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      Volume 44, Issue 8

      August 2019

    • Pre-stretch and frequency variation effect on the dielectric permittivity of a dielectric elastomer: an amended permittivity model


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      In the present letter, we model the pre-stretch and frequency parameter effect on the dielectric permittivity of a dielectric elastomer. The present work is the extension of our most recent work (Kumar and Sarangi in Mech Mater 128:1–10, 2019) in case of deformable smart material. In particular, pre-stretching aswell as frequency parameter variables majorly affect the deformation mechanism of a dielectric elastomeric material. In line with this, we first develop a new amended permittivity model of a dielectric elastomeric material based on the fundamental laws of physics. This amended permittivity model successfully enrols the prestretch and frequency parameter effect on the dielectric permittivity of a dielectric elastomer. Additionally, the amended permittivity model also successfully resolves the existing numerical inaccuracies of the previously known permittivity models in large deformations. Next, the formulated amended permittivity model is calibrated with some available experimental data, and compared to a known permittivity model existing in the literature.

    • Optimal Assembly Sequence generation through computational approach


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      Optimal assembly sequence (OAS) is always an interesting aspect for an industrial engineer to minimize assembly time and cost, which gives number of assembly levels and sequence of assembly operations. An assembly sequence with more number of parallel possible stable sub-assemblies significantly reduces theoverall assembly time for large scale products. Finding such optimal sequences from huge set of all assembly sequences (SAAS) is challenging due to involvement of multiple assembly feasibility validation criteria namely; assembly coherence, geometric feasibility, part stability and mechanical feasibility. In this paper, an efficient computational method is proposed to generate optimal assembly sequences. The method considers extended assembly stability relations to identify stable sub-assemblies for parallel execution. The method is proven ingenerating optimal solutions for any given product effectively. The method is well discussed and compared with prominent computational methods with suitable product illustrations.

    • Thermal-diffusion and diffusion-thermo effects on squeezing flow of unsteady magneto-hydrodynamic Casson fluid between two parallel plates with thermal radiation


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      Present numerical study examines the heat and mass transfer characteristics of unsteady magnetohydrodynamic squeezing flow of Casson fluid between two parallel plates with viscous and Joule dissipation effects in the presence of chemical reaction. The influence of Soret and Dufour parameters on squeezing flow is investigated along with thermal radiation and heat source/sink effects. The heat and mass transfer behaviour of squeezing flow is analysed by considering the rheological Casson fluid model. The present physical problem is governed by the set of nonlinear coupled time-dependent partial differential equations (PDEs). The method of similarity transformation approach is used to reduce the system of PDEs to a system of nonlinear ordinary differential equations (ODEs). Further, the Runge–Kutta fourth order integration scheme with shooting method(RK-SM) is used to solve the reduced ODEs. Numerical computations are performed for different sets of control parameters. The non-Newtonian flow behaviour of Casson fluid is presented in terms of graphs and tables. It isremarked that the temperature field is enhanced for increasing values of Hartmann number. Also, increasing Casson fluid parameter increases the velocity field. Concentration field is diminished for enhancing values of Soret parameter. Finally, the comparison between present similarity solutions and previously published results shows the accuracy of the current results.

    • Performance evaluation of sorption compressor based J-T refrigerator using R134a and mixture refrigerants as working fluids


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      The idea of adsorption based refrigerator was conceived in the year 1961 by Vickers. The present work reports development of a sorption compressor based J-T refrigerator with R134a alone as a working fluid and a three component mixture of R134a, Ethane and Methane. Commercially available activated carbon,obtained from coconut shell, is used as an adsorbent. The reported compressor is a four cell structure and uses isenthalpic expansion of R134a for cooling purpose. A lowest temperature of -8°C is obtained giving 5 W of refrigeration effect for R134a. The work is further extended to study the effect of various parameters likeadsorption-desorption cycle time, heater power input and capillary tube length on the low temperature obtained from the refrigerator. Experiments are then carried out using a three component mixed refrigerant, a low temperature of -54°C at no load is achieved. Also a continuous trouble-free operation is observed.

    • An EPQ model for three-layer supply chain with partial backordering and disruption: Triangular dense fuzzy lock set approach


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      This article deals with three-echelon supply chain (SC) network involving flow of raw materials with imperfect quality, the manufacturer and multiple retailers under the effect of learning experiences in fuzzy decision-making process. Existing literature explores the SC model under full backordering and disruption.Thus, in this study we first develop a production-inventory control problem accompanied with partial backlogging and random disruptions. Any batch received from the supplier is inspected by the manufacturer and if any of them are found to be flawed then all the goods in the inspected batch are rejected. However, we present a case study for problem definition and to comprehend the model into practical applicability. To minimize the aggregate cost of the SC we have utilized the Triangular dense fuzzy lock set for controlling the cost vector of the proposed objective function of the model. Utilizing new defuzzification method and applying the proper keys, chosen by the decision maker, it is possible to minimize the average system cost exclusively. Finally, graphical illustrations and sensitivity analysis are made to justify the model.

    • An approach based on classifier combination for online handwritten text and non-text classification in Devanagari script


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      In this article, a method of analysing features of elliptical regions and combining outcomes of classifiers using Dempster–Shafer Theory (DST) is presented to classify online handwritten text and non-text data of any online handwritten document in the most popular Indic script—Devanagari. Although a few worksexist in this regard in different non-Indic scripts, to our knowledge, no study is available to classify handwritten text and non-text document in online mode in any Indic script. The present method uses various structural and directional features analysed in elliptical regions to extract feature values from strokes of text and non-text data. The features are then studied separately in classification platforms based on Support Vector Machine (SVM) and Hidden Markov Model (HMM). The probabilistic outcomes of these two classification platforms are then combined using DST to improve the system performance. The efficiency of the present system has been measured on a self-generated dataset and it provides promising result.

    • The effects of carbon nanotubes added polyvinyl alcohol nanofibers on mechanical properties of carbon reinforced composite laminates


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      This study investigates tensile and flexural behaviors of carbon fiber reinforced epoxy (CFRE) composite laminates strengthened in different weights multi walled carbon nanotubes (MWCNT) with/without polyvinyl alcohol (PVA) nanofiber mats. First, PVA nanofiber mats modified with 1, 3, 5 wt% MWCNT were produced by electro spinning. Characterization of 1, 3 and 5 MWCNT reinforced/unreinforced PVA nanofiber mats was achieved via transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Then, the produced nanofiber mats were placed in the middle of eight-layer twill carbon fabrics by hand layupafter carbon composites were produced by vacuum infusion. Three flexural tests were performed in accordance with ASTM D 7264/D standard so that flexural strength properties of the composites and flexural modulus of elasticity can be found. After that, tensile test was carried out in accordance with ASTM D 3039 for the composites to have single axis tensile strength and modulus of elasticity nanofibers. The tensile strengths of PVA nanofiber mats and 1 wt% MWCNT/PVA nanofiber mats reinforced CFRE composites increased by 4% and 34%, respectively when compared to the CFRE composite.

    • Analysis of sum spectrum efficiency in multiple antennas multi-user MIMO cellular system for millimeter wave communications


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      In this paper, sum spectrum efficiency of two cell multiple-input multiple-output (MIMO) system having multiple antennas at base station (BS) and multiple user equipments (UEs) is analysed. The maximum ratio (MR) and multi-cell minimum mean squared error (M-MMSE) techniques are utilized for detection/precoding in the uplink/downlink scenario. In this paper, two boundary cases of propagation channel model: line of sight (LoS) and non-line of sight (NLoS), and generalized propagation channel model of millimeter wave (mmWave) are compared using MR and MMSE detection techniques. The closed bound expressions of sum spectrum efficiency of MR are expressed and simulated, whereas for M-MMSE, Monte-Carlo simulations are performed on the basis of its weighting vector. The fundamental limits on the system performance, using largeantenna arrays and many UEs satisfying practical constraints like desired signal to noise ratio (SNR), low complexity in signal processing, gain of inter cell interference and finite-dimensional channels are analysed.

    • A novel approach to word sense disambiguation in Bengali language using supervised methodology


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      An attempt is made in this paper to report how a supervised methodology has been adopted for the task of Word Sense Disambiguation (WSD) in Bengali with necessary modifications. At the initial stage, four commonly used supervised methods, Decision Tree (DT), Support Vector Machine (SVM), Artificial NeuralNetwork (ANN) and Naı¨ve Bayes (NB), are developed at the baseline. These algorithms are applied individually on a data set of 13 most frequently used Bengali ambiguous words. On experimental basis, the baseline strategyis modified with two extensions: (a) inclusion of lemmatization process into the system and (b) bootstrapping of the operational process. As a result, the levels of accuracy of the baseline methods are slightly improved, which is a positive signal for the whole process of disambiguation as it opens scope for further modification of the existing method for better result. In this experiment, the data sets are prepared from the Bengali corpus, developed in the Technology Development for Indian Languages (TDIL) project of the Government of India andfrom the Bengali WordNet, which is developed at the Indian Statistical Institute, Kolkata. The paper reports the challenges and pitfalls of the work that have been closely observed during the experiment.

    • Modified fuzzy c-mean for custom-sized clusters


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      Fuzzy c-mean (FCM) is one of the widely used data clustering methods. FCM method not only divides a data set into several clusters but also determines the potential belongingness of each data in different clusters. The size of clusters generated by FCM cannot be controlled by the inherent mechanism. However,sometimes real life situations demand that the clusters should have some pre-specified size. In this study, the FCM method is further extended to obtain clusters with specified size. In the first step of the proposed method, FCM algorithm is executed; later the potential belongingness matrix passes through an optimization model to yield clusters with specified sizes. In the proposed technique, the centres of the clusters obtained from FCM are considered but the boundary elements are redistributed to achieve equal or custom-sized clusters. The methodology has been explained further with examples.

    • An efficient approach based on selective partitioning for maximal frequent itemsets mining


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      We present a maximal frequent itemset (MFI) mining algorithm based on selective partitioning called SelPMiner. It makes use of a novel data format named Itemset-count tree—a compact and optimized representation in the form of partition that reduces memory requirement. It also does selective partitioning of the database, which reduces runtime to scan database. As the algorithm progressively searches for longer frequent itemsets in a depth-first manner, it creates new partitions with even smaller sizes having less dimensions and unique data instances, which results in faster support counting. SelPMiner uses a number of optimizations toprune the search space. We also prove upper bounds on the amount of memory consumed by these partitions. Experimental comparisons of the SelPMiner algorithm with popular existing fastest MFI mining algorithms on different types of datasets show significant speedup in computation time for many cases. SelPMiner works especially well when the minimum support is low and consumes less memory.

    • Impact of pile foundations adjacent to tunnels in sandy stratum


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      In recent years, with rapid urbanization and construction of underground pipeline facilities for the transmission of electricity, supply of water, sewage disposal or provision of facilities like telephone lines, gas pipe lines, etc., it is highly probable to encounter an existing pipeline system in the vicinity of a proposed foundation of a structure. Hence, design and construction of new foundation structure near the existing subsurface pipeline system is imperative and should be addressed for keeping either a minimum safe clearance between tunnel/buried pipe and pile without compromising the capacity of pile or estimating the reducedcapacity due to existing nearby pipeline or tunnel, which is an important aspect in the analysis and design of pile foundation. Present study demonstrates a model and numerical study of the behaviour of a single pile in the vicinity of existing tunnel/buried pipe in a cohesionless soil. During experimental work, a small scale pile model was tested for its load–settlement behaviour without and with the existence of buried PVC pipe modelled as a tunnel in the vicinity near the shaft. The complete experimental set-up consisted of a steel box filled with sand attwo different relative density values and vertical concentric load was applied on the model pile through a hydraulic jack and reaction frame arrangement connected with a proving ring. Results of pile loading test have been provided, which demonstrate the tunnel–pile interaction problem effect on the pile capacity, and it was also numerically verified using commercially available finite-element tool. With due verification, parametric study is performed, through finite-element analysis, by varying the range of input parameters such as unit weight, internal friction angle, diameter of pile and elastic modulus of pile material to the soil modulus ratio. Based on the results of numerical analysis in terms of load–settlement curves, it is noted that there is 15–20% reduction in the pile capacity of a single pile to be installed in cohesionless soil in the vicinity of the existing buried pipe ortunnel, which depends on the geometries of the pile and tunnel construction, properties of the in situ soil and zones of influence due to relative stiffness of soil and pipe materials.

    • Three-dimensional finite element modelling of excavation-induced tunnel wall movement and damage: a case study


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      A three-dimensional elastoplastic finite element modelling is conducted for the back analysis of a tunnel collapse accident that happened at the Hobart Myer construction site, including the deformation and failure processes of an existing tunnel in close proximity to a basement excavation as well as further excavationinduced tunnel wall damage and collapse. The full three-dimensional tunnelling process and the basement excavation process are modelled using step-by-step approaches through the successive removal and installationof the solid and structural elements, respectively. Furthermore, following the field observations, the storminduced water pressure in the existing tunnel is taken into consideration and three further small-scale pit excavations without support installation in the sidewall of the basement towards the tunnel are also performed in the numerical modelling process. The obtained results are discussed in comparison to the observed failures at the construction site, to highlight the deformation and failure mechanisms induced by the excavations andstormwater and to examine the trend of the damage and collapse of the tunnel wall and its support system. It is concluded that although the collapse of the tunnel wall is comprehensively the result of nearby basement excavation before and after the heavy rainfall, the storm-induced water pressure is the main factor resulting inthe final collapse of the tunnel wall. Further excavations of three small pits only have relatively slight effects on the instability of the tunnel. The well-developed finite element method provides a valuable tool for the study of the stability of shallow tunnels in the presence of nearby excavations under various conditions.

    • Influence of cutting parameters on cutting forces and surface roughness in dry turning of Al using PCD and different coated tools


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      Aluminium (Al) is the suitable material for aerospace and automotive industries due its light weight, corrosion resistance, weldability, non-magnetic and mechanical properties. But, machining of Al and its alloy and finding the suitable tool is really a big challenge because of its formation of BUE (Built-up Edge) andBUL (Built-up Layer). This paper presents the influence of cutting parameters (speed, feed and depth of cut) and its effect on the cutting force and the surface finish. Five different advanced cutting tool inserts (SPUN WC, SPGN WC, PCD, WC + TiN and WC + Ti(C, N) TiN + Al₂O₃) at different cutting speed (Vc) ranging between 300 m/min and 700 m/min and feed rate (f) of 0.045, 0.06, 0.09 and 0.125 mm/rev at a depth of cut of 0.2 mm (constant throughout the experiment) were taken for the experiment. Tool inserts were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. The cutting forces were measured using Kistler force dynamometer. Amongst all tools, PCD provided a better result in all aspects butsurprisingly WC tool provided a better surface finish with lesser tool wear. For all cutting conditions, high speed (670 m/min) and low feed rate (0.045 mm/rev) were recommended.

    • Performance analysis of planar microcoils for biomedical wireless power transfer links


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      Planar microcoils are significant components of inductive devices used for biomedical wireless power transfer applications. Biomedical devices implanted inside the human body needs to be powered up at regular intervals which can be done electromagnetically through a planar microcoils’ setup. Different types ofplanar microcoils such as spiral and non-spiral planar microcoils are compared in this work in terms of their electrical parameters. An analytical model is also developed which is validated using experimental results. The fabrication advantages and low power dissipation of non-spiral coil structures make them a strong alternative for conventional spiral planar coils. Though the magnitude of magnetic flux density is slightly lesser for non-spiral coils, series resistance required for wireless power link is found to be better for the same. The fabrication of nonspiral planar microcoils of various geometries is shown using a single mask level. Coupling factors of various wireless power links are also simulated using different non-spiral planar microcoil geometries to select the optimum geometry for the wireless power link application.

    • Dual flexible rotor system with active magnetic bearings for unbalance and coupling misalignment faults analysis


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      Rotating machines are the backbone of the present industrial world. Early fault detection and conditioning of these machines are primary concern of the researchers associated in this field. There are various faults (assembly error, coupling misalignment, looseness, imbalance, rotor crack, etc.) that cause malfunction of rotating machinery. Imbalance is one of the oldest problem and still challenging to perfectly balance the rotor. Imbalance leads to another inherent fault, i.e., coupling misalignment, especially in dual rotor or rotor trainsystem. Imbalance and misalignment cause excessive vibration in the system that tends to shatter failure of the critical components of rotating machinery. In this article, active magnetic bearings (AMBs) are utilized to suppress the excessive vibration generated due to imbalance and misalignment. To regulate the controllingcurrent of AMB a proportional integral derivative (PID) feedback controller is employed. A quantification technique is suggested to evaluate the tuned AMB characteristics along with imbalance and coupling misalignment dynamic parameters. A finite element method (FEM) modelling with high-frequency reduction scheme is utilized to acquire reduced system equations of motion. There are two advantages of employing condensation scheme, first, it reduces the number of sensors required and second, only linear (practicallymeasurable) degrees of freedom are present in equations of motion derived. A SIMULINKTM code is prepared to solve a reduced linear differential equation. The time series feedback signals (current and displacement)obtained are transformed into a frequency series utilizing Fast Fourier Transformation (FFT) and utilized in developed algorithm. To establish the accuracy and effectiveness of the methodology, the estimated parametersare evaluated under two different frequency bands against measurement and modelling error (5% variation in mass of the disc and bearing characteristic parameters).

    • Experimental study on cyclic tensile behaviour of air-entrained concrete after frost damage


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      To investigate fatigue tensile behaviour of air-entrained concrete after the freeze–thaw damage, fatigue tensile tests with four different loading paths were conducted on air-entrained concrete after 0, 100, 200 and 400 freeze–thaw cycles. The four different loading paths contained the monotonic (M) test where theenvelope stress–strain curve was obtained, the cycles with constant strain increment (CSI) test where the variation of elastic modulus on the whole stress–strain curve was studied, the cycles to variable maximum strain amplitude (VMS) test where the low-cycle fatigue behaviour at different strain levels was analysed and the cycles with CMS’ test, which was designed to analyse the post-peak behaviour of the specimens. Experimental results indicated that the properties of the air-entrained concrete basically remained unchanged under 200freeze–thaw cycles, including the mass loss rate, tensile strength, elastic modulus and the dissipated energy per unit volume. While the freeze–thaw cycles increased over the critical value, the energy resulted from the cyclic load was not released from the materials and accumulated inside the materials fast. Energy accumulation directly led to the deterioration of the air-entrained concrete. To observe the pore structure of the air-entrained concrete, the scanning electron microscope test (SEM) was also adopted in this paper.

    • Effect of synthetic jet parameters on flow control of an aerofoil at high Reynolds number


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      In this work, flow separation control has been conducted for the S809 aerofoil at a high Reynolds number using synthetic jet technology. The aerodynamic characteristics of the aerofoil have been compared in detail at different angles of attack, for the cases with and without adoption of synthetic jet. Numerical methodsare employed for predicting flow structure and performance of the aerofoil. In addition, main parameters of the synthetic jet are optimized by the orthogonal experimental design, and dual jets are also employed for the comparison to a single jet. The results show that the flow separation at large angles of attack can be eliminated or greatly reduced by the synthetic jet, due to the mixing of low-energy fluid in boundary layer with high-energy fluid produced by the synthetic jet. The lift-to-drag ratio has been considerably increased by the synthetic jet forthe critical condition, deep stall condition and complete stall condition as well. The maximum jet velocity of the synthetic jet is found to have the biggest effect on flow separation control. Furthermore, compared with single synthetic jet, the dual jets can make much better improvement on flow separation control of the aerofoil,especially at the complete stall condition.

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