The Lateral Vibration Of The Riser And Buoyancy Distribution Optimization

Riser is an important device connected to the offshore drilling platform and wellheads. In poor and complicated Marine environment, marine riser fatigue damage problem is increasingly prominent.The transverse vibration of Marine riser is an important factor that lead to fatigue damage. Buoyancy block configuration has a great influence on the lateral vibration, so transverse vibration characteristics and buoyancy block configuration optimization is of great theoretical and practical significance.The following aspects are discussed in this paper.First,environmental load of the riser was researched and made a basic assumptions for the system of the riser and simplified the constraint conditions reasonably. The riser’s mechanical model was finally established.Second, considering the influence of the uniform distribution of axial force and the top tense, transverse vibration mechanics model of the riser was established. Based on Newton’s law and the vertical and horizontal bending beam theory and the stress analysis of micro unit, transverse free vibration of fourth order linear partial differential equation of the riser was achieved. Using the method of separation of variable to simplify it as fourth order ordinary differential equation with variable coefficients. To get the analytic solution of transverse free vibration natural frequency, integral method was used.Again, considering the influence of buoyancy to the riser’s inherent frequency and vibration mode, used the method of integral to solve it.Finally, using finite element method to optimize buoyancy block configuration scheme. The riser was discreted into several units, and considered the top tension, distribution of axial force and axial concentrated force of riser element stiffness,.flexibility matrix method was used to solve the response of the riser under the the ocean current and the waves.