Day-to-day Traffic Dynamics with Strategic Commuters

In the era of connected and automated mobility, commuters (connected drivers or automated vehicles) will possess strong computation capability and their travel decisions can be algorithmic and strategic. This paper investigates the day-to-day travel choice evolution of such strategic commuters who are capable of long-term planning and computation. We model the commute problem as a mean field game and examine the mean field equilibrium to derive the evolution of the network traffic flow pattern. The proposed model is general and can be tailored to various travel choices such as route or departure time. Under various conditions, we prove the existence and uniqueness of the day-to-day equilibrium traffic evolution pattern as well as its convergence to stationarity. Connection with traditional Wardropian equilibrium is established by examining the physical interpretation of the stationary solution

Design of a wireless active sensing unit for localized structural health monitoring

The recent years have witnessed an increasing interest in using wireless structural monitoring as a low-cost alternative to tethered monitoring systems. Previous work considered wireless sensors strictly as passive elements in the monitoring system, responsible only for collection of response measurements. This paper explores expansion of the wireless structural monitoring paradigm by including actuation capabilities in the design of a wireless active sensing unit. To validate the performance of the prototype unit in structural health monitoring applications, an aluminum plate monitored by piezoelectric active sensors is used. Piezoelectric actuators mounted to the surface of the plate are commanded by the wireless active sensing unit to excite and record the element. System identification models are then used to model the linear relationship between the input excitation and the corresponding plate response. A novel damage detection methodology is proposed that uses the characteristic equation roots obtained from an autoregressive with exogenous input time-series model. Complex roots (poles) of the model's characteristic equation are sensitive to structural damage causing a change in their location on the complex plane. Using the mean value of pole clusters, the migration of model poles are shown to be well correlated to the severity of crack damage intentionally introduced in the plate. Copyright © 2005 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48702/1/77_ftp.pd

Linear classification of system poles for structural damage detection using piezoelectric active sensors

The identification of damage in structural systems, including characterization of damage location and severity, is of extreme interest to the structural engineering profession. To date, many damage detection methods have been proposed that utilize global structural response measurements in the time and frequency domains to hypothesize the existence of structural damage. The accuracy and robustness of current damage detection methodologies could be improved through the use of active sensors. Active sensors, such as piezoelectric pads, impart low-energy acoustic excitations into structural elements and can record the corresponding system behavior. In this study, a novel methodology utilizing the input-output behavior of actively sensed structural elements is proposed. The poles of ARX time-series models describing modal frequencies and damping ratios are plotted upon the discrete-time complex plane and Perceptron linear classifiers employed to determine if poles of the structural element in an unknown state (damaged or undamaged) can be separated with those of the undamaged structure. If poles of the unknown state are separable from those of the undamaged state, the system is diagnosed as damaged. A simple cantilevered aluminum plate damaged by hack saw cuts is actively sensed by piezoelectric pads to show the efficacy of the proposed damage detection methodology. Furthermore, the number of misclassified poles and the final value of the Perceptron criterion function can be shown to be correlated to the severity of the damage

Spatial conductivity mapping of carbon nanotube composite thin films by electrical impedance tomography for sensing applications

This paper describes the application of electrical impedance tomography (EIT) to demonstrate the multifunctionality of carbon nanocomposite thin films under various types of environmental stimuli. Carbon nanotube (CNT) thin films are fabricated by a layer-by-layer (LbL) technique and mounted with electrodes along their boundaries. The response of the thin films to various stimuli is investigated by relying on electric current excitation and corresponding boundary potential measurements. The spatial conductivity variations are reconstructed based on a mathematical model for the EIT technique. Here, the ability of the EIT method to provide two-dimensional mapping of the conductivity of CNT thin films is validated by (1) electrically imaging intentional structural defects in the thin films and (2) mapping the film’s response to various pH environments. The ability to spatially image the conductivity of CNT thin films holds many promises for developing multifunctional CNT-based sensing skins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58135/2/nano7_31_315501.pd

Wireless sensing and vibration control of civil structures

Significant advances have been made in deploying wireless sensors and sensing network technologies for monitoring the health and safety of civil structures [4]. For monitoring applications, sensors are often used passively to measure structural responses. Equipped with an actuation interface, wireless sensors can be extended to command actuators [7]. This pape

Truck-based mobile wireless sensor networks for the experimental observation of vehicle–bridge interaction

Heavy vehicles driving over a bridge create a complex dynamic phenomenon known as vehicle–bridge interaction. In recent years, interest in vehicle–bridge interaction has grown because a deeper understanding of the phenomena can lead to improvements in bridge design methods while enhancing the accuracy of structural health monitoring techniques. The mobility of wireless sensors can be leveraged to directly monitor the dynamic coupling between the moving vehicle and the bridge. In this study, a mobile wireless sensor network is proposed for installation on a heavy truck to capture the vertical acceleration, horizontal acceleration and gyroscopic pitching of the truck as it crosses a bridge. The vehicle-based wireless monitoring system is designed to interact with a static, permanent wireless monitoring system installed on the bridge. Specifically, the mobile wireless sensors time-synchronize with the bridge's wireless sensors before transferring the vehicle response data. Vertical acceleration and gyroscopic pitching measurements of the vehicle are combined with bridge accelerations to create a time-synchronized vehicle–bridge response dataset. In addition to observing the vehicle vibrations, Kalman filtering is adopted to accurately track the vehicle position using the measured horizontal acceleration of the vehicle and positioning information derived from piezoelectric strip sensors installed on the bridge deck as part of the bridge monitoring system. Using the Geumdang Bridge (Korea), extensive field testing of the proposed vehicle–bridge wireless monitoring system is conducted. Experimental results verify the reliability of the wireless system and the accuracy of the vehicle positioning algorithm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90810/1/0964-1726_20_6_065009.pd

Implementation of a closed-loop structural control system using wireless sensor networks

Wireless sensor networks have rapidly matured in recent years to offer data acquisition capabilities on par with those of traditional tethered data acquisition systems. Entire structural monitoring systems assembled from wireless sensors have proven to be low cost, easy to install, and accurate. However, the functionality of wireless sensors can be further extended to include actuation capabilities. Wireless sensors capable of actuating a structure could serve as building blocks of future generations of structural control systems. In this study, a wireless sensor prototype capable of data acquisition, computational analysis and actuation is proposed for use in a real-time structural control system. The performance of a wireless control system is illustrated using a full-scale structure controlled by a semi-active magnetorheological (MR) damper and a network of wireless sensors. One wireless sensor designated as a controller automates the task of collecting state data, calculating control forces, and issuing commands to the MR damper, all in real time. Additional wireless sensors are installed to measure the acceleration and velocity response of each system degree of freedom. Base motion is applied to the structure to simulate seismic excitations while the wireless control system mitigates inter-storey drift response of the structure. An optimal linear quadratic regulation solution is formulated for embedment within the computational cores of the wireless sensors. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60230/1/214_ftp.pd

An experimental investigation of the data delivery performance of a wireless sensing unit designed for structural health monitoring

This study explores the reliability of a wireless sensing unit by testing it in a real-world university laboratory environment. The unit employs off-the-shelf products for their key components, while a flexible payload scheme was adopted for radio packet transmission to maximize throughput and minimize latency. The testing consists of two main parts: (1) a series of loopback tests using two off-the-shelf radio components with carrier frequencies of 900 MHz and 2.4 GHz, respectively, and (2) wireless transmission of a shake table response to a periodic swept sine excitation. The performance of the wireless channel is examined in each part of the study. Through this experimental investigation, it is validated that a loopback test may be used as a fast prototyping approach to characterize the complex transmitting environment of a structure in which a wireless monitoring system is installed. Various factors leading to signal attenuation are ranked according to their effects on packet delivery performance. Transmitting range and building materials are among the leading factors causing packet loss (and therefore data loss) in this specific testing environment. The severity of interference from 802.11b wireless systems in close proximity to the wireless sensing unit was investigated. Some preliminary results on the influence of operating rotating machinery and human activities are to wireless sensors were investigated. The results presented herein offer a guideline for applying wireless sensing within real-world structures so that the reliability of the wireless monitoring system is maximized. Due to uncertainties associated with the reliability of wireless communications, statistical analysis is performed on the collected time histories to reveal the underlying patterns associated with data loss. Temporal correlations of data loss were measured and found to be related to the adopted radio. A statistical distribution of the size of consecutive lost data points was further derived from the collected data. Such results have identified the need to further develop: (1) reliable communication protocols to reduce these losses in data and information, and (2) robust data processing and system identification tools to anticipate and explicitly handle any data loss. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60229/1/205_ftp.pd