Design Specification for the Structural Health Monitoring System of London Water Supply System - Case Study Example

Topic: Design Specification for the Structural Health Monitoring System of London Water Supply System Presented to (Course/Subject) (Institution/University) (City, State) (Date) Design Specification for the Structural Health Monitoring System of London Water Supply System 1. Abstract Wireless sensor networks (WSN) provide viable solutions towards monitoring of the environment, health conditions of structures as well as the security and safety of water. The development of monitoring system bridges wireless sensor networks with advanced hydraulic and water quality processing. The wireless sensor networks are responsible for collecting application data like hydraulic pressure transients, leak detection and monitoring of water quality parameters and levels in combined sewer outflows (CSO). Water supply and sewer networks are detected for leaks, water quality and contamination resulting from sewer overflows. 2. Introduction Most water distribution systems face the challenge of significant water loss through leakage that is translated to economic loss. Reduction in leakage through well strategized actions in water network management translates into economic benefits. Leakage of fresh water can cause severe damage while that of waste water lead to contamination of soil and environment. The clean up process may be very expensive. Catastrophic failures result to environment degradation, loss of human life and production of large masses of demolished waste. Building codes and design methods are used to produce structures safe for public utility. At times, structures are exposed to harsh conditions through loads and the surrounding not planned for during the design process. These harsh conditions normally produce long-term structural deterioration. Structures, therefore, need continuous assessment through various techniques. The common techniques used are; Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM). Commercial technology is used in NDE technique. The SHM technique involves the collection of data from sensors. The sensors are permanently mounted on the structure. Collected data are processed according to the selected methods of damage detection. A system used to detect damages in engineering infrastructure is referred to as Structural Health Monitoring. This technique is used to monitor fresh water mains and sewerage pipes. In the technique, the following are observed: a. Failure mechanisms b. Parameters to be measured c. Range, accuracy, resolution and sampling regime for preferred parameters and processes. 3. Case study- London Water Supply System The largest water project responsible for supply of water in London is the Thames Water Ring Main (TWRM). Five different treatment works supply drinking water to more than six million clients. Gravitational force forces the water to eleven pumping stations installed with shafts. The pumping stations are located at southern, central and north-western areas of the metropolis. Delivery is done directly to water supply zones or to service reservoirs. Objectives of water project were determined by many factors. The factors are; Satisfaction of average and peak demands for water in London to cushion leakage through control action plan effects Maintainan quality and acceptable service to clients in regard to pressure Control hazards related to water supply operations to the environment and social life. Maintain and improve water supply infrastructure in London Control cost at short and long term levels in relation to manpower and energy spent in pumping (Bensted, 1994 p.1-4). 4. Failure Mechanisms Damage refers to changes that occur to material or geometric properties of a structure and completely affects its performance. All engineering material used in construction of any system posses inherent initial flaws. Flaws generated from the environment and operational loading develop continuously and lead to component level failure. System level failure results with time due to continuous loading. The duration and time scales related to damage evolution must be continuously considered (Farrar and Todd, 2006). Water supply is divided into two systems – transmission and distribution systems. Transmission system consists of all components designed to deliver water in large amounts to great distances. In most cases, it occurs between major facilities located within the system. Distribution systems are responsible for transportation of water from transmission pipelines to residential areas. These systems have different topology, pipe sizes and materials as well as hydraulic profiles. 4.1 Damage Identification Methods The process of damage identification contains the following: The presence of damage, Damage locations, Types of damage, and Severity of damage. Damage identification methods are classified into two: Damage identification and Damage Prognosis. Damage Identification focuses on, first, microscopic flaw that is used in the development of material failure models. Secondly, component level damage or incipient; macroscopic material that is categorised into non-destructive evaluation. This is could be local or off-line inspection and wave-propagation which relies on structural health monitoring. Thirdly, component damage failure or system level damage. This consists of structural health monitoring, condition monitoring, health usage monitoring systems and statistical process control. Damage prognosis is a damage identification method that adds prediction of remaining life capability to structural health monitoring. 4.2 Pipe Failure Infrastructure deterioration entails pipe failure. This is a multi-step process normally difficult to detect. The duration between time intervals and failure mechanism are dependent. There are five steps in pipe development failure: a. Installation phase, b. Initiation of corrosion, c. Crack development before leakage, d. Partial failure and finally, e. Complete failure. The process of corrosion starts after the pipes have been installed and operational for some time. The corrosion process takes place on the internal and external surface of pipes. After corrosion, cracks, corrosion pits and graphitization occurs. At times, cracks result from mechanical stress originating from human activities and seismic waves. These anomalies are not severe to cause leakage. These modes of failure reduce the residual strength of pipe wall, making it susceptible to internal and external stresses. Later, the pipe wall will break and leakage begins. Failure is identified through water seepage on the ground or specific change in the system’s hydraulic balance (Rizzo, 2010 p.2). These steps progress in a downward trend with time and service reliability respectively. The main events in pipe failure are: Partial failure that develops from a leak or burst, although the pipe is still in service and Complete pipe failure that develops from influenced hydraulic balance of the system. For this particular type of failure, repair or replacement is necessitated (Misiunas, no date. p. 648,649). 4.3 Pipe Deterioration Pipe deterioration could be structural or internal. Structural failure results when pipe resiliency and its ability to withstand stress decreases. The later happens as a result of diminished hydraulic capacity or water quality or appearance of severe internal corrosion. Pipe breakages likely occur to pipes affected by corrosion, degradation, poor workmanship during installation or defects that occur during the manufacturing process. 5. Parameters to be Measured In management of water network, coordination of different actions are required in monitoring failure mechanisms. Actions that should be taken are; Detection and repair of leaks This is possible for large leaks that are easily identified. However, most leaks are from small leaks that are not economical in terms of detection and repair. Facilitation of pipe rehabilitation programmes Pipe rehabilitation programmes are expensive but very effective to leakages and the quality of water delivered to clients. Operational pressure control This is the most common practice to water supply systems. The orifice equation creates the relationship in leakage flow to size of crack or opening in the pipe and difference in pressure between in-pipe flow and surroundings of the pipe. When operating pressure is reduced, the leakage flow through leak hole in pipe is also reduced. The costs associated to this operation are relatively low and reduces risks related to failure of pipes. Pressure management in water network play a significant role in controlling frequency of new leaks, rate of water flow of all leaks and bursts. The loss of water through leaks depends on system service pressure. Any increase in average service pressure leads to a proportional increase in leakage. 6. Management of pressure in the UK To prevent or avoid mechanisms associated with leaks and pipe bursts, UK water utilities apply pressure control technique. This reduces background leakage and prevents pipe bursts. To implement pressure control and manage background leaks, water supply systems use District Metered Areas (DMAs). DMAs cover 1500 properties, with inlets and outlets. Water flow is monitored through these inlets and outlets that are closed in other boundaries. Hydraulically controlled Pressure Reducing Valves (PRVs) supply and control pressure to DMAs. As a result, an automatic adjustment of pressure outlet for given pressures upstream. Furthermore, outlet pressure is maintained despite fluctuations in inlet pressure. Particular critical points identified from DMAs set the basis in selection of PRV set points. The points represent DMA minimum pressures. Single-feed DMA affect the quality of water and rate of water supply interruption. Multi-feed DMAs overcome these setbacks and hence preferred. They are developed from existing DMAs. The advantages linked to multi-feed DMAs are improved security in terms of water supply and quality. Despite the advantages, it is difficult to set up and manage. Several PRVs in multi-feed DMAs create instability and fluctuating hydraulic conditions. This increases discolouration risks and failure in pipes (Borotoulas, 2009 p.3). 7. The Structural Health Monitoring Process Time-based approaches to systems monitoring are preferred because of the factors surrounding engineering system. This largely depends upon location, size of the system and conditions under which it operates. A change from time-based maintenance to condition-based maintenance is developed by this system. It is important in combating the readiness of an asset. Basically, it is not convenient for pattern recognition. Time-based methods are suitable for buried water and wastewater pipes. The processes involved in Structural Health Monitoring are – operational evaluation, data acquisition, feature extraction and statistical model development for feature discrimination. 7.1 Operational Evaluation This stage identifies the damage that need to be detected and starts to give solutions related to issues for structural health monitoring system. 7.2 Data Acquisition The sensing hardware and data necessary for feature extraction process are categorically defined. 7.3 Feature Extraction In this process, information about damage is identified in relation to the measured data. 7.4 Statistical Model Development for Feature Discrimination In this category, feature distributions are classified as damaged or undamaged. Data acquisition, feature extraction and statistical model development for feature discrimination are implemented by software and or hardware. The software or hardware processes the data through the following steps: Data Cleansing Data Normalisation Data Fusion and Data Compression. 8. Structural Health Monitoring Systems Designs SHM predicts, identifies and locate onset of damage to structures. Smart sensor technologies are used to assist in the identification of weak structural abnormalities. The abnormalities rely on measured structural response parameters. Real time valuable information about the behaviour of a structure or its environmental conditions is achieved through the use of structural sensors. The sensors commonly used are: a. Accelerometers b. Displacement transducers c. Strain gauges and d. Thermometers. The success of SHM relies on data acquisition (DAQ) system. This system is important in the collection of sensor measurements and storage of data collected in a centralised location. Traditional DAQ systems are expensive in terms of time and money consumption. The reason behind this is because of the design. Cables are installed either permanently or for short-term vibration tests. The cables relay sensor data to central data repository. Developments in microelectromechanical systems (MEMS) and wireless communications have reduced installation costs. MEMS technology has developed systems that are affordable, conserve power and are easy to install. The wireless technology allows transmission of sensor measurements in the absence of cables. Design of the wireless sensing unit is divided into two; hardware and software design. 8.1 Hardware Design of a Wireless Sensing Unit A simple star-topology wireless sensor network is developed from an integrated software and hardware design. Multiple wireless sensing units are connected to a central server that coordinates all network activities. The central server could be a laptop or desktop computer connected to wireless transceivers compatible to it. With the use of wireless transceiver, the central server can relay information to wireless sensing units, located in the structure. Wireless sensing units acquire sensor measurements, analyse data and relay it to the central server for permanent storage, if not data interrogation. The hardware designs of wireless sensing units include controlled power consumption, peer-to-peer communication range that is long and the capability to process data locally. The modules for the design are- sensing interface, computational core and the wireless communication channel. Sensing interface is responsible for the conversion of analog sensor signals to a digital format. This enhances communication with computational core. High-speed Serial Peripheral Interface (SPI) port transfers data to computational core. External Static Random Access Memory is integrated with computational core for data storage and analysis. Communication between computational core and MaxStream 9XCite wireless transceiver is necessitated by a Universal Asynchronous Receiver and Transmitter (UART) interface. A wireless connection is enhanced between the unit and the central server. Communication between sensors and data repository vital in structural health monitoring applications entails robust data. 8.2 Software Design of a Wireless SHM System The functions of the central server are: Command all wireless sensing units to collect data tasks, Synchronise internal clocks of wireless sensing units Receive data from wireless network and Store measurement data to the file server. The software used for wireless structuring monitoring system is developed into two parts: computer software responsible for central server and embedded software, used for wireless sensing units. The two units communicate interactively. The design allows seamless integration and coordination. State diagram encodes a sequence of actions for the central server and wireless sensing units. This encoding process assists efficient handling of problematic scenarios encountered in unreliable wireless channel (Wang, Y., Lynch, P. J. and Law, H. K. no date p.11). 9. Conclusion Structural Health Monitoring systems contribute to effective management and monitoring of water network structures. Reliability, availability, safety and efficiency of London water supply is improved. Wireless technology allows a systematic condition assessment that is faster and cheaper that the traditional techniques practiced. Proactive failure management is effective, increasing reliability of water supply system. Rehabilitation process is easily planned for because of availability of information about the current state of water network system. The benefits acquired through structural health monitoring system are; automated detection of leaks and bursts in water transmission, real-time operation, low costs in monitoring water network and well maintained data collection and storage. Bibliography Bensted, H.I., 1994. Historical Perspective and Corporate overview- paper 10574. Proc. Instn Civ. Engnrs, Civ Engng. Tahmes Water Ring Main. Farrar, R.C. and Todd, D.M. 2006. Introduction to Structural Health Monitoring and Feature Extraction. UCSD Jacobs School of Engineering. UK. Misiunas, D. No date. Failure Monitoring and Asset Condition Assessment in Water Supply Systems. Vilnius Gediminas Technical University, Faculty of Environmental Engineering, Sauletekio al; Lithuania. Rizzo, P. 2010. Water and Wastewater Pipe Nondestructive Evaluation and Health Monitoring: A Review. Advances in Civil Engineering, Vol. 2010. New York; NY. Hindawi Publishing Corporation. Wang, Y., Lynch, P. J. and Law, H.K. No date. A wireless Structural Health Monitoring System with Multithreaded Sensing Devices: Design and Validation. Department of Civil and Environmental Engineering, Stanford University, Stanford: USA. Borotoulas, L. 2009. Experimental Evaluation of the Dynamic Performance of Pressure Reducing Valves. Imperial College, London. Read More