Please read the abstract in the front of the document. / Dissertation (MSc)--University of Pretoria, 2009. / Physics / unrestricted

Floods are considered to be among of the deadliest, costliest and most common natural disasters. Rapid onset, catastrophic floods inundate the shore quickly and manifest as deep water with high velocities. The deep water and high velocities caused by these floods inflict great pressures and forces on the built and natural environments and pose a threat to human safety. Recent disasters such as Hurricane Katrina in the Southern United States and the Sumatra tsunami in the Indian Ocean have revealed that communities at risk require improved preparations for these types of dangerous events. Current building codes, design practices and disaster planning methods account for potential earthquake and wind loads on simple wood frame buildings typical of North American residential construction, however, flood impacts have not been considered in the same level of depth. The objectives of this research are to develop a theoretical model that describes flood impacts on wood frame residential buildings and relates building response to physical flood properties such as depth and velocity. This thesis provides a brief synopsis of previous approaches used to describe building response to flooding. An overview of the major loads caused by rapid onset flooding, along with a description of the structural system utilized in wood design to resist these forces is provided. The failure mechanisms considered and the model logic are described and applied to assess the response of a typical Canadian wood frame home to flood conditions that might be experienced in a rapid onset flood event like a tsunami. Building response results are discussed along with recommendations for future analysis and applications. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Lattice materials are used as the core of sandwich panels to construct light and strong structures. This thesis focuses on metallic sandwich structures and has two main objectives: (i) explore how a surface treatment can improve the strength of a lattice material and (ii) investigate the collapse response of two competing prismatic sandwich cores employed in ship hulls. First, the finite element method is used to examine the effect of carburisation and strain hardening upon the compressive response of a pyramidal lattice made from hollow tubes or solid struts. The carburisation surface treatment increases the yield strength of the material, but its effects on pyramidal lattices are not known. Here, it is demonstrated that carburisation increases the plastic buckling strength of the lattice and reduces the slenderness ratio at which the transition from plastic to elastic buckling occurs. The predictions also showed that strain hardening increases the compressive strength of stocky lattices with a slenderness ratio inferior to ten, but without affecting the collapse mode of the lattice. Second, the quasi-static three-point bending responses of simply supported and clamped sandwich beams with a corrugated core or a Y-frame core are compared via experiments and finite element simulations. The role of the face-sheets is assessed by considering beams with (i) front-and-back faces present and (ii) front face present, but back face absent. These two beam designs are used to represent single hull and double hull ship structures, and they are compared on an equal mass basis by doubling the thickness of the front face when the back face is absent. Beams with a corrugated core are found to be slightly stronger than those with a Y-frame core, and two collapse mechanisms are identified depending upon beam span. Short beams collapse by indentation and for this collapse mechanism, beams without a back face outperform those with front-and back faces present. In contrast, longbeams fail by Brazier plastic buckling and for this collapse mechanism, the presence of a back face strengthens the beam. Third, drop weight tests with an impact velocity of 5 m/s are performed on simply supported and clamped sandwich beams with a corrugated core or a Y-frame core. These tests are conducted to mimic the response of a sandwich hull in a ship collision. The responses measured at 5 m/s are found to be slightly stronger than those measured quasi-statically. The measurements are in reasonable agreement with finite element predictions. In addition, the finite element method is used to investigate whether the collapse mechanism at 5 m/s is different from the one obtained quasi-statically. The predictions indicate that sandwich beams that collapse quasi-statically by indentation also fail by indentation at 5 m/s. In contrast, the simulations for beams that fail quasi-statically by Brazier plastic buckling show that they collapse by indentation at 5 m/s. Finally, the dynamic indentation response of sandwich panels with a corrugated core or a Y-frame core is simulated using the finite element method. The panels are indented at a constant velocity ranging from quasi-static loading to 100 m/s, and two indenters are considered: a flat-bottomed indenter and a cylindrical roller. For indentation velocities representative of a ship collision, i.e. below 10 m/s, the predictions indicate that the force applied to the front face of the panel is approximately equal to the force transmitted to the back face. Even at such low indentation velocities, inertia stabilisation effects increase the dynamic initial peak load above its quasi-static value. This strengthening effect is more important for the corrugated core than for the Y-frame core. For velocities greater than 10 m/s, the force applied to the front face exceeds the force transmitted to the back face due to wave propagation effects. The results are also found to be very sensitive to the size of the flat-bottomed indenter; increasing its width enhances both inertia stabilisation and wave propagation effects. In contrast, increasing the roller diameter has a smaller effect on the dynamic indentation response. Lastly, it is demonstrated that material strain-rate sensitivity has a small effect on the dynamic indentation response of both corrugated and Y-frame sandwich panels.

No description available.

The bifurcation phenomenon occurring in twisted square plates with free edges subject to contrary self-equilibrating corner loading was examined. In order to eliminate lateral deflection of the test plates due to their own weight, a special loading apparatus was constructed which held the plates in a vertical plane. The complete strain field occurring at the plate centre was measured using two strain gauge rosettes mounted on opposing sides of the plate at the centre. Principal curvatures were calculated and related to corner load for several plates with differing edge length/thickness ratios. A Southwell plot was used relating mean curvature to the ratio mean curvature/Gaussian curvature, from which the Gaussian curvature occurring at bifurcation was determined. The critical dimensionless twist ka was then calculated for each plate size. It was found that there is a linear relation between the critical dimensionless twist ka occurring at bifurcation, and the thickness to edge length ratio h/a ratio, specifically: ka = 10.8h/a. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The effects of wave directionality on the loads and motions of long structures is investigated in this thesis. A numerical method based on Green's theorem is developed to compute the exciting forces and hydrodynamic coefficients due to the interaction of a regular oblique wave train with an infinitely long, semi-immersed floating cylinder of arbitrary shape. Comparisons are made with previous results obtained using other solution techniques. The results obtained from the solution of the oblique wave diffraction problem are used to determine the transfer functions and response amplitude operators for a structure of finite length and hence the loads and amplitudes of motion of the structure in short-crested seas. The wave loads and body motions in short-crested seas are compared to corresponding results for long-crested seas. This is expressed as a directionally averaged, frequency dependent reduction factor for the wave loads and a response ratio for the body motions. Numerical results are presented for the force reduction factor and response ratio of a long floating box subject to a directional wave spectrum with a cosine power type energy spreading function. Applications of the results of the present procedure include such long structures as floating bridges and breakwaters. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A numerical method is described to study directional wave effects on large offshore structures of arbitrary shape, based on an extension of linear diffraction wave theory for regular waves. A computer program has been developed to compute loading transfer functions and response amplitude operators and hence the loading and response spectra for both long- and short-crested random waves. Cosine powered directional spreading functions which are independent of frequency have been used to account for the shortcrestedness of waves. Comparisions of the results for long- and short-crested seas show that there is a significant reduction in the loading, and hence in the response, due to shortcrestedness of waves. The probabilistic properties of the components of the loading and response are described. Since the sea surface is assumed to follow a Gaussian distribution, these are also random Gaussian variables. In short-crested waves, the loading and response components occur both in-line and transverse to the principal wave direction. Thus the maximum horizontal loading and response may occur in an arbitrary horizontal direction. An analytical method is developed to describe also the probabilistic properties of the maxima of the components and the maxima of their horizontal resultants. In the present study, results are described for a freely floating box. Comparisons are made with published results and are found to be quite favourable. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The present investigation considers the hydrodynamic forces acting on a slender structure subjected to a combined wave and current flow regime. The experimental aspect of the study measured the in-line peak-to-peak forces on a vertical cylinder mounted in a wave-current flume. Although there were some inconsistencies in the data, the general trend indicated a substantial increase in the force with a positive underlying current and a less pronounced increase for a negative current. A numerical analysis of the problem evaluated Morison's equation using the current-invariant force transfer coefficients and flow kinematics obtained through Stokes Fifth Order Wave Theory. The results of this analysis revealed a trend qualitatively similar to that found experimentally. The important distinction between the results obtained through the experimental investigation and those obtained numerically was the consistent over-prediction observed in the numerical analysis. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This study examines the formation of a unique chromatic and formal language in Musica Ricercata by György Ligeti. The study begins by examining statements from an interview with Ligeti conducted by Ove Nordwall in 1979. The interview discusses his compositional experiments from the early 1950s, the period in which Musica Ricercata was composed. Working from Ligeti’s words, “simple structures” are defined as repeating formations of rhythms and intervals with easily discernable features. These features must be salient such that when the structure is altered, it is still clearly and audibly recognizable. The musical and political environment in Hungary at the time is established, providing context for this early experimentation with compositional parameters. The analysis begins with an overview of the entire work, outlining developments of pitch-class density, symmetrical pitch-class structures, and notated accelerandi over the course of the multi-movement work. Analyses of simple structures in each movement elucidate both Ligeti’s experimental approaches to chromaticism, along with more traditional aspects, with special reference to Bartók’s compositional style.

In recent years, extreme natural phenomena such as tsunamis or storm surges have affected populated coastal regions around many coastal regions around the world and with particular impact for countries bordering the Indian, Pacific and Atlantic Oceans. Such extreme events caused significant loss of life and extensive damage to coastal communities. Field surveys conducted from the 1992 Nicaragua Tsunami to the relatively recent 2011 Tohoku Japan Tsunami have recorded lots of evidence of scour around damaged buildings and bridge foundations. It is documented that scouring is one of the significant causes of coastal structural damages. In post-tsunami forensic engineering surveys of India and Thailand following the 2004 Great Sumatra Andaman tsunami, researchers were able to document local scour occurrences not only at buildings located close to shore, but also hundreds of meters inland. (Yeh and Li 2008, Nistor et al. 2012 and Li et al. 2012). The most damaging 2011 Tohoku Tsunami provided an outstanding opportunity to document (Chock et al., 2013) a variety of failure modes of infrastructure including coastal and onshore structures. This research program encompassed a comprehensive experimental and numerical investigation and analysis for the scour mechanism and vortex structures due to inland-propagating tsunami-like bores on a dry or flooded horizontal mobile bed, representing comprehensive tsunami-induced scour study. The primary objective of this thesis was to investigate the influence of different parameters on the bore propagation characteristics and how they affect the scouring process. To achieve this objective, a series of hydraulic bores consistent with the dam-break wave theory were generated. Extensive experiments were conducted to perform parametric analysis on both bore propagation and local scour (e.g., influence of structure size, bore height, bed initial condition, bed material size and second tsunami wave). The secondary objective involved development of a numerical model to simulate local scour and predict the threedimensional (3D) flow pattern around a structure induced by tsunami–like bore. The open source TelemacMascaret numerical model was used to determine flow characteristics adjacent to the structure and the associated bed evolution and resulting local scour. The 3D hydrodynamic Telemac model couples internally with the sediment transport module SISYPHE to solve bed evolution equations. The efficiency of the numerical model was assessed and compared quantitatively and qualitatively with the results of the physical experiments. The studies show a longer duration of a turbulent bore induced more scour depth compared to that generated by solitary or long waves. The short duration and very turbulent nature of the bores induced rapid scour. It was shown that the location of maximum scour depth and sediment deposition pattern downstream of the structure are well captured by the numerical model, however; magnitude of scour depth is underpredicted compared to that of the experimental work. It was found that the ASCE (2016) prescriptions on estimating scour underpredicts the maximum scour depth and thus, the use of the ASCE (2016) provisions, may lead to undesirable underestimations of maximum scour depth. The results of this study have contributed to the American Society of Civil Engineers (ASCE) 7 Chapter 6, which is the first standard written in mandatory language in the world, which specifically prescribes guidance for the design of tsunami resilient critical infrastructure using also a probabilistic framework for the determination of the extent of coastal inundation.