Space Information Network (SIN) is a multi-purpose heterogeneous network. Due to the large-scale of SIN, its secure and stable operation is vulnerable to various threats. Much of current threat analysis for SIN is based on the network function or architecture. However, this approach cannot clearly divide the relation between threats and secure communication measures for a highly integrated network. Furthermore, it will lead to overlapping in segregation of secure duties. This paper presents a comprehensive review of threats and corresponding solutions in SIN from the perspective of network security attributes. In order to make the analysis applicable to more scenarios, the following three most essential attributes, confidentiality, integrity and availability, are selected as the threatened objectives. At the same time, for cross-reference with the analysis based on network function or architecture, this paper relates network layers to network security attributes through secure communication mechanisms. Specifically, the confidentiality includes confidential information-exchange and Authentication and Key Agreement (AKA), the integrity includes information identification and information restoration, and the availability includes link establishment, routing mechanism, and mobility management. According to above framework, this paper provides a cross-layer perspective for analyzing threat and enhancing the security and stability of SIN. Finally, this paper concludes with a summary of challenges and future work in SIN.

In the lining of water conveyance tunnels, the expansion joint is susceptible to leakage issues, significantly impacting the long-term safety of tunnel operations. Polyurea is a type of protective coating commonly used on concrete surfaces, offering multiple advantages such as resistance to seepage, erosion, and wear. Polyurea coatings are applied by spraying them onto the surfaces of concrete linings in water conveyance tunnels to seal the expansion joint. These coatings endure prolonged exposure to environmental elements such as water flow erosion, internal and external water pressure, and temperature variations. However, the mechanism of polyurea coating’s long-term leakage prevention failure in tunnel operations remains unclear. This study is a field investigation to assess the anti-seepage performance of polyurea coating in a water conveyance tunnel project located in Henan Province, China. The testing apparatus can replicate the anti-seepage conditions experienced in water conveyance tunnels. An indoor accelerated aging test plan was formulated to investigate the degradation regular pattern of the cohesive strength between polyurea coating and concrete substrates. This study specifically examines the combined impacts of temperature, water flow, and water pressure on the performance of cohesive strength. The cohesive strength serves as the metric for predicting the service lifetime based on laboratory aging test data. This analysis aims to evaluate the polyurea coating’s cohesive strength on the tunnel lining surface after five years of operation.

Salt precipitation is generated near the injection well when dry supercritical carbon dioxide (scCO₂) is injected into saline aquifers, and it can seriously impair the CO₂ injectivity of the well. We used solid saturation (Ss) to map CO₂ injectivity. Ss was used as the response variable for the sensitivity analysis, and the input variables included the CO₂ injection rate (QCO2), salinity of the aquifer (XNaCl), empirical parameter m, air entry pressure (P0), maximum capillary pressure (Pmax), and liquid residual saturation (Splr and Sclr). Global sensitivity analysis methods, namely, the Morris method and Sobol method, were used. A significant increase in Ss was observed near the injection well, and the results of the two methods were similar: XNaCl had the greatest effect on Ss; the effect of P0 and Pmax on Ss was negligible. On the other hand, with these two methods, QCO2 had various effects on Ss: QCO2 had a large effect on Ss in the Morris method, but it had little effect on Ss in the Sobol method. We also found that a low QCO2 had a profound effect on Ss but that a high QCO2 had almost no effect on the Ss value.

Salt precipitation from the drying-out process has a profound effect on the well injectivity during the storage of carbon dioxide (CO₂) in deep saline aquifers. Both gravity and reservoir heterogeneity have a significant impact on CO₂-plume behavior and CO₂ storage capacities. The collective effect of gravity and heterogeneity on the drying-out process by site-scale numerical simulation based on the Sleipner project had been investigated. Three site-scale permeability heterogeneous models and a fracture model had been built; simulation results showed that the gravity effect significantly increased the solid saturation at the injection well in the homogeneous model; changing the position of the injection well can change the distance that gravity can act and affect the amount of salt precipitation near the injection well. A novel conclusion is gravity and heterogeneity showed a mutual resistance relationship when considering the collective effect of gravity and heterogeneity on solid saturation. Gravity effects reduced the amount of salt deposited in the fracture model; at low CO₂ injection rate, gravity force dominated CO₂ flow; increased rock heterogeneity suppressed the production of salt precipitates; at high CO₂ injection rate, viscous force dominated flow; and increased heterogeneity increased salt precipitation. This research is of important guiding significance for the design of site screening and injection schemes from the perspective of avoiding a large amount of salt precipitation and pressure build-up.