for the design criteria and sustainable management of the hydraulic structures. Previously, various researches on its process in the equilibrium state have been suggested with experimental and numerical approaches. In this study, relatively long-term laboratory experiments of local scouring at the downstream of fixed bed in an open channel were conducted with mono-granular sediment bed and analyzed about maximum scour depth and its temporal development. In particular, we conducted experiments with relatively low Froude number (less than 0.5) and their duration of tests was exceeded over 700 hours. We modified the relationship between the dimensionless time and length scales of the maximum scour depth of the local scour hole based on the turbulent shear layer thickness. A new functional relationship between dominant factors and the maximum scour depth in the equilibrium state were suggested and compared with previously suggested formula. Also, from the results by nonlinear regression, Froude number was founded as a dominant factor on the prediction of equilibrium maximum scour depth.