PhD Theses (Mechanical Engineering)

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Investigation of Anodic Dissolution Process to Overcome the Challenges during Micro-Manufacturing
(2023) Kumar, Abhinav
The present thesis focuses on solving the two major challenges of micro-manufacturing via the electrochemical-based method. The significant advantage of this method is high dimensional accuracy and better surface integrity. The thesis is divided into two sections. The first section includes the development of electrochemical micromachining (EMM) setup and the fabrication of microtools. The second section consists of developing an electropolishing (EP) setup and improving the surface integrity of electrical discharge machined components.
Near Field Examination of Sonic/supersonic Nozzle flows
(2023) Jraisheh, Ali
This thesis presents a numerical study on compressible flow within and downstream sonic/supersonic nozzles. It is a close look on the effects of thermodynamics and geometry configuration on the gas flow inside and downstream the ducts. An in-house CFD solver is developed to accommodate the complex flow structure that accompanies the under expanded jet and impose the proper boundary conditions, in order to simulate the flow field. More focus is drawn to the phenomenon of Mach disk that occurs in case of highly under expanded flow, its location and height are thoroughly studied and analysed.
On-Site Flexible Rotor Balancing and Crack Characterization in Rotor-Bearing System Through Virtual Excitation by Active Magnetic Bearings
(2022) Ranjan, Gyan
The conventional influence coefficient method is being widely utilized for on-site balancing of the rotor system. For the balancing of the flexible rotor, the system is required to be operated above critical speeds, which is difficult in the presence of residual unbalances. Also, repetitive stopping and the opening and closing of the casing of the rotor system for the manual addition of trial unbalances (conventional method), the system may get contaminated with foreign particles. To solve the above difficulties, a new balancing method has been proposed using the Virtual Trial Excitation Influence Coefficient Method (VTEICM) for a flexible rotor system integrated with Active Magnetic Bearing (AMB). The AMB is utilized for both controlling vibrations while accelerating through various critical speeds during measurements and generating virtual trial unbalance (VTU) as magnetic excitation. The VTU allows the identification of unbalances with a lesser number of rotor runs and manual effort than the conventional method. Initially, for numerical illustration of the VTEICM, the mathematical model of the rotor-AMB system is developed using the finite element method. The effectiveness of the VTEICM is shown through the balancing of the rotor-AMB system with the estimated unbalances. However, the occurrence of failure in the system while surpassing critical speed even in the presence of a control structure is required to be reduced. The periodic balancing of the flexible rotor system with the change in the level of unbalances is required to be carried out while operating the system at low speeds. A new technique is developed with Virtual Excitation at Low-Speed for High-Speed Balancing (VELSHSB) that utilizes the influence coefficients obtained at high speed and unbalances identified at the low speed to effectively estimate the balance masses required for the high-speed flexible rotor balancing. The influence coefficients at high speeds are required to be obtained just once, whereas the balance masses can be estimated periodically by identifying the unbalances at low speeds. The methodology is extended to balance the dual rotor system that is widely utilized in aero-engines because of its compact structure and efficient operation. Due to the compact structure of the system, it is difficult to balance the rotor system with the manual addition of the trial unbalances. Hence, a novel balancing strategy, i.e., Multiple Virtual Excitation for Dual rotor Balancing (MVEDRB), has been utilized to balance the dual rotor system with AMB control and excitation. Also, the rotor system with multiple faults such as cracked rotor system are required to be analyzed with the utilization of AMBs. Therefore, an identification algorithm is designed to obtain the fault parameters in the cracked rotor system integrated with AMB based on the Multiple Harmonic Influence Coefficient Method (MHICM). The present approach allows us to monitor the behavior of a fatigue crack in the system and to successfully estimate the additive crack stiffness, residual unbalances, and the internal damping factor in the system. There is a lot of practical difficulty in high-speed balancing with accelerating the rotor system above its critical speed in the presence of AMB. The control structure of the AMB requires a large magnitude of bias current to accommodate the excessive control current near the critical speed that increases the heating of coils and power consumption. So, the implementation of VTEICM for high-speed balancing of experimental rotor test rig supported on the conventional bearings and integrated with the AMB is also carried out. The control structure with PID controller is developed on dSPACE-SIMULINK platform based on the differential driving mode control. To limit the utilization of bias current, the switching of bias current is performed that allows the rotor-AMB system to switch between high and low values of the bias current on the requirement. The practical difficulties in synchronizing the excitation frequency of VTU and operating speed are addressed with voltage/speed factor and phase-lag correction in the motor speed control unit.
Convergence Acceleration of Fluid-Flow Computation with Special Emphasis on Multigrid Technique
(2022) Kalita, Subhra Sankar
This thesis is concerned with the study and analysis of various convergence-acceleration strategies that can help CFD practitioners to obtain their simulation results quickly. Convergence-acceleration can be achieved either by choosing a fast algorithm or by parallelizing the solution strategy. The multigrid method lies in the former category and is considered as one of the most powerful convergence-acceleration strategies. CUDA, which is a relatively new method for parallelizing CFD codes falls under the second category and as a part of the convergence-acceleration efforts embodied in this thesis, CUDA is used to parallelize LBM-based computations
Design And Development Of A Novel Ball-On-Cup Tribometer For The Characterization Of An Ingenious Total Hip Prosthetic Liner Made Of Uhmwpe And Its Composite
(2023) Jana, Ashirbad
Total hip replacement (THR), regarded as the orthopaedic operation of the 20th century, uses ultra-high molecular weight polyethylene (UHMWPE) as the acetabular liner since 1960s. However, the life of a metal-on-plastic THR is often limited to 15-20 years, primarily due to excessive wear debris generation during its operation, leading to osteolysis and aseptic loosening of the prosthetic joint leaving behind a painful revision surgery. Presently worldwide research is dedicated in improving the life of a metal-on-plastic THR by the improvement of tribological characteristics of an UHMWPE acetabular liner.
Thermodynamic Analysis of Active and Passive Drag Reduction Techniques for Elevated Enthalpy Hypersonic Reacting Flows
(2023) Patil, Ajay Vijay
Initial investigations are based on counter flow injection and spike based drag reduction techniques to compare them on a common platform. Test case of supersonic flow over hemisphere, provided with counterflow injection, portrayed monotonic variation for percentage drag reduction and percentage exergy destruction for increase in injection pressure ratio. However, injection effectiveness, suitable assessment parameter for counterflow injection, shows inversion characteristics with a peak at specific injection pressure ratio. Mounting of a spike also shows similar trend for percentage drag reduction and percentage exergy destruction. Present investigations recommend percentage exergy destruction as a unified performance assessment parameter for passive and active drag reduction techniques. Afterwards, investigations are carried to examine the effect of higher freestream stagnation enthalpy on flow field alteration for counter−jet drag reduction technique for a hemispherical object. Drag coefficient is found to reduce with freestream total enthalpy in the presence of real gas effects. Higher pressure ratio of the jet has resulted in lower surface pressure and Stanton number on the object. Then, efforts are further continued to reveal the thermodynamic behaviour of opposing jet technique which includes variation of entropy generation rate, exergy destruction and drag force analysis considering real gas effects. Results revealed that linear reduction in drag forces and sharp rise in entropy generation rate and exergy destruction is obtained with jet momentum ratio irrespective of freestream and jet parameters. At last, real gas effects on surface pressure and flow field are analysed for the combinatorial technique (opposing jet and cavity) for hypersonic flow over the blunt body. A new thermodynamic parameter named entropy generation rate is proposed which can be used as a tool to analyze the performance of any drag reduction technique. Results showed that perfect gas assumption over−estimates the surface pressure and wave drag. Introduction of cavity reduces the surface pressure, drag and entropy generation rate but significant reduction in these parameters is noted when the opposing jet is turned on. For given jet pressure ratio, opposing jet technique predicts lower drag and entropy generation rate as compared to combinatorial technique.
Robust Control Schemes for a Pediatric GAit Exoskeleton System in Passive-assist and Active-assist Mode
(2023) Narayan, Jyotindra
Over the years, a significant rise in neurological disorders has been observed for different age groups, such as stroke, spinal cord injury (SCI), and cerebral palsy (CP). Many pediatric subjects face dyskinesia and muscle atrophy in their lower limbs. In the last few years, the proliferation of exoskeleton technology has enabled the therapy process to be less cumbersome and more sustainable. However, there are minimal exoskeleton devices available for pediatric gait rehabilitation. Moreover, the control design to achieve the desired gait training in different therapy modes is still open to research and a benchmark problem statement due to significant parametric perturbations and external disturbances (PPED) in pediatric exoskeleton systems. Therefore, this thesis proposes a few robust control schemes for a newly designed pediatric exoskeleton in passive- and active-assist rehabilitation mode.
Analysis of Three Phase Carbon/(CNT+Epoxy) Composites with Flaws
(2024) Rao, Chukka Atchuta
Three phase FRP composites like carbon/(CNT+epoxy) are developed where the matrix dominated properties of FRP composites are enhanced to improve the performance. FRP composites though possess a very high specific strength and stiffness sometimes show poor performance when their interlaminar strengths are challenged. Especially when defects like ply break and embedded delaminations occur due to events like low velocity impact, delaminations usually grows at the interface of the broken and intact plies leading to the final fracture. These defects are sub-surface in nature many a time go unnoticed and results in catastrophic failure. It is therefore extremely important to strengthen the laminates against such failure. Resistance against such failures are decided predominantly by matrix dominated properties like interlaminar strengths. Therefore, three phase composites such as carbon/(CNT+epoxy) with modified matrix properties is expected to provide improved resistance against such failure. The present thesis thus aimed at investigating the performance of three phase carbon/(CNT+epoxy) laminates having internal flaws like ply break and impact induced embedded delamination subjected to loading with the specific objective of understanding qualitatively and quantitatively how adding CNTs to the epoxy enhances the resistance delamination growing from such defects. To study this, full 3D finite element analyses (FEA) have been carried out for carbon/(CNT+epoxy) laminates having two types of flaws viz. ply break and embedded delamination. Delamination at the interface has been modelled using a very thin resin rich layer and the interlaminar stresses around the ply break and embedded delaminations are obtained from the 3D FEA. Using the stresses and displacements from FEA, Virtual Crack Closure Integral (VCCI) has been used to determine strain energy release rate (SERR) components as measures of propensity of delamination. FE results show that delamination from such defects is a mixed mode phenomenon and in the case of embedded delamination the mode mix ratio also varies along the delamination front making the estimation of delamination growth difficult. Delamination at the interface arising from such flaws are observed to be influenced by many factors such as size, shape, relative fiber orientation, loading condition. Critical SERR as a measure of resistance to such delamination has been evaluated in the present work using stress based criteria and virtual crack closure integral from LEFM. From the results, it is clear that in the case of three phase carbon/(CNT+epoxy), addition of CNTs to epoxy leads to significant improvement in resistance to delamination at the interface from ply bear as well as from embedded delamination in all the cases studied. In addition, it was also observed that tendency of two neighbouring delamination to grow as a large delamination is also reduced by adding CNTs to the epoxy. However, results from the FE simulations also show that there is a limit till which CNTs could be added to the epoxy for best performance and beyond this the performance further reduces and it is important to know the limit to the adding CNTs will enhance the resistance to such delamination.
Development of Pseudopotential-Based LBM Solver to Explore the Microdynamics of Liquid-Vapor Phase Change Processes
(2022) Mukherjee, Aritra
The pseudopotential-based LB multiphase model has enormous potential in the simulation of phase-change heat transfer problems. It facilitates the natural development and migration of interfaces during the multiphase simulation as well as saves a lot of computational time. Along with these, this model enjoys several advantages like simple implementation procedure, excellent parallelizability, and easy applicability in complex domains. Due to these superiorities, it is becoming increasingly popular among researchers working on numerical simulation of multiphase flow. A pseudopotential model based thermal multiphase flow solver is developed as this thesis work, which is employed in several phase change heat transfer problems related to boiling and condensation. The first problem successfully explores the capability of the pseudopotential-based thermal lattice Boltzmann model in emulating the underlying thermohydrodynamics of subcooled flow boiling in a narrow fluidic horizontal channel in detail. The next study uses the multiple-relaxation time based LB model to explore the role of surface morphology and cold spot temperature in determining the visual state of the condensate droplet, i.e. Cassie and Wenzel mode of droplet nucleation and associated rates of energy and mass interactions in temperature controlled condensation process. The same numerical framework is employed to study condensate droplet formation and movement on several vertical and inclined microstructured surfaces, and corresponding mass condensation and heat transfer rates are analyzed thoroughly. Being motivated by the prime weakness of the pseudopotential based thermal LB model about its incapability of simulating boiling problems with a large density ratio, the last work of this thesis focuses on augmentation of the basic pseudopotential based thermal multiphase algorithm by enhancing the isotropy of the discrete equation and thermodynamic consistency of the overall formulation, to expedite simulation of pool boiling at higher-density ratios. Various pool boiling scenarios, and all three regimes of pool boiling have aptly been captured with both plain and structured heaters, allowing the development of the boiling curve. The predicted value of critical heat flux for the plain heater agrees with Zuber correlation within 10%, illustrating both quantitative and qualitative capability of the proposed algorithm.
Effective Utilization of Data for Enhancing the Performance of Manufacturing
(2024) Chatterjee, Kaustabh
The effective utilization of data is becoming increasingly important for enhancing the performance of manufacturing processes. In the era of Industry 4.0, advancements in technology have enabled the collection of vast amounts of data from various manufacturing processes, making it possible to analyze the data and derive insights that can help enhance the performance. One of the main advantages of using data-driven manufacturing is the ability to identify quality issues early in the production process. It reduces the likelihood of defective products, thereby enhancing customer satisfaction, reducing wastage and improving the profitability.
Experimental and Computational Studies on Exit-Hole-Free Friction Stir Spot Welding Processes
(2024) Bhardwaj, Nitish
This thesis contributes to understanding friction stir spot welding (FSSW) by investigating friction, heat generation and exit-hole elimination. Lubricants were applied during FSSW of aluminum alloy sheets resulting in a 44–55% reduction in torque and 12–24% reduction in plunge force requirements. More than 50% reduction in energy requirement while maintaining good joint strength is observed. This suggested the more important role of plastic deformation in heat generation as compared to friction. The study introduces an inverse approach to model friction during FSSW, utilizing finite element (FE) simulations in DEFORM 3D and validating with experiments. Further, this thesis investigates ways of producing exit-hole-free welds during FSSW. In one method the exit-hole is filled with waste aluminum chips and friction stir processing is performed over it. The process delivered 16% and 84% higher load-bearing capacities during T-peel tests compared to conventional FSSW with and without pin, respectively. A novel method of using consumable pin during FSSW is introduced to produce exit-hole-free joints. The feasibility and performance of FSSW using three consumable pin materials viz., AA6061-T6, mild steel and oil hardened non-shrinking die steel, are explored. Additionally, the research evaluates the impact of rotational speed and plunge rate on joint quality. It is found that the joint strength increases with increase in rotational speed up to 900 RPM and further increase in rotational speed decreases joint strength. A 1.7 times increase in joint strength at 900 RPM compared to 360 RPM is achieved. On the other hand, optimum plunge rate for highest joint strength is found to be 15 mm/min. A 4% increase in lap shear strength at 15 mm/min plunge rate compared to 6 mm/min, with an 8.5% decrease in energy requirements is obtained. A good match between experiments and FE simulations is obtained. Adhesive-bonded consumable pin along with application of lubrication is suggested for industrial application, which results in faster production speed and lower energy requirement while delivering good joint quality. This study provides a comprehensive understanding of FSSW, spanning friction, heat generation, exit-hole-free FSSW joints, parametric study and the integration of lubricants and adhesive-bonded consumable pins.
Application of Cold Metal Transfer Technology for Cladding of ER70S-6 Alloy on AA 6061-T6 Aluminum Alloy
(2024) Das, Bappa
The Cold Metal Transfer (CMT) process is a specialized welding technique used for cladding and coating, which involves applying a layer of metal onto a base material. In fact, CMT cladding is an efficient additive manufacturing technology that finds application in the automotive, defence, and power plant sectors. As Additive Manufacturing evolves, new welding methods have emerged, including CMT, an advanced version of Metal Inert Gas (MIG) welding known for reduced spatter and low heat input. CMT-based cladding processes have gained attention for improved aesthetics and lower heat input. Utilizing a wire as feedstock and a robotic arm for deposition enables precise material placement in complex shapes, with heat input determined by process parameters like voltage, current, wire feed speed, and stand-off distance.
Performance Evaluation of Lubricated Polymer Gears
(2023) Bharti, Sarita
Injection molded polymer gears are being widely utilized as they offer several advantages, such as lightweight, good damping capacity, easy production, low manufacturing cost, and good mechanical properties for low and moderate-load applications. Many works have been earlier attempted to improve mechanical properties by incorporating fiber reinforcement. In this work, an attempt has been made to investigate the potential of using oil lubrication for performance improvement. In addition, the present study also aims to check the feasibility selective laser sintering (SLS) process and elastomeric material (thordon SXL) for gearing application. The sliding contact performance of these materials was also investigated using pin on disc configuration. The surface durability of the test gear was investigated using a house-developed gear rig at various loading conditions and a constant rotational speed under dry and lubricated conditions by observing the thermal response of gear teeth, lubricant temperature, periodically monitoring gear teeth surface, and failure morphology.
Development and Performance Investigation of a Biomass-fired grain dryer Coupled with Solar Air Heaters
(2022) Kumar, Dhananjay
In the present investigation, a cost-effective and efficient biomass-solar hybrid dryer has been developed for meeting the drying demand of agricultural products suitable for developing countries. The dryer mainly consists of a furnace, rectangular chamber, PCM tray, drying chamber, drying tray, solar air heaters, PVC pipe, sensible thermal storage (pebbles), and latent thermal storage (paraffin wax). In the present study, thermal analysis of the dryer is done for optimum removal of moisture. Energy and exergy analysis of the biomass-operated dryer, natural convection solar dryer, and forced convection solar dryer has been carried out. The drying characteristics of paddy have also been studied in the dryer. In the biomass-operated dryer, the effect of the sensible heat storage medium in the rectangular chamber was studied and found that the use of a sensible heat storage medium reduces the energy losses from the rectangular chamber (brick wall). It also reduces the exergy destruction in the rectangular chamber and retains a higher temperature for a longer period. Hence, it enhances the performance of the biomass-operated grain dryer. The effect of flue gas energy recovery has also been studied and found that the energy recovery technique reduces the wastage of energy in the flue gas. The use of a regulator valve in the exhaust pipe increases the temperature in the drying chamber
Numerical and Experimental Investigations for Electromagnetic Crimping and Welding of Multi-Material Tubular Components
(2023) Kumar, Deepak
Multi-material components have become necessities of the present time because of their ability to offer benefits of properties of multiple materials such as corrosion-resistant, lightweight, higher strength, and electrical conductivity in one single component. Joining multi-material combinations such as Cu-SS, Cu-Al, Al-Steel, and D9-SS 316LN by conventional fusion welding techniques is difficult due to the difference in their mechanical and physical properties, causing hot cracking; therefore, electromagnetic joining (EMJ), which is based on cold forming can be a viable alternative to conventional fusion welding processes. EMJ offers many advantages in the efficient manufacturing of multi-material components, yet it has not been widely adopted in industries. Therefore, this thesis aims to expand upon various forms of the EMJ process for tubular components to expedite its adaptation.
Stability and control of flow past elliptic cylinders
(2022) Kumar, Deepak
Linear stability analysis of steady two-dimensional flow past elliptic cylinders of different aspect ratio (Ar) is conducted. Computations are carried out for flow Reynolds number (Re) in the range 30-200. First, the main characteristics of the steady flow, like the bubble length, bubble width, separation Reynolds number, separation angle, drag coefficient, coefficients of the front and rear stagnation pressure, and the maximum vorticity on the cylinder surface have been obtained. The effect of blockage on the steady flow results has been studied by varying the location of the side boundaries. In certain cases, the flow properties are found to vary in a nonmonotonic fashion with change in the blockage. From the linear stability calculations, we find that there are three sets of complex eigenmodes (PWM, SWM and TWM) which become unstable with increase in Re. The critical Re for the onset of instability of these modes and the corresponding Strouhal number (St) have been computed. The effect of blockage on the linear stability results is also studied. Structural sensitivity analysis is conducted to find the region best suited for effecting control of the unstable modes. We carry out unsteady computations by selectively suppressing one or more linear modes to see the kind of flow which evolves and, as a result, make an attempt to understand the role of the unstable linear modes in the fully developed nonlinear flow.
Design and Development of Metal Hydride System for Thermal Energy Storage and Hydrogen Storage Applications
(2022) Prasad, J Sunku
The world is progressing toward renewable energy resources because of the increase in demand for energy, the price of fossil fuels and the global warming effect. A major shift from fossil fuels to renewable energy sources is needed to save the environment from global warming and climate change. Renewable energy sources are often limited for commercial use due to their intermittent nature, i.e., inconsistent energy supply and demand. This issue in concentrated solar thermal power (CSTP) technology can be addressed by integrating a thermal energy storage (TES) system. The excess thermal energy is stored in the TES system during sunshine hours. The stored energy is retrieved for producing electricity during the off-sun hours, making the CSTP plant operate continuously throughout the day and night. Thermal energy can be stored in three different ways: sensible heat storage (SHS), latent heat storage (LHS), and thermochemical energy storage (TCES). The TCES system offers high energy density, wide operating temperatures, and long-term storage among all TES systems. Another promising technology for storing excess renewable energy is in the form of hydrogen. Hydrogen as an energy carrier offers a large-scale, long-term, and seasonal storage of excess renewable energy. The excess electricity produced by renewables (primarily wind and solar PV) during low energy demand periods generates hydrogen using an electrolyzer. The stored hydrogen is utilized in stationary fuel cells for combined power and heat as per the demand.
Design Development and Control of a Compact Autonomous Underwater Vehicle
(2022) Sahoo, Avilash
Unmanned Underwater Vehicles (UUVs) are robotic devices used for various underwater applications. UUVs have gained popularity in scientific community because of their potential applications ranging from military and research establishments to marine industries. Most of these devices are expensive, bulky and developed for deep ocean applications. To extend the benefits of this technology to small-scale industries and general public, affordable compact AUVs are need of the hour. Here the design and development of an affordable compact underwater robot is presented. After identifying the design requirements, the robot model is designed using 3D modeling software ``SOLIDWORKS". Matlab optimization toolbox is used for the estimation of optimal position of internal components. Shape optimization with Ansys Fluent is carried out for drag coefficient minimization. The designed model has been analyzed using Finite Element Analysis to ensure its structural integrity in the underwater environment. Here stress analysis is used to show that the UUV with glass fiber composite body can withstand the underwater pressure at 100m depth with 1.8 factor of safety. Computational Fluid Dynamics (CFD) study is used to estimate the drag and lift coefficients, and the maximum velocity of the robot. The validated design is used to manufacture the UUV body using glass fiber composite. The developed robot is neutrally buoyant and has a three-part modular structure. This robot has 4 Degrees of Freedom (DOF) and uses three thrusters for propulsion. It has a closed-frame watertight enclosure, which houses different essential components such as battery, depth and temperature sensors, camera, Raspberry pi computer, Pixhawk controller and thrusters. During operation, the robot is connected to the computer on the ground using tethered connect for transmission of live underwater footage, sensor data, and control signal. Detailed cost analysis of the developed robot is also presented. The robot was successfully tested in a swimming pool, nearby river, and lakes, and the results are discussed.
Dynamic analyses of PZT based active nonlinear vibration absorbers
(2022) Mohanty, Sibananda
There are many physical systems such as engineering structures or machines which undergo severe vibration and need a reduction in vibration by using passive or active vibration absorbers. In the passive vibration absorber, structural modification is carried out by attaching an additional spring-mass-damper system to the vibrating main or primary system to reduce its vibration. Whereas in the active vibration absorber (AVA) various sensors and actuators are integrated with the passive vibration absorber to suppress the vibration of the primary system. The vibration absorbers are generally designed based on the assumption that the absorber structure possesses linear characteristics. However, an effective vibration absorber vibrates with a large amplitude leading to the dominance of structural nonlinearity. Thus, the linearity assumption regarding the elastic properties of the absorber substructure does not hold good in reality. Also, nonlinearity is inherently present in the main vibrating primary systems due to prolonged use, certain applications, or being subjected to various forms of external excitations. The available passive and active vibration absorbers also come up short to suppress the vibration in nonlinear primary systems under varied resonance conditions. Since the existence of nonlinearity in the primary systems and the absorber system are inevitable. It is observed from the literature that with the available passive or active vibration absorbers the vibration reduction of the primary system under varied resonance conditions is still high or limited to a very narrow range of operating frequencies. Also, complete vibration suppression of the nonlinear vibrating primary system is not achieved under various resonance conditions. The investigations of AVA with acceleration or combination feedbacks (displacement, velocity and acceleration) and its effectiveness in vibration suppression are also not explored. So, in the present thesis, a modified designed piezoelectric stack actuator based active nonlinear vibration absorber (ANVA) with various feedbacks and time delay is considered, where the frequency of the absorber can be actively changed to suppress the vibration of the primary system. In the modified designed ANVA the PZT (lead zirconium titanate) stack actuator is connected in series connection with a spring in the absorber configuration for a fail-safe design.
Numerical Investigation of the Unsteady Aerodynamics of ‘Passer Domesticus’ Inspired Biomimetic Wing
(2022) Shaik, Masuruddin
The flapping flight, which is governed by the unsteady aerodynamics, deals with inherent complexities especially at low Reynolds number (Re). Understanding the low physics behind these intricacies may lead to a great chance of enhancing the aerodynamic performance of Flapping Wing Micro Air Vehicles (FW-MAVs). Nature provides a variety of small flying birds and insects to achieve this goal via biomimicry. However, direct copying of concepts available in nature may not lead to feasible solutions. The balance between engineering implementation and exploitation of concepts from nature may lead to successful designs. The work presented in this dissertation attempts at bringing this vision a little closer to realization.

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