Reliability-Based Structural Optimization of Wave Energy Converters

Abstract

More and more wave energy converter (WEC) concepts are reaching prototype level. Once the prototype level is reached, the next step in order to further decrease the levelized cost of energy (LCOE) is optimizing the overall system with a focus on structural and maintenance (inspection) costs, as well as on the harvested power from the waves. The target of a fully-developed WEC technology is not maximizing its power output, but minimizing the resulting LCOE. This paper presents a methodology to optimize the structural design of WECs based on a reliability-based optimization problem and the intent to maximize the investor's benefits by maximizing the difference between income (e.g., from selling electricity) and the expected expenses (e.g., structural building costs or failure costs). Furthermore, different development levels, like prototype or commercial devices, may have different main objectives and will be located at different locations, as well as receive various subsidies. These points should be accounted for when performing structural optimizations of WECs. An illustrative example on the gravity-based foundation of the Wavestar device is performed showing how structural design can be optimized taking target reliability levels and different structural failure modes due to extreme loads into account.

A Survey of WEC Reliability, Survival and Design Practices

“…Fatigue analyses have been used increasingly in studies of WECs [104][105][106]. These have begun to provide some guidance on the calibration of design factors when considering fatigue in a WEC and have also allowed for some more refined estimates of reliability and maintenance [107].…”

Design Parameters Analysis of Point Absorber WEC via an evolutionary-algorithm-based Dimensioning Tool

“…Pelec is presented in terms of ZPTO to ease the optimum values calculation: (18) where: ZPTO is the mechanical impedance imposed by the PTO when it exerts the force according to a certain control strategy.…”

“…From expression Equation (18), it is possible to solve a maximization problem (of Pelec) taking into account that ZPTO may be real, and the ZPTO value has to constrain the PTO force maximum value to its rated value. The expression of the ZPTO optimal value, obtained again by applying the Lagrange multipliers theory, is shown in Equation (19):…”

“…The design algorithm is addressed as a numerical optimization problem in previous works found in the literature [14][15][16][17][18][19], including approaches such as the economic analysis of the whole design of a WEC, the dimensioning of particular equipment, the optimization of the complete water contact surface and the WEC dimensions optimization in order to take advantage of pitch movement.…”

Economic Assessment of Overtopping BReakwater for Energy Conversion (OBREC): A Case Study in Western Australia

“…However, after that, a production efficiency-based design is proposed; a second stage of design for Reliability, Availability, and Maintainability (RAM) is required [34]. A RAM study models the impact of operations and maintenance activities on power production availability and costs.…”