Peifeng Ma, Ole Secher Madsen


Open boundaries (OBs) are usually unavoidable in numerical coastal circulation simulations. At OBs, appropriate open boundary conditions (OBCs) are required and a good OBC should be able to let outgoing waves freely pass to the exterior of a computational domain without creating reflections at the OBs. In the present study, a methodology has been developed to predict two parameters, phase speed c_r and decay time T_f, in a standard OBC formulation, so that the OBC is significantly improved compared to commonly used existing OBCs with specified c_r and T_f. For the conditions where wave period is unknown, the OBC with approximated c_r and T_f may be applied and a test reveals that this OBC is able to yield good results in typical coastal flow conditions. In addition, a Swing-Door Boundary Condition (SDBC) is proposed and tested for application at an offshore open boundary where both incoming and outgoing waves exist.


open boundary condition; bottom friction; phase speed; decay time; swing door boundary condition; numerical coastal model

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Blumberg A. F. and Kantha L. H. 1985. Open Boundary condition for circulation models, J. Hydraul. Eng., Vol. 111, No. 2, 237-255.

Chapman D. C. 1985. Numerical treatment of cross-shelf boundaries in a barotropic coastal ocean model, J. Phys. Oceanogr., Vol. 15, 1060-1075.<1060:NTOCSO>2.0.CO;2

Chen, C., Beardsley, R. C., and Cowles, G. 2006. An unstructured grid, finite-volume coastal ocean model, FVCOM User Manual, Second Edition.

Grant, W. D. and Madsen, O. S. 1979. Combined wave and current interaction with a rough bottom, J.

Geophys. Res., Vol. 84(C4), 1979-1808.

Madsen, O. S., 2002. Sediment Transport Outside the Surf Zone. Chapter III.6 in Coastal Engineering

Manual, Part III Coastal Processes. (T. Walton, ed.), Engineer Manual 1110-2-1100, U.S. Army Corps of Engineers, Washington, DC.

Orlanski, I. 1976. A simple boundary condition for unbounded hyperbolic flows, J. Comput. Phys., Vol. 21, 251-269.