The use of ray tracing in the analysis of certain daytime ionograms recorded at Grahamstown is discussed in this thesis. A computer program has been modified and used to trace rays in the frequency range 1 - 30 MHz. Vertical, short distance oblique, and long distance oblique ionograms have been synthesized from the results and compared with experimental ionograms for Grahamstown, the Alice - Grahamstown transmission path (64 km), and the SANAE - Grahamstown transmission path (4470 km) respectively. Ray paths have been calculated and related in detail to the models of the ionosphere and geomagnetic field. The main features of the vertical and short distance oblique ionograms can, in general, be reproduced using spherically stratified ionosphere models with electron density profiles derived from vertical ionograms. A suitable model for the geomagnetic field is a tilted dipole equivalent to the actual field at Grahamstown. The two-hop mode is shown to be, usually, the lowest on the long distance oblique records. The ionosphere model is the principal limiting factor in reproducing such ionograms, and the most satisfactory results have been those obtained with a model in which electron density is assumed to vary linearly with latitude between the profiles at SANAE and Grahamstown. The promising results obtained by ray tracing with normal ionospheric conditions indicate that the method has further possibilities which could usefully be explored. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

This Master's Thesis deals with geometric modeling methods and theirs implementation in Octave (Matlab), which is ideal for the practical realization. The first part of the thesis is focused on a very simplified image source method, which is able to calculate and render the 2D impulse response of rectangular rooms. The next part is aimed on~the same method, but extended by three-dimensional simulation of polyhedral prism-shaped rooms. There is both an explanation of theoretical and mathematical aspects and a~documentation of the implemented source code. Extended image source method is able to generate sound representation of impulse response characteristics, and use it for auralization, which is achieved by using convolution of both the input sound source and the calculated impulse response. At the end there are two practical examples for both methods with explanatory illustrations.

This term project addresses the construction of kD tree acceleration structures and parallelization of this construction using GPU. At the beginning, there is an introduction of the reader into CUDA platform for parallel programming. There is a decription of generic principles as well as specific features that will be used in this thesis. Following that the reader is put into the issue of acceleration structures for Ray tracing. These structures are described and the kD tree acceleration structure and its variants are portrayed in detail. After that the analysis of chosen kD tree variant is broken down and the problems and issuse of its parallel implementation are adressed. As a part of implementation discription, there is a short descripton of CPU variant and detailed specifications of the CUDA kernels. The testing section brings the results of implementation in form of CPU vs GPU comparison, as well as evaluation of how much the metric set in design was fulfilled. In the end there is a summary of achieved goals and results followed by possible future improvements for the implementation.

Solar energy is one of a very few low-carbon energy technologies with the enormous potential to grow to a large scale. Currently, solar power is generated via the photovoltaic (PV) and concentrating solar power (CSP) technologies. The ability of CSPs to scale up renewable energy at the utility level, as well as to store energy for electrical power generation even under circumstances when the sun is not available (after sunset or on a cloudy day), makes this technology an attractive option for sustainable clean energy. The levelised electricity cost (LEC) of CSP with thermal storage was about 0.16-0.196 Euro/kWh in 2013 (Kost et al., 2013). However, lowering LEC and harvesting more solar energy from CSPs in future motivate researchers to work harder towards the optimisation of such plants. The situation tempts people and governments to invest more in this ultimate clean source of energy while shifting the energy consumption statistics of their societies from fossil fuels to solar energy. Usually, researchers just concentrate on the optimisation of technical aspects of CSP plants (thermal and/or optical optimisation). However, the technical optimisation of a plant while disregarding economic goals cannot produce a fruitful design and in some cases may lead to an increase in the expenses of the plant, which could result in an increase in the generated electrical power price. The study focused on a comprehensive optimisation of one of the main CSP technology types, the linear Fresnel collector (LFC). In the study, the entire LFC solar domain was considered in an optimisation process to maximise the harvested solar heat flux throughout an imaginary summer day (optical goal), and to minimise cavity receiver heat losses (thermal goal) as well as minimising the manufacturing cost of the plant (economic goal). To illustrate the optimisation process, an LFC was considered with 12 design parameters influencing three objectives, and a unique combination of the parameters was found, which optimised the performance. In this regard, different engineering tools and approaches were introduced in the study, e.g., for the calculation of thermal goals, Computational Fluid Dynamics (CFD) and view area approaches were suggested, and for tackling optical goals, CFD and Monte-Carlo based ray-tracing approaches were introduced. The applicability of the introduced methods for the optimisation process was discussed through case study simulations. The study showed that for the intensive optimisation process of an LFC plant, using the Monte Carlo-based ray-tracing as high fidelity approach for the optical optimisation objective, and view area as a low fidelity approach for the thermal optimisation objective, made more sense due to the saving in computational cost without sacrificing accuracy, in comparison with other combinations of the suggested approaches. The study approaches can be developed for the optimisation of other CSP technologies after some modification and manipulation. The techniques provide alternative options for future researchers to choose the best approach in tackling the optimisation of a CSP plant regarding the nature of optimisation, computational cost and accuracy of the process. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

Concern over the altering climate due to the release of anthropogenic greenhouse gases has caused a major shift in the developments of ways to minimise human impact on the climate. Solar energy is seen as one of the most promising sources to transform the energy market for low-carbon energy generation. Currently, solar power is generated via photovoltaic (PV) and concentrating solar power (CSP) technologies. The advantage of CSPs to scale up renewable energy to utility level, as well as to store thermal energy for electrical power generation when the sun is not available (after sunset or during cloudy periods) makes this technology an attractive option for sustainable clean energy. CSP development, however, is still in its infancy, and for it to be a competitive form of energy-generation technology, techno-economic developments in this field need to improve the efficiency and decrease the costs of this technology. A policy report by the European Academies’ Science Advisory Council (EASAC) (2011) indicated that central receiver (solar tower) CSP systems show the greatest margin for technological improvements (40% to 65% is estimated), and that an improvement in receiver technology could make the greatest contribution to increase efficiency. This study therefore focused on analysing the optical and thermal performance of a new proposed solar cavity molten salt receiver design for a central receiver CSP system using a numerical approach. In this study, the receiver’s performance was analysed by first selecting an existing heliostat field, Planta Solar 10 (PS-10). For the numerical analysis to reflect conditions that are as realistic as possible, numerical models for different aspects were selected and validated. For modelling the sun, the solar tracking numerical model proposed by Iqbal (1983) was selected and implemented after literature and comparison showed adequate results. The direct normal irradiation (DNI) was modelled by applying a clear sky model, with the parameterisation model C proposed by Iqbal (1983) as the chosen model. The variables in this model that were subject to temperature, and humidity values were more accurately presented by adding numerical approximations of the region’s actual weather data. The DNI model reflected realistic fluctuations. For the thermal modelling, a validation study was conducted on impingement flow heat transfer to select an appropriate Reynolds-averaged Navier-Stokes (RANS) model that would provide accurate results when conducting the thermal performance test on the receiver. The study concluded that the transitional Shear Stress Transport (SST) turbulence model performed the best. A new method was also developed and validated that allows one to not only simulate complex geometries within the Monte Carlo ray tracing environment SolTrace, but also to apply the results obtained by simulating this model as a heat source within the computational fluid dynamics (CFD) environment ANSYS Fluent. This allows SolTrace modelling to be more accurate, since models do not need to be approximated to simple geometries. It also provides an alternative for solar modelling in ANSYS Fluent. The optical analysis was conducted by first performing an analysis on the receiver aperture and studying its sensitivity on the captured flux. This was followed by analysing the optics of the proposed receiver, the flux distributions on a simplified absorber surface area, and how these distributions are altered by changing some parameters. An in-depth analysis was finally done on the absorber area by applying the aforementioned model to simulate complex geometries within SolTrace, with the results illustrating the difference of the detailed geometry on optical modelling. An alternative receiver design with improved optical features was proposed, with an initial study providing promising results. The thermal analysis was done within the CFD environment, with only a section of the absorber surface area considered, and by applying the solar flux simulated during the optical analysis as heat source within the geometry model. This allowed the model to simulate the effects of re-radiation at the surface of the absorber while simulating the heat transfer at the fluid molten salt side simultaneously. The results showed that, for the current design and requirements, the absorber surface temperature reaches impractical temperatures. Altering the design or being more lenient on the requirements has, however, shown dramatic improvements in terms of thermal performance. Sensitivity studies for both the optical and thermal analyses have shown that changes in design can dramatically improve the performance of the design, making it a possible feasible receiver design for central receiver systems. / Dissertation (MEng)--University of Pretoria, 2019. / National Research Foundation (NRF) / Mechanical and Aeronautical Engineering / MEng / Unrestricted

A key aspect of immersive audio is realistic acoustics. To get plausible acoustics for an environment the impulse response can be generated using acoustic simulations and should ideally be updated in real-time for interactive applications. In this thesis the listening experience of sound generated with an interactive sound propagation engine was explored and compared to spatial sound produced with a static impulse response. The aim was to evaluate the sound experience for applications outside of virtual reality, with computational cost in consideration. This was done by conducting a user study where the participants got to interact and compare the two sound methods in different environments. The study was performed using a custom developed application integrated with a pre-existing sound propagation engine. The results from the user study showed no obvious perceptive difference between the two sound rendering methods that could justify the extra computations. Overall there was even a slight preference for the stereo method that used a static impulse response. However, there were qualities to both sound rendering methods that were preferred depending on the environment. Another thing that was investigated in the work of this thesis was how the varying accuracy of localization of sound in different directions can be used in acoustic ray tracing algorithms. An alternative sampling method was developed that uses a biased distribution based on spatial resolution of human hearing instead of traditional uniform sampling. The computation time of the random sampling phase increases, but could potentially reduce the number of ray samples needed. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

Ray tracing is widely used technique for realistic rendering of computer scenes. Its major drawback is time needed to compute the image, therefore it's usually parallelized. This thesis describes parallelization and ray tracing in general. It explains the possibility of how can be ray tracing parallelized as well as it defines the problems which may occur during the process. The result is parallel rendering application which uses selected ray tracing software and measurement of how successful this application is.

This thesis brings an overview about scene rendering using the ray tracing method. It describes aspects used when creating the application which uses this method such as intersection computation, lighting and shading models etc. It also describes the basic algorithm used for rendering one frame. Each class of the object oriented design is described. There is also detail explanation what is the purpose of the each class in the model and what are the most important used methods. The work also contains demonstration application showing the usage of model in practice.

Goal of this diploma thesis is to get knowledge about history and evolution of computer graphic in area of realistic image synthesis, get knowledge about rendering system mental ray and about writing shader for it and write several shader. Create manual about writing  shaders for mental ray. Get knowledge about program Maya and create a tutorial hot to get the shader into it.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19504号 / 理博第4164号 / 新制||理||1598(附属図書館) / 32540 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田口 聡, 教授 家森 俊彦, 教授 余田 成男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM