Abstract
The numerical procedures for dynamic analysis of mooring lines in the time domain and frequency domain were developed in this work. The lumped mass method was used to model the mooring lines. In the time domain dynamic analysis, the modified Euler method was used to solve the motion equation of mooring lines. The dynamic analyses of mooring lines under horizontal, vertical, and combined harmonic excitations were carried out. The cases of single-component and multicomponent mooring lines under these excitations were studied, respectively. The case considering the seabed contact was also included. The program was validated by comparing with the results from commercial software, Orcaflex. For the frequency domain dynamic analysis, an improved frame invariant stochastic linearization method was applied to the nonlinear hydrodynamic drag term. The cases of single-component and multicomponent mooring lines were studied. The comparison of results shows that frequency domain results agree well with nonlinear time domain results.
Highlights
It can be seen that the modified Euler method is very simple, and it can lead to accurate response evaluations
12 ofAc18 cording to the results of the dynamic analysis in the time domain, it can be seen that this program can perform as well as the commercial software, and the difference is within 3%
The dynamic analysis thefor time domain was simulated to the frequency domain
Summary
The time- or frequency domain dynamic analysis can be carried out to estimate the dynamic mooring line response. The normal wave–particle acceleration across the half of the upper segment that connects the i-th node is. The tangential wave particle velocity ui,τ i+1/2 across the half of the upper segment that connects the i-th node is τ ui,i (8). The inertia force on the upper and lower half segment on the side of node i is as follows:. The inertia forces on node i including two lines segments on either side of the node are. Where DAi±1/2 = 81 πρD2 Can li±1/2 , and the normally added mass coefficient Can = Cm. i where mi represents the mass of two mooring line segments on each side of the i-th node. Vn where CD ri,i +1/2 is the normal relative velocity to the upper segment connected with node i, respectively.
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