Monopiles are the backbone of European offshore wind energy. However, these massive steel structures are constantly exposed to current and wave forces that trigger a physical process at the seabed: scour. This involves the washing away of sediment around the pile, which can significantly impact the stability and service life of the entire installation.
The Scaling Gap in Research
Although scientists have been developing formulas to predict these erosion processes for decades, a persistent problem remains in practice: models that function at a small laboratory scale often cannot be precisely transferred to the vast dimensions of actual offshore wind farms.
Our current study identifies one of the primary causes for these inaccuracies: the neglect of the pile Reynolds number (Re_D). This dimensionless parameter describes the ratio of inertial forces to viscous forces and is a decisive factor in how turbulently water flows around the foundation. It directly influences the interaction of complex vortex systems - specifically the horseshoe and lee-wake vortices - which are responsible for sediment transport.
New Data for Precise Predictions
To bridge this knowledge gap, we analyzed two new experimental datasets with pile diameters of up to 0.57 m. By combining these with existing studies, a comprehensive database of over 100 data points was established, covering a wide range of Reynolds numbers (from 1.4 x 10^4 to 4.4 x 10^5).
The key findings of our study:
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Significant Increase in Accuracy: By integrating the Reynolds number into the time-scale equation (for Re_D > 2.5 x 10^4), we were able to vastly improve the statistical coefficient of determination (R²) from 0.14 to 0.70.
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Optimized Design Formulas: We propose an improved equation for equilibrium scour depth, reaching a reliability of R² = 0.67 across the entire dataset.
More precise prediction models allow engineers to design foundations more efficiently. This not only saves material costs during construction but also reduces the risk of unexpected maintenance. Our research contributes to securing the interface between hydrodynamics and geotechnics for the next generation of offshore installations.
For more in-depth details, please refer to the full paper:
Hoballah Jalloul, M., Satari, R., Schendel, A., Welzel, M., Kerpen, N. B., Visscher, J., Neuweiler, I., Schlurmann, T. (2026). The influence of the pile Reynolds number on monopile scour prediction across experimental length scales under combined wave-current loading. Coastal Engineering, 206(104951), 104951. doi:10.1016/j.coastaleng.2026.104951
