MATHEMATICAL MODEL AND ANALYTICAL SOLUTION FOR THE VIBRATION OF INCLINED FLUID-TRANSPORTING SUBMARINE PIPELINES

Due to the complexity of submarine environments, the nature of the dynamic response of free-spanning submarine pipelines, particularly inclined pipelines, is unclear. This paper aims to theoretically analyze the vibration behaviors of inclined fluid-transporting free-spanning submarine pipelines in the deepwater area. The mathematical model for the vibration of inclined fluid-transporting pipelines is established considering the influence of gravity on vibration response, and a non-linear wake oscillator is employed to model the vortex shedding behind the pipeline free span. The partial differential equation system is solved through the generalized integral transform technique (GITT), which is an analytical or semi-analytical method. Parametric analysis are carried out to investigate the effects of the inclination on the dynamic response of fluid-transporting pipelines. It is found that the inclination of the free- spanning pipeline will radically alter the natural frequency of the structure, and consequently the VIV lock-in region. In addition, the slope of the seabed will cause a more significant internal flow effect. The thorough theoretical understanding of inclined fluid-transporting pipelines helps increase the design accuracy for pipelines installed on a seabed with a highly irregular topography.

Parametric Behaviour Of A Vortex-Induced Vibration Model Of Cylinders With 2 Degrees Of Freedom Using A Wake Oscillator

A model recently proposed by Qu and Metrikine (2020) to predict Vortex-Induced Vibrations of a rigid cylinder elastically mounted with 2 Degrees of Freedom is analyzed and its response is compared with different experimental responses presented in the literature. As the authors themselves pointed out in their work, a comprehensive parametric sensitivity analysis and calibration with more experiments must still be done using this model. The model uses only one equation for the wake oscillator, with a total of three tuning parameters. One database with the tuning parameters for different mass ratios and damping ratios is presented. This will provide a set of pre-defined tuning parameters for different experimental conditions. Thus, the task of trial and error to find the most suitable values for these parameters for a given application is facilitated including the information of the parametric sensibility. After conducting a performance analysis, the model shows to be efficient in predict the maximum amplitude of vibration in the cross-flow direction when compared to experimental data for mass ratios varying from 2.36 to 12.96. For mass ratios higher than 7.91, the model do not predict the correct reduced velocity where the lock-in range initiates. The results are in good agreement with experimental data for damping ratios from 0.002 to 0.4, predicting correct values for the reduced amplitude in both directions. The model shows to be less sensitive to variations in the damping ratio when compared to variations in the mass ratio.