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In recent years, subsea tunnels have been constructed at greater depths, higher groundwater tables, and longer drives than those built previously. Controlling the water pressure and inflow rate of groundwater, i.e., the design of the drainage system, is a major challenge in subsea tunnels in terms of achieving hydraulic stability and ensuring economical operations. This has significant cost implications during construction and operation for long and deep subsea tunnels. In this study, the drainage system of subsea tunnels is optimized using the particle swarm optimization (PSO) algorithm, in which hydraulic boundary conditions, including size of the tunnel, number of sump pits and pumps, and pump operation plans, are allocated section-by-section and simulated to achieve economic optimization. Additionally, parametric studies are conducted to evaluate the influencing factors, including the drainage condition, hydrostatic pressure, radius of the tunnel, and initial stress. It is shown that optimal drainage is established under full drainage, nondrainage, and sometimes partial drainage systems depending on the hydraulic conditions. A tentative application of the proposed simulation method to a specific subsea tunnel illustrated that the construction cost can be significantly reduced through the optimization of the tunnel drainage system. [ABSTRACT FROM AUTHOR]

To develop a novel selective catalytic reduction (SCR) system, V 2 O 5 -WO 3 /TiO 2 and Cu-zeolite catalysts were combined within one canister with the former upstream and the latter downstream. The nitrogen oxides (NOx) and N 2 O emissions for the combined catalyst were investigated under operating conditions of engine loads and speeds in a 3.4 L diesel engine. The results from the combined catalyst were compared with those from the vanadium-based and Cu-zeolite catalysts alone. The NO conversion efficiencies for all the catalysts were higher than approximately 80% at temperatures ranging from 200 to 410 °C, which corresponds to the NO 2 excess range. In other words, the NO 2 /NOx ratio was higher than 50% for the temperature range between 200 and 410 °C, although the maximum NO 2 /NOx ratio was obtained at 270 °C. Beyond 410 °C, the efficiency of the Cu-zeolite catalyst remained high; however, the vanadium-based catalyst started to deteriorate at 410 °C. The deterioration of the combined catalyst was not much larger than that of the vanadium-based catalyst owing to the superior capability of the Cu-zeolite catalyst. For the NO 2 conversion efficiency, the combined catalyst mostly followed the Cu-zeolite catalyst. The vanadium-based catalyst exhibited an efficiency drop at approximately 270 °C, which is the temperature of the highest NO 2 /NOx ratio; however, this efficiency drop was avoided in the combined catalyst. For N 2 O produced over the catalysts, the Cu-zeolite catalyst produced the most N 2 O, while the vanadium-based catalyst produced the least. Because the amount of N 2 O produced behind the SCR was at most five times that in front of the SCR, efforts to inhibit N 2 O production from SCR are required when considering the global warming potential of N 2 O. The combined catalyst produced intermediate levels of N 2 O. [ABSTRACT FROM AUTHOR]

This article presents the effect of fractured zones on subsea tunnels. Generally, a subsea tunnel is designed to support high water pressure so that the hydraulic condition is of fundamental interest. In cases where fractured zones exist along the tunnel route, attention should be paid to it at the design stage. However, there is not much information about the hydraulic influences on the fractured zones. Pore water pressure and inflow rates are the main hydraulic factors to be considered in the design. In this article, the hydraulic effects on the fractured zones of a subsea tunnel under construction and during operation have been investigated using a numerical method and small scale model tests. The Vardø tunnel, which is a subsea tunnel in Norway (Grønhaug and Lynnegerg, 1984), is used for the numerical modeling. Based on the analysis results, the significance of fractured zones in subsea tunnels is identified. [ABSTRACT FROM AUTHOR]