Final Report Summary - WI-HEALTH (A wireless network with autonomously powered and active long range acoustic nodes for total structural health monitoring of bridges)
Executive Summary:
Maintaining the structural integrity of safety critical constructions, such as bridges, becomes increasingly difficult as they age. A vital part is the periodic inspection for detecting degredation, such as fatigue cracks and corrosion that are not always visible to the typical manual and visual inspections alone, but may eventually lead to catastrophic failure. There are several aspects that need to be considered in periodic inspections using conventional techniques only; flaws may grow to failure between inspections, access to conduct the inspection may be poor and it may be difficult to determine the significance of any flaw that has been detected and decide whether failure is imminent or if it can be left until a more propitious time for repair.
There is therefore strong interest in replacing periodic inspections with full-time, continuous Structural Health Monitoring (SHM), with networks of sensors that are permanently installed on the structure and are sensitive to defect development. Where these structures are very large, wireless sensor networks offer significant benefits. Although there are many promising SHM technologies applicable to a variety of civil and defence infrastructure, most of them use expensive components, bulky equipment and have prohibitive power requirements, which prevent permanent, large-scale, installations of networked sensors across remote locations.
Such interest has led a consortium of small-to-medium sized enterprises to sponsor research with support from the European Union’s FP7 research programme to develop a wireless sensor network technology for the SHM of bridges. The 2-year project which commenced in October 2011 is called 'Wi-Health’. The main objective of Wi-Health project is to develop technology for multi-purpose wireless networks that combine the Long Range Ultrasonic (LRU) and Acoustic Emission (AE) monitoring techniques in autonomously powered nodes for the detection of defect growth at damage-prone areas of bridges, such as welded plate structures. As the unprocessed data streams produced by these monitoring techniques require a high bandwidth, data processing at the node devices has been used to greatly reduce the bandwidth requirement of each node, which makes large numbers of wirelessly networked monitoring devices possible. Embedded software has been used to drive the structural health monitoring system for defect identification by incorporating the use of trend analysis and data processing.
Project Context and Objectives:
At the beginning of the Wi-Health project, it was defined that the developed system should be modular and scalable, such that it could find useful application from small bridges, such as a railway bridge crossing a minor road, to large bridges, such as a kilometre long suspension bridge.
The key features of the Wi-Health system were identified as follows:
• Network infrastructure for synchronised SHM (Structural Health Monitoring)
• Sensor Operation
• Wireless communication system
• Renewable energy power options
• Software for device operation
• Software for data management, data processing, analysis and results presentation, and systems configuration
To accomplish the project objectives, the work activities have been organised into a number of discrete Work Packages. Those were divided into research (WPs 1 to 6), demonstration (WP7), dissemination and exploitation (WP8) and management (WP9).The description for those work packages are shown below:
WP1 – System functional design, hardware and software architecture
WP2 – LRU (active) and passive sensors and the associated electronic hardware
WP3 – Signal pre and post processing
WP4 – Wireless LAN and data communication system
WP5 – Renewable energy node power pack
WP6 – System integration and testing
WP7 – System Demonstration
WP8 – Exploitation and dissemination of knowledge
WP9 – Project Management & Coordination
Project Results:
The details of technical and scientific results for each work package are presented as follows:
WP1 – System functional design, hardware and software architecture is 100% complete at the end of the project. There were two deliverables re-submitted for this work package: D1.1 - Project specifications and test piece sections for laboratory validation of the system and D1.2 - System functional design, hardware and software architecture. Both deliverables were prepared with the collaboration of consortium.The overall objective of this Work Package (WP) was to set detailed specifications for all the other WPs in the project. The structure of the Wi-Health system has been determined as a tree hierarchy involving a Central Server, Node Devices and Sensor Devices.
- The Central Server to manage the SHM network operations and reporting.
- The Node Devices to manage groups of Sensor Devices in each region.
- Sensor Devices to conduct AE, LRU and parametric sensing.
The communications, including the messaging required, have been designed. This design was planned to be scalable, networked SHM that has the potential to be mass produced at a commercially viable cost and can be adapted to a wide range of SHM applications.
WP2 – LRU (active) and passive sensors and the associated electronic hardware is 100% complete at the end of the project. There were two deliverables submitted for this work package: D2.1 - Design of the WI-HEALTH Sensor array and sensor collar and D2.2 - SHM LRU based Sensor array with driving and reception hardware electronics. Within WP2, the objective was to define and complete the production of a sensor array that can provide sufficient information to determine location, severity and characteristics of the defect as well as information to determine fitness for service, maintenance and upkeep requirements and service life extension programmes. The design of the Wi-Health sensor array to cover inspection of the areas discussed at the partner meetings and described in Deliverables D1.1 and D1.2 , was reported in the first reporting period. Generally the approach used for inspection or monitoring with Ultrasonic Guided Waves is to establish a means of transmitting waves through a structure and receiving them after they have interacted with potential defects. The signals are interpreted to identify features of the signals that correspond to defects, and often the emphasis of the technique development is on producing a system that yields simple signals so that a human can easily see from the signals where defects occur. This often introduces a requirement for many sensors and elaborate electronics to simultaneously operate the sensors. Also, current commercial AE monitoring equipment usually involves several transducers, each with an integral pre-amplifier, long copper cable from each transducer to carry power and signals and a bulky multi-channel acquisition and processing system. The integral pre-amplifiers are expensive and power consuming as they are required to continuously transmit, with high fidelity over long distances, analog signals from the transducer back to the data acquisition system. The bulky and expensive acquisition system needs to be carefully situated away from the potentially exposed transducers to avoid damage. The installation of the long, expensive copper cabling for signal and power transmission is, itself, very costly. In the first reporting period, different types of transducers have been investigated during the initial laboratory work, to understand their behaviour and optimize the design of sensor array to cover the inspection of the various bridge sections with the minimal number of sensors. The modelling, experimental work and design have been detailed in Deliverable D2.1. The electronic hardware to drive and receive signals from all sensors including the system microcontroller hardware has been produced in the second half of the project and progress was reported in D2.2.
WP3 – Signal pre and post processing is complete 100% at the end of the project and reported in D3.1 - Software modules for running the computer base station and on board microcontroller. It has delivered functioning and tested software systems to:
1. Acquire, process and transmit parameterised data from acoustic emission (AE) and long range ultrasonic (LRU) sensors (the NDT Sensor Array of the On-Board Control System)
2. Synchronise and manage the sensors at the communication and power managing node (the Node of the On-Board Control System)
3. An easy to use but feature rich Graphic User Interface (GUI) for the bridge control personnel to manage all the Wi-Health system functionalities (such as processing and interpreting the NDT data),
4. An enterprise standard database schema to manage the significant data warehousing that would be required for a production system,
5. A Structural Health Monitoring software system to interrogate the NDT data, to generate alerts of deterioration and to assist interpreting the NDT data by enabling correlation with existing bridge data (such as bridge traffic) and external systems.
The Wi-Health Base Station Control System incorporates all the above features in a single easy to use GUI and controls the NDT inspections on the bridge and monitors the overall condition of the bridge.
WP4 – Wireless LAN and data communication system is 100% complete at Month 24 and the progress was reported in D4.1 - Construction of transmitter and receiver hardware and D4.2 - Wireless LAN and data communications system. Communications between the BS and Node, Node and sensor and Sensor COMS and sensor Measurement was developed and reported in the deliverables and Periodic Report 2
WP5 – Renewable energy node power pack is 100% complete and reported as D5.1 - Specification of the renewable energy harvesting system and D5.2 - On board Renewable energy system and node power pack. The power subsystem consists of:
• A wind turbine (Details have been provided in the work package deliverables and Periodic Report 2)
• A solar panel (Details have been provided in the work package deliverables and Periodic Report 2)
• Wind turbine regulator (Details have been provided in the work package deliverables and Periodic Report 2)
• Battery (Details have been provided in the work package deliverables and Periodic Report 2)
• Supporting hardware (cables, fuses, terminal adaptors, etc.) (Details have been provided in the work package deliverables and Periodic Report 2).
WP6 – System integration and testing is complete 100% at the end of the project and reported as D6.1 - Completion of WI-HEALTH system laboratory and field trials. This work package has described the components, integration and operation of the completed Wi-Health system and the trials performed to prove the proposed method for monitoring the progression of defects in vulnerable parts of a suspension bridge structure.The efficacy of the proposed guided wave monitoring technique has been demonstrated at the final meeting. The samples used for this demonstration were of the same geometry as sections of a real bridge, ensuring that the results are directly applicable to the target structure. The superior performance of the transducer array relative to conventional isolated transducers is clear from the improved defect detection capability. The sensitivity of the technique has also been demonstrated showing that defects less than 6mm deep can be reliably detected.
WP7 – System Demonstration was completed and reported in D7.1 - Completion of WI-HEALTH system final trials. The system was demonstrated to work very well at the Wi-Health final project meeting. The system worked to the satisfaction of the SME partners. Simulated acoustic emission events generated in the final meeting were detected, analysed and positions calculated which agreed very well with the positions of the source. The system was shown to be repeatable. The temperature sensors were demonstrated to be accurate with acceptable precision and repeatability.
Potential Impact:
Bridge collapses arouse strong public concern. Most major collapses have resulted in significant loss of life and serious economic losses resulting from the interruption to transport and the need for reinstatement. Routine inspection can help detect developing flaws so that remedial action can be taken, but full-scale, regular inspection of large structures is often cost prohibitive and is often not done as frequently as it is desired. The Wi-Health project developed an advanced integrated system for Structural Health Monitoring (SHM) for bridges (and other large engineering structures), which could be used to reduce the need for inspection thus reducing the cost of maintenance and making structures safer. Several technological developments under Wi-Health have contributed to the development of this system.
An active long range ultrasonic method of monitoring welded structures for the presence of developing fatigue cracks and corrosion was developed. This method makes use of Ultrasonic Guided Waves by monitoring the changes to the way the sound is scattered by developing flaws. This method was trialled on large replica parts of some bridge components and was shown to detect flaws (with characteristics similar to those of concern to industry) as they were introduced in the lab. Passive ultrasonic (Acoustic Emission) techniques have already been established for structures of this kind, but do not support Acoustic Emission between wirelessly connected sensors. Under Wi-Health this difficulty was overcome. The hardware developed was shown to wirelessly support both the active and passive ultrasonic monitoring techniques. A small scale array of ultrasonic sensors was shown to be effective for use in both the passive and active ultrasonic methods. By using sparsely distributed, multipurpose sensors, this demonstrated that a footprint of many square meters of a structure can be monitored with both techniques whilst using relatively few sensors.
Wireless methods of data transmission and device management (communication protocols) were designed and analysis within the project demonstrated that these methods had the potential to support a SHM network with potentially thousands of sensors.
Support for multiple methods of provision of power (including by small-scale wind turbines and solar panels) was demonstrated, making it possible to power individual devices or small groups of devices autonomously.
Software for managing the sensor network and the database of monitoring data was developed. This was designed to allow control and oversight of the monitoring whilst it was on-going on. It was also designed to enable integration with other information systems.
These developments mean that for the first time a very large scale wirelessly integrated network of devices could be used to ultrasonically monitor for structural flaws (and make use of other parametric inputs such as temperature) whilst being managed in real-time from a single computer in a centrally organised way with the potential to be more cost effective than existing, more limited alternatives.
The main purpose of the dissemination activities is to raise awareness of the project results in order to promote the widest dissemination of knowledge gained during the Wi-Health project. The project website (www.wi-health.eu) was created and updated with news and project activities throughout the project term. Further dissemination is planned to continue via the project website.
The project flyer was designed, printed and distributed in various events to increase public awareness about the project. A project video was produced. The video will not be released any public domain until SMEs further notice since some of the results are subject to patent application. There were 5 papers prepared and presented in various events thoughout the project. These have been all reported in the D8.4 - Final Plan for the dissemination and use of foreground (PUDF) and later in this report.
List of Websites:
The public website address for the project is www.wi-health.eu. This website will be kept as the main platform for any communications related to the Wi-Health project beyond the project term.
Project Co-ordinator:
Kamer Tuncbilek – kamer.tuncbilek@twi.co.uk
Granta Park, Great Abington
Cambridge CB21 6AL, UK
