An investigation of the changes in the natural frequency of a pile affected by scour

Scour around bridge foundations is one of the leading causes of bridge failure. Up until recently, the monitoring of this phenomenon was primarily based around using underwater instrumentation to monitor the progression of scour holes as they develop around foundation systems. Vibration-based damage detection techniques have been used to detect damage in bridge beams. The application of these vibration based methods to the detection of scour has come to the fore in research in recent years. This paper examines the effect that scour has on the frequency response of a driven pile foundation system, similar to those used to support road and rail bridges. The effect of scour on the vibration characteristics of the pile is examined using laboratory and field testing. It is clear that there is a very clear reduction in the natural frequency of the pile as the severity of scour increases. It is shown that by combining state-of-the-art geotechnical techniques with relatively simple finite element modelling approaches, it is possible to accurately predict the natural frequency of the pile for a given scour depth. Therefore, the paper proposes a method that would allow the estimation of scour depth for a given observed pile frequency.     

A solution-scheme for the convective-diffusion equation

This paper presents a versatile solution-scheme for the convective-diffusion equation. A small-time, asymptotic, solution for an instantaneous point source of scalar contaminant is expressed as a three-dimensional, Hermite polynomial expansion and manipulated, using superposition, to generate the contaminant concentration field that results at larger times and for arbitrary, continuous or instantaneous, source contaminant distribution. This equation is commonly used to model contaminant dispersion in complex environmental flows so that the considerable degree of generality, flexibility and efficiency of this solution-scheme highly commends it to this application. The off-diagonal terms in the diffusivity tensor and the non-zero gradient of this term and the mean-velocity field are shown to make a significant contribution to the evolution of the contaminant concentration field resulting from the instantaneous release of contaminant from a point source.

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Zusammenfassung Die vorliegende Arbeit gibt eine vielseitig brauchbare Lösungsmethode für die konvektive Diffusionsgleichung. Die für kurze Zeiten gültige asymptotische Lösung für eine plötzlich wirkende Punktquelle der diffundierenden Skalargröße wird als dreidimensionale Entwicklung in Hermite'schen Polynomen dargestellt. Dies wird benützt um das Feld für größere Zeiten darzustellen, für beliebige, kontinuierliche oder diskontinuierliche Quellverteilungen. Diese Gleichung wird allgemein benützt als Modell für Dispersion von Schadstoffen in komplizierten Strömungen bei natürlichen Umgebungsverhältnissen; die Allgemeingültigkeit, Anpassungsfähigkeit und Wirksamkeit der Lösung machen die Methode für diese Anwendungen besonders geeignet. Es wird gezeigt, daß die Nichtdiagonalterme des Diffusionstensors sowie die nichtverschwindenden Gradienten dieses Termes und der mittleren Geschwindigkeit wesentliche Beiträge zur Entwicklung des Feldes leisten, die von der Punktquelle erzeugt wurde.

     

Peroxymercuration-demercuration of lipid hydroperoxides

The course of mercuric-ion catalyzed cyclization of lipid hydroperoxides and the demercuration of the resulting cyclic peroxides is reported. The cyclization products depend on the mercuric ion utilized and the course of demercuration can be altered by conditions of reduction and oxygenation.     

Freeze-out conditions in ultrarelativistic heavy-ion collisions

We present recent results on single particle transverse momentum distributions of pions, kaons and protons, measured in CERN Experiment NA44, of 200 AGeV/c S+S and 158 AGeV/c Pb+Pb central collisions. By comparing these data with thermal and transport models, freeze-out parameters like the temperatureT _fo and the chemical potentials (μ _q ,μ _s ) are extracted and discussed.     

Thermoelasticity of networks in swelling equilibrium with mixed diluents: Specific polymer-diluent interactions

Thermoelasticity studies of poly(vinyl alcohol) networks swollen in aqueous glycol indicate that the effects of specific polymer-diluent interactions diminish at high swelling, much as in the situation of poly(vinyl alcohol) in pure water reported earlier. In 20% glycol, the ratio of the energy component f_e of the force to the total force f was found to be ?0.59 at high swelling. Swelling was controlled by the degree of network crosslinking. Evidence that f_e/f could be determined under the condition of a null thermal expansion coefficient was not obtained; in fact, the contrary was indicated.     

Laminar free convection due to a point source of Buoyancy

Similarity solutions are found for the laminar flow arising from a point source of buoyancy. Approximate analytic solutions in closed form are derived for the non-dimensional velocity and density distributions as a function of the Prandtl number. These approximations are shown to compare favourably with numerical solutions given by Fujii and to include the exact solutions of Yih for Prandtl numbers of 1 and 2.