考虑内流作用的钢悬链线立管动力特性分析

Dynamic Characteristics Analysis of Steel Catenary Riser with Internal Flow

考虑内流的作用,研究钢悬链线立管动力特性。采用细长柔性杆模型,建立内流作用下钢悬链线立管运动方程,运用有限元法进行离散,通过求解动力特性方程得到立管的固有频率和模态,基于Matlab平台编写相应计算程序,探讨内流流速、顶张力和顶端压强对钢悬链线立管动力特性的影响。结果表明:随着内流流速的增加,立管的固有频率降低,高阶模态的反转点向立管底端移动;随着顶张力的增加,立管的固有频率增加,高阶模态的反转点向立管顶部移动;随着管内顶端压强的增加,立管的固有频率降低。

Effect of internal flow is taken into account in the dynamic characteristics analysis of steel catenary riser in this paper.Slender rods model,which describes the behavior of long thin bar in terms of the position of the center line of the bar and can solve the issue of geometrical nonlinearity,is used to establish the motion equation of steel catenary riser.And finite element method is used to solve the motion equation.Based on Matlab,a calculation program is developed.The calculation program is used to analyze the dynamic characteristic of steel catenary riser and the calculation results are consistent with the results calculated by commercial software.Internal flow velocity,top tension and internal top pressure are taken into consideration and the results indicate that internal flow velocity,top tension and internal top pressure influence the dynamic characteristics of steel catenary riser.With the increase of internal flow velocity,natural frequencies of riser decrease,and the reversal points of high modes move to the bottom of riser.With the increase of mode order,this feature becomes more and more obvious.Although the internal flow velocity won’t be too high in actual marine engineering,while with the increase of internal flow velocity,natural frequencies of steel catenary riser may decrease into lock-in domains,which can lead to dynamic amplification of steel catenary riser.With the increase of top tension,natural frequencies of steel catenary riser increase,and the reversal points of high modes move to the top of riser.The reason is that effective tension of each steel carenary riser element increases with the increase of top tension.Steel catenary riser’s stiffness increases and natural frequencies of steel catenary riser increase eventually.Natural frequencies of riser decrease with the increase of internal top pressure.The reason is that steel catenary riser’s stiffness decreases with the increase of internal top pressure.And natural frequencies of steel catenary riser decrease with the riser’s stiffness decrease.Steel catenary riser can reach several kilometers long in deepwater environments.Compared to shallow water,deepwater is easier to stimulate steel catenary riser high-order modes.As a result,the effect of internal flow velocity,top tension and internal top pressure to steel catenary riser’s natural frequencies should be paid much attention to.