36 research outputs found

    Validated reduced order models for simulating trajectories of bio-inspired artificial micro-swimmers

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    Autonomous micro-swimming robots can be utilized to perform specialized procedures such as in vitro or in vivo medical tasks as well as chemical surveillance or micro manipulation. Maneuverability of the robot is one of the requirements that ensure successful completion of its task. In micro fluidic environments, dynamic trajectories of active micro-swimming robots must be predicted reliably and the response of control inputs must be well-understood. In this work, a reduced-order model, which is based on the resistive force theory, is used to predict the transient, coupled rigid body dynamics and hydrodynamic behavior of bio-inspired artificial micro-swimmers. Conceptual design of the micro-swimmer is biologically inspired: it is composed of a body that carries a payload, control and actuation mechanisms, and a long flagellum either such as an inextensible whip like tail-actuator that deforms and propagates sinusoidal planar waves similar to spermatozoa, or of a rotating rigid helix similar to many bacteria, such as E. Coli. In the reduced-order model of the microswimmer, fluid’s resistance to the motion of the body and the tail are computed from resistive force theory, which breaks up the resistance coefficients to local normal and tangential components. Using rotational transformations between a fixed world frame, body frame and the local Frenet-Serret coordinates on the helical tail we obtain the full 6 degrees-of-freedom relationship between the resistive forces and torques and the linear and rotational motions of the swimmer. In the model, only the tail’s frequency (angular velocity for helical tail) is used as a control input in the dynamic equations of the micro-swimming robot. The reduced-order model is validated by means of direct observations of natural micro swimmers presented earlier in the literature and against; results show very good agreement. Three-dimensional, transient CFD simulations of a single degree of freedom swimmer is used to predict resistive force coefficients of a micro-swimmer with a spherical body and flexible tail actuator that uses traveling plane wave deformations for propulsion. Modified coefficients show a very good agreement between the predicted and actual time-dependent swimming speeds, as well as forces and torques along all axes

    In-channel experiments on vertical swimming with bacteria-like robots

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    Bio-inspired micro-robots are of great importance as to implement versatile microsystems for a variety of in vivo and in vitro applications in medicine and biology. Accurate models are necessary to understand the swimming and rigidbody dynamics of such systems. In this study, a series of experiments are conducted with a two-link cm-scale bioinspired robot moving vertically without a tether, in siliconefilled narrow cylindrical glass channels. Swimming velocities are obtained for a set of varying tail and wave geometries, and employed to validate a resistive force theory (RFT) model using modified resistance coefficients based on measured forward velocity and body rotation rates

    Experiment-based kinematic validation of numeric modeling and simulated control of an untethered biomimetic microrobot in channel

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    Modeling and control of swimming untethered microrobots are important for future therapeutic medical applications. Bio-inspired propulsion methods emerge as realistic substitutes for hydrodynamic thrust generation in micro realm. Accurate modeling, power supply, and propulsion-means directly affect microrobot motility and maneuverability. In this work, motility of bacteria-like untethered helical microrobots in channels is modeled with the resistive force theory coupled with motor dynamics. Results are validated with private experiments conducted on cm-scale prototypes fully submerged in Si-oil filled glass channel. Li-Po battery is utilized as the onboard power supply. Helical tail rotation is triggered by an IR remote control. It is observed that time-averaged velocities calculated by the model agree well with experimental results. Finally, time-dependent performance of a hypothetical model-based position control scheme is simulated with upstream flow as disturbance

    Numerical analysis of a planar wave propagation based micropropulsion system

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    Micropropulsion mechanisms differ from macro scale counterparts owing to the domination of viscous forces in microflows. In essence, propulsion mechanisms such as cilia and flagella of single celled organisms can be deemed as nature’s solution to a challenging problem, and taken as a basis for the design of an artificial micropropulsion system. In this paper we present numerical analysis of the flow due to oscillatory planar waves propagating on microstrips. The time-dependent three-dimensional flow due to moving boundaries of the strip is governed by incompressible Navier-Stokes equations in a moving coordinate system, which is modeled by means of an arbitrary Lagrangian-Eulerian formulation. The fluid medium surrounding the actuator boundaries is bounded by a channel, and neutral boundary conditions are used in the upstream and downstream. Effects of actuation parameters such as amplitude, excitation frequency, wavelength of the planar waves are demonstrated with numerical simulations that are carried out by third party software, COMSOL. Functional-dependencies with respect to the actuation parameters are obtained for the average velocity of the strip and the efficiency of the mechanism

    Numerical simulations of a traveling plane-wave actuator for microfluidic applications

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    Continuous forming and propagation of large planar deformations on a thin solid elastic film can create propulsion when the film is immersed in a fluid. Microscopic organisms such as spermatozoa use similar mechanisms to propel themselves. In this work, we present a numerical analysis of the effect of traveling plane-wave deformations on an elastic-film actuator within a fluid medium inside a channel. In particular, we analyzed a micropump that consists of a wave actuator, which is placed in a channel to pump the fluid in the direction of the planedeformation waves. The unsteady flow over the moving boundary between the parallel plates has very low Reynolds number, and, hence, is modeled using the two-dimensional time-dependent Stokes equations. The fluid-structure interaction due to moving boundary is modeled with the arbitrary Lagrangian Eulerian (ALE) method incorporating the Winslow smoothing. COMSOL is used to solve two-dimensional timedependent Stokes equations on a deforming mesh, and to carry out simulations of the flow. Effects of the deformation amplitude, wavelength, frequency and channel height on the flow rate are presented

    Numerical analysis of the 3D flow induced by propagation of plane-wave deformations on thin membranes inside microchannels

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    Propulsion mechanisms of microorganisms are based on either beating or screw-like motion of thin elastic biopolymers. Arguably, this motion is optimal for propulsion at very low Reynolds numbers. Similar actuation mechanisms can be utilized in the design of an autonomous microswimmer or even a micropump. In principle, propagation of plane-wave deformations on a thin-membrane placed inside a channel can lead to a net flow in the direction of the wave propagation. In this study we present effects of the amplitude, frequency, and the width of the membrane on the time-averaged flow rate and the rate of work done on the fluid by the membrane by means of threedimensional transient simulations of flows induced by plane-wave deformations on membranes. Navier- Stokes and continuity equations are used to model the flow on a time-varying domain, which is prescribed with respect to the motion of the membrane. Third party commercial software, COMSOL, is used in to solve the finite-element representation of the 3D time-dependent flow on moving mesh. Numerical simulations show that the flow inside the microchannel depend on the square of the amplitude and is proportional to the excitation frequency. Lastly, characteristic flow rate vs. pressure head curve and efficiency of a typical pump are obtained from 3D transient simulations, and presented here

    Experiments on in-channel swimming of an untethered biomimetic robot with different helical tails

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    Experiments are carried out with a cm-scale bio-mimetic swimming robot, which consists of a body and a rigid helical tail and mimics typical eukaryotic micro organisms, inside circular channels filled with viscous fluids. The body of the robot is made of a cylindrical capsule, which includes an onboard power supply, a dedicated DC-motor, and a driving circuitry with IR-receiver for remote control purposes. In experiments geometric parameters of the helical tail, wavelength and amplitude, and the diameter of the circular channels are varied to understand the effect of those parameters on the swimming speed of the robots. Models, based on slender body theory (SBT) and resistive force theory (RFT), are implemented to predict the swimming speeds, which are then compared with experimentally measured values. A simple model for the DC-motor dynamics is included to account for the contact friction effects on the body rotation rates. Model results agree reasonably well with experimental measurements

    Computationally-validated surrogate models for optimal geometric design of bio-inspired swimming robots: helical swimmers

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    Research on micro-swimming robots without tether is growing fast owing to their potential impact on minimally invasive medical procedures. Candidate propulsion mechanisms of robots are vastly based on micro-organisms with rotating helical tails. For design of swimming robots, accurate models are necessary to compute velocities with corresponding hydrodynamic forces. Resistive force theory (RFT) provides an excellent framework for six degrees-of-freedom (dof) surrogate models in order to carry out effective design studies. However, resistance coefficients reported in literature are based on approximate analytical solutions for asymptotical cases, and do not address the effect of hydrodynamic interactions between the body and the tail, even in unbounded fluid media. Here, we use hydrodynamic interaction coefficients that multiply the body resistance coefficients along with no further modification to local resistance coefficients of the tail. Interaction coefficients are obtained from the solution of the inverse problem once for a fixed representative design with a computational fluid dynamics (CFD) simulation or an experiment. Results of the RFT-based hydrodynamic model are compared against further CFD simulations, and indicate that the model with hydrodynamic interaction coefficients obtained from a representative design provides a viable surrogate for computationally intensive three-dimensional time-dependent CFD models for a range of design variables. Finally, the validated hydrodynamic model is employed to investigate efficient geometric designs with helical wave propagation method within a wider range of design parameters
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