Numerical Modelling of Coast Guard Buoys in Shallow Water

This paper describes recent attempts by the Coast Guard R&D Center to analyze the dynamics of typical Coast Guard buoys moored with synthetic line in shallow water, using an existing numerical model. Large-scale model wavetank tests have shown that the weight and drag of the synthetic line are negligible when compared to tension forces, so that catenary effects may be ignored. This allows the use of a single linear segment in the modelling of the mooring line, thus eliminating numerical convergence problems commonly experienced in time-domain simulation of shallow water dynamics. A unique system for measuring buoy position in wavetank tests is discussed. The procedure for abstracting buoy hydrodynamic coefficients from wavetank data is outlined, along with the current capabilities of the numerical model to estimate mooring line tensions and buoy attitudes in various wave conditions.