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This study presents an analysis of the fatigue damage experienced by mooring systems under extreme and operational wave conditions, with a discussion on the Reference Model 3 (RM3), a widely recognized point absorber wave energy converter (WEC), and the Reference Model 5 (RM5), a floating oscillating surge wave energy converter (FOSWEC). Utilizing the combined strengths of WEC-Sim and MoorDyn, both open-source simulation tools, the study investigates the dynamic behavior of mooring lines over the operational wave condition and a 100-year return period extreme wave condition. This study highlights the relationship between tension force and fatigue damage in mooring lines. The tension forces at various nodes of the mooring lines are calculated, revealing that the complex mooring design is causing a complex trend on the fatigue damage. Instead, variations in tension force show a more significant impact on cumulative fatigue damage, as evidenced by the higher damage observed in nodes experiencing greater tension variation. The findings contribute to a better understanding of the factors influencing fatigue damage in mooring lines of WECs and fatigue damage of different types of WECs, offering insights for more effective monitoring and strategies for WEC design optimization. 

Abstract Thermoelectric generators convert heat energy to electricity and can be used for waste heat recovery, enabling sustainable development. Selective Laser Melting (SLM) based additive manufacturing process is a scalable and flexible method that has shown promising results in manufacturing high zT Bi2Te3 material and is possible to be extended to other material classes such as Mg2Si. The physical phenomena of melting and solidification were investigated for SLM-based manufacturing of thermoelectric (Mg2Si) powders through comprehensive numerical models developed in MATLAB. In this study, Computational Fluid Dynamics (CFD)-based techniques were employed to solve conservation equations, enabling a detailed understanding of temperature evolution within the molten pool. This approach was critical for optimizing processing parameters in our investigation, which were also used for printing the Mg2Si powders using SLM. Additionally, a phase field-based model was developed to simulate the directional solidification of the Mg2Si in MATLAB. Microstructural parameters were studied to correlate the effects of processing parameters to the microstructure of Mg2Si. 

Monitoring fish migration, which can extend over distances of thousands of kilometers, via fish tags is important to maintain healthy fish stocks and pre-serve biodiversity. One constraint of current fish tags is the limited power of their batteries. Attaching a piezoelectric element to an oscillating part of the fish body has been proposed to develop self-powered tags. To determine the functionality and potential of this technology, we present an analysis showing variations of the generated voltage with specific aspects of the tail’s response. We also perform numerical simulations to validate the analysis and determine the effects of attaching a piezoelectric element on performance metrics including thrust generation, propulsive efficiency, and harvested electric power. The tail with the attached piezoelectric element is modeled as a unimorph beam moving at a constant forward speed and excited by sinusoidal pitching at its root. The hydrodynamic loads are calculated using three-dimensional unsteady vor-tex lattice method. These loads are coupled with the equation of motion, which is solved using the finite element method. The implicit finite different scheme is used to discretize the time-dependent generated voltage equation. The analysis shows that the harvested electric power depends on the slope of the trailing edge, a result that is validated with the numerical simulations. The numeri-cal simulations show that, depending on the excitation frequency, attaching a piezoelectric element can increase or decrease the thrust force. The balance of required hydrodynamic power, generated propulsive power and harvested elec-trical power shows that, depending on the excitation frequency, relatively high levels of harvested power can be harvested without a high adverse impact on the hydrodynamic or propulsive power. For a specified frequency of oscillations, the approach and results can be used to identify design parameters where harvested electrical power by a piezoelectric element will have a minimal adverse impact on the hydrodynamic or propulsive power of a swimming fish.