Abstract
As Wave Energy Converters technology is becoming more mature, a new generation of large-scale units developed by private industry has emerged and is expected to become a common feature of the blue economy. The majority of these large converters are moored to the seafloor, and the ability to produce energy both efficiently and reliably is tied to the very design of the mooring mechanism.
The authors initially developed a wireless apparatus, coined PADLOC, for the continuous monitoring and analysis of mooring lines using load cells, acquisition electronics and an underwater acoustic modem [1-2]. Every PADLOC unit could acquiring, storing and wirelessly transmitting data to a remote user. Load cell data were both stored over the course of months for post-processing and transmitted (in the form of statistical values or raw data at a reduced rate) wirelessly to a remote operator using the built-in underwater acoustic communication technology. The PADLOC technology thus allowed for the combined high-resolution data collection and transmission of information for continuous monitoring of the WEC mooring lines. As an outcome of this research, a total of eight PADLOC units were built (four of the first generation, and four upgraded units) [1-2].
Throughout the project, the experimental data indicated that a careful analysis of the mooring of operational and future moored Wave Energy Converters was necessary, for the purpose of predicting the mechanical robustness of the mooring and the efficiency of certain types of converters in capturing the wave energy. The experimental aspect of this analysis focused on a specific part of the mooring, where belts are used to couple the wave-induced motion of the wave to the power takeoff units. These belts are attached to the mooring lines on one end, and to the power takeoff unit on the other end.
To do so, a single-axis load cell or a dual-axis load cells were operated with the PADLOC units in a controlled environment, using a Material Testing System available in the Department of Ocean and Mechanical Engineering at Florida Atlantic University. This work went in pair with a model analysis performed at Sandia National Laboratories, to complete a comparative study between modeled results and field results.
This research focuses on the experimental data collection and analysis, using the stress-strain response of two types of belts identified by Sandia National Laboratories. The testing included the impact of pitch, roll and yaw in the load cell assembly to evaluate the impact of the load cell orientation and belt on the measurements. The applied load was time-varying or static, and remained within 10 kN. The estimated variation of each angle is within ±5 degrees. This conference paper provides the details of the experimental approach, setup, key results obtained with this set of belts, and conclusions.