Mechanical Engineering

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In the present paper, a refined trigonometric higher-order shear deformation theory has been presented with the conjunction of nonlocal theory for the vibrational response of functionally graded (FG) porous nanoplate. The displacement field is chosen based on assumptions that the out of the plane displacement consists of bending and shear components whereas the transverse shear-strain has nonlinear variation along the thickness direction. The number of unknown variables is four, as against five in other renowned shear deformation theories. The governing equations have been derived using Hamilton's principle. A generalized porosity model has also been developed to accommodate both even and uneven type of distribution of porosity in the FG nanoplates. The closed-form solution of simply-supported FG porous nanoplates is obtained and the results are compared with the available reported results. In finite element solution, a C0 continuous isoparametric quadrilateral element has been used with various conventional and unconventional boundary conditions. The effects of various parameters like small-scale effect, aspect ratio, volume fraction index, porosity volume fraction, and thickness ratio have been investigated. The significant influence of small-scale effects and porosity inclusions have been observed in the reported results. It has been reported that both closed-form and finite element solutions with the present theory can make accurate predictions of the free vibration response. © 2021 Techno-Press, Ltd. All Rights Reserved.

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(SoE) School of Engineering

Advances in Nano Research

Size-dependent vibration response of porous graded nanostructure with FEM and nonlocal continuum model

In the present work, environment friendly non-fluorinated superhydrophobic composite coatings were developed using naturally available carnauba wax from palm tree, Copernicia prunifera. The hierarchically structured coating morphologies were composed of micro-scale protrusions along with submicroscopic pores (non-composite) and protrusion (composite). The hierarchically structured carnauba wax coatings showed extreme de-wetting with superhydrophobicity (θ > 150°) and low hysteresis (<5°). In contrast, the other mineral and animal waxes showed mild hydrophobic behavior with high hysteresis (>10°) owing to flat morphology. These peculiarities in morphology and hence de-wetting properties are related with the viscosity differences. Further, the composite wax coating also showed high resilience to simulated rain and weathering due to high roughness and mechanical strength. The composite wax showed high ultimate strength (14 MPa) and elastic modulus (427 MPa) than the non-reinforced wax (8.8 MPa and 97 MPa, respectively). The results showed that composite carnauba wax coatings provide an effective and environment friendly solution for developing superhydrophobic self-cleaning surfaces. © 2021 Elsevier B.V.

Industrial Crops and Products

Development of natural wax based durable superhydrophobic coatings

Group maintenance deals with performing preventive maintenance (PM) on other components when the system stops due to induced failure or scheduled PM interval of a particular component. Group maintenance actions save downtime costs and other production losses. However, simultaneous maintenance of all units is not always economically beneficial. As a consequence, the decision to which group of components is maintained is very selective due to economic and stochastic interdependencies. In the present paper, we propose a novel and efficient group maintenance model in the multi-unit series system for grouping under PM intervals. The objective is to obtain an optimum group of components and PM intervals which minimizes the expected total maintenance cost of the system per unit time. A recently developed meta-heuristic named teaching–learning-based optimization (TLBO) algorithm is applied to optimize the objective function. The peculiarity of TLBO is that unlike other evolutionary-based heuristics it is a parameterless algorithm which makes it computationally easy to understand and implement. Computational results yield the effectiveness of the proposed approach when compared with traditional maintenance practices. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Group Preventive Maintenance Model for Multi-unit Series System: A TLBO Algorithm-Based Approach

Owing to their rapid charge-discharge, extremely low maintenance, high power density, versatile operating temperatures and durability, supercapacitors are widely used as electrochemical storage devices in advanced energy applications. In recent years, transition metal oxides, especially nano-textured CuO structures have gained much attention as a low cost and widely available electrode material for supercapacitors. However, the existing techniques for developing nano-textured CuO involve a large number of processing steps through multiple chemical treatments. Further, the performance of nano-structured copper oxides needs to be significantly enhanced to make them commercially viable. Here, we report a facile, two step approach comprising surface activation through thermomechanical treatment and electrochemical dealloying of a Cu-Zn alloy for developing a 3-dimensional hierarchical CuO microstructure. Surface activation prior to dealloying significantly accelerates the reaction kinetics and the hierarchical microstructure comprising micro and nano-scale porosity develops in a few seconds only. Electrochemical studies revealed that the surface activated electrode possesses a high areal capacitance of 1.68 F cm−2at a current density of 5 mA cm−2, exhibits an excellent cycling stability with 90% retention for 5000 cycles at a current density of 15 mA cm−2and a high energy density of 0.33 mW h cm−2. The reported specific capacitance is one of the highest values obtained for copper-based alloys which is attributed to its unique 3D hierarchical microstructure that favours rapid ion intercalation and the increased surface area for energy storage. Electrochemical analysis indicates intercalation pseudo-capacitance as the primary charge storage mechanism. The current approach is highly generic and can be applied for a wide number of material systems which signifies its huge potential in the emerging field of advanced supercapacitors, and portable and flexible electronics. © The Royal Society of Chemistry 2021.

Journal of Materials Chemistry A

High performance CuO@brass supercapacitor electrodes through surface activation

Coupling nonlinear dynamical systems can lead to a host of phenomena, one of which leads to the complete cessation of their oscillations. This phenomenon is referred to as amplitude death (AD) in the dynamical systems literature. Recently, there is a growing interest to mitigate oscillatory or dynamic instabilities in a variety of engineering systems using AD. Deriving impetus from the same, we investigate the possibility of cessation of oscillatory instabilities in aeroelastic systems using the concept of AD. In specific, the suppression of flutter instability that arises in aeroelastic systems due to highly nonlinear fluid–structure interactions is investigated from the purview of AD. To that end, we consider two identical airfoils that are exposed to input fluid forces along the axial directions. The airfoils, via translational and rotational springs, are allowed to oscillate in plunge and pitch degrees of freedom. To augment the findings to in-field scenarios, we consider the individual cases of the input flow to be either uniform (deterministic) or possess randomly time varying components, respectively. To promote coupled interactions, the airfoils are coupled using a linear torsional spring. The coupled interaction of the airfoils at the flutter regime are then studied by obtaining the pitch and plunge responses. Further, the strength of the coupling and the time delay between the airfoils are systematically varied to investigate its effect on the regime of AD. The ability of AD to suppress flutter instability and thereby serve as a possible flutter suppression mechanism in both deterministic and stochastic input flow cases is then demonstrated. Finally, the phase delay values between the airfoils is computed to heuristically present a relationship between the coupling parameters and the post coupling signatures. © 2020 Elsevier Ltd

International Journal of Non-Linear Mechanics

Investigating amplitude death in a coupled nonlinear aeroelastic system

The paper deals with Nonlinear Energy Sinks (NES), utilizing piezoelectric transduction mechanism, focusing on the degree of effect the auxiliary nonlinear stiffness has on the performance of the NES and the performance of NES with the primary system subjected to random excitation. Hence, a parametric sweep of the auxiliary nonlinear stiffness over a broad range of values has been done and the variations in primary vibration suppression and voltage generation by the NES have been observed for its corresponding values. It has been conducted with the NES attached to a linear primary system and then an essentially nonlinear one. Comparison of results and validation of the performance of NES for both the cases have been performed. Following that, performance of the NES has been investigated when a linear primary system is subjected to random excitation. Two separate cases have been utilized to randomize the excitation. Results regarding vibration control and voltage generated have been derived for both and compared to those obtained for deterministic excitation. By and large, it is found that NES is successful in protecting a primary system and broadening the operation bandwidth, while satisfyingly generating voltage, irrespective of the type of excitation on the primary system. © 2021, Springer Nature Singapore Pte Ltd.

Investigations into Nonlinear Energy Sinks for a Stochastic Dynamical Oscillator

To solve the increasing power demand of the growing population without increasing carbon footprint, energy efficiency for renewable sources needs to be improved. This paper focuses on the performance improvement of Savonius vertical axis wind turbine, commonly utilized to harness low wind speed potentials. Such turbines can find excellent use in places where the wind speed is not sufficient for introducing traditional horizontal axis wind turbines. To develop a better aerodynamic design that can reduce drag, dimples introduced on the blade profile. The effect of endplate also studied for improving the performance of the turbine. The design and comparative analysis performed with an endplate and dimpled blade profile. Computational fluid dynamics simulations carried out for understanding the performance of the turbine with dimples and endplates when subjected to low incoming wind velocity. Comparative analysis performed between the proposed design with the baseline design, i.e. with endplates, without endplates and with dimples on blades to show how it affects the efficiency of the turbine. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021.

Numerical analysis of savonius vertical axis wind turbine with dimpled blades

In this study, the authors fabricated a hierarchically structured aluminum surface through facile hot-water treatment and abrasive machining. The developed surfaces were composed of nanoflakes exhibiting extreme wetting states, superhydrophilicity (θ s less than 5°) and superhydrophobicity (θ s greater than 150°) following salinization. The engendered surface morphologies composed of different length scales showed a significant influence on the wetting and durability characteristics. The stability of the observed Cassie state showed a direct correlation with the geometric parameters, particularly the interspatial distance. The critical surface tension for the transition from the Cassie to the Wenzel state increased with the interspatial distance. The surfaces structured with a smaller interspatial distance also exhibited high wetting resilience under dynamic conditions involving single-droplet impacts corresponding to We = 585 owing to a high negative capillary pressure. Further, the fine-structured hierarchical surfaces also exhibited appreciable antifogging and anticorrosion characteristics. Under simulated rain testing, the fine-structured hierarchical surfaces showed better durability than the coarser counterpart, enduring low contact angle hysteresis (CAH) (<10°) even after multiple cycles. Further, weathering tests performed on these samples showed an insignificant influence on their de-wettability. The present study highlights the fabrication of durable metallic surfaces through facile and sustainable fabrication method for multifunctional applications. © 2022 ICE Publishing: All rights reserved.

Surface Innovations

Facile approach for modulating wetting of hierarchically structured metallic surface

Thermal spraying is a scalable surface engineering technique used to add or to restore functionality of a solid surface by applying a coating. Examples of this include protection against wear, erosion, abrasion, and heat. In a specific sense, thermal spraying is particularly used to deposit thermal barrier coatings (TBCs) which finds use in transportation, power generation and automotive sector. As being a surface technique, thermal spraying much like other surface coating techniques can avoid the use of excessive bulk materials and in turn offers longevity to the life of the component, so it already contributes to the reduction of global warming by virtue of avoiding the use of excessive scarce materials and improving fuel efficiency. In terms of its contribution to the cause of global warming, thermal spraying stands in sharp contrast to the energy-intensive processes such as melting, casting, extrusion and welding. With the rise of additive manufacturing, it is possible to use thermal spray to complement that process in many ways and “cold spray additive manufacturing” (CSAM) is already gaining popularity. The thermal spraying technique relies on using selective types of gases—hydrogen being one of them and few types of metals/alloys which are now classed as critical raw materials due to them being on the supply risk register. Efforts to consider recycling and reuse and to find alternatives to these are very timely to continue drawing the advantage of thermal spraying being a relatively green technique. In particular, the green energy initiatives and the drive to develop energy storage and battery technologies could challenge the supply of raw materials such as hydrogen gas and rare earth elements. This underlines the research and development need for alternate materials and processes to address the issue of climate change which is the major focal point of the COP 26 Summit at Glasgow in 2021. The combination of digital technologies and thermal spray coatings will reduce gas, powder and power consumption, which will make this manufacturing process even greener. © 2021, The Author(s).

Fulltext

Emergent Materials

Role of thermal spray in combating climate change

Thermal analysis of Silicon Carbide (SiC) power semiconductor packages is a crucial design step to ensure highly reliable device performance at elevated temperatures. The square-root-t extrapolation method is widely adopted to approximate the temperature development within the SiC die for short time transients when device temperature measurements cannot be performed. The reduced thermal resistance of the SiC die leads to smaller thermal time constants. Therefore, the approximation of the heat propagation in SiC devices also has to include the die attach. This paper analyzes the thermal behavior of SiC power semiconductor packages by means of comprehensive FEM simulations, allowing to more precisely determine the error of the temperature estimation based on the square-root-t approximation for SiC power devices. © 2021 IEEE.