David C. Swanson

A general prognostic tracking algorithm for predictive maintenance

Prognostic health management (PHIM) is a technology that uses objective measurements of condition and failure hazard to adaptively optimize a combination of availability, reliability, and total cost of ownership of a particular asset. Prognostic utility for the signature features are determined by transitional failure experiments. Such experiments provide evidence for the failure alert threshold and of the likely advance warning one can expect by tracking the feature(s) continuously. Kalman filters are used to track changes in features like vibration levels, mode frequencies, or other waveform signature features. This information is then functionally associated with load conditions using fuzzy logic and expert human knowledge of the physics and the underlying mechanical systems. Herein is the greatest challenge to engineering. However, it is straightforward to track the progress of relevant features over time using techniques such as Kalman filtering. Using the predicted states, one can then estimate the future failure hazard, probability of survival, and remaining useful life in an automated and objective methodology.

Prognostic Health Management of Aircraft Power Generators

In this paper, prognostic tools are developed to detect the onset of electrical failures in an aircraft power generator, and to predict the generators remaining useful life (RUL). Focus is on the rotor circuit since failure mode, effects, and criticality analysis (FMECA) studies indicate that it is a high priority candidate for condition monitoring. A signature feature is developed and tested by seeded fault experiments to verify that the initial stages of rotor faults are observable under diverse generator load conditions. A tracking filter is used to assess the damage state and predict generator RUL. This information helps to avoid unexpected failures while reducing the overall life-cycle cost of the system.

Signal Processing for Intelligent Sensor Systems

Fundamentals of digital signal processing: sampled data systems the Z-transform digital filtering linear filter applications. Frequency domain processing: the Fourier transform spectral density wavenumber transforms. Adaptive system identification and filtering: linear least-squared error-modelling recursive least-squared techniques recursive adaptive filtering. Wavenumber sensor systems: narrowband PD and FAR wavenumber field estimation adaptive beamforming. Signal processing applications: intelligent sensor systems transducers, electronics, and noise reduction techniques.

Sound equalization in enclosures using modal reconstruction

The equalization of complex sound pressure in an enclosure is investigated in this paper. The sound field in the enclosure is modeled with the sum of a series of modes. This sound field is controlled by multiple sources distributed in the enclosure so that a certain region in the enclosure has a desired complex sound pressure. First, the optimum solution which minimizes the average potential energy of the error pressure over the region is derived, where the error is defined as the difference between the desired sound pressure and the sound pressure caused by the sources. By using the optimum solution, the achievable best performance can be known for the given region and the source distribution. The optimum solution can also be a useful tool for finding an effective source distribution since the performance of the optimum solution depends only on the source distribution. Furthermore, the eigenvalues of the source coupling matrix, which appears in the derivation of the optimum solution, indicates the effectiveness of the source distribution. The effectiveness of source distribution is discussed with nine examples of source distributions in a two‐dimensional enclosure. The multipoint equalization method to approximate the optimum solution is also discussed for the practical use.

Planar near-field acoustical holography in a moving medium

Near-field acoustical holography (NAH) is a well-established method to study acoustic radiation near a stationary sound source in a homogeneous, stationary medium. However, the current theory of NAH is not applicable to moving sound sources, such as automobiles and trains. In this paper, the inclusion of a moving medium (i.e., moving source and receiver) is introduced in the wave equation and a new set of equations for plannar NAH is developed. Equations are developed for the acoustic pressure, particle velocity, and intensity when mean flow is either parallel or perpendicular to the hologram plane. If the source and the measurement plane are moving at the same speed, the frequency Doppler effect is absent, but a wave number Doppler effect exists. This leads to errors when reconstructing the acoustic field both towards and away from the source using static NAH. To investigate these errors, a point source is studied analytically using planar NAH with flow in one direction. The effect of the medium moving parallel to the hologram plane is noted by a shift of the radiation circle in wave number space (k-space). A k-space Greens function and a k-space filter are developed that include the effects of the moving medium.

Modal coupling in acoustic waveguides: planar discontinuities

Abstract A new derivation for a scattering matrix for reflection and transmission of higher order modes at the planar junction of two waveguides is presented. The derivation is extended to include finite junction wall impedance and offset waveguides. The resulting matrix equations are analyzed and the physical significance of the matrices is explained. As an example of the theory, analytical expressions for the coupling coefficients at a size change in a rectangular duct are developed and the resulting reflection and transmission coefficients are computed. The results should be of interest to the HVAC noise control community. The paper also shows the effects of modal truncation on the accuracy and convergence of the solution. It is shown that the proper selection of the ratio of the number of modes on either side of the discontinuity is related to the ratio of the characteristic sizes of the waveguides. Finally it is shown that at least one higher mode should be included for reasonable accuracy in the computation of plane wave reflection and transmission coefficients except at the very lowest frequencies.

A method of optimizing source configuration in active control systems using Gram-Schmidt orthogonalization

A method for optimizing the number and the configuration of control sources in an active control system is proposed. In the optimization process, sources are selected one by one so that the corresponding transfer impedance vector is the most linearly independent. From the results of the simulation, it is shown that the optimized configuration yields not only a small average control error but also a small condition number in the transfer impedance matrix, which contributes to the robustness of the system against environmental change.

Linear independence method for system identification/secondary path modeling for active control

A novel method for noninvasive system identification/secondary path modeling has been developed for single‐ and multi‐channel filtered‐x LMS‐based active noise control (ANC). The problem of on‐line secondary path modeling is recognized as one of linear dependence associated with an underdetermined system, a one‐equation/two‐unknown problem in which the highly correlated primary source and secondary source contributions to the error signal are not readily distinguishable. The method resolves this uniqueness issue by introducing a second equation with similar unknowns. The critical linear independence of the two equations, hence the proposed designation, is achieved with a single perturbation of the control filter output thereby making the system solvable. This new secondary path modeling strategy was implemented using a novel real‐time DSP control architecture and tested on a novel transducer‐less system devised to investigate the behavior of ANC algorithms. Results of narrow‐band, broadband, and multi‐cha...

Acoustic scintillations and angle-of-arrival fluctuations observed outdoors with a large planar vertical microphone array

A vertical planar array of 32 microphones (eight elements in the vertical direction and four in the horizontal; overall dimensions approximately 6 m by 3 m) was used to image the scintillations and angle-of-arrival fluctuations from a source 770 m distant. Data sets of 20-min duration were collected in a variety atmospheric conditions. On a windy afternoon, the source image underwent dramatic scintillations and fluctuations in its apparent position. For still nighttime conditions, the image was much more stable, although deep fading still occurred.

Optimization of control source configuration in active control systems using Gram-Schmidt orthogonalization

In active control systems, the configuration of the control sources greatly affects the performance. In this paper, a method for optimizing the number and location of control sources is proposed. As a criterion for the optimization, the linear independence of the transfer impedance vector is employed. A physical interpretation of the linear independence of the transfer impedance vector is the independent contribution of each control source that is not substitutable by the other sources. In the optimization process, control sources are determined one by one using Gram-Schmidt orthogonalization so that the corresponding transfer impedance vectors are the most linearly independent. The results of the simulation show the optimized configuration to have small control error. Moreover, for the optimized configuration, the transfer impedance matrix exhibits a small condition number, which results in robustness of the system in the face of changes in the environment.