基于非线性模型的深水隔水管横向振动固有频率分析

Analysis of the natural frequency of transverse vibration of a deep water riser based on a nonlinear model

论文利用微元法建立了隔水管横向振动控制方程,假设轴向力为线性变化得到了隔水管的非线性模型,利用共振法获取隔水管固有频率,采用有限差分法求解非线性模型。分析了隔水管长度、隔水管壁厚、顶部张紧力、钻井液与海水附加质量等因素对隔水管横向振动固有频率的影响,结果表明:隔水管长度增加时,其固有频率减小;随着隔水管壁厚增加,其固有频率增大;顶部张紧力越大,隔水管固有频率越高,可通过改变张力比来有效地改变系统固有特性;计算时需考虑内部钻井液,但钻井液密度对隔水管固有频率影响不大,但附加质量对固有频率的影响较大,必须考虑由海水引起的附加质量。研究内容为评估深水隔水管作业风险,提供了重要理论依据。

In this paper, the transverse vibration control equation of a riser is established by using the element method. Assuming the axial force changes linearly, a nonlinear riser model can be obtained. The model is solved by the method of finite difference. Then, the influence of various factors on the natural frequency of the riser is analyzed. The results show-： When the length of the riser increases, its natural frequency decreases; As the riser＇s wall thickness increases, the natural frequency increases; and that the greater the top tension is, the higher the natural frequency of the riser is, so changing the tension ratio can effectively avoid the resonance frequency; Drilling fluid should be considered in calculations, but its density has little effect on the natural frequency; The effect of additional mass on the natural frequency cannot be ignored. The research content provides an important theoretical basis for assessing risks of deep water riser operation.