Journal Articles
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Item A Review of Superconducting Magnetic Bearings and Their Application(Institute of Electrical and Electronics Engineers Inc., 2022) Supreeth, D.K.; Bekinal, S.I.; Shivamurthy, S.R.; Doddamani, M.Magnetic bearings are being researched for high-speed applications, such as flywheel energy storage devices, to eliminate friction losses. As per Earnshaw's theorem, stable levitation cannot be achieved for a static passive magnetic bearing system. Fully passive stable levitation can be achieved with the help of superconducting magnetic bearings (SMB). This article provides an in-depth review of the modeling, analysis, and development of SMB. The different SMB configurations are highlighted, together with essential methodologies for estimating and improving their performance. The advancements in mathematical models used and the optimization of bearing characteristics are thoroughly discussed. Further, key developments in the application of SMB in flywheel energy storage systems are also reviewed. © 2002-2011 IEEE.Item Polymer-based composite materials possess superior properties such as high strength-to-weight ratio, stiffness-to-weight ratio, and good corrosive resistance and therefore, are preferred for high-performance applications such as in the aerospace, defense, and sport goods industries. Drilling is one of the indispensable methods for building products with composite panels. Drilling tests have been conducted on glass fiber-reinforced plastic composite GFRP laminates using an instrumented CNC milling center. Machining parameters such as drill size, feed rate, and cutting speed have been observed for damage-free drilling of GFRP materials. A series of drilling experiments have been conducted on glass fiber-reinforced polyester laminates and the responses experienced such as thrust force and torque as functions of feed rate and drill size have been characterized to develop a semiempirical relationship which correlated well with an established model in terms of cutting parameters. Results indicated that experimental values correlated better with the model of thrust for 6mm drill size than for 10mm and torque correlated better for lower feed ranges than for the higher feed ranges. © 2005 Sage Publications.(Machining of fiber-reinforced thermoplastics: Influence of feed and drill size on thrust force and torque during drilling) Mohan, N.S.; Ramachandra, A.; Kulkarni, S.M.2005Item Strength deformation behaviour of circular concrete filled steel tubes subjected to pure bending(2009) Chitawadagi, M.V.; Narasimhan, M.C.The strength deformation behaviour of circular steel tubes filled with different grades of concrete under flexure is presented. The effects of steel tube thickness, the cross sectional area of concrete, strength of in-filled concrete and the confinement of concrete on moment capacity and curvature of Concrete Filled steel Tubes (CFTs) are examined. Measured flexural strengths are compared with the values predicted by EC4-1994 and LRFD-AISC-1999 code provisions. A total of ninety nine specimens, all one metre long, were tested with concrete fills of 20, 30 and 40 N/mm2 characteristic strength and with D / t ratio 22.3 to 50.8. Based on the experimental results, an interaction model to predict moment and curvature of the CFT sample is developed. © 2009 Elsevier Ltd. All rights reserved.Item Stone Columns with Vertical Circumferential Nails: Laboratory Model Study(2010) Shivashankar, R.; Dheerendra Babu, M.R.D.; Nayak, S.; Manjunath, R.This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the improvement in stiffness, load carrying capacity and resistance to bulging of stone columns installed in soft soils. A new method of reinforcing the stone columns with vertical nails installed along the circumference of the stone column is suggested for improving the performance of these columns. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. It is found that stone columns reinforced with vertical nails along the circumference have much higher load carrying capacity and undergo lesser compression and lesser lateral bulging as compared to conventional stone columns. The benefit of vertical circumferential nails increases with increase in the diameter, number and depth of embedment of the nails. The improvement in the performance of stone column was found to be more significant, even with lower area ratio. It is found that reinforcing stone column with vertical circumferential nails at the top portion to a depth equal to three times the diameter of stone columns, will be adequate to prevent the column from excessive bulging and to improve its load carrying capacity substantially. © 2010 Springer Science+Business Media B.V.Item Experimental Studies on Behaviour of Stone Columns in Layered Soils(2011) Shivashankar, R.; Dheerendra Babu, M.R.D.; Nayak, S.; Rajathkumar, V.Stone columns are found to be effective and economical ground improvement technique in soft grounds. Understanding its behaviour when they are installed in stratified soils, in particular when the upper layer consists of weak soil, will be of great practical significance. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behaviour of stone columns in layered soils, consisting of weak soft clay overlying a relatively stronger silty soil, for various thicknesses of the top layer. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. Laboratory tests were carried out on a column of 90 mm diameter surrounded by layered soil, for an area ratio of 15%. It is found that the depth of top weak layer thickness has a significant influence on the stiffness, load bearing capacity and bulging behavior of stone columns. © 2011 Springer Science+Business Media B.V.Item Effects of soil parameters and moisture content on stiffness of unsaturated blended laterite using tri-axial tests for rural roads(2011) George, V.; Nageshwar Rao, C.; Shivashankar, R.Evaluation of subgrade strength and stiffness is essential in the design of pavements and construction of embankments for highways in order to ensure that roads perform their functions satisfactorily over a longer period. The grain size distribution and compaction moisture-content have an immense influence on the strength and stiffness of subgrades. Among the various laboratory tests for evaluation of shear strength parameters, and the modulus of elasticity of subgrades, the tri-axial test plays a major role in describing the geotechnical characteristics of the subgrade. This paper deals with an experimental investigation on unsaturated laterite soils blended with varying percentages of fines. It focuses on a study of the influence of various soil parameters on the stiffness and strength of soil samples compacted at optimum moisture content (OMC), at the drier side of OMC, and also at the wetter side of OMC, and the development of meaningful correlations. © 2011 CAFET-INNOVA TECHNICAL SOCIETY.Item Performance of granular columns in dispersive soils(Thomas Telford Services Ltd ttjournals@ice.org.uk, 2014) Nayak, S.; Dheerendra Babu, M.R.; Shivashankar, R.; James, N.The soils found abundantly along the Konkan belt in peninsular India are lateritic soils and lithomargic clays. The locally available lithomargic clayey soils are problematic in the sense that their strength reduces drastically under saturation conditions, which is typical behaviour of the dispersive type of soil. Most foundations are placed on this soil layer. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behavior of granular columns in these weak (lithomargic clay) grounds. Tests are carried out with two types of loading: with the entire area in the unit cell tank loaded, to estimate the stiffness of the improved ground; and with only the granular column area loaded, to estimate its limiting axial capacity. Investigations were carried out by varying the area ratio (or spacing), diameter of granular columns, end condition and column configuration. The load-settlement behaviour, stiffness and bulging behaviour of granular columns are analyzed. It is found that the ground treated with granular columns exhibits a high load-carrying capacity and stiffness, and a significant reduction in settlement, compared with the untreated ground. © Ice publishing: All rights reserved.Item Magnetic field and frequency dependent LVE limit characterization of magnetorheological elastomer(Springer Verlag service@springer.de, 2017) Poojary, U.R.; Gangadharan, K.V.Magnetorheological elastomer (MRE) based semi-active isolators have the potential to replace conventional passive isolators to achieve wide frequency range isolation. The effectiveness of MRE isolator depends on the control strategies developed based on viscoelastic constitutive relations. The theory of linear viscoelasticity is the basis for viscoelastic constitutive relations which can predict the material behavior within a certain strain limit referred as linear viscoelastic (LVE) limit. Beyond the LVE limit, the performance of MRE semi-active isolator exacerbates as the control strategies turns out to be ineffective. In the present study, variation in LVE limit of MRE with the magnetic field and frequency is investigated through forced vibration tests. To exclude the effect of terminal non-linearity on the measurement, the blocked transfer stiffness method described in the ISO 10846-2 is adopted. The results revealed that the LVE limit of MRE is strongly dependant on the magnetic field and exhibited a weak dependency on the operating frequency. Under magnetized state, the transition from linear to non-linear behavior of MRE is at lower strain levels indicating the increased friction energy dissipation at particle–matrix interface. © 2016, The Brazilian Society of Mechanical Sciences and Engineering.Item Empirical potential influence and effect of temperature on the mechanical properties of pristine and defective hexagonal boron nitride(Institute of Physics Publishing helen.craven@iop.org, 2017) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.The major objective of this work is to present results of a classical molecular dynamics study to investigate the effect of changing the cut-off distance in the empirical potential on the stress-strain relation and also the temperature dependent Young's modulus of pristine and defective hexagonal boron nitride. As the temperature increases, the computed Young's modulus shows a significant decrease along both the armchair and zigzag directions. The computed Young's modulus shows a trend in keeping with the structural anisotropy of h-BN. The variation of Young's modulus with system size is elucidated. The observed mechanical strength of h-BN is significantly affected by the vacancy and Stone-Wales type defects. The computed room temperature Young's modulus of pristine h-BN is 755 GPa and 769 GPa respectively along the armchair and zigzag directions. The decrease of Young's modulus with increase in temperature has been analyzed and the results show that the system with zigzag edge shows a higher value of Young's modulus in comparison to that with armchair edge. As the temperature increases, the computed stiffness decreases and the system with zigzag edge possesses a higher value of stiffness as compared to the armchair counterpart and this behaviour is consistent with the variation of Young's modulus. The defect analysis shows that presence of vacancy type defects leads to a higher Young's modulus, in the studied range with different percentage of defect concentration, in comparison with Stone-Wales defect. The variations in the peak position of the computed radial distribution function reveals the changes in the structural features of systems with zigzag and armchair edges in the presence of applied stress. © 2017 IOP Publishing Ltd.Item Analysis of Foundation of Tall R/C Chimney Incorporating Flexibility of Soil(Springer India sanjiv.goswami@springer.co.in, 2017) Jayalekshmi, B.R.; Jisha, S.V.; Shivashankar, R.Three dimensional Finite Element (FE) analysis was carried out for 100 and 400 m high R/C chimneys having piled annular raft and annular raft foundations considering the flexibility of soil subjected to across-wind load. Stiffness of supporting soil and foundation were varied to evaluate the significance of Soil-Structure Interaction (SSI). The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic material behaviour. FE analyses were carried out for two cases of SSI namely, (1) chimney with annular raft foundation and (2) chimney with piled annular raft foundation. The responses in raft such as bending moments and settlements were evaluated for both the cases and compared to those obtained from the conventional method of analysis of annular raft foundation. It is found that the responses in raft vary considerably depending on the stiffness of the underlying soil and the stiffness of foundation. Piled raft foundations are better suited for tall chimneys to be constructed in loose or medium sand. © 2017, The Institution of Engineers (India).