Akash Choudhary - Academia.edu (original) (raw)

Papers by Akash Choudhary

Journal of Thermal Stresses, 2004

This paper summarizes the thermal fatigue testing conditions that can be found in the literature ... more This paper summarizes the thermal fatigue testing conditions that can be found in the literature about shape-forming tools. The importance of the local geometry of the tools is discussed. The key point of the study is to demonstrate that a reproduction of thermal fatigue conditions must take into account a size effect: the same apparent thermal shock does not have the same effect in a large, thick tool as it has in a small, thin laboratory specimen. This paper proposes a method to evaluate what kind of thermal shock to perform on the laboratory specimen to replicate a thermal shock observed in the large and thick tool. A global method of design of a thermal fatigue experiment is given for a cylindrical specimen, provided that the maximum temperature, maximum thermal stresses, and the corresponding time in the cycle have been previously determined. A method to determine the required data is proposed. A definition of the intensity of the thermal shocks is proposed and damages on specimen surfaces are illustrated with regard to that definition. Keywords fatigue testing, thermal fatigue, thermal stresses, thermomechanical fatigue, tool steels, tools, transient heat transfer The authors are grateful to the French Technical Center for Foundry, the Fonderie Aluminium Cléon and St. Gobain Pont à Mousson for their financial support. The various studies performed with them helped us arrive at this theoretical analysis of thermal fatigue.

Communications Physics, 2022

The transport of motile microorganisms is strongly influenced by fluid flows that are ubiquitous ... more The transport of motile microorganisms is strongly influenced by fluid flows that are ubiquitous in biological environments. Here we demonstrate the impact of fluid inertia. We analyze the dynamics of a microswimmer in pressure-driven Poiseuille flow, where fluid inertia is small but non-negligible. Using perturbation theory and the reciprocal theorem, we show that in addition to the classical inertial lift of passive particles, the active nature generates a ‘swimming lift’, which we evaluate for neutral and pusher/puller-type swimmers. Accounting for fluid inertia engenders a rich spectrum of complex dynamics including bistable states, where tumbling coexists with stable centerline swimming or swinging. The dynamics is sensitive to the swimmer’s hydrodynamic signature and goes well beyond the findings at vanishing fluid inertia. Our work will have non-trivial implications on the transport and dispersion of active suspensions in microchannels.

Soft Matter, 2022

The current work studies the dynamics of a microswimmer in pressure-driven flow of a weakly visco... more The current work studies the dynamics of a microswimmer in pressure-driven flow of a weakly viscoelastic fluid.

Bulletin of the American Physical Society, 2018

The European physical journal. E, Soft matter, 2021

Chemically active Janus particles generate tangential concentration gradients along their surface... more Chemically active Janus particles generate tangential concentration gradients along their surface for self-propulsion. Although this is well studied in unbounded domains, the analysis in biologically relevant environments such as confinement is scarce. In this work, we study the motion of a Janus sphere in weak confinement. The particle is placed at an arbitrary location, with arbitrary orientation between the two walls. Using the method of reflections, we study the effect of confining planar boundaries on the phoretic and hydrodynamic interactions, and their consequence on the Janus particle dynamics. The dynamical trajectories are analyzed using phase diagrams for different surface coverage of activity and solute-particle interactions. In addition to near wall states such as 'sliding' and 'hovering', we demonstrate that accounting for two planar boundaries reveals two new states: channel-spanning oscillations and damped oscillations around the centerline, which wer...

Physics of Fluids, 2021

Janus particles self-propel by generating local tangential concentration gradients along their su... more Janus particles self-propel by generating local tangential concentration gradients along their surface. These gradients are present in a layer whose thickness is small compared to the particle size. Chemical asymmetry along the surface is a pre requisite to generate tangential chemical gradients, which gives rise to diffusioosmotic flows in a thin region around the particle.This results in an effective slip on the particle surface. This slip results in the observed "swimming" motion of a freely suspended particle even in the absence of externally imposed concentration gradients. Motivated by the chemotactic behavior of their biological counterparts (such as sperm cells, neutrophils, macrophages, bacteria etc.), which sense and respond to external chemical gradients, the current work aims at developing a theoretical framework to study the motion of a Janus particle in an externally imposed linear concentration gradient. The external gradient along with the self-generated concentration gradient determines the swimming velocity and orientation of the particle. The dominance of each of these effects is characterized by a nondimensional activity number (ratio of applied gradient to self-generated gradient). The surface of Janus particle is modelled as having a different activity and mobility coefficient on the two halves. Using the Lorentz Reciprocal theorem, an analytical expression for the rotational and translational velocity is obtained. The analytical framework helps us divide the parameter space of surface activity and mobility into four regions where the particle exhibits different trajectories.

Physical Review Fluids, 2021

A recent article (Khair and Kabarowski; Phys. Rev. Fluids 5, 033702) has studied the crossstreaml... more A recent article (Khair and Kabarowski; Phys. Rev. Fluids 5, 033702) has studied the crossstreamline migration of electrophoretic particles in unbounded shear flows with weak inertia or viscoelasticity. That work compares their results with those reported in two of our previous studies (Choudhary et al. J. Fluid Mech. 874; J. Fluid Mech. 898) and reports a disagreement in the derived analytical expressions. In this comment, we resolve this discrepancy. For viscoelastic flows, we show that Khair and Kabarowski have not accounted for a leading order surface integral of polymeric stress in their calculation of first-order viscoelastic lift. When this integral is included, the resulting migration velocity matches exactly with that reported in our work (J. Fluid Mech. 898). This qualitatively changes migration direction that is reported by Khair and Kabarowski for viscoelastic flows. For inertial flows, we clarify that Khair and Kabarowski find the coefficient of lift to be 1.75π, compared to 2.35π in our previous work (J. Fluid Mech. 874). We show that this difference occurs because Khair and Kabarowski accurately include the effect of rapidly decaying ∼ O(1/r 4) velocity field (a correction to the stresslet field ∼ 1/r 2), which was neglected in our previous work (J. Fluid Mech. 874).

International Journal of Engineering Technologies and Management Research, 2020

Technology is getting better and better day by day, Robots is being introduced as an alternative ... more Technology is getting better and better day by day, Robots is being introduced as an alternative of humans. In this era it is necessary that all parts of the society grow equally either it is space research , medical or automobile same thing applies on the domestic sector nowadays cleaning method is being shifted towards robotic cleaners. This paper presents the design and development of Fully Automated Hybrid Home Cleaning Robot. It can perform tasks like moping and vacuum cleaning without any help of humans.

Journal of Fluid Mechanics, 2019

There has been a recent interest in integrating external fields with inertial microfluidic device... more There has been a recent interest in integrating external fields with inertial microfluidic devices to tune particle focusing. In this work, we analyse the inertial migration of an electrophoretic particle in a two-dimensional Poiseuille flow with an electric field applied parallel to the walls. For a thin electrical double layer, the particle exhibits a slip-driven electrokinetic motion along the direction of the applied electric field, which causes the particle to lead or lag the flow (depending on its surface charge). The fluid disturbance caused by this slip-driven motion is characterized by a rapidly decaying source-dipole field which alters the inertial lift on the particle. We determine this inertial lift using the reciprocal theorem. Assuming no wall effects, we derive an analytical expression for a ‘phoretic lift’ which captures the modification to the inertial lift due to electrophoresis. We also take wall effects into account, at the leading order, using the method of refl...

Chemical Engineering Science, 2017

The objective of this research was to investigate the effects of total chlorine free (TCF) and el... more The objective of this research was to investigate the effects of total chlorine free (TCF) and elemental chlorine free (ECF) bleaching on optical and mechanical properties of bleached bagasse soda pulp. For this purpose, some unbleached bagasse soda pulp was randomly selected from Pars Paper industry. Then pulp was bleached with one, two or three stage sequences applying P, OP, OPY, O(Ep)P, EHP and O(Ep)H bleaching stages denoting oxygen(O), hydrogen peroxide(P), alkali extraction with hydrogen peroxide(Ep), sodium hypochlorite(H) and sodium dithionite(Y). The hand sheets with 70 gr/m 2 were prepared from the abovementioned bleached pulps, and then the optical and mechanical properties were measured using TAPPI standard test methods and compared. The results showed that brightness, greenness, tear (except EHP stages), tensile, burst, breaking length strengths and folds were increased and opacity and a* factor were decreased by ECF and TCF bleaching sequences. The effects of TCF bleaching sequence were more sensible than ECF bleaching sequence in improving bagasse soda pulp properties. In general, role of three stage OPY and O(Ep)H and two stage OP bleaching were better than EH(control) and unbleached bagasse soda pulps mill in improving brightness and paper strengths.

2007 Annual Conference & Exposition Proceedings

Journal of Fluid Mechanics