sujatha chandramohan - Academia.edu (original) (raw)
Papers by sujatha chandramohan
International Journal of Engineering, Transactions B: Applications, 2017
Abstract: <i>Introduction</i><br/><br/>A magnetorheological elastomer (MR... more Abstract: <i>Introduction</i><br/><br/>A magnetorheological elastomer (MRE) is a composite material with magnetic particles suspended or arranged within a non-magnetic elastomer matrix [1]. On the application of the magnetic field, it exhibits controllable stiffness and damping properties. When compared to a magnetorheological fluid, MRE has added advantage that it is leak-proof, deposition resistant, has a wide range of controllable properties, compatibility to mechanical components, and has a fast response and low power requirements. These advantages make it a very good option in various engineering applications. Changes in composition, shape and size of the MRE has led to a wide range of applications in vibration absorber, adaptive base isolator, and sandwich beams [2].<br/>The magnetic field generated inside the MRE plays an important role in evaluating its properties based on the external load. However, due to non-availability of B-H curve data for...
Mechanisms and machine science, Oct 7, 2022
International Journal of Heavy Vehicle Systems, 2021
Proceedings of the 10th ECCOMAS Thematic Conference on MULTIBODY DYNAMICS, 2021
Tribology International, 2009
Gears are one of the most common mechanisms for transmitting power and motion and their usage can... more Gears are one of the most common mechanisms for transmitting power and motion and their usage can be found in numerous applications. Studies on gear teeth contacts have been considered as one of the most complicated applications in tribology. Depending on the application, the speed and load conditions of teeth may change triggering several types of failures on teeth surface such as wear, scuffing, micro-pitting and pitting. The above-mentioned faults influence changes in vibration and acoustic signals, due to changes in operating conditions such as increase in temperature and decrease in lubricant film thickness and specific film thickness. These abnormal changes result in cumulative effects on localised or distributed faults on load bearing surfaces of gears. Such damages cause reduction in tooth stiffness and severity of damage can be assessed by evaluating the same using vibration-based signals. This paper presents the results of experimental investigations carried out to assess wear in spur gears of back-to-back gearbox under accelerated test conditions. The studies considered the estimation of operating conditions such as film thickness and their effects on the fault growth on teeth surface. Modal testing experiments have been carried out on the same gear starting from healthy to worn out conditions to quantify wear damage. The results provide a good understanding of dependent roles of gearbox operating conditions and vibration parameters as measures for effective assessment of wear in spur gears.
International Journal of Automotive Technology, 2011
We study the excitonic dynamics of a driven quantum dot under the influence of a phonon environme... more We study the excitonic dynamics of a driven quantum dot under the influence of a phonon environment, going beyond the weak exciton-phonon coupling approximation. By combining the polaron transform and time-local projection operator techniques we develop a master equation that can be valid over a much larger range of exciton-phonon coupling strengths and temperatures than the standard weak-coupling approach. For the experimentally relevant parameters considered here, we find that the weak-coupling and polaron theories give very similar predictions for low temperatures (below 30 K), while at higher temperatures we begin to see discrepancies between the two. This is due to the fact that, unlike the polaron approach, the weak-coupling theory is incapable of capturing multiphonon effects, while it also does not properly account for phonon-induced renormalisation of the driving frequency. In particular, we find that the weak-coupling theory often overestimates the damping rate when compared to that predicted by the polaron theory. Finally, we extend our theory to include non-Markovian effects and find that, for the parameters considered here, they have little bearing on the excitonic Rabi rotations when plotted as a function of pulse area.
SAE Technical Paper Series, 2017
A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in in... more A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in increased gait function. In this work, a hydraulic damper and a magnetorheological (MR) damper are designed as controllers with an objective of evaluating their performance in controlling swing-phase damping in an above-knee prosthesis. Parametric models are utilized to represent dynamic properties of the dampers. Based on the models, control parameters that govern damping force and displacement of the dampers are identified. Parameters of the dampers are determined through optimization that minimizes the error between the prosthesis knee angle trajectories and a desired knee angle trajectory for normal level ground walking from experimental data. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to determine sets of control parameters. Furthermore, input thigh motion is also deviated to evaluate robustness of the controllers in real application. Com...
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...
Journal of Intelligent Material Systems and Structures, 2021
The aim of this embodiment is to present an analytical analysis of a functionally graded piezoele... more The aim of this embodiment is to present an analytical analysis of a functionally graded piezoelectric energy harvester consisting of a flexible functionally graded piezoelectric layers carrying magnetic mass at the free end. The magnetic tip mass is in interaction with a permanent magnet which is located at a distance from the top of the tip mass. The oscillation of the harvester happens via excitation of the base. Using Rayleigh’s beam theory and Hamilton’s principle and considering geometric nonlinearity, the coupled electromechanical governing equations have been developed. The nonlinear frequency response of the piezoelectric energy harvester beam has also been studied under base excitation. A parametric study has been carried out to investigate the effect of grading index and magnetic force on responses of both free vibration and induced excitation cases. The results were compared with those obtained using three-dimensional finite element model developed in COMSOL Multiphysics...
The primary purpose of this paper is to identify performance indices and evaluate a design of a m... more The primary purpose of this paper is to identify performance indices and evaluate a design of a mono-tube MR damper valve, as a result of which relations among performance indices and possible design approaches are explored. To achieve this, initial design of a mono-tube MR damper valve is considered. Common MR damper valve configuration is adopted to which initial design parameters are specified. Performance indices that need to be considered while evaluating the design of a mono-tube magnetorheological (MR) damper valve are identified, and mathematical models are developed. The performance indices of the damper valve depend upon the magnetic circuit design of the valve; hence, for the adopted MR damper valve configuration, finite element model is built to analyze and investigate the performance indices of a 2-D axisymmetric MR damper valve. All performance indices of the damper valve are simulated within given range of input current and number of turns of coil. The simulation resu...
Human gait is characterized by periodic repetitions of two phases: a stance phase in which a foot... more Human gait is characterized by periodic repetitions of two phases: a stance phase in which a foot is in contact with the ground, followed by a swing phase in which the lower limb swings through after toe-off. The functional necessities of above-knee prostheses are to provide knee locking during the stance phase and damping during the swing phase. Most of the conventional above-knee prostheses are based on passive mechanisms with constant mechanical properties such as friction, spring and damping coefficients. However, these designs are unstable while mimicking the natural gait, due to lack of active knee joint control. On the other hand, active type prostheses, such as those with hydraulic actuation (C Leg, Otto Bock) and a magnetorheological (MR) brake (Rheo Knee, Össur) can produce a gait similar to that of normal persons effectively, but they are expensive, heavy and consume significant energy. Therefore, in this paper a platform for designing semi-active type above-knee prosthes...
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 ...
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 ...
With the increasing demand for the accessibility of tractor-semitrailers in remote locations, the... more With the increasing demand for the accessibility of tractor-semitrailers in remote locations, they face the problem of off-tracking, which is the ensuing difference in path radii between the front and rearmost axles of a vehicle as it manoeuvres a turn. One of the passive methods to reduce off-tracking is by implementing Split fifth wheel coupling (SFWC) which has been proposed earlier. In the present work, the tractor-semitrailer with SFWC is subjected to zero-speed off-tracking analysis, wherein the effect of speed is neglected and the results are compared with those of Conventional fifth wheel coupling (CFWC) model. In the current paper, two turning manoeuvres are studied, viz., 90° turn and 180° turn. It is observed that for all the combinations of chosen type of turning manoeuvre and turning radius, the SFWC model noticeably reduces off-tracking when compared to the tractor-semitrailer of similar dimensions with CFWC.
International Journal of Engineering
The main purpose of this paper is to study various configurations of a magnetorheological (MR) da... more The main purpose of this paper is to study various configurations of a magnetorheological (MR) damper valve and to evaluate their performance indices typically dynamic range, valve ratio, inductive time constant and pressure drop. It is known that these performance indices (PI) of the damper depend upon the magnetic circuit design of the valve. Hence, nine valve configurations are considered for which mathematical models are developed. A finite element model is built to analyze and investigate the PI of a 2-D axi-symmetric MR damper valve. All configurations of the damper valve are simulated within a given range of input current and number of turns of coil, and within this range, damping force, dynamic range, valve ratio, inductive time constant and achieved pressure drop have been evaluated. The simulation results show that the PI of the MR damper are highly dependent on the shapes of valves and hence the valve shape should be selected based on the intended application. The results obtained in this work provide an insight for designers to create application-specific MR dampers.
International Journal of Engineering
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.
International Journal of Engineering, Transactions B: Applications, 2017
Abstract: <i>Introduction</i><br/><br/>A magnetorheological elastomer (MR... more Abstract: <i>Introduction</i><br/><br/>A magnetorheological elastomer (MRE) is a composite material with magnetic particles suspended or arranged within a non-magnetic elastomer matrix [1]. On the application of the magnetic field, it exhibits controllable stiffness and damping properties. When compared to a magnetorheological fluid, MRE has added advantage that it is leak-proof, deposition resistant, has a wide range of controllable properties, compatibility to mechanical components, and has a fast response and low power requirements. These advantages make it a very good option in various engineering applications. Changes in composition, shape and size of the MRE has led to a wide range of applications in vibration absorber, adaptive base isolator, and sandwich beams [2].<br/>The magnetic field generated inside the MRE plays an important role in evaluating its properties based on the external load. However, due to non-availability of B-H curve data for...
Mechanisms and machine science, Oct 7, 2022
International Journal of Heavy Vehicle Systems, 2021
Proceedings of the 10th ECCOMAS Thematic Conference on MULTIBODY DYNAMICS, 2021
Tribology International, 2009
Gears are one of the most common mechanisms for transmitting power and motion and their usage can... more Gears are one of the most common mechanisms for transmitting power and motion and their usage can be found in numerous applications. Studies on gear teeth contacts have been considered as one of the most complicated applications in tribology. Depending on the application, the speed and load conditions of teeth may change triggering several types of failures on teeth surface such as wear, scuffing, micro-pitting and pitting. The above-mentioned faults influence changes in vibration and acoustic signals, due to changes in operating conditions such as increase in temperature and decrease in lubricant film thickness and specific film thickness. These abnormal changes result in cumulative effects on localised or distributed faults on load bearing surfaces of gears. Such damages cause reduction in tooth stiffness and severity of damage can be assessed by evaluating the same using vibration-based signals. This paper presents the results of experimental investigations carried out to assess wear in spur gears of back-to-back gearbox under accelerated test conditions. The studies considered the estimation of operating conditions such as film thickness and their effects on the fault growth on teeth surface. Modal testing experiments have been carried out on the same gear starting from healthy to worn out conditions to quantify wear damage. The results provide a good understanding of dependent roles of gearbox operating conditions and vibration parameters as measures for effective assessment of wear in spur gears.
International Journal of Automotive Technology, 2011
We study the excitonic dynamics of a driven quantum dot under the influence of a phonon environme... more We study the excitonic dynamics of a driven quantum dot under the influence of a phonon environment, going beyond the weak exciton-phonon coupling approximation. By combining the polaron transform and time-local projection operator techniques we develop a master equation that can be valid over a much larger range of exciton-phonon coupling strengths and temperatures than the standard weak-coupling approach. For the experimentally relevant parameters considered here, we find that the weak-coupling and polaron theories give very similar predictions for low temperatures (below 30 K), while at higher temperatures we begin to see discrepancies between the two. This is due to the fact that, unlike the polaron approach, the weak-coupling theory is incapable of capturing multiphonon effects, while it also does not properly account for phonon-induced renormalisation of the driving frequency. In particular, we find that the weak-coupling theory often overestimates the damping rate when compared to that predicted by the polaron theory. Finally, we extend our theory to include non-Markovian effects and find that, for the parameters considered here, they have little bearing on the excitonic Rabi rotations when plotted as a function of pulse area.
SAE Technical Paper Series, 2017
A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in in... more A prosthetic swing-phase control mechanism simulates the action of thigh musculature to aid in increased gait function. In this work, a hydraulic damper and a magnetorheological (MR) damper are designed as controllers with an objective of evaluating their performance in controlling swing-phase damping in an above-knee prosthesis. Parametric models are utilized to represent dynamic properties of the dampers. Based on the models, control parameters that govern damping force and displacement of the dampers are identified. Parameters of the dampers are determined through optimization that minimizes the error between the prosthesis knee angle trajectories and a desired knee angle trajectory for normal level ground walking from experimental data. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to determine sets of control parameters. Furthermore, input thigh motion is also deviated to evaluate robustness of the controllers in real application. Com...
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...
Journal of Intelligent Material Systems and Structures, 2021
The aim of this embodiment is to present an analytical analysis of a functionally graded piezoele... more The aim of this embodiment is to present an analytical analysis of a functionally graded piezoelectric energy harvester consisting of a flexible functionally graded piezoelectric layers carrying magnetic mass at the free end. The magnetic tip mass is in interaction with a permanent magnet which is located at a distance from the top of the tip mass. The oscillation of the harvester happens via excitation of the base. Using Rayleigh’s beam theory and Hamilton’s principle and considering geometric nonlinearity, the coupled electromechanical governing equations have been developed. The nonlinear frequency response of the piezoelectric energy harvester beam has also been studied under base excitation. A parametric study has been carried out to investigate the effect of grading index and magnetic force on responses of both free vibration and induced excitation cases. The results were compared with those obtained using three-dimensional finite element model developed in COMSOL Multiphysics...
The primary purpose of this paper is to identify performance indices and evaluate a design of a m... more The primary purpose of this paper is to identify performance indices and evaluate a design of a mono-tube MR damper valve, as a result of which relations among performance indices and possible design approaches are explored. To achieve this, initial design of a mono-tube MR damper valve is considered. Common MR damper valve configuration is adopted to which initial design parameters are specified. Performance indices that need to be considered while evaluating the design of a mono-tube magnetorheological (MR) damper valve are identified, and mathematical models are developed. The performance indices of the damper valve depend upon the magnetic circuit design of the valve; hence, for the adopted MR damper valve configuration, finite element model is built to analyze and investigate the performance indices of a 2-D axisymmetric MR damper valve. All performance indices of the damper valve are simulated within given range of input current and number of turns of coil. The simulation resu...
Human gait is characterized by periodic repetitions of two phases: a stance phase in which a foot... more Human gait is characterized by periodic repetitions of two phases: a stance phase in which a foot is in contact with the ground, followed by a swing phase in which the lower limb swings through after toe-off. The functional necessities of above-knee prostheses are to provide knee locking during the stance phase and damping during the swing phase. Most of the conventional above-knee prostheses are based on passive mechanisms with constant mechanical properties such as friction, spring and damping coefficients. However, these designs are unstable while mimicking the natural gait, due to lack of active knee joint control. On the other hand, active type prostheses, such as those with hydraulic actuation (C Leg, Otto Bock) and a magnetorheological (MR) brake (Rheo Knee, Össur) can produce a gait similar to that of normal persons effectively, but they are expensive, heavy and consume significant energy. Therefore, in this paper a platform for designing semi-active type above-knee prosthes...
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 ...
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 ...
With the increasing demand for the accessibility of tractor-semitrailers in remote locations, the... more With the increasing demand for the accessibility of tractor-semitrailers in remote locations, they face the problem of off-tracking, which is the ensuing difference in path radii between the front and rearmost axles of a vehicle as it manoeuvres a turn. One of the passive methods to reduce off-tracking is by implementing Split fifth wheel coupling (SFWC) which has been proposed earlier. In the present work, the tractor-semitrailer with SFWC is subjected to zero-speed off-tracking analysis, wherein the effect of speed is neglected and the results are compared with those of Conventional fifth wheel coupling (CFWC) model. In the current paper, two turning manoeuvres are studied, viz., 90° turn and 180° turn. It is observed that for all the combinations of chosen type of turning manoeuvre and turning radius, the SFWC model noticeably reduces off-tracking when compared to the tractor-semitrailer of similar dimensions with CFWC.
International Journal of Engineering
The main purpose of this paper is to study various configurations of a magnetorheological (MR) da... more The main purpose of this paper is to study various configurations of a magnetorheological (MR) damper valve and to evaluate their performance indices typically dynamic range, valve ratio, inductive time constant and pressure drop. It is known that these performance indices (PI) of the damper depend upon the magnetic circuit design of the valve. Hence, nine valve configurations are considered for which mathematical models are developed. A finite element model is built to analyze and investigate the PI of a 2-D axi-symmetric MR damper valve. All configurations of the damper valve are simulated within a given range of input current and number of turns of coil, and within this range, damping force, dynamic range, valve ratio, inductive time constant and achieved pressure drop have been evaluated. The simulation results show that the PI of the MR damper are highly dependent on the shapes of valves and hence the valve shape should be selected based on the intended application. The results obtained in this work provide an insight for designers to create application-specific MR dampers.
International Journal of Engineering
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.