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Interactions of the individual metal powders, with boundaries (substrate and container wall), were characterized, and coefficients of friction between the powders and boundaries were calculated. Evolution of the repose angle, slope surface speed, slope surface roughness, and the dynamics of powder clusters at the powder front were revealed and quantified. Here, we studied particle-scale powder dynamics during the powder spreading process by using in-situ high-speed high-energy x-ray imaging. However, powder spreading behavior under additive manufacturing condition is still not clear, largely because of the lack of particle-scale experimental study. As with recent studies, we conclude propulsive performance is more sensitive to kinematics rather than the shape and bending behavior of the caudal fin.Powder spreading is a key step in the powder-bed-based additive manufacturing process, which determines the quality of the powder bed and, consequently, affects the quality of the manufactured part. The average peak propulsive performance for the tail models was ηp =0.43 and CT =0.3. Propulsive performance trends and values were similar for all our tail models and to previous experiments investigating a similar parametric space, where the peak propulsive performance was observed for all tail models and hydrofoils at Sttip =0.35 and α_max =20º. About half of those generated sufficient thrust to counter the whole body drag estimates (CT ≥0.19). For the 30 motion regimes the mean thrust over a tail-beat was positive. Flow structures were visualized by means of particle image velocimetry (PIV). Propulsive efficiencies and thrust coefficients were calculated from force and torque measurements. Each model was actuated in a water tunnel by a computer controlled, motorized system to follow motion paths typical for a tuna. A computed tomography scanner and a polyjetTM 3-Dimensional printer were used to make three tail models: two with materials of similar properties to the caudal fin, and one of uniform stiffness. Our goal was to assess the propulsive performance of the Atlantic bluefin tuna, Thunnus thynnus, which is our case study for thunniform propulsion, by an experimental approach of the highest bio-fidelity currently performed. But these experiments oversimplify the animal (motion, shape or material property) and/or the flow condition.
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Therefore, indirect approaches are used, such as theoretical and experimental studies. However, there is no direct empirical evidence to support this common idea, due to the difficulty of obtaining force measurements for these animals. Thunniform propulsion is assumed to have the highest propulsive performance of all swimming modes, meaning high propulsive efficiency at fast swimming speeds. For these reasons, thunniform propulsion has received considerable attention from biologists and bio-inspired engineers. To propel themselves these animals use the thunniform propulsion mode, and are physically characterized by having streamlined bodies with narrow necking of the caudal peduncle and a high aspect ratio lunate tail generating lift-based thrust. Tunas, lamnid sharks and whales are some of the fastest sustained swimming animals.