Department of Mechanical Engineering

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IIT Jodhpur

This paper reports a finite element based numerical framework for simulating the electromechanical behavior of nonlinear anisotropic dielectric elastomer actuators at finite strains. Based on the existing models for incompressible anisotropic neo-Hookean hyperelastic solids and ideal dielectric elastomers, a theory of anisotropic dielectric elastomers is outlined. The analytical expressions are derived for the tangent moduli of the anisotropic materials. A computationally efficient staggered solution algorithm is presented for solving the coupled nonlinear equations by decoupling displacement and electric potential fields. Selective reduced integration technique is used for alleviating the volumetric locking due to material incompressibility. The model is implemented into an in-house finite element program. We first validate the accuracy of the finite element implementation by considering the cases of homogeneous deformation, with a particular emphasis on the electromechanical instability. Subsequently we demonstrate the utility of the proposed numerical framework by analyzing two representative cases (bending and buckling actuators) involving inhomogeneous deformations. In both the cases, anisotropy in the mechanical properties of the elastomer is found to have a favorable influence on the actuation performance. Finally, for various mesh sizes, a comparison of the computation time required by the monolithic solution approach and the proposed staggered approach is presented to highlight the computational efficacy of the latter. © 2018 Elsevier B.V.

World University root node

Computer Methods in Applied Mechanics and Engineering

A numerical framework for modeling anisotropic dielectric elastomers

Many studies in the theory of composite materials are based on the homogenization approach, which consists of the substitution of the heterogeneous medium by a homogeneous one with certain effective properties. These effective properties are obtained from internal asymptotics which excludes boundary layer effects. However, at the boundary of the individual ply the periodic solution is disrupted. This loss of periodicity of the interior asymptotic solution needs to be accounted for. Here, the boundary layer solution is a correction in the micro solution which accounts for the applied boundary condition. This error gives rise to a sharp boundary layer which decays very quickly when it travels to the interior of the domain, leaving behind a tail which has to be added to the interior solutions to get the correct representation of the global displacement field. It is shown that this correction is significant, local and affects local stress and strain predictions, which are missed by meso or classical micro mechanical solutions. This important outcome of the study proves the theoretical estimates available in the literature (via error estimates in L2 and H1 - norms) emphasizing significant improvement in the local solution at the boundary. It is shown, through numerical examples, that the corrected solution can significantly alter damage initiation predictions at the boundary. © 2019 Elsevier Ltd

Composites Part B: Engineering

Boundary layer effect at the edge of fibrous composites using homogenization theory

International Society of Air Breathing Engines

Turbulence Model Development for Low \&amp; High Pressure Turbines Using a Machine Learning Approach

The design of low-pressure turbines (LPTs) must account for the losses generated by the unsteady interaction with the upstream blade row. The estimation of such unsteady wake-induced losses requires the accurate prediction of the incoming wake dynamics and decay. Existing linear turbulence closures (stress-strain relationships), however, do not offer an accurate prediction of the wake mixing. Therefore, machine-learnt, nonlinear turbulence closures (models) have been developed for LPT flows with unsteady inflow conditions using a zonal-based model development approach, with an aim to enhance the wake mixing prediction for unsteady Reynolds-averaged Navier-Stokes calculations. High-fidelity time-averaged and phase-lock averaged data at a realistic isentropic Reynolds number and two reduced frequencies, i.e., with discrete incoming wakes and with wake “fogging,” have been used as reference data for a machine learning algorithm based on gene expression programing to develop models. Models developed via phase-lock averaged data were able to capture the effect of certain prominent physical phenomena in LPTs such as wake-wake interactions, whereas models based on the time-averaged data could not. Correlations with the flow physics lead to a set of models that can effectively enhance the wake mixing prediction across the entire LPT domain for both cases. Based on a newly developed error metric, the developed models have reduced the a priori error over the Boussinesq approximation on average by 45%. This study thus aids blade designers in selecting the appropriate nonlinear closures capable of mimicking the physical mechanisms responsible for loss generation. Copyright © 2019 by ASME

Journal of Turbomachinery

Machine-Learnt Turbulence Closures for Low-Pressure Turbines With Unsteady Inflow Conditions

There are enormous functional materials which have been explored for gas sensing applications due to the fact that when a particular gas interacts with their surfaces, some alteration in their properties (optical, electrical, etc.) is observed. These functional materials are also termed as sensing films, to be utilized as one of the essential components in a gas sensor. Other components include electrodes connected with sensing film and data acquisition system coupled with it. During the past several decades, various metals, semiconductors, ceramics, and hybrid materials have been extensively explored for gas sensing applications. Selection of functional film is dependent on the gas to be detected. A gas sensor should have some characteristics, viz., higher sensitivity, selectivity for target gas, least response and recovery time, higher reproducibility, and stability. Therefore, selection of appropriate sensing film is highly required for a well-efficient gas sensor development. This article reviews the various kinds of sensing films, their fundamental aspects along with the sensing mechanisms. Morphological changes in the materials and doping of other functional materials also affect the performance of a gas sensor. Hence, issues related to the efficient gas sensing are also covered in this article. © 2019, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Functional Films for Gas Sensing Applications: A Review

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Journal of Nanotechnology

Carbon Nanostructures for Energy and Sensing Applications

Safe delivery of drugs inside living organism is always a great challenge. Drug intake below and above prescribed limits may cause unseen and severe health problems. In addition to the amount of dose, another critical issue is to deliver drugs inside the body. Preferable drug delivery modes are oral, inhalation, nasal, rectal routes, or via injection. Further, there are situations when a drug has to be released over a specific duration in a controlled mode. In order to have scientific solutions to the problems and challenges faced, researchers have come up with various drug delivery devices. This field has resorted to various micro-fabrication techniques and fluidic principles coupled with the assistance of electrical and mechanical engineering knowledge. It has observed a series of developments in device optimization. These devices have been developed for real-time monitoring and measurement of drug delivery and thus may have several components (micro-pump, micro-needles, microfluidic channels, micro-sensors, essential electronic circuits, and so on). Keeping up with the vast development in the field of drug delivery devices, this chapter provides an insight into the basics of various drug delivery devices, their principles, description of various components used in the micro-electro-mechanical system (MEMS) device manufacturing, along with the state-of-the-art review of existing MEMS-based drug delivery devices. © 2019 Elsevier Ltd. All rights reserved.

Bioelectronics and Medical Devices: From Materials to Devices - Fabrication, Applications and Reliability

Micro-electro-mechanical system-based drug delivery devices

The sodium acetate trihydrate is commonly used as energy storage phase change material in heating pads for body or hand warmer in cold climates. The undercooled melt of sodium acetate trihydrate kept at room temperature results in an exothermic reaction when solidification seed is nucleated. In presentwork, modeling of denritic growth in an undercooled solution of sodium acetate trihydrate has been carried out. The enthalpy method has been used to compute solid-liquid interface growing in undercooled melt. The interface temperature, concentration and grain growth have been modeled considering curvatureeffect and solutal undercooling. A 2-D computational grid of square control volumes has been used and discreatized governing equations were solved explicitly. The crystal anisotropy was imposed explicitly. The results are validated using experimental data. © The Authors, published by EDP Sciences, 2019.

E3S Web of Conferences

Modeling of dendrite growth in undercooled solution sodium acetate trihydrate

SUMMARY This paper discusses the concept and parameter design of a robust stair-climbing compliant modular robot, capable of tackling stairs with overhangs. Geometry modifications of the periphery of the wheels of our robot helped in tackling overhangs. Along with establishing a concept design, the robust design parameters are set to minimize performance variations. The Grey-based Taguchi method is applied to provide an optimal setting for the design parameters of the robot. The robot prototype is shown to have successfully scaled stairs of varying dimensions, with overhang, thus corroborating the analysis performed. © Cambridge University Press 2018.

Robotica

Design of a robust stair-climbing compliant modular robot to tackle overhang on stairs

This paper numerically studies heat transfer and fluid flow from an evaporating meniscus of a wetting fluid within a heated capillary. A simplified steady state mathematical model is developed for predicting the wicking height of the meniscus and the evaporation mass flow rate which includes: (1) one-dimensional flow and energy equations for the liquid and vapor regions, (2) one-dimensional model for the evaporating meniscus region, and (3) two-dimensional energy equation for the capillary wall. Three parameters, namely, apparent contact angle, cumulative heat transfer, and evaporating meniscus height characterize the evaporating meniscus region. In this paper, the apparent contact angle in the evaporating meniscus is uniquely deduced from the meniscus curvature at the centre of the capillary using the thickness profile obtained from standard extended meniscus theory (which includes the evaporating thin film and bulk meniscus regions). Correlations are obtained for the cumulative heat transfer, apparent contact angle and evaporating meniscus height as a function of the difference between the wall and saturation temperatures from the evaporating thin film theory for the meniscus region, which is called as micromodel. The macroscopic model accounts for wall heat conduction and heat transfer with fluid flow in the liquid and vapor regions. The micromodel deals with heat transfer and fluid flow in the evaporating meniscus region. In this paper, a novel scheme to link the “macroscopic” momentum and energy equations in the capillary slot and the evaporating meniscus through the correlations developed above is proposed. Using this numerical model, the wicking height and the evaporation mass flow rate are estimated and the results are compared with previously conducted experiments. The trends in the numerical results of the mathematical model correlate reasonably well with the experimental data. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.