Notch Filtering Suitable for Real Time Removal of Power Line Interference

This paper presents a high performance notch filtering for real time suppression of power line interference in a general signal. The disturbing signal is suppressed using an optimal notch FIR filter with tunable notch frequency. The tuning of the filter preserves its selectivity, most importantly the specified attenuation at the notch frequency. One example and two Matlab functions demonstrate the performance, robustness and usefulness of the proposed procedure for the design and tuning of optimal notch FIR filters suitable in the real time notch filtering

An Investigation of the AFIT 2-Inch Shock Tube as a Flow Source for Supersonic Testing

An investigation of the AFIT high pressure shock tube was conducted to determine how closely it followed ideal shock tube theory and to determine the available test times for an attached Mach 3 nozzle. The driver section was five feet (1.52 m) long and the driven section was 25 feet (7.62 m) long. The driver gas used for this study was helium while the driven gas was atmospheric air. The pressure rise measured behind the incident shock wave was, on average, 30% lower than predicted by the ideal shock tube relations. Behind the reflected shock, the pressure rise was 65% lower than predictions based on initial driver gas pressure. Due to supply pressure limits and lower than predicted pressures behind the shock waves, fully expanded flow in the Mach 3 nozzle was not attained. However, steady overexpanded flows of Mach 2.74-2.96 were observed for periods of 4-12 milliseconds

Evaluation of seals for high-performance cryogenic turbomachines

An approach to computing flow and dynamic characteristics for seals or bearings is discussed. The local average velocity was strongly influenced by inlet and exit effects and fluid injection, which in turn drove zones of secondary flow. For the restricted three-dimensional model considered, the integral averaged results were in reasonable agreement with selected data. Unidirectional pressure measurements alone were insufficient to define such flow variations. However, for seal and bearing leakage correlations the principles of corresponding states were found to be useful. Also discussed are three phenomena encountered during testing of three eccentric nonrotating seal configurations for the Space Shuttle Main Engine (SSME) Program. Fluid injection, choking within a seal, and pressure profile crossover are related to postulated zones of secondary flow or separation and to direct stiffness

Induction motor diagnosis by advanced notch FIR filters and the wigner-ville distribution

During the last years, several time-frequency decomposition tools have been applied for the diagnosis of induction motors, for those cases in which the traditional procedures, such as motor current signature analysis, cannot yield the necessary response. Among them, the Cohen distributions have been widely selected to study transient and even stationary operation due to their high-resolution and detailed information provided at all frequencies. Their main drawback, the cross-terms, has been tackled either modifying the distribution, or carrying out a pretreatment of the signal before computing its time-frequency decomposition. In this paper, a filtering process is proposed that uses advanced notch filters in order to remove constant frequency components present in the current of an induction motor, prior to the computation of its distribution, to study rotor asymmetries and mixed eccentricities. In transient operation of machines directly connected to the grid, this procedure effectively eliminates most of the artifacts that have prevented the use of these tools, allowing a wideband analysis and the definition of a precise quantification parameter able to follow the evolution of their state. © 1982-2012 IEEE

Evaluation of Computing Symmetrical Zolotarev Polynomials of the First Kind

This report summarize and compares with each other various methods for computing the symmetrical Zolotarev Polynomial of the first kind and its spectrum. Suitable criteria are suggested for the comparison. The best numerical stability shows the method employing Chebyshev polynomial recurrence. In case of the polynomial spectrum computation the best method is the one using the difference backward recursion introduced by M. Vlcek. Both methods are able to generate the polynomial of high degree up to, at least, 2000, using 32-bit IEEE floating point arithmetics