SUBFRAME

SUBFRAME (Subsea Underwater Buoyancy and Frame Research for Artificial Reefs and Monitoring Engineering) was developed to improve the design and stability assessment of underwater structures used for nature enhancement and monitoring in offshore wind farms. As the deployment of artificial reefs, oyster restoration structures, and monitoring frames increases in the North Sea, there is a growing need for a practical tool that enables rapid stability assessments during the design phase.

 

The project aimed to develop a user-friendly calculation tool for assessing the stability of underwater structures on the seabed, evaluate existing stability methodologies, identify strengths and limitations of current approaches, and provide practical guidance for future deployments of nature-enhancing structures and monitoring equipment.

Program: Nature Regeneration North Sea (NN)

2025 -2026

Project dates

Primarily focused on offshore windfarm application in the Dutch North Sea

Location

Nature Regeneration North Sea, Seaward, Waterproof, The Rich North Sea

Project lead and partners

Not specified 

Target species

Methods

The SUBFRAME project focused on the development and evaluation of a stability assessment tool for underwater structures deployed on the seabed. The study was initiated in response to the increasing deployment of artificial reefs, oyster restoration structures and ecological monitoring equipment in offshore wind farms, and the need for a practical method to rapidly assess their stability under waves and currents.

 

The project combined a review of existing stability assessment methods with the development of a Python-based calculation tool. The SUBFRAME calculator applies the Morison equation, linear wave theory (Airy waves), current velocity profiles and structural stability calculations to estimate hydrodynamic forces, sliding risk and overturning risk. Geometry information was derived from 3D CAD and mesh models, allowing parameters such as volume, frontal area and centre of gravity to be incorporated into the analysis.

 

To evaluate the methodology, deployment data from offshore structures in the North Sea were reviewed. Three case studies were selected for detailed analysis: an oyster spat collector, an ARC Marine artificial reef structure and the MIXLander monitoring frame. Stability calculations generated by SUBFRAME were compared with existing WaterProof assessments and evaluated against known deployment outcomes and environmental conditions.

 

The combined results were used to assess the applicability, strengths and limitations of the methodology and to provide recommendations for the future design and deployment of nature-enhancing structures and monitoring equipment in offshore environments.

Results

The SUBFRAME project successfully delivered a Python-based stability assessment tool for underwater structures deployed on the seabed. The calculator combines hydrodynamic loading calculations, wave and current modelling, and stability analyses into a single workflow, enabling rapid evaluation of alternative designs during the early stages of project development.

 

Comparison with existing WaterProof stability assessments showed that SUBFRAME generally produces results within approximately 20% of detailed engineering calculations. The closest agreement was found for relatively simple and closed structures, while larger differences were observed for more complex and open-frame designs. Despite these differences, the tool proved suitable for providing reliable order-of-magnitude estimates and identifying potential stability risks during preliminary design phases.

 

The methodology was evaluated using three representative case studies: an oyster spat collector, an ARC Marine artificial reef structure and the MIXLander monitoring frame. Results demonstrated that the approach can be applied to a wide range of underwater structures used for ecological restoration and environmental monitoring. The analysis also highlighted the importance of accurate geometry information, centre-of-gravity calculations and mesh quality when performing stability assessments.

 

Overall, the project demonstrated that SUBFRAME can support more efficient design iterations and improve the accessibility of stability assessments for nature-enhancing structures. The study concludes that the tool provides a practical first step towards a validated and widely applicable design platform that can support the safe deployment and scaling-up of artificial reefs, oyster restoration structures and monitoring equipment in offshore wind farms.

 

Download full report:

Project SUBFRAME final report

Tips & Tricks

  • Rapid stability assessments can significantly improve the design process for offshore nature-enhancement structures by identifying potential stability issues early in the design phase. The SUBFRAME project demonstrated that simple screening tools can provide valuable insights before undertaking detailed engineering analyses.
  • Accurate geometry data are essential for reliable stability predictions. The quality of the 3D model, particularly estimates of volume, frontal area and centre of gravity, has a direct influence on calculated forces and stability margins. Where possible, these parameters should be verified rather than relying solely on automatically generated values.
  • The study showed that stability predictions are generally more accurate for simple and closed structures than for complex open-frame designs. For more complex structures, additional checks, manual adjustments and detailed engineering assessments may be required.
  • Environmental conditions are a key driver of stability. Reliable wave, current and water-depth data should be used during the design process, and sensitivity analyses are recommended to understand how changing conditions may affect structure performance.
  • The project recommends using SUBFRAME as a preliminary design tool and validating final designs with more detailed assessments, particularly for critical deployments or when calculated safety factors approach stability limits.Although decommissioning was not specifically addressed, the stability assessment methodology could support future evaluations of installed structures and help inform decisions regarding maintenance, relocation or removal.
  • No specific permitting activities were required as part of this software development project. The study relied on data from existing deployments and previously permitted projects.

Let's talk

Would you like to know more about this project or get involved? Send an email to the project lead.

Frank@seaward.blue