Floating bridge global responses with hydrodynamic interaction

Hydrodynamic interaction between pontoons is studied for the global response computation of a floating bridge. Different issues related to bridge hydrodynamic interaction modeling are discussed. The pontoon's hydrodynamic coefficients become highly oscillating in the wind wave region under interaction. Wave trapping was observed in the numerical solution and proved by a decay test of the mid-pontoon in a three-pontoon model test. Model test results were compared with computations applying different free surface damping levels, which proved no free surface damping was needed for the current design. To facilitate the time-domain simulation of a bridge with many pontoons, simplification is necessary. It is proposed that the mid-pontoon hydrodynamic coefficients be applied instead of the coupled full hydrodynamics matrices of all the pontoons. By modal analysis, it was shown that dense frequencies in the hydrodynamic-interaction-affected region are important for the identification of bridge modes. Computation was compared with model tests in the ocean basin, where one, three pontoons and a hydro-elastic bridge were tested. The proposed simplification strategy was validated. Further, the comparison shows that hydrodynamic interaction is important in the global analysis of the floating bridge in the study.