Faculty Publications
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Item Design of bypass rotary vane magneto rheological damper for prosthetic knee application(International Conference on Adaptive Structures and Technologies, 2019) Saini, R.S.S.; Kumar, H.; Chandramohan, S.; Sujatha, S.In this paper, a bypass rotary vane type magneto rheological (MR) damper suitable for prosthetic knee application is designed. The torque and angular velocity requirements of the normal human knee are used as design limits. In the proposed design, the rotary vane chamber and the MR valve are connected by hydraulic cables and ports and are designed separately. The rotary vane chamber is designed based on the cross-sectional size limits of the normal human knee, while the MR valve is designed with the objective of obtaining the maximum on-state damping torque, minimum weight, and minimum off-state torque. © copyright Environment and Climate Change Canada.Item Design of twin-rod flow mode magneto rheological damper for prosthetic knee application(American Institute of Physics Inc. subs@aip.org, 2019) Saini, R.S.S.; Kumar, H.; Chandramohan, S.; Sujatha, S.In the present study, a twin-rod magneto rheological (MR) damper working in flow mode is designed. The piston core, annular fluid gap, outer sleeve, and the outer cylinder forms the magnetic flow path. A nonlinear constrained optimization problem is formulated to obtain the geometric dimensions of the piston assembly. The flow mode equations of the damper and the electromagnetic circuit design equations, assuming constant magnetic field links are coupled together to form an optimization problem. The design torque and angular velocity requirements of the normal human knee are converted to damping forces and linear velocity using the knee and damper geometry based on the previous study. The damping force design constraints and the constraints related to current requirements and magnetic field saturation are imposed. The obtained optimum dimensions of the piston assembly yielded an off state damping force of 56.8 N and a maximum on-state damping force of 1582 N at a current of 1.6 A for a design velocity of 0.1 m/s. Magnetostatic analysis of the piston assembly using the optimized dimensions is performed which showed that the annular gap is exposed to a field of 0.6 T, as assumed and the piston core is subjected to a field of 1.8 T which is below the saturation limit of the core material. © 2019 Author(s).Item Optimal Design of Rotary Magneto-Rheological Drum Brake for Transfemoral Prosthesis(Springer Science and Business Media Deutschland GmbH, 2021) Saini, R.S.T.; Kumar, H.; Chandramohan, S.; Sujatha, S.Semi-active technology offers good advantages in terms of controllability and adaptability. Magneto-rheological (MR) fluid is a class of smart fluids which display significant changes in its rheological properties under the influence of a magnetic field. Previous studies carried out using MR brake for the transfemoral prosthetic device were of multi-plate models which are complex in design and also to manufacture. Therefore, in the present study, a multi-coil rotary inverted drum brake is optimized with braking torque as the objective function. One of the advantages of the multi-coil design from multi-plate is that the former has fewer components and leads to a simpler design. The outermost geometric constraints are decided based on the knee cross-sections in anterior-posterior and mediolateral directions. Four design geometric variables are selected which are: coil depth, coil height, casing axial thickness, and casing radial thickness. A design of experiments technique is used to obtain 27 combinations of design variables. Magnetostatic analysis at each design point is performed and average flux densities in the annular and the radial gaps are determined. Regression analysis is conducted on the design data to obtain braking torque as a function of four design variables. Later, genetic algorithm is used to obtain the optimum geometric dimensions. A total maximum braking torque of 13.4 Nm is obtained using the optimum dimensions for a design current of 2 A. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item A Suspended Polymeric Microfluidic Sensor for Liquid Condition Monitoring(International Society for Structural Health Monitoring of Intelligent Infrastructure, ISHMII, 2022) Oseyemi, A.E.; Sedaghati, R.; Chandramohan, S.; Kumar, H.; Packirisamy, M.The measurability of fluid properties like density and viscosity comes with a huge potential in numerous sensing applications, ranging from physical to biological to chemical. A vital quality of a lubricant is its viscosity. In general, liquids with high viscosity have molecules with higher cohesion capacity (higher flow resistance) while those with low viscosity have less cohesion ability, allowing for higher flow rates. This makes viscosity an essential indicator in condition monitoring programs, as information about the cohesive strength of the layers of a liquid can allow us to assess the liquid's ability to form a physical barrier between moving parts. This study proposes a microcantilever-based microfluidic platform that leverages the interaction between cal barrier flow and the bending characteristics of the beam for high sensitivity detection of changes in fluid properties, such as dynamic viscosity, density, and kinematic viscosity, from which valuable information about the health of structures engaging the liquid can be obtained. © 2022 International Conference on Structural Health Monitoring of Intelligent Infrastructure: Transferring Research into Practice, SHMII. All rights reserved.Item Analytical Studies on Ride Quality and Ride Comfort in Chennai Mass Rapid Transit System (MRTS) Railroad Vehicle(Springer, 2018) Gangadharan, K.V.; Chandramohan, S.In this paper analytical ride index studies and ISO 2631 based ride comfort analysis of a suburban MRTS railroad vehicle is presented. Track power spectral densities (PSDs) were used as inputs to a finite element (FE) model of the vehicle and track and the acceleration responses were computed using random vibration theory. From these responses, ride quality and ride comfort have been computed at different locations of the vehicle at different speeds in the vertical and lateral directions. © 2017, The Institution of Engineers (India).Item Semi-active control of a swing phase dynamic model of transfemoral prosthetic device based on inverse dynamic model(Springer, 2020) Saini, R.S.T.; Kumar, H.; Chandramohan, S.Improving the gait of transfemoral amputees and making it biomimetic and stable has always been a major effort. A dynamic model of the prosthetic device can predict the kinetic and kinematic performances, when incorporated with a musculoskeletal model. In this regard, a dynamic model of a recent trend of variable damping technology will help a great deal in evaluating the performance of the prosthetic device and also in studying the effect of various parameters on the prostheses. The current paper presents the dynamic model of a single axis two segmental prosthetic knee implemented with a magneto-rheological (MR) damper as a variable damping element. The MR damper is modeled mathematically using Bouc–Wen model with model parameters evaluated by minimizing the error norms for time, displacement and velocity between the experimental and the model-generated results using a genetic algorithm. Two different experimental data sets are used, one for mathematical modeling and other to assess the accuracy of the fit model. A Proportional Derivative plus Controlled Torque controller is employed, and the parameters are tuned to minimize the error between the desired and control input torques. Further, an inverse dynamic model using Bouc–Wen model variables is assumed and validated later. This model predicts the current directly and avoids the necessity of solving any quadratic equation, which is required in the case of inverse models based on modified Bouc–Wen. The dynamic model of the prosthesis is analyzed for the swing phase alone, and the results show that the model traces the desired knee angle and also the shank reaches full knee extension at the end of this phase with terminal velocity small enough to be handled by an extension stop. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.Item Optimal design of inverted rotary MR brake with waveform boundary using a novel combined magnetostatic approach(IOP Publishing Ltd, 2020) Saini, R.S.T.; Kumar, H.; Chandramohan, S.In the present work, an inverted rotary drum magneto rheological (MR) brake with waveform arc boundary suitable for prosthetic knee application is optimally designed. Often, the magnetostatic analysis is performed assuming linear magnetic systems and solving a lumped parametric equivalent magnetic model (EMM). Although, this reduces the computational time but compromises the accuracy of the solution. On the other hand, finite element magnetostatic (FEMS) analysis combined with a search-based optimization technique requires more time and effort. In this work, an approach combining the EMM and FEMS methods is proposed to optimally design the MR brake. This method requires the optimization algorithm to maintain an external repository so that individuals which are non-dominated at each generation get stored in the repository and only those individuals are allowed to use FEMS method. This approach reduces the number of function calls made to FEMS method and thus reduces the computational time substantially. A recently proposed multi-objective particle swarm optimization (MOPSO) which evaluates the global best using minimum distance of point of line (MDPL) method is implemented with the proposed combined magnetostatic method. While FEMS method alone resulted in an average computational time of 7.25 h, the proposed method evaluated a similar Pareto front solution in 38 min. Finally, the optimal design is compared to other prosthetic knee MR brakes from the literature. © 2020 IOP Publishing Ltd.Item Design of bypass rotary vane magnetorheological damper for prosthetic knee application(SAGE Publications Ltd, 2021) Saini, R.S.T.; Chandramohan, S.; Sujatha, S.; Kumar, H.Semi-active systems using magnetorheological fluids have been realized in many novel devices such as linear dampers, rotary dampers, brakes, and so on. Rotary vane-type magnetorheological damper is one such device that uses magnetorheological fluid as a hydraulic medium and a controllable magnetorheological valve to generate variable resistance. This device, due to its limited angle motion, lends itself to a natural application for prosthetic knee joint. In this article, a bypass rotary vane-type magnetorheological damper suitable for prosthetic knee device is designed. In the proposed design, the rotary vane chamber and the bypass magnetorheological valve are connected using hydraulic cables and ports. The design of rotary cylinder is implemented based on the largest possible dimensions within the envelope of a healthy human knee, while the magnetorheological valve is designed optimally using a multi-objective genetic algorithm optimization. Off-state braking torque, induced on-state braking torque and mass of the valve are selected as three objectives. The torque and angular velocity requirements of the normal human knee are used as design limits. The optimal solution is chosen from the obtained Pareto fronts by prioritizing the objective of weight reduction of magnetorheological valve. The optimal solution is capable of producing a damping torque of 73 Nm at a design speed of 8.4 rpm and current supply of 1.9 A. Potential benefits offered by this design when compared with multi-plate magnetorheological brake are flow mode operation, large clearance gap, and fewer design components, thus reducing the manufacturing complexity. © The Author(s) 2020.Item Optimal design of ow mode semi-active prosthetic knee dampers(Sharif University of Technology, 2022) Saini, R.S.T.; Kumar, H.; Chandramohan, S.Magnetorheological (MR) fluid devices operate in four modes: ow, shear, squeeze, and pinch. Among these, the flow mode is the most efficient one and results in large field-induced pressure differences. Despite being the least efficient, shear mode is the most commonly used in numerous applications, including prosthetic knees, due to its ease of construction. Additionally, shear mode designs require larger shear areas and reduced fluid gap tolerance compared to their ow mode counterparts, resulting in a complex design such as the commercially available multi-plate MR brake. Therefore, in this study, two ow mode designs, twin-rod and rotary vane MR dampers, are optimally designed for prosthetic knee application. The optimal designs obtained from solving a multi-objective particle swarm optimization problem are fabricated and experimentally characterized for various harmonic excitations of varying amplitudes, frequencies, and currents. The optimal designs are compared with many MR fluid-based prosthetic knee design configurations. Based on the results, a twin-rod MR damper with a mass of 0.71 kg and a damping force of 1020 N at 1 A is identified as the optimal design configuration for prosthetic knee application. © 2022 Sharif University of Technology. All rights reserved.