Integrated Cyber-Physical Simulation of Intelligent Water Distribution Networks

In cyber-physical systems (CPSs), embedded computing systems and communication capability are used to streamline and fortify the operation of a physical system. Intelligent critical infrastructure systems are among the most important CPSs and also prime examples of pervasive computing systems, as they exploit computing to provide "anytime, anywhere" transparent services. While the added intelligence offers the promise of increased utilization, its impact must be assessed, as unrestricted cyber control can actually lower the reliability of existing infrastructure systems. As a practical example, water distribution networks (WDNs) are an emerging CPS domain. Physical components, e.g., valves, pipes, and reservoirs, are coupled with the hardware and software that support intelligent water allocation. An example is depicted in Fig. 1. The primary goal of WDNs is to provide a dependable source of potable water to the public. Information such as demand patterns, water quantity (flow and pressure head), and water quality (contaminants and minerals) is critical in achieving this goal, and beneficial in guiding maintenance efforts and identifying vulnerable areas requiring fortification and/or monitoring. Sensors dispersed in the physical infrastructure collect this information, which is fed to algorithms (often distributed) running on the cyber infrastructure. These algorithms provide decision support to hardware controllers that are used to manage the allocation (quantity) and chemical composition (quality) of the water. As WDNs become larger and more complex, their reliability comes into question. Modeling and simulation can be used to analyze CPS performability, as direct observation of critical infrastructure is often infeasible. Accurate representation of a CPS encompasses three aspects: computing, communication, and the physical infrastructure. Fundamental differences exist between the attributes of cyber and physical components, significantly complicating representation of their behavior with a single comprehensive model or simulation tool. Specialized simulation tools exist for the engineering domains represented in critical infrastructure, including power, water, and transportation. These tools have been created with the objective of accurately reflecting the operation of the physical system, at high spatial and temporal resolution. As is the case with specialized models of physical systems, intelligent control is not reflected in these tools. Despite the existence of simulation tools for cyber aspects such as computing and communication, differences in temporal resolution and 7