In this paper an introduction is given into the rising offshore renewable energy market. It's pointed out that dynamic stiffness is a key requirement for mooring ropes in these systems. Axial stiffness is explained, as well as the difference between static and dynamic load regime, from the material morphology point of view. For dynamic stiffness the influencing parameters mean load, load range and frequency are distinguished and it is mentioned that according to previous research in a real wave situation the parameters load range and frequency can be ignored.
A first example case discusses a renewable wave energy device, where the rope construction and rope layout was completely custom designed to fit the application. Studies were done into permanent Chinese Fingers pulling slings and full scale pulling eyes. These special slings assist in performing the installation and de-installation (recuperation) most efficiently.
For a specific and recent offshore renewable wind energy project, a comparison is made between different high modulus fiber materials, to which material is the most economically suitable. The application requires a high dynamic stiffness and low creep elongation, besides 25 year fatigue lifetime. Different high modulus fiber materials like Vectran UM, Twaron 2200, Dyneema SK78 and Carbon fiber (TohoTenax STS40) are compared. The main conclusion is that in the range of service loads considered, many materials can be competitive, and therefore future work should test the suitability and cost efficiency of these materials on subrope level.
