【Authors】Joseph Jonathan Magouaa, Fei Wanga, Nan Lia,b,*
a Dept. of Construction Management, Tsinghua Univ., Beijing, China
b Hang Lung Center for Real Estate, Tsinghua Univ., Beijing, China
【Corresponding e-mail】nanli@tsinghua.edu.cn
【Journal information】Simulation Modelling Practice And Theory 118 (2022) 102529
【DOI】https://doi.org/10.1016/j.simpat.2022.102529
【Abstract】Interdependencies among urban critical infrastructure systems (CISs) significantly impact the reliability and performance of CISs and the resilience of modern societies. Although several approaches exist for modeling interdependent CISs and studying their behavior, models developed in previous studies often fail to incorporate CIS domain knowledge, capture systemic heterogeneities among the CISs, and accurately model CISs interdependencies. Consequently, existing models have a limited ability to simulate interdependent CISs with sufficient detail and accuracy. To address these limitations, this study proposes a high-level architecture (HLA)-based framework for modeling interdependent CISs that can leverage and integrate well-tested practices, knowledge, data and simulation tools accumulated over years of wide usage in various CIS domains. The framework provides a methodology for co-simulating heterogeneous fine-grained CIS domain-specific models and modeling complex interactions between them and with their external environments, hence reproducing with high fidelity the complex coupled systems. A case study of two interdependent power and water systems was conducted, which demonstrated the efficacy of the proposed framework. Simulation results revealed that the HLA-based CISs model could capture the heterogeneous behaviors of the CISs and reveal a variety of failure-induced system vulnerabilities and feedback loops which may not be observable when using other existing modeling approaches.
Keywords: Critical infrastructure system; High level architecture; Co-simulation; Interoperability; Interdependency; Domain knowledge; Systemic heterogeneity
【Methodology】To improve the level of detail and granularity of interdependent CISs models and by so doing improve the resilience assessment of interdependent CISs, it is important to integrate the knowledge, data, models and tools that are specific to each CIS domain. To achieve this goal, we leveraged the capabilities of the HLA standards to propose a framework for co-simulating interdependent CISs. The architecture of the proposed framework depicted in Fig. 1 consists of four module types that communicate via a central middleware (RTI). Each module consists of domain-specific data, models or tools responsible for simulating a particular CIS, disaster scenario, and other agents. The RTI ensures the synchronization and interoperability among the heterogeneous components of the framework. The data exchange mechanism depicted in Fig. 2 demonstrates how data is shared, managed and interpreted by the CIS models in the proposed framework.
Fig.1. The proposed interdependent CISs federation.
Fig.2. Data exchange and management mechanism of the proposed federation.
【Case study】The proposed framework was adopted in a case study to model the interdependent water and power supply systems of Shelby County, Tennessee (TN), United States, as depicted in Fig.3. The Shelby County case has been extensively studied in the existing literature on interdependent CISs, with detailed data available to model the CISs with high fidelity. The power-water-interplay presents strong bi-directional functional dependencies that are ideal to showcase the capabilities of the proposed framework in modeling complex influence mechanisms such as feedback loops. Moreover, documented scenarios and data exist about the Shelby County case that were used to compare and verify the findings of the present study. Fig. 4 shows the high level of details and granularity of the simulation results obtained using the proposed framework. The results also help identify feedback loops among the interdependent CISs and the impact of different hardware configurations on the simulation performance, Table 1.
Fig. 3. (a) Topology of the power system; (b) Topology of the water system.
Fig. 4. (a) Pump statuses; (b) Loads on substations; (c) Water levels at the elevated water tanks; (d) Water pressures at the distribution nodes; (e) Serviceability of power generators.
Table 1. Summary of the simulation performance under different hardware configurations.
【Discussions and conclusions】
As modern CISs are becoming increasingly complex, so are the interdependencies existing among them. An event that may have been considered irrelevant to a particular CIS can still potentially affect it because of its strong dependence on other CISs. This study explored the feasibility of adopting an HLA-based framework to model and simulate the behavior of interdependent CISs. The framework addressed the limitations of existing simulation approaches by proposing a methodology to leverage, integrate and coordinate well-tested practices, knowledge, data and simulation tools from various CIS domains. The conducted case study showed that the interdependent CISs model developed based on the proposed framework could incorporate the domain knowledge specific to each CIS and capture various systemic heterogeneities among the CISs, resulting in a more detailed and accurate simulation of CISs behavior. The case study results indicated that the proposed framework has the potential to push the boundaries of research on interdependent CISs by addressing most of the limitations and challenges identified in related literature. Moreover, the proposed framework can also provide researchers and industry professionals with a useful methodology for testing and analyzing CIS designs, and predicting complex system behaviors such as cascading failures in different simulation environments or scenarios, so as to provide safer and more resilient infrastructure systems.
One limitation of the proposed framework is that compared to other modeling approaches, the proposed approach may result in relatively longer computational time. This is due to the conservative time management mechanism adopted by the framework. As the number of federates and complexity of the federation increases, the difference in computational time may become more significant. Moreover, when adopting HLA standards developers have to address important but challenging topics, such as fault-tolerance for federation robustness and load balancing across hosts, to improve the performance of their federations. Nevertheless, a growing amount of resources, such as open-source software, add-ons, toolboxes, and so on, has been made available to facilitate the design and implementation of HLA federations.
In future works, the framework will be further improved by testing other approaches for implementing the organizational and communication layers of the CIS modules that can address the above limitations. Moreover, the framework will be adopted in more complex simulation scenarios in which the model developed in the case study will be re-used and expanded by adding extra modules and federates for studies on the cascading failure and restoration of interdependent CISs, and the incorporation of human factor in the modeling of interdependent CISs.
