Efficiently mapping high-performance early vision algorithms onto multicore embedded platforms

The combination of low-cost imaging chips and high-performance, multicore, embedded processors heralds a new era in portable vision systems. Early vision algorithms have the potential for highly data-parallel, integer execution. However, an implementation must operate within the constraints of embedded systems including low clock rate, low-power operation and with limited memory. This dissertation explores new approaches to adapt novel pixel-based vision algorithms for tomorrow's multicore embedded processors. It presents : - An adaptive, multimodal background modeling technique called Multimodal Mean that achieves high accuracy and frame rate performance with limited memory and a slow-clock, energy-efficient, integer processing core. - A new workload partitioning technique to optimize the execution of early vision algorithms on multi-core systems. - A novel data transfer technique called cat-tail dma that provides globally-ordered, non-blocking data transfers on a multicore system. By using efficient data representations, Multimodal Mean provides comparable accuracy to the widely used Mixture of Gaussians (MoG) multimodal method. However, it achieves a 6.2x improvement in performance while using 18% less storage than MoG while executing on a representative embedded platform. When this algorithm is adapted to a multicore execution environment, the new workload partitioning technique demonstrates an improvement in execution times of 25% with only a 125 ms system reaction time. It also reduced the overall number of data transfers by 50%. Finally, the cat-tail buffering technique reduces the data-transfer latency between execution cores and main memory by 32.8% over the baseline technique when executing Multimodal Mean. This technique concurrently performs data transfers with code execution on individual cores, while maintaining global ordering through low-overhead scheduling to prevent collisions.Ph.D.Committee Chair: Wills, Scott; Committee Co-Chair: Wills, Linda; Committee Member: Bader, David; Committee Member: Davis, Jeff; Committee Member: Hamblen, James; Committee Member: Lanterman, Aaro

Simulation of Airbus-A320 fuselage surface pressure fluctuations at cruise conditions in "Aeroacoustics research in Europe: The CEAS-ASC report on 2019 highlights"

The fuselage surface pressure fluctuations on an Airbus-A320 aircraft at cruise conditions are simulated by solving a Poisson equation. The right-hand-side source terms of the Poisson equation, including both the mean-shear term and the turbulence-turbulence term, are realized with synthetic anisotropic turbulence generated by the Fast Random Particle-Mesh Method. The stochastic realization is based on time-averaged turbulence statistics derived from a RANS simulation under the same condition as in the flight tests, conducted with DLR's Airbus-A320 research aircraft. The fuselage surface pressure fluctuations are calculated at three streamwise positions from front to rear corresponding to the measurement positions in the flight tests. One- and two-point spectral features of the pressure fluctuations relevant to the fuselage surface excitation are obtained and analysed

Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator

The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortex tubes in the center of the impingement region. The causality method based on Lighthill's acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill's stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic FJID models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data

ReSCon '12, Research Student Conference: Book of Abstracts

The fifth SED Research Student Conference (ReSCon2012) was hosted over three days, 18-20 June 2012, in the Hamilton Centre at Brunel University. The conference consisted of 130 oral and 70 poster presentations, based on the high quality and diverse research being conducted within the School of Engineering and Design by postgraduate research students. The conference is held annually, and ReSCon plays a key role in contributing to research and innovations within the School

Development of Imaging Fourier-Transform Spectroscopy for the Characterization of Turbulent Jet Flames

Recent advances in computational models to simulate turbulent, reactive flow fields have outpaced the ability to collect highly constraining data--throughout the entire flow field--for validating and improving such models. In particular, the ability to quantify in three dimensions both the mean scalar fields (i.e. temperature & species concentrations) and their respective fluctuation statistics via hyperspectral imaging would be a game-changing advancement in combustion diagnostics, with high impact in both validation and improvement efforts for computational combustion models. This research effort establishes imaging Fourier-transform spectrometry (IFTS) as a valuable tool (which complements laser diagnostics) for the study of turbulent combustion. Specifically, this effort (1) demonstrates that IFTS can be used to quantitatively measure spatially resolved spectra from a canonical turbulent flame; (2) establishes the utility of quantile spectra in first-ever quantitative comparisons between measured and modeled turbulent radiation interaction (TRI); (3) develops a simple onion-peeling-like spectral inversion methodology suitable for estimating radial scalar distributions in axisymmetric, optically-thick flames; (4) builds understanding of quantile spectra and demonstrates proof of concept for their use in estimating scalar fluctuation statistics

Case Studies in Invertebrate Visual Processing: I. Spectral and Spatial Processing in the Early Visual System of Drosophila melanogaster II. Binocular Stereopsis in Sepia officinalis

This thesis addresses two aspects of visual processing in two different invertebrate organisms. The fruit fly, Drosophila melanogaster, has emerged as a key model for invertebrate vision research. Despite extensive characterisation of motion vision, very little is known about how flies process colour information, or how the spectral content of light affects other visual modalities. With the aim to accurately dissect the different components of the Drosophila visual system responsible for processing colour, I have developed a versatile visual stimulation setup to probe for the combinations of spatial, temporal and spectral visual response properties. Using flies that express neural activity indicators, I can track visual responses to a colour stimulus (i.e. narrow bands of light across the spectrum) via a two-photon imaging system. The visual stimulus is projected on a specialised screen material that scatters wavelengths of light across the spectrum equally at all locations of the screen, thus enabling presentation of spatially structured stimuli. Using this setup, I have characterised spectral responses, intensity-response relationships, and receptive fields of neurons in the early visual system of a variety of genetically modified strains of Drosophila. Specifically, I compared visual responses in the medulla of flies expressing either a subset or all photoreceptor opsins, with differing levels of screening pigment present in the eye. I found layer-specific shifts of spectral response properties correlating with projection regions of photoreceptor terminals. I also 3 found that a reduction in screening pigment shifts the general spectral response in the neuropil towards the longer wavelengths of light. I have also mapped receptive fields across the different layers of the medulla for the peak spectral response wavelength. My results suggest that receptive field dimensions match the expected size predicted by the conservation of a columnar organisation in the medulla, with little variation from layer to layer. In a subset of these cells, we see an elongated receptive field suggestive of static orientation selectivity with an apparent split in the preferred axis of orientation of these receptive fields, with a near-orthogonal angle between the summed vectors of the split populations. The camera type eyes of vertebrates and cephalopods exhibit remarkable convergence, but it is currently unknown if the mechanisms for visual information processing in these brains, which exhibit wildly disparate architecture, is also shared. I chose to investigate the visual processing mechanism known as stereopsis in the cuttlefish Sepia officinalis. Stereoscopic vision is used to assess depth information by comparing the disparity between left and right visual fields. This strategy is commonplace in vertebrates having evolved multiple times independently but has only been demonstrated in one invertebrate: the praying mantis. Cuttlefish require precise distance estimation during their predatory hunt when they extend two tentacles in a ballistic strike to catch their target. Using a 3D perception paradigm whereby the cuttlefish were fitted with anaglyph glasses, I show that these animals use stereopsis to resolve distance to their prey. Although this is not an exclusive depth perception mechanism for hunting, it does shorten the time and distance covered prior to striking at a target. Furthermore, stereopsis in cuttlefish works differently to vertebrates, as cuttlefish can extract stereopsis cues from anti-correlated stimuli.BBSRC Doctoral Training Partnershi

NASA Tech Briefs, November 2010

Topics covered include: Portable Handheld Optical Window Inspection Device; Salience Assignment for Multiple-Instance Data and Its Application to Crop Yield Prediction; Speech Acquisition and Automatic Speech Recognition for Integrated Spacesuit Audio Systems ; Predicting Long-Range Traversability from Short-Range Stereo-Derived Geometry; Browser-Based Application for Telemetry Monitoring of Robotic Assets; Miniature Low-Noise G-Band I-Q Receiver; Methods of Using a Magnetic Field Response Sensor Within Closed, Electrically Conductive Containers; Differential Resonant Ring YIG Tuned Oscillator; Microfabricated Segmented-Involute-Foil Regenerator for Stirling Engines; Reducing Seal Adhesion in Low Impact Docking Systems; Optimal Flow Control Design; Corrosion-Resistant Container for Molten-Material Processing; Reusable Hot-Wire Cable Cutter; Deployment of a Curved Truss; High-Volume Airborne Fluids Handling Technologies to Fight Wildfires; Modeling of Alkane Oxidation Using Constituents and Species; Fabrication of Lanthanum Telluride 14-1-11 Zintl High-Temperature Thermoelectric Couple; A Computer Model for Analyzing Volatile Removal Assembly; Analysis of Nozzle Jet Plume Effects on Sonic Boom Signature; Optical Sidebands Multiplier; Single Spatial-Mode Room-Temperature-Operated 3.0 to 3.4 micrometer Diode Lasers; Self-Nulling Beam Combiner Using No External Phase Inverter; Portable Dew Point Mass Spectrometry System for Real-Time Gas and Moisture Analysis; Maximum Likelihood Time-of-Arrival Estimation of Optical Pulses via Photon-Counting Photodetectors; Handheld White Light Interferometer for Measuring Defect Depth in Windows; Decomposition Algorithm for Global Reachability on a Time-Varying Graph; Autonomous GN and C for Spacecraft Exploration of Comets and Asteroids; Efficient Web Services Policy Combination; Using CTX Image Features to Predict HiRISE-Equivalent Rock Density; Isolation of the Paenibacillus phoenicis, a Spore-Forming Bacterium; Monolithically Integrated, Mechanically Resilient Carbon-Based Probes for Scanning Probe Microscopy; Cell Radiation Experiment System; Process to Produce Iron Nanoparticle Lunar Dust Simulant Composite; Inversion Method for Early Detection of ARES-1 Case Breach Failure; Use of ILTV Control Laws for LaNCETS Flight Research;and Evaluating Descent and Ascent Trajectories Near Non-Spherical Bodies

Investigation of near and post stall behaviour of axial compression systems

The design of modern gas-turbine engines is continuously being improved towards better performance, better efficiency and reduced cost. This trend of aero-engine design requires compression systems which produce higher pressure ratios and thus, have higher loaded blades and a closer spacing between blade rows. Such designs are more prone to aerodynamic instabilities and consequent stall and surge can be catastrophic. The majority of the research conducted on compressor stall and surge is limited to old designs with lower pressure ratios or single stage compression systems. In this thesis, the near and post stall behaviour of a modern multi-stage high-speed intermediate pressure compressor rig and an aero-engine three-shaft compression system are studied in detail. The main objective is to develop and validate reliable CFD models to predict surge and rotating stall and shed light on the underlying physical mechanism of the phenomena. CFD computations were performed to gain understanding of the current capability to model the flow behaviour of a multi-stage compressor rig near stall condition. Two turbulence models were tested and an extensive grid discretization study was performed. In order to improve the prediction of the compressor's stability boundary, a modification in the widely known Spalart-Allmaras turbulence model is proposed. Subsequently, unsteady CFD computations were carried out to evaluate the impact of flow unsteadiness in the performance prediction of this compressor rig. It was found that for operating conditions characterized by non-axisymmetric flow features, an unsteady full annulus model is required to predict the compressor performance. For low speeds, these flow features develop over a wide range of operating conditions. When the compressor operates at high speeds, these flow features are limited to operating conditions near the stability boundary. The above findings were validated against experimental results. Early stages of this research revealed that numerical calibration of a CFD surge computation in a three-shaft engine is a challenging task due to compressor matching. Hence, an iterative methodology for matching the compressors was introduced and validated against experimental data. This study considered a surge event where the engine was initially operating at mid power condition. When comparing the numerical result with measured data, it was found that the engine bleed system has a major impact on the aerodynamic loading predictions in the core system. Therefore, this system needs to be considered by component designers when accounting for robustness to surge loads. The post stall response of a three-shaft engine compression system which is initially operating at design was investigated. It was found that the maximum surge over-pressures are caused by a combined effect between a surge induced shock wave and high pressure gas travelling towards the core inlet during the surge blow-down period. Furthermore, it was demonstrated that the maximum surge loads are obtained for a surge event initiated by fuel-spike. Finally, a cheaper computational approach to model surge in axial compression systems is proposed. This approach consisted of using an unsteady single passage model to predict the flow behaviour during the surge event. After comparison with full annulus results for three different scenarios, it was concluded that the single passage is capable of predicting the blow-down period of surge which is characterized by a long period of flow reversal. This model fails to predict the correct time and length scales during surge onset and flow transition between reverse to forward flow at the beginning of recovery. These time instants are characterized by non-axisymmetric flow features. However, the single passage model shows a good correlation with the results obtained using a full annulus model for estimation of average values of static pressure and mass flows during surge. This can drastically reduce simulations times from months to days during compressor surge analysis.Open Acces

Experimental Investigation of Supersonic Jets Using Optical Diagnostics

The complexity of many fluid flows and phenomena is a well-known characteristic driven primarily by turbulence, which has been a focal point of study for decades. Most engineering applications in fluids will encounter turbulence, and hence the need to understand how turbulence might influence the problem at hand is omnipresent. In many turbulent flows, there are large-scale coherent structures which directly influence macro-scale processes of engineering relevance, such as noise production. Over decades of study, it has been demonstrated that similar structures are often observed across many flowfields, despite differences in characteristic parameters, and this has led to the pursuit of simplified models through the use of these dominant, shared structures. Large-scale, coherent structures are of particular importance in turbulent jets, as they represent efficient sources of sound. Noise reduction of subsonic and supersonic fluid jets represents a large interest in the study of acoustic production in jets, and much of it is viewed in the context of controlling these large-scale structures. Supersonic jets in particular may emit an intense sound known as jet screech as a consequence of these structures. This noise source easily has the potential to be damaging to both structures and humans in close proximity, and is a particular target of noise reduction efforts. Turbulent flowfields from two supersonic, underexpanded, screeching jets are analyzed by means of three non-intrusive, high-speed, optical diagnostics. The first technique is high-speed schlieren. The second technique is pulse-burst particle image velocimetry (PB-PIV). The third technique is known as focused laser differential interferometry (FLDI). Extensive spectral, statistical, and modal decomposition analyses are used in this work to identify, extract, and characterize the most energetic features and coherent structures associated with jet screech. The large field of view of the image-based datasets is fully taken advantage of by creating spatial maps of spectral and statistical quantities, which highlight regions of increased fluctuations or activity. These are shown to agree with, or demonstrate additional features that could not be reproduced by the modal analyses. Modal analyses are used to evaluate the structure of the most energetic components in the flow of both screeching jets