Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> http://www.scielo.org.za/rss.php?pid=1021-201920170001&lang=pt vol. 59 num. 1 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Vorticity filaments beneath regular turbulent flow</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100001&lng=pt&nrm=iso&tlng=pt Two-dimensional vorticity flow fields created in the wake of a plunging breaker were investigated for regular turbulent flow at a Reynolds number of 30 000. Velocity flow fields obtained from an earlier study that had employed digital particle image velocimetry, were analysed to determine vorticity shedding patterns and the interactions between the vorticity filaments as flow progressed. Central difference approximations were applied to the velocity fields to determine vorticity at each point in the field. Most of the strong instantaneous vorticity observed in the flow field was in the form of filaments. A hierarchy of filaments of different lengths were observed, with the longest being as long as the height of the wave used. During the early phases of the flow, instantaneous vorticity tended to organise into thin filaments of counter-rotating pairs. Eventually, the co-rotating vorticity filaments coalesced and ultimately merged in the turbulent flow as flow progressed, while counter-rotating vorticity filaments were cancelled by viscous dissipation. The results suggested that filaments travel more slowly than the wave velocity and drifted towards the bed as they became elongated, and the number of filaments remaining in the flow were observed to decrease as flow progressed. Whereas phase-resolved instantaneous vorticity results showed pairs of counter-rotating vorticity filaments near the crest, the phase-averaged vorticity description of flow fields showed a dominant primary positive vorticity filament around the shear boundary layer. <![CDATA[<b>Planning for desalination in the context of the Western Cape water supply system</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100002&lng=pt&nrm=iso&tlng=pt As water demands continue to grow, South Africa is starting to consider seawater desalination as a potential future supply source, and it is currently being investigated at a feasibility level in a number of coastal cities, including Cape Town. Desalination is different to conventional surface and groundwater supply sources in that it is climate-resilient, having an assurance of supply of essentially 100 percent. However, the increased reliability comes at a great cost. This paper presents a methodology developed for modelling a proposed desalination plant as an integrated component of the Western Cape Water Supply System, in order to optimise system operating rules and cost. The modelling entailed short-term and long-term system analyses in the Water Resources Yield Model and Water Resources Planning Model, and estimation of first-order capital and operating costs in order to calculate and compare Unit Reference Values. The maximum increase in yield was found to occur when the seawater desalination plant is used as a base supply, operational all the time. There was little benefit, in terms of system yield, in using the desalination plant as an emergency supply source only. Unit reference values for the desalination plant decrease as the percentage supply from the plant increases, meaning that the lowest possible cost per cubic metre of water supplied is when the desalination plant is used as a base supply. It was also apparent that the unit reference values decrease with an increase in desalination plant capacity, suggesting that, from an economic perspective, the optimal solution would be to have one large desalination plant operational immediately. <![CDATA[<b>Numerical modelling of flexible pavement incorporating cross-anisotropic material properties. Part I: Surface circular loading</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100003&lng=pt&nrm=iso&tlng=pt Accurate numerical modelling of the behaviour of road pavement layers is an important requirement for the design and evaluation of road pavements. This modelling includes the prediction of pavement performance under the action of traffic loading and environmental factors. Depending on the complexity of the models, properties of pavement layers that may be considered are wide-ranging - from linear or nonlinear elastic to cross-anisotropic through to linear visco-elasto-plastic. Some properties, such as cross-anisotropic, are not only related to placement and compaction of the pavement layers, but are also inherent to the materials used. Other properties, such as linear visco-elasto-plastic, are specific to asphalt concrete and depend on the speed and magnitude of traffic loading, as well as the environment (temperature) in which the road is located. This paper presents basic theoretical derivation of numerical modelling of a flexible pavement considering cross-anisotropic material properties (with isotropic properties as a special case). The solutions derived in this paper are based on Hankel transformation of Navier's equations. The accuracy and validity of the solutions are verified through comparisons with a proprietary finite element method (FEM) package. For this purpose, a pavement structure composed of five main layers constituted by isotropic and cross-anisotropic (also known as transversely isotropic) material properties is analysed. In order to vary some of the layer properties with depth, the main layers were sub-layered, resulting in a 17-layer pavement system. <![CDATA[<b>Numerical modelling of flexible pavement incorporating cross-anisotropic material properties. Part II: Surface rectangular loading</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100004&lng=pt&nrm=iso&tlng=pt In order to better understand the impact of increased loading on roads, studies on tyre-road interaction have gained prominence in recent years. Tyres form an essential interface between vehicles and road pavement surfaces. These are the only parts of the vehicle that are in contact with the road and transmit the vehicle loading to the road surface. The use of the Cartesian coordinate system is convenient in dealing with a uniform/non-uniform tyre load acting over a rectangular area, but few research reports are available that provide any form of theoretical solutions for pavement responses. This paper presents analytical solutions of responses due to rectangular loading acting on the surface of a multi-layered pavement system. The solutions developed incorporate both isotropic and cross-anisotropic material properties. The method followed is based on classical trigonometric integral and Fourier transformation of Navier's equations. Accuracy and validity of the solutions are verified through comparisons with a proprietary finite element method (FEM) package. For this purpose, a pavement structure composed of five main layers constituted by isotropic and cross-anisotropic (also known as transversely isotropic) material properties is analysed. In order to vary some of the layer properties with depth, the main layers were sub-layered, resulting in a 17-layer pavement system. <![CDATA[<b>Potential solution to pollution of groundwater by diffusion of volatile organic compounds through the primary HDPE geomembrane in composite lining systems of landfills</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100005&lng=pt&nrm=iso&tlng=pt Waste in a landfill is exposed to the chemicals and heat generated over time, producing harmful fluids in the form of leachate or landfill gas that migrate from the landfill towards the liner or capping, and include organic contaminants. The high-density polyethylene (HDPE) geomembrane (GM) component of the landfill liner is often believed to be the primary barrier to contaminant transport, but volatile organic compounds (VOCs) diffuse through geomembranes at appreciable rates. The aim of this study was to obtain reliable data on the reduction in diffusion of VOCs through the HDPE GM component in the composite liner systems of landfills by extracting air through the leakage detection layer or drainage layer of the composite liner. It was shown that introducing a flow of air through a pervious zone adjacent to the GM layer in a landfill liner would significantly reduce the concentrations of VOCs in the groundwater beneath landfills and waste containment facilities. <![CDATA[<b>Updated provisions of SANS 10160-4 for steel structures</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192017000100006&lng=pt&nrm=iso&tlng=pt A forthcoming revision of SANS 10160-4 (Seismic actions and general requirements for buildings) addresses the omission of structural steel design provisions from the standard, as well as contradictions between SANS 10160 and SANS 10162, the steel design standard. This note discusses the background to the proposed provisions.