Ph.D. Thesis
Virginia Tech, Blacksburg, VA, 24060
Aashish Shaju, Steve Southward, and Mehdi Ahmadian. 2023. "PID-Based Longitudinal Control of Platooning Trucks" Machines 11, no. 12: 1069. https://doi.org/10.3390/machines11121069
Aashish Shaju, Steve Southward, and Mehdi Ahmadian. 2024. "Enhancing Autonomous Vehicle Navigation with a Clothoid-Based Lateral Controller" Applied Sciences 14, no. 5: 1817. https://doi.org/10.3390/app14051817
Conducting a simulation study of semi tractor-trailer platooning utilizing a co-simulation framework developed with TRUCKSIM and SIMULINK.
Developed a longitudinal control algorithm for platooning trucks which enhanced overall performance and efficiency, striking a balance between fuel optimization, and maintaining secure distances to optimally capitalize on platooning advantages.
Conducting a comprehensive study on improving lateral control in autonomous vehicles potentially applicable to platooning scenarios using a clothoid-based controller integrated with an adaptive lookahead strategy. The clothoid based controller relies on waypoint navigation with locally generated hyper clothoids at each time step which are really beneficial due to their gradual curvature variation. This minimizes abrupt steering corrections and aligns well with the natural steering behavior of vehicles. After establishing local path planning with clothoids, my objective is to employ an optimization based closed loop control for precise tracking of the locally fitted clothoids.
Master's Thesis
Indian Institute of Technology Hyderabad
Aashish Shaju and Ashok Kumar Pandey, 2020, "Modelling transient response using PAC 2002-based tyre model," Vehicle System Dynamics.
2nd Indo Japan Bilateral Symposium on Futuristic Materials and Manufacturing for Next Generation Electric Vehicles and High-Speed Railway, Indian Institute of Technology Madras, "Analysis of improved transient tire modeling", 2020.
The objective of this research is to develop, implement, and validate a general transient handling tire model to improve the capturing of transient tire forces and torques using the well-established and widely popularized PAC model. The transient dynamics have been modeled in an improved manner using a second-order lag equation resulting in lagged slip quantities (κ_L and α_L), which are functions of their respective relaxation lengths r_x and r_y. Significant work has also been done towards the analytical estimation of these relaxation lengths. Further, these relaxation lengths were also extended to include the coupling effects of longitudinal and lateral tire dynamics.
Finally, following the implementation of the model in MATLAB and subsequent validation, we analyzed the variation of tire forces and moments for different dynamic maneuvers (given above). Simulation results reveal the difference between the steady-state and transient forces and, most importantly, show how transient forces may differ substantially from steady-state forces during severe maneuvering/braking, etc.
Virginia Tech
Developed an MPC-based framework to enhance trajectory tracking for a tractor-trailer system, addressing the non-holonomic constraints, and optimizing control authority.
Achieved successful path tracking on both an 8-shaped and circular trajectory, demonstrating the efficacy of the control system through comprehensive simulation results.
Conducted robustness analysis revealing the controller’s resilience to parameter variations, with a focus on minimizing tracking errors and maintaining desired velocity.
Virginia Tech
The project was done in two stages:
1] The first stage (accounts for at least 60% of the project) focused on the development/validation of a controllable and observable model of the open-loop plant (black box MIMO system) through “LINEAR SYSTEM IDENTIFICATION” techniques.
Ø We used frequency response-based system ID methods for our model estimation. So, a major task was figuring out the proper excitation signal that could excite all of the dynamic modes in the bandwidth of interest and at the same time avoid clipping both the control and response signals.
Ø After achieving acceptable signal-to-noise ratios associated with each path, we computed the H1 frequency response function estimates for all four paths.
Ø We then obtained discrete-time transfer functions for each of the four paths based on the frequency response function estimates and converted them to corresponding discrete-time LTI state-space object.
Ø Performed a model order reduction based on the Hankel Singular values to generate a balanced realization of the discrete SS model.
Ø Lastly, we validated the estimated model with the actual plant in both frequency as well as time domains.
2] The second stage dealt with the design of an output feedback control system that can regulate the responses of the dynamic plant.
Ø First, an LQR-based state feedback control law with appropriate performance specifications was implemented. This was done to get an optimal full state feedback gain matrix “G” for the discrete-time estimated open-loop model.
Ø Finally, a full state feedback control with Kalman state estimator (output feedback control) was implemented and simulated. The tuning parameter for the Kalman estimator (in our case QN-process noise covariance matrix) was tweaked to satisfy the required estimation convergence and then eventually control performance.
Virginia Tech
The aim of this simulation study was to develop a MIMO control system to regulate the flexible modes and the rigid body (i.e., pointing) modes of a satellite with flexible solar panels. The satellite has two bi-directional attitude control thrusters to help maintain the proper orientation of its solar panels and to actively damp out unwanted vibrations induced by attitude repositioning. For the sensing part, a total of four sensors were distributed along the length of the solar panels to measure the motions of the panels.
The final design objective was to develop an output feedback control system (i.e., full state-feedback with a state estimator) that can regulate (i.e., drive to zero) the four sensor measurements (Outputs) using the two attitude control thrusters (Inputs).
Major snapshots were:
1) Evaluation of the open-loop response (controllability, output stability, observability, etc.)
2) Design of a full state feedback control with the required performance.
3) Design of an output feedback control with state estimation based on the Luenberger observer.
4) Designing and validating an LQR optimal compensator.
IIT Delhi
1] Implemented an analytical model of a rigid Rotor bearing system with 4 DOF. This was followed by the study of variation of natural frequencies with RPM along with the identification of whirl nature (like Backward or Forward whirl) at each frequency. Secondly, animations of various mode shapes exhibited by the rotor at those natural frequencies were also generated.
2] Performed MATLAB-based numerical simulation of a Jeffcott rotor coasting up past its critical speed to its operating range. The simulation was then extended to include the effects of various rotor defects like transverse crack, stiffness asymmetry, Bent rotor, and rotor with rotor-stator rub.
3] Implemented a generic FEM model in MATLAB for the dynamic analysis of a rotor-bearing system with bearing characteristics. Further various analyses were performed like generation of critical speed map, unbalanced rotor vibration response, animation of operation deflection curves, etc.
IIT Delhi
A Fuzzy logic-based diagnostic model was implemented in MATLAB.
First, an analytical model of a three-phase induction motor along with its various commonly occurring faults have been implemented in MATLAB. Following that, the model's output (three-phase currents I_a, I_b, I_c) were observed based on which the input and output membership functions were arrived at. The Fuzzy logic rules were set to be the most commonly used rules given in the literature. Finally, the Fuzzy logic output (Stator condition - SC) were plotted and analyzed for different cases (both with and without faults).
CONCLUSION - A highly versatile technology for condition monitoring and fault analysis of electro-mechanical systems !!!
Term Project at IIT Hyderabad
The longitudinal governing equations of a three-mass train were solved to get the kinematic quantities of each compartment along with the coupler forces between them with respect to time. Secondly, lateral stability analysis of a simple wheel-set subjected to different initial conditions has been done to get the lateral displacement as well as its yaw angle variation with time.
Term Project at IIT Hyderabad
In this study work, primarily, the Kinematic analysis of an Airplane landing gear was performed by giving a desired input motion to one of the predetermined links, and the resulting animation was created using the same position, velocity, and acceleration values obtained. Furthermore, for the same input, a forward dynamic analysis was performed to get the joint forces and torques. Additionally, an Inverse dynamic analysis was also done to get the kinematic values of the various links for the given input torque variation given to a particular link.
Term Project at IIT Hyderabad
The objective was to identify the major sources of noise in a Vacuum cleaner through source characterization techniques followed by setting a target dB level after ranking them. Finally, appropriate noise reduction methods were implemented (in this case, mufflers for airborne noise and damping material mounts for reducing structure-borne noise) to meet the target level. During this project, we came up with an indigenously written MATLAB code for providing us with the 1/3rd octaves and overall sound level in dB from the sound clip measured using our smartphones. Although there will be some errors involved due to the non-uniform sound sensitivity characteristics of our smartphone microphones, the results were satisfactorily close to the ones given by a B&K professional sound analyzer.