Biology subjects

Ford, M. P.

Publications and source records attributed to Ford, M. P..

4 recordsLinked to original sources

bioRxiv2021

Hybrid metachronal rowing augments swimming speed and acceleration via increased stroke amplitude

Numerous aquatic invertebrates use drag-based metachronal rowing for swimming, in which closely spaced appendages are oscillated starting from the posterior, with each appendage phase-shifted in time relative to its neighbor. Continuously swimming species such as Antarctic krill generally use "pure metachronal rowing" consisting of a metachronal power stroke and a metachronal recovery stroke, while burst swimming species such as many copepods and mantis shrimp typically use "hybrid metachronal rowing" consisting of a metachronal power stroke followed by a synchronous or nearly synchronous recovery stroke. Burst swimming organisms need to rapidly accelerate in order to capture prey and/or escape predation, and it is unknown whether hybrid metachronal rowing can augment acceleration and swimming speed compared to pure metachronal rowing. Simulations of rigid paddles undergoing simple harmonic motion showed that collisions between adjacent paddles restrict the maximum stroke amplitude for pure metachronal rowing. Hybrid metachronal rowing similar to that observed in mantis shrimp (Neogonodactylus bredini) permits oscillation at larger stroke amplitude while avoiding these collisions. We comparatively examined swimming speed, acceleration, and wake structure of pure and hybrid metachronal rowing strategies by using a self-propelling robot. Both swimming speed and peak acceleration of the robot increased with increasing stroke amplitude. Hybrid metachronal rowing permitted operation at larger stroke amplitude without collision of adjacent paddles on the robot, augmenting swimming speed and peak acceleration. Hybrid metachronal rowing generated a dispersed wake unlike narrower, downward-angled jets generated by pure metachronal rowing. Our findings suggest that burst swimming animals with small appendage spacing, such as copepods and mantis shrimp, can use hybrid metachronal rowing to generate large accelerations via increasing stroke amplitude without concern of appendage collision.

bioengineering↗

bioRxiv2021

Closer appendage spacing augments metachronal swimming speed by promoting tip vortex interactions

Numerous species of aquatic invertebrates, including crustaceans, swim by oscillating multiple closely spaced appendages. The coordinated, out-of-phase motion of these appendages, known as "metachronal paddling", has been well-established to improve swimming performance relative to synchronous paddling. Invertebrates employing this propulsion strategy cover a wide range of body sizes and shapes, but the ratio of appendage spacing (G) to the appendage length (L) has been reported to lie in a comparatively narrow range of 0.2 < G/L [≤] 0.65. The functional role of G/L on metachronal swimming performance is unknown. We hypothesized that for a given Reynolds number and stroke amplitude, hydrodynamic interactions promoted by metachronal stroke kinematics with small G/L can increase forward swimming speed. We used a dynamically scaled self-propelling robot to comparatively examine swimming performance and wake development of metachronal and synchronous paddling under varying G/L, phase lag, and stroke amplitude. G/L was varied from 0.4 to 1.5, with the expectation that when G/L is large, there should be no performance difference between metachronal and synchronous paddling due to a lack of interaction between vortices that form on the appendages. Metachronal stroking at non-zero phase lag with G/L in the biological range produced faster swimming speeds than synchronous stroking. As G/L increased and as stroke amplitude decreased, the influence of phase lag on the swimming speed of the robot was reduced. For smaller G/L, vortex interactions between adjacent appendages generated a horizontally-oriented wake and increased momentum fluxes relative to larger G/L, which contributed to increasing swimming speed. We find that while metachronal motion augments swimming performance for closely spaced appendages (G/L < 1), moderately spaced appendages (1.0 [≤] G/L [≤] 1.5) can benefit from metachronal motion only when the stroke amplitude is large.

bioengineering↗

bioRxiv2020

Inter-species variation in number of bristles on forewings of tiny insects does not impact clap-and-fling aerodynamics

Flight-capable miniature insects of body length (BL) < 2 mm typically possess wings with long bristles on the fringes. Though their flight is challenged by needing to overcome significant viscous resistance at chord-based Reynolds number (Rec) on the order of 10, these insects use clap-and-fling mechanism coupled with bristled wings for lift augmentation and drag reduction. However, inter-species variation in the number of bristles (n) and inter-bristle gap (G) to bristle diameter (D) ratio (G/D) and their effects on clap-and-fling aerodynamics remain unknown. Forewing image analyses of 16 species of thrips and 21 species of fairyflies showed that n and maximum wing span were both positively correlated with BL. We conducted aerodynamic force measurements and flow visualization on simplified physical models of bristled wing pairs that were prescribed to execute clap-and-fling kinematics at Rec=10 using a dynamically scaled robotic platform. 23 bristled wing pairs were tested to examine the isolated effects of changing dimensional (G, D, span) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. Within biologically observed ranges of n and G/D, we found that: (a) increasing G provided more drag reduction than decreasing D; (b) changing n had minimal impact on lift generation; and (c) varying G/D produced minimal changes in aerodynamic forces. Taken together with the broad variation in n (32-161) across the species considered here, the lack of impact of changing n on lift generation suggests that tiny insects may experience reduced biological pressure to functionally optimize n for a given wing span. SUMMARY STATEMENTIntegrating morphological analysis of bristled wings seen in miniature insects with physical model experiments, we find that aerodynamic forces are unaffected across the broad biological variation in number of bristles.

bioengineering↗

bioRxiv2020

On the role of phase lag in multi-appendage metachronal swimming of Euphausiids

Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important euphausiid species such as Antarctic krill (E. superba) swim constantly by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag ({phi}) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ( krillbot) capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits of E. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimming E. superba. In addition to examining published kinematics with uneven{phi} between pleopod pairs, we modified E. superba kinematics to uniformly vary{phi} from 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW with{phi} between 15%-25%, coincident with{phi} range observed in FFW gait of E. superba. In contrast to synchronous rowing ({phi}=0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing ({phi} >0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.

bioengineering↗