Peter Wright

Ultra High Resolution Computed Tomography of Damage in Notched Carbon Fiber—Epoxy Composites:

This article presents the first use of synchrotron radiation computed tomography (SRCT) to achieve sub-micron resolution of damage in aerospace grade carbon fiber—epoxy composites. The structure and interaction of the damage can be visualized in 3-D on a scale not previously observed in practical engineering configurations. The ability to detect and accurately measure features down to individual fiber breaks provides a valuable platform for future research; from the rigorous evaluation of damage models to understanding the fundamental physical mechanisms governing crack growth in composites. In particular the key role of intra-laminar cracks and delaminations in localizing fiber fractures is unambiguously identified for the first time.

What's in a name? — Descriptive or genetic implications of ‘ridge and runnel’ topography

Abstract The first use of the term ‘ridge and runnel’ for the morphological highs and intervening lows found trending parallel or subparallel to the coastline on certain beaches, had distinct genetic connotations in that the ridges were swash bars originating and developing only in the intertidal zone. In the last ten years or so the use of the term has become more widespread and is now taken to include other morphologically similar, although genetically different, features found in both the intertidal and subtidal zones. This, largely North American, usage is described and compared with the original British application and features given the same name are shown to be genetically different. In order to avoid further confusion we suggest that the use of the term ‘ridge and runnel’ be restricted to that first proposed by King and Williams in 1949.

SHINGLE TRACING BY A NEW TECHNIQUE

Numerical modelling of rivers, estuaries and shallow seas has attracted increasing interest over the last two decades. The models have developed from one dimensional (ID) applications to tidal propagation and flood routing through two and, finally, three dimensional applications to motions ranging from pseudo-turbulence to annual mean residual flows. The present account describes the development, over the last five years, of the modelling studies carried out by the author concerning the hydrodynamics of the southern North Sea and River Thames. The objective is to identify those major points which have emerged that may have a wider significance.The equations describing conservation of mass, momentum and energy in a turbulent free surface flow are derived for a controle volume extending over the whole depth. The effect of the turbulent surface oscillations are discussed but neglected in the following analysis, where the equations are applied to the energy balance in a surf zone wave motion. This leads to results for the wave height variation and the velocity of propagation. The results cannot be reconciled completely with measurements and the concluding discussion is aimed at revealing how the model can be improved.A three-dimensional morphodynamic model of sequential beach changes Is presented. The model Is based on variations in breaker wave power generating a predictable sequence of beach conditions. The spectrum of beach conditions from fully eroded-dissipatlve to fully accreted reflective is characterised by ten beach-stages. Using the breaker wave power to beach-stage relationship the model Is applied to explain temporal, spatial and global variations In beach morphodynamlcs.Fast-response electromagnetic flowmeters were used in a marginal flood channel of an ebb tidal delta to assess the importance of wave contributions to the flood dominance of these channels. Measurements were made at a single point in the channel in both ebb and flood currents. The oscillatory motion of waves was a very significant feature of the velocity records, and its magnitude was comparable with the mean flow at all stages of the tide. This observation shows that flowmeters capable of responding accurately to wave velocities are needed to obtain accurate values of mean flow. Some earlier measurements made with slow response flowmeters are probably unreliable. Wave contributions to the mean flow were assessed by looking at the correlation between the low frequency (>17.5s) oscillations of the along-channel current and the low frequency envelope of the wave velocities. Surprisingly little correlation was found for any time lag, suggesting that wave effects were not important in the mean tidal currents in the channel studied. However, close to low tide on the ebb, conditions existed which appear to have been favourable for the wave pump mechanism suggested by Bruun andViggisson (1973). Significant correlation between the wave envelope and low frequency fluctuations was observed at this time. It is therefore suggested that wave effects can be important to the mean flow in marginal channels with rapidly converging and shoaling mouths which are oriented towards the dominant incident wave direction.The agents of initial damage to the dunes are water, which undermines them, and animals (including man) which damage the protective vegetation by grazing or trampling. Of these, man has recently assumed predominant local importance because of the popularity of sea-side holidays and of the land-falls of certain marine engineering works such as oil and gas pipelines and sewage outfalls. The need is therefore increasing for active dune management programmes to ensure that under these accentuated pressures, the coast retain an equilibrium comparable with that delicately balanced equilibrium which obtains naturally at a particular location.