No description available.

No description available.

Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

D.Ing. (Mechanical Engineering) / This research proposed to develop a mathematical model for the prediction of aeolian vibration levels on overhead transmission lines in order to be able to ensure that damping systems are designed optimally in future. In order to enhance the understanding of aeolian and wake-induced vibration further, it also proposed to implement and apply the fluid flow simulation technique of Computational Fluid Dynamics (CFD) to both single conductors and conductor bundles. The Introduction of the CFD tool to the field of transmission line vibration, will ensure that bundles could be optimally designed for future applications. Wind-induced vibrations are known to cause expensive damage to the conductors and related hardware through fatigue or clashing of the bundled conductors. The primary cause of conductor aeolian vibration is the alternate shedding of wind-induced eddies from the top and bottom sides of the conductor, whereas wake-induced oscillations is peculiar to bundled conductors and arises from effects of the shielding of leeward conductors in bundles by windward ones. In order to study the phenomenon of aeolian vibration, research was undertaken utilising a full scale transmission line test station close to Kroonstad in the Orange Free State. Commercially available computer based packages were used for the development and simulation of both the mathematical model and fluid flow. During the flow simulations, an actual Zebra conductor and Zebra bundle configuration were utilised. For the development of the mathematical model, the pratical results, as measured at the Kroonstad transmission line test station during Phase I, were utilised. From the tests performed during Phase I, it was concluded that the damping solutions, currently used by Eskom as tested during Phase I, are all effective in controlling the aeolian vibration. The Stockbridge damper proved to be avery effective damper. Two models for the prediction of aeolian vibration levels were derived. Results showed that the vibration levels could be estimated to the correct order of magnitude and in many cases the precise values. The accuracy of the model was further improved by the inclusion of the Strouhal number as a function of windspeed. It has been decided by the author 10 develop and design a low cost vibration activity indicator for aeolian vibration measurements. The T-R-I-V-A-I has shown that it is a repeatable, reliable device, Ideally suited for line vibration detection. A new device, the W-I-V-I, has also been designed and implemented by the author for the detection and quantification of wake-induced vibration. During the simulation of the flows around a conductor in the steady state, it was established that the flow around as smooth cylinder and a Zebra conductor, is very similar, however, it was established that the rough outer surface of the Zebra conductor acts as a vortex generator. It has been found that a stability relationship exists between the degree of symmetry of the pressure cell, directly in front of the leeward conductor and the wake-induced vibration. Results for the unsteady flow situation showed the initiation and dispersion of the vortices as they are generated alongside the conductor. It is recommended that the developed model's accuracy be further enhanced. It should be established if .there are families of curves and data that belong together and that contribute to the amount of scatter in the parameters measured such as vibration amplitude, Strouhal number, etc. The applicability of CFD to the transmission line field should be enhanced, with the view of increasing bundle performance, both from an electrical and mechanical point of view.

Overhead electrical transmission lines vibrate due to the action of a prevailing wind. These cable vibrations can be classified into two categories— high-frequency and low-frequency. The high-frequency vibrations, "aeolian" vibrations or "singing wires," is a low-amplitude phenomenon. It has been largely controlled with the use of various mechanical dampers [l, 2],

No description available.

Thesis (Ph.D.) -- University of Western Sydney, 2004. / Includes bibliography.

Dynamic optimization has several key advantages. This includes the ability to work on binary code in the absence of sources and to perform optimization across module boundaries. However, it has a significant disadvantage viz-a-viz traditional static optimization: it has a significant runtime overhead. There can be performance gain only if the overhead can be amortized. In this paper, we will quantitatively analyze the runtime overhead introduced by a dynamic optimizer, DynamoRIO. We found that the major overhead does not come from the optimizer's operation. Instead, it comes from the extra code in the code cache added by DynamoRIO. After a detailed analysis, we will propose a method of trace construction that ameliorate the overhead introduced by the dynamic optimizer, thereby reducing the runtime overhead of DynamoRIO. We believe that the result of the study as well as the proposed solution is applicable to other scenarios such as dynamic code translation and managed execution that utilizes a framework similar to that of dynamic optimization. / Singapore-MIT Alliance (SMA)

Many industrial workplaces involve tasks that require work to be performed in overhead postures. Epidemiological evidence suggests that working in these unavoidable, awkward postures leads to development of shoulder fatigue, pain and several musculoskeletal disorders. The accumulation of localized muscle fatigue has been strongly associated with the development of work-related musculoskeletal injuries (Armstrong et al., 1993). In order to prevent injury, minimizing muscular fatigue during short-cycled, repetitive work through different work organization schemes has been suggested (Dempsey et al., 2010). Previous research has examined the interactive effect of altering contraction level, duty cycle and cycle times on shoulder muscle fatigue. However, isolation of one factor while maintaining a constant workload has not been examined for overhead work tasks. The purpose of the study was to determine whether cycle time affected the progression of fatigue at the shoulder since the postural load during overhead tasks is inherently fatiguing. Ten university aged females performed a task rotation between an intermittent overhead pressing task and a neutrally located assembly task. Four conditions were defined by cycle time (15s, 30s, 60s and 120s) and each cycle consisted of one complete rotation. In order to quantify the progression of fatigue over time, four dependant measures were systematically collected for all conditions until exhaustion or to a maximum of three hours. These included root mean square (RMS) amplitude and median power frequency (MdPF) calculated from surface electromyography of nine muscles surrounding the shoulder, static strength capability, and rating of perceived exertion. Endurance time was also included as a fifth measure of fatigue. Linear regression was used to determine the slope of static strength and perceived exertion over time, and magnitude changes over normalized time were calculated for EMG measures. For all dependant measures, repeated measures ANOVA were used to identify significant differences across conditions. As the only independent factor investigated, cycle time influenced two out of the five dependent measures. Conditions induced differences in endurance time (F[3,24]=3.96, p=0.02) and RMS amplitude of the middle (F[24,189]=3.10, p<0.0001) and posterior deltoid (F[24,189]=2.52, p=0.0003). Performing overhead work in long cycles (120s) induced a shorter average endurance time (118.67min), and the shortest cycle time (15s) resulted in a longer average endurance time (152.44min). Over time, the rate of increase in RMS amplitude of both deltoid muscles was higher when working at the longest cycle time (120s). Although six muscles showed an indication of fatigue through significant decreases in MdPF in at least one condition, cycle time did not affect MdPF over time for any muscle examined. Similarly, the rate of static strength capability and rating of perceived exertion over time were not affected by cycle time. Two of five measures indicated that cycle time played a significant role in fatigue progression, making its effectiveness as a work organizational method for overhead work tasks unclear. Results indicate that that intermittent overhead work should be performed in shorter cycles to reduce the risk of shoulder injury. Identifying additional effects of cycle time on fatigue measures through increasing statistical power would provide ergonomists with more confidence in recommending this organizational strategy to mitigate the risk of musculoskeletal injury.

Because of the restriction on structure hazard and instruction data dependence, the quantity of NOP instructions fills up a program for VLIW Architectures. This problem causes a waste of program memory, so that an instruction compression mechanism is a must for VLIW Architectures. The vectorized instruction in DVB-T (Digital Video Broadcasting - Terrestrial) DSP will collect the discrete vectors into one continuous vector. This mechanism is based on the software-pipeline of the zero overhead looping mode. It is important to improve the efficiency of instruction fetcher. Additionally, the branch instruction can cause the non-continuous behavior of a program and the damage of the efficiency of instruction fetcher. The mechanism of compressed instructions causes the irregular length of long instruction in fetch packet. The problem becomes difficult designed. The thesis implements a design of improving instruction stream buffer, which can keep the repeat block in buffer. This mechanism overcomes the effects of zero overhead looping and branch instruction. It can also improve the efficiency of continuously fetch instructions. The simulation result shows that the mechanism has a good efficiency in FFT, FIR and DCT.