Parametric instability analysis of the top-tensioned riser in consideration of complex pre-stress distribution

Leixin Li,Luyun Chen

doi:10.1177/1687814017753894

Abstract

The parametric vibration instability of a riser is studied in consideration of a complex pre-stress distribution. Differential equations of the riser are derived according to Euler–Bernoulli beam theory, and a method to solve the differential equations is proposed. With the parametric vibration of a top-tensioned riser as an example, the effects of the amplitude and direction of complex pre-stress on frequency, mode shapes, and instability characteristics are investigated. Results show that welding residual stress influences the dynamic response of the riser structure. A new approach to eliminate the complex loading of the riser is obtained.

Highlights

With the growing demand for crude oil and gas in recent years, deep-water exploitation has become the focus of offshore equipment
The longitudinal vibration of risers is caused by the heaving of a floating platform, which leads to the destruction of risers
With the increase in the order, the influence of complex pre-stress on natural frequency becomes increasingly significant. These results show that the peak value of welding residual stress distribution is not too evident in natural frequency

Summary

Introduction

With the growing demand for crude oil and gas in recent years, deep-water exploitation has become the focus of offshore equipment. The non-linear resonance arising from parametric excitation problems has been discussed, and closed-form solutions for a riser have been obtained on the basis of first and second modes through extensive mathematical manipulations.[1] The parametric vibration caused by the wave-induced motions of a floating platform is practically important because it can destroy risers.[2] A stability analysis of the riser structure was performed in a previous study using Lyapunov stability theory, in which the top boundary controller is considered.[3,4] The finite element method has been employed to analyze the influence of water depths, environmental conditions, and vessel motions under combined parametric and forcing excitations.[5] Structural natural frequency is an important structural dynamic property of riser structure. The natural frequencies of riser structure possess a low modal, and these

Objectives

Conclusion