To advance the design of hypersonic vehicles, high-fidelity multi-physics CFD is used to characterize 3-D scramjet flow-fields in two novel streamline traced configurations. The two inlets, Jaws and Scoop, are analyzed and compared to a traditional rectangular inlet used as a baseline for on/off-design conditions. The flight trajectory conditions selected are Mach 6 and a dynamic pressure of 1,500 psf (71.82 kPa). Analysis of these hypersonic inlets is performed to investigate distortion effects downstream with multiple single cavity combustors acting as flame holders, and several fuel injection strategies. The best integrated scramjet inlet/combustor design is identified. The flow physics is investigated and the integrated performance impact of the two innovative scramjet inlet designs is quantified. Frozen and finite rate chemistry is simulated with 13 gaseous species and 20 reactions for an Ethylene/air finite-rate chemical model. In addition, URANS and LES modeling are compared to explore overall flow structure and to contrast individual numerical methods. The flow distortion in Jaws and Scoop is similar to some of the distortion in the traditional rectangular inlet, despite design differences. The baseline and Jaws performance attributes are stronger than Scoop, but Jaws accomplishes this while eradicating the cowl lip interaction, and lessening the total drag and spillage penalties. The innovative inlets work best on-design, whereas for off-design, the traditional inlet is best. Early pressure losses and flow distortions in the isolator aid the mixing of air and fuel, and improve the overall efficiency of the system. Although the trends observed with and without chemical reactions are similar, the former yields roughly 10% higher mixing efficiency and upstream reactions are present. These show a significant impact on downstream development. Unsteadiness in the combustor increases the mixing efficiency, varying the flame anchoring and combustion pressure effects upstream of the step.

A full Strouhal number thermo-acoustic model is purposed for the feedback control of self excited noise driven combustors. The inclusion of time delays in the volumetric heat release perturbation models create unique behavioral characteristics which are not properly reproduced within current low Strouhal number thermo acoustic models. New analysis tools using probability density functions are introduced which enable exact expressions for the statistics of a time delayed system. Additionally, preexisting tools from applied mathematics and control theory for spectral analysis of time delay systems are introduced to the combustion community. These new analysis tools can be used to extend sensitivity function analysis used in control theory to explain limits to control effectiveness in self-excited combustors. The control effectiveness of self-excited combustors with actuator constraints are found to be most sensitive to the location of non-minimum phase zeros. Modeling the non-minimum phase zeros correctly require accurate volumetric heat release perturbation models. Designs that removes non-minimum phase zeros are more likely to have poles in the right hand complex plane. As a result, unstable combustors are inherently more responsive to feedback control.

Made available in DSpace on 2014-10-09T12:50:22Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:51Z (GMT). No. of bitstreams: 1 10890.pdf: 10562798 bytes, checksum: 063bd7e321751780a6d96cafecfe45bc (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:01/06837-2

Made available in DSpace on 2014-10-09T12:50:22Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:51Z (GMT). No. of bitstreams: 1 10890.pdf: 10562798 bytes, checksum: 063bd7e321751780a6d96cafecfe45bc (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:01/06837-2

The thesis follows up a topic of fake news within the borders of Czech Republic. This frequently discussed phenomena is often linked to the pro-Kremlin propaganda, whose aim is to evoke fear across the citizens, as well as raise distrust towards reigning authorities, western institutions, a functionality of liberal democracy and at last but not least - distrust towards public media and mainstream media in general. This is being achieved by production of fake news, also known as fictive, false or manipulative articles, that are being spread through the social media. Despite its low credibility the news often make their way into the public discussion, forming the general opinion and as a result affecting many political decisions. In order to follow this topic up further, I will put in use the Adam Klein's concept, also known as information laundering.This concept describes the ways how these hateful articles, personal opinions and straight up false news are getting legitimised within the online world and subsequently spread through the social media under the disguise of respectable journalism. The thesis is aiming to map out the entire sphere of fake news media, its websites and Facebook and YouTube social profiles as well as describe individual aspects of the entire mechanism using quantitative analysis. In...

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Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The automotive industry in South Africa is expanding as a result of pressure on the world economy that forces vehicle manufacturers to outsouree work to developing countries. In order to add value to automotive engine development, the capability to perform state-of-the-art engineering must be developed in this country. Threedimensional fluid flow simulation is one such area and is being developed in this study in order to enhance the ability to develop combustion systems. Another capability being developed at the University of Stellenbosch is the simulation of valve train dynamics. It was realised that there is a lack of research results of in-cylinder flow characteristics and how they influence combustion chamber processes. This project focuses on the investigation of two different combustion chamber geometries and how they influence the flow and combustion processes in two different combustion chambers. The aim is to gain a better understanding of combustion chamber flow as an indirect result from comparing the flow in two fundamentally different engines under similar operating conditions. The difference in the engines is that one was developed for reduced exhaust gas emissions while the other was developed to achieve high performance. The numerical simulation capability is developed in the process of achieving this goal. To achieve the above-mentioned aim, a literature study was performed on the different combustion chamber flow characteristics and how they are influenced by different configurations. An experimental method of measuring combustion characteristics is studied in order to establish the ability to perform the latter. Theory of numerical flow simulation is also studied with this same goal in mind. Experimental testing is performed and combustion analysis is done on the results. In conjunction to the experimental work, numerical flow simulations are performed on the two different combustion chambers. The results from experimental testing and numerical simulations have shown that obstructions in the flow into the combustion chamber, together with a port configuration that cause flow around the longitudinal axis of the cylinder, increases the rate at which fuel burns in the combustion chamber and thereby reduce the production of toxic emissions from the engine. The study also proved that reducing resistance to flow increases the amount of air that is breathed by the engine and thereby results in increased torque generation. Through this study, opportunities for further research are identified. The results of the study can be used when new combustion systems are developed, especially in the light of ongoing tightening of emission regulations. The contribution to numerical flow simulation capabilities developed in this study add value to the ability to develop new combustion systems in the future, especially when complimented by some of the further research topics identified. / AFRIKAANSE OPSOMMING: Die motorbedryf in Suid-Afrika is besig om vinnig te ontwikkel as direkte gevolg van druk op die wêreldekonomie wat internasionale motorvervaardigers forseer om werk na ontwikkelende lande uit te kontrakteer. Hoogs gesofistikeerde ingenieurstegnieke moet ontwikkel word in Suid-Afrika met die doelom waarde toe te voeg aan enjin ontwikkeling. Drie-dimensionele vloei simulasie is een van hierdie vermoëns en word tydens hierdie studie ontwikkelom die verbrandingstelsel ontwikkelings-vaardighede te bevorder. Nog 'n vaardigheid wat tans ontwikkel word aan die Universiteit van Stellenbosch is die vermoë om nok-en-klepstelsel dinamika te simuleer. Daar bestaan egter 'n leemte in navorsingsresultate van vloei eienskappe binne in die verbrandingsruim en hoe dit verbrandingsruim prosesse beïnvloed. Die projek fokus dus op 'n ondersoek van twee verskillende geometriese konfigurasies van die verbrandingsruim en hoe dit die vloei- en verbrandingsprosesse in die twee konfigurasies beïnvloed. Die doel is om 'n beter begrip te ontwikkel van verbrandingsruim prosesse as 'n indirekte gevolg van die vergelyking tussen twee fundamenteel verskillende enjins onder eenderse bedryfstoestande. Die verkil tussen die twee enjins is dat een ontwikkel is met die doelop verlaagde uitlaatgas emmissies en die ander ontwikkel is om verbeterde werkverrigting. Die numeriese simulasie vermoë is ontwikkel in die proses om die doel te bereik. Om bogenoemde doel te bereik is 'n literatuurstudie gedoen wat verskillende vloeieienskappe in die verbrandingsruim ondersoek, asook hoe dit deur verskillende konfigurasies beïnvloed word. 'n Eksperimentele metode III die bepaling van verbrandingseienskappe is ook bestudeer met die doelom laasgenoemde uit te voer. Teorie aangaande numeriese vloei simulasie is ook bestudeer met bogenoemde doel. Eksperimentele toetse is gedoen en verbrandingsanalise uitgevoer op die resultate. In kombinasie met die eksperimentale werk is numeriese simulasies van die prosesse in die twee verbrandingsruim konfigurasies uitgevoer. Die resultate van die eksperimentele toetse en numeriese simulasies toon dat obstruksies in die vloei na die verbrandingsruim, gesamentlik met die poort konfigurasie wat veroorsaak dat lug om die longitudinale as van die silinder vloei, die tempo waarteen die lug-brandstof mengsel verbrand verhoog en sodoende die vrystelling van skadelike uitlaatgasse na die atmosfeer verminder. Die studie het ook getoon dat die vermindering van weerstand teen vloei, die hoeveelheid lug wat in die verbrandingsruim invloei vermeerder en sodoende die wringkrag wat deur die enjin gelewer word verhoog. Deur die studie is verdere navorsingsgeleenthede uitgewys. Die resultate van die studie kan gebruik word in die ontwikkeling van nuwe verbrandingstelsels, veral in die lig van verstrengende regulasies rakende uitlaatgas emmissies. Die bydrae tot numeriese vloei simulasie vermoëns ontwikkel in hierdie studie voeg waarde toe tot die vermoë om nuwe verbrandingstelsels te ontwikkel, veral wanneer dit gekomplimenteer word met van die verdere navorsingsonderwerpe wat geïdentifiseer is.

This thesis investigates the use of the Stagnation-Point Reverse-Flow (SPRF) combustor geometry for burning low-grade solid fuels that are attractive for specific industrial applications because of their low cost and on-site availability. These fuels are in general, hard to burn, either because of high moisture and impurity-content, e.g. biomass, or their low-volatiles content, e.g., petroleum-coke. This results in various challenges to the combustor designer, for example reduced flame stability and poor combustion efficiency. Conventional solutions include preheating the incoming flow as well as co-firing with high-grade fuels. The SPRF combustor geometry has been chosen because it was demonstrated to operate stably on standard gaseous and liquid-fuels corresponding to ultra fuel-lean conditions and power densities at atmospheric-pressure around 20-25 MW/m3. Previous studies on the SPRF combustor have proven that the unique, reverse flow-geometry allows entrainment of near-adiabatic products into the incoming reactants, thereby enhancing the reactivity of the mixture. Further, the presence of the stagnation-end created a region of low mean velocities and high levels of unsteadiness and mixing-rates that supported the reaction-zones. In this study, we examine the performance of the SPRF geometry on a specific low grade solid fuel, petroleum coke. There are three main goals of this thesis. The first goal is the design of a SPRF combustor to operate on solid-fuels based on a design-scaling methodology, as well as demonstration of successful operation corresponding to a baseline condition. The second goal involves understanding the mode of operation of the SPRF combustor on solid-fuels based on visualization studies. The third goal of this thesis is developing and using reduced-order models to better understand and predict the ignition and quasi-steady burning behavior of dispersed-phase particles in the SPRF combustor. The SPRF combustor has been demonstrated to operate stably on pure-oxygen and a slurry made from water and petroleum-coke, both at the baseline conditions (125 kW, 18 g/s, ~25 µm particles) and higher power-densities and powder sizes. For an overall combustor length less than a meter, combustion is not complete (global combustion efficiency less than 70%). Luminance imaging results indicate the incoming reactant jet ignites and exhibits intense burning at the mid-combustor region, around 15 jet diameters downstream of the inlet, most likely due to enhanced mixing as a result of the highly unsteady velocity field. This roughly corresponds to the location of the reaction zones in the previous SPRF combustors operating on gas and liquid fuels. Planar laser visualization of the reacting flow-field using particle-scattering reveals that ignition of a significant amount of the reactants occurs only after the incoming jet has broken into reactant packets. Post-ignition, these burning packets burn out slowly as they reverse direction and exit the combustor on either side of the central injector. This is unlike the behavior in liquid and gas-fueled operation where the incoming reactants burned across a highly corrugated, thin-flame front. Based on these findings, as well as the results of previous SPRF studies, an idealized model of combustor operation based on a plug flow reactor has been developed. The predictions suggest that fuel-conversion efficiency is enhanced by the combustor operating pressure and lowered by the heat-losses. Overall, this effort has shown the SPRF geometry is a promising compact-combustor concept for self-sustained operation on low-grade solid-fuels for typical high-pressure applications such as direct steam-generation. Based on these findings, it is recommended that future designs for the specific application previously mentioned have a shorter base-combustor with lower heat-losses and a longer steam-generation section for injection of water.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Electromagnetic shielding plays a significant role in the protection of electronic equipment. Its application is essential for mitigating radio-frequency interference for the Karoo Array Telescope (MeerKAT) project in the Karoo region of the Northern Cape. In this context, time-domain (TD) methodology for small enclosure shielding effectiveness (SE) is developed using a reverberated environment technique. Interest revolves around measurement time speed-up and an extended SE response which covers the under-moded condition of small enclosures. Recommended IEC standard 61000-4-21 [1] e ciency of 0.75, for log-periodic dipole array (LPDA) antenna, is also validated from a reverberation chamber (RC) characterisation of a printed circuit-board (PCB) LPDA e ciency. A built-in pulse generator and the Square Kilometre Array (SKA) receiver RATTY form the main elements of the TD metrology. For validation purpose, a reference coaxial airline is built. The cable is characterised with computational codes (CST and FEKO) and is also modelled with Vance and Kley's analytical expressions. The results are compared with TD transfer impedance (Zt) measurement within the RC. The study shows that the cable fixture within an RC shapes the cable under-test (CUT) Zt. The airline itself is also introducing an oscillating component within Zt. The resonance is proportional to the CUT length and it is visible within the measurement data and the simulations. It is not, however, taken into account by the theoretical models. The consequence of an incorrect antenna efficiency on RC applications is also addressed using a PCB LPDA antenna efficiency investigation. The unknown LPDA is simulated with CST for the study. The result is compared to an RC measurement validating the IEC 61000-4-21 standard efficiency recommendation of 0.75 [1]. This methodology characterised the unknown antenna parameter from a reference dipole antenna efficiency we investigated with FEKO. Simulated Wheeler-cap techniques permitted the reference antenna validation. We found that an inaccurate LPDA efficiency has little effect at higher frequency if the IEC efficiency is adopted. However, a difference of more than 7 dB can arise at low frequency if the real efficiency differs by more than 0.3 with respect to the IEC value. The study highlights the importance of a correct antenna efficiency for accurate RC applications. The nested-enclosure technique is regarded as the conventional method of investigating small enclosures SE [2]. The technique is in general time-consuming and works for a frequency range higher than three times the enclosure under test (EUT) lowest cut-o value. Our TD metrology covers a frequency band up to 1.4 GHz which coincides with our enclosure under-moded region. The SE characterisation is not well-documented within this particular region. The dissertation contributes to this field using a non-stirred nested-enclosure configuration. In contrast to the conventional use of the nested-enclosure methodology [2], the source is placed here within the EUT and the enclosure is treated as a normal radiator. The SE definition according to the IEEE standard in [2] is followed and the enclosure total transferred-power is computed from the port's reflection coeficient. The approach does not require a stirrer for the EUT. Our measurement shows an SE agreement between the modfied and the appropriate nested-enclosure technique from 390 MHz up to 4 GHz. The investigation is faster, but in addition the TD spectrum gives a more detailed SE response than the FD approach. / AFRIKAANSE OPSOMMING: Elektromagnetiese skerming speel n belangrike rol in die beskerming van elektroniese komponente. Die toepassing daarvan is noodsaaklik vir die versagting van radiofrekwensie steurings in die Karoo Array Telescope (MeerKAT) projek wat tans ontwikkel word in die Karoo omgewing van die Noord-Kaap. In hierdie konteks is daar op n tydsgebied metode vir klein-omhulsel beskermingse ektiwiteit (BE) gefokus, deur gebruik te maak van n weerkatingsomgewing tegniek. Die belangstelling handel om metingstye te verkort en n uitgebreide BE reaksie wat die lae-modus toestand van klein omhulsels dek. Aanbeveelde International Electrotechnical Commission (IEC) standaard 61000-4-21 [2] e ektiwiteit van 0.75, vir log-periodiese dipool-skikking (LPDA) antennas, is ook bekragtig deur n weerkaatsingskamer karakterisering van n gedrukte-stroombaanbord (PCB) LPDS antenna e ektiwiteit. n Ingeboude impulsgenerator en die Square kilometre Array (SKA) ontvanger, RATTY, vorm deel van die hoof elemente van die tydsgebiedmetings. Vir bekragtigings doeleindes is n koaksiale lugtransmissielyn gebou. Hierdie kabel is gekarakteriseer deur numeriese sagteware (CST en FEKO) en is ook gemoduleer met behulp van Vance en Kley se analitiese uitdrukkings. Die resultate is vergelyk met tydsgebied-oordragsimpedansie (Zt) metings, wat in die weerkaatsingskamer gedoen is. Die studie wys dat kabel posisie binne in die weerkaatsingskamer die Zt van die kabel-onder-toets vervorm. Die lugstreep voeg ook n ossillerende component by tot die gemete Zt. Die resonansie is eweredig aan die lengte van die kabel en is duidelik sigbaar binne die meting- en simulasiedata. Dit is egter nie in-berekening gebring in die analitiese modelle nie. Die gevolge van n verkeerde antenna e ektiwiteit in die weerkaatsingskamer toepassing is ook aangespreek deur ondersoek na die e ektiwiteit van n PCB LPDA. Die onbekende LPDA is gesimuleer met CST vir hierdie studie. Die resultate is vergelyk met n weerkaatsingskamer meting, wat die IEC 61000-4-21 standaard e ektiwiteit van 0.75 [1] bekragtig. Die metode karakteriseer die onbekende antenna veranderlike deur n verwysings dipool antenna e ektiwiteit wat ge-ondersoek is in FEKO. Gesimuleerde Wheeler-cap tegnieke het die veri kasie van die verwysings antenna resultate toegelaat. Daar is gevind dat n onakkurate LPDA e ektiwiteit n klein e ek op die ho er frekwensies het, as die IEC e ektiwiteit aangeneem is. Daar kan egter n verskil van 7dB voorkom by laer frekwensies, as die werklike e ektiwiteit met meer as 0.3 van die IEC waarde verskil. Hierdie studie lig die belangrikheid van n korrekte antenna e ektiwiteit uit vir akkurate weerkaatsingskamer toepassings. Die geneste-omhulsel tegniek word beskou as die konvensionele metode vir die bestudering van beskermingse ektiwiteit vir klein omhulsels. Die tegniek is gewoontlik tyd-rowend en werk net vir frekwensies wat drie maal ho er is as die af-sny waarde van die omhulselonder- toets. Ons tydgebiedmeting dek net n frekwensieband tot 1.4GHz, wat ooreenstem met ons omhulsel lae-modus gebied. Die beskermingse ektiwiteit karakterisering, in hierdie spesi eke veld, is nie goed gedokumenteer nie. Hierdie verhandeling dra by tot hierdie veld deur gebruik te maak van n onversteurde geneste-omhulsel kon gurasie. In teenstelling met die konvensionele gebruik van die geneste-omhulsel metode, is die bron geplaas binne die omhulsel-onder-toets en word dit gebruik as n gewone uitstraler. Die de nisie van beskermingse ektiwiteit volgens die IEEE standaard in [2], is gevolg en die totale oordragskrag van die omhulsel is bereken deur gebruik te maak van n poort se re eksie ko e si ent. Die benadering benodig nie n steurder vir die omhulsel-onder-toets nie. Ons metings se beskermingse ektiwiteit het ooreengestem met die veranderde - en die geskikte geneste-omhulsel tegniek, van 390MHz tot 4GHz in die spektrum. Hierdie ondersoek is vinniger en lewer n meer gedetailleerde beskermingse ektiwiteit reaksie as die frekwensiegebied benadering.

Several Supreme Court cases in the latter half of the 20th Century established a criminal defendant's due process right to put forward an effective defense. To put forward an effective defense, one must be able to introduce exculpatory evidence on one's behalf. A defendant's witness may claim the right against self-incrimination, in which case the defendant may request immunity for the witness so that he will testify. If that request is denied, a defendant's due process right to put forward an effective defense may be implicated. The refusal to grant defense witness immunity is one instance of suppression of evidence. In a string of cases in the Third Circuit, the courts have implemented a test for determining under what conditions a due process violation occurs in this situation. But, there is significant reason to believe that in implementing the test the court has relied on incorrect assumptions. This paper discusses how the court has relied on unwarranted assumptions to make due process determinations, and concludes that in so doing it has imposed too high a standard for a due process violation. First, the court interprets the test as a test for a due process violation, when there is reason to believe that the court articulating the test meant it to be a test for the appropriateness of judicially created immunity as the remedy for an existing due process violation. Second, the court makes an unwarranted assumption that any strong governmental interest countervails against a grant of witness immunity. Third, the court imposes too high a standard for determining what counts as a strong governmental interest because it does not give sufficient weight the context of the determination. These three unwarranted assumptions suggest that the court has imposed too high a standard for determining due process violations. / text