Abstract

Offshore pipelines are occasionally exposed to scouring processes; detrimental impacts on their safety are inevitable. The process of scouring propagation around offshore pipelines is naturally complex and is mainly due to currents and/or waves. There is a considerable demand for the safe design of offshore pipelines exposed to scouring phenomena. Therefore, scouring propagation patterns must be focused on. In the present research, machine learning (ML) models are applied to achieve equations for the prediction of the scouring propagation rate around pipelines due to currents. The approaching flow Froude number, the ratio of embedment depth to pipeline diameter, the Shields parameter, and the current angle of attack to the pipeline were considered the main dimensionless factors from the reliable literature. ML models were developed based on various setting parameters and optimization strategies coming from evolutionary and classification contents. Moreover, the explicit equations yielded from ML models were used to demonstrate how the proposed approaches are in harmony with experimental observations. The performance of ML models was assessed utilizing statistical benchmarks. The results revealed that the equations given by ML models provided reliable and physically consistent predictions of scouring propagation rates regarding their comparison with scouring tests.

Highlights

  • Received: 12 December 2021Offshore pipeline structures are commonly employed to transport various fluids, such as oil, gas, oil-gas mixtures, and water

  • Various machine learning (ML) models based on evolutionary computing and classification concepts have been utilized to predict the scouring propagation rate around offshore pipelines exposed to currents

  • Effective dimensionless parameters (i.e., 1 – e/D, 1 + sinα, θ C, FrP ) obtained from dimensional analysis of the scouring tests were directly incorporated into the presented equations through the performance of ML models

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Summary

Introduction

Offshore pipeline structures are commonly employed to transport various fluids, such as oil, gas, oil-gas mixtures, and water. Cheng et al [6] studied the three-dimensional scour rate of propagation along offshore pipelines after the scouring process was initiated They found that some experimental variables (e.g., embedment depth of the offshore pipeline, live-bed motion state of seabed sediments due to currents, and flow incident angle) had meaningful impacts on the scouring propagation velocities along the pipeline. Wu and Chiew [7,8] carried out experimental investigations under clear-water conditions to understand the three-dimensional mechanism of scouring propagation beneath pipelines of various diameters They emphasized that the rate of scouring propagation was controlled by the Froude number, the Shields parameter, and the initial embedment depth of the offshore pipeline.

Dimensional Analysis
Description of Experimental Data
D tan φ q L
Gene-Expression Programming
Multivariate Adaptive Regression Splines
Evulotionary Polynomial Regression
M5 Model Tree
Statistical Measures
Statistical Performance of ML Models
Comparisons between ML Models and Related Works Regarding Complexity
Effects of the Pipeline Embedment Depth
Effects of the Shields Parameter
Findings
Effects of the Approach Flow Froude Number
Conclusions
Full Text
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