The use of passive telemetry in rotor fault diagnosis

The sensors most commonly used for monitoring machine health are wired accelerometers because of their high performances and good stability. However, these transducers are usually large in size; require an external power source. Hence, there is a need for cheaper and reliable alternative for the conventional accelerometers. This thesis reports the development of a wireless accelerometer based on Micro-Electro-Mechanical System (MEMS) inertial sensor and off-the-shelf digital RF communication modules. It is small enough to be installed on the rotating shaft of a machine. In addition, it has a high enough resolution to be used to analyse the dynamic behaviour of rotating shaft. The wireless sensor is mounted with its sensitive axis in the tangential direction with respect to the centre of the rotor. This position allows the sensor to perform high resolution tangential acceleration measurements and nullifies the centripetal acceleration. To assist in the validation of the wireless sensor, a mathematical model was derived to simulate the vibration signals from the test rig. Experimental and simulated results both confirmed the effectiveness of the wireless sensor in detecting different degrees of misalignments and unbalance of a flexible rotor system. The wireless sensor has been confirmed to possess the capability of detecting small degrees of misalignment using the spectral amplitude of the peak at 2X running speed compared to other conventional sensors (wired accelerometers, laser vibrometers). In addition, the results of the experiment and simulation have also confirmed the capacity of the wireless sensor to detect different shaft unbalance grades at 1X running speed using spectral and order magnitudes. However, the wired sensors used for comparison failed to show any clear separation of the different grades of shaft unbalance. Moreover, it has been observed that the instantaneous angular speed (IAS) derived directly from the wireless sensor correlates well with that obtained from a shaft encoder and showed the capacity to detect the main features of rotor dynamics. An advanced algorithm has been developed to remove the gravity effect. The application of the algorithm has made the IAS computed from the wireless sensor more indicative to that obtained by a shaft encoder

Signal Detection Techniques for Diagnostic Monitoring of Space Shuttle Main Engine Turbomachinery

An investigation to develop, implement, and evaluate signal analysis techniques for the detection and classification of incipient mechanical failures in turbomachinery is reviewed. A brief description of the Space Shuttle Main Engine (SSME) test/measurement program is presented. Signal analysis techniques available to describe dynamic measurement characteristics are reviewed. Time domain and spectral methods are described, and statistical classification in terms of moments is discussed. Several of these waveform analysis techniques have been implemented on a computer and applied to dynamc signals. A laboratory evaluation of the methods with respect to signal detection capability is described. A unique coherence function (the hyper-coherence) was developed through the course of this investigation, which appears promising as a diagnostic tool. This technique and several other non-linear methods of signal analysis are presented and illustrated by application. Software for application of these techniques has been installed on the signal processing system at the NASA/MSFC Systems Dynamics Laboratory

Event-related potential studies of somatosensory detection and discrimination.

This thesis contains four studies, the first examining methodology issues and four subsequent ones examining somatosensory cortical processing using event-related potentials (ERPs). The methodology section consists of 2 experiments. The first compared the latency variability in stimulus presentation between 3 computers. The second monitored the applied force of the vibration stimuli under experimental conditions to ensure that the chosen method for somatosensory stimulus presentation was consistent and reliable. The next study involved 3 experiments that aimed to characterize the mid to long latency somatosensory event-related potentials to different duration vibratory stimuli using both intracranial and scalp recording. The results revealed differences in the waveform morphology of the responses to and on-off responses, which had not previously been noted in the somatosensory system. The third and fourth studies each consisted of 2 experiments. These examined the discrimination between vibratory stimuli using an odd-ball paradigm to try to obtain a possible 'mismatch' response, similar to that reported in the auditory system. The aim of this study was to clarify some of the discrepancies in the literature surrounding the somatosensory mismatch response and to further characterize this response. The results from intracranial and scalp ERP recordings showed a two-component, negative-positive mismatch response over the anterior parietal region and a negative component over the superior pre-frontal region in response to changes in both frequency and duration. The negative component over the frontal region had never before been described. The last study explored possible interactions between somatosensory and auditory cortical potentials in response to spatially and temporally synchronized auditory and vibratory stimuli. The results showed clear interactions in the cortical responses to combined auditory and somatosensory stimuli in both standard and mismatch conditions

SLDV technology for measurement of mistuned bladed disc vibration

Bladed discs are very sensitive structures and the amplitude vibration of each blade can vary significantly from blade to blade due to a series of factors such as geometrical inhomogeneity between blades or material properties. These factors lead to bladed disks mistuned thus the forced response amplitudes can be much higher than the level predicted for a tuned assembly. Designed models need to be “validate” to predict the response of a real bladed disc within the tolerances set by the manufactures and this process is very expensive as well as difficult. The validation process needs “reference data” as fundamental input against what all predictions can be compared and validated. Data that can be provided both under stationary conditions and under rotating conditions and the latter is the most difficult to achieve, especially for bladed disc assemblies which are very sensitive to any structural modification as it could be attaching a transducer to measure vibrations. There are contact-less measurement techniques available which, however, provide limited information because they can measure only limited areas of the vibrating structures. The aim of this study is to design measurement methods, using a standard Scanning Laser Doppler Vibrometer (SLDV) and to integrate it into a software platform which will be able to handle a series of measurement tasks both under stationary and rotating conditions. The main contribution of this thesis is to extend the use of Continuous Scanning LDV (CSLDV) to the rotating structures, such as bladed discs, thus to perform synchronous measurements. Hence, a bladed disc is needed to be designed to perform vibration predictions and measurements and a mathematical model of the measurement test to control, critically, all possible sources of errors involved in measurement under rotating conditions; all these to produce a robust measurement method. While the primary focus is the measurement method, the study also extends to evaluation of the sensitivity properties of the bladed disk test pieces that are the object of the measurement tool

Development of In-Vitro and In-Vivo Devices to Study the Mechanobiology of Ligament Healing

Ligament injuries are the most common sports injury in the United States. The current clinical practice for treating ligament injuries leaves many patients with significant pain and joint laxity for years following the initial injury. Controlled mechanical stimulation of the tissue after injury is necessary for robust healing, but the optimal mechanical environment for ligament healing is not fully understood. Alternative therapies, such as instrument assisted soft tissue mobilization (IASTM), offer a form of mechanical stimulation that is non-invasive and has shown promising clinical outcomes but the optimal dosage for IASTM treatments is unknown. The objective of this study was to develop in-vitro and in-vivo experimental devices that can help determine the specific mechanical loads that strengthen and accelerate ligament healing. Two devices were developed. The in-vitro device is a novel multi-axis mechanical stimulation bioreactor that can accurately apply tensile and combined tensile/compressive stress states to 3D fibroblast seeded tissue constructs. The bioreactor consists of two independently controlled actuators, one tensile, one compressive, a tablet computer, and data acquisition hardware. The bioreactor was validated using gelatin constructs to simultaneously apply cyclic forces from 0 – 0.2N with an accuracy of approximately 0.01N, and a high degree of repeatability. The in-vivo device is a hand-held device to control the frequency and magnitude of applied force during IASTM treatments on rats after ligament transection. The device consists of a force sensor, tablet computer, and custom software to guide the application of user-specified loading parameters during IASTM treatments. The device accuracy was measured by applying a combination of force and stroke frequencies to rigid foam and was experimentally validated over a 3-week animal experiment. The device was demonstrated to apply forces between 0 – 5N at frequencies from 0 – 1Hz with a high degree of accuracy and repeatability. The devices validated in this study provide a framework for future studies. The in-vitro device can provide insight into the mechanobiological effects of different loading configurations on fibroblast seeded constructs, including the simultaneous application of tensile and compressive loading, which is similar to IASTM treatment. The in-vivo device will be used to perform animal studies that can assess the effects of varying applied force and frequency parameters during IASTM treatments