Generic flow profiles induced by a beating cilium

We describe a multipole expansion for the low Reynolds number fluid flows generated by a localized source embedded in a plane with a no-slip boundary condition. It contains 3 independent terms that fall quadratically with the distance and 6 terms that fall with the third power. Within this framework we discuss the flows induced by a beating cilium described in different ways: a small particle circling on an elliptical trajectory, a thin rod and a general ciliary beating pattern. We identify the flow modes present based on the symmetry properties of the ciliary beat.Comment: 12 pages, 6 figures, to appear in EPJ

A photoelastic investigation of partially debonded rigid line inclusion

An inverse three-quarters singularity with an oscillatory behavior exists at the tip of a partially debonded rigid line inclusion. The studies on partially debonded rigid line inclusion are hitherto confined to analytical solutions. There exists no work until now that studies partially debonded rigid line inclusions experimentally. In this paper, we experimentally investigate the mechanics of a rigid line inclusion that is bonded to one of its surface. Debonded rigid line inclusion specimens oriented along the direction of loading and perpendicular to the loading direction are considered. Digital photoelastic technique is employed to extract the whole field stress distribution near the debonded inclusion tip. Here, the emphasis is laid on the experimental aspects, starting from the specimen realization to data extraction. The nature of singularity at the tip is investigated, and a multi-parameter stress field equation for a partially debonded rigid line inclusion problem is derived. A complex stress intensity factor is defined at the inclusion tip to quantify the magnitude of singularity and is estimated experimentally using a linear over-deterministic least-squares approach involving the digital photoelasticity. © 2022 Elsevier Lt

A comparison of domain integral and multi-parameter methods for the strain intensity factor estimation of rigid line inclusion using digital image correlation

A comparative study is carried out between two methods to estimate the strain intensity factor of a rigid line inclusion using the displacement and strain fields from digital image correlation (DIC). The two methods are (i) a proposed hybrid domain integral method and (ii) the linear over-deterministic least-squares technique involving multi-parameter displacement field equations (multi-parameter method). The multi-parameter method uses the displacement data obtained from the DIC experiments to find the unknowns in the multi-parameter equation. The proposed hybrid methodology uses a domain integral method to calculate the strain intensity factor using the full-field displacement and strain data obtained from DIC. The strain intensity factor estimated using the proposed domain integral method, and the multi-parameter method agrees with the analytical estimate. The influence of the size of the annular region and the mesh sensitivity is also reported. The sensitivity to the variance and bias errors in measurement for both the methods is investigated. To investigate the effect of variance error, a Gaussian noise is introduced over the reference and deformed images before post-processing, and its influence on the strain intensity factor estimate is discussed. The effect of random perturbations of displacements and strains on the strain intensity factor estimates is also investigated. The domain integral method is less sensitive to the variance error when compared to the multi-parameter solution approach. Further, the bias errors due to uncorrected lens distortions, over-smoothing of data, and DIC algorithm adopted are introduced into the measurements, and its effect on both the methods is investigated. The multi-parameter method is less sensitive to bias errors when compared to the domain integral method. Therefore, it is recommended that the domain integral method may be used for the experimental determination of strain intensity factor in measurements with variance errors and the multi-parameter method for measurements with bias errors

Magnetically Actuated Artificial Cilia: The Effect of Fluid Inertia

Natural cilia are hairlike microtubule-based structures that are able to move fluid on the micrometer scale using asymmetric motion. In this article, we follow a biomimetic approach to design artificial cilia lining the inner surfaces of microfluidic channels with the goal of propelling fluid. The artificial cilia consist of polymer films filled with superparamagnetic nanoparticles, which can mimic the motion of natural cilia when subjected to a rotating magnetic field. To obtain the magnetic field and associated magnetization local to the cilia, we solve the Maxwell equations, from which the magnetic body moments and forces can be deduced. To obtain the ciliary motion, we solve the dynamic equations of motion, which are then fully coupled to the Navier−Stokes equations that describe the fluid flow around the cilia, thus taking full account of fluid inertial forces. The dimensionless parameters that govern the deformation behavior of the cilia and the associated fluid flow are arrived at using the principle of virtual work. The physical response of the cilia and the fluid flow for different combinations of elastic, fluid viscous, and inertia forces are identified.

Fluid propulsion using magnetically-actuated artificial cilia : experiments and simulations

We conducted a combined modelling and experimental approach to explore the underlying physical mechanisms responsible for fluid flow caused by magnetically-actuated plate-like artificial cilia. After independently calibrating the elastic and magnetic properties of the cilia, the model predictions are observed to be in excellent agreement with the experimental results. We show that the fluid propelled is due to a combination of asymmetric motion and fluid inertia forces. The asymmetric motion of the cilia and inertial forces contribute equally to the total fluid flow. We have performed a parametric study and found the cilia thickness and magnetic field that should be applied in order to maximise the fluid transport

Fluid propulsion using magnetically-actuated artificial cilia : experiments and simulations

We conducted a combined modelling and experimental approach to explore the underlying physical mechanisms responsible for fluid flow caused by magnetically-actuated plate-like artificial cilia. After independently calibrating the elastic and magnetic properties of the cilia, the model predictions are observed to be in excellent agreement with the experimental results. We show that the fluid propelled is due to a combination of asymmetric motion and fluid inertia forces. The asymmetric motion of the cilia and inertial forces contribute equally to the total fluid flow. We have performed a parametric study and found the cilia thickness and magnetic field that should be applied in order to maximise the fluid transport