Дисертації з теми "Ray-tracing modelling"

In response to the requirement for a more detailed channel model based on the physical characteristics of the environment within which indoor radio communications operate, this thesis presents a channel model based on ray tracing techniques. The mathematical basis for the model is presented in terms of the electromagnetic properties of simple objects. The resulting model is coded into a simulation system which takes a description of a building in terms of the structure of internal walls, floors and ceilings. Through repeated application of the reflection process, a description of the channel impulse response is created for a given transmitter and receiver position from the multipath components generated. This model is applied, in progressing degrees of complexity, to two buildings for which narrowband physical measurements are available. Comparison is made between the measured results and the narrowband simulation results which leads to an analysis of the various propagation mechanisms involved in in-building communications. It is found that the model, while not accurately predicting the measured results, does produce a model that, considering the unknown parameters of the environment and experimental procedure, relates well to the channel experienced by a communication system. Wideband channel characteristics are determined from the simulation model, and found to give access to more detailed information on the channel than is obtainable through physical measurement. The results of the wideband simulations are compared with published material containing measurement results, and the relationship to the narrowband results already presented is shown.

A visualisation procedure was developed which predicts excited hydroxyl (OH*) radiation from the Computational Fluid Dynamics (CFD) solutions of cryogenic hydrogen-oxygen rocket flames. The model of backward ray tracing through inhomogeneous media with a continuously changing refractive index was implemented. It obtains the optical paths of light rays that originate in the rocket chamber, pass through the window and enter a simulated camera. Through the use of spectral modelling, the emission and absorption spectra eλ and κλ are simulated on the ray path from information about temperature, pressure and concentration of constituent species at relevant points. By solving a radiative transfer equation with the integration of emission and absorption spectra along the ray line-by-line, a spectral radiance is calculated, multiplied with the spectral filter transmittance and then integrated into total radiance. The values of total radiances at the window edge are visualised as a simulated 2D image. Such images are comparable with the OH* measurement images. The modelling of refraction effects results in up to 20 % of total radiance range absolute difference compared to line-of-sight integration. The implementation of accurate self-absorption corrects significant over-prediction, which occurs if the flame is assumed to be optically thin. Modelling of refraction results in images with recognisable areas where the effect of a liquid oxygen (LOx) jet core can be observed, as the light is significantly refracted. The algorithm is parallelised and thus ready for use on big computational clusters. It uses partial pre-computation of spectra to reduce computational effort.

Optical wireless networks-on-chip (OWiNoC) are considered as a promising solution to overcome the communication bottleneck due to wired interconnects in modern chip multiprocessor systems. The efficient implementation of optical wireless links requires considering many different aspects, including analysis and deep understanding of the effects on the propagation of the electromagnetic field induced by the discontinuities that can be found in a realistic scenario. Optical Wireless Networks on Chip have become an ambitious but attractive solution to increase computing performances in multi-core/multi-chip architectures. To assess the benefit of the wireless optical solution a truthful characterization of the wireless channel at the chip scale has to be carried out. Propagation in Optical Wireless Network on Chip occurs in a layered environment, where the layer thickness is often very small compared to the link distance: a high order of multiple reflections/refraction bounces is therefore necessary, triggering strong multipath effect. In this thesis the effectiveness of different propagation models, taking into account different propagation mechanisms are investigated, through comparison with measurements. The outcome will be a set of tools permitting the design and the performance evaluation of on-chip wireless optical communications as a function of the main parameters of the link components and geometries, including the presence of interference from other transmitters, opening the possibility to design new architectures for many-core and kilo-core CMPs.

Concentrated Solar Power (CSP) constitutes one suitable solution for exploiting solar resources for power generation. In this context, parabolic dish systems concentrate the solar radiation onto a point focusing receiver for small-scale power production. Given the modularity feature of such system, the scale-up is a feasible option; however, they offer a suitable solution for small scale off-grid electrification of rural areas. These systems are usually used with Stirling engines, nevertheless the coupling with micro-gas turbines presents a number of advantages, related to the reliability of the system and the lower level of maintenance required. The OMSoP project, funded by the European Union, aims at the demonstration of a parabolic dish coupled with an air-driven Brayton cycle. By looking at the integrated system, a key-role is played by the solar receiver, whose function is the absorption of the concentrated solar radiation and its transfer to the heat transfer fluid. Volumetric solar receivers constitute a novel and promising solution for such applications; the use of a porous matrix for the solar radiation absorption allows reaching higher temperature within a compact volume, while reducing the heat transfer losses between the fluid and the absorption medium. The aim of the present work is to deliver a set of optimal design specifications for a volumetric solar receiver for the OMSoP project. The work is based on a Multi-Objective Optimization algorithm, with the objective of the enhancement of the receiver thermal efficiency and of the reduction of the pressure drop. The optimization routine is coupled with a detailed analysis of the component, based on a Computational Fluid Dynamics model and a Mechanical Stress Analysis. The boundary conditions are given by the OMSoP project, in terms of dish specifications and power cycle, whilst the solar radiation boundary is modelled by means of a Ray Tracing routine. The outcome of the analysis is the assessment of the impact on the receiver performance of some key design parameters, namely the porous material properties and the receiver geometrical dimensions. From the results, it is observed a general low pressure drop related to the nominal air mass flow, with several points respecting the materials limitations. One design point is chosen among the optimal points, which respects the OMSoP project requirements for the design objectives, i.e. a minimum value of efficiency of 70%, and pressure losses below 1%. The final receiver configuration performs with an efficiency value of 86%, with relative pressure drop of 0.5%, and it is based on a ceramic foam absorber made of silicon carbide, with porosity value of 0.94.  Moreover, the detailed analysis of one volumetric receiver configuration to be integrated in the OMSoP project shows promising results for experimental testing and for its actual integration in the system.

An investigation into the light scattering properties of Saharan dust grains is presented. An electrodynamic trap has been used to levitate single dust particles. By adjusting the trap parameters, partial randomisation of the particle orientation has been introduced. While levitated, the particles were illuminated by a laser, and a rotating half-wave retarder enabled selection of vertically or horizontally polarized incident light. A laser diffractometer and linear photodiode array have been used to measure intensity at scattering angles between 0.5° and 177°. Combining these measurements with Fraunhofer diffraction as calculated for a range of appropriately-sized apertures allows the calculation of the phase function and degree of linear polarization. The phase functions and degree of linear polarisation for four case study particles are presented - the phase functions are found to be featureless across most of the scattering region, with none of the halo features or rainbow peaks associated with regularly shaped particles such as hexagonal columns or spheres. Particle models comprised of large numbers of facets have been constructed to resemble the levitated particles. Utilizing Gaussian random sphere methods, increasing levels of roughness have been added to the surfaces of these models. A Geometric Optics model and a related model, Ray Tracing with Diffraction on Facets, have been modified to calculate scattering on these particle reconstructions. Scattering calculations were performed on each of these reconstructions using a range of refractive indices and two rotation regimes – one where the orientations of the reconstructed particle were limited to match those observed when the particle was levitated, and one where the orientation was not limited. Qualitative comparisons are performed on the phase functions and degree of linear polarization, where it is observed that the addition of roughness to the modelled spheroids causes the computed phase functions to increasingly resemble those from the levitated particles. Limiting the orientation of the particles does not affect the scattering noticeably. The addition of a very small absorption coefficient does not change the comparisons considerably. As the absorption coefficient is increased, however, the quality of the comparisons decreases rapidly in all cases but one. The phase functions are quantitatively compared using RMS errors, and further comparison is performed using the asymmetry parameter.

The non-hydrostatic dynamical core ENDGame (Even Newer Dynamics for the General Atmospheric Modelling of the Environment) is extended into the thermosphere to test its feasability as a whole-atmosphere dynamical core that can simulate the large scale fluid dynamics of the whole atmosphere from the surface to the top of the thermosphere at 600km. This research may have applications in the development of a Sun-to-Earth modelling system involving the Met Office Unified Model, which will be useful for space weather forecasting and chemical climate modelling. Initial attempts to raise the top boundary of ENDGame above ∼100km give rise to instabilities. To explore the potential causes of these instabilities, a one dimensional column version of ENDGame: ENDGame1D, is developed to study the effects of vertically propagating acoustic waves in the dynamical core. A 2D ray-tracing scheme is also developed, which accounts for the numerical effects on wave propagation. It is found that ENDGame’s numerics have a tendency towards the excessive focussing of wave energy towards vertical propagation, and have poor handling of large amplitude waves, also being unable to handle shocks. A key finding is that the physical processes of vertical molecular viscosity and diffusion prevent the excessive growth of wave amplitudes in the thermosphere in ENDGame, which may be crucial to improving ENDGame’s stability as it is extended upwards. Therefore, a fully implicit-in-time implementation of vertical molecular viscosity and diffusion is developed in both ENDGame1D and the full three-dimensional version of ENDGame: ENDGame3D. A new scheme is developed to deal with the viscous and diffusive terms with the dynamics terms in a fully coupled way to avoid time-splitting errors that may arise. The combination of a small amount of off-centring of ENDGame’s semi-implicit formulation and the inclusion of vertical molecular viscosity and diffusion act to make ENDGame significantly more stable, as long as the simulation is able to remain stable up to the molecularly diffused region above an altitude of ∼130km.

Ces travaux de recherche s’inscrivent dans la problématique scientifique de reconstruction du relief sous un couvert végétal à partir d’observations aéroportées. Le scanner laser aéroporté est une technique d’imagerie très prometteuse, notamment pour l’observation des zones forestières. Sa déclinaison "onde complète" consiste à émettre une impulsion laser et à enregistrer temporellement l’intégralité des échos de retour réfléchis par la scène. La forme des échos de retour fournit des informations sur l’épaisseur optique du couvert végétal. De nombreux systèmes commerciaux sont en exploitation, en particulier en topographie ou en bathymétrie. Mais ces systèmes ne sont pas dédiés à l’observation de la végétation. L’objectif de cette thèse est l’étude de l’intérêt de ces systèmes pour la construction de modèle numérique de terrain (MNT) sous couvert végétal. Elle est basée sur le développement d’outils de simulation du signal temporel incident au capteur lidar et de traitement des données. Dans un premier temps, le modèle physique de lidar onde complète, DELiS (n-Dimensional Estimation of Lidar Signals) a été développé. Il permet de simuler l’observation de scènes de végétation réalistes, tout en incluant la prise en compte de l’environnement extérieur (atmosphère, soleil) ainsi que des caractéristiques de la source et de la chaîne de détection (bruits de mesure). DELiS a été validé par confrontation à des résultats analytiques. Ensuite, DELIS a permis de comprendre et d’évaluer l’importance des diffusions multiples dans le couvert en fonction du champ de vue du lidar mais aussi de justifier l’utilisation d’acquisitions aéroportées petit champ pour simuler le signal d’un lidar spatial plus grand champ. Dans une deuxième étape, ses capacités de simulation ont été utilisées afin d’étudier l’intérêt du lidar onde complète pour la reconstruction d’un MNT sous couvert végétal. Dans ce but, nous avons développé et implémenté numériquement une méthode originale de traitement et de classification des données lidar onde complète permettant de séparer les échos lidar provenant du sol de ceux provenant de la végétation. Après classification des échos, nous avons reconstruit la géométrie du sol et des objets occultés par la végétation. Enfin, nous avons étudié comment combiner des données aéroportées acquises sous différents points de vue afin d’améliorer les reconstructions. Nos travaux montrent que le scanner laser aéroporté onde complète pourrait permettre d’obtenir en milieux forestier des reconstructions de la géométrie du terrain à des résolutions sub-métriques et avec une précision de l’ordre de 10 à 20 centimètres. La combinaison de visées multi-angulaire permet, par l’apport d’une quantité importante d’information supplémentaire, d’améliorer encore la reconstruction du MNT. Nous montrons cependant que les visées inclinées sont plus sensibles à la présence des troncs et branchages des arbres, éléments qui sont susceptibles d’introduire une erreur importante dans les processus de classification et de reconstruction. Pour cette raison, nous recommandons l’utilisation de la visée nadir pour la reconstruction mono-vue des modèles numériques de terrain, et nous proposons une méthode permettant de choisir de façon optimale les visées inclinées à ajouter pour l’observation détaillée d’une portion plus restreinte de la scène
This research work regards the scientific challenge of reconstructing the ground and the object presents under a vegetation cover from airborne observations. Airborne laser scanning is a promising technology. Full-waveform devices are able to record the complete temporal return signal following the emission of a short laser pulse towards the ground. This offers a great potential for remote sensing of forested areas, since the laser pulse will travel through the vegetation. Many commercial systems are already operated for topography or bathymetry. Scientists have been using these systems for vegetation observation, even if they are not dedicated to this purpose. The objective of this thesis is to study the relevance of full-waveform lidars for the geometric reconstruction of digital terrain models (DTM) under vegetation. We also aim at developing simulation and data processing toolsthat will help design and optimize future sensors dedicated to vegetation observation. Our first task was the development of a new physical simulator for full-waveform lidar measurement. The DELiS model (n-Dimensional Estimation of Lidar Signals) is able tosimulate the observation of complex and realistic vegetation scenes while accounting for atmosphere and sun perturbations, and simulating the multiple scattering of the laser pulse in the canopy. We have also implemented a sensor model for simulation of the measurement, amplification and digitization noises. This operational simulation tool is a key asset for future physical studies as well as for designing and optimizing future sensors and data processing methods. After validating the DELiS model by confrontation with analytical results, we have used it for studying the interest of full-waveform lidar for digital terrain models reconstruction under vegetation. For this purpose, we have developed a full-waveform lidar data processing method for decomposition of the signals and classification of the lidar echoes into two classes : ’ground’ and ’vegetation’. We were then able to reconstruct ground geometry.Finally, we have led a study on the combination of multi-angular acquisitions for improvement of the reconstructions.Our work shows that airborne full-waveform lidar observations may allow ground reconstruction with sub-metric resolutions and a precision of 10 to 20 centimeters in forested areas. Combining multiple viewing angles provides additional data, and helps improving the precision of the reconstructions. Yet, we show that non-nadir viewing is much more sensitive to trunks and branches. These elements may be the cause of an additional error in the classification and reconstruction processes. For this reason, we recommend using nadir viewing for single-view ground reconstruction, and propose a method for optimally selecting non-nadir views for the detailed observation of restricted areas of interest

The use of lasers for diagnosis and treatment in medical and cosmetic applications is increasing worldwide. Not all of these modalities are superficial and many require laser light to penetrate some distance into the tissue or skin to reach the treatment site. Human skin is highly scattering for light in the visible and near infrared wavelength regions, with a consequent reduction of the fluence rate. Melanin, which occurs in the epidermis of the skin, acts as an absorber in these wavelength regions and further reduces the fluence rate of light that penetrates through the epidermis to a treatment site. In vivo fluence rate measurements are not viable, but validated and calibrated computer models may play a role in predicting the fluence rate reaching the treatment site. A layered planar computer model to predict laser fluence rate at some depth into skin was developed in a commercial raytracing environment (ASAP). The model describes the properties of various skin layers and accounts for both the absorption and scattering taking place in the skin. The model was validated with optical measurements on skin-simulating phantoms in both reflectance and transmission configurations. It was shown that a planar epidermal/dermal interface is adequate for simulation purposes. In the near infrared wavelength region (676 nm), melanin (consisting of eumelanin and pheomelanin) is the major absorber of light in the epidermis. The epidermal absorption coefficient is one of the required input parameters for the computer model. The range of absorption coefficients expected for typical South African skin phototypes (ranging from photo-sensitive light skin, phototype I on the Fitzpatrick scale, to the photo-insensitive darker skin phototype V) was not available. Non-invasive diffuse reflectance spectroscopy measurements were done on 30 volunteers to establish the expected range of absorption coefficients. In the analysis it became apparent that the contributions of the eumelanin and pheomelanin must be accounted for separately, specifically for the Asian volunteers. This is a new concept that was introduced in the diffuse reflectance probe analysis. These absorption coefficient measurements were the first to be done on the expected range of skin phototypes for the South African population. Other authors dealing with diffuse reflectance probe analysis only account for the dominant eumelanin. Both the epidermal absorption coefficient and thickness are important in the prediction of the fluence rate loss. The computer model was used to evaluate the effect of the epidermal absorption coefficient (a parameter dictated by an individual’s skin phototype) and the epidermal thickness on the fluence rate loss through the skin. The epidermal absorption is strongly wavelength dependent with the higher absorption at the shorter wavelengths. In the computer model a longer wavelength of 676 nm (typical for a photodynamic treatment (PDT) of cancer) was used. For the darker skin phototypes (V) only about 30% of the initial laser fluence rate reached a depth of 200 ìm into the skin (just into the dermis). For the PDT application, results from the computer model indicated that treatment times need to be increased by as much as 50% for very dark skin phototypes when compared to that of very light phototypes.
Thesis (PhD)--University of Pretoria, 2012.
Physics
unrestricted

Masters thessis deals with the problematics of wireless signal propagation modeling inside buildings. The theoretical part of this thessis describes principles and methods of electromagnetic waves spreading in open areas and in indoor deployment. There are also described methods used for calculating the path of signal propagation ray-launching and ray-tracing. This part also includes description of an algorithm and equations used for simulating 5GHz WiFi signal propagation inside the Department of telecommunications corridors. Second part of this thessis includes a description of a NS-3 module mmWave, which was used for simulations of IEEE 802.11ad (WiGig) standard. There are also results of these simulations and their detailed description. At the end of this thessis comparison of these results with values gained by real environment measurements can be found.

In 3D modelling software, deformations are used to add, to remove, or to modify geometric features of existing 3D models to create new models with similar but slightly different details. Traditional techniques for deforming virtual 3D models require users to explicitly define control points and regions of interest (ROIs), and to define precisely how to deform ROIs using control points. The awkwardness of defining these factors in traditional 3D modelling software makes it difficult for people with limited experience of 3D modelling to deform existing 3D models as they expect. As applications which require virtual 3D model processing become more and more widespread, it becomes increasingly desirable to lower the "difficulty of use" threshold of 3D model deformations for users. This thesis argues that the user experience, in terms of intuitiveness and ease of use, of a user interface for deforming virtual 3D models, can be greatly enhanced by employing sketch-based 3D model deformation techniques, which require the minimal quantities of interactions, while keeping the plausibility of the results of deformations as well as the responsiveness of the algorithms, based on modern home grade computing devices. A prototype system for sketch-based 3D model deformations is developed and implemented to support this hypothesis, which allows the user to perform a deformation using a single deforming stroke, eliminating the need to explicitly select control points, the ROI and the deforming operation. GPU based accelerations have been employed to optimise the runtime performance of the system, so that the system is responsive enough for real-time interactions. The studies of the runtime performance and the usability of the prototype system are conducted to provide evidence to support the hypothesis.

Background. Rasterization of triangle geometry has been the dominating rendering technique in the real-time rendering industry for many years. However, triangles are not always easy to work with for content creators. With the introduction of hardware-accelerated ray tracing, rasterization-based lighting techniques have been steadily replaced by ray tracing techniques. This shift may signify the opportunity of exploring other, more easily manipulated, geometry-type alternatives compared to triangle geometry. One such geometry type is implicit surfaces. Objectives. This thesis investigates the rendering speed, editing speed, and image quality of different implicit surface rendering techniques using a state-of-the-art, hardware-accelerated, path tracing implementation. Furthermore, it investigates how implicit surfaces may be edited in real time and how editing affects rendering. Methods. A baseline direct sphere tracing algorithm is implemented to render implicit surfaces. Additionally, dense and narrow band discretization algorithms that sphere trace a discretization of the implicit surface are implemented. For each technique, two variations that provide potential benefits in rendering speed are also tested. Additionally, a real-time implicit surface editor that can utilize all the mentioned rendering techniques is created. Rendering speed, editing speed, and image quality metrics are captured for all techniques using different scenes created with the editor and an existing hardware-accelerated path tracing solution. Image quality differences are measured using mean squared error and the image difference evaluator FLIP. Results. Direct sphere tracing achieves the best image quality results but has the slowest rendering speed. Dense discretization achieves the best rendering speed in most tests and achieves better image quality results compared to narrow band discretization. Narrow band discretization achieves significantly better editing speed than both direct sphere tracing and dense discretization. All variations of each algorithm achieve better or equal rendering and editing speed compared to their standard implementation. All algorithms achieve real-time rendering and editing performance. However, only discretized methods display real-time rendering performance for all scenes, and only narrow band discretization displays real-time editing performance for a larger number of primitives. Conclusions. Implicit surfaces can be rendered and edited in real time while using a state-of-the-art, hardware-accelerated, path tracing algorithm. Direct sphere tracing degrades in performance when the implicit surface has an increased number of primitives, whereas discretization techniques perform independently of this. Furthermore, narrow band discretization is fast enough so that editing can be performed in real time even for implicit surfaces with a large number of primitives, which is not the case for direct sphere tracing or dense discretization.
Bakgrund. Triangelrastrering har varit den dominerande renderingstekniken inom realtidsgrafik i flera år. Trianglar är dock inte alltid lätta att jobba med för skapare av grafiska modeller. Med introduktionen av hårdvaruaccelererad strålspårning har rastreringsbaserade ljussättningstekniker stadigt ersatts av strålspårningstekniker. Detta skifte innebär att det kan finnas möjlighet för att utforska andra, mer lättredigerade geometrityper jämfört med triangelgeometri, exempelvis implicita ytor. Syfte. Detta examensarbete undersöker rendering- och redigeringshastigheten, samt bildkvaliteten av olika renderingstekniker för implicita ytor tillsammans med en spjutspetsalgoritm för hårdvaruaccelererad strålföljning. Den undersöker även hur implicita ytor kan redigeras i realtid och hur det påverkar rendering. Metod. En direkt sfärspårningsalgoritm implementeras som baslinje för att rendera implicita ytor. Även algoritmer som utför sfärstrålning över en kompakt- och smalbandsdiskretisering av den implicita ytan implementeras. För varje teknik implementeras även två variationer som potentiellt kan ge bättre prestanda. Utöver dessa renderingstekniker skapas även ett redigeringsverktyg för implicita ytor. Renderingshastighet, redigeringshastighet, och bildkvalité mäts för alla tekniker över flera olika scener som har skapats med redigeringsverktyget tillsammans med en hårdvaruaccelererad strålföljningsalgoritm. Skillnader i bildkvalité utvärderas med hjälp av mean squared error och evalueringsverktyget för bildskillnader som heter FLIP. Resultat. Direkt sfärspårning åstadkommer bäst bildkvalité, men har den långsammaste renderingshastigheten. Kompakt diskretisering renderar snabbast i de flesta tester och åstadkommer bättre bildkvalité än vad smalbandsdiskretisering gör. Smalbandsdiskretisering åstadkommer betydligt bättre redigeringshastighet än både direkt sfärspårning och kompakt diskretisering. Variationerna för respektive algoritm presterar alla lika bra eller bättre än standardvarianten för respektive algoritm. Alla algoritmer uppnår realtidsprestanda inom rendering och redigering. Endast diskretiseringsmetoderna uppnår dock realtidsprestanda för rendering med alla scener och endast smalbandsdiskretisering uppnår realtidsprestanda för redigering med ett större antal primitiver. Slutsatser. Implicita ytor kan renderas och redigeras i realtid tillsammans med en spjutspetsalgoritm för hårdvaruaccelererad strålföljning. Vid användning av direkt sfärstrålning minskar renderingshastigheten när den ytan består av ett stort antal primitiver. Diskretiseringstekniker har dock en renderingshastighet som är oberoende av antalet primitiver. Smalbandsdiskretisering är tillräckligt snabb för att redigering ska kunna ske i realtid även för implicita ytor som består stora antal primitiver.

La previsione della copertura RF in ambiente urbano è oggi comunemente considerato un problema risolto, con decine di modelli proposti in letteratura che mostrano una buona approssimazione rispetto alle misure. Tra questi, il ray tracing è considerato come uno dei più accurati tra i modelli disponibili. In questo lavoro si dimostra però come sia ancora necessario parecchio lavoro per fare in modo che il ray tracing possa essere effettivamente impiegato per scopi pratici.

Integrating concentrated solar thermal energy into fossil-fuels for the production of power/clean fuels is receiving growing attention as the combination of the two energy sources can provide lower emissions of carbon and other pollutants, lower cost, and continuous supply. Various types of hybrid concepts have been proposed. However, all of these concepts employ stand-alone solar receivers and standalone combustors. The University of Adelaide has developed an alternative approach with which to fully integrate a combustor into a solar cavity receiver. This offers the potential for significant savings from reduced infrastructure investment and reduced start-up and shut-down losses. In addition, this hybrid also results in the direct interaction between concentrated solar radiation and a flame, which is theoretically known to be coupled. However, the influence of concentrated solar radiation (CSR) on the flame has not been experimentally investigated. Hence this thesis aims at filling this gap. High flux solar simulators, comprising an array of high-intensity-discharge lamps coupled with elliptical reflectors, have been widely employed to study concentrated solar thermal energy systems. The use of electrical solar simulators holds the advantage over natural solar radiation in providing repeatable performance without the variability of the solar resource. Reliable models which predict the heat flux generated by a solar simulator are desirable because they enable efficient and systematic optimization of the system to meet the required trade-off between cost and performance. To this end, a concentric multilayer model of the light source is developed in this study to accurately predict the spatial distribution of the heat flux at the focus using a commercial Monte Carlo ray-tracing code. These simulations were validated with measurements of both the radiant intensity of the light source and the distribution of the concentrated heat flux. Further to that, on the experimentally validated ray tracing model, the geometry and surface reflectance of the additional concentrators were also assessed of two high flux solar simulators: one employs a single lamp, the other uses a seven-lamp array. In addition, the time-resolved spectra of solar simulators employing a metal halide and a xenon arc lamp are also measured, which provides the first experimental results of this kind that acquired from the same spectrometer to allow for direct comparison. This thesis also reports the first set of measurements of the influence of concentrated solar radiation on the soot volume fraction and temperature in a laminar sooty flame. Detailed laser diagnostics was performed on a laminar sooty flame with and without the irradiance of CSR, because laser diagnostics are demonstrated to hold the advantages of being non-intrusive, lower interferences and of being applicable to environments with high flux radiation. The current measurement using laser induced incandescence shows that the soot volume within the laminar flame was increased by 55% by CSR. In addition, the measurement of temperature using two-line atomic fluorescence shows that the flame temperature was increased by around 8% under CSR. In addition to the detailed laser diagnostics, an assessment of the influence of soot volume fraction on the global performance of the flames was also performed through a systematic study of flames using fuels of different soot propensities, which is achieved by blending hydrogen into hydrocarbon fuels, with hydrogen volume fraction ranging from 0 to 100%. Results show that flames with higher soot volume fraction have higher radiant fraction and lower NOx emissions. The principle contribution of the thesis is that the first measurement of the influence of concentrated solar radiation on the soot volume fraction and temperature of a flame was performed, which pushed forward the existing understanding of the interaction between broadband solar radiation and combustion. Its second major contribution is establishing an experimentally validated ray-tracing model that accurately predicts the concentrated heat flux from the solar simulator, and on this model, new design and optimization of solar simulators were performed. While this ray-tracing model is developed for metal halide lamps, the methodology is applicable more generally to solar simulators employing other types of discharge arc lamps.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2016