Big Offshore Coupling

Solar parks at sea are an ideal solution for countries with little space and lots of water. SolarDuck recently put its first floating farm into operation successfully. Large assemblies offshore is the next step, and an upgrade in the connections is required to cope with the high waves and strong winds. Flexibility at the required strength are key elements and combining these, normally contradictory demands, require innovative solutions.

TNO and SolarDuck are therefore going to collaborate on research into the development of a robust coupling that has both spring and damping properties.

By introducing damping, the system will last longer, can be of a larger scale and have lower maintenance costs. Specifically this project focuses on: 

1. Investigations into the requirements of the coupling and design of a coupling 
2. Modelling of behaviour of the coupling under longer term operating conditions 
3. Testing and measurements to validate model performance and design functionality 
4. Optimisation of design parameters through tests

The following results are expected at the end of this project

• A prototype spring/damper unit
• A validated calculation method for prediction of the effectiveness of damping and spring functionalities and loads
• A significant reduction in peak loads and vibration levels 

This coupling will provide a reduction in peak loads. This will result in lowering the cost and help in reducing cost of the structural design of the coupled platforms.

End of project summary

Offshore Floating Solar designs generally consist of a multitude of platforms connected to each other. SolarDuck’s solar plant is an example of such a design. To connect the platforms flexible connections are required, like for example cylinders. SolarDuck and TNO embarked on a project with the aim of gaining more insight in the use of a robust coupling. Ultimately this should reduce the peak load in the system and hence reduce cost and allow for a maintenance-free life. Reducing peak loads and the need for maintenance are key factors in reducing the LCoE of offshore floating platforms. 

The scope of the project was to provide numerical methods for gas cylinder calculations, including temperature effects due to the flow through orifices and extreme compression and expansion.

During the project, a concept design of the cylinder was made using analytical calculations to provide stiffness and damping boundary conditions. A numerical model including an explicit integration scheme that allowed for a full-time domain analysis of the gas cylinder was developed. In which, all effects such as heat transfer (convection, conduction, and radiation), heat storage in gases and solids, pressure losses over piping and orifices, and acceleration effects were considered. This model allowed for studying and optimizing gas volumes, initial filling pressure, orifice setting (damping), geometry, weight, and volume arrangement. Besides also aiding mechanical design in terms of limit management like (dynamic) temperatures, pressures, stroke and force.  

TNO prepared and experimented with a small-scale model to demonstrate the physical process of the cylinder. It showed that this concept has potential. The required forces, stroke and mainly thermodynamic effects seen in the extended model were such that only full-scale testing could provide relevant results. It was therefore decided that the real prototype cylinder was to be tested on the SolarDuck Merganser pilot project.