The objective of this research is to develop advanced distributed monitoring and control systems for civil infrastructure. The approach uses a cyber-physical co-design of wireless sensor-actuator networks and structural monitoring and control algorithms. The unified cyber-physical system architecture and abstractions employ reusable middleware services to develop hierarchical structural monitoring and control systems.
The intellectual merit of this multi-disciplinary research includes (1) a unified middleware architecture and abstractions for hierarchical sensing and control; (2) a reusable middleware service library for hierarchical structural monitoring and control; (3) customizable time synchronization and synchronized sensing routines; (4) a holistic energy management scheme that maps structural monitoring and control onto a distributed wireless sensor-actuator architecture; (5) dynamic sensor and actuator activation strategies to optimize for the requirements of monitoring, computing, and control; and (6) deployment and empirical validation of structural health monitoring and control systems on representative lab structures and in-service multi-span bridges. While the system constitutes a case study, it will enable the development of general principles that would be applicable to a broad range of engineering cyber-physical systems.
This research will result in a reduction in the lifecycle costs and risks related to our civil infrastructure. The multi-disciplinary team will disseminate results throughout the international research community through open-source software and sensor board hardware. Education and outreach activities will be held in conjunction with the Asia-Pacific Summer School in Smart Structures Technology jointly hosted by the US, Japan, China, and Korea.
Though the basic hardware required to form a wireless smart sensor-actuator network (WSAN) has existed for more than a decade, full-scale deployment for civil engineering structures has been extremely limited. The overarching goal of this project is to develop a cyber-physical systems framework for distributed structural health monitoring and control (SHMC) based on wireless sensor and actuator networks. The key intellectual merit is a cyber-physical co-design approach that closely integrates the cyber components (WSANs) and the physical components (SHMC) in a distributed system architecture. This research has pioneered an open-source, customizable hardware and software framework for WSAN nodes that has resulted in an inexpensive, commercially-available, wireless sensor-actuator platform that is able to deliver the high-fidelity and high-precision data needed for vibration monitoring of civil, mechanical, and aerospace structures. The ability of wireless sensor hardware, originally tailored for structural health monitoring (SHM), to meet the real-time requirements of control is challenging; data acquisition hardware tailored for SHM can introduce significant latency due to oversampling and digital filtering. A low-latency hardware solution for wireless control addresses the whole control loop, acquisition and actuation, to limit and loss of real-time performance due to hardware. The acquisition board, centered on a SAR-type ADC, significantly reduces the latency in the system due to hardware from 30 milliseconds to 200 microseconds. Additionally, an on-board tri-axis MEMS accelerometer offers easy application of acceleration feedback for control. The innovative hardware developments created under this project are complimented by pioneering work in the creation of scalable programming and analysis tools for WSAN applications. Because WSANs represent a highly distributed computing platform, successful control algorithms must be distributed across a large number of nodes with tight synchronization in their execution. These innovative strategies for the embedment of SHMC on wireless smart sensor-actuator networks are coming to be viewed as the gold standard for the field. The ActorNet programming language and runtime environment provides a high-level actor programming language: users can write dynamic applications for a single cross-platform runtime environment with support for heterogeneous and physically separated WSANs. This shields application developers from some hardware-specific concerns. Moreover, unlike other programming systems for WSANs, ActorNet supports agent mobility. In addition, a WSAN application schedulability analysis tool based on model checking has been developed and applied to the schedulability analysis of an SHMC application. This tool enables application developers to automatically and exhaustively check all possible schedules of a distributed WSAN application for deadline violations that can potentially cause bugs, thus resulting in more robust and reliable software for cyberphysical systems.
