Improved SoiL-cable Interaction mooriNG simulaTiONs

Project Information

ISLINGTON

Grant agreement ID: 101068736

DOI

10.3030/101068736

Project terminated on 12 July 2024

EC signature date 12 October 2022

Start date 1 December 2022

End date 30 November 2024

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 214 934,40

Coordinated by

AALBORG UNIVERSITET
Denmark

Periodic Reporting for period 1 - ISLINGTON (Improved SoiL-cable Interaction mooriNG simulaTiONs)

Reporting period: 2022-12-01 to 2024-11-30

Summary of the context and overall objectives of the project

Mooring is a vital sub-system for marine renewables. In the oil and gas (O&G) industry there is a large degree of redundancy in the design to account for uncertainties. It is unlikely that marine renewables - in order to obtain a competitive levelised cost of energy (LCOE) can afford such redundancy in the mooring design. ISLINGTON had the overall objective to reduce uncertainties in estimated fatigue damage of mooring cables due to soil-cable interaction in the touch down zone (TDZ); and subsequently lower the economic cost of mooring systems for marine renewables. To achieve this objective, the following research actions have been carried out:
1) Improving the numerical modelling of the cable-soil interaction in the TDZ for mooring cables by allowing for time-dependent granular soil dynamics. Application Programming Interface (API) inside a granular particle soil solver was developed to allow a two-way coupling to a mooring cable solver providing position and motion of the mooring cable.
2) Experimental data was generation for mooring line trenching to be used for validation. This was done by forced oscillations of a cable in a wave flume with sandy bottom and log the development of the trenching under different forcing.
3) Numerical investigation of the effect of trenching on fatigue of mooring cables.
The work carried out during the ISLINGTON project, although it does not generate a direct market opportunity, it provides a first step to reducing the uncertainty of mooring design of offshore floating structures. This research has the potential to contribute to the competitiveness and growth of the floating offshore wind sector reducing the LCOE through improved numerical simulation tools for the design phase. The results of the projects can be exploited in two ways: on one hand, universities can use the project results to further advance the state-of-the-art of granular soil modelling enabling multidisciplinary approaches from a hydrodynamics and geotechnical point of view. On the other hand, technology developers, due to the open release of the API and the experimental dataset can implement the proposed novel approach into their numerical tools, or validate their own developments.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The two main research outputs of the ISLINGTON project are:
1. Development of an Application Programming Interface (API) using a Finite Element Method (FEM) solver for waves-current-soil-object interaction.
2. Generating an experimental dataset for benchmarking of mooring line solvers.
The API developed consists of a coupling between the mooring line solver Moody and the FEM granular soil solver DEM-Engine. Firstly, a study of the numerical implementations of the two models was performed in order to identify the best approach to couple them. Secondly, a first secondment was held at Vigo University to complement the initial literature review with specific training on coupling multi-physics engines. After that, the core API was developed taking into account the following steps:
1. Identifying the mooring system parameters that need to be transferred between the two models: anchor position, cable position, cable internal forces, ground reaction forces and cable properties.
2. Identifying how to represent the mooring system in DEM-Engine: use of existing mesh elements to obtain the contact forces between the mooring system and the granular soil.
3. Building the wrapper to connect Moody and DEM-Engine.
4. Generating sample test cases for verifying compilation errors of the API, code verification and numerical validation.
Once the API development was completed, an experimental campaign was designed in collaboration between the Ocean and Coastal Engineering Research Group of Aalborg University and the Geotechnical Engineering and Offshore Foundations Research Group of Aalborg University. During the experimental campaign, different mooring line configurations over a granular soil bed were tested at the wave flume of the Ocean and Coastal Engineering Laboratory, Aalborg University, Denmark. The experimental campaign resulted on an experimental dataset for benchmarking of mooring line solvers. These data were later used for the experimental validation of the Moody-DEM-Engine API showing good agreement between the experimental data and the numerical simulations. Finally, a second secondment was held at Sigma AB with the objective of improving the API functionalities and sketch the numerical benchmarking of the model. Two publications regarding the API and the experimental dataset are scheduled to be submitted before the end of 2024, while the preliminary results of the API implementation and the experimental dataset have been presented at the RENEW 2024 conference.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

During the ISLINGTON project, a new numerical tool -- obtained by coupling a high-fidelity granular soil dynamics model with a state-of-the-art finite element mooring model -- has been developed. The research output comprises the first work, to the researcher’s best knowledge, that couples a mooring line solver with a Discrete Element Method (DEM) solver to model time-dependent mooring line trenching over a granular seabed. The work carried out during the action outlines the numerical work of establishing a two-way coupling between the mooring solver moody and the granular soil solver DEM-Engine. Additionally, the implementation has been validated against experimental data generated specifically to be used as benchmarking of numerical mooring models. The experimental dataset includes different set-ups of a catenary chain in dry conditions under surge, sway and heave motions. The experiments were carried out in air as that it greatly simplified both the characterization and the scanning of the soil in the experiments to provide reliable data of the mooring line trenching and the tensions measured at the fairlead of the mooring chain.