The paper deals with important details of a detailed thermal hydraulic network model, a prevailing approach in building transformer thermal design tools. Oil flow components in a space between the tank and the transformers' active parts are explored using FEM CFD. These flows can significantly influence the overall temperature distribution in transformers with OF-cooling and ON-cooling with highly positioned radiators. Two heat run tests on a real OFAF transformer 125 MVA, 150/36 kV with different cooling arrangements (coolers of rated power 250 kW and 320 kW) are used for the analysis and experimental validation. The paper considers three oil flow components between the active part and the tank: oil bypass, oil near the tank with losses generated due to the stray flux, and oil near the outer winding with no cylinder on its outer surface. The 2-D axisymmetric FEM CFD simulations pointed out that frictional pressure drop in oil by-pass is equal to zero. Recommendations for modelling the three oil flow components in THNM are proposed. The influence of the insulation bulging on the oil flow and temperatures is investigated. The bulging was evaluated based on the heat run test result with the 250 kW cooler. After such calibration, temperatures were calculated for the case of320 kW cooler, and the THNM results were compared with the heat run test.
The results of a wide survey with 10 000 participants in 20 European cities suggest that mobility patterns in 2021 were still affected by the Covid-19 pandemic. The survey explores the factors that influence the respondents’ choices as regards trip generation, distribution and modal choice. The behavioural changes resulting from mobility restrictions in 2020 and the adoption of technological alternatives such as teleworking, video-conferencing, or online shopping limited the number of trips, but the gradual return to normality is also leading to a rebound in transport activity. The results reveal an increased use of cars for daily urban mobility, which may be sustained in the future. The main reason seems to be an increased level of users’ risk aversion and their avoidance of public transport or other shared modes. Such a trend can be also alarming as regards the future prospects of emerging technologies and business models, e.g. micro-mobility or Mobility-as-a-Service applications.
Following a brief description of the context and of the project as a whole, the report presents the solution adopted for the excavation of the Cut&Cover Tunnel planned at the beginning of the 2nd lot, before the excavation of the mining method tunnel. The Cut&Cover Tunnel, 136 m long, will house the main axis, characterized by a platform with a total width of 8.5 m (two lanes of 3.5 m plus two docks of 0.75 m) and two ramps, one for the entrance and one for the exit, with lane widths of 5.2 m and 5.5 m respectively. The geometric complexity and the resulting size of the work, as well as the boundary conditions typical of a highly anthropized environment, led to a top-down excavation method, up to a depth of approximately 20 m, with large diameter (1.2 m) perimetral piles, 1.5 m spacing and intermediate 1,0 m piles, the casting of the roof slab in cast in situ reinforced concrete and temporary tie rods during the lowering phases of the excavation, before the construction of the inner shell in cast in situ reinforced concrete.
