Intake Ground Vortex Prediction Methods

For an aircraft turbofan engine in ground operations or during the take-off run a ground vortex can occur which is ingested and could potentially adversely affect the engine performance and operation. The vortex characteristics depend on the ground clearance, intake flow capture ratio and the relative wind vector. It is a complex flow for which there is currently very little appropriate quantitative preliminary design information. These aspects are addressed in this work where a range of models are developed to provide a method for estimating the key metrics such as the formation boundary and the ground vortex size and strength. Three techniques are presented which utilize empirical, analytical and semi-empirical approaches. The empirical methods are primarily based on a large dataset of model-scale experiments which quantitatively measured the ground vortex characteristics for a wide range of configurations. These include the effects of intake ground clearance, approaching boundary layer thickness, intake Mach number and capture velocity ratio. Overall the models are able to predict some of the key measured behaviours such as the velocity ratio for maximum vortex strength. With increasing empiricism for key sub-elements of the model construction, an increasing level of agreement is found with the experimental results. Overall the three techniques provide a relatively quick and easy method in establishing the important vortex characteristics for a given headwind configuration which is of significant use from a practical engineering perspective

The simulation of transient cross winds on passenger vehicles.

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Etäisyyden huomioiva kaksiulotteinen viivakoodi mobiilikäyttötapauksiin

Global internet use is becoming increasingly mobile, and mobile data usage is growing exponentially. This puts increasing stress on the radio frequency spectrum that cellular and Wi-Fi networks use. As a consequence, research has also been conducted to develop wireless technologies for other parts of the electromagnetic spectrum – namely, visible light. One approach of using the visible light channel for wireless communication leverages barcodes. In this thesis, we propose a 2D barcode that can display different information based on the distance between the barcode and the scanner. Earlier research on distance-sensitive barcodes has focused on providing a closer viewer more information as a closer viewer can see more detail. In contrast, we target use cases where a clear physical separation between users of different roles can be made, such as presentation systems. We evaluate two methods of achieving distance-awareness: color-shifting of individual colors, where a color changes tone at longer distances, and color blending, where two colors blend into a third color at longer viewing distances. Our results show that a modern smartphone is capable of leveraging color-shifting in ideal conditions, but external changes such as ambient lighting render color-shifting unusable in practical scenarios. On the other hand, color blending is robust in varying indoor conditions and can be used to construct a reliable distance-aware barcode. Accordingly, we employ color blending to design a distance-aware barcode. We implement our solution in an off-the-shelf Android smartphone. Experimental results show that our scheme achieves a clear separation between close and far viewers. As a representative use case, we also implement a presentation system where a single barcode provides the presenter access to presentation tools and the audience access to auxiliary presentation material.Maailmanlaajuinen internetin käyttö muuttuu yhä liikkuvammaksi, ja mobiilidatan käyttö kasvaa eksponentiaalisesti. Tämä kohdistaa yhä suurempia vaatimuksia radiotaajuusspektriin, jota mobiili- ja Wi-Fi-verkot käyttävät. Näin ollen tutkijat ovat kehittäneet langattomia teknologioita hyödyntäen myös muita sähkömagneettisen spektrin osia – erityisesti näkyvää valoa. Yksi näkyvän valon sovellus langattomassa viestinnässä ovat viivakoodit. Tässä työssä kehitämme kaksiulotteisen viivakoodin, joka pystyy välittämään eri tietoa katselijoille eri etäisyyksillä. Aiempi etäisyyden huomioivien viivakoodien tutkimus on keskittynyt tarjoamaan lähellä olevalle katselijalle enemmän tietoa, koska läheinen katselija näkee viivakoodin tarkemmin. Sitä vastoin me keskitymme käyttötapauksiin, joissa eri käyttäjäroolien välillä on selkeä etäisyydellinen ero, kuten esimerkiksi esitelmissä puhujan ja yleisön välillä. Tarkastelemme kahta menetelmää: yksittäisten värien muutoksia etäisyyden muuttuessa ja kahden värin sekoittumista etäisyyden kasvaessa. Tulostemme perusteella nykyaikainen älypuhelin pystyy hyödyntämään yksittäisten värien muutoksia ihanteellisissa olosuhteissa, mutta ulkoiset tekijät, kuten ympäristön valaistus, aiheuttavat liian suuria värimuutoksia käytännön käyttötapauksissa. Toisaalta värien sekoittuminen on johdonmukaista muuttuvassa sisäympäristössä ja sitä voidaan käyttää luotettavan viivakoodin luomisessa. Näin ollen me suunnittelemme etäisyyden huomioivan viivakoodin hyödyntäen värien sekoittumista. Toteutamme ratkaisumme yleisesti saatavilla olevalle Android-älypuhelimelle. Kokeellisten tulostemme perusteella menetelmämme saavuttaa selkeän erottelun läheisten ja kaukaisten katselijoiden välillä. Esimerkkikäyttötapauksena toteutamme myös esitelmäjärjestelmän, jossa sama viivakoodi antaa lähellä olevalle puhujalle nopean pääsyn esitystyökaluihin ja kauempana olevalle yleisölle pääsyn esityksen apumateriaaliin

Three-dimensional contact patch strain measurement inside rolling off-Road tyres

The forces generated in the tyre contact-patch are important for vehicle dynamics analysis. The tyre contact patch is not directly visible due to the terrain. Measuring the strain in the contact patch region may give insight into the forces generated by the tyre as it deforms. Strain measurement in the contact patch is often limited to discrete points, using strain gauges or other techniques which limits data capture to once per revolution. In this study stereovision cameras are used to capture unique features in the pattern painted on the tyres inner surface. An in-tyre mechanically stabilized camera system allows the contact patch to be captured continuously and the stereovision cameras allow for full field measurement of the tyre inner surface. In post processing the features are tracked and triangulated to form point-clouds for each time step. Point-clouds are compared to determine the strain of common points in two directions. The system is applied to an agricultural tyre with large tread-blocks. The wheel is instrumented to measure pressure and forces. The tyre is tested statically in a series of tyre tests where the lateral, longitudinal and vertical displacement is controlled. The strain measured in the tyre contact patch region is compared to the forces measured at the wheel centre. It is noticed that as the measured forces increases so too does the magnitudes of the strains. Unique patterns are found in the contact patch strain for each test type. These patterns could be used to identify the type of forces experienced by the wheel while the strain magnitude could give an indication of the magnitude of the forces. Future work could allow for strain measurement in the contact patch as the tyre rolls over deformable terrain where displacement is not easily controlled.Dissertation (MEng)--University of Pretoria, 2019.Mechanical and Aeronautical EngineeringMEngUnrestricte

High Speed Camera Chip

abstract: The market for high speed camera chips, or image sensors, has experienced rapid growth over the past decades owing to its broad application space in security, biomedical equipment, and mobile devices. CMOS (complementary metal-oxide-semiconductor) technology has significantly improved the performance of the high speed camera chip by enabling the monolithic integration of pixel circuits and on-chip analog-to-digital conversion. However, for low light intensity applications, many CMOS image sensors have a sub-optimum dynamic range, particularly in high speed operation. Thus the requirements for a sensor to have a high frame rate and high fill factor is attracting more attention. Another drawback for the high speed camera chip is its high power demands due to its high operating frequency. Therefore, a CMOS image sensor with high frame rate, high fill factor, high voltage range and low power is difficult to realize. This thesis presents the design of pixel circuit, the pixel array and column readout chain for a high speed camera chip. An integrated PN (positive-negative) junction photodiode and an accompanying ten transistor pixel circuit are implemented using a 0.18 µm CMOS technology. Multiple methods are applied to minimize the subthreshold currents, which is critical for low light detection. A layout sharing technique is used to increase the fill factor to 64.63%. Four programmable gain amplifiers (PGAs) and 10-bit pipeline analog-to-digital converters (ADCs) are added to complete on-chip analog to digital conversion. The simulation results of extracted circuit indicate ENOB (effective number of bits) is greater than 8 bits with FoM (figures of merit) =0.789. The minimum detectable voltage level is determined to be 470μV based on noise analysis. The total power consumption of PGA and ADC is 8.2mW for each conversion. The whole camera chip reaches 10508 frames per second (fps) at full resolution with 3.1mm x 3.4mm area.Dissertation/ThesisMasters Thesis Electrical Engineering 201

Algorithms for Fault Detection and Diagnosis

Due to the increasing demand for security and reliability in manufacturing and mechatronic systems, early detection and diagnosis of faults are key points to reduce economic losses caused by unscheduled maintenance and downtimes, to increase safety, to prevent the endangerment of human beings involved in the process operations and to improve reliability and availability of autonomous systems. The development of algorithms for health monitoring and fault and anomaly detection, capable of the early detection, isolation, or even prediction of technical component malfunctioning, is becoming more and more crucial in this context. This Special Issue is devoted to new research efforts and results concerning recent advances and challenges in the application of “Algorithms for Fault Detection and Diagnosis”, articulated over a wide range of sectors. The aim is to provide a collection of some of the current state-of-the-art algorithms within this context, together with new advanced theoretical solutions

Rock-shape and its role in rockfall dynamics

Rockfall threaten infrastructure and people throughout the world. Estimating the runout dynamics of rockfall is commonly performed using models, providing fundamental data for hazard management and mitigation design. Modelling rockfall is made challenging by the complexity of rock-ground impacts. Much research has focused on empirical impact laws that bundle the rock-ground impact into a single parameter, but this approach fails to capture characteristics associated with the impact configuration and, in particular, the effects of rock-shape. While it is apparent that particular geological settings produce characteristic rock-shapes, and that different rock-shapes may produce characteristic runout dynamics, these aspects of rockfall are poorly understood. This study has focused on investigating the mechanics behind the notion that different rock-shapes produce characteristic runout dynamics and trajectories. The study combines field data on rockfall runout, trajectory and dynamics, laboratory analogue testing in controlled conditions, and numerical modelling of the influence of rock-shape. Initially rock-shape, deposition patterns and rockfall dynamics were documented at rockfall sites in Switzerland and New Zealand. This informed a detailed study of individual rock-ground impacts on planar slopes in which laboratory-scale and numerical rockfall experiments were combined to isolate the role of rock-shape on runout. Innovatively, the physical experiments captured the dynamics of impacts and runout paths using high speed video tracking and a sensor bundle with accelerometers and gyroscopes. Numerical experiments were performed using a 3-D rigid-body rockfall model that considers rock-shape, and has allowed the variability of rockfall behaviour to be explored beyond the limitations of physical experimentation. The main findings of the study were on understanding rockfall-ground impacts, the influence of rock-shape on rockfall dynamics, and influence of rock sphericity. By measuring velocity, rotational speed, impact and runout character, it has been possible to quantify the variability of individual rock-ground impacts as a function of rock-shape. Investigation of single rebounds reveals that if classical restitution coefficients are applied, $R_n$ values greater than unity are common and rebounds are highly variable regardless of constant contact parameters. It is shown that this variability is rooted in the inherent differences in the magnitudes of the principal moment of inertia of a rock body brought about by rock-shape. Any departure from a perfect sphere induces increased range and variability in rock-ground rebound characteristics. In addition to the popular description of a rock bouncing down slope, rebounds involve the pinning of an exterior edge point on the rock, creating a moment arm which effectively levers the rock into ballistic trajectory as it rotates. Observations reveal that the angle of the impact configuration plays a key role in the resulting rebound, whereby low angles produce highly arched rebounds, while large impact angles produce low flat rebounds. The type of rebound produced has a strong bearing on the mobility of the rocks and their ability to maintain motion over a long runout. The mobility of rocks is also shown to be related to rotation, which is governed by the differences in the principal inertial axes as a function of rock-shape. Angular velocity measurements about each principal inertial axis indicate that rocks have a tendency to seek rotation about the axis of largest inertia, as the most stable state. Rotations about intermediate and small axes of inertia and transitions between rotational axes are shown to be unstable and responsible for the dispersive nature of runout trajectories, which are inherent characteristics of different rock-shapes. The findings of this research demonstrate the importance of rock-shape in rockfall runout dynamics and illustrate how it is essential that the rock-shape is included in rockfall modelling approaches if the variability of rockfall behaviour is to be simulated

The simulation of transient cross-wind gusts and their aerodynamic influence on passenger cars.

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