Fluid Mechanics

Manta-Ray Like Underwater Vehicle “Manta-Bot”

Bio-inspired Robotics, Fluid Mechanics /

While major bio-inspired underwater vehicles have demonstrated a fish-like swimming pattern (similar appearance, caudal fin propulsion, etc), many of them cannot carry a large load and are unable to achieve sharp maneuvers. We developed a manta-ray-inspired underwater vehicle (manta-bot) that can achieve elegant swimming underwater just like a real manta-ray. With a built-in control system (ROS), […]

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Scaling laws for 3D pitching hydrofoils

Bio-inspired, Fluid Mechanics, Scaling Laws, Vortex Dynamics /

Building on our previous work on 2-D pitching airfoils, we explored how forces and torques scale for 3-D pitching airfoils. The terms we added to existing theories were inspired by the 3-D elliptical ring shapes of wake vortices. We validated the new terms by comparing our predictions with water channel experiments over a range of

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Stable equilibria exist for near-surface swimmers and fliers

Bio-inspired, Fluid Mechanics, Fluid Structure Interactions, Ground Effects, Vortex Dynamics /

Fish and birds experience different forces when they swim/fly near a flat surface (e.g. seabed, solid ground, still lake). We discovered that the vertical forces they feel switch from negative (downward) to positive (upward) at a particular distance from the surface. In other words, there’s a stable equilibrium altitude where they are neither pushed down

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Modeling lateral station-keeping in fish

Bio-inspired, Fluid Mechanics, Scaling Laws, Vortex Dynamics /

Fish flap their tails asymmetrically to maneuver around obstacles. In contrast, classic fish tail models assume symmetric motions in a uniform flow. We tested how well these classic models work for maneuvering tails. In some cases, the models work well: even 2D wakeless models were able to predict the phase of high frequency lateral displacements.

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How dorsal fins make fish faster and more efficient

Bio-inspired, Bio-inspired Robotics, Fluid Mechanics, Fluid Structure Interactions, Vortex Dynamics /

The dorsal and anal fins of fish interact with the tail fins to produce higher thrust and efficiency. We focused on thin elongated dorsal fins, like those of jackfish. We discovered that dorsal fins can act like the wing strakes of fighter jets, promoting flow attachment on a main lifting surface (wing/tail) by inducing spanwise

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How thrust and efficiency change if you swim near the bottom of the pool

Fluid Mechanics, Fluid Structure Interactions, Ground Effects, Scaling Laws, Vortex Dynamics /

We developed a model that estimates how thrust and efficiency change as a pitching hydrofoil gets closer to a planar boundary. Our model predicts that the modified forces are caused by an increasing amount of virtual mass and an increasingly distorted wake. We validated the model by comparing with water channel experiments and inviscid flow

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How aspect-ratio affects near-ground swimmers

Bio-inspired, Fluid Mechanics, Fluid Structure Interactions, Ground Effects, Scaling Laws, Vortex Dynamics /

Animals and bio-inspired robots can swim/fly faster near solid surfaces like the seafloor. In the past, researchers had quantified how strong these effects were for two-dimensional airfoils. We studied how these results extend to the three-dimensional fins. We found that lowering the aspect ratio weakens the effect of the surface: thrust enhancements become less noticeable,

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Tunable stiffness enables fast and efficient swimming in fish-like robots

1 Comment / Bio-inspired Robotics, Fluid Mechanics /

Underwater vehicles haven’t changed much since the submarines of World War II. They’re rigid, fairly boxy and use propellers to move. And whether they are large manned vessels or small robots, most underwater vehicles have one cruising speed where they are most energy efficient. Fish take a very different approach to moving through water: Their bodies

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