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Power generation is becoming an increasing problem in South Africa. South Africa produces approximately 90% of its electricity from coal-fired power stations and only 5% from hydroelectric power stations and pumped storage. Durban has a very steep topography, which results in high pressure in certain parts of the water distribution network (WDN). Leakage is costly and contributes to a large extent to non-revenue water (NRW) in the network. Pressure reducing valves (PRVs) are used in WDNs to control the pressure in the pipework to reduce leakage. This excess pressure can be used to generate electricity by a pump acting as a turbine (PAT). The electricity generated is a function of the flow rate and the pressure reduction through the PAT. The hydraulic modelling software EPANET 2.2 is used for the analysis of the Cornubia Integrated Human Settlement Development Phase 2A WDN in Durban. EPANET is used to determine the strategic placement of PATs in the WDN and their setting and configuration to extract the most energy and reduce pressure in the system. A configuration of five PATs of different sizes extracts a total power output of 166.31 kW and reduces leakage in the WDN by 45.59 kL per month, which is an 18.16% reduction in leakage. [ABSTRACT FROM AUTHOR]

The natural ocean/river currents energy can be harvested using Flow Induced Motion (FIM) phenomena. The effect of damping-ratio and mass-ratio on Flow Induced Motion energy harnessing of a square cylinder are numerically investigated for Reynolds number 15500 < Re < 232000 (0.2 m/s < flow velocity <3.0 m/s). Four typical regions can be observed in the Flow Induced Motion responses, including Vortex Induced Vibration (VIV) Initial Branch, Vortex Induced Vibration Upper Branch, Vortex Induced Vibration-Galloping Transition and Galloping. Results indicate that as the velocity increases, the number of vortices shed per cycle increases, and the harnessed power increases without upper limit. The energy conversion efficiency increases up to the highest value until the Vortex Induced Vibration upper branch. Then, it starts decreasing and tends to a relatively small value in the galloping region. Increasing mass-ratio will shorten the velocity range of Vortex Induced Vibration. High damping-ratio has a negative impact on oscillation amplitude, but provides a boost for energy harnessing. In all tests, the power (143 W) is considerable at damping-ratio = 0.6. As the damping-ratio reaches up to 0.8 (nearing critical damping), galloping will no longer occur. [ABSTRACT FROM AUTHOR]

Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed. [ABSTRACT FROM AUTHOR]