An efficient reliability technique has been developed based on Response Surface Methodology (RSM) in conjunction with the First Order Second Moment (FOSM) reliability method. The technique is applied when the limit state function cannot be obtained explicitly in terms of the design variables, i.e., when the analysis is performed using numerical techniques such as finite elements. The technique has proven to be efficient because it can handle problems with large numbers of design variables and correlated as well as nonnormal random variables. When compared with analytical results, the method has shown excellent agreement. The technique contains a sensitivity analysis scheme which can be used to reduce the computation time resulting in nearly the same accuracy. This technique allows the extension of most finite element codes to account for probabilistic analysis, where statistical variations can be added to the design variables. An explicit solution for rocket motors consisting of propellant and steel case under environmental temperature variations is compared to the RSM technique. The method is then used for the analysis of rocket motors subjected to mechanical loads for which the stress analysis is performed using the finite element method. The technique is also applied to study the reliability of a laminated composite plate with geometric nonlinearity subjected to static and time dependent loadings. Different failure modes were considered as well as different meshes. Results have shown that when the relative size of the element is introduced into the probabilistic model, the same reliability value is obtained regardless of the number of elements in the mesh. This is good because it allows the technique to be used for problems where the failure region is unknown. / Ph. D.

Downy mildew has been a potentially devastating constraint to crop production within the Brassicaceae family worldwide (CABI, 2022) and on the Central Coast of California (Smukler, et al, 2008; Koike, et al. 2007). Downy mildew is a foliar disease, caused by the pathogens in the Hyaloperonospora genus on plants within the Brassicaceae family (Goker, et al, 2009). Downy mildew is a disease that is common in region of the world with Coastal climates that provide humidity and moderate temperatures (Sarahan, et al, 2017). Crops within the Brassicaceae family maintain a predominant role in agricultural systems worldwide (Cartea, et al, 2011) and on the Central Coast of California, in Monterey, San Luis Obispo, Santa Cruz, San Benito, and Ventura Counties (Hidalgo, et al, 2022; Settevendemie, et al, 2022; Sanford, et al, 2022; Griffin, et al, 2022; Chang, et al, 2022; Williams, et al, 2022). The crop production within the Brassicaceae family includes broccoli, cabbage, and cauliflower, and the spring mix production of wild arugula, cultivated arugula, and baby kale. In the first study, an in-lab screening of wild arugula (Diplotaxis tenuifolia) for downy mildew resistance was conducted to identify accessions that contain potential resources of resistance to Hyaloperonospora diplotaxidis. The germplasm of 199 wild arugula accessions was grown out under greenhouse conditions and inoculated with a v single isolate of H. diplotaxidis. A subset of 40 accessions of wild arugula were further inoculated with an additional three isolates of H. diplotaxidis and the ten most resistant accessions were selected for further inoculations. The inoculations of the final subset of ten accessions with the same three isolates were replicated an additional two times. When a factorial ANOVA was conducted to test the interaction between the isolate and accession used, it was found that the impact of the accession on disease incidence was independent from the isolate (P=0.993). Three accessions, 185, 79, and 17 were identified as a potential source of resistance to the isolates utilized in this study, for maintaining a disease incidence below 1%. To compare the results found in the in-lab resistance screening, a field trial was conducted with a subset of wild arugula accessions with diverse reactions to downy mildew. When a regression was conducted comparing the disease incidence under field and lab conditions, the R2 value was found to be 0.37. A second study was conducted to characterize the genetic, morphological, and host range diversity of downy mildew causing pathogens in the Hyaloperonospora genus of hosts in the Brassicaceae family. An isolate collection of approximately 40 isolates of Hyaloperonospora spp. was established and the phylogenetic relationships of these isolates were analyzed by creating two phylogenetic trees using their cox2 mtDNA and ITS rDNA sequences. The H. brassicae and H. diplotaxidis isolates from this study formed separate monophyletic groups in both the cox2 mtDNA and ITS rDNA phylogenetic analyses. When the host range of H. brassicae and H. diplotaxidis were characterized by inoculating a genetically and morphologically diverse set of four host plant species, the H. brassicae and H. diplotaxidis were found to have distinct host ranges. The H. brassicae isolate was found to be parasitic of all B. oleracea morphotypes including broccoli, cabbage, kale, kohlrabi, and ornamental cabbage. The H. diplotaxidis isolate was found to only be parasitic on wild arugula, not cultivated arugula, wild mustard, or any of the B. oleracea morphotypes. The difference between sporangia of H. brassicae and H. diplotaxidis were found to be statistically significant, where the sporangia of H. brassicae were nearly circular and the sporangia of H. diplotaxidis were closer to an oval.

Optimizing launcher trajectories is essential for effective mission planning, and specialized software like ASTOS provide an initial, precise overview. However, as launcher development progresses, there is a growing need for the creation of an autonomous flight trajectory software that offers greaterflexibility in adjusting simulation parameters and better represents actual, real-life trajectories. Thisreport introduces an initial version of a comprehensive six-degree-of-freedom launcher trajectory calculation software developed using MATLAB and Simulink. The emphasis is on the development strategy, encompassing discussions on dynamics equations, essential features, and crucial models necessary for accurate simulations. Real-world scenarios often deviate from optimized trajectories, and the software addresses these deviations using sensitivity analysis through Monte Carlosimulations, enabling a thorough examination of uncertainties in input parameters and their impact on trajectories. The article delves into the establishment of the dispersion analysis tool and offers suggestions for further enhancements for both the Simulink model and this dispersion analysis tool. / Optimering av flygbanor är avgörande för effektiv uppdragsplanering, och specialiserad programvara som ASTOS ger en initial, exakt översikt. Men när flygbanans utveckling fortskrider finns det ett växande behov av att skapa en autonom flygbana som erbjuder större flexibilitet när det gäller attjustera simuleringsparametrar och bättre representerar faktiska, verkliga banor. Den här rapporten introducerar en initial version av en omfattande beräkningsprogramvara utvecklad med MATLAB och Simulink för sex frihetsgraders lanseringsbana. Tyngdpunkten ligger på utvecklingsstrategin, som omfattar diskussioner om dynamikekvationer, väsentliga funktioner och avgörande modeller som är nödvändiga för exakta simuleringar. Scenarier i verkligheten avviker ofta från optimerade banor, och programvaran adresserar dessa avvikelser med känslighetsanalys genom Monte Carlo-simuleringar,vilket möjliggör en grundlig undersökning av osäkerheter i inmatningsparametrar och deras påverkan på banor. Rapporten går in i skapandet av spridningsanalysverktyget och erbjuder förslag till ytterligare förbättringar för både Simulink-modellen och detta dispersionsanalysverktyg.

This thesis is concerned with the development and application of laser induced thermal grating spectroscopy (LITGS) as a tool for thermometry in reacting and non-reacting flows. LITGS signals, which require resonant excitation of an absorbing species in the measurement region to produce a thermal grating, are acquired for systematic measurements of temperature in high pressure flames using OH and NO as target absorbing species in the burned gas. The signal obtained in LITGS measurements appears in the form of a time-based signal with a characteristic frequency proportional to the value or the sound speed of the local medium. With knowledge of the gas composition, the temperature can be derived from the speed of sound measurement. LITGS thermometry using resonant excitation of OH in the burned gas region of in oxygen enriched CH4/O2/N2 and CH4/air laminar flames was performed at elevated pressure (0.5 MPa) for a range of conditions. Measurements were acquired in oxygen enriched flames to provide an environment in which to demonstrate LITGS thermometry under high temperature conditions (up to 2900 K). The primary parameters that influence the quality of LITGS signal were also investigated. The signal contrast, which acts as a marker for the strength of the frequency oscillations, is shown to increase with an increase in the burnt gas density at the measurement point. LITGS employing resonant excitation of NO is also demonstrated for quantitative measurements of temperature in three environments – a static pressure cell at ambient temperature, a non-reacting heated jet at ambient pressure and a laminar premixed CH4/NH3/air flame operating at 0.5 MPa. Flame temperature measurements were acquired at various locations in the burned gas close to a water-cooled stagnation plate, demonstrating the capability of NO-LITGS thermometry for measuring the spatial distribution of temperature in combustion environments. In addition, the parameters that in influence the local temperature rise due to LITGS were also investigated in continuous vapour flows of acetone/air and toluene/air mixtures at atmospheric conditions. Acetone and toluene are commonly targeted species in previous LITGS measurements due to their favourable absorption characteristics. Results indicate that LITGS has the potential to produce accurate and precise measurements of temperature in non-reacting flows, but that the product of the pump intensity at the probe volume and the absorber concentration must remain relatively low to avoid significant localised heating of the measurement region.

Thesis (MPhil)--Stellenbosch University / ENGLISH ABSTRACT: The current level of literacy in South Africa is cause for concern. The Annual National Assessment of Literacy and Numeracy, conducted nationally by the National Department of Education of South Africa, shows that only 28% of Grade 3 learners and 35% of Grade 6 learners passed these tests in 2011 (Department of Basic Education (a), 2011). According to the policy on progression and promotion issued by the National Department of Education, learners may only be retained once in a phase, which means that these learners may lack essential academic literacy skills when they reach high school. The main concern addressed in this thesis is whether high school teachers can help improve academic literacy by using reading comprehension software, like Reading Rocket, as an intervention tool to help learners who struggle with reading comprehension, and whether Reading Rocket is in fact an effective program to use for such purposes. This study was conducted by using data from one school within the Western Cape which has been using Reading Rocket for the past three years. Use of the program forms part of their timetable, and Grade 8 and 9 learners spend twice per cycle working with the program. Learners are first tested on entering Grade 8 and group reports are retrieved from the program each term to monitor their progress. These reports give a summary of the reading level, the percentage gained in the reading exercises, reading speed in w.p.m and a spelling score in percentage. This data was used to compile a summary of the results obtained over six terms Term 1 2010 until Term 3 2011. These results were compared with quarterly classroom (paper‐based) comprehension and language tests in order to determine is a correlation between the program data and the paper‐based test data. There is no control group for this study as all the Grade 8 and 9 learners use the program. There is no conclusive evidence that the program is an effective intervention tool, but findings show a positive correlation between program data and paper‐based test data which indicates that the program may be used as a tool to determine on what grade level learners read. Given the numerous responsibilities and duties of teachers, it is essential that they are given an effective measuring tool for literacy and because computer software is essentially objective and time‐effective in provide results, using computer technology for such purposes may be part of a solution to improve literacy in South Africa. / AFRIKAANSE OPSOMMING: Die huidige toestand van geletterdheid in Suid‐Afrika is kommerwekkend. Resultate in 2011 van die jaarlikse nasionale assesseringstoetse vir geletterdheid en gesyferdheid wat nasionaal deur die Nasionale Onderwysdepartement gedoen word, wys dat net 28% van Graad 3‐leerders en 35% van Graad 6‐leerders hierdie toetse slaag (Department of Basic Education (a), 2011). Volgens die beleid van progressie en promosie van die Nasionale Onderwysdepartement mag leerders net eenkeer in ‚n schoolfase agtergehou word wat beteken dat bogenoemde leerders dalk nie die geleentheid het om voldoende te verbeter voordat hulle die hoërskoolfases betree nie. Die hoofkwessie wat in hierdie tesis aangespreek word is of hoërskoolonderwysers rekenaar sagteware soos Reading Rocket as ʼn intervensie metode kan gebruik om leerders se akademiese leesbegrip te verbeter, en of Reading Rocket wel ʼn effektiewe intervensiemiddel is. ʼn Studie is gedoen deur die data van een skool in die Wes‐Kaap te gebruik wat Reading Rocket al vir die afgelope drie jaar gebruik. Dit vorm deel van hulle skoolrooster en graad 8 en 9‐leerders spandeer twee keer per siklus aan die program. Groepverslae wat deur die program opgedateer word elke kwartaal getrek om progressie te monitor. Die verslae bevat ʼn opsomming van die leerders se leesvlak, leesbegrip in persentasie, leesspoed in w.p.m en ʼn persentasie vir spelling. Hierdie data is gebruik om ‘n opsomming saam te stel van die resultate oor ses kwartale (kwartaal 1 2010 tot kwartaal 3 2011). Die programresultate is vergelyk met resultate van klaskamer (papiergebaseerde) begripstoetse en eksamens wat hulle vir dieselfde kwartale geskryf het. Omdat al die graad 8 en 9‐leerders aan die program blootgestel word, is daar nie ʼn kontrolegroep vir die studie nie. Daar is nie konkrete bewys dat die program ʼn effektiewe intervensiemiddel is nie, maar statistieke wys wel dat daar ʼn positiewe korrelasie tussen die programdata en die papiergebasseerde data is en daarom word die gevolgtrekking gemaak dat die program wel as ʼn instrument kan gebruik word om die leerders se leesbegrip op enige stadium van die jaar te toets. Weens vele verantwoordelikhede is dit essensieel dat onderwysers ʼn effektiewe metingsinstrument vir leesbegrip tot hulle beskikking het. Omdat rekenaarsagteware soos Reading Rocket tydbesparend en objektief in die voorsiening van resultate is, mag die gebruik van sulke tegnologie deel van ʼn plan vorm om geletterdheidsvlakke in Suid‐Afrika te verbeter.

Ces cinquantes dernières années, la majorité des paramètres de conception des moteurs cryotechniques ont été ajustés en l'absence d'une compréhension détaillée des phénomènes de combustion, en raison des limites des diagnostiques expérimentaux et des capacités de calcul. L'objectif de cette thèse est de réaliser des simulations numériques instationnaires d'écoulements réactifs transcritiques de haute fidélité, pour permettre une meilleure compréhension de la dynamique de flamme dans les moteurs cryotechniques et finalement guider leur amélioration. Dans un premier temps, la thermodynamique gaz-réel et son impact sur les schémas numériques sont présentés. Comme la Simulation aux Grandes Echelles (SGE) comporte des équations filtrées, les effets de filtrages induits par la thermodynamique gaz-réel sont ensuite mis en évidence dans une configuration transcritique type et un opérateur de diffusion artificiel, spécifique au gaz réel, est proposé pour lisser les gradients transcritiques en SGE. Dans un deuxième temps, une étude fondamentale du mélange turbulent et de la combustion dans la zone proche-injecteur des moteurs cryotechniques est menée grâce à la Simulation Numérique Directe (SND). Dans le cas non-réactif, les lâchers tourbillonnaires dans le sillage de la lèvre de l’injecteur jouent un rôle majeur dans le mélange turbulent et provoquent la formation de structures en peigne déjà observées expérimentalement dans des conditions similaires. Dans le cas réactif, la flamme reste attachée à la lèvre de l'injecteur, sans extinction locale, et les structures en peigne disparaissent. La structure de flamme est analysée et différents modes de combustion sont identifiés. Enfin, une étude de flamme-jet transcritique H2/O2, accrochée à un injecteur coaxial avec et sans retrait interne, est menée. Les résultats numériques sont d'abord validés par des données expérimentales pour l'injecteur sans retrait. Ensuite, la configuration avec retrait est comparée à la solution de référence sans retrait et à des données experimentales pour observer les effets de ce paramètre de conception sur l'efficacité de combustion. / In the past fifty years, most design parameters of the combustion chamber of Liquid Rocket Engines (LREs) have been adjusted without a detailed understanding of combustion phenomena, because of both limited experimental diagnostics and numerical capabilities. The objective of the present thesis work is to conduct high-fidelity unsteady numerical simulations of transcritical reacting flows, in order to improve the understanding of flame dynamics in LRE, and eventually provide guidelines for their improvement. First real-gas thermodynamics and its impact on numerical schemes are presented. As Large-Eddy Simulation (LES) involves filtered equations, the filtering effects induced by real-gas thermodynamics are then highlighted in a typical 1D transcritical configuration and a specific real-gas artificial dissipation is proposed to smooth transcritical density gradients in LES. Then, a Direct Numerical Simulation (DNS) study of turbulent mixing and combustion in the near-injector region of LREs is conducted. In the non-reacting case, vortex shedding in the wake of the lip of the injector is shown to play a major role in turbulent mixing, and induces the formation of finger-like structures as observed experimentally in similar operating conditions. In the reacting case, the flame is attached to the injector rim without local extinction and the finger-like structures disappear. The flame structure is analyzed and various combustion modes are identified. Finally, a LES study of a transcritical H2/O2 jet flame, issuing from a coaxial injector with and without inner recess, is conducted. Numerical results are first validated against experimental data for the injector without recess. Then, the recessed configuration is compared to the reference solution and to experimental results, to scrutinize the effects of this design parameter on combustion efficiency.

Combustion in cryogenic engines is a complex phenomenon, involving either liquid or supercritical fluids at high pressure, strong and fast oxidation chemistry, and high turbulence intensity. Due to extreme operating conditions, a particularly critical issue in rocket engine is wall heat transfer which requires efficient cooling of the combustor walls. The concern goes beyond material resistance: heat fluxes extracted through the chamber walls may be reused to reduce ergol mass or increase the power of the engine. In expander-type engine cycle, this is even more important since the heat extracted by the cooling system is used to drive the turbo-pumps that feed the chamber in fuel and oxidizer. The design of rocket combustors requires therefore an accurate prediction of wall heat flux. To understand and control the physics at play in such combustor, the Large Eddy Simulation (LES) approach is an efficient and reliable numerical tool. In this thesis work, the objective is to predict wall fluxes in a subcritical rocket engine configuration by means of LES. In such condition, ergols may be in their liquid state and it is necessary to model liquid jet atomization, dispersion and evaporation.The physics that have to be treated in such engine are: highly turbulent reactive flow, liquid jet atomization, fast and strong kinetic chemistry and finally important wall heat fluxes. This work first focuses on several modeling aspects that are needed to perform the target simulations. H2/O2 flames are driven by a very fast chemistry, modeled with a reduced mechanism validated on academic configurations for a large range of operating conditions in laminar pre- mixed and non-premixed flames. To form the spray issued from the atomization of liquid oxygen (LOx) an injection model is proposed based on empirical correlations. Finally, a wall law is employed to recover the wall fluxes without resolving directly the boundary layer. It has been specifically developed for important temperature gradients at the wall and validated on turbulent channel configurations by comparison with wall resolved LES. The above models are then applied first to the simulation of the CONFORTH sub-scale thrust chamber. This configuration studied on the MASCOTTE test facility (ONERA) has been measured in terms of wall temperature and heat flux. The LES shows a good agreement compared to experiment, which demonstrates the capability of LES to predict heat fluxes in rocket combustion chambers. Finally, the JAXA experiment conducted at JAXA/Kakuda space center to observe heat transfer enhancement brought by longitudinal ribs along the chamber inner walls is also simulated with the same methodology. Temperature and wall fluxes measured with smooth walls and ribbed walls are well recovered by LES. This confirms that the LES methodology proposed in this work is able to handle wall fluxes in complex geometries for rocket operating conditions.

The Kentucky Re-entry Universal Payload System (KRUPS) is an adaptable testbed for atmosphere entry science experiments, with an initial application to thermal protection systems (TPS). Because of the uniqueness of atmospheric entry conditions that ground testing is unable to replicate, scientists principally rely on numerical models for predicting entry conditions. The KRUPS spacecraft, developed at the University of Kentucky, provides an inexpensive means of obtaining validation data to verify and improve these models. To increase the technology readiness level (TRL) of the spacecraft, two sub-orbital missions were developed. The first mission, KUDOS, launched August 13th, 2017 on a Terrier-Improved Malamute rocket to an altitude of ~150 km. The second mission, KOREVET, launched on March 25th, 2018 on the same type of rocket to an altitude of ~170 km. The chief purpose of both missions was to validate the spacecraft design, ejection mechanism, on-board power, data transmission, and data collection. After both missions, the overall TRL improved from 4 to 5 by validating most subsystems in a relevant environment. Both of these missions were invaluable preparation for the project's ultimate goal of releasing multiple experimental testbeds from the ISS.

This dissertation is concerned with the mathematical modeling of the flow in a porous cylinder with a focus on applications to solid rocket motors. After discussing the historical development and major contributions to the understanding of wall injected flows, we present an inviscid rotational model for solid and hybrid rockets with arbitrary headwall injection. Then, we address the problem of pressure integration and find that for a given divergence free velocity field, unless the vorticity transport equation is identically satisfied, one cannot find an analytic expression for the pressure by direct integration of the Navier-Stokes equations. This is followed by the application of a variational procedure to seek novel solutions with varying levels of kinetic energies. These are found to cover a wide spectrum of admissible motions ranging from purely irrotational to highly rotational fields. Subsequently, a second law analysis as well as an extension of Kelvin's energy theorem to open boundaries are presented to verify and corroborate the variational model. Finally, the focus is shifted to address the problem of laminar viscous flow in a porous cylinder with regressing walls. This is tackled using two different analytical techniques, namely, perturbation and decomposition. Comparisons with numerical Runge--Kutta solutions are also provided for a variety of wall Reynolds numbers and wall regression speeds.

This thesis aims at studying the breakup of swirling liquid sheets discharging from the outer orifice of gas centered swirl coaxial atomizers. Such atomizers are considered as propellant injection systems for semi-cryogenic liquid rocket engines. A gas centered swirl coaxial type atomizer discharges an annular swirling liquid sheet which is atomized by a gaseous jet issuing from the central orifice of the atomizer. The primary objectives of this work were to understand the fluid dynamic interaction process between the outer liquid sheet and the central gas jet and its role on the breakup process of the liquid sheet. Cold flow experiments were carried out by constructing custom made gas centered swirl coaxial atomizers. Two different atomizer configurations with varying swirl effect were studied. The jets were injected into ambient atmospheric air medium with tap water and air as experimental fluids. The flow conditions were described in terms of Weber number (Wel) and Reynolds number (Reg) for liquid sheet and the air jet respectively. Spray images were captured by employing an image acquisition system comprising a high resolution digital camera and a strobe lamp. The captured spray images at different combinations of Wel and Reg were analyzed to extract quantitative measurements of breakup length (Lb), spray cone angle (θs), spray width (SW) and two-dimensional surface profile of liquid sheets. Quantitative analysis of the variation of Lb with Reg with different values of Wel suggested that low inertia liquid sheets undergo an efficient breakup process. High inertia liquid sheets ignore the presence of central air jet at lower values of Reg however undergo air jet breakup at higher values of Reg. Qualitative analysis of experimental observations revealed that the entrainment process, established between the inner surface of the liquid sheet and the boundary of central jet, triggers the air assisted sheet breakup by drawing the liquid sheet closer to the spray axis. The entrainment process may be developing corrugations on the surface of liquid sheet which promotes the production of thick liquid ligaments from the sheet surface. The level of surface corrugations on the liquid sheet, quantified by means of tortuosity of liquid sheet profile, increases with increasing Reg. Limited studies on the effect of variation swirl intensity on the air assisted breakup process of liquid sheets did not show any significant influence for the atomizers examined in the present work.