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Call number: LD2668 .R4 1966 S875

In concrete reinforced buildings, the steel framework is required to be bonded and is often used as a cost effective method of lightning protection. In defining lightning protection zones, it is essential to understand where the lightning current due to a direct strike will flow. A number of models exist to evaluate the current distribution, but are often applied to relatively simple structures. Using Maxwell’s equations, an approximate skin effect model is proposed and used to eval- uate the lightning current distribution in a complex structure. A reduced scale model of a structure, consisting of conductors arranged in rings, is developed to verify the model. Particular attention is given to the return path of the current, ensuring an even distrib- ution of the current in the structure. The equivalent circuit showed an even distribution of current across each conductor at dc and low frequencies and a distribution that concentrated in the outer conductors for higher frequencies. The measurements from the structure confirmed that the current con- centrates in the outer conductors at high frequencies. Applying a reduced scale lightning impulse, it is shown that the majority of the current flows on the outermost conductors. Any current on the inner conductors is not only greatly decreased in magnitude, but significantly slower in time than the applied impulse.

Interest is continually being shown in the replacement of variable speed DC machines with an equivalent inverter fed AC machine. This is as true in the field of highly rated machines for traction use. as in the field of smaller industrial drives. In the following work, a general design method is presented that is suitable for the design of induction, and slip ring synchronous machines of the round rotor or salient pole type. The method is based upon machine models that employ surface quantities. This type of model clearly displays the interaction between flux and current, and is readily adaptable for design use. as the amount of detail required is kept to a minimum. Several designs are presented for induction and synchronous machines that satisfy the requirements of a traction motor for use in a high speed locomotive. Performance predictions, based on sinusoidal supply considerations and operating under two commonly used control schemes are shown. The traction motors satisfy the main overall requirement for a minimum size and weight design. In practice the AC traction motors would be supplied by a variable frequency inverter. In view of this, an analysis of the performance of the most suitable induction and synchronous motor designs is presented, when each is being supplied with an inverter of the preferred type. Two inverters are considered, one of the constant voltage type, and one of the constant current type. Computer models are used to predict the machine, voltage current and torque waveforms when both inverters are operated In the 120 degree conduction mode. Experimental results are shown, to verify the computer model of the current source inverter. A 5KVA laboratory squirrel cage induction machine is used for this purpose, in conjunction with a force measuring platform that enables the steady state torque pulsations to be recorded.

MOCNESS plankton tows, sediment traps and sedimentary material are used to determine the linkage between bio-physical forcing and foraminiferal response over a range of time scales from the event scale to the glacial interglacial cycle. The annually averaged planktic foraminiferal fauna of the modem California Current is a diverse community composed of individuals from subarctic, transitional, and subtropical foraminiferal assemblages. This community is more diverse, but less abundant in total standing stock and shell flux than the subarctic community of the Gulf of Alaska. The use of plankton tow and isotopic data allow us to partition the foraminiferal community into shallow dwelling euphotic zone species and deep dwelling sub-thermocline species. On both the event and seasonal time scales, heterotrophic species were most abundant in cold, biomass rich coastal waters. In contrast, species which harbored endosymbionts were more abundant in oligotrophic waters with higher ambient light levels. During the Last Glacial Maximum (LGM), the diverse modern fauna was replaced with a low diversity, high flux, heterotrophic community similar to that of the modern Gulf of Alaska. Modern analog temperature estimates suggest the California Current was roughly 3��C cooler during the LGM than today. Coupled with oxygen isotopic results from G. bulloides, the surface thermal structure implies an equatorward flowing glacial California Current at these sites. The Polar Front thus remained north of these locations during the LGM. Comparison of glacial G. bulloides carbon isotopes and shell accumulation rates with organic carbon flux estimates implies the glacial California Current was (1) higher in nutrient content, (2) lower in plankton biomass, and (3) lower in export carbon flux than its modem counterpart. This description suggests that during the LGM the plankton community of the California Current was very similar to the modern plankton community of the Gulf of Alaska. / Graduation date: 1996