Analysis On Dynamic Characteristics Of Marine Rise Under A Parametric Excitation

As the connection of offshore platform and subsea facilities, marine riser is one of the most important parts in transporting marine oil and gas resource. However, it is also one of the most fragile parts in the marine. The complicacy of the marine environment will be also increased by the depth of water. Especially, when parametric excitation frequency of the marine riser approaches its inherent frequency, the resonance can occur and lead to the destruction of the risers. The destruction not only inflicts economic damage, but also causes severe contamination. Therefore, higher requests should be set in marine engineering. Consequently, the study of marine riser’s dynamic property under the parametric excitation is of great importance.In this paper, a simplified schematic diagram of marine riser system was designed on the dynamic properties of marine risers under the parametric excitation, and then the boundary conditions were obtained by reasonable assumptions. Also, the governing equation was deduced by means of Hamilton principle, of which the dynamic equation contains the time varying tension. The method of finite element was used to disperse the oscillation equation, the riser’s stiffness matrix and mass matrix were also obtained. The inherent frequency was worked out by the method of MATLAB and discrete finite element equation.Considering that the effective tension can be changed in practice, this essay demonstrates the impact of the effective tension towards the riser’s inherent frequency. It shows that the marine riser’s inherent frequency arises with the increase of the effective tension, which gives some suggestions to the operators. Other results show that the marine riser’s inherent frequency falls with the increase of its length and the augment of its external diameter. The difference of riser’s vibrational frequency was also studied, which shows different types of fluent lead to distinct dynamic properties.