A Structural Framework for the Design, Analysis, and Development of Marine Energy Turbines

Abstract

Marine and Hydrokinetic (MHK) energy offers a predictable and strategically valuable clean-energy resource, particularly for coastal, maritime, and distributed power applications. However, broader adoption of MHK turbine technologies remains limited by structural reliability, manufacturing scalability, limited open validation data, and the need for blade architectures that can survive severe marine loading while remaining economically practical. This dissertation addresses these challenges through the investigation of composite and additively manufactured MHK turbine blade structures, with emphasis on structural tailoring, finite element modeling, manufacturability, and experimental validation. The work first establishes bend-twist coupling as a passive load-mitigation mechanism for composite marine hydrokinetic blades. Research-scale carbon fiber-reinforced polymer blade spars with controlled fiber-angle variation were manufactured, tested, and modeled to quantify the relationship between laminate orientation, bending stiffness, twist response, and natural frequency. The results show that bend-twist coupling can be deliberately introduced through unbalanced composite layups, but that useful coupling must be balanced against stiffness loss and dynamic response. Validated computational models provide a benchmark framework for extending bend-twist coupling design to larger blade architectures. Expanding the work above to a more generalized structure, a hybrid shell-infill composite architecture was studied using a simplified box-beam model and high-fidelity finite element models to isolate shear-transfer mechanisms relevant to thin-walled blade sections. The results show that while a compliant isotropic infill can substantially reduce peak edge shear without behaving as primary bending members, it can also introduce tradeoffs in stiffness, mass, natural frequency, and bend-twist coupling response. The dissertation then extends to the development of a full-scale open-source composite blade from a common reference geometry. A tiered computational workflow was developed in which low fidelity models enabled rapid layup iteration, while high fidelity composite finite element models refined strain distributions, ply drops, bondline behavior, and failure margins under more realistic loading. The resulting blade satisfied the primary strain and deflection requirements, was manufactured using composite blade fabrication methods, and provides an openly interpretable benchmark platform for future marine hydrokinetic blade studies. Finally, a complementary additive manufacturing pathway was also investigated through the design, fabrication, and testing of a 316L stainless steel structural spar produced by laser metal deposition, providing an alternative structural and manufacturing approach to the conventional composite lay-up blade while addressing the same marine turbine blade design envelope and loading requirements. The spar was designed to follow the complex twist and taper of the MHKF1 blade while serving as the primary load-bearing member. Mechanics-based sizing, finite element modeling, manufacturing, post-processing, and static proof testing demonstrated the structural feasibility of the concept, including successful validation to 150% of the design load. Process-induced effects, including surface waviness, heat accumulation, and residual-stress-related distortion, were further examined through exploratory directed energy deposition process simulation, highlighting both the promise and current limitations of predictive additive manufacturing modeling. The combined findings demonstrate that reliable marine hydrokinetic turbine blade development requires integrated consideration of material architecture, structural capacity, design and manufacturing constraints, as well as validation. Overall, this dissertation advances a structural mechanics framework for designing interpretable, manufacturable, and experimentally grounded blade technologies for next-generation MHK systems.