SUBHARMONIC COMPONENTS IN HAWSER AND FENDER FORCES

J.H. van Oorschot

Abstract


Forces in mooring lines and fenders of a moored vessel exposed to waves have a mixed harmonic and a subharmonic character. The subharmonic oscillations, with periods well beyond the range of wave periods, may cause forces that are as large as, or even larger than the forces associated with the harmonic oscillations. The origins of the subharmonic oscillations are discussed and it is shown that in model testing, the correct reproduction of both the mooring arrangement and the irregular wave motion is essential. The subharmonic motions, and consequently the total forces, can be partially reduced by specially adapted mooring arrangements as tests on various mooring systems have shown.

Keywords


hawser force; fender force; subharmonic components

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