Faculty Publications

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    Capacitance computation is an important step in the development of a spacecraft equivalent circuit model for predicting the surface charge build up. Since different parts of the spacecraft may be represented in terms of standard geometrical shapes, this paper presents a numerical procedure developed for computing the capacitance of such standard objects located in free space. The objects considered are conducting and hence the analysis assumes an equipotential surface having an unknown charge distribution. The charge distribution and the total charge are evaluated using the moment method by triangular patch modelling of the surface. The capacitance in free space of planar, cubic and wedge shaped conducting geometries have been numerically computed using the above technique. The results obtained for some of these geometries have been compared with the results available in the literature.
    (Free space capacitance of conducting surfaces) Hariharan, V.K.; Shastry, S.V.K.; Chakraborty, A.; Katti, V.R.
    1998
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    Strength retention characteristics of concrete cubes subjected to elevated temperatures
    (2010) Yaragal, S.C.; Clarke, K.S.; Mahesh Babu, K.; Ashokumar, S.; Venkataramana, K.; Babu Narayan, K.S.; Chinnagiri Gowda, H.C.; Reddy, G.R.; Sharma, A.
    Concrete in structures is likely to be exposed to high temperatures during fire. The relative properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great interest to the designer. Physical changes like cracking, colour change, spalling and chemical changes like decomposition of Ca(OH)2 and the C-S-H gel take place when subjected to elevated temperatures. This work reports the characteristics of concrete at elevated temperatures. Popular normal strength grades (M20, M25, M30, M35, M40 and M45) produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes) to obtain more meaningful and realistic data. In the preliminary phase 150 mm cubes were cast, cured and tested by destructive method for gathering data on strength characteristics. Later these test samples were subjected to elevated temperatures ranging from 100°C to 800°C, in steps of 100°C with a retention period of 2 hours. After exposure, weight losses were determined and then again destructive tests were conducted to estimate the residual compressive strength. Test results indicated that weight and strength significantly reduces with an increase in temperature. © 2010 CAFET-INNOVA TECHNICAL SOCIETY.
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    Studies on normal strength concrete cubes subjected to elevated temperatures
    (2010) Yaragal, S.C.; Babu Narayan, K.S.; Venkataramana, K.; Kulkarni, K.S.; Gowda, H.C.C.; Reddy, G.R.; Sharma, A.
    Concrete in structures is likely to be exposed to high temperatures during fire. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great importance and interest to the designer. Popular normal strength grades of concrete produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes), cured and tested by destructive method for gathering data on strength characteristics. Later, these test samples were subjected to elevated temperatures ranging from 100 C to 800 C, in steps of 100 C with a retention period of 2 hours. After exposure, weight losses and the residual compressive strength retention characteristics are studied. Test results indicated that weight and strength significantly reduces with an increase in temperature. Residual compressive strength prediction equations are proposed for normal strength concretes subjected to elevated temperatures.
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    Iterative zone-reclassification in trip generation, and cube-based distribution for Bangalore
    (2012) George, V.; Subramanyam, U.V.; Mahendrakar, A.S.
    This study deals with the development of an approach to model trip-generation and distribution for the City of Bangalore using data compiled in 2002. Since the initial attempts at development of reliable trip-generation regressions using SPSS were un-successful, an iterative zone-reclassification approach was adopted in modelling the trip-productions and attractions. The reclassification of zones was performed based on the assumed influence of various groups of zones, the location of production and attraction centres and their nearness, and the improvement in the R-square value of regressions developed at each iteration. Finally, the 159 zones of the city were broadly categorized into twelve influence areas, and the trip-generation and distribution studies were performed using CUBE software. The predictions for the base year were verified with the actual data. Predictions for 2011 and 2021 were then performed. © 2012 CAFET-INNOVA TECHNICAL SOCIETY.
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    A framework for estimating geometric distortions in video copies based on visual-audio fingerprints
    (Springer-Verlag London Ltd, 2015) Roopalakshmi, R.; Guddeti, G.R.M.
    Spatio-temporal alignments and estimation of distortion model between pirate and master video contents are prerequisites, in order to approximate the illegal capture location in a theater. State-of-the-art techniques are exploiting only visual features of videos for the alignment and distortion model estimation of watermarked sequences, while few efforts are made toward acoustic features and non-watermarked video contents. To solve this, we propose a distortion model estimation framework based on multimodal signatures, which fully integrates several components: Compact representation of a video using visual-audio fingerprints derived from Speeded Up Robust Features and Mel-Frequency Cepstral Coefficients; Segmentation-based bipartite matching scheme to obtain accurate temporal alignments; Stable frame pairs extraction followed by filtering policies to achieve geometric alignments; and distortion model estimation in terms of homographic matrix. Experiments on camcorded datasets demonstrate the promising results of the proposed framework compared to the reference methods. © 2013, Springer-Verlag London.
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    Sensitivity of Pushover Curve to Material and Geometric Modelling-An Analytical Investigation
    (Elsevier Ltd, 2015) Panandikar, N.; Babu Narayan, K.S.
    Nonlinear static analysis or pushover analysis developed over the last two decades and became the preferred procedure for design and seismic performance evaluation, as this procedure is relatively simple and considers post-elastic behaviour. It provides information on seismic demands imposed by the design ground motion on the structural system and its components. Generation of pushover curve from analysis for reinforced concrete structure involves tremendous amount of computational efforts as the input data for analysis itself is quite exhaustive. The analysis results are very sensitive to the techniques employed in geometric and material modelling. This paper envisages presenting the sensitivity of pushover analysis results to geometric and material modelling parameters by comparing the analysis results with that of experimental investigations. Attempt has been made to understand the sensitivity of parameters like variation in material properties, inaccuracies in placement of reinforcement, effect of confinement of concrete and modelling techniques for elements and plastic hinges. SAP-2000 has been utilised in the current investigation and results have been highlighted suggesting strategies to enhance pushover analysis capabilities. © 2015 Elsevier B.V.
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    A Closed-Form Solution for the Effect of Free Edges on Melt Pool Geometry and Solidification Microstructure in Additive Manufacturing of Thin-Wall Geometries
    (Springer Boston, 2016) Gockel, J.; Klingbeil, N.; Bontha, S.
    Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free edges. In the current study, the Rosenthal solution is modified to include the effects of free edges. This is accomplished by the superposition of two point-heat sources approaching one another, with the line of symmetry representing the free edge. The result is an exact solution for the case of temperature-independent properties. Dimensionless results for melt pool geometry are determined, and plotted as a function of distance from the free edge. Results are plotted on solidification maps to predict trends in microstructure for Ti-6Al-4V. Finite element analysis is used to verify results. Results suggest that melt pool geometry is more sensitive to free edges than solidification microstructure. © 2015, The Minerals, Metals & Materials Society and ASM International.
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    Axis switching in impinging premixed methane-air flame jets
    (Elsevier Ltd, 2016) Hindasageri, V.; Kuntikana, P.; Tajik, A.R.; Vedula, R.P.; Prabhu, S.V.
    Axis switching in non-circular tube burner flame jets is studied. Experimental data of heat flux is obtained for square and rectangular burners of different aspect ratios: 1, 1.55, 2.1 and 3.73. A three dimensional CFD simulation is carried out to explain the phenomenon of axis switching in premixed flame jets. From the CFD simulations it is observed that the vortices formed near the corner of the tube exit are responsible for the axis switching phenomenon. These vortices control the spreading (in a preferential manner) of the flame jet along the tube axis. This preferential spreading of the flame jet is responsible for switching of contours of heat flux on the impingement plate. Furthermore, for the rectangular burner, elliptical lobes of heat flux distribution on the impingement plate are observed and this is again attributed to vortex structures. © 2016 Elsevier Ltd
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    The effect of higher order model on the geometric nonlinear analysis of antisymmetric angle ply laminates
    (Smithers Rapra, 2016) Swaminathan, K.; Sangeetha, D.M.
    Geometric nonlinear analysis of simply supported antisymmetric angle-ply laminated composite plates are investigated based on first order and higher order displacement models with five degrees of freedom. Analytical formulations and solutions are developed based on Von-Karman nonlinear plate theory and Taylor's series expansion of displacement components. Equations of equilibrium are obtained using Principle of Minimum Potential Energy (PMPE) and closed form solutions using Navier's Solution technique. A four layered square plate is considered for the present study. Parametric studies are performed on both the models to study the behaviour of displacements and stresses in laminated composite plates. Comparative studies are performed on both the models and the effect of geometric nonlinearity is discussed. © 2016 Smithers Information Ltd.
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    Comparative study of pool boiling heat transfer from various microchannel geometries
    (Elsevier Ltd, 2018) Walunj, A.; Sathyabhama, A.
    This paper presents the experimental investigation of pool boiling heat transfer enhancemrent using open microchannels. Rectangular, parabolic and stepped microchannels are fabricated on the 10 mm diameter circular copper test piece and their boiling characteristics are compared with that of the plain surface at saturated condition of distilled water. The effect of channel shape and geometrical parameter on the boiling heat transfer is studied. The channel top width and channel base width are varied from 250 ?m to 500 ?m and 500 ?m to 800 ?m, respectively. The fin tip thickness is varied from 200 ?m to 500 ?m. The channel height is fixed at 500 ?m. The morphology of bubble is observed by using high-speed camera. Compound study of bubble departure diameter and bubble frequency has proved the significant performance of parabolic and stepped microchannel. All the microchannel geometries enhanced the heat transfer rate. The modification of rectangular channel into parabolic and stepped microchannel resulted in the maximum of 88% and 169% enhancement, respectively at 11.7 °C wall superheat. At heat flux of 100 kW/m2, the heat transfer coefficient increased by 21.49–35.37% for different microchannels. The incipient temperature reduced by 13.72–23.18%. A semi-analytical model is developed to estimate the bubble departure diameter of the microchannel which predicts the present experimental data with mean absolute error of 5.58%. © 2017 Elsevier Ltd