Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

Abstract

Attempts to measure the propulsive forces produced by swimming dolphins have been limited. Previous uses of computational hydrodynamic models and gliding experiments have provided estimates of thrust production by dolphins, but these were indirect tests that relied on various assumptions. The thrust produced by two actively swimming bottlenose dolphins (Tursiops truncatus) was directly measured using digital particle image velocimetry (DPIV). For dolphins swimming in a large outdoor pool, the DPIV method used illuminated microbubbles that were generated in a narrow sheet from a finely porous hose and a compressed air source. The movement of the bubbles was tracked with a high-speed video camera. Dolphins swam at speeds of 0.7 to 3.4 m s −1 within the bubble sheet oriented along the midsagittal plane of the animal. The wake of the dolphin was visualized as the microbubbles were displaced because of the action of the propulsive flukes and jet flow. The oscillations of the dolphin flukes were shown to generate strong vortices in the wake. Thrust production was measured from the vortex strength through the Kutta-Joukowski theorem of aerodynamics. The dolphins generated up to 700 N during small amplitude swimming and up to 1468 N during large amplitude starts. The results of this study demonstrated that bubble DPIV can be used effectively to measure the thrust produced by large-bodied dolphins.

Effects of added drag on cetaceans : fishing gear entanglement and external tag attachment

“…COT was one of the few metabolic parameters that was not significantly different between individuals, which reinforces the frequent use of this measure for inter-individual and inter-species comparisons (Tucker, 1970;Schmidt-Nielsen, 1972;Williams, 1999). Tagged (6.52±1.42 W/kg), non-tagged (7.83±1.66 W/kg) and predicted (9.22±1.99 W/kg) power estimates fall well within the range (0.3-23.7 W/kg) of mass-specific power estimates for T. truncatus using a variety of modeling methods across speeds 1-6 m/s (reviewed by Fish et al, 2014).…”

“…Adjusting frequency instead of amplitude may be a strategy to reduce body distortion required for large-amplitude movements, that would further increase drag (Fish, 2003); there may also be limitations on the amount of work per stroke (Lovvorn et al, 2004). Changes in amplitude are less common in the literature compared to frequency, but may be especially useful in generating high thrust when especially needed, such as rapid accelerations (Fish et al, 2014) or at the initiation of dives (Fig. 3B).…”

“…Glide deceleration (Lang and Daybell, 1963;Bilo and Nachtigall, 1980) remains one of best methods to determine passive drag coefficients of live, free-swimming animals (see Fish et al, 2014, for a review). The method employs the concept that when an animal passively glides horizontally through the water the forces acting on the body can be simplified to only the drag forces opposing the movement of the body and therefore slowing it down.…”

“…In addition to glide deceleration, wind tunnels with physical models (Hanson, 2001;Jones et al, 2013), tow experiments with live animals in a rigid body position (Feldkamp, 1987), and particle image velocimetry (Fish et al, 2014) have been used to determine drag forces and coefficients for static and swimming animals. These techniques facilitate the measurement of drag loading in a controlled experimental environment, but provide less realistic measurement environments or situations.…”

Swimming kinematics and efficiency of entangled North Atlantic right whales

“…Adjusting frequency instead of amplitude may be a strategy to reduce body distortion required for large-amplitude movements that would further increase drag (Fish et al 2003); there may also be limitations on the amount of work per stroke (Lovvorn et al 2004). Changes in amplitude are less common in the literature compared to frequency, but may be particularly useful in generating high thrust when especially needed, such as for rapid accelerations (Fish et al 2014) or at the initiation of dives (Fig. 3B).…”