Vulnerability analysis of interdependent infrastructure systems: A methodological framework

Infrastructure systems such as power and water supplies make up the cornerstone of modern society which is essential for the functioning of a society and its economy. They become more and more interconnected and interdependent with the development of scientific technology and social economy. Risk and vulnerability analysis of interdependent infrastructures for security considerations has become an important subject, and some achievements have been made in this area. Since different infrastructure systems have different structural and functional properties, there is no universal all-encompassing ‘silver bullet solution’ to the problem of analyzing the vulnerability associated with interdependent infrastructure systems. So a framework of analysis is required. This paper takes the power and water systems of a major city in China as an example and develops a framework for the analysis of the vulnerability of interdependent infrastructure systems. Four interface design strategies based on distance, betweenness, degree, and clustering coefficient are constructed. Then two types of vulnerability (long-term vulnerability and focused vulnerability) are illustrated and analyzed. Finally, a method for ranking critical components in interdependent infrastructures is given for protection purposes. It is concluded that the framework proposed here is useful for vulnerability analysis of interdependent systems and it will be helpful for the system owners to make better decisions on infrastructure design and protection.     

Attack structural vulnerability of power grids: A hybrid approach based on complex networks

Power grids have been studied as a typical example of real-world complex networks. Different from previous methods, this paper proposes a hybrid approach for structural vulnerability analysis of power transmission networks, in which a DC power flow model with hidden failures is embedded into the traditional error and attack tolerance methodology to form a new scheme for power grids vulnerability assessment and modeling. The new approach embodies some important characteristics of power transmission networks. Furthermore, the simulation on the standard IEEE 118 bus system demonstrates that a critical region might exist and when the power grid operates in the region, it is vulnerable to both random and intentional attacks. Finally, a brief theoretical analysis is presented to explain the new phenomena.     

Diameter vulnerability of GC graphs

Concern over fault tolerance in the design of interconnection networks has stimulated interest in finding large graphs with maximum degree Δ and diameter D such that the subgraphs obtained by deleting any set of s vertices have diameter at most D′, this value being close to D or even equal to it. This is the so-called (Δ,D,D′,s)-problem. The purpose of this work has been to study this problem for s=1 on some families of generalized compound graphs. These graphs were designed by Gómez (Ars Combin. 29-B (1990) 33) as a contribution to the (Δ,D)-problem, that is, to the construction of graphs having maximum degree Δ, diameter D and an order large enough. When approaching the mentioned problem in these graphs, we realized that each of them could be redefined as a compound graph, the main graph being the underlying graph of a certain iterated line digraph. In fact, this new characterization has been the key point to prove in a suitable way that the graphs belonging to these families are solutions to the (Δ,D,D+1,1)-problem.     

延安宝塔山景区滑坡地质灾害风险评估

机匣与叶片的相对转动是影响涡轮叶顶间隙流动的重要因素之一. 对LISA 1.5级轴流涡轮间隙内部流动的数值计算结果表明：叶片转动对涡轮间隙流动有阻塞作用. 叶片静止时,由于阻塞作用消失,导致间隙入口速度增大,间隙流量增加,并且通过间隙的 流体全部卷起形成间隙涡. 同时在叶片顶部吸力面侧前缘、中部各形成一个间隙涡,使得间 隙流动损失增加. 而且转速下降会加剧动叶出口截面气流过偏/偏转不足现象. 同时叶片静止 时,间隙前部各个弦长截面内静压自间隙入口开始一直呈增加趋势,直到叶片尾缘附近截面, 间隙截面内静压才逐渐稳定.     

Modeling Earthquake Vulnerability of Highway Networks

In this study, we investigate the earthquake vulnerability of highway networks whose links are subject to failure. We propose a model called α-conservative failure model that aims to capture the dependency among link failures in the event of an earthquake. According to this model, we calculate a path-based accessibility measure to assess the expected weighted average shortest distance to serve a unit demand after the earthquake. We test the proposed link failure model on a case study of the earthquake vulnerability in Istanbul.     

Evaluation of network robustness using a node tearing algorithm

Until recently the study of failure and vulnerability in complex networks focused on the role of high degree nodes, and the relationship between their removal and network connectivity. Recent evidence suggested that in some network configurations, the removal of lower degree nodes can also cause network fragmentation. We present a disassembling algorithm that identifies nodes that are core to network connectivity. The algorithm is based on network tearing in which communities are defined and used to construct a hierarchical structure. Cut-nodes, which are located at the boundaries of the communities, are the key interest. Their importance in the overall network connectivity is characterized by their participation with neighbouring communities in each level of the hierarchy. We examine the impact of these cut-nodes by studying the change in size of the giant component, local and global efficiencies, and how the algorithm can be combined with other community detection methods to reveal the finer internal structure within a community.     

Deep information from limited observation of robust yet fragile systems

We show how one can completely reconstruct even moderately optimized configurations of the Forest Fire model with relatively few observations. We discuss the relationship between the deep information from limited observations (DILO) to the robust-yet-fragile (RYF) property of the Forest Fire model and propose that DILO may be a general property of RYF complex systems.     

False targets efficiency in defense strategy

The paper analyzes the efficiency of deploying false targets as part of a defense strategy. It is assumed that the defender has a single object that can be destroyed by the attacker. The defender distributes its resource between deploying false targets and protecting the object from outside attacks. The attacker cannot distinguish the false targets from the defended object (genuine target). Therefore the attacker has no preferences for attacking one target rather than another target. The defender decides how many false targets to deploy whereas the attacker decides how many targets to attack. The article assumes that both the defender and attacker have complete information and full rationality. The optimal number of false targets and the attacked targets are obtained for the case of fixed and variable resources of the defender and the attacker as solutions of a non-cooperative game between the two agents.     

Transforming a complex network to an acyclic one

Acyclic networks are a class of complex networks in which links are directed and do not have closed loops. Here we present an algorithm for transforming an ordinary undirected complex network into an acyclic one. Further analysis of an acyclic network allows one to find the structural properties of the network. With our approach one can find the communities and key nodes in complex networks. Also we propose a new parameter of complex networks which can mark the most vulnerable nodes of the system. The proposed algorithm can be applied to finding communities and bottlenecks in general complex networks.     

Fuzzy VIKOR approach for assessing the vulnerability of the water supply to climate change and variability in South Korea

This study assessed the vulnerability of the water supply to climate change and variability in the South Korean provinces for the present and future with a fuzzy VIKOR approach. The key indicators of vulnerability were profiled with the Delphi surveys based on the IPCC-based vulnerability concept, in which vulnerability is defined as a function of sensitivity, adaptive capacity and climate exposure. The fuzzy VIKOR was used to aggregate the key indicators into a vulnerability score because it can provide a compromise solution considering overall satisfaction and regret of the selection of wrong provinces. Markedly different rankings between the fuzzy VIKOR and a conventional weighted sum for overall satisfactions suggest the importance of regret component of the selection of wrong provinces and inclusion of the uncertainty of information in the vulnerability assessment and consequent decision making for adaptation. Furthermore, diverse vulnerability rankings with the six different future scenarios suggest the need for robust decision making given such uncertainty.