Modelling Jet Trenching in Cohesive Soil

Computational Fluid Dynamics Simulation for Sedimentation Processes of Clay Particles

Master thesis (2024)

Authors

Contributors

G.H. Keetels Offshore and Dredging Engineering - Mechanical, Maritime and Materials Engineering (supervisor 1)
S.M.S. Alhaddad Offshore and Dredging Engineering - Mechanical, Maritime and Materials Engineering (supervisor 2)
Q. Bourdos (supervisor 2)
H.S. Daanen (supervisor 2)
Faculty
Mechanical Engineering
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Published Date

14-05-2024

Language

English

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Faculty

Mechanical Engineering

Abstract

Jet trenching operations in sandy seabeds have been extensively studied and are well understood, offering a preferred method for offshore cable installation due to its relatively low environmental impact. However, the transition to clay seabeds presents significant challenges, demanding a deeper comprehension of jet trenching dynamics in cohesive soils. Recognizing this need, DEME NL Offshore, a Dutch company specializing in offshore operations, seeks to develop a predictive model tailored for jet trenching in cohesive soil environments.

This thesis addresses the complexity of jet trenching in clay seabeds through a comprehensive computational fluid dynamics (CFD) modelling approach. Beginning with an extensive literature review, various methods for modelling jet trenching processes are explored, highlighting the critical parameters influencing trenching outcomes. While existing models primarily focused on jet penetration depth, this study identifies the need to integrate fluid dynamics principles and particle behavior to achieve a better understanding of jet trenching dynamics. A CFD model is developed to cover the fluid dynamics in the trench behind the jetting sword. Subsequently, a langrangian model is applied to determine the trajectory of cohesive particles of different diameter in the trench.

Key Findings:
• For the scenarios considered in this thesis, jet trenching in clay soils is not feasible by the accumulation of particles at the trench bottom before the cable touchdown point.

• Particle diameter significantly influences trenching outcomes, underscoring the importance of further investigation.

• Existing models inadequately account for clay block formation and behavior, indicating a gap in understanding.

• Empirical validation and field testing are essential to enhance model accuracy and reliability.

• Integration of field observations and experimental data can refine the model for real-world scenarios.

In response to these findings, recommendations for future research endeavors are proposed, emphasizing the importance of empirical validation and field testing to enhance model accuracy and reliability. By integrating field observations and experimental data, trenching models can be refined to better predict real-world trenching scenarios, thereby optimizing offshore cable installation processes.

In conclusion, this thesis contributes valuable insights into the challenges of jet trenching operations in cohesive seabeds and lays the groundwork for future research in the field. By addressing the recommendations outlined herein, future endeavors can advance trenching methodologies, ultimately improving the efficiency, reliability, and sustainability of offshore cable installation.