In nature, cephalopods, particularly squids, achieve exceptional maneuverability and propulsive efficiency by combining fin activity with jet propulsion. Their fins undulate or beat synchronously or independently to provide thrust and lift, while rhythmic mantle contractions coupled with a flexible funnel generate pulsed jets. Funnel deformability and traveling waves modulate vortex-ring formation, jet entrainment, and exit-pressure impulse-mechanisms that enable squid to enhance thrust for efficient propulsion. Inspired by the biological funnel, we design passively deforming, flexible nozzles for underwater propulsion and conduct three-dimensional, strongly coupled, partitioned fluid-structure interaction simulations based on the Arbitrary Lagrangian-Eulerian framework. Our study probes how nozzle flexibility and geometry govern wave propagation, vortex dynamics, and hydrodynamic impulse.
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