“Optimization of Mooring Line Axial Stiffness Characteristics for Offshore Renewable Energy Applications”
Abstract: Expanding on existing methodologies for the design optimization of mooring systems for offshore renewable energy devices, this paper explores the optimization of the axial stiffness of a mooring system, a key property that governs the motion of the moored renewable energy device. The optimization using a covariance matrix adaptation evolutionary strategy is executed with respect to both the motion response of the moored device, and the cumulative fatigue damage in the mooring lines. Previous mooring system optimization work has focused on geometry optimization of the system considering known material properties, whilst this paper explores the optimization of the axial stiffness properties of the mooring system identifying ways in which the response of the system can be optimized through changes in the material properties. Considering the case of a moored heaving buoy similar to an offshore renewable energy device, the present case study optimizes the mooring system simultaneously minimizing the cumulative fatigue damage in the mooring lines while also maximizing the heave response which is responsible for the energy generated by the device.
2. Xuanlie Zhao, Dezhi Ning, Xuanlie Zhao, Lars Johanning, Bin Teng
“Numerical Investigation on Hydrodynamic Performance of a WEC Array Integrated into a Pontoon”
Abstract: High construction-cost is one of the barriers that limited the developments of wave energy utilization. Integrating wave energy converters (WECs) into other marine structures may reduce the construction cost of WECs effectively. In this paper, an integrated system with a medium array (11 devices) of heaving point absorber WECs (PAWECs) arranged at the weather side of a fixed pontoon-type structure is proposed. The hydrodynamics of the PAWECs are investigated numerically by using higher-order boundary element method (HOBEM) code package (i.e., WAFDUT), which is developed based on linear potential flow theory. The hydrodynamic performance (including interaction factor, wave exciting force and heave response) of the WEC array with the rear pontoon is investigated with focus on the influence of the spacing between the WEC array and the pontoon (WEC-pontoon spacing). For sake of comparisons, the results corresponding to the isolated WEC array, i.e., without the pontoon, are presented. Results show that the performance of the pontoon-integrated WEC array performs better than that without the pontoon.