Sujatha Chandramohan - Academia.edu (original) (raw)

Papers by Sujatha Chandramohan

Applied Mathematical Modelling, 2012

In this paper, three-dimensional elasticity solution is extended to investigate a FGPM finite len... more In this paper, three-dimensional elasticity solution is extended to investigate a FGPM finite length, simply supported shell panel under dynamic pressure excitation. The host panel is assumed to be of some functionally graded piezoelectric material (FGPM). The ordinary differential equations (o.d.e.) are derived from the highly coupled partial differential equations (p.d.e.) using series expansions of mechanical and electrical displacements. The resulting system of ordinary differential equations is solved by means of Galerkin finite element method. At last, numerical examples are presented for a FGPM shell panel. To verify the validity of code and formulation, the results of a FGM panel and a FGM plate are compared with the published results.

EUROSENSORS 2018, 2018

In this paper, the behavior of a piezoelectric stack generator subject to a direct mechanical for... more In this paper, the behavior of a piezoelectric stack generator subject to a direct mechanical force, such as that experienced by pedestrian loads, is characterized and modelled. A lumped element model is developed that describes the electrical output of piezoelectric stack generators for quasi-static, off-resonance and random input conditions which are typical of underfloor or supporting structure energy harvesters. This research demonstrates the ability for accurate predictions of output voltage and current based on the material properties and geometry of the piezoelectric stack. The behavior of real-world random loading patterns is incorporated in the model, pairing mechanical input with interfacing circuitry requirements in order to maximize energy transfer. The developed model facilitates time-efficient design by reducing the simulation time to the order of seconds.

Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2007

The present paper describes the conceptual design, simulation, and fabrication of a magnetorheolo... more The present paper describes the conceptual design, simulation, and fabrication of a magnetorheological (MR) fluid variable-valve actuation (WA) system. Two set-ups, one for testing the conceptual design and the other for application of the MR valve on a real engine, have been developed. The test set-up measures the displacement of the valve, which operates by the cam-follower mechanism. The results of valve lifts at different speeds and control currents are presented. To implement the MR fluid VVA system, a four-stroke single-cylinder Kirloskar TV1 vertical diesel engine has been selected. Inlet and exhaust manifolds have been modelled to estimate volumetric efficiency. The equations governing the unsteady air flow in the ducts have been solved using the method of characteristics. A numerical code to simulate the entire gas exchange process has been developed, and the results have been compared with the experimental results. Further, this code has been used to identify the optimal v...

ASME 2013 Gas Turbine India Conference, 2013

Aero-elastic excitation can result in excessive blade vibration, which can cause blades to fail i... more Aero-elastic excitation can result in excessive blade vibration, which can cause blades to fail in high cycle fatigue (HCF). A severe aero-elastic failure can result in a complete blade separation and loss of thrust and loss of a blade can mean the loss of an aircraft. The primary aeromechanical design concerns are blade flutter and forced vibration that need to be quantified at the early part of engine tests. This paper details the experimental investigation carried out on a transonic shroudless low aspect ratio fan bladed disk that experienced subsonic/transonic stall flutter and forced vibration excitation. Experiments are performed on a full scale engine using tip timing sensors flush mounted on the fan casing to characterize the vibratory responses during flutter and forced vibration conditions during engine operation. Numerical simulations are performed using computational fluid dynamic (CFD) analysis. Blade natural frequencies and mode shapes are obtained from finite element ...

Critical hunting speed and running safety are important aspects of the dynamic behavior of railwa... more Critical hunting speed and running safety are important aspects of the dynamic behavior of railway vehicles. In this paper, a study of the dynamic behaviour of a single railway vehicle truck running on tangent and curved tracks is carried out using a mathematical model of the combined system. It is seen from literature that there are no reported studies using the combined truck/curved track system in which rail lateral displacement is computed considering two point wheel/rail contact for evaluation of critical hunting speed, as well as derailment due to wheel climb. In this study, the truck (Figure 1) consists of the truck frame with suspended wheelsets (Figure 2), while the track is idealized as a laterally flexible rail modelled as a spring mass damper system (Figure 3). The combined truck/track system has 10 degrees of freedom (DOF), consisting of the lateral displacement and yaw angle of the wheelsets and truck frame, as well as the lateral displacement of the left and right rai...

2020 6th International Conference on Control, Automation and Robotics (ICCAR), 2020

Vehicle rollovers are known to produce the highest number of deaths amongst vehicle accidents. Ro... more Vehicle rollovers are known to produce the highest number of deaths amongst vehicle accidents. Rollover prevention systems currently available in commercial vehicles attempts to prevent any wheel lift-off the ground to avoid a subsequent rollover. In literature, attempts that were made to recover a vehicle from a tip-over point after a wheel lift-off has occurred are only a few. The present article proposes a State Dependent Riccati Equation (SDRE) based anti-rollover controller to recover a vehicle from tip-over point. SDRE method delivers a simple yet effective solution to the nonlinear optimal control problem. An Inverted Double Pendulum on a Cart Model (IDPC) acts as the base model in the controller. The tip-over point of the IDPC model is an unstable equilibrium point of the model and the gravity torque has a negligibly small effect in this vicinity. In the SDRE method, this unstable equilibrium point acts as a singularity point. A virtual rollover torque is used with the IDPC ...

Journal of The Institution of Engineers (India): Series C, 2017

Strategies often proposed to combat the growing traffic congestion problems of urban environments... more Strategies often proposed to combat the growing traffic congestion problems of urban environments target enhancements to increase the use of bus transit. Therefore, service providers are keen to identify and understand factors that could attract more transit riders. Other than affordability, most researchers explored convenience and stress factors such as schedule uncertainty, waiting time, travel time, crowding, noises, and smells. However, few studies evaluated the significance of ride quality. The high cost to collect and analyze roughness data likely deters such studies. This work developed a low-cost smartphone based method and associated data transforms to characterize ride quality for non-uniform speed profiles. The method distinguished between vibrations induced from road unevenness and operator behavior. The authors validated the accuracy of the method by conducting surveys to characterize the perceived roughness intensities from buses traveling routes of distinctly different roughness levels. The surveys found that smooth rides mattered to most passengers, and that rough rides could even lead to some loss of ridership. Additionally, the authors proposed a theory of roughness acclimation and provided some evidence that unlike objective measurements, subjective assessments of ride quality could lead to significant biases and inconsistencies.

Journal of The Institution of Engineers (India): Series C, 2018

Designing the suspension system of a tracked combat vehicle (CV) is really challenging as it has ... more Designing the suspension system of a tracked combat vehicle (CV) is really challenging as it has to satisfy conflicting requirements of good ride comfort, vehicle handling and stability characteristics. Many studies in this field have been reported in literature and it has been found that torsion bars satisfy the designer's conflicting requirements of good ride and handling and thus have reserved a place for themselves as the most widely used suspension system for military track vehicles. Therefore, it is imperative to evaluate the effectiveness of the torsion bar under dynamic conditions of undulating terrain and validating the same by correlating it with computer simulation results. Thus in the present work, the dynamic simulation of a 2N ? 4 degrees of freedom (DOF) mathematical model has been carried out using MATLAB Simulink and the vibration levels were also measured experimentally on a 12 wheel stationed high mobility military tracked infantry combat vehicle (ICV BMP-II) traversing different terrain, that is, Aberdeen proving ground (APG) and Sinusoidal, at a constant vehicle speed. The dynamic force transmitted to the hull CG through the 12 torsion bar suspension systems was computed to be around 26,700 N and found to match the measured values. The vibration isolation of the torsion bar in bounce was found to be effective, with a transmissibility from the road wheel to the hull of about 0.6.

SAE Technical Paper Series, 2019

International Journal of Engineering, 2019

In this work, a magnetorheological (MR) damper based above-knee prosthesis is design and evaluate... more In this work, a magnetorheological (MR) damper based above-knee prosthesis is design and evaluated based on its performance in swing phase and in stance phase. Initially, a dynamic system model for swing phase of a prosthetic leg incorporating a single-axis knee with ideal MR damper was built. The dynamic properties of the damper are represented with Bingham parametric model. From Bingham model, governing damper parameters that determine the damping force and piston displacement of the damper are identified and optimized so as to enable the single-axis knee to nearly mimick the natural swing phase trajectory of a healthy person for level-ground walking as obtained from experimental data. Then, with the optimal damper parameters, an MR damper valve constrained in a desired cylindrical volume is developed. Finally, the prosthetic knee with the MR damper is evaluated for its performance during stance phase, based on ISO standard loading condition for the intended application. The results show that, compare to Rheo knee ® , the MR damper based prosthetic knee has achieved up to 68% reduction by volume and 40% reduction by weight.

IETE Journal of Research, 1986

An approach to design a digital fibre optic receiver is given. Various types of receivers designe... more An approach to design a digital fibre optic receiver is given. Various types of receivers designed so far are reviewed with emphasis on long wavelength systems and compared both from the design and performance points of view.

SAE Technical Paper Series, 2017

Tribology Online, 2010

Gear teeth wear, in most cases, by a smooth process giving initially good contact conditions, fol... more Gear teeth wear, in most cases, by a smooth process giving initially good contact conditions, followed by a very slow and gradual process. Further, continuous progression of tooth wear may cause unfavorable changes of surface topography, thereby, giving rise to worsened contact situations. The metal removed from the worn teeth surfaces enter into the machine system and can, in turn, cause failure of other components, finally resulting in a severe form of tooth failure. The causes and subsequent prevention of the damage due to wear can be studied by oil/wear particle analysis of lubricants under operating conditions. This paper describes the results of experimental studies performed for evaluation of lubricant film thickness, wear particle analysis based on their morphology, metal composition analysis of lubricants using X-ray fluorescence, atomic absorption spectrometry (AAS) and Energy dispersive spectrometry (EDS). These results have been correlated with wear.

Journal of Vibration and Control, 2011

The most common gear wear mechanisms, such as micropitting, pitting and scouring often occur in t... more The most common gear wear mechanisms, such as micropitting, pitting and scouring often occur in the early stage of failure. For the geared system operating in the presence of such surface failures, the load acts only over a finite region and contact stress tends to increase enormously in the contact area of the mating teeth surface. The propagation of tooth damage causes instantaneous reduction in tooth stiffness. The vibration signal of gear transmission varies as the stiffness changes. Therefore the connection between surface fatigue failure, stiffness and vibration signal are of significant importance in monitoring gear defects. The purpose of this study is to conduct experimental investigations on the measurement of reduction in the gear teeth stiffness along with vibrations parameters. A pair of spur gears was tested under an accelerated test condition in an oil bath lubricated back-to-back gearbox. Experimental measurement of stiffness was carried out using modal analysis in c...

International Journal of Engineering, Transactions B: Applications, 2017

Smart Materials and Structures, 2019

International Journal of Automotive Technology, 2011

In the design and development of high-speed tracked vehicles, it is necessary to have an understa... more In the design and development of high-speed tracked vehicles, it is necessary to have an understanding of the interrelationship between the terrain factors and the vehicle characteristics during steering. The handling behavior of skidsteered tracked vehicles is more complex than that of wheeled vehicles because of non-linear characteristics arising from the sliding interface between the track and the ground. In the present work, a five degree-of-freedom (DOF) steering model of a tracked vehicle is developed, and the handling behavior during non-stationary motion is studied when operating at high and low speeds. It is demonstrated that the inclusion of roll and pitch DOF changes the steering response when compared to the response from three DOF models proposed earlier by several researchers. This is due to the strong coupling between the pitch and yaw motions. The effect of the initial forward velocities on the trajectory of the vehicle during non-stationary motion is also studied. It is observed from the results that the stability is influenced by the type of steering input, steering ratio and vehicle forward speed.

Journal of vibration engineering & technologies, Apr 18, 2023

Mechanisms and machine science, Oct 7, 2022