The design of mooring system of VLFS is one of the most important technical problems, since support of these mooring systems is crucial for the VLFS in enduring severe exciting loads by waves. The location and the numbers of the mooring points are significant factors as the structural behaviors of the VLFS are influenced by these factors  in addition to the environmental wave loadings to the structure. Structural response of the structure to the encountering wave can be many times of that determined statically when the wave-loading frequency is near the natural flexural frequency of the structure.  In this paper, a VLFS structure and associated mooring system is designed to have sound behaviors by avoiding resonance, eventually avoiding the so-called dynamic amplification of the response. Suitable natural frequencies and corresponding mode shapes obtained from an eigenvalue analysis of the structure with desirable mooring points and location are provided for the total structure. Finite Element Analysis combined with ANSYS code, using different modeling of the VLFS and mooring points and location is carried out to obtain proper ways of positioning the dolphin mooring system, resulting in sound preliminary design of VLFS and mooring system.

modal analysis, finite element method, structural response, natural frequency.