Crack initiation and propagation in the bladed disks of aero-engines caused by high-cycle fatigue under cyclic loads could result in the breakdown of the engines if not detected at an early stage. Although a number of fault detection methods have been reported in the literature, it still remains very challenging to develop a reliable online technique to accurately diagnose defects in bladed disks. One of the main challenges is to characterize signals contaminated by noises. These noises caused by very dynamic engine operation environment. This work presents a new technique for engine bladed disk crack detection, which utilizes advanced analysis of clearance and time-of-arrival signals acquired from blade tip sensors. This technique involves two stages of signal processing: 1) signal pre-processing for noise elimination from predetermined causes; and 2) signal post-processing for characterizing crack initiation and location. Experimental results from the spin rig test were used to validate technique predictions.

Ancient basin-floor strata are exceptionally well exposed in the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera. Data from the Castle Creek outcrop, where strata of the upper Kaza Group crop out, and the Mt. Quanstrom outcrop, where the middle Kaza is exposed, form the main dataset for this study. The aim of this study is to describe and interpret the strata starting at the bed scale, followed by stratal element scale, lobe scale and ultimately fan scale. Strata of the Kaza Group comprise six sedimentary facies representing deposition from a variety of fluid and cohesive sediment gravity flows. These, in turn, populate seven stratal elements that are defined by their basal contact, cross-sectional geometry and internal facies distribution. The lithological characteristics of stratal elements vary little from proximal to more distal settings, but their relative abundance and stacking pattern do, which, then, forms the basis for modeling the internal architecture of lobes. Lobes typically comprise an assemblage of stratal elements, which then are systematically and predictably arranged in both space (along a single depositional transect) and time (stratigraphically upward). Lobes typically became initiated by channel avulsion. In the proximal part of the system scours up to several meters deep, several tens of meters wide are interpreted to have formed by erosion downflow of the avulsion node. Erosion also charged the flow with fine-grained sediment and on the lateral margins and downflow avulsion splays were deposited. Later flows then exploited the basin-floor topography and on the proximal basin-floor carved a feeder channel, which then fed a downflow depositional lobe. At the mouths of feeder channels flows became dispersed through a network of distributary channels that further downflow shallow and widen until eventually merging laterally in sandstone-rich terminal splays. During the lifespan of a single lobe the feeder channel remains fixed, but the distributary channel network and its associated terminal splays wander, causing them to stack and be intercalated laterally and vertically. Eventually an upstream avulsion terminates local sediment supply, causing a new lobe to be initiated elsewhere on the fan, and the process repeats.

South Africa is currently facing a major electricity crisis due to the continuous growth in electricity demand. Eskom, the largest electricity supplier in South Africa, have enabled numerous methods to support energy reduction in both the residential and industrial sectors. Programs developed by Eskom to help the different major electricity consuming industries with the development of energy efficient and load shift strategies, have already been put into practice. These programs solely focus on the potential savings in megawatts each production sector might consist of. The key features of the Eskom electricity reduction initiative are driven by the energy efficiency concept and the peak demand load shift capability. Both the load shift and energy efficient initiatives are mostly active in the mining industry, because of the high electricity consumption levels of a standard mining operation. One of the most inefficient systems currently active within a mining operation is the ventilation control system. This dissertation describes the energy efficient and load shift research on the current underground ventilation system by means of certain design methodologies that might improve the inefficient operational features on both the standard underground auxiliary fans and the main surface fans. The operational features of a standard 2-pole 45 kW issued auxiliary fan were tested, by using a fan-testing column to compare the performance criteria to that of an improved auxiliary fan design. An energy saving potential on a single 45 kW unit of 11 kW was evident during the testing analysis. This amounted to an estimated annual energy saving potential of R 370,000.00 with a total saving of 561 kW on all the installed 45 kW units at Kopanang goldmine, by means of an investment in the replacement of the current installed units with that of the improved units. A secondary study was to gather information on the main surface fan operational features at Kopanang and Mponeng goldmines. The gathered information showed an estimated possibility for load shift and efficiency initiatives, which will result in fan operating life expansion and electricity savings capabilities. Annual electricity savings of up to R I ,500,000.00 were calculated on efficiency and load shift strategies and gave an indication on how costly inefficient operations are. The calculated I 0% increase in main fan efficiency resulted in an annual saving of nearly R 1,100,000.00 with a reduction of 1,05 MW at Mponeng goldmine and an annual saving of nearly R 721,000.00 with a reduction of 675 kW at Kopanang goldmine. The load shift potential at Mponeng and Kopanang goldmines were nearly 3,5 MW and 2,25 MW respectively. Capital investments from either Eskom or alternative investors will definitely play a crucial part in the realization of energy efficiency and load shift measures. It may include, improved fan installations, variable speed drives for the main fans and real time management systems. If the mine should decide to invest in these efficient strategies, the proposed Eskom DSM program might result in a net energy savings potential for any mining operation. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2007.

Systems based on the vapor compression cycle are the most widely used in a variety of air conditioning applications. Despite the vast growth of modern control systems in the field of air conditioning systems, industry standard control is still thermostat based on-off control, in other words cycle control. This thesis proposes an approach to find the optimal profiles for the expansion valve and the evaporator fan for an air conditioning system for a given period of on-off cycle of the compressor. The research will consist of two phases, the development of a simulation model and an experimental analysis. In this thesis, the profiles for the expansion valve and the evaporator fan are parameterized by an S-curve equation so that the optimization problem will have less numbers of parameters. The first step is a simulation model that predicts startup/shutdown characteristics. This model is used as a tool to understand the effect that the S-curve parameters has on the system cycle efficiency. Several key vapor compression system dynamics are identified as causes for increasing/decreasing system's cyclic efficiency. Refrigerant migration and fan delay at shutdown are determined as crucial issues that have an effect on the A direct search optimization algorithm, namely the simplex search algorithm, is then used to search for the optimal S-curve parameters. Valve/fan strategies that ultimately resulted in a better superheat control are assessed as the most energy efficient. Extensive experimental tests conducted on a 3-ton residential air conditioner are then presented to intuitively understand the effect of expansion valve and evaporator fan cycling in a real system. A real time optimization method is explored and the feasibility, recommendations for a successful online method are proposed. The heuristics for the expansion valve and evaporator fan profiles from the optimization results could be easily hard coded into any commercial air conditioning system to perform the much preferred cycle control. Thus a significant improvement in the energy performance was observed without the use of any advanced control techniques.

The technology of UAV (Unmanned Aerial Vehicle) has developed since its conception many years ago. UAVs have several features such as, computerised and autonomous control without the need for an on-board pilot. Therefore, there is no risk of loss of life and they are easier to maintain than manned aircraft. In addition, UAVs have an extended range/endurance capability, sometimes for several days. This makes UAVs attractive for missions that are typically

Comic books are one of the many popular cultural forms that attract, as part of their audience, a committed readership that engages in a participatory relationship as part of a shared interest in the text. In common with other media forms, this engagement expresses itself in a variety of ways, including interaction with other readers online and face-to-face at conventions, correspondence with producers, and the creation of textual products. Other features of the discourses and practices of this community may be more specific to the comic book readership. One of the most interesting of these is a participatory belief, widely expressed by readers, that they can influence the story content of the published comic book and that comic books are unique among other media forms in this. In this thesis, I investigate several aspects of this belief, in order to offer a more nuanced understanding of the participatory involvement that readers have in comic books, particularly the superhero comic books that dominate American comic book culture. First, I examine whether this participatory belief is supported by evidence from published comic books by undertaking a content analysis of the letter columns and story pages of comic books. Next, I explore the discourses of online comic book culture that relate to authorship and the boundaries of participation and show how the rules of textual engagement that are held by readers shape the interactions between readers and producers. Finally, I look for alternative participatory spaces that are available to comic book readers, finding these in a contested form of engagement with comic books, that of exploring the fictional universes of the text. This approach imagines the text as the representation of a non-actual world, to which the comic book is an incomplete window. Theorising this mode of engagement leads to a conceptualisation of participation that makes visible a participatory space that has been previously overlooked by academic fan studies, and that complicates the existing models of participatory culture.

Comic books are one of the many popular cultural forms that attract, as part of their audience, a committed readership that engages in a participatory relationship as part of a shared interest in the text. In common with other media forms, this engagement expresses itself in a variety of ways, including interaction with other readers online and face-to-face at conventions, correspondence with producers, and the creation of textual products. Other features of the discourses and practices of this community may be more specific to the comic book readership. One of the most interesting of these is a participatory belief, widely expressed by readers, that they can influence the story content of the published comic book and that comic books are unique among other media forms in this. In this thesis, I investigate several aspects of this belief, in order to offer a more nuanced understanding of the participatory involvement that readers have in comic books, particularly the superhero comic books that dominate American comic book culture. First, I examine whether this participatory belief is supported by evidence from published comic books by undertaking a content analysis of the letter columns and story pages of comic books. Next, I explore the discourses of online comic book culture that relate to authorship and the boundaries of participation and show how the rules of textual engagement that are held by readers shape the interactions between readers and producers. Finally, I look for alternative participatory spaces that are available to comic book readers, finding these in a contested form of engagement with comic books, that of exploring the fictional universes of the text. This approach imagines the text as the representation of a non-actual world, to which the comic book is an incomplete window. Theorising this mode of engagement leads to a conceptualisation of participation that makes visible a participatory space that has been previously overlooked by academic fan studies, and that complicates the existing models of participatory culture.

Comic books are one of the many popular cultural forms that attract, as part of their audience, a committed readership that engages in a participatory relationship as part of a shared interest in the text. In common with other media forms, this engagement expresses itself in a variety of ways, including interaction with other readers online and face-to-face at conventions, correspondence with producers, and the creation of textual products. Other features of the discourses and practices of this community may be more specific to the comic book readership. One of the most interesting of these is a participatory belief, widely expressed by readers, that they can influence the story content of the published comic book and that comic books are unique among other media forms in this. In this thesis, I investigate several aspects of this belief, in order to offer a more nuanced understanding of the participatory involvement that readers have in comic books, particularly the superhero comic books that dominate American comic book culture. First, I examine whether this participatory belief is supported by evidence from published comic books by undertaking a content analysis of the letter columns and story pages of comic books. Next, I explore the discourses of online comic book culture that relate to authorship and the boundaries of participation and show how the rules of textual engagement that are held by readers shape the interactions between readers and producers. Finally, I look for alternative participatory spaces that are available to comic book readers, finding these in a contested form of engagement with comic books, that of exploring the fictional universes of the text. This approach imagines the text as the representation of a non-actual world, to which the comic book is an incomplete window. Theorising this mode of engagement leads to a conceptualisation of participation that makes visible a participatory space that has been previously overlooked by academic fan studies, and that complicates the existing models of participatory culture.

Comic books are one of the many popular cultural forms that attract, as part of their audience, a committed readership that engages in a participatory relationship as part of a shared interest in the text. In common with other media forms, this engagement expresses itself in a variety of ways, including interaction with other readers online and face-to-face at conventions, correspondence with producers, and the creation of textual products. Other features of the discourses and practices of this community may be more specific to the comic book readership. One of the most interesting of these is a participatory belief, widely expressed by readers, that they can influence the story content of the published comic book and that comic books are unique among other media forms in this. In this thesis, I investigate several aspects of this belief, in order to offer a more nuanced understanding of the participatory involvement that readers have in comic books, particularly the superhero comic books that dominate American comic book culture. First, I examine whether this participatory belief is supported by evidence from published comic books by undertaking a content analysis of the letter columns and story pages of comic books. Next, I explore the discourses of online comic book culture that relate to authorship and the boundaries of participation and show how the rules of textual engagement that are held by readers shape the interactions between readers and producers. Finally, I look for alternative participatory spaces that are available to comic book readers, finding these in a contested form of engagement with comic books, that of exploring the fictional universes of the text. This approach imagines the text as the representation of a non-actual world, to which the comic book is an incomplete window. Theorising this mode of engagement leads to a conceptualisation of participation that makes visible a participatory space that has been previously overlooked by academic fan studies, and that complicates the existing models of participatory culture.

[Truncated abstract] The subject of fan noise generating mechanisms and its control has been studied intensively over the past few decades as a result of the ever-increasing demand for more powerful fans. A unique feature of fan noise is that it consists of high-level discrete frequency noise related to the blade passing frequency, and low-level broadband noise due mostly to turbulent airflow around the fan. Of the two types of fan noise, the discrete frequency noise is the more psychologically annoying component. Past research into fan noise has shown that the discrete frequency fan noise are dipole in nature and are caused predominantly by the fluctuating lift acting on the surfaces of the fan blades. Based on this, several theoretical models have been established to correlate these fluctuating lift forces to the far-field sound pressure. However, one general assumption in these models is that the fan blades are assumed rigid, and the consequence of such an assumption is that it is unclear if the far-field sound pressure is caused solely by the aerodynamic lift force, or whether the blade vibration also plays a substantial role in the generation of the far-field fan noise. One of the goal of this thesis was thus to experimentally quantify the contribution of blade vibration to far-field fan noise and it was found that blade vibration, whilst coherent with the far-field fan noise, did not contribute significantly. Aside of this, several experiments aimed at filling knowledge gaps in the understanding of fan noise characteristics were also be conducted, in particular, to understand the relationship between far-field sound pressure level to blade lengths as well as the number of blades on the fan. The experiments showed that for fans with many blades, the dependency of the far-field sound pressure on blade length is stronger than fans with less blades. Furthermore, dipole measurements showed that the dipole characteristics of fan noise does not occur only at the discrete frequencies, but also within a range of broadband frequencies, implying that the source for both discrete and broadband is the same. The second section of this thesis deals with the study of vortex shedding and its active control. When a circular cylinder (or any object) is placed in a flow within a specified Reynolds number range, flow separation and periodical wake motion is formed behind the cylinder, which is known as vortex shedding. It has been found in previous research that this wake motion is affected by acoustic field imposed on it via loudspeakers. This suggests that there is a strong acoustic-vortex relationship. However, little of this relationship is understood as conventional methods of studying vortex centre around the use of hot-wire anemometry, which effectively measures the velocity fluctuation in the flow. This thesis is the first in using a microphone to study the acoustic characteristic of the vortex wake, and experimental results shows that the two parallel shear layers of the wake carry the strongest pressure signals at the vortex shedding frequency, whilst the entrapped region between the layers carries the strongest pressure signals at the first harmonic.