Articles written in Sadhana

    • Magneto-thermo-visco-elastic waves in an initially stressed conducting layer

      Amit Kumar Rakshit P R Sengupta

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      The aim of this paper is to investigate magneto-thermo-viscoelastic surface waves in electrically and thermally conducting layers involving time rates of strain and stress of ordern, the media being under an initial stress in the nature of hydrostatic tension or compression. The theory of magneto-thermo-visco-elastic surface waves in the conducting medium involving strain rate and stress rate ofnth order is derived under initial stress. This theory is then employed to obtain wave velocity equations in specific cases. Results obtained in the above cases reduce to well-known classical results when additional fields are absent.

    • Optimal way of selecting cities and conveyances for supplying coal in uncertain environment

      Amit Kumar Amarpreet Kaur

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      In this paper, the limitations and shortcomings of the existing methods for solving fuzzy solid transportation problem are pointed out and to overcome these shortcomings, a new method is proposed for solving fuzzy solid transportation problem. The advantages of the proposed method over the existing methods are discussed. To illustrate the proposed method, an existing fuzzy solid transportation problem is solved. Also, to show the application of the proposed method in real life problems an existing real life fuzzy solid transportation problem is solved by the proposed method.

    • A new method for solving single and multi-objective fuzzy minimum cost flow problems with different membership functions

      Amit Kumar Manjot Kaur

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      Several authors have proposed different methods for solving fuzzy minimum cost flow (MCF) problems. In this paper, some single and multi-objective fuzzy MCF problems are chosen which cannot be solved by using any of the existing methods and a new method is proposed for solving such type of problems. The main advantage of the proposed method over existing methods is that the fuzzy MCF problems which can be solved by using the existing methods can also be solved by the proposed method. But, there exist several fuzzy MCF problems which can be solved only by using the proposed method i.e., it is not possible to solve these problems by using the existing methods. To illustrate the proposed method and also to show the advantages of the proposed method over existing methods some single and multiobjective fuzzy MCF problems which cannot be solved by using the existing methods are solved by using the proposed method and the obtained results are discussed.

    • A method for unbalanced transportation problems in fuzzy environment

      Deepika Rani T R Gulati Amit Kumar

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      In this paper, we consider the fully fuzzy unbalanced transportation problem in which the total availability/production is more than the total demand and propose a method to solve it. Such problems are usually solved by adding a dummy destination. Since the dummy destination has no existence in reality, the excess availability is not transported at all and is held back at one or more origins. The method proposed in this paper gives the additional information that to which of the destination(s) the excess availability be transported for future demand at minimum cost. The advantage of the proposed method over the existing method is that the fuzzy optimal solution obtained does not involve the dummy destination. The method has been illustrated with the help of an example.

    • Computations of incompressible fluid flow around a long square obstacle near a wall: laminar forced flow and thermal characteristics


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      Computations of incompressible fluid flow and heat transfer around a square obstacle with a near by adiabatic wall have been performed in a horizontal plane. The ranges of dimensionless control parameters considered are Prandtl number (Pr) = 10–100, Reynolds number (Re) = 1–150 and gap ratio (G) = 0.25–1.The steady-flow regime is observed up to Re = 121 for G = 0.5, and beyond this Re, time-periodic regime is observed. The shift to a time-periodic regime from a steady regime occurred at greater Re than that for an unconfined square obstacle. With increasing Pr, increase in average Nusselt number values is recorded for all Re and G studied. The heat transfer augmentation is approximately 1332% at Re = 150 (Pr = 100, G = 0.25) with regard to the corresponding values at Re = 1. Lastly, a correlation for jh factor is determined for the preceded conditions.

    • Single-current-sensor-based active front-end-converter-fed four quadrants induction motor drive


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      Induction motor (IM) is a workhorse of the industry, whose dynamics can be modified close to that of a separately excited DC machine by field-oriented control technique, which is commonly known as vector control of induction machine. This paper presents a complete performance of the field-oriented control of IM drive in all four quadrants with a single-current-sensor-based active front end converter whose work is to regulate DC link voltage, draw pure sinusoidal currents at unity power factor and to facilitate bi-directional power flow between the grid and the drive. The entire system is completely modelled in MATLAB/SIMULINK and the results are discussed in detail. The vector control analogy of the back to back converters is highlighted along with the experimental results of field-oriented control of induction machine using a dsPIC30F6010A digital signal controller.

    • Control of AC–DC grid side converter with single AC current sensor


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      Conventionally, two AC side current sensors are needed in vector control of grid side converter for AC–DC bidirectional power conversion. The present paper proposes a technique where the control can be achieved with the use of only one AC side current sensor. The control principle utilises the information of unsensedsecond current sensor for its estimation, which is embedded and readily available in conventional control technique itself. In the proposed method, the grid side d–q axis reference currents of the current controllers are used for estimation of b-axis component of grid current, while the a-axis component of grid current is calculated by one AC side current sensor. Effect of voltage unbalance on the control is also studied in this paper. The proposed control is validated with detailed simulation and experimental observations for both steady-state andtransient conditions. The proposed control gives satisfactory performance.

    • Maximum power per VA control of vector controlled interior permanent magnet motor


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      Maximum Torque Per Ampere is the commonly used technique for operating interior permanent magnet (IPM) motor while little work is reported towards maximum power-factor operation i.e., Maximum Power Per Volt-Ampere (MPVA). The MPVA operation allows maximum-utilization of the drive-system. Thecontrol technique is developed using detailed mathematical model of IPM motor in MPVA, and the solution to the quartic equations involved is derived and analyzed. The solution is utilized to develop LUT for implementation of MPVA control. The comparison of MTPA and MPVA technique is established to demonstrate itsmerits and demerits. The proposed algorithm is supported by simulation and experimental results on a 5.5 KW vector controlled IPM drive.

    • Simplified current minimization control of vector controlled Interior Permanent Magnet motor


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      This paper presents a simplified current minimizing technique for Interior Permanent Magnet (IPM) motor. This is primarily achieved by utilizing normalized 2D-Look Up Table (LUT) that is parameter independent except for saliency ratio. In addition, torque-flux reference frame is considered for implementation to reduce the complexity generally present in conventional methods utilizing ids - iqs current reference frame. The proposed algorithm also incorporates both the aspects that lead to field weakening operation, i.e., increase in speed and reduction of dc link voltage. A novel compensation method for incorporating saturation effect is also addressed. The current minimizing technique is analyzed in detail, supported by experimental results.

    • Formulation of new correlations in terms of extraterrestrial radiation by optimization of tilt angle for installation of solar photovoltaic systems for maximum power generation: case study of 26 cities in India


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      This paper deals with finding of optimum tilt angle for installation of optimized solar photovoltaic system in India. The optimization of tilt angles is performed using measured solar radiation data for 26 cities in India. The tilt angle is changed from 0° to 90° at step of 1° to find out optimum tilt angle for which monthly average solar radiation is maximum. It was found that the optimum tilt angle varies between 0° and 63° throughout the year in India. The monthly optimum tilt angle is maximum in December for all cities in India. It is found that increase in maximum solar radiation at monthly optimum tilt angle in comparison to latitude based tilt angle and annual optimum tilt angle varies from 5.85% to 8.08% and 5.95% to 8.34%, respectively, showing monthly optimum tilt angle is beneficial for maximum power generation for different cities in India. The novelty of this study is new correlations of optimum tilt angle in terms of extraterrestrial radiation are developed for estimating monthly optimum tilt angle for installation of photovoltaic systems at different sites in India. The root mean square error in correlation equations varies from 0.1256 to 0.9771.

    • Harmonics reduction in standalone DFIG-DC system by shunt active filter controlled in stator flux reference frame


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      The presence of diode rectifier in standalone Doubly Fed Induction Generator-Direct Current (DFIGDC) system leads to considerable current, voltage and torque harmonics and requires reactive power from the machine. A unique shunt active filter arrangement is proposed for addressing these requirements. The DC Link ofDFIG-DC itself acts as input to shunt active filter and there is no requirement of creating and regulating a separate one. Since the stator flux reference frame is known in FOC of DFIG-DC system; the same can be used as PLL for thegeneration of current references for harmonics and reactive compensation in active filter control scheme. Hence, the AC voltage sensing is not needed in the proposed active filter control. In this paper, it is shown that current, voltageand torque harmonics are reduced with the help of shunt active filter, which have lower rating compared to the rotor side converter. The proposed scheme is verified by detailed experiments on a 5.5 kW slip-ring induction machine.

    • Voltage minimization control of vector controlled interior permanent magnet motor


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      Maximum Torque Per Voltage trajectory has been utilized only during field weakening operation of Interior Permanent Magnet (IPM) motor. In this paper, the voltage minimization control from zero-speed is proposed. Voltage minimization results in maximum torque per voltage control of IPM motor. The control implementation is also simple in comparison to current minimization, as the operation is always along the current-limit locus irrespective of operation in field-weakening. Voltage minimization technique minimizes the core losses whereas current minimization would minimize the copper losses. The mathematical model of IPM motor following voltage minimization is derived and the solution to the 4th order quartic equations is obtained using Ferrari’s method. The solution obtained is utilized to develop a look-up table for vector control of IPM motor. A comparative analysis of voltage minimization and current minimization is established which is supported by simulation results and demonstrated by detailed experimental results.

    • Experimentation modelling and optimization of electrohydrodynamic inkjet microfabrication approach: a Taguchi regression analysis


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      Electrohydrodynamic (EHD) inkjet is a modern non-contact printing approach, which uses a direct writing technology of functional materials to achieve micro/nanoscale of printing resolution. As an alternative to conventional inkjet technology, the goal of the EHD inkjet printing is to generate uniformly minimized droplets on a substrate. In this study, the effects of applied voltage, standoff height and ink flow rate on droplet diameter formation in EHD inkjet printing process were analysed using Taguchi methodology and regression analysis.Several experiments were carried out using an L27 (313) orthogonal array. Based on signal to noise (S/N) ratioand mean response, optimal droplet diameter was achieved. The analysis of variance (ANOVA) was used to find the significance and percentage of contribution of each input parameter along with their interaction on the output droplet diameter. Analysis of the results revealed that the ink flow rate was the dominant factor that affected the droplet diameter mostly. The effect of the applied voltage is significant until regular ejection starts. It helps reduce droplet diameter more than five times compared with its initial droplet diameter in the absence of the electric field. A confirmation test was carried out with a 90% confidence level to illustrate the effectiveness of the Taguchi optimization method. Both linear and quadratic regression analysis were applied to predict the output droplet diameter. The predicted result from the model and actual test results are very close to each other,justifying the significance of the models.

    • An information-theoretic graph-based approach for feature selection


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      Feature selection is a critical research problem in data science. The need for feature selection has become more critical with the advent of high-dimensional data sets especially related to text, image and microarray data. In this paper, a graph-theoretic approach with step-by-step visualization is proposed in the context of supervised feature selection. Mutual information criterion is used to evaluate the relevance of the features with respect to the class. A graph-based representation of the input data set, named as feature information map (FIM) is created, highlighting the vertices representing the less informative features. Amongst the more informative features, the inter-feature similarity is measured to draw edges between features having high similarity. At the end, minimal vertex cover is applied on the connected vertices to identify a subset of features potentially havingless similarity among each other. Results of the experiments conducted with standard data sets show that the proposed method gives better results than the competing algorithms for most of the data sets. The proposed algorithm also has a novel contribution of rendering a visualization of features in terms of relevance andredundancy.

    • Mehar approach for solving dual-hesitant fuzzy transportation problem with restrictions


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      Recently, a new type of transportation problems (named as dual-hesitant fuzzy transportation problem) as well as an approach to find the optimal solution of dual-hesitant fuzzy transportation problems have been proposed in the literature. In this paper, some dual-hesitant fuzzy transportation problems are considered toshow that the existing approach is inappropriate as (i) The existing approach fails to find the optimal solution of dual-hesitant fuzzy transportation problems. (ii) On applying the existing approach different optimal transportation costs are obtained corresponding to alternative optimal solutions. Also, to resolve the inappropriateness of the existing approach, a new expression (named as Mehar score function) is proposed to transform a dualhesitant fuzzy set into a real number. Furthermore, a new approach (named as Mehar approach), based upon the proposed Mehar score function, is proposed to find the optimal solution of dual-hesitant fuzzy transportation problems

    • Volumetric shrinkage estimation of benchmark parts developed by rapid tooling mold insert


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      This paper estimates the volumetric shrinkage for thermoplastic Polypropylene (PP) injection molded components made using digital Acrylonitrile butadiene styrene (ABS) mold. The parameters affecting volumetric shrinkage for the digital ABS mold are mold temperature and injection temperature, cooling time,hold pressure and injecting speed. Therefore, twelve standard benchmark CAD model were selected with different geometric attributes. Subsequently, simulation analysis was performed on all CAD model using MoldflowÒ (MFA) simulation software. Additionally, regression analysis is applied to identify the effect ofinjection molding parameters on the volumetric shrinkage of part made using rapid tooling mold insert of digital ABS material. It is found that maximum volumetric shrinkage (18.75%) is observed for square pyramid frustum,conical frustum, and solid torus. On the contrary, hollow rectangular prism shows minimum shrinkage effect having 12.61% of volumetric shrinkage. This study predicted that shrinkage is the main concern for these three geometric features (i.e., square pyramid frustum, conical frustum, and solid torus) and must be looked for its minimization. The results are experimentally validated, with 3D scanner integrated with COMET plus and Inspect plus softwares. Since shrinkage estimation for digital ABS mold using Rapid Tooling technique has notbeen attempted before, therefore, this study provides guidance for the optimum parameter selection and assigning suitable shrinkage compensation values for digital ABS mold made using direct rapid tooling

    • Effect of individual phase properties and volume fractions on the strain partitioning, deformation localization and tensile properties of DP steels


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      Deformation band localization modes, uniform tensile strength, and uniform elongation of Ferrite-Martensite Dual-Phase (DP) steels are analyzed by finite element (FE) study. Treating the microstructure inhomogeneity as the sole cause of imperfection, failure initiation is predicted as the natural fallout of plasticinstability caused by load drop because of localized plastic strain in the Representative Volume Element (RVE) during straining. Strain partitioning between two phases (ferrite matrix and martensite island) are investigated onRVEs, and it reveals that the increase of martensite yield stress decreases the plastic deformation and increases the stress state in martensite. Whereas, a decrease in martensite island volume fraction (Vm) results in the reduction of plastic deformation and stress state in the island. Studies are then carried out to investigate the effects of the ferrite-martensite flow properties and martensite volume fraction on the macroscopic tensile deformation behavior and band localization of DP steels. Micromechanical based FE simulation resultsemphasize that an increase in initial yield strength and volume fraction of martensite increases the ultimate tensile stress (UTS) with the decrease in uniform elongation. Similarly, as the hardening rate of ferrite increases,it increases the ultimate tensile stress (UTS) and uniform elongation. Additionally, deformation band localization modes alter from inclined to perpendicular to the loading axis with an increase in martensite volume fraction and initial yield strength of martensite. The knowledge of this work can be used to design DP steels with desired mechanical properties.

    • A strong intuitionistic fuzzy feature association map-based feature selection technique for high-dimensional data


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      In this work, a graph-based approach has been adopted for feature selection in case of highdimensional data. Feature selection intends to identify an optimal feature subset to solve the given learning problem. In an optimal feature subset, only relevant features are selected as ‘‘members’’ and features that haveredundancy are considered as ‘‘non-members’’. This concept of ‘‘membership’’ and ‘‘non-membership’’ of a feature to an optimal feature subset has been represented by a strong intuitionistic fuzzy graph. The algorithm proposed in this work at first maps the feature set of the data as the vertex set of a strong intuitionistic fuzzy graph. Then the association between features represented as an edge-set is decided by the degree of hesitation between the features. Based on the feature association, the Strong Intuitionistic Fuzzy Feature Association Map (SIFFAM) is developed for the datasets. Then a sub-graph of SIFFAM is derived to identify features with maximal non-redundancy and relevance. Finally, the SIFFAM based feature selection algorithm is applied on very high dimensional datasets having features of the order of thousand. Empirically, the proposed approach SIFFAM based feature selection algorithm is found to be competitive with several benchmark feature selection algorithms in the context of high-dimensional data

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