Faculty Publications
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Item A comparison of the non-conforming and conforming sector finite element for free vibration of circular discs(Elsevier Ltd, 2020) Avvaru, H.T.; Joladarashi, S.; Kadoli, R.A twelve-term non-conforming and a sixteen-term conforming displacement polynomial are obtained from Pascal's triangle to deduce the shape functions for a sector element. Using the sector element circular disc is discretized. The number of degrees of freedom for the sector element at a given node is three and four. Kirchhoff's plate theory is the basis for strain energy and kinetic energy because of the transverse motion of the circular plate. Associated stiffness and mass matrices for the sector element are derived in closed form using MATHEMATICA. Using the Lagrange equation, the free vibration equation of motion for the circular disc is derived. A validation study is conducted, and non-dimensional frequencies from the finite element solution are compared with the analytical solutions reported in the literature. Subsequently, the natural frequencies of Al-Al2O3functionally graded circular disc with gradation in the thickness direction are evaluated for a variety of boundary conditions. © 2020 Elsevier Ltd. All rights reserved.Item A new approach for channel blind identification based on second order cyclostationary statistics and the group delay has been proposed. In this, two methods are proposed. In both the methods, the correction is applied to the basic phase estimate for both the poles and zeros, in the group delay domain. The basic phase estimate is derived from the spectral correlation density (SCD) of the system output. In the first method, the phase correction is based on magnitude group delay. In the second method, not only the phase correction but also an improved system magnitude estimate of better variance and frequency resolution is derived based on modified magnitude group delay. The results indicate a significant improvement in performance for both the methods. For the first method in the absence of noise, the percentage normalized mean square error is reduced by about 85% over that of the existing non-parametric method. The second method in the presence of noise (SNR=5 dB), provides a reduction of 74% over the existing non-parametric method and 57% over the existing combined parametric and non-parametric methods. © 2005 Elsevier B.V. All rights reserved.(Channel blind identification based on cyclostationarity and group delay) Narasimhan, S.V.; Hazarathaiah, M.; Giridhar, P.V.S.2005Item Linear thermal buckling and free vibration analysis are presented for functionally graded cylindrical shells with clamped-clamped boundary condition based on temperature-dependent material properties. The material properties of functionally graded materials (FGM) shell are assumed to vary smoothly and continuously across the thickness. With high-temperature specified on the inner surface of the FGM shell and outer surface at ambient temperature, 1D heat conduction equation along the thickness of the shell is applied to determine the temperature distribution; thereby, the material properties based on temperature distribution are made available for thermal buckling and free vibration analysis. First-order shear deformation theory along with Fourier series expansion of the displacement variables in the circumferential direction are used to model the FGM shell. Numerical studies involved the understanding of the influence of the power-law index, r/h and l/r ratios on the critical buckling temperature. Free vibration studies of FGM shells under elevated temperature show that the fall in natural frequency is very drastic for the mode corresponding to the lowest natural frequency when compared to the lowest buckling temperature mode. © 2005 Elsevier Ltd. All rights reserved.(Academic Press, Buckling and free vibration analysis of functionally graded cylindrical shells subjected to a temperature-specified boundary condition) Kadoli, R.; Ganesan, N.2006Item Higher order refined computational models for the free vibration analysis of antisymmetric angle ply plates(2008) Swaminathan, K.; Patil, S.S.Analytical formulations using two higher order refined displacement models have been developed and solutions presented for the first time to the natural frequency analysis of antisymmetric angle-ply composite and sandwich plates. These computational models already reported in the literature are based on Taylor's series expansion of the displacements in the thickness coordinate and consider the realistic parabolic distribution of transverse shear strains through the laminate thickness. One of them, with 12 degrees of freedom, considers the effects of both transverse shear and normal strain/stress while the other with 9 degrees of freedom includes only the effect of transverse shear deformation. In addition to above, a few higher order models and the first order model developed by other investigators and available in the literature are also considered for the evaluation. A simply supported plate is considered throughout as a test problem. The equations of motion are obtained using Hamilton's principle. Solutions are obtained in closed form using Navier's technique by solving the eigenvalue equation. Plates with varying slenderness ratios, number of layers, fiber orientations, degrees of anisotropy, edge ratios and thickness of core to thickness of face sheet ratios are considered for the analysis. Accuracy of the theoretical formulations and the solution method is first ascertained by comparing the results with those already available in the literature. After establishing the accuracy of the solutions, extensive numerical results are presented for the free vibration analysis of multilayer antisymmetric angle-ply composite and sandwich plates using all the models, which will serve as a benchmark for future investigations. © SAGE Publications 2008.Item Influence of masonry infill on fundamental natural frequency of 2D RC frames(2010) Chethan, K.; Ramesh Babu, R.; Venkataramana, K.; Sharma, A.Reinforced Concrete (RC) framed structures with Un-Reinforced Masonry (URM) infill panels form a major portion of all the RC framed structures worldwide. The URM panels are considered as non-structural members, which is fairly good assumption under gravity loads, however, it is not the same under lateral forces. Under seismic loads, the stiffness additions due to infill panels modify the dynamic behavior of the structure significantly by altering the frequency of the structure. A research project has been taken up at Earthquake Engineering and Vibration Research Centre (EVRC), Central Power Research Institute (CPRI), Bangalore to investigate the influence of masonry infill on fundamental natural frequency of RC frames. 2D RC frames of one bay and two bay having single storey, double storey and three storeys are cast and tested for bare frame and many combinations of URM infill panels. Tri-axial shake table is used for testing. The details of the numerical analysis and experimentation carried out in the research project are brought out in this paper.Item Studies on the influence of infill on dynamic characteristics of reinforced concrete frames(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2011) Chethan, K.; Ramesh Babu, R.; Venkataramana, K.; Sharma, A.The basic investigation under dynamic loads starts with the estimation of the natural frequencies of the structure or system under consideration. This is an important parameter under dynamic analysis. Hence a detailed study has been carried out on the influence of masonry infill (MI) on fundamental natural frequency of RC frames. MI though considered as non-structural element largely affect the strength, stiffness and ductility of the framed structure during the application of lateral forces such as wind and earthquake loads. Experimental and Numerical studies are carried out on RC frames under different configurations of MI in addition to bare frames. The RC frames are designed and detailed as per the relevant Indian standard codes. A simple numerical method has been formulated to obtain the natural frequencies of RC frames with MI using FE analysis. Tri-axial shake table is used for the determination of natural frequencies experimentally. This is a part of the collaborative project between BARC, Mumbai and CPRI, Bangalore focusing on the Response evaluation of RC frames under dynamic loading. This paper consists of numerical formulation, FE analysis, Shake table tests and comparison of results. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Free vibration studies of box type laterite masonry structures(2012) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.Box-type laterite masonry structures are widely seen in south-west coastal areas of India. Not many studies are available in the literature on the dynamic response of such structures. Free vibration analysis of box-type laterite masonry structures has been attempted in this study, as a preliminary to a detailed dynamic analysis. Finite element analysis has been conducted to And the natural frequencies and corresponding mode shapes of box-type laterite masonry buildings. Results of detailed parametric studies conducted to find the effect of various parameters like modulus of elasticity of laterite masonry, provision of a lintel band or a roof slab, openings in long walls and aspect ratio on the natural frequencies and their mode shapes of box-type laterite masonry buildings are presented and discussed in this paper.Item Effect of soil-foundation-structure interaction on fundamental frequency of rc chimneys(2013) Jayalekshmi, B.R.; Menon, D.The construction of tall reinforced concrete chimneys has been increasing, worldwide, in recent times due to industrialization. These tall and slender structures are usually wind-sensitive, requiring a dynamic analysis, to account for a proper assessment of responses under along-wind and across-wind directions and also under seismic loading. The modelling is usually carried out assuming the base (usually raft foundation supported on soil) as fixed. However, in reality, the base is compliant, due to compressibility of the soil, and this can significantly alter the dynamic characteristics of the chimney. This paper presents a comprehensive assessment of modification in the fundamental natural frequency of tapered RC chimneys in the height range of 100m to 400m due to the effect of soil-foundation-structure interaction (SFSI) through a parametric study. The parameters considered for the investigation are the height to mean base diameter ratio of the chimney, rigidity of raft foundation and the flexibility of soil. The flexibility of the supporting soil is represented by a series of Winkler springs, attached to the bottom of the raft foundation, corresponding to soft, medium and hard soils. The results of modal analysis of the three dimensional finite element model of the integrated soil-raft foundation-chimney system are compared with that of a chimney with fixed base.Item Effect of containment reinforcement on the seismic response of box type laterite masonry structures-an analytical evaluation(2013) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.Laterite blocks are used for construction of masonry walls since ages in the South-western coastal areas of India. The south-west coastal areas of India lie in zone III of seismic zonation map of Indian code IS 1893-2002. In spite of the fact that laterite is the most favored masonry material in these regions of India, the structural performance of laterite masonry has not been systematically investigated. Again there are no previous studies addressing, in detail, the seismic performance of laterite masonry buildings. Now that these areas are becoming more and more important from point of view of trade and commerce, there is a need for a detailed research on the seismic response of laterite masonry structures located in these areas. The present paper reports the results of such a study of the seismic response of box-type laterite masonry structures. Time history analysis of these structures under El-Centro acceleration has been performed using commercial finite element software ANSYS. Effect of 'containment reinforcement' on the seismic response of box type laterite masonry structures has been evaluated. © 2013 Techno-Press, Ltd.Item Dynamic soil-structure interaction studies on 275m tall industrial chimney with openings(Techno Press technop2@chollian.net, 2014) Jayalekshmi, B.R.; Thomas, A.; Shivashankar, R.In this paper, a three dimensional soil-structure interaction (SSI) is numerically simulated using finite element method in order to analyse the foundation moments in annular raft of tall slender chimney structures incorporating the effect of openings in the structure and the effect of soil flexibility, when the structure-soil system is subjected to El Centro (1940) ground motion in time domain. The transient dynamic analysis is carried out using LS-DYNA software. The linear ground response analysis program ProShake has been adopted for obtaining the ground level excitation for different soil conditions, given the rock level excitation. The radial and tangential bending moments of annular raft foundation obtained from this SSI analysis have been compared with those obtained from conventional method according to the Indian standard code of practice, IS 11089:1984. It is observed that tangential and radial moments increase with the increase in flexibility of soil. The analysis results show that the natural frequency of chimney decreases with increase in supporting soil flexibility. Structural responses increase when the openings in the structure are also considered. The purpose of this paper is to propose the need for an accurate evaluation of the soil-structure interaction forces which govern the structural response. © 2014 Techno-Press, Ltd.