Mechanical Engineering

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The present study includes the free vibration analysis of geometrically imperfect and discontinuous porous functionally graded bi-directional plate (B-FGP) resting on an elastic foundation in a thermal environment. The geometric discontinuity is present in the form of a circular cutout at the center of the plate whereas initial imperfections have been incorporated in terms of geometric as well as porosity inclusions. The kinematic formulation is based on the refined non-polynomial trigonometric higher-order shear deformation theory (HSDT). A new porosity model has been developed to incorporate the influence of the microstructure defect on the effective material properties of the B-FGP. The gradation of properties is done along the thickness (z-direction) as well as the length (x-direction) of the plate using the power-law distribution. A new expression has been given to obtain the solution of the non-linear temperature rise along the thickness of the B-FGP. A (Formula presented.) continuous Lagrangian four-noded quadrilateral element has been used to perform the finite element formulation with eight degrees of freedom per node. The equations of motion have been derived using a variational approach. The validation and comparative study have been done to authenticate the present formulation. The influence of the cutout radius, elastic foundation parameters, porosity, thermal environment, geometric imperfection, and volume fraction indexes has been discussed in detail. © 2021 Taylor & Francis Group, LLC.

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Mechanics Based Design of Structures and Machines

Vibration response of a geometrically discontinuous bi-directional functionally graded plate resting on elastic foundations in thermal environment with initial imperfections

Friction stir spot welding (FSSW) is a solid-state welding process, wherein the properties of a weld joint are influenced by the state of friction and localised thermodynamic conditions at the tool-workpiece interface. An issue well-known about FSSW joints is their lack of reliability since they abruptly delaminate at the weld-faying interface (WFI). This study explores the origins of the delamination of multiple lap welded aluminium alloy (AA 5754-H111) sheets joined by FSSW at different rotational speeds typically used in industry. Experimental techniques such as the small punch test (SPT), Vickers hardness test, Scanning Electron Microscopy (SEM), Scanning Acoustic Microscope (SAM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and Frequency-Modulated Kelvin Probe Force Microscopy (FM-KPFM) were employed. The experimental results revealed that a complex interplay of stress-assisted metallurgical transformations at the intersection of WFI and the recrystallised stir zone (RSZ) can trigger dynamic precipitation leading to the formation of Al3Mg2 intermetallic phase, while metallic oxides and nanopits remain entrapped in the WFI. These metallurgical transformations surrounded by pits, precipitates and oxides induces process instability which in turn paves way for fast fracture to become responsible for delamination. © 2021 The Authors

International Journal of Machine Tools and Manufacture

In-depth microscopic characterisation of the weld faying interface revealing stress-induced metallurgical transformations during friction stir spot welding

Here, we report a facile approach for the development of unique nanoporous MnO2-Cu architecture through a combination of severe surface deformation and dealloying. The severe surface deformation of Cu-Mn alloy prior to selective dealloying resulted in the precipitation of nanoporous MnO2 in the Cu-rich substrate. The in situ grown nanoporous MnO2-Cu architecture demonstrated an areal capacitance of 2.8 F/cm2 at a current density of 5 mA/cm2 and exhibits an excellent cyclic stability of 95% retention for 4000 cycles at 15 mA/cm2 current density. The MnO2-Cu composite structure showed small charge transport resistance of 1.9 Ω as determined using impedance spectroscopy. The asymmetric supercapacitor fabricated using nanoporous MnO2-Cu as anode and reduced graphene oxide as cathode delivers specific energy of 5.55 Wh kg−1 at a specific power of 249.75 W kg−1. The superior performance of nanoporous MnO2-Cu architecture was attributed to its unique microstructure that ensures high surface area, small internal resistance with rapid charge transport. The current approach can be applied to different material systems and is potentially transformative in the emerging field of advanced supercapacitors. © 2021 Elsevier Ltd

Journal of Energy Storage

Facile synthesis of MnO2-Cu composite electrode for high performance supercapacitor

One of the prime commodities in modern civilization is energy. The amount of energy consumption has become the indicator for the standard of living and the degree of industrialization. People use fossil fuels to meet nearly all of their energy needs, such as powering vehicles, producing electricity for light and heat and running factories, thus greatly exhausting the fossil fuel reserves along with polluting the environment with greenhouse gases. Renewable energy sources are viable alternatives, and among the various types of renewable energy sources available, wind energy is the sector which has a lot of untapped potential. Our objective is to improve the efficiency of a Savonius-type vertical-axis wind turbine (VAWT) which currently has the least efficiency among existing wind turbine designs. Savonius turbines have a very compact structure and can run at low wind speeds which are desirable characteristics for commercial-scale power production. This research paper focuses on improving the efficiency of Savonius wind turbine. Since Savonius-type wind turbines are drag-based wind turbines, we need to reduce the impulsive force acting on the negative face in order to increase the drag difference between the positive and negative side of the rotor blades thereby improving the efficiency of the turbine.&nbsp;Our proposition for attaining higher efficiency is by incorporating the concept of dimples (inspired from golf ball) on the negative side of the rotor blade and tubercles (inspired from whales) on the leading edge of the rotor blade. Dimples reduce the amount of wake region in the case of golf ball by increasing turbulence which is one of the desirable characteristics in the case of Savonius wind turbine. Tubercles help in reducing the wake region behind the rotor blades by increasing the turbulence of air near the surface of the rotor thereby improving the efficiency of the turbine. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Performance Enhancement of a Savonius Vertical Axis Wind Turbine with Bio-Inspired Design Modifications

In this paper, the reflection of acoustic waves obliquely incident onto various fluid–solid interfaces is investigated. This study aims to measure the influence of solid material properties on the acoustic attenuation magnitude, for oblique incidence at varying frequencies. A detailed comparison is documented by plotting the reflection coefficient curve for each case, while meticulously varying the porosity &amp; permeability of the poroelastic solid. Further attention is focused on identifying the shift in the pseudo-Brewster angle and the dip in the reflection coefficient minima for the aforementioned permutations in attenuation to measure its acoustic response. To enable this, the reflection and absorption of acoustic plane waves incident upon half-space and two-layer interfaces are modelled (by including viscous and thermal losses) and studied. Based on the findings, the study draws significant conclusions on the strong influence of the propagating media on the shape of the reflection coefficient curve and the relative influence of the permeability, porosity, and driving frequency on the pseudo-Brewster angle and the curve minima. © 2020

Applied Acoustics

Reflection of oblique incident acoustic waves at various fluid–solid interface for varying material properties

Slurry erosion–corrosion is a severe issue for many engineering components used in marine, petrochemical, and agricultural sectors. The deleterious effects of the slurry erosion–corrosion significantly lower the service life and enhance the maintenance cost. For limiting the slurry erosion–corrosion effects, there is a need for high-performance advanced materials. In the present work, equimolar MoNbTaTiZr high-entropy alloy (HEA) was developed, and its slurry erosion–corrosion behavior was investigated. For comparison, conventionally used stainless steel SS316L was also investigated. The detailed microstructural characterization showed the presence of a two-phase bcc crystal structure in the HEA. The major bcc phase was predominantly composed of Ta, Mo, and Nb with the interdendritic region being rich in Ti and Zr. The MoNbTaTiZr HEA showed 2 times higher hardness than the SS316L steel. Under slurry erosion–corrosion condition, the HEA showed 3.5 times higher resistance while under erosive conditions, two times better performance than the reference material. The analysis of the eroded surface morphology showed the presence of a mixed ductile–brittle erosion response for the HEA. The improved performance of the HEA is predominantly related to the high hardness and extremely high corrosion resistance. Electrochemical corrosion testing revealed that the HEA has 80 times lower current density than SS316L and high pitting resistance, resulting in low corrosion rates. The electrochemical impedance spectroscopy (EIS) findings showed a denser and highly stable passive layer. The results indicated that MoNbTaTiZr HEA could be effectively used for countering the slurry erosion–corrosion and corrosive conditions. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.

Journal of Bio- and Tribo-Corrosion

Slurry Erosion–Corrosion Resistance of MoNbTaTiZr High Entropy Alloy

There has been a significant disruption in the energy market because of the pandemic. Now the focus is shifting towards investing more in renewable energy to address the present health and energy crisis. Wind power has gained special prominence in our clean energy transition as wind energy is the easiest to harvest, most efficient resources, and lowest carbon emitter among the available technologies. The prime focus of this study is towards implementing an array configuration of Savonius turbines beside the train track to maximize the power production. A model is set up on OpenFOAM platform and studied for the different arrangements of turbine clusters. The effect of energy production by the series of turbines was assessed by varying distance among turbines in a staggered or inline manner and the location from the train as well. A systematic characterization of the optimum Savonius turbine cluster in a railway tunnel, which is relatively an unexplored area in the energy harvesting community, has been taken up in this study. It is exciting to note that our computer-oriented result matches well with the benchmark solution and proved to be a viable green energy resource that can possibly erase the energy crisis at remote places. © 2021 Elsevier Ltd

Renewable Energy

An OpenFOAM based study of Savonius turbine arrays in tunnels for power maximisation

A novel concept of rotating circular ribs as artificial roughness has been employed within a two-dimensional rectangular duct to understand their effects on heat transfer and air flow characteristics using CFD. The effects of design parameters such as roughness height, roughness pitch, relative roughness height, relative roughness pitch, and rotational speed of the circular rib are simulated for Reynolds number ranging from 3800 to 18,000 under solar air heater boundary conditions. 54% increase in Nusselt number is observed for rib height of 1.4 mm, pitch of 10 mm, circular rib rotation of 10000 rpm at Re = 3800 as compared with fixed ribs. The maximum thermo-hydraulic performance factor of 1.57 is achieved at Reynolds number of 3800 for the circular ribs—relative roughness height of 0.042 and relative roughness pitch of 25— rotating counter to flow with 10000 rpm. For a given rotational speed of the circular ribs, thermo-hydraulic performance factor decreases at higher flow velocities. Significant increase in Nusselt number with rotating ribs as artificial roughness establishes the potential of this novel approach for solar air heaters. © 2021 Elsevier Ltd

Sustainable Energy Technologies and Assessments

Thermal performance evaluation of a solar air heater with rotating turbulators

Linear vibratory feeders and vibratory bowl feeders are widely used as part feeders in mass production industries. Making the helical track of the bowl feeder requires special tooling. This makes it expensive to adapt to product changes. Linear feeders are simpler in construction and relatively flexible enough to accommodate a variety of products. This paper provides an alternate design to vibratory bowl feeders. A balanced feeder experimental setup with wiper blades was developed and optimized to maximize the conveying velocity with no part clogging. © 2021 Author(s).

AIP Conference Proceedings

Balanced feeder design: An alternative to vibratory bowl feeders

The motion of a part on a curved surface mounted upon a linear vibratory feeder is of great importance in mass production. In this article, the conveying surface or track is modelled by a bilinear surface inclined to all axes with the curvature varying throughout the surface. An experimental test rig is fabricated to study the part motion on the feeder surface. Dynamics of the part on the surface is derived and the path traced by the part is obtained numerically. The numeric model closely correlates with experimental results. Based on the control parameters two distinct regimes—slide and hop—are presented, highlighting their relation to frequency and amplitude of vibration of the feeder. © IMechE 2021.