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MPM - A Paradigm Shift in Leg Penetration Assessments

Introduction

Welcome to the dynamic world of offshore wind energy, where jackup vessels - the marvels of marine engineering - play a pivotal role. These vessels elevate from the sea to provide a stable platform for offshore wind turbine installation. The stability of the their 'feet' on the seabed is calculated in a Leg Penetration Assessment (LPA). LPA is more than just a technical process; it's a cornerstone of operational safety, determining how these vessels interact with the complex seabed. Traditional LPA methods have been instrumental, but the evolving demands of offshore operations call for innovation.


Today, I'm excited to introduce an innovative app designed to revolutionise the LPA in the offshore wind sector by introducing large deformation Material Point Modelling (MPM). This process is a significant step forward, integrating advanced technology with real-world insights to enhance the safety and efficiency of jackup vessels. Aimed not only at engineers but also at the wider community passionate about sustainable energy, this app represents a leap towards optimising offshore operations and advancing the renewable energy revolution.


Bridging Gaps: The Role of Soil Plug in LPA

Traditional methods to calculate the LPA curve rely on a mechanism-based methods or a strength averaging methods. Though these methods have been successfully applied over the past decades, they ultimately present a very simplified calculation model with limitations in capturing how the soil layers interact as the spudcan penetrates into the seabed.


One of the factors which is often ignored is the formation of a soil plug beneath the spudcan. Soil plug formation occurs when the spudcan, the 'foot' vessel’s leg, presses into the seabed, displacing and compacting soil beneath it. The movement of the soil plug with the spudcan makes that the spudcan can rely on higher soil resistance at deeper layers. Ignoring this effect typically results in conservative LPA estimates that may not reflect real-world conditions.


Innovating LPA: The Mechanism-Based Method Meets MPM

MPM, a cutting-edge computational technique, brings a new level of detail and accuracy to LPA. Unlike traditional methods, MPM can simulate the intricate interactions between the spudcan and the seabed, considering variables such as detailed layering, improved spudcan geometry modelling and the effects of the soil plug. This integration offers a more holistic view of the leg-seabed interaction, providing insights that were previously unattainable. Moreover, the MPM technique can show soil layers during spudcan penetration, providing a clear, visual understanding of the underlying mechanics.

By comparing the results of the trusted mechanism-based method with the detailed analysis capability of MPM side by side, the app improves understanding of the spudcan-soil interaction and provides a robust tool for predicting and managing the risks associated with offshore vessel operations. The figure below compares the results in a complex layering where the punching, squeezing and a soil plug all play a role:

  • In the mechanism based approach, you can see the effect of the spudcan cone (-0.8m to 0m) followed by punching in the sand layer (0m - 2m), squeezing in the clay layer (2m - 4m), punching in the sand layer (4m - 8m) and finally the uniform bearing capacity in the deep clay layer (8m - 10m).

  • In the MPM model, we can see that a higher soil resistance is achieved at a shallower depth due to the formation of the sand plug (0 - 4m) and beyond this, the results are closely aligned with the punching mechanism (4m - 8m) and the uniform bearing capacity in the deep clay layer (8m - 10m).

  • Note that in this specific MPM simulation, the cone of the spudcan was not modelled, which is the reason for the discrepancy between -0.8m and 0m.



Conclusion

As we embrace this innovation of MPM modelling for LPA, we're not just advancing technology; we're charting a new, safer, and more efficient course for the future of Leg Penetration Assessments. As we progress with the validation of the analyses, we aim to make an MPM calculation standard for every LPA.


🔗 Access the app here


We'd love to hear from you! Whether you're an offshore engineer, a safety expert, or just passionate about renewable energy, share your thoughts, questions, or insights. Let's discuss how this app can reshape our industry.



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