Calibrating the Loss Coefficient of a Porous Plate

Abstract

Marine structures are sometimes represented in coastal ocean circulation models as a porous plate that exerts drag on the flow and dissipates energy. Such a representation requires that a loss coefficient be specified to reduce the flow speed to some prescribed fraction of the upstream incident flow. To provide guidance and a framework for this problem, the case of a uniform channel that is partially blocked by a porous structure is considered. Drawing on existing results from actuator disc theory, simple analytical relations are presented for the dependence of the flow speed through a porous plate on the loss coefficient. It is shown that limitations on representing structures with high hydrodynamic loading using an actuator disc in an unbounded region can be avoided by allowing for weak geometrical blockage by lateral boundaries.