LOWER BOUNDS FOR THE BUCKLING PRESSURE OF SPHERICAL SHELLS

Hydrostatic buckling pressure calculations for spherical shell

Detection and remediation of switch faults on a fault tolerant permanent magnet motor drive with reduncancy

Copyright © 2007 IEEE. All Rights Reserved.Fault-tolerant motor drives are becoming more important in safety critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have a fault-tolerant capability. This paper considers a dual motor drive system on a common shaft to introduce redundancy. The paper provides a systematic classification for the potential electrical faults which may occur in a real motor drive. In the paper, the switch and winding short circuit fault detection and identification methods are studied and experimental results are presented. In addition, the effects of switch faults on the phase currents and output torque are discussed, and remedial strategies for these faults are proposed. Furthermore, it was also demonstrated using simulation results that the proposed remedial strategies can compensate for the loss of torque due to the switch faults and can keep the peak-to-peak torque ripple factor comparable to healthy operation of the drive.Jingwei Zhu; Ertugrul, N.; Wen Liang Soon

Minimum torque ripple current control strategy in dual fault tolerant PM AC motor drive

Copyright © 2008 IEEEIn this paper a dual fault tolerant motor drive utilizing brushless permanent magnet AC motors is investigated for safety critical applications. The motor modules are designed to provide both magnetic and electrical isolation between the phases, and the use of two modules also offers redundancy. This paper addresses an important issue, torque ripple and torque compensation due to the loss of a phase or phases in a practical dual motor drive. The mathematical models for reference current calculation in both healthy and various faulty operation modes are established under the zero torque ripple factor and minimum copper loss constraint conditions. These models are suitable for both sinusoidal and trapezoidal fault tolerant motor drives. The experimental results under various fault conditions are provided to verify the proposed fault remedial strategy.Jingwei Zhu, Nesimi Ertugrul, and Wen Liang Soon

Fault analysis and remedial strategies on a fault-tolerant motor drive with redundancy

Copyright © 2007 IEEEFault-tolerant motor drives are required in a range of safety-critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have an effective fault-tolerant capability. Although a single motor fault-tolerant drive system may be sufficient in many critical applications, a higher degree of fault tolerance requires redundancy in the motor system as considered in this paper. This is achieved by using a dual motor module on a common shaft. The simulation model of the entire drive system and the analysis of the various faults are presented in this paper. The effects of fault(s) on the phase current and output torque are provided. Three remedial operating modes are proposed and their features are compared. In addition, an experimental setup was introduced, which is based on dual electrically and magnetically isolated brushless AC motor modules, H-bridge inverters for individual phases and dsPICDEM MCU motor controller. © 2007 IEEE

Carotenoids are the likely precursor of a significant fraction of marine dissolved organic matter.

The ocean's biota sequester atmospheric carbon dioxide (CO2) in part by producing dissolved organic matter (DOM) that persists in the ocean for millennia. This long-term accumulation of carbon may be facilitated by abiotic and biotic production of chemical structures that resist degradation, consequently contributing disproportionately to refractory DOM. Compounds that are selectively preserved in seawater were identified in solid-phase extracted DOM (PPL-DOM) using comprehensive gas chromatography (GC) coupled to mass spectrometry (MS). These molecules contained cyclic head groups that were linked to isoprenoid tails, and their overall structures closely resembled carotenoid degradation products (CDP). The origin of these compounds in PPL-DOM was further confirmed with an in vitro β-carotene photooxidation experiment that generated water-soluble CDP with similar structural characteristics. The molecular-level identification linked at least 10% of PPL-DOM carbon, and thus 4% of total DOM carbon, to CDP. Nuclear magnetic resonance spectra of experimental CDP and environmental PPL-DOM overlapped considerably, which indicated that even a greater proportion of PPL-DOM was likely composed of CDP. The CDP-rich DOM fraction was depleted in radiocarbon (14C age > 1500 years), a finding that supports the possible long-term accumulation of CDP in seawater. By linking a specific class of widespread biochemicals to refractory DOM, this work provides a foundation for future studies that aim to examine how persistent DOM forms in the ocean

IPM synchronous machine drive response to symmetrical and asymmetrical short circuit faults

Copyright © 2003 IEEEA closed-form solution is presented for the steady-state response of interior permanent magnet (IPM) synchronous machines to symmetrical short circuits including the effects of q-axis magnetic saturation. Machine response to single-phase asymmetrical short circuits is also investigated. Experimental data are presented to verify predicted behavior for both types of short circuits. It is shown that single-phase asymmetrical short circuit faults produce more severe fault responses with high pulsating torque and a significant threat of rotor demagnetization. A control strategy that purposely transitions such faults into symmetrical three-phase short circuits can minimize the fault severity and associated demagnetization risks. Implications for the design of IPM machines with improved fault tolerance are discussed.Brian A. Welchko, Thomas M. Jahns, Wen L. Soong and James M. Nagashima

ASTRO-H Soft X-Ray Telescope (SXT)

ASTRO-H is an astrophysics satellite dedicated for X-ray spectroscopic study non-dispersively and to carry out survey complementally, which will be borne out of US-Japanese collaborative effort. Among the onboard instruments there are four conically approximated Wolter-I X-ray mirrors, among which two of them are soft X-ray mirrors\ of which the energy range is from a few hundred eV to 15 keY, currently being fabricated in the X-ray Optics Lab at Goddard Space Flight Center. The focal point instruments will be a calorimeter (SXS) and a CCD camera (SXI), respectively. The reflectors of the mirror are made of heat-formed aluminum substrate of the thickness gauged of 152 micron, 229 micron, and 305 micron of the alloy 5052 H-19, followed by epoxy replication on gold-sputtered smooth Pyrex cylindrical mandrels to acquire the X-ray reflective surface. The epoxy layer is 10 micron nominal and surface gold layer of 0.2 micron. Improvements on angular response over the Astro-El/Suzaku mirrors come from error reduction on the figure, the roundness, and the grazing angle/radius mismatching of the reflecting surface, and tighter specs and mechanical strength on supporting structure to reduce the reflector positioning and the assembly errors. In this paper, we report the results of calibration of the engineering model of SXT (EM), and project the quality of the flight mirrors

Cross-national gender differences in the socioeconomic factors associated with smoking in Australia, the United States of America and South Korea

Objectives: We compared rates of smoking among those aged 45 years and older in Australia, the United States of America and South Korea, and examined cross-national gender differences in key socioeconomic differentials in smoking. Methods: We conducted weighted analyses on cross-sectional data from nationally representative surveys conducted in 2006. Results: Current smoking was more prevalent for males than females in all countries; the gender difference was largest in Korea. Being unpartnered increased the likelihood of smoking in all countries, while greater wealth reduced it. In Korea these effects interacted with gender; both indicators showed larger differentials among women than men. Lower educational attainment increased the likelihood of smoking for all groups except Korean women, among whom high school educated women were less likely to smoke than the tertiary educated. Conclusions: Our findings support a cultural interpretation of gender differences in smoking: in countries with low gender empowerment, gender differences in smoking are greater. With increasing divorce and female tertiary education rates in nations like Korea, we highlight the need for health promotion messages targeted towards older and more educated women

Calibration of the Soft X-ray Telescopes (SXT) Onboard the ASTRO-H Satellite

ASTRO-H is an astrophysics satellite dedicated for non-dispersive X-ray spectroscopic study on selective celestial X-ray sources. Among the onboard instruments there are four Wolter-I X-ray mirrors of their reflectors' figure in conical approximation. Two of the four are soft X-ray mirrors, of which the energy range is from a few hundred eV to 15 keV. The focal point instruments will be a calorimeter (SXS) and a CCD camera (SXI), respectively. The mirrors were in quadrant configuration with photons being reflected consecutively in the primary and secondary stage before landing on the focal plane of 5.6 m away from the interface between the two stages. The reflectors of the mirror are made of heat-formed aluminum substrate of the thickness gauged of 152 m, 229 m, and 305 m of the alloy 5052 H-19, followed by epoxy replication on gold-sputtered smooth Pyrex cylindrical mandrels to acquire the X-ray reflective surface. The epoxy layer is 10 m nominal and surface gold layer of 0.2 m. Improvements on angular response over its predecessors, e.g. Astro-E1/Suzaku mirrors, come from error reduction on the figure, the roundness, and the grazing angle/radius mismatching of the reflecting surface, and tighter specs and mechanical strength on supporting structure to reduce the reflector positioning and the assembly errors. Each soft x-ray telescope (SXT), FM1 or FM2, were integrated from four independent quadrants of mirrors. The stray-light baffles, in quadrant configuration, were mounted onto the integrated mirror. Thermal control units were attached to the perimeter of the integrated mirror to keep the mirror within operating temperature in space. The completed instrument went through a series of optical alignment, thus made the quadrant images confocal and their optical axes in parallel to achieve highest throughput possible. Environmental tests were carried out, and optical quality of the telescopes has been confirmed. The optical and x-ray calibrations also include: angular resolution, effective area in the energy range of ~ 0.4 - 12keV, off-axis response, etc. Some of those are being carried out by our counterpart at JAXA/ISAS, Japan. We report the calibration results of the FM1 and FM2 that were obtained at Goddard Space Flight Center

Novel high-speed induction motor for a commercial centrifugal compressor

Copyright © 2000 IEEEThis paper describes the electrical, mechanical, and metallurgical design, construction, and testing of a novel low-cost high-speed high-efficiency induction motor to drive a new type of small centrifugal compressor in industrial cooling applications. The 28-shaft-hp 50-kr/min motor features a unique laminated rotor with a multifunction high-strength copper-alloy cage brazed with a novel process. Relatively thin high-silicon steel laminations were used to achieve low losses and high mechanical strength at low cost. Different heat treatments for the stator and rotor laminations were used to optimize the mechanical and magnetic properties. The preprototype motors achieved about 94% (electromagnetic) efficiency at the rated point, including inverter harmonics, while meeting cost (less than one-tenth of aerospace practice) and produceability goals.Wen L. Soong, Gerald B. Kliman, Roger N. Johnson, Raymond A. White, and Joseph E. Mille