Coupled dynamic analysis of moored floating structures by a hybrid Laplace-time domain method

Abstract

The coupled dynamic analysis of moored floating structures has often been conducted in the time domain by iteratively solving the Cummins equation, treating the mooring effects as an additional nonlinear load. However, the time domain (TD) method requires performing a convolution integral at each time step, which is costly in computational time. This paper innovatively develops an efficient hybrid Laplace-time domain method (HLTD) on implementing the coupled dynamic analysis of moored floating structures. The proposed method divides the external load into a number of segments and models the mooring system by the catenary theory. Under each segment, while the iterative operations used in the TD method is borrowed to handle the coupled behavior, the HLTD method computes the motions of the floating structure under each iteration by the pole-residue operations in the Laplace domain (LD). As the complicated convolutional integral computation required in the TD method is replaced by simple algebraic pole-residue calculations in the complex plane, the HLTD method is more efficient. Additionally, the HLTD method derives analytical response solutions for the moored floating system. Its efficiency and accuracy are demonstrated by comparing with the TD method through a moored float-over barge to irregular waves.