A full-bridge, parallel-loaded, resonant, zero current/zero voltage switching converter has been developed for DC-DC voltage transformation. The power supply was used to condition power sourced by a 28-V, 400-A Neihoff alternator installed in a HMMWV that delivered power to a 5-kW mobile radar. This design focuses on achieving maximum power density at reasonable efficiency (i.e. > 80%) by operating at the highest resonant and switching frequencies possible. A resonant frequency of 392-kHz was achieved while providing rated power. The high resonant frequency was facilitated by the development of an extremely low inductance layout (< 20 nH) capable of conducting the high resonant currents associated with this converter topology. A design methodology is presented for parallel-loaded, resonant voltage boost converters utilizing the development of a converter prototype as a basis. The experimental results are presented as validation of the methodology.

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Steady two-dimensional natural convection in air-filled, regular and irregular inclined enclosures has been investigated numerically. The effect of various configurations of bidirectional temperature gradients on mode transition of thermal convection inside the cavity has been investigated. Numerical treatment of temperature discontinuity at the comer points of the cavity and its effect on the calculated Nusselt number has been discussed. Rayleigh numbers range between 103 and 104, aspect ratio (width/height) =1,2,4, and angle of inclination in the range between 0 and 90°. While the cavity bottom and top walls were kept at constant temperatures at Th (heated) and at Tc (cooled), respectively, thermal conditions of end walls were varied. In addition to the base case of insulated end walls, seven different configurations of thermal conditions of the two side walls have been studied. Results show that numerically predicted heat transfer rates strongly depend on the numerical treatment of temperature discontinuities at cavity comer points. Results also indicate that thermal conditions of cavity end walls have a significant effect on mode-transition of thermal convection flows; and hence, on heat transfer effectiveness inside the cavity, and on the Hysteresis phenomenon occurred as the cavity angle of inclination varied from zero (horizontal position) to 90 ° (vertical position) and back to zero. The effect of curved bottom is carried out by replacing flat bottom of the cavity with a curved one. Only insulated end walls were discussed in curved case. Results indicated that heat transfer rate and mode transition are strongly dependent on the height of curvature of the bottom wall, which offers more flexibility in controlling flow mode-transition, and hence, effectiveness of heat transfer inside the cavity. / Thesis / Master of Applied Science (MASc)

Bedload transport is a complicated phenomenon in gravel-bed streams. Several factors account for this complication, including the different hydrologic regime under which different stream types operate and the wide range of particle sizes of channel bed material. Based on the hydrologic regime, there are two common types of gravel-bed streams: perennial and ephemeral. In terms of channel bed material, a gravel bed may have either unimodal or bimodal sediment. This study examines more closely some aspects of bedload transport in gravel-bed streams and proposes explanations based on fluvial mechanics. First, a comparison between perennial and ephemeral gravel-bed streams is conducted. This comparison demonstrates that under a wide range of Shields stresses, the trends exhibited by the bedload transport data of the two stream types collapse into one continuous curve, thus a unified approach is warranted. Second, an empirical bedload transport relation that accounts for the variation in the make-up of the surface material within a wide range of Shields stresses is developed. The accuracy of the relation is tested using available bedload transport data from streams with unimodal sediment. The relation is also compared against other formulae available in the literature that are commonly used for predicting bedload transport in gravel-bed streams. Third, an approach is proposed for transforming the bimodal sediment into two independent unimodal fractions, one for sand and another for gravel. This transformation makes it possible to carry out two separate computations of bedload transport rate using the bedload relation developed in this study for unimodal sediment. The total bedload transport rate is estimated by adding together the two contributions. / Ph. D.