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

Realization of Underwater Acoustic Networks.

This work contains a study of underwater acoustic networks. The concept of underwater acoustic networks has been presented with its benefits and drawbacks. An overview of the marine research areas oceanography, seismology, waterside security, marine pollution and marine biology has been made and a review of conventional methods and instrumentation committed. The research methods used today have been compared with the potential of underwater acoustic networks as a platform for maritime applications. Underwater acoustic networks were reviewed as feasible within all areas with some restrictions. The fact that respectable data rate is best achieved for nodes deployed in a high density grid give limitations on the coverage area. Battery as an energy source limits the life span of an underwater acoustic network and makes it best suited for missions for short term monitoring, if not a recharging technology is applied. The energy restrictions also put constraint on the amount of sensing done and the temporal solution in measurements. Underwater acoustic networks were found applicable for intrusion detection in waterside security to increase the range of current ultrasonic surveillance systems or realize distributed systems for passive diver detection. In oceanography and pollution monitoring current in situ sensors may enable underwater acoustic networks to do autonomous synoptic sampling of limited areas to measure a number of parameters, e.g. oxygen, turbidity, temperature and salinity. For seismic exploration this technology might save costs for permanent seismic installations in constant monitoring of producing oil fields. It might also aid marine biologists in habitat monitoring

Modeling, Analysis and Testing of a Semi-Active Control System for Landing Gear Applications

There have been several recent studies on the potential benefits of controllable dampers. Controllable dampers can use a fluid with controllable properties, such as Magneto - Rheological fluid (MR fluid), or control the damping force by changing orifice size. For this project, controllable dampers were created using MR fluid. When exposed to a magnetic fluid, the viscosity of MR fluid can change significantly. By replacing the standard damper oil in an aircraft landing gear and exposing the system to an appropriate magnetic field, the damping coefficients of the system can be changed almost instantaneously to accommodate nearly any situation. This trait allows a real time controller to monitor the system and adjust damping characteristics to match current conditions. Using the \u27no-jerk\u27 Skyhook control strategy, the control system attempts to minimize the acceleration, force and displacement transmitted to the fuselage from the ground. This reduction in applied load can translate into reduced aircraft weight, and longer fatigue life for some components. Unlike previous studies, the controllable damper configuration for this project used an externally mounted electromagnet located between the damper and remote reservoir, as opposed to an electromagnet located internal to the damper body. This design allows landing gear to use semi-active MR dampers with few modifications to existing designs. A set of dampers were tested in the standard and controllable configurations on a shock dynamometer. A SimMechanics model, which was calibrated using the dynamometer data and from limited 2-DOF experimental test data, was used to predict the improvement in transmissibility resulting from these modifications. The results indicate that controllable dampers using a ‘no jerk\u27 skyhook control policy can reduce transmissibility of ground input to the fuselage

Structural health monitoring of fatigue cracks using acoustic emission technique

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonIn the oil and gas industry, failure due to vibration-induced fatigue is considered as an important cause of loss of integrity. There have been increasing incidents of vibration-induced fatigue in pipelines both in offshore and onshore petrochemical plants. To mitigate this problem, a Structural Health Monitoring (SHM) method using Acoustic Emission (AE) was developed, using specific damage identification strategies. A number of contributions are highlighted in this research work, which includes the fundamental understanding of wave propagation in thick and thin structures. The application of Rayleigh waves and Lamb waves is important in damage identification, being demonstrated in experimental works and finite element analysis (FEA). The identification of damage by vibration-induced fatigue crack demands a dedicated instrumentation and signal processing techniques. A novel method using Bayesian estimation of the effective coefficient (EC) was introduced, which measure the uncertainties of the located events measured by AE technique, calibrated using the information derived from pencil lead break tests. The EC was formulated in such a way the AE signals from each sensor were cross-correlated and the calculated coefficients were corrected taking into account the minimum coefficients from each sensor combination. Cross-correlation was then used to improve the identification of Lamb waves generated by the crack development. The calculated time difference between the fundamental wave modes increases the accuracy of the located events using a Single Sensor Modal Analysis Localization technique (SSMAL). Using a similar approach, the ratio of symmetric (S0) and asymmetric waves (A0) amplitudes was determined and used for damage extent assessments. In summary the AE is shown to be a very effective method for SHM of vibration-induced fatigue damage.National Structure Integrity Research Centr

Data bases and data base systems related to NASA's Aerospace Program: A bibliography with indexes

This bibliography lists 641 reports, articles, and other documents introduced into the NASA scientific and technical information system during the period January 1, 1981 through June 30, 1982. The directory was compiled to assist in the location of numerical and factual data bases and data base handling and management systems

Arm length stabilisation for advanced gravitational wave detectors

Currently the Laser Interferometric Gravitational-wave Observatory (LIGO) is undergoing upgrades from Initial LIGO to become Advanced LIGO. Amongst these upgrades is the addition of a signal recycling mirror at the output port of the interferometer; upgrades of the mirror suspensions to quadruple pendulums; the implementation of less invasive and hence weaker test mass actuators; and the change of readout scheme from a heterodyne based RF readout to a homodyne based DC readout. The DC readout scheme requires the installation of an Output Mode Cleaner (OMC), to stop `junk light' generated in the interferometer from making its way to the DC photodetector where it can limit the sensitivity of the gravitational wave detector. The steering of the interferometer beam into the OMC will be handled by Tip Tilt mirrors designed at the Australian National University. The first core piece of work presented in this thesis was the characterisation of a prototype Tip Tilt mirror, which involved measuring the various eigenmodes of the mirror

Seismic Soil-Structure Interaction and Foundation Rocking in Unsaturated Ground

Strong earthquake motions often cause severe damage to buildings and foundation systems, during which the interaction between the soil, foundation, and structure may dominate the seismic response. Most shallow foundations are located on, or embedded in, unsaturated and partially saturated soil deposits. Unsaturated soil layers are particularly common in zones above the water table where water can rise through different mechanisms like capillary action. Additionally, the degree of saturation throughout a soil deposit can vary both seasonally and yearly due to groundwater table fluctuation related to infiltration and evaporation. Properties of soil layers below foundations impact the seismic response of structural systems. Since soil moisture impacts soil properties, it is expected that changes in groundwater table depth would impact the seismic response of foundations and structures. However, the understanding of the mechanisms by which the degree of saturation and water table depth influences the foundation and structural response needs improvement. This dissertation aimed to evaluate the effect of the depth of the groundwater table on the seismic response of soil-foundation-structure systems and to extend current seismic design guidelines leading to the implementation of rocking foundations in practice.Three sets of dynamic centrifuge experiments were conducted on four physical models representing three prototype structures. The prototype structures included elastic and inelastic single-degree-of-freedom structures as well as single- and two-span bridge systems. The elastic single-degree-of-freedom structure and bridge systems were designed to incorporate rocking foundations, while the inelastic single-degree-of-freedom structure incorporated structural fuses designed to guide plastic deformations to above-ground structural locations. Physical models were slightly embedded in sandy silt layers with various groundwater table depths and subjected to a series of seismic motions. The experimental findings highlight the influence of the groundwater table depth on changes to the foundation and structural deformations and rotations, foundation-level overturning moments, period lengthening, and damping ratios. Furthermore, design procedures to predict several seismic response properties of a structure resting on unsaturated soil layers are derived in this research based on the fundamentals of unsaturated soil mechanics. These properties include the overturning moment capacity of the foundation, the initial rotational stiffness of the foundation, and the period lengthening and foundation damping ratio. Properties derived from these design guidelines are compared to the experimental results to judge the viability of implementation in practice or signify the need for further improvement

Vision-Based Control of Unmanned Aerial Vehicles for Automated Structural Monitoring and Geo-Structural Analysis of Civil Infrastructure Systems

The emergence of wireless sensors capable of sensing, embedded computing, and wireless communication has provided an affordable means of monitoring large-scale civil infrastructure systems with ease. To date, the majority of the existing monitoring systems, including those based on wireless sensors, are stationary with measurement nodes installed without an intention for relocation later. Many monitoring applications involving structural and geotechnical systems require a high density of sensors to provide sufficient spatial resolution to their assessment of system performance. While wireless sensors have made high density monitoring systems possible, an alternative approach would be to empower the mobility of the sensors themselves to transform wireless sensor networks (WSNs) into mobile sensor networks (MSNs). In doing so, many benefits would be derived including reducing the total number of sensors needed while introducing the ability to learn from the data obtained to improve the location of sensors installed. One approach to achieving MSNs is to integrate the use of unmanned aerial vehicles (UAVs) into the monitoring application. UAV-based MSNs have the potential to transform current monitoring practices by improving the speed and quality of data collected while reducing overall system costs. The efforts of this study have been chiefly focused upon using autonomous UAVs to deploy, operate, and reconfigure MSNs in a fully autonomous manner for field monitoring of civil infrastructure systems. This study aims to overcome two main challenges pertaining to UAV-enabled wireless monitoring: the need for high-precision localization methods for outdoor UAV navigation and facilitating modes of direct interaction between UAVs and their built or natural environments. A vision-aided UAV positioning algorithm is first introduced to augment traditional inertial sensing techniques to enhance the ability of UAVs to accurately localize themselves in a civil infrastructure system for placement of wireless sensors. Multi-resolution fiducial markers indicating sensor placement locations are applied to the surface of a structure, serving as navigation guides and precision landing targets for a UAV carrying a wireless sensor. Visual-inertial fusion is implemented via a discrete-time Kalman filter to further increase the robustness of the relative position estimation algorithm resulting in localization accuracies of 10 cm or smaller. The precision landing of UAVs that allows the MSN topology change is validated on a simple beam with the UAV-based MSN collecting ambient response data for extraction of global mode shapes of the structure. The work also explores the integration of a magnetic gripper with a UAV to drop defined weights from an elevation to provide a high energy seismic source for MSNs engaged in seismic monitoring applications. Leveraging tailored visual detection and precise position control techniques for UAVs, the work illustrates the ability of UAVs to—in a repeated and autonomous fashion—deploy wireless geophones and to introduce an impulsive seismic source for in situ shear wave velocity profiling using the spectral analysis of surface waves (SASW) method. The dispersion curve of the shear wave profile of the geotechnical system is shown nearly equal between the autonomous UAV-based MSN architecture and that taken by a traditional wired and manually operated SASW data collection system. The developments and proof-of-concept systems advanced in this study will extend the body of knowledge of robot-deployed MSN with the hope of extending the capabilities of monitoring systems while eradicating the need for human interventions in their design and use.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169980/1/zhh_1.pd

Survey Plan For Characterization of the Subsurface Underlying the National Aeronautics and Space Administration's Marshall Space Flight Center in Huntsville, Alabama

Topic considered include: survey objectives; technologies for non-Invasive imaging of subsurface; cost; data requirements and sources; climatic condition; hydrology and geology; chemicals; magnetometry; electrical(resistivity, potential); optical-style imaging; reflection/refraction seismics; gravitometry; photo-acoustic activation;well drilling and borehole analysis; comparative assessment matrix; ground sensors; choice of the neutron sources; logistic of operations; system requirements; health and safety plans