Quality-of-service-centric design and analysis of unmanned aerial vehicles

Recent years have witnessed rapid development and great indignation burgeoning in the unmanned aerial vehicles (UAV) field. This growth of UAV-related research contributes to several challenges, including inter-communication from vehicle to vehicle, transportation coverage, network information gathering, network interworking effectiveness, etc. Due to ease of usage, UAVs have found novel applications in various areas such as agriculture, defence, security, medicine, and observation for traffic-monitoring applications. This paper presents an innovative drone system by designing and developing a blended-wing-body (BWB)-based configuration for next-generation drone use cases. The proposed method has several benefits, including a very low interference drag, evenly distributed load inside the body, and less radar signature compared to the state-of-the-art configurations. During the entire procedure, a standard design approach was followed to optimise the BWB framework for next-generation use cases by considering the typically associated parameters such as vertical take-off and landing and drag and stability of the BWB. Extensive simulation experiments were performed to carry out a performance analysis of the proposed model in a software-based environment. To further confirm that the model design of the BWB-UAV is fit to execute the targeted missions, the real-time working environments were tested through advanced numerical simulation and focused on avoiding cost and unwanted wastages. To enhance the trustworthiness of this said computational fluid dynamics (CFD) analysis, grid convergence test-based validation was also conducted. Two different grid convergence tests were conducted on the induced velocity of the Version I UAV and equivalent stress of the Version II UAV. Finite element analysis-based computations were involved in estimating structural outcomes. Finally, the mesh quality was obtained as 0.984 out of 1. The proposed model is very cost-effective for performing a different kind of manoeuvring activities with the help of its unique design at reasonable mobility speed and hence can be modelled for high-speed-based complex next-generation use cases

Pattern formation and hydrogen production in suspensions of swimming green algae

This thesis concerns two aspects of microorganism behaviour. Firstly, the phenomenon of bioconvection is explored, where suspensions of motile microorganisms that are denser than the fluid in which they swim spontaneously form concentrated aggregations of cells that drive fluid motion, forming intricate patterns. The cells considered herein orientate by gyrotaxis, a balance between a gravitational torque due to uneven starch deposits causing cells to be bottom heavy and a viscous torque due to fluid flow gradients, and phototaxis, biased movement towards or away from a light source. In Chapters 2 and 3, a stochastic continuum model for gyrotaxis is extended to include phototaxis using three physically diverse and novel methods. A linear stability analysis is performed for each model and the most unstable wavenumber for a range of parameter values is predicted. For two of the models, sufficiently strong illumination is found to stabilize all wavenumbers compared to the gyrotaxis only case. Phototaxis is also found to yield non-zero critical wavenumbers under such strong illumination. Two mechanisms that lead to oscillatory solutions are presented. Dramatically different results are found for the third model, where instabilities arise even in the absence of fluid flow. In Chapter 4, an experimental study of pattern formation by the photo-gyrotactic unicellular green alga species Chlamydomonas nivalis is presented. Fourier analysis is used to extract the wavelength of the initial dominant mode. Variations in red light illumination are found to have no significant effect on the initial pattern wavelength. However, fascinating trends for the effects of cell concentration and white light intensity on cells illuminated either from above or below are described. This work concludes with comparisons between theoretical predictions and experimental results, between which good agreement is found. Secondly, we investigate the intracellular pathways and processes that lead to hydrogen production upon implementation of a two-stage sulphur deprivation method in the green alga C. reinhardtii. In Chapter 5, a novel model of this system is constructed from a consideration of the main cellular processes. Model results for a range of initial conditions are found to be consistent with published experimental results. In Chapter 6, a parameter sensitivity of the model is performed and a study in which different sulphur input functions are used to optimize the yield of hydrogen gas over a set time is presented, with the aim of improving the commercial and economic viability of algal hydrogen production. One such continuous sulphur input function is found to significantly increase the yield of hydrogen gas compared to using the discontinuous two-stage cycling of Ghirardi et al. (2000)

High-Voltage Integrated Circuits design and validation for automotive applications

Electronic Integrated Circuits (ICs) are an important pillar of the automotive market, especially since legal and safety requirements have been introduced to manage vehicles emissions and behaviors. Furthermore, the harsh environment and the tight safety requirements, summed with the market that is pushing to reduce the development lead time and to increase the system complexity, require to develop dedicated ICs for the automotive applications. This thesis presents some peculiar high-power and high-voltage ICs for automotive applications that have been studied, designed and developed taking into account all the requirements that automotive grade ICs have to respect, with emphasis on performance, quality and safety aspects. Particularly the thesis reports the design and validation of power management blocks and output drivers for inductive loads, showing how to fulfill in an effective way the performance, quality and safety targets according to the guidelines and the constraints of the latest automotive standards, like ISO26262 and AEC-Q100. All the designed ICs has been simulated and manufactured, including layout drawings, in a 0.35um HV-CMOS technology from AMS. The effectiveness and robustness of the proposed circuits has been validated on silicon and corresponded measurement results has been reported

NEGATIVE BIAS TEMPERATURE INSTABILITY STUDIES FOR ANALOG SOC CIRCUITS

Negative Bias Temperature Instability (NBTI) is one of the recent reliability issues in sub threshold CMOS circuits. NBTI effect on analog circuits, which require matched device pairs and mismatches, will cause circuit failure. This work is to assess the NBTI effect considering the voltage and the temperature variations. It also provides a working knowledge of NBTI awareness to the circuit design community for reliable design of the SOC analog circuit. There have been numerous studies to date on the NBTI effect to analog circuits. However, other researchers did not study the implication of NBTI stress on analog circuits utilizing bandgap reference circuit. The reliability performance of all matched pair circuits, particularly the bandgap reference, is at the mercy of aging differential. Reliability simulation is mandatory to obtain realistic risk evaluation for circuit design reliability qualification. It is applicable to all circuit aging problems covering both analog and digital. Failure rate varies as a function of voltage and temperature. It is shown that PMOS is the reliabilitysusceptible device and NBTI is the most vital failure mechanism for analog circuit in sub-micrometer CMOS technology. This study provides a complete reliability simulation analysis of the on-die Thermal Sensor and the Digital Analog Converter (DAC) circuits and analyzes the effect of NBTI using reliability simulation tool. In order to check out the robustness of the NBTI-induced SOC circuit design, a bum-in experiment was conducted on the DAC circuits. The NBTI degradation observed in the reliability simulation analysis has given a clue that under a severe stress condition, a massive voltage threshold mismatch of beyond the 2mV limit was recorded. Bum-in experimental result on DAC proves the reliability sensitivity of NBTI to the DAC circuitry

Rocket-Based Combined-Cycle (RBCC) Propulsion Technology Workshop. Tutorial session

The goal of this workshop was to illuminate the nation's space transportation and propulsion engineering community on the potential of hypersonic combined cycle (airbreathing/rocket) propulsion systems for future space transportation applications. Four general topics were examined: (1) selections from the expansive advanced propulsion archival resource; (2) related propulsion systems technical backgrounds; (3) RBCC engine multimode operations related subsystem background; and (4) focused review of propulsion aspects of current related programs

End-of-Life and Constant Rate Reliability Modeling for Semiconductor Packages Using Knowledge-Based Test Approaches

End-of-life and constant rate reliability modeling for semiconductor packages are the focuses of this dissertation. Knowledge-based testing approaches are applied and the test-to-failure approach is approved to be a reliable approach. First of all, the end-of-life AF models for solder joint reliability are studied. The research results show using one universal AF model for all packages is flawed approach. An assessment matrix is generated to guide the application of AF models. The AF models chosen should be either assessed based on available data or validated through accelerated stress tests. A common model can be applied if the packages have similar structures and materials. The studies show that different AF models will be required for SnPb solder joints and SAC lead-free solder joints. Second, solder bumps under power cycling conditions are found to follow constant rate reliability models due to variations of the operating conditions. Case studies demonstrate that a constant rate reliability model is appropriate to describe non solder joint related semiconductor package failures as well. Third, the dissertation describes the rate models using Chi-square approach cannot correlate well with the expected failure mechanisms in field applications. The estimation of the upper bound using a Chi-square value from zero failure is flawed. The dissertation emphasizes that the failure data is required for the failure rate estimation. A simple but tighter approach is proposed and provides much tighter bounds in comparison of other approaches available. Last, the reliability of solder bumps in flip chip packages under power cycling conditions is studied. The bump materials and underfill materials will significantly influence the reliability of the solder bumps. A set of comparable bump materials and the underfill materials will dramatically improve the end-of-life solder bumps under power cycling loads, and bump materials are one of the most significant factors. Comparing to the field failure data obtained, the end-of-life model does not predict the failures in the field, which is more close to an approximately constant failure rate. In addition, the studies find an improper underfill material could change the failure location from solder bump cracking to ILD cracking or BGA solder joint failures