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Abstract Grid-tied renewable energy sources (RES) with battery-behind-meter (BBM) architectures have successfully been used to ensure effective energy cooperation between the grid and RES-based microgrids. Such environments are quite stochastic, thus making power management very challenging. This paper presents the use of an asynchronous Q-learning in performing a power flow management task in a multi-source electric vehicle charging station with the integration of vehicle-to-microgrid technology. The power scheduling problem is first formulated as a Markov decision process. Asynchronous Q-learning is then used to solve it. The algorithm is tested with a typical charging station load profile over a 24-hour period and compared with a simple rule-based algorithm. Simulation results show that the proposed method is able to select a power schedule that reduces the energy cost with a better utilization of both the battery storage system and the vehicle to microgrid energy compared to the rule-based method.

Thesis (MEng)--Stellenbosch University, 2018. ; ENGLISH ABSTRACT: The development of a prototype variable valve duration reciprocating steam expander was undertaken. A variable valve duration system was developed which could vary the cut-off ratio from 15 % to 90 %. An existing internal combustion engine was converted into the prototype reciprocating steam engine. Thermodynamic models were developed to determine the theoretical power output and working fluid consumption of the manufactured prototype engine. Proof of concept tests were performed on the engine. The engine was operated at 500 rpm where the output power and air consumption were measured. Tests were performed for various cut-off ratios to determine the influence on output power and air consumption. The experimental results showed a strong correlation to the theoretical effect of cut-off ratio on power output and air consumption. The maximum experimental output achieved was 1.396 kW at an 80 % cut-off ratio. The experimental power output was lower than the theoretical results which neglected mechanical losses in the system. The thermodynamic model over predicted the air consumption due to the assumption of instantaneous valve events. ; AFRIKAANSE OPSOMMING: Die ontwikkeling van 'n prototipe veranderlike klep duur wederkerige stoom uitsitter is onderneem. 'n Veranderlike klep-duurstelsel is ontwikkel wat die afsnyverhouding van 15% tot 90% kan wissel. 'n Bestaande verbrandingsmotor was omskep as die bewys van konsep wederkerige stoom-enjin. Termodinamiese modelle was ontwikkel om die teoretiese kraguitset en werkvloeistofverbruik van die vervaardigde prototipe-enjin te bepaal. Bewys van konseptoetse is op die enjin uitgevoer. Die enjin is teen 500 rpm bedryf en die uitlaatkrag en lugverbruik was gemeet. Toetse is uitgevoer vir verskillende afsnyverhoudings om die invloed op die uitsetkrag en lugverbruik te bepaal. Die eksperimentele resultate het 'n sterk verband getoon met die teoretiese effek van afsnyverhouding op kraguitset en lugverbruik. Die ...

Abstract This paper presents a near optimal hoist scheduling and control program for rock winders found in South African deep level mines in the context of demand side management and time-of-use (TOU) tariffs. The objective is to achieve a set hoist target at minimum energy cost within various system constraints. The development of a discrete dynamic and constrained mixed integer linear programming model for a twin rock winder system is presented on which a half-hourly model predictive control (MPC) algorithm containing an adapted branch and bound methodology is applied for near optimal scheduling. Simulation results illustrate the effectiveness of the control program by minimising the energy costs through scheduling according to the TOU tariff and controlling output and ore levels within their boundaries even in the case of significant random delays in the system. Scheduling according to the TOU tariff shows a possible 30.8% reduction in energy cost while approximately 6 h of delays in the system resulted in a mere 14% increase in energy cost.

Spider webs must be able to absorb the energy of impacting insects, and similarly, rock support must absorb the energy of ejected rock in rockbursts. A consideration of the properties of spider webs shows that spider silks (threads) are extremely strong, typically three times as strong as common steel. Spiders also construct their webs with yielding mechanisms to enhance their energy-absorbing capability. In this paper, the techniques employed in web construction are compared with those used in rock support in excavations prone to rockbursting. It is shown that the design of rockburst support could benefit from some of the capabilities used by spiders in the construction of their webs.

Significance Species with narrow distributions provide unique opportunities for understanding the mechanisms that limit their spread. We studied a marine invader that exhibits ecological dominance within its range and has the capacity to fundamentally alter the coastal habitat when introduced to new locations. We found evidence of the species’ potential to establish itself far beyond its present introduced range from both genomic data and species distribution modeling. Therefore, minor oceanographic changes (due to, for example, contemporary climate change) or alteration to human-mediated dispersal may trigger a large-scale invasion along vast stretches of coastlines. Our work provides a holistic framework to assess potential changes in the distribution of invasive species.

Ethanol is an attractive alternative fuel because it is a renewable bio-based resource and it is oxygenated, thereby providing the potential to reduce particulate emissions in compression-ignition engines. In this review the properties and specifications of ethanol blended with diesel fuel are discussed. Special emphasis is placed on the factors critical to the potential commercial use of these blends. These factors include blend properties such as stability, viscosity and lubricity, safety and materials compatibility. The effect of the fuel on engine performance, durability and emissions is also considered. The formulation of additives to correct certain key properties and maintain blend stability is suggested as a critical factor in ensuring fuel compatibility with engines. However, maintaining vehicle safety with these blends may entail fuel tank modifications. Further work is required in specifying acceptable fuel characteristics, confirming the long-term effects on engine durability, and ensuring safety in handling and storing ethanol-diesel blends.

The sequential or co-inoculation of grape must with non-Saccharomyces yeast species and Saccharomyces cerevisiae wine yeast strains has recently become a common practice in winemaking. The procedure intends to enhance unique aroma and flavor profiles of wine. The extent of the impact of non-Saccharomyces strains depends on their ability to produce biomass and to remain metabolically active for a sufficiently long period. However, mixed-culture wine fermentations tend to become rapidly dominated by S. cerevisiae, reducing or eliminating the non-Saccharomyces yeast contribution. For an efficient application of these yeasts, it is therefore essential to understand the environmental factors that modulate the population dynamics of such ecosystems. Several environmental parameters have been shown to influence population dynamics, but their specific effect remains largely uncharacterized. In this study, the population dynamics in co-fermentations of S. cerevisiae and three non-Saccharomyces yeast species: Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima, was investigated as a function of oxygen availability. In all cases, oxygen availability strongly influenced population dynamics, but clear species-dependent differences were observed. Our data show that L. thermotolerans required the least oxygen, followed by T. delbrueckii and M. pulcherrima. Distinct species-specific chemical volatile profiles correlated in all cases with increased persistence of non-Saccharomyces yeasts, in particular increases in some higher alcohols and medium chain fatty acids. The results highlight the role of oxygen in regulating the succession of yeasts during wine fermentations and suggests that more stringent aeration strategies would be necessary to support the persistence of non-Saccharomyces yeasts in real must fermentations.

The move towards renewable energy and technological advancements in the generation, distribution and transmission of electricity have increased the popularity of microgrids. The popularity of these decentralised applications has coincided with advancements in the field of telecommunications allowing for the efficient implementation of these applications. This convenience has, however, also coincided with an increase in the attack surface of these systems, resulting in an increase in the number of cyber-attacks against them. Preventative network security mechanisms alone are not enough to protect these systems as a critical design feature is system resilience, so intrusion detection and prevention system are required. The practical consideration for the implementation of the proposed schemes in practice is, however, neglected in the literature. This paper attempts to address this by generalising these considerations and using the lessons learned from water distribution systems as a case study. It was found that the considerations are similar irrespective of the application environment even though context-specific information is a requirement for effective deployment.