The hydrodynamics of self-rolling locomotion driven by the flexible pectoral fins of 3-D bionic dolphin

The novel autonomous rolling performance is realized by the pair of pectoral fins of a three-dimensional(3-D)bionic dolphin in this paper numerically.3-D Navier-Stokes equations are employed to simulate the viscous fluid around the bionic dolphin.The effect of self-rolling manoeuvrability is ex-plored using the dynamic mesh technology and user-defined function(UDF).By varying the parameter ratios,the interaction of flexible pectoral fins is divided into two motion modes,amplitude differential and frequency differential mode.As the primary driving source,the differential motion of a pair of pec-toral fins can effectively provide the rolling torque,and the trajectory of the entire rolling process is approximately the clockwise spiral.The results demonstrate that the rolling angular velocity and driving torque in the steady state can be improved by increasing parameter ratios,and the rolling efficiency can reach the maximum under the optimal parameter ratio.Meanwhile,different parameter ratios do not af-fect the rolling radius of the self-rolling dolphin.The evolution process around the pair of pectoral fins is shown by the flow structures in self-rolling swimming,reasonably revealing that self-rolling locomotion is produced by the pressure and wake vortices surrounding the pair of pectoral fins,and the wake struc-tures depend primarily on the variation of parameter ratio.It properly turns out that the application of the pair of pectoral fins can realize the self-rolling performance through parameter differential modes.

Hydrodynamics study of dolphin’s self-yaw motion realized by spanwise flexibility of caudal fin

The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper,we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility,especially the spanwise flexibility of the caudal fin.The kinematics of the chordwise flexible body and the spanwise flexible caudal fin are explored through dynamic mesh technology and user-defined functions(UDF).The 3-D Navier-Stokes equations are applied to simulate the viscid fluid surrounding the bionic dolphin.The study focuses on quantitative problems about the fluid dynamics behind the specific motion law,including speed of movement,energy loss and working efficiency.The current results show that the self-yaw can be composed of two motions,autonomous propulsion and active steering.In addition,the degree of the flexible caudal fin can produce different yaw effects.The chordwise phase differenceФis dominant in the propulsion function,while the spanwise phase differenceδhas a more noticeable effect on the steering function.The pressure distribution on the surface of the dolphin and the wake vortex generated in the flow field reasonably reveal the evolution of self-yaw.It properly turns out that the dolphin can combine the spanwise flexible caudal fin and the chordwise flexible body to achieve self-yaw motion.

Multifunctional Polypyrrole-silver Coated Layered Double Hydroxides Embedded into a Biodegradable Polymer Matrix for Enhanced Antibacterial and Gas Barrier Properties

In this study,polypyrrole-silver coated layered double hydroxides(LDHs@PPy-Ag)was prepared by chemical polymerization of pyrrole(Py)with silver ions.Silver nanoparticles(AgNPs)could be uniformly reduced onto PPy coatings in situ by redox reaction during simultaneous polymerization process.And LDHs@PPy-Ag/poly(ε-caprolactone)(PCL)nanocomposites were fabricated by solution casting method.It is revealed that spherical AgNPs are loaded on PPy coatings uniformly.Particularly,compared with pure PCL,LDHs@PPy-Ag/PCL nanocomposites with incorporation of only 1 wt%LDHs@PPy-Ag show a 17%increase in tensile strength(36.5 MPa)and a 29%increase in elongation at break(822%).Upon PPy-Ag coatings onto original LDHs,oxygen relative permeability of LDHs@PPy-Ag/PCL nanocomposites decreases to 52%with the same addition.Meanwhile,due to the double antibacterial activity of PPy and AgNPs,the antibacterial rate of LDHs@PPy-Ag reaches 100%.And the corresponding LDHs@PPy-Ag/PCL nanocomposites also show outstanding antibacterial activity.Considering the superiority of their comprehensive performance,antibacterial LDHs@PPy-Ag/PCL nanocomposites can be used further for the application as biodegradable polymeric active packaging materials.