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  • Author or Editor: D. R. Topham x
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D. R. Topham and R. G. Perkin


The response characteristics of a family of conductivity cells typical of those employed in profiling instruments has been examined from a theoretical standpoint, and the conditions established under which such a cell exhibits a linear transfer function. The necessary conditions are that conductivity changes are small, and that the molecular diffusion of conductivity within the cell is negligible over times of interest. The first of these conditions is almost always satisfied, as is the second for the diffusion of salt; for conductivity changes arising from temperature, however, molecular diffusion of temperature imposes a severe limit on the linearity of the response.

The analysis fully accounts for the fluid flow within the cell, and includes the effect of the internal frictional losses on the cell entry flow speed—an important effect on cell response. Numerical results of the step responses of the Neil Brown and Guildline cells are presented and those for the former closely match available experimental data over a wide range of fall speeds. Simple algebraic correlations of the numerical results allow easy prediction of the response of the Neil Brown cell and an approximate algorithm is presented, which can be applied to a wide range of cell designs.

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H. D. Pite, D. R. Topham, and B. J. van Hardenberg


A review of the upper structure of the Arctic Ocean and its overlying ice cover suggests that significant potential exists for the generation of internal wave fields by the deeper drafts of the pressure ridge keels. Laboratory measurements are presented of the drag force on two-dimensional ice keel models of varying degrees of slenderness in both homogeneous and two-layer fluid systems. The experiments were performed in a towing tank 10 m long and covered the range from subcritical to fully supercritical flows. MW results show that the two-layer stratification increases the drag dramatically over that in a corresponding homogeneous flow, reaching a maximum in the transcritical flow regime as a result of the establishment of a system of internal waves. The increase in drag was greatest for the most slender obstacle, approaching the values to be expected from simple hydraulic theory. For the more steeply sloped obstacles, the wave growth is limited by dispersion, with a corresponding reduction in the peak drag force, Comparison with both simple hydraulic theory and the forced, extended Korteweg-de Vries equation shows that while the trend of the measurements is reproduced, a good description of the flows over the obstacles is obtained only for a limited range of conditions. Scaling the laboratory measurements to the Arctic Ocean suggests that the deeper ice keels may exert a considerable influence on the ice-ocean drag forces.

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