This study reveals the complexity of 3D vortex wake flows produced by nekton with hydrodynamically distinct propulsors. Propulsive efficiency (η) increased with speed irrespective of swimming orientation, and η for swimming sequences with clear isolated jet vortex rings was significantly greater (η=78.6☗.6%, mean±s.d.) than that for swimming sequences with clear elongated regions of concentrated jet vorticity (η=67.9☑9.2%). For both swimming orientations, the fins sometimes acted as stabilizers, producing negative thrust (drag), and consistently provided lift at low/intermediate speeds (<2.0 DML s −1) to counteract negative buoyancy. The jet generally produced the majority of thrust during rectilinear swimming, increasing in relative importance with speed, and the fins provided no thrust at speeds >4.5 DML s −1. Although there was considerable complexity in the wakes of these multi-propulsor swimmers, 3D vortex rings and their derivatives were prominent reoccurring features during both tail-first and arms-first swimming, with the greatest jet and fin flow complexity occurring at intermediate speeds (1.5–3.0 DML s −1). Defocusing digital particle tracking velocimetry, a volumetric velocimetry technique, and high-speed videography were used to study arms-first and tail-first swimming of brief squid Lolliguncula brevis over a broad range of speeds in a swim tunnel. Given the complexity of the squid multi-propulsor system, 3D velocimetry techniques are required for the comprehensive study of wake dynamics. The nozzle.Squids use a pulsed jet and fin movements to swim both arms-first (forward) and tail-first (backward). Results show that in the bursting phase its peak speed depends on the size of the body, theĭeformation time, the amount of volume change during the deformation, and the size of Novel method to calculate the propulsive efficiency.įinally, a potential-flow-based rendition of a 3D squid-inspired propulsion systemis developed to explore the swimming process and the dynamic characteristics. Moreover, it enables the separation of thrust andĭrag forces on the body (a classical problem in free-swimming bodies) so that it leads to a the effects of jet speed profile, jet acceleration,īackground flow and nozzle geometry. Underlying physics of force generation, e.g. In the thrust decomposition method the jet-related thrust isĬalculated as the summation of three components, the jet flux force, the exit normal stressĪnd the flow momentum force inside the chamber. The 2D IBM-based model is then extended to an axi-symmetric numerical rendition.Based on control volume analysis, a thrust-drag decoupling strategy and a thrust decomposition method are proposed. Parameter determining the hydrodynamics of the swimmer. Parametric studies, it is found that the body oscillation frequency is the most important Of long-distance swimming through cyclic deflation-inflation shape change. Systematic simulations we demonstrate that the 2D squid-inspired swimmer is capable Regeneration, and is thus suitable for problems involving large body deformations. To understand the physical mechanisms of squid-like jet propulsion, computational simulations are conducted to explore the underlying fluid dynamics and fluid-structure interaction problems.Ī two-dimensional fluid-structure numerical model is firstly developed by usingthe Immersed Boundary Method (IBM), which avoids the complexity of body-fitted grid A squid-inspired robot is expected to possess multiple advantages such as mechanical simplicity, high swimming speed, and low environmental footprint. Inspired by the locomotion method of cephalopods such as squids, we propose a novel concept of underwater propeller that utilizes pulsed jet for thrust generation.
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