Dynamic tension of cables in a random sea: analytic approximation for the envelope probability density function

When a random sea is filtered by the transfer function of a floating system a narrow banded excitation at the suspended end of risers and mooring line s is, in general, obtained. Using then this gaussian narrow banded signal a s input and the algebraic expression for the dynamic tension derived in Ara nha and Pinto [Dynamic tension in risers and mooring lines: an algebraic ap proximation for harmonic excitation (2001), submitted], the probability den sity function (pdf) for the envelope of the dynamic tension in the risers a nd mooring lines can be analytically approximated. The obtained expression differs, in general, from the Rayleigh distribution and it is compared, in the present work, with numerical results in the time domain, the agreement being fair even in the cases where the risers become dynamically compressed . From a more practical point of view, given then the transfer function of the floating body and the wave energy spectrum, the statistics of the dynam ic tension can be estimated directly from some few integral parameters of t he static configuration introduced in Aranha and Pinto [Dynamic tension in risers and mooring lines: an algebraic approximation for harmonic excitatio n (2001), submitted], avoiding the simulation in time of the riser's dynami cs. (C) 2001 Elsevier Science Ltd. All rights reserved.