Real-time wave field mapping for the offshore renewable energy industry

Real-time wave field mapping for the offshore renewable energy industry
Role: Researcher Co-Investigator and Technical Lead
Funding organisation: EPSRC
Funder project reference: EP/F062583/1
Period:1/04/08 → 30/09/09
Value: £294,226.00

This research aimed to improve the quality and availability of wave field information available to the developers and operators of wave energy converters (WECs) to aid in their design and operation through the develop of novel marine sensors.

This research aimed to improve the quality and availability of wave field information available to the developers and operators of wave energy converters (WECs) to aid in their design and operation through the develop of novel marine sensors.
Applications relate to improving performance in varying wave climates, reducing extreme and fatigue-causing loads and reducing risk in critical marine operations through providing access to array-based and near-realtime surface elevation information.
WaveTape involved design, assembly, commissioning and testing of multiple novel sensors featuring technical work spanning mechanical, electrical, communications, signal processing and manufacturing disciplines.

Findings are reported in the resulting PhD thesis of the Researcher Co-Investigator, Dr Brian G. Sellar. Summary text from this thesis is provided below:
Three experimental procedures are outlined which were used to test the feasibility of a novel instrument conceived to meet the potential requirement for improved surface elevation data in large hydraulic test facilities and at sea. The first involves a method in the laboratory to assess the physical ("mechanical-only") surface tracking ability of long, floating, ribbon-like sensor elements that are aware of their position in two dimensions. Showing mean errors in wave height tracking of 6% and wave period tracking errors of 0.1% in irregular waves, across the widest available test range, results from surface tracking tests justify the subsequent testing of actual sensor implementations.
Two approaches are taken: the first involves the modification and testing of a sensor technology comprising position-aware optical fibres with the second approach involving the design, fabrication and testing of floating sensors based on micro-electro-mechanical (MEM) sensor technology.
Whilst wave period errors (individual time domain wave-by-wave comparisons) remain low for the optical fibre system at approximately 1% with standard deviations of approximately 10%, wave height errors are significant. Mean wave height error (depending on processing technique) range from -6% to 4% with standard deviations of 18% to 25% across irregular sea states. Performance is shown to be affected by wave steepness with wave trough tracking showing higher performance compared to wave crest tracking. Preliminary testing of the MEM-based sensor ribbons (in array form capable of measuring position in three dimensions) show wave height errors in regular waves to be on average 1.3% with standard deviations of relative error of 8.4%. Wave period errors and their standard deviations were below 1%. In irregular waves, mean significant wave height is under-predicted, across a range of directional seas, by 3% with standard deviation, across the tests and individual ribbons forming the array, of 7.5%. Peak wave period is under-predicted by 1.3% with standard deviation of 2.2%.