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Axial ventilation fans are used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. Ventilation fans are one of the most harmful sources of noise due to their close proximity to occupied areas and widespread use. The prolonged exposure to hazardous noise levels can lead to noise-induced hearing loss. Consequently, there is a critical need to reduce noise levels from ventilation fans. Since fan noise scales with the 4-6th power of the fan tip speed, minimizing the fan tip speed and optimizing the duct geometry are effective methods to reduce fan noise. However, there is a tradeoff between reducing fan speed, noise and aerodynamic efficiency. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated and implemented using a multi-objective genetic algorithm. The methodology incorporates a control vortex design approach that results in a spanwise chord and twist distribution of the blades that maximize the volumetric flow rate contribution of the outer radii, i.e. the axial flow velocity increases from the fan hub to the tip. The resulting blade geometry generates a given volumetric flow rate at the minimum fan tip speed. The fan design is complemented by the design of the optimum inlet duct geometry to maximize volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades and enable lower fan speeds and noise. Good agreement between experiments and predictions indicate that traditional blade element momentum methods can be implemented in conjunction with multi-element airfoil aerodynamic characteristics with good accuracy. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi-element airfoils aerodynamically outperform single element fans. / Doctor of Philosophy / Axial ventilation fans are widely used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. However, high noise levels from ventilations fans are a harmful source of noise that can lead to irreversible noise-induced hearing loss. Therefore, this work addresses a critical need for quiet and efficient ventilation fans. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated, implemented, and tested. The methodology optimizes the fan geometry to maximize the volumetric flow rate and minimize noise. The fan design is complemented by the design of the optimum inlet duct geometry to increase the volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi-element airfoils aerodynamically outperform single element airfoil fans.

Made available in DSpace on 2014-10-09T12:49:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:31Z (GMT). No. of bitstreams: 1 09814.pdf: 3649987 bytes, checksum: 2ebdfca1ffee2ffc9e0dc65e2ac1df10 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:49:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:31Z (GMT). No. of bitstreams: 1 09814.pdf: 3649987 bytes, checksum: 2ebdfca1ffee2ffc9e0dc65e2ac1df10 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:49:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:07Z (GMT). No. of bitstreams: 1 10282.pdf: 3788200 bytes, checksum: 89ccf6d2ea9e26c2736dc1bbebcde360 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEn-CNEN/SP

Made available in DSpace on 2014-10-09T12:54:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:21Z (GMT). No. of bitstreams: 1 12434.pdf: 5335647 bytes, checksum: a56abda29440b5de525348eee5d618da (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

Made available in DSpace on 2014-10-09T12:49:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:07Z (GMT). No. of bitstreams: 1 10282.pdf: 3788200 bytes, checksum: 89ccf6d2ea9e26c2736dc1bbebcde360 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEn-CNEN/SP

Made available in DSpace on 2014-10-09T12:54:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:21Z (GMT). No. of bitstreams: 1 12434.pdf: 5335647 bytes, checksum: a56abda29440b5de525348eee5d618da (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

The impact of agricultural practices on wetland ecosystems in the Prairie Pothole Region (PPR) has long been recognized but little is understood about impacts on the biogeochemistry of the wetlands at depth. Understanding the relationship of multi-elements within the wetland and surrounding landscape can aid in wetland restoration and provide guidance for wetland management. The objectives of this study were to: 1) identify biogeochemical characteristics of PPR wetlands; 2) identifying differences or similarities in biogeochemical characteristics of the landscape; 3) assess the vertical variation in chemical composition at depth in wetland, wetland and fringe, footslope and backslope soils; and 4) interpret the soil chemistry of undisturbed sites (good quality; prairie vegetation) and disturbed sites (poor quality; cultivated) relative to differences in landscape position locations. A field study was conducted on six disturbed (DW) and 6 undisturbed (UW) wetlands with evaluation of fringe (F), footslope (FS), or backslope (BS) positions. Using redundancy analysis (RDA) with selected environmental variables models of element concentrations at depth in each position were generated. The RDA ordination plots of element concentrations to depth of 1m was constrained by variables sand, silt, clay, depth, bulk density, site, organic matter, electrical conductivity, and pH. Pearson correlation coefficients between soil properties and the five most prominent soil elements differed between landscape positions. Anthropogenic activity likely influenced the subsurface hydrology but differed in physical and chemical properties. These differences appear to be related to the vegetation, levels of soil disturbance of surrounding landscapes and unique chemical and physical characteristics of parent material.

Over the past several years, energy efficiency and power density have become the top concerns for power conversion. Rising energy intensity leads to a higher cost of delivering power. Meanwhile, the demand for compact power supplies grows significantly. It requires power supplies with high efficiency, low profile and high power density. Dc-dc power conversion has been widely applied for industry, medial, military and airspace applications. Conventional PWM dc-dc converters have relatively low power transfer efficiency and low power density. In contrast, resonant dc-dc converters have numerous advantages for dc-dc power conversions. In this work, topologies and system optimization of resonant converters are investigated to meet challenges of high efficiency, high power density, low EMI, easy startup and over current protection. LLC resonant converters can achieve zero-voltage-switching (ZVS) for primary side devices and zero-current-switching (ZCS) for the secondary side rectifiers. The switching loss is minimized. LLC is very attractive to overcome the issues of conventional circuits. However, challenges still remain. First of all, for low-voltage high-current applications, the synchronous rectifier (SR) with lower conduction loss is a must for high efficiency. To solve the driving issues of SRs, a novel synchronous driving scheme is proposed. Experimental results demonstrate the considerable loss reduction with utilization of the proposed driving scheme. Secondly, dc-dc converters are required to meet EMI standard. This work proposes an EMI mode. Based on the proposed model, EMI analysis and noise attenuation techniques are proposed and verified by experiments. Thirdly, startup and over-load protection are another issues of LLC resonant converters. With proposed multi-element resonant converters, the current limit issues can be resolved. In addition, the proposed multi-element resonant converters can utilize higher-order harmonics to enhance power transfer. Fourthly, for high-current applications, the secondary side structure becomes very critical. An improved secondary side construction is proposed to alleviate ac termination losses and SR paralleling issues. Novel winding structures are proposed to reduce the winding loss. The magnetic integration technique is proposed and analyzed, and an optimal integrated transformer design is proposed, which has low loss and compact size. / Ph. D.