Axial dynamic analysis of marine riser in installation

In this paper, the riser is regarded as continuous system with infinite degrees of freedom and the mechanical model to analyze its axial dynamic characteristics during installation has been established according to the basic principle of vibration mechanics. The model has taken the influence of damping on vibration into consideration, and the axial vibration differential equation has been deduced. The equation has been solved on the basis of boundary conditions and initial conditions. Besides, the variations of water depth, riser size, weight of Blowout Preventers (BOPs) on axial vibration natural frequency and axial vibration load have been discussed. Results show that axial vibration is given priority to the first order vibration mode and the maximum vibration load point located at the riser top. With the increase of water depth and riser wall thickness, the natural frequency increases gradually. The natural frequency decreases with the increase of weight of BOPs. However, the maximum axial vibration load decreases with the increase of the above mentioned factors. Whatʹs more, the riser bottom trends compression when the water up to a certain depth. The study has shed some light on safe and quick installation of marine riser.