Conformally mapped viscous gravity current

We show how the conformal mapping technique can be applied to analyse specific problems in the context of viscous gravity current theory. We examine the edge of steady thin planar viscous gravity currents in the presence of complex external low Reynolds flows. In addition to the uniform ambient flow we look at the case of viscous gravity currents spreading in positively strained flows and around cylindrical bodies. These external flows exert shear stress on the gravity current, which drives it in the streamwise direction. The idealised conditions are re-created in the laboratory using a Hele–Shaw cell with a point source on the bottom plate where the saline is introduced into the flow. The mapped laboratory results are compared to a known similarity solution and the agreement is good. We conclude by identifying a broad class of viscous gravity current problems where this technique may be applied

Advances in Evaluating Tsunami Forces on Coastal Structures

At source, tsunami waves have relatively small wave heights (typically 0.5-2m), but very long wavelengths. As these waves approaches the shoreline and enter the shallower waters, their wavelength reduces and their wave height increases dramatically. The resulting waves can cause violent impacts on infrastructure and structures, and the long wavelengths lead to extensive inundation inland causing destruction over large areas of coast as seen recently in Japan (2011). Clearly there is a need for a systematic analysis of the physics of tsunami flows in and around buildings and the forces and pressures they produce on structures as a function of time. The first steps towards such a study are presented. This paper presents preliminary observations obtained from sets of unique physical experiments designed to study the impact of tsunami-like waves on coastal structures towards the development of tsunami design/assessment guidance

Advances in Evaluating Tsunami Forces on Coastal Structures

At source, tsunami waves have relatively small wave heights (typically 0.5-2m), but very long wavelengths. As these waves approaches the shoreline and enter the shallower waters, their wavelength reduces and their wave height increases dramatically. The resulting waves can cause violent impacts on infrastructure and structures, and the long wavelengths lead to extensive inundation inland causing destruction over large areas of coast as seen recently in Japan (2011). Clearly there is a need for a systematic analysis of the physics of tsunami flows in and around buildings and the forces and pressures they produce on structures as a function of time. The first steps towards such a study are presented. This paper presents preliminary observations obtained from sets of unique physical experiments designed to study the impact of tsunami-like waves on coastal structures towards the development of tsunami design/assessment guidance

Bandwidth Enhancement Technique for Bipolar Single Stage Distributed Amplifier Design

This work reports a novel approach to extending the bandwidth of single stage distributed amplifiers (SSDAs). The three-stepped technique involves scaling down the inductance on the input artificial transmission line (ATL); creating a high frequency resonance peak by the addition of shunt capacitance on the input ATL; and compensating for the resulting increased reflection with adapted negative resistance attenuation compensation techniques. Compared with the inductive-peaked cascode technique applied in the SSDA which currently has the highest reported bandwidth, simulation results, based on full foundry transistor models, predict up to 30% improvement in gain-bandwidth (GBW) performance for the same active device at the same bias. In addition, the reduction in the length of the input ATL effectively reduces transmission line losses, thereby improving the overall gain performance

Liquid oxygen/liquid hydrogen boost/vane pump for the advanced orbit transfer vehicles auxiliary propulsion system

A rotating, positive displacement vane pump with an integral boost stage was designed to pump saturated liquid oxygen and liquid hydrogen for auxiliary propulsion system of orbit transfer vehicle. This unit is designed to ingest 10% vapor by volume, contamination free liquid oxygen and liquid hydrogen. The final pump configuration and the predicted performance are included

Extended Bell and Stirling numbers from hypergeometric exponentiation

Exponentiating the hypergeometric series 0FL(1,1,...,1;z), L = 0,1,2,..., furnishes a recursion relation for the members of certain integer sequences bL(n), n = 0,1,2,.... For L >= 0, the bL(n)'s are generalizations of the conventional Bell numbers, b0(n). The corresponding associated Stirling numbers of the second kind are also investigated. For L = 1 one can give a combinatorial interpretation of the numbers b1(n) and of some Stirling numbers associated with them. We also consider the L>1 analogues of Bell numbers for restricted partitions

Ladder operators and endomorphisms in combinatorial Physics

Starting with the Heisenberg-Weyl algebra, fundamental to quantum physics, we first show how the ordering of the non-commuting operators intrinsic to that algebra gives rise to generalizations of the classical Stirling Numbers of Combinatorics. These may be expressed in terms of infinite, but row-finite, matrices, which may also be considered as endomorphisms of C[x]. This leads us to consider endomorphisms in more general spaces, and these in turn may be expressed in terms of generalizations of the ladder-operators familiar in physics