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Publications (61)
The NVH design of cavities in aircraft, cars and other transportation equipment are mainly based on use of vibro-acoustic FE models to analyze low frequency structural vibration and interior noise. In order to improve the accuracy and reliability of these vibro-acoustic models, uncertainties associated with modeling of boundary conditions, joints,...
The Modal FxLMS algorithm is recently proposed for reduction of global level of noise in vibro-acoustic cavities. The algorithm minimizes acoustic potential energy expressed in modal domain which allows a choice of acoustic modes whose modal amplitudes are desired to be minimized. The working of the algorithm and its effectiveness has been demonstr...
This paper proposes a method for global active noise control in vibro-acoustic cavities using acoustic sensing under the presence of both structural and acoustic disturbances. Global active noise control has earlier been carried out by minimizing the acoustic potential energy in the cavity expressed as the sum of squares of the acoustic pressures a...
Theoretical investigations on rotor-stator rub phenomenon are available on wide range of problems. However the experimental studies are limited in numbers. Further, the measurement studies on torsional vibration during rub are hardly any. The present work reports and discusses measurement of rotor’s torsional vibrations during its contact with the...
Interior noise in vibro-acoustic cavities may be generated due to acoustic and structural disturbances. Earlier studies have shown that for global control, the maximum reduction in acoustic potential energy can be realised by using an optimum combination of acoustic and structural actuators. However, it is observed that this reduction in interior n...
In recent years, considerable research has been carried out to improve the safety of the railways. Much of the research has been in the area of development of sensors to capture health of the railway equipment. So far, no comprehensive review of literature has been carried out for condition monitoring of the railways. Most of the accidents in the r...
The present day rotors are more susceptible to rub due to reduced clearance that adversely affects the performance of the machines. In most of the theoretical investigations on rub, the structural connectivity between rotor and the stator casing is ignored and the dynamics of the rotor are studied with stator interaction as external to the system....
Investigations on rotor stator rub have always been of great significance for researches on rotating machineries. The most common model for rub investigation is friction model until recently; where some studies are carried out using contact mechanics based interaction. This technique ensures correct enforcement of constraint on the contacting bodie...
The ever-increasing need of highly efficient rotating machinery causes reduction in the clearance between rotating and non-rotating parts and increase in the chances of interaction between these parts. The rotor-stator contact, known as rub, has always been recognized as one of the potential causes of rotor system malfunctions and a source of secon...
Investigations on rotor-stator rub have been based mainly on simple friction model. Recently, some studies are carried out using contact mechanics based interaction, which presents a more realistic modelling approach. For analysing the interaction of rotor and stator parts, among various methods of constraint enforcement, Lagrange method is commonl...
The filtered-x least mean square algorithm (FxLMS) is a widely used technique in active noise control. In a conventional FxLMS algorithm, the value of convergence coefficient is kept constant which may not yield optimum performance if frequency of the primary noise changes. For some frequencies, this may result into a slower convergence and for som...
Interior noise in cavities of motorized vehicles is of increasing significance due to the lightweight design of these structures. Accurate coupled vibro-acoustic FE models of such cavities are required so as to allow a reliable design and analysis. It is, however, experienced that the vibro-acoustic predictions using these models do not often corre...
Interior noise due to structure-borne sources has always been a cause of concern in the cavities encountered in aerospace, automotive and other applications. In the design of such cavities, the coupled vibro-acoustic model is the key to evaluate its structural and acoustic design. It can also be used as a diagnostic tool to identify the potential n...
Finite element model updating techniques are used to update the finite element model of a structure in order to improve its correlation with the experimental dynamic test data. These techniques are well developed and extensively studied for the case of purely structural dynamic systems. However, the cavities encountered in automotive, aerospace and...
This paper summarizes research on dynamics of composite shafts, with an objective to develop light weight rotor systems. A review of available literature post-1996 is presented here, since a comprehensive review on similar topic was published in 1997 by Singh et al. Specifically the various aspects covered are, theories for dynamic analysis of fibe...
The present paper focuses on the dynamic behavior of fiber reinforced composite discs. Rotating discs are an important sub-component of any rotor dynamic system. Variation of natural frequencies for different fiber reinforcement configurations against rotational speed due to stress stiffening effect has been studied in detail. Critical Speed of var...
Two spool aeroengine rotors commonly have one or more intershaft rolling element bearings. Researchers have proposed some designs of intershaft bearing with squeeze film in order to reduce cross-excitation between the low pressure and the high pressure shafts of two spool rotor. These designs have a limitation, because the rotating squeeze film bec...
Parallel or/and angular misalignment between rotors connected by flexible coupling causes deformation of coupling elements and rotor shafts both. The forces and moments from flexible coupling act on driver and driven rotors simultaneously and depend upon dynamic response of coupled rotor system. The authors' aim in the present work is to propose a...
In this paper six automotive propeller shafts made of different materials are designed. Finite element modeling based on shell element is used in the eigenvalue analysis. Shaft weights, buckling torque and dynamic performance for different design alternatives, have been studied. Simulated Annealing (SA) Algorithm is used for optimization. Results o...
Analysis, design, and testing of a Magneto-Rheological Fluid (MRF) based finite Squeeze Film Damper
(SFD) integrated in a rotor-bearing system are presented herein. In numerical simulations, Reynolds
equation for a finite MRF SFD has been solved to obtain the film pressure and consequently stiffness and
damping coefficients. A mathematical model fo...
In this paper, we present the analysis of chaotic vibrations in double pendulum by experimental means. We shall illustrate the sensitivity of its motion to initial conditions i.e., the angles of each pendulum from the vertical, θ and Φ at initial time t=0. Here we present the method of video processing as an experimental technique to study the moti...
Finite element (FE) model updating is now recognized as an effective approach to reduce modeling inaccuracies present in an FE model. FE model updating has been researched and studied well for updating FE models of purely structural dynamic systems. However there exists another class of systems known as vibro-acoustics in which acoustic response is...
The higher order effects from ball bearing nonlinearities cause complex vibration characteristics in rotor ball bearing systems. The sources of nonlinearities are internal radial clearance, Hertzian contact forces between balls and races and varying compliance effect. The same authors in their earlier work have identified the sets of parameters cor...
The paper addresses some of the issues involved in the development of an all-composite aero gas turbine engine rotor with a view to reducing the total engine weight and increasing the thrust-weight ratio beyond 20: I. It identifies the materials to be used for different components, i.e. shafts, discs and blades in the high and iow temperature regio...
The study provides an insight into the non-linear dynamic analysis of a two spool aero gas turbine rotor system. A nonlinear finite element model of the twin spool system is developed using Timoshenko beam element, considering the elastic deflections of the bearings and resulting nonlinear Hertz contact forces, coupled with the radial clearances pr...
Analysis, design, and testing of a Magneto-Rheological Fluid (MRF) based finite Squeeze Film Damper (SFD) integrated in a rotor-bearing system are presented herein. In numerical simulations, Reynolds equation for a finite MRF SFD has been solved to obtain the film pressure and consequently stiffness and damping coefficients. A mathematical model fo...
The flexible rotor modeling has an advantage over rigid rotor modeling, by its suitability to model rotors of complex shapes
with multiple discs and bearings. In this paper, the non-linear dynamic behavior of a horizontal unbalanced flexible rotor
supported on deep groove ball bearings is theoretically studied in detail for instability and chaos. A...
In this paper, a horizontal flexible rotor supported on two deep groove ball bearings is theoretically investigated for instability and chaos. The system is bi-periodically excited. The two sources of excitation are: rotating imbalance and self excitation due to varying compliance effect of ball bearing. A generalized Timoshenko beam FE formulation...
Application of two smart materials, namely shape memory alloy (SMA) and magnetorheological fluid (MRF) for rotor vibration control is explored to control the synchronous vibration of rotors crossing resonance condition. First a single degree of freedom system is analyzed to study the effect of SMA and MR fluid damper individually, and then the simu...
Free and forced vibration experiments are performed on a two blade system coupled with a floating friction pin. Primary motivation is to understand the system behavior and the effective damping provided by the frication pin as a function of the pin normal force. The blades lock up at low amplitudes and the effect of pin normal force on this is also...
Large resonant amplitudes during passage through critical speed lead to higher value of bending stresses and a possibility of fatigue failure or reduction in the life of the rotor. In this paper, structural component in the form of support springs made of Shape Memory Alloy have been used in the rotor support in an attempt to avoid resonance condit...
The rotor-bearing systems having rolling element bearings are commonly prone to resonance and instability due to its low inherent damping characteristics. Thus, squeeze film dampers (SFD) are normally used to enhance the damping in such systems. In order to have controllable damping characteristics of squeeze film damper, Magneto-rheological Fluid...
In the present work, the nonlinear dynamic response of an unbalanced horizontal flexible rotor supported by deep groove ball bearing is studied. Nonlinearity effects in rolling element bearings arise from Hertzian contact force deformation relationship and clearance between rolling elements and races. The system is bi-periodically excited due to va...
In this paper the natural frequencies of composite tubular shafts have been analysed. Equivalent modulus beam theory (EMBT) with shear deformation, rotary inertia and gyroscopic effects has been modified and used for the analysis. The modifications take into account effects of stacking sequence and different coupling mechanisms present in composite...
This article examines the effect of radial gap between impeller and diffuser on vibration and noise in a centrifugal pump under different flow conditions. Three radial gaps are considered in this study. For each radial gap, the flow is varied by throttling of delivery and suction valves, respectively. For each case of radial gap and flow condition,...
Theoretical and experimental studies have been carried out on deflection and cross-section deformation of tubular composite shafts subjected to point static loading. Out of plane displacement, which is absent for metallic shaft/beams, is observed. Experimental result for (±45°)2 shaft compares qualitatively with that obtained theoretically.
An experimental analysis has been done to analyze the effect of ball bearing support for a rigid, horizontal rotor. The effect of radial internal clearance of a ball bearing on its stiffness is studied by setting up a rigid, horizontal Jeffcott rotor supported by same type of ball bearings with known radial internal clearance. The nonlinear dynamic...
In this study a fiber-reinforced composite shaft design is optimized. The optimization procedure is carried out in two stages. First, the shaft natural frequency is maximized with the constraint imposed on the shaft buckling torque and torsional strength. In the second stage of optimization, shaft weight is minimized with the constraint imposed on...
The response of a balanced horizontal rigid motor rotor supported by a deep groove ball bearing is theoretically simulated. The effect of radial internal clearance of the ball bearing on the dynamic response of the rotor is studied. The system equations have been numerically integrated, the results of which have been validated with harmonic balance...
The non-linear dynamic analysis of a horizontal rigid rotor having unbalance and supported on ball bearings has been done. The non-linearity is both due to Hertzian contact and the radial internal clearance. The system is excited by the varying compliance frequency and the rotational frequency. For finding out the fixed point and stability of the s...
The low pressure last stage blades in a steam turbine are some of the most severely stressed machine elements under centrifugal loading. The stresses in the root region near a strain raiser are in the plastic range. The conventional analysis is based on elastic theories and any stresses found beyond the ultimate tensile strength in a small zone are...
An eight noded mixed shell element for the vibration analysis of rotating cambered helicoidal blades is presented. The strain displacement relations of Gol den’veizer are used and Reissner’s functional is adopted in deriving this element. The effect of initial in-plane stresses is also included. Also, expressions for the pressure difference between...
Investigation of failures in connectors of compressor suction and discharge lines in roof mounted package air conditioners designed for use in passenger coaches of Indian Railways was the objective of the study. The connectors consisted of copper pipe and corrugated red brass flexible tubing reinforced with bronze wire braiding. Resonance between t...
A procedure for the vibration analysis of rotating cambered helicoidal blades using curved shell finite element based on Mindlin theory is given. The strain displacement relations of Gol den’veizer are used in the development of a thick doubly curved helicoidal shell element including initial in-plane stress effect. The method is applied to rotatin...
Rotordynamic experiments are performed on two hollow tubular Carbon/Epoxy filament wound composite shafts. The experiments comprise of determination of critical speed and unbalance response as well as orbital and spectrum analysis. Step-wise progressive balancing near the critical speed was needed to operate the shaft in the super-critical region....
Rotordynamic experiments are performed on two hollow tubular Carbon/Epoxy filament wound composite shafts. The experiments comprise of determination of critical speed and unbalance response as well as orbital and spectrum analysis. Step-wise progressive balancing near the critical speed was needed to operate the shaft in the super-critical region....
A carbon-epoxy shaft is fabricated by a filament winding technique. Delaminations are introduced during fabrication. A simple experimental setup for rotation of a composite shaft is designed and fabricated. The composite shaft is subjected to cyclic loadings because of unbalance excitation. The delamination zones are radiographed to determine the c...
A dual rotor rig is developed and is briefly discussed. The rig is capable of simulating dynamically the two spool aeroengine, though it does not physically resemble the actual aeroengine configuration. Critical speeds, mode shape, and unbalance response are determined experimentally. An extended transfer matrix procedure in complex variables is de...
The main objective of the paper is to study the effect of rotary inertia and gyroscopic moments due to lumped masses on the dynamics of two spool aeroengine rotors. Since the rotary inertia effect is well established, the thrust of the paper is on the effect of gyroscopic moments. Quantitative as well as qualitative aspects are studied. Effect of g...
Free vibration characteristics of a rotating pretwisted small aspect ratio blade, mounted on a disc at a stagger angle, are determined using classical bending theory of thin shells. Differential geometry of the blade in curvilinear coordinates are analysed and strain-displacement relations are established. The strain and kinetic energies of the rot...
This paper is concerned with experimental determination of overall damping in a rotating turbine disc-blade system. A test spin rig has been designed and fabricated. Nozzle Passing Excitation is simulated by electromagnets. Transient excitation of rotating blades is caused by suddenly shutting off the excitation to the rotating blades. Frequency an...
A pretwisted cantilever plate is treated as a thin shallow shell. Its potential and kinetic energies in torsional vibration are determined by assuming an appropriate displacement field. Applying Hamilton's principle, the problem is reduced to a fourth-order ordinary differential equation with constant coefficients, which is solved to obtain the fir...
