R. Andrew Swartz

Strategic Network Utilization in a Wireless Structural Control System for Seismically Excited Structures

The benefits associated with structural control include the mitigation of undesired structural responses and reduction in the probability of damage to structural components during seismic events. Structural control systems in current use depend on extensive wired communication systems to connect sensors and actuators with a centralized controller. While wired architectures are appropriate when control systems are small, the cost and installation complexity of tethered systems increases as the control system grows large (i.e., defined by hundreds of nodes). Alternatively, wireless sensors are proposed for use in large-scale structural control systems to keep costs low and to improve system scalability. Wireless sensors are capable of collecting state data from sensors, communicating data between themselves, calculating control actions, and commanding actuators in a control system. However, bandwidth and range limitations of the wireless communication channel render traditional centralized control solutions impractical for the wireless setting. While computational abilities embedded with each wireless sensor permit fully decentralized control architectures to be implemented, strategic utilization of the wireless channel can improve the performance of the wireless control system. Toward this end, this paper presents a partially decentralized linear quadratic regulation control scheme that employs redundant state estimation as a means of minimizing the need for the communication of state data between sensors. The method is validated using numerical simulations of a seismically excited six-story building model with ideal actuators. Additional experimental validation is conducted using a full-scale physical realization of the six-story building. A wireless sensor network commanding magnetorheological dampers is shown to be effective in controlling a multistory structure using the partially decentralized control architecture proposed.

Hybrid wireless hull monitoring system for naval combat vessels

There is increasing interest by the naval engineering community in permanent monitoring systems that can monitor the structural behaviour of ships during their operation at sea. This study seeks to reduce the cost and installation complexity of hull monitoring systems by introducing wireless sensors into their architectural designs. Wireless sensor networks also provide other advantages over their cable-based counterparts such as adaptability, redundancy, and weight savings. While wireless sensors can enhance functionality and reduce cost, the compartmentalised layout of most ships requires some wired networking to communicate data globally throughout the ship. In this study, 20 wireless sensing nodes are connected to a ship-wide fibre-optic data network to serve as a hybrid wireless hull monitoring system on a high-speed littoral combat vessel (FSF-1 Sea Fighter). The wireless hull monitoring system is used to collect acceleration and strain data during unattended operation during a one-month period at sea. The key findings of this study include that wireless sensors can be effectively used for reliable and accurate hull monitoring. Furthermore, the fact that they are low-cost can lead to higher sensor densities in a hull monitoring system thereby allowing properties, such as hull mode shapes, to be accurately calculated.

Performance evaluation of decentralized wireless sensing and control in civil structures

A structural control system consists of sensors, controllers, and actuators integrated in a single network to effectively mitigate building vibration during external excitations. The costs associated with high-capacity actuators and system installation are factors impeding the wide spread adoption of structural control technology. Wireless communication can potentially lower installation costs by eliminating coaxial cables and offer better flexibility and adaptability in the design of a structural control system. This paper introduces a prototype wireless sensing and control unit that can be incorporated in a real-time structural control system. Tests are conducted using a 3-story half-scale laboratory structure instrumented with magnetorheological dampers to validate the feasibility of the wireless structural control system. This paper also addresses the serious issue of time delay and communication range inherent to wireless technologies. Numerical simulations using different decentralized structural control strategies are conducted on a 20-story steel structure controlled by semi-active hydraulic dampers.

Design and validation of acceleration measurement using the martlet wireless sensing system

The adoption of wireless sensing technology by the structural health monitoring community has shown advantages over traditional cable-based systems, such as convenient sensor installation and lower system cost in many applications. Recently, a new generation of wireless sensing platform, named Martlet, has been collaboratively developed by researchers at the University of Michigan, Georgia Tech, and Michigan Tech. Martlet adopts a Texas Instruments Piccolo microcontroller running up to 90 MHz clock frequency, which enables Martlet to support high-frequency data acquisition and high-speed onboard computation. The extensible design of the Martlet printed circuit boards allows convenient incorporation of various sensor boards. In order to obtain accurate acceleration data and meanwhile reduce the sensor cost, a new Martlet sensor board, named integrated accelerometer wing, is developed. The integrated accelerometer wing adopts a commercial-off-the-shelf MEMS (microelectromechanical systems) accelerometer and contains an onboard signal conditioner performing three basic functions, including mean shifting, anti-aliasing filtering and signal amplification. One distinct feature of the signal conditioner is the on-the-fly programmable cut-off frequency and amplification gain factor. To validate the performance of Martlet and the integrated accelerometer wing, experiments are carried out on a laboratory four-story aluminum shear-frame structure. The laboratory experiment results demonstrate that the performance of the wireless sensing system is comparable to that of cabled reference sensors. In addition, using data collected by wireless sensors, vibration modal properties of the structure are identified and finite element (FE) model updating is performed.© 2014 ASME

Near real-time system identification in a wireless sensor network for adaptive feedback control

Migration of the identified system poles for a dynamical system indicates changes in its global properties. In civil engineering structures, these changes are most often due to changes in global stiffness or damping parameters associated with both environmental effects as well as deterioration of the structure. In structures that employ automated feedback control systems to mitigate unwanted vibrations, feedback control laws and state estimators (if used) are reliant upon a theoretical or identified model of the plant. Any loss in fidelity between the plant model and its actual condition will result in degradation of the controller performance. Low-cost, wireless control networks that by nature are more likely to utilize state-estimation, are therefore more vulnerable to problems associated with property changes in the system. In this paper, recursive identification of system poles is proposed for use in a wireless sensing network engaged in feedback control. Because it is based on system poles, the algorithm is ideally suited for adaptive control methods that update control and estimation gains as system properties change. The algorithm proposed is based on the fast transversal filter and is designed to minimize computation as well as data transmission requirements to optimally utilize the distributed data that is stored within a low-power wireless sensor network.

Investigation of Time Series Representations and Similarity Measures for Structural Damage Pattern Recognition

This paper investigates the time series representation methods and similarity measures for sensor data feature extraction and structural damage pattern recognition. Both model-based time series representation and dimensionality reduction methods are studied to compare the effectiveness of feature extraction for damage pattern recognition. The evaluation of feature extraction methods is performed by examining the separation of feature vectors among different damage patterns and the pattern recognition success rate. In addition, the impact of similarity measures on the pattern recognition success rate and the metrics for damage localization are also investigated. The test data used in this study are from the System Identification to Monitor Civil Engineering Structures (SIMCES) Z24 Bridge damage detection tests, a rigorous instrumentation campaign that recorded the dynamic performance of a concrete box-girder bridge under progressively increasing damage scenarios. A number of progressive damage test case datasets and damage test data with different damage modalities are used. The simulation results show that both time series representation methods and similarity measures have significant impact on the pattern recognition success rate.

Decentralized wireless structural sensing and control with multiple system architectures operating at different sampling frequencies

Recent years have seen growing interest in applying wireless sensing and embedded computing technologies for structural health monitoring and control. The incorporation of these new technologies greatly reduces system cost by eliminating expensive lengthy cables, and enables highly flexible system architectures. Previous research has demonstrated the feasibility of decentralized wireless structural control through numerical simulations and preliminary laboratory experiments with a three-story structure. This paper describes latest laboratory experiments that are designed to further evaluate the performance of decentralized wireless structural control using a six-story structure. Commanded by wireless sensors and controllers, semi-active magnetorheological (MR) dampers are installed between neighboring floors for applying real-time feedback control forces. Multiple centralized/decentralized feedback control architectures have been investigated in the experiments, in combination with different sampling frequencies. The experiments offer valuable insight in applying decentralized wireless control to larger-scale civil structures.

Gyroscopic Effects of Horizontal Axis Wind Turbines Using Stochastic Aeroelasticity via Spinning Finite Elements

Horizontal axis wind turbine (HAWTs) structures, throughout the years, have presumed to be of relatively simple construction, but wind-induced aerodynamic vibrations, wind-field conditions, and power requirements tend to lead to the need for increasingly complicated designs. One phenomenon that requires special attention is the gyroscopic or Coriolis effect. In general, blades design codes are written to optimize for lightness and slenderness, but also to withstand excitations at high frequency. As a result, gyroscopic motion derives as a nonlinear dynamic condition in the out-of-plane direction that is difficult to characterize by means of the well-known vibrational theory that has been established for their design and analysis. The present study develops and presents a probabilistic analysis of the precession — gyroscopic — effects of a wind turbine model developed for tapered-swept cross-sections of nt degree with nonlinear variations of mass and geometry along the body of the blade. A dynamic orthogonal decoupling method is utilized to successfully perform the aeroelastic analysis by decoupling the damped-gyroscopic equations of motion, as a result of the addition of Rayleigh damping — symmetric proportional mass and stiffness — within the linear system in study. Results are valid for yaw-free rotor configurations by means of unknown and random (though bounded) yaw rates. Simultaneously, those results can easily be expanded for yaw-controlled mechanisms. The yaw-free assumption presents a higher risk of potential reliability expectations, given the stochastic impairment of the gyroscopic nature that is present for out-of-plane axis motions, requiring special attention at higher frequencies. This impairment becomes particularly troublesome for blade profiles with tapered-swept cross-section variations. This uncertainty can be minimized by incorporating a mathematical framework capable of characterizing properly the yaw action such that gyroscopic effects can be fully interpreted and diagnosed. In summary, the main goal is to decipher the complexity of gyroscopic patterns of flexible rotor blades with complex shape configurations, but also to provide substantial elements to successfully approach yaw-mechanics of tapered-swept rotor blades.Copyright

Autonomous Scour Monitoring of Bridges and Embankments Using Bio-Inspired Whisker Flow Sensor Arrays

Detection of damage to the boundary conditions of structures can be equally important as detection of structural damage. Civil structures sit on foundations which are, ideally, constant over time and are integral to collapse prevention. Any processes that compromise the foundations or the soil around them also constitutes damage to the structure. Bridge structures as well as embankments near roadways and viaducts can be particularly prone to this kind of attack when high-velocity water flows transport sediment away from the bridge foundation (scour). This process can be difficult to detect because 1) it happens out of sight, underwater; and 2) scour holes tend to grow and shrink at time progresses and materials are either carried away or deposited by the water. In this study, use of a buried-rod scour detection system based on magnetostrictive and magnetic flow sensor arrays is investigated. For buried-rod scour detection systems, an array of small, flexible, strain-sensitive rod sensors is distributed around the foundations which generate dynamic signals they are waterborne and static signals when buried. The pattern of static and dynamic signals reveals the depth of scour around the structure. Magnetostrictive sensors are appealing for this application due to their robustness. In this paper the effectiveness signal processing and scour detection algorithms are explored for water-coupled magnetostrictive whisker sensors of varying geometries to determine their sensitivity and the thresholds for false alarms and missed alert conditions at varying flow rates. Experimental laboratory data is utilized for this study.© 2014 ASME

A Framework for Embedded Load Estimation from Structural Response of Wind Turbines

The international push in the development of energy that is sustainable in the long term is driving technological improvements in the area of wind-generated energy. Pushing the limits of current knowledge, turbines now feature increasingly slender towers, larger gear boxes, and significantly longer blades in search of greater capacities and improved efficiency. In addition, siting concerns are leading planners to build these structures in increasingly challenging environments where they are subject to harsh and poorly characterized loadings (particularly in off-shore applications where wind and wave interactions are poorly understood). Future safe and economical designs require accurate characterization of design loads, however direct measurement of wind loads on turbines can be problematic due to the disturbance caused by the wind’s interaction with the turbine blades. This paper presents a novel means of estimating wind loading from the dynamic response of the turbine tower to these loads. A model of the structure is derived using the assumed modes method and then updated using dynamically collected acceleration data a there the input-output relationships are established and input loading spectra estimated. The method relies on reduced-order modal space models making it suitable for real-time operation or embedment in a low-cost autonomous (perhaps wireless) monitoring system. Results derived for a full scale structure under lateral seismic loading are presented.