Department of Mechanical Engineering

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In present research work, multi-pass friction stir processing was utilized for the as-cast Al–17%Si alloy. The multi-pass friction stir processing reproduced the aluminum (Al) matrix with a uniform distribution of the ultra-fine silicon (Si) particles. The multi-pass friction stir processing also resulted in the formation of refining cast microstructure with negligible porosity. The significant reduction in silicon particle size was measured and it reduced from 204 µm to 0.86 µm after the first pass and up to 0.30 µm after two pass friction stir processing. The frequency of fine Si particles was increased after two pass friction stir processing as compared to single pass friction stir processing. The engineering stress–strain curves revealed a significant enhancement in ductility and strength after one and two passes of friction stir processing as compared to the as-cast alloy. After one and two passes of friction stir processing, the ultimate tensile strength of as-cast alloy was enhanced by 24% and 31% and ductility was increased by 300% and 500%, respectively. The secondary electron micrograph of fracture surfaces of tensile specimens was taken before and after friction stir processing. The fractographs revealed the transformation from brittle mode to ductile dimples fracture after the multi-pass friction stir processing process. © IMechE 2017.

World University root node

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Ductilizing of cast hypereutectic Al–17%Si alloy by friction stir processing

Interior noise in vibro-acoustic cavities may be generated due to acoustic and structural disturbances. Earlier studies have shown that for global control, the maximum reduction in acoustic potential energy can be realised by using an optimum combination of acoustic and structural actuators. However, it is observed that this reduction in interior noise may also be accompanied with an increase in kinetic energy of the cavity structure. This paper presents the development of a feedforward technique for active noise control in vibro-acoustic cavities ensuring that the noise reduction does not lead to an increase in kinetic energy. The problem is formulated as a constrained minimisation problem to minimise the acoustic potential energy subject to a constraint that the kinetic energy does not increase. Through a numerical study, it is shown that the optimum solution of the above problem indeed is favourable in terms of reduction in acoustic potential energy in the cavity and kinetic energy of the structure. The paper further proposes a method for solution of this constrained minimisation problem using a penalty function method and solution of sequential unconstrained problems. The proposed method is validated through a numerical study on a car-like cavity for single- and multi-tonal noise. © 2018 Acoustical Society of America.

Journal of the Acoustical Society of America

Global feedforward active noise control in vibro-acoustic cavities without increasing structural vibrations

This paper proposes an algorithm called as ‘Modal filtered-x LMS algorithm’ for global active noise control in vibro-acoustic cavities. The proposed algorithm is a formulation of the conventional filtered-x least mean square algorithm in modal domain to reduce acoustic potential energy in a cavity. The formulation leads to a concept of what has been called as ‘modal secondary path’ in the paper. The active control method makes use of the reference signal filtered using modal secondary paths instead of the reference signal filtered using physical secondary paths as done in the conventional FxLMS algorithm. The method requires knowledge of acoustic modal pressures which in the present paper are estimated using acoustic pressure measurements at a discrete number of points in the cavity. The proposed method allows a modal based control of acoustic potential energy in the cavity. The proposed method also has an advantage that it reduces the computational burden associated with filtering of the reference signal with secondary paths for global control. A numerical study to actively control noise due to structural and acoustic disturbances acting on a car-like cavity is presented. Results of modal based control are compared with maximum reduction that is possible for given disturbances and control sources. It is found that the noise reduction obtained using the modal based approach is close to the maximum possible but at a lower computational cost. © 2018 Elsevier Ltd

Mechanical Systems and Signal Processing

Modal filtered-x LMS algorithm for global active noise control in a vibro-acoustic cavity

The d2 law, commonly used to assess the accuracy of computational solvers, corresponds to evaporation under steady-state conditions and in an infinite gaseous domain. In the present work, we propose new alternative benchmarks that relax those constraints. The benchmarks are developed for a spherical as well as a circular drop. First, steady-state analytical relations are derived that are applicable to a finite domain. A radially-symmetric transient model is then proposed that can provide transient benchmark solutions in finite domains. Adaptive mesh-refinement and body-fitted mesh are used for numerical solution and to ensure highly accurate transient results. The proposed steady-state and transient benchmarks are examined in several evaporation problems, and the evolution of drop diameter, temperature and vapor mass fraction fields are analyzed. In one such problem, we report a secondary transient phenomenon that appears towards the end of drop lifetime. The benchmarks proposed in this work are straightforward to be implemented for systematic validation of computational solvers. © 2018 Elsevier Ltd

International Journal of Heat and Mass Transfer

Steady-state and transient solutions to drop evaporation in a finite domain: Alternative benchmarks to the d2 law

Indo-Korea joint network centre on robotics, Daejeon, Korea

Indian side of Indo-Korea Joint Network Centre on Robotics

The PCM based heat source and heat sink devices can be effectively used for various heating and cooling applications and can store and release heat in the form of latent heat. This latent heat can be utilized for maintaining body temperature within comfort range of 33 ± 2°C. The present work focuses on developing a 2-D numerical model to evaluate the performance of PCM cool pack configuration in terms of the evolution of average skin temperature with respect to time. The numerical model is first validated with a 1-D semi-analytical for a simple PCM pack configuration. Once the model is validated, the next level of studies involves the comparison of performance analysis for different PCMs with more realistic cooling pack configuration. Optimal thermal conductivity (which can be engineered by introducing PCM-Graphite composites) is also predicted for different PCMs in order to obtain thermal comfort for a prolonged duration of 3 hrs. The studies do not include the perspiration model; however, incorporation of the skin layer within the model domain took the approach closer to the real condition. © 2018 by the authors of the abstracts.

International Conference on Computational Methods for Thermal Problems

Performance evaluation of latent heat based cool pack configuration for thermal comfort: A numerical approach

Inspired by the flexible wings and fins of flying and swimming animals, we investigate the flow induced by the interaction between a flapping flexible surface and the surrounding fluid for the limiting case of Strouhal number St ? 8 (zero free-stream speed). The model selected for this purpose is a two-dimensional sinusoidally pitching rigid symmetric foil to which is attached at the trailing edge a thin chordwise flexible surface (along the chord line). The flow so generated is a coherent jet aligned along the foil centreline, containing a reverse Bénard–Kármán vortex street and delivering a corresponding unidirectional thrust. We analyse the flow and thrust generation process. The measured velocity field suggests that the flow and thrust generation mainly occurs during the phases when the trailing edge is near the centreline. Flexibility of the surface is important in accelerating the near-wake flow and in transferring momentum and energy to the fluid. We present a detailed account of when and where the momentum and energy are added to the fluid. This study shows that the deformations of the flexible surface are responsible for generating a favourable pressure gradient along the jet direction, and for the observed unsteady actuator disc-type action. © 2018 The Author(s) Published by the Royal Society. All rights reserved.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

Physics of unsteady thrust and flow generation by a flexible surface flapping in the absence of a free stream

SiO2-Al2O3-B2O3-Na2O based glass sealant compositions were designed for the development of GMJ using extreme vertices methodology. The effect of the glass sealant individual constituent on wettability, Glass transition temperature (Tg), Crystallization temperature (Tc), thermal conductivity, and density was analyzed with the help of analysis of variance technique (ANOVA). The increase in SiO2 constituent in glass sealant decreased the spreading area (mm2) of glass sealant and increased the value of contact angle (θ) formed by glass sealant over the SS304 metal substrate. The Tg and Tc of glass sealant also increased as SiO2 content increased. The addition of B2O3 and Na2O in glass sealant system reduced the Tg and Tc of glass sealant. The developed regression model was validated and it was observed that the experimental and predicted results nearly matched with an error less than 5% in most of the cases. © 2018 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Design and development of SiO2-Al2O3-B2O3-Na2O based glass sealant for the glass-metal joint

The use of bimetallic weld joints is widespread in thermal and nuclear energy generation. It is evident from literature survey that the weld and ferritic steel HAZ region of bimetallic joints are prone to failures. The failures can be attributed to the generation of residual stresses in bimetallic welds. A typical bimetallic weld joint, representing a joint being tested for use in Indian Nuclear Reactors was fabricated between SA 516 Grade 65 and 304 austenitic stainless steel with and without the use of SS 309 L buttering layer. The buttering layer thickness was varied and surface and subsurface residual stresses were assessed using the hole drilling technique and neutron diffraction measurements. It was found that the SS 309 L buttering layer with thickness of around 6 mm employed in the bimetallic weld joint reduces the surface and sub-surface residual stresses in the critical region (ferritic steel HAZ) of the bimetallic weld joint. Copyright © 2018 ASME.

ASME 2018 13th International Manufacturing Science and Engineering Conference, MSEC 2018

Residual stresses in bimetallic weld joint with varying buttering layer thickness

This paper presents the high-temperature wettability studies carried out during glass-metal joining for parabolic trough solar receiver tube. The bonding characteristics of the glass and metal directly depend upon the wettablity measured in terms of (contact angle) the types of oxide formed at the metal surface and the microstructural changes during the fabrication process. In this research work three different substrate materials, namely, Austenitic Stainless Steel SS304, copper and low carbon steel (AISI 1018) were polished against different grades of emery paper in order to generate variations in their surface roughness. Borosilicate glass pallet was melted over these specimens and high-temperature wettablity (contact angle) of glass over candidate material substrate specimen was examined. X-ray diffraction was used to detect the types of oxide formed on the substrate during the wetability study. Microstructural and macroscopic examination of the substrates revealed the morphological changes on substrate surfaces at different length scales. The wettablity of borosilicate glass over Austenitic Stainless steel SS 304 substrate was better as compared to copper and low carbon steel substrates. In the case of low carbon steel, metal specimen got distorted at joining temperature because of poor thermal stability of low carbon steel and no bonding was observed. © 2017 Elsevier Ltd