摘要
深海钻井系统一旦发生紧急脱离,钻井液需下泄入海防止悬挂立管系统固有频率与波浪频率接近而发生共振破坏,同时海水必须注入管内以防止立管挤毁。此时悬臂立管机构为一典型低端含集中质量(低端总成)悬臂输流管系统。该系统采用伽辽金法计算固有频率时通常采用两种方法:将集中质量作为边界条件;利用狄拉克函数将集中质量嵌入输流管模型。内流速度为零时两种方法计算结果一致。但当内流速度不为零时两种方法计算结果差别较大,Paodoussis指出此时第一种方法错误,但并未给出合理解释。重新推导集中质量作为边界条件时悬臂梁系统固有模态正交条件,提出改进方法进行重新计算,与第二种方法及文献结果比较完成验证。并对比自由端含集中质量悬臂输流管系统内流效应试验结果,发现基于改进方法可正确预测临界内流速度及失稳振动频率。可解释自由端含集中质量悬臂输流管系统固有频率计算悖论,同时为不同边界条件下输流管系统动力学分析提供参考。
Once deep-sea drilling system is disconnected in an emergency case,drilling fluid needs to be discharged into sea to prevent resonance failure caused due to natural frequencies of suspension riser system being close to wave frequencies.At the same time,sea water must be injected into riper to prevent riper collapse.At this time,cantilever riser mechanism is a typical cantilever fluid-conveying pipe system with low end concentrated mass,i.e.,low end assembly.When Galerkin method is used to calculate the system,s natural frequencies,usually two ways are employed including the end-mass being taken as a boundary condition,and Dirac function being adopt to embed the endmass into the pipe model.When the internal flow velocity is zero,the results using the two ways are consistent.However,when the internal flow velocity is not zero,the calculation results using the two ways are quite different.Paidoussis pointed out that at this time,the first way is wrong.But they did not give a reasonable explanation.Here,the orthogonal condition of natural modes of a cantilever beam system was re-deduced when the end-mass was used as a boundary condition,and an improved method was proposed for re-calculation.The new results were compared with those using the second way and those published in literature for verification.By comparing the new results with test results of the internal flow effect of cantilever fluid-conveying pipe system with an end-mass,it was shown that the improved method proposed here can correcdy predict the critical internal flow velocity and unstable vibration frequencies;it can explain the paradox in natural frequency calculation of cantilever fluid-conveying pipe system with an end-mass,and provide a reference for dynamic analysis of fluid-conveying pipe systems under different boundary conditions.
作者
赵桂欣
孟帅
车驰东
陈俐
ZHAO Guixin;MENG Shuai;CHE Chidong;CHEN Li(State Key Lab of Ocean Engineering,Shanghai Jiao Tong University,Shanghai 200240,China)
出处
《振动与冲击》
EI
CSCD
北大核心
2023年第7期18-24,共7页
Journal of Vibration and Shock
基金
国家自然科学基金面上项目(51879161)。
关键词
悬臂输流管
集中质量
伽辽金法
模态正交性
固有频率
cantilever fluid-conveying pipe
end-mass
Galerkin method
modal orthogonality
natural frequency
