Session: 09-09-01: Advances in Wind and Ocean Energy

Paper Number: 164553

Robust Swivel-Based Mooring System for Marine Energy Devices to Improve System Reliability 

The coastal region in the United States (U.S.) has meaningful resource availability. However, there are many challenges facing marine energy (ME) technologies. Point-absorber wave energy converters (WECs) are constantly challenged by twisting and cyclical axial loading of the primary mooring line. This persistent behavior can cause damage to cables and consequently decrease device performance. To address this challenge, common practice is to add anti-spin anchor lines, despite their less than optimal performance (e.g., increased cost, fatigue, device premature failure, increased entanglement risk, and potential damping of energy available for the power take-off). Therefore, we propose a robust slip ring-swivel mooring system to enhance the reliability and performance of several types of ME systems. The proposed slip ring-swivel device is capable of handling (1) axial rotation and (2) tensile loading while maintaining the transmission of electricity and fluids (e.g., desalinated water). This general approach can be extended to include transmission of other signals (e.g., communication and instrumentation). The slip ring-swivel system contains a slip ring and swivel joint that are concentrically oriented to permit transfer of electricity and fluids, respectively, and also contains an integrated spring-damper system for mitigation of axial loading of the associated lines and cables. While there are some similar commercially available products, none of the identified commercial products are directly suitable for the target ME environment (e.g., ≤ IP-68) and they do not incorporate a design feature to mitigate the anticipated axial loading during deployments.  The proposed slip ring-swivel system provides widespread versatility across multiple technology types, such as small-scale Powering the Blue Economy (PBE) devices (e.g., wave energy converters), for a range of ocean environments (e.g. waves, currents, and tides).  This work first includes a requirements specification to characterize the environmental conditions and design requirements (e.g., functional, performance, user, policy and regulatory, and interface requirements, design constraints, etc.).  Then, this work details the design approach (e.g., conceptual and preliminary design, including design options and selection), followed by analysis to validate the design. The design analysis includes simulation-based models to characterize the anticipated loads in the marine environment, which are used as an input to the design requirements, and computational analysis (e.g., finite element models to evaluate stress and deflection in the device). Based on the evaluation, the results provide confidence the proposed approach will satisfy the requirements for this application to improve performance and reliability of deployed ME devices. The system promises to reduce deployment and operational expenses, increase time between maintenance periods, and likely increase the ME device’s period of performance, thus lowering a ME device’s levelized cost of electricity and/or freshwater. Ultimately, the slip ring-swivel system offers to make ME devices more competitive and help advance the ME industry. Future work will include additional detailed design for a range of devices (i.e., device scalability), with scaled and full-scale prototype testing to validate the proposed design (e.g., laboratory tests of mechanical systems, aqueous functional and environmental tests, ocean deployments).

Presenting Author: Michael Smith University of North Carolina at Charlotte

Presenting Author Biography: Michael Smith (Member: ANS, ASME, IEEE Senior Member, SME) received a B.S. in Mechanical Engineering Technology (2005), M.S. in Mechanical Engineering (2008), M.S. in Electrical Engineering (2012), and Ph.D. in Electrical Engineering (2015) from the University of North Carolina at Charlotte, Charlotte, NC, USA. He is currently an Assistant Professor in the Department of Engineering Technology and Construction Management (within the William States Lee College of Engineering) at the University of North Carolina at Charlotte, Charlotte, NC, USA. His background includes instrumentation-based process control, process modeling, data analytics, data-driven decision making, and software development, with over 10 years of industrial experience in the energy industry and more than 15 years of teaching experience. With a particular interest in industry applications, his research focus areas include: (a) control systems (e.g., adaptive control, optimal control, system dynamics, and stability), (b) process modeling and data analytics (e.g., physics-based and data-driven methods, including machine learning), and (c) monitoring/instrumentation. His research interests include applied energy, process automation and optimization, electromechanical systems, and manufacturing.

Authors:

Michael Smith University of North Carolina at Charlotte
Caroline Lowcher Coastal Studies Institute - ECU
Trip Taylor Coastal Studies Institute - ECU
Justin Logan UNC Charlotte
Devin Hill UNC Charlotte
Ulises Guillen UNC Charlotte