2. Thesis and Dissertations

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Author: search.filters.author.P., Jeyaraj

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    Sound Absorption Characteristics of Areca Husk Fiber Reinforced Flexible Pu Foam Composites
    (National Institute of Technology Karnataka, Surathkal., 2024) M.B., Santosh; P., Jeyaraj; G.C., Mohan Kumar
    In recent years, sound pollution has affected the quality of human life. Sound quality enhancement is the primary concern of automobiles, aviation, industries, and commercial and residential places. Currently, it focuses on utilizing eco-friendly, sustainable, biodegradable, and recyclable materials to control unwanted sound and improve sound quality. Most materials presently used for sound absorption (SA) applications are rock wool, glass wool, plastics, melamine foams, and synthetic fibers. Furthermore, synthetic fibers are highly toxic and adversely affect human health and the environment. These fibers are derived from petrochemical products and have issues with decomposition. Need for replacement of these materials motivated the researchers to explore developing economical and environmentally sustainable green products for sound-absorbing materials. Materials such as flexible fibrous foams, porous structures, perforated panels, granular membranes, and natural fiber composites are recommended for SA applications. Fibers extracted from plant wastes can be used for SA applications in vehicles due to their lightweight and porosity. Natural fillers or fibers-reinforced composite materials have many advantages, such as being biodegradable, inexpensive, widely available, lightweight, low cost, easy to process, economical, eco-friendly, and suitable for SA over a broad frequency region. Areca (betel nut) fruit shell husk consists of a significant amount of natural fiber known as areca fiber (AF), which covers the outside of the fruit. The fruit of the areca palm tree (areca catechu linnaeus) is a species of palm belonging to the palmecea family. The SA capability of raw areca fibers bundle (RAFB) as a function of the density and thickness of the test specimen is analyzed. Experimental results obtained using the impedance tube approach reveal that an increase in the specimen bulk density and thickness remarkably improves the SA capability of RAFB. Similarly, air volume behind the sample enhances the SA in the lower frequency range. Theoretical results predicted using the Johnson–Champoux–Allard (JCA) model matches well with the experimental predictions. The ability of the RAFB to absorb sound is demonstrated to be equivalent to other commercially available natural and artificial fibers by comparing the results available in the literature. The effect of unprocessed raw areca fiber (AF) particle reinforcement on the SA behavior of polyurethane (PU) foam composites is investigated. Influences of fiber weight percentage and graded distribution of fiber with varying fiber weight percentage on the SA coefficient (SAC) of the composite foams are examined through the impedance tube approach. Morphological studies are carried out with the help of FESEM images to investigate the acoustic energy dissipation mechanism of PU foam and its composites. The composite foam's SA capability is enhanced by increased fiber weight percentage, graded distribution of fiber wt.%, varying sample thickness, and air cavity length. In general, PU-AF composite specimens show a peak SA value of 0.95 around 450 Hz, which is not the case for other natural fiber results in the literature. Theoretical results predicted using the JCA model agree with the experimental results. The effect of filling unprocessed areca fiber (AF) particles reinforced polyurethane (PU) foam in the cavities of 3D-printed hexagonal and square honeycomb core cells is studied. Influences of unit cell size and graded cell size distributions on the SA coefficient are analyzed. The findings demonstrate that larger unit cell size and graded cell size distributions significantly enhance the SA capacity. The samples exhibited notable peak SA values of 0.94 at 650 Hz and 0.90 at 470 Hz for hexagonal and square cores, respectively, which found to be higher than the values reported in the literature.
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    Design and Optimization of a Switched Reluctance Motor for a Two-Wheeler and Three Wheeler Application
    (National Institute of Technology Karnataka, Surathkal., 2024) B., Sandesh Bhaktha; K.V., Gangadharan; P., Jeyaraj
    Among the available traction motors, switched reluctance motors (SRMs) are gaining a lot of attention as a potential choice to propel electric vehicles (EVs) since they are magnet-free, and mechanically robust with a longer constant power range. Although SRM has several benefits, high torque ripple causing abnormal noise and vibrations has proven to be a major hindrance to its wide-scale use. Moreover, SRMs possess a lower torque density as compared to other permanent magnet-based motors. A motor solution with a higher torque density is highly preferred for in-wheel (IW) EV applications due to limited space inside the wheel hub. The performance of an SRM is commonly assessed using a variety of electromagnetic performance metrics such as starting torque, torque density, efficiency, and torque ripple. The electromagnetic performance metrics are highly sensitive to the type of SRM topology, their design, and excitation control parameters. Any modification to these excitation control or design factors has a distinct effect on the performance metrics, with varying degrees of potential benefit and drawback. As a result, within the design and development framework of an SRM, numerous optimization techniques have been widely employed to optimize these design and excitation control parameters. This thesis comprehensively investigates the sensitivity of the electromagnetic performance metrics with the dimensions of the geometric design variables for an SRM. The influence of the dimensions of the various geometric design variables such as rotor diameter, pole arc angles, and yoke thicknesses on the electromagnetic performance metrics such as average torque and torque ripple has been analyzed using static two dimensional (2D) electromagnetic finite-element analysis (FEA). The reason for the change in static characteristics due to variation in reluctance between SRM designs has not been detailed so far in the literature. This is addressed in the present work by the magnetic equivalent circuit (MEC) model that simplifies the design analysis. Results indicate that stator pole reluctance needs to be given due importance while studying the influence of rotor diameter. Also, it is imperative to set an adequate thickness of the stator and rotor yokes to minimize the effect of saturation on the performance. Rotor diameter and stator pole arc angle have a pronounced influence on the average torque and torque ripple while the influence of rotor pole arc angle and yoke thicknesses was relatively less. v Further, previously published research articles on SRM optimization intended to be used for EV applications have mostly focused on the optimization of their design and control variables only at the rated conditions. In EV applications, the load operating points (LOPs) of a traction motor are dynamic and spread widely across the torque speed envelope. To enhance their overall performance, it is vital to include them in the design optimization process. Therefore, in this thesis, a novel procedure for implementing the multi-objective design optimization (MODO) of an SRM based on a driving cycle has been demonstrated for an Electric rickshaw (E-rickshaw) application. Higher starting torque, and torque density with reduced electromagnetic losses throughout the driving cycle are established as the design objectives, subject to practical restrictions on current density and slot fill factor. The design objectives have been accurately evaluated through transient finite element analysis (FEA) and a computationally efficient SRM drive model (developed in MATLAB/Simulink) with consideration of the excitation control parameters. Kriging models have been constructed to reduce the computation cost of FEA during the optimization process. Then, a nondominated sorting genetic algorithm II (NSGA II) based multi-objective optimization coupled with the constructed Kriging models is conducted to generate a Pareto-optimal set. An optimal design that offers the best balance between the design objectives is selected from the Pareto-optimal set and the dimensions of corresponding design variables are used to build a prototype. Finally, the static and dynamic performance of the SRM prototype are experimentally evaluated and validated with the FEA simulations. Working conditions and design restrictions are more challenging for IW motors (typically used in electric two-wheeler applications) since a reducer is not utilized. Among the available SRM topologies, Multi-teeth (MT) SRM topology is a promising candidate for IW applications since it retains the inherent simplicity and cost effectiveness offered by traditional SRM designs. However, the design of IW-MTSRM topologies and their electromagnetic performance have not been explored sufficiently. In this thesis, a design formula governing the selection of the number of MT and rotor poles for MTSRMs has been proposed. Using this, a novel four-phase 8/18 IW MTSRM is derived. The characteristics of the 8/18 IW-MTSRM SRM are numerically compared with a conventional 8/10 SRM based on magnetic characteristics, vi efficiencies, and steady-state operation for the complete torque-speed range for an electric scooter (E-scooter) application. Results indicate that the 8/18 MTSRM has a higher peak torque capacity, torque density, superior drive cycle efficiency, and reduced torque ripple.
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    Vibro-Acoustics of Beams Under Variable Axial Loads
    (National Institute Of Technology Karnataka, Surathkal., 2024) S., Naidu Balireddy; P., Jeyaraj
    Stiffeners and beam like structural elements used in aircraft structures are subjected to variable axial loads. These structural elements are subjected to steady state mechanical excitations as well. The nature of variable axial load influences static stability and hence dynamic characteristics of the structural elements are also effected. Furthermore, the vibration and acoustic responses caused by steady state excitation need to be analyzed to take care of dynamic stress and human comfort. Numerical simulation studies carried out on a beam to analyze its vibroacoustic response under the action of variable axial loads (VALs) is presented. Effects of six different types of VALs and three types of end conditions on buckling, free vibration and sound radiation characteristics of an isotropic beam is carried out initially. Static buckling and free vibration characteristics are analyzed using shear and normal deformable theorem and Ritz method. Forced vibration response is obtained using modal super-position method and the acoustic response parameters are obtained using Rayleigh integral. The nature of variation of VALs and end conditions are influencing buckling and free vibration characteristics remarkably. Results indicate that the acoustic response is highly sensitive to the nature of VAL and intensity of the VAL. In general, sound power at resonance decreases when the magnitude of VAL is increased. In continuation, static stability and dynamic characteristics of a bi-directional functionally graded beams subjected to VALs using the Ritz method and Reddy’s beam theory has been carried out. The material property is varied as a function of the gradation pattern along with the length and thickness directions. The influence of uniform, linear, and parabolically varying axial loads on buckling and free vibration frequencies is investigated. There is a remarkable variation observed in both the characteristics, by changing the material properties from isotropic to bi-direction functionally graded. Furthermore, the study reveals that higher stiffness is achieved by the material gradation index increment along the thickness direction compared to the lengthwise gradation index increment. Buckling and free vibration modes are also highly sensitive to the nature of variable axial loads and gradation index.Similarly, a detailed investigation is carried out on the effects of bi-directional gradation, length-to-height ratio, and end conditions on the sound radiation behaviour of bi-directional functional graded beams subjected to quadratically decreasing axial load. The study reveals that the highest value in the gradation indexes in both directions significantly influences the sound power levels. The directivity pattern reveals that bi-directional functionally graded beams exhibits higher sound pressure levels around the critical buckling load. It is also observed that both structural and end conditions are influential factors in sound power levels (dB) and sound pressure levels (dB). Finally, an investigation on the influence of bio-inspired laminate reinforced composite material on the static and dynamic responses of the beams, with a particular emphasis on the acoustic study is also done. The responses demonstrates the significance of variable axial loads, boundary stiffness, material composition, lay up pattern and aspect ratios highly influences the non-dimensional buckling loads of bio-inspired beams. The study further revealed that the vibration analysis are following the buckling trends, and the fundamental frequency is approaching minimum value at the critical buckling load. The study also includes the behaviour of the bio-inspired in comparison to vibrational responses at various modes and parameter variations. It is found that quasi isotropic-symmetric (QI) bio-inspired beam has poor buckling, vibration and acoustic behaviours, while uni-directional bio-inspired beams has better characteristics.