10 research outputs found
Towards efficient flight: insights on proper morphing-wing modulation in a bat-like robot
In this article, we address the question of how the flight efficiency of Micro Aerial Vehicles with variable wing geometry can be inspired by the biomechanics of bats.We use a bat-like drone with highly articulated wings using shape memory alloys (SMA) as artificial muscle-like actuators. The possibility of actively changing the wing shape by controlling the SMA actuators, let us study the effects of different wing modulation patterns on lift generation, drag reduction, and the energy cost of a wingbeat cycle. To this purpose, we present an energy-model for estimating the energy cost required by the wings during a wingbeat cycle, using experimental aerodynamic and inertial force data as inputs to the energy-model. Results allowed us determining that faster contraction of the wings during the upstroke, and slower extension during the downstroke enables to reduce the energy cost of flapping in our prototype
A numerical study of fin and jet propulsions involving fluid-structure interactions
Fish swimming is elegant and efficient, which inspires humans to learn from them to design
high-performance artificial underwater vehicles. Research on aquatic locomotion has made
extensive progress towards a better understanding of how aquatic animals control their
flexible body and fin for propulsion. Although the structural flexibility and deformation of
the body and fin are believed to be important features to achieve optimal swimming
performance, studies on high-fidelity deformable body and fin with complex material
behavior, such as non-uniform stiffness distributions, are rare.
In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI)
solver is developed to investigate the flow field evolution and propulsion performance of
caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver,
the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the
finite volume method with a multi-block grid system. The solid dynamics are solved by a
nonlinear finite element method. The coupling between the two solvers is achieved in a
partitioned approach in which convergence check and sub-iteration are implemented to
ensure numerical stability and accuracy. Validations are conducted by comparing the
simulation results of classical benchmarks with previous data in the literature, and good
agreements between them are obtained.
The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion
involving body deformation. Specifically, the effect of non-uniform stiffness distributions of
fish body and/or fin, key features of fish swimming which have been excluded in most
previous studies, on the propulsive performance is first investigated. Simulation results of a
sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger
thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g.,
increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a
uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable
fish body stiffness does not yield fish-like midline kinematics observed in real fish,
suggesting that fish movement involves significant active control that cannot be replicated
purely by passive deformations.
Subsequent studies focus on the jet propulsion inspired by squid locomotion using the
developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet
propulsion system, whose inflation is actuated by an added external force that mimics the
muscle constriction of the mantle and deflation is caused by the release of elastic energy of
the structure, suggest larger mean thrust production and higher efficiency in high Reynolds
number scenarios compared with the cases in laminar flow. A unique symmetry-breaking
instability in turbulent flow is found to stem from irregular internal body vortices, which
cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion
system in the presence of background flow is studied by prescribing the body deformation
and jet velocity profiles. The effect of the background flow on the leading vortex ring
formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet
are revealed as well.
Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a
cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the
actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically
tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from
an initial position to a target location and then hold the station there. Despite the same
swimming distance, a swimmer whose departure location is closer to the cylinder requires
less energy consumption to reach the target and hold the position there.Fish swimming is elegant and efficient, which inspires humans to learn from them to design
high-performance artificial underwater vehicles. Research on aquatic locomotion has made
extensive progress towards a better understanding of how aquatic animals control their
flexible body and fin for propulsion. Although the structural flexibility and deformation of
the body and fin are believed to be important features to achieve optimal swimming
performance, studies on high-fidelity deformable body and fin with complex material
behavior, such as non-uniform stiffness distributions, are rare.
In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI)
solver is developed to investigate the flow field evolution and propulsion performance of
caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver,
the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the
finite volume method with a multi-block grid system. The solid dynamics are solved by a
nonlinear finite element method. The coupling between the two solvers is achieved in a
partitioned approach in which convergence check and sub-iteration are implemented to
ensure numerical stability and accuracy. Validations are conducted by comparing the
simulation results of classical benchmarks with previous data in the literature, and good
agreements between them are obtained.
The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion
involving body deformation. Specifically, the effect of non-uniform stiffness distributions of
fish body and/or fin, key features of fish swimming which have been excluded in most
previous studies, on the propulsive performance is first investigated. Simulation results of a
sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger
thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g.,
increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a
uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable
fish body stiffness does not yield fish-like midline kinematics observed in real fish,
suggesting that fish movement involves significant active control that cannot be replicated
purely by passive deformations.
Subsequent studies focus on the jet propulsion inspired by squid locomotion using the
developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet
propulsion system, whose inflation is actuated by an added external force that mimics the
muscle constriction of the mantle and deflation is caused by the release of elastic energy of
the structure, suggest larger mean thrust production and higher efficiency in high Reynolds
number scenarios compared with the cases in laminar flow. A unique symmetry-breaking
instability in turbulent flow is found to stem from irregular internal body vortices, which
cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion
system in the presence of background flow is studied by prescribing the body deformation
and jet velocity profiles. The effect of the background flow on the leading vortex ring
formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet
are revealed as well.
Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a
cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the
actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically
tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from
an initial position to a target location and then hold the station there. Despite the same
swimming distance, a swimmer whose departure location is closer to the cylinder requires
less energy consumption to reach the target and hold the position there