Green hydrogen has become a central topic in discussions about the global energy transition, seen as a promising solution for decarbonizing economies and meeting climate goals. As part of the process of decarbonization, green hydrogen can replace fossil fuels currently in use, helping to reduce emissions in sectors vital to the global economy, such as industry and transport, as well as in the power and heat sectors. Whilst there is significant potential for green hydrogen, there are also challenges. The upfront costs for infrastructure and technology are high, and the availability and accessibility of the renewables needed for production varies by region. Green hydrogen production and storage technologies are continuously evolving and being promoted as the demand for hydrogen in many applications grows. Considering this, this paper presents the main methods for its production and storage, as well as its economic impact. Hence, the trend of governments and international organizations is to invest in research and development to make this technology more accessible and efficient, given the carbon reduction targets.

European seas have a strong economic role both in terms of transport and tourism. Providing more knowledge, regarding the mean and extreme values of the wind and sea state conditions in the areas characterized by high maritime traffic, helps to improve navigational safety. From this perspective, six zones with high maritime traffic are studied. ERA5 database, a state-of-the-art global reanalysis dataset provided by ECMWF (European Centre for Medium-Range Weather Forecasts), is used to assess the average values and the percentiles for the wind speed and the main wave parameters in the target areas considering the period 2001–2020. The main European routes and the extreme conditions along them as well as the areas characterized by high values of wind speed and high waves were also identified. A more comprehensive picture of the expected dynamics of the environmental matrix along the most significant shipping routes is useful because in this way the most dangerous areas could be avoided by ships for the safety of passengers and transported goods.

An alternative to experiments is the use of numerical model tests, where the performances of ships can be evaluated entirely by computer simulations. In this paper, the free surface viscous flow around a bare hull model is simulated with three Computational Fluid Dynamics (CFD) software packages (FINE Marine, ANSYS CFD and SHIPFLOW) and compared to the results obtained during the experimental tests. The bare hull model studied is the Duisburg Test Case (DTC), developed at the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) for benchmarking and validation of the numerical methods. Hull geometry and model test results of resistance, conducted in the experimental facility at SVA Postdam, Nietzschmann, in 2010, are publicly available. A comparative analysis of the numerical approach and experimental results is performed, related to the numerical simulation of the free surface viscous flow around a typical container ship. Further, a comparative analysis between the results provided by NUMECA, ANSYS and SHIPFLOW is performed. Regarding the solution obtained, a satisfactory agreement between the towing test results and the computation results can be noticed. The minimum mean error was obtained through the SHIPFLOW case, 2.011%, which proved the best solution for the case studied.

Danube River represents a critical axis of ecological and economic importance for the countries along its course. From this perspective, this paper aims to assess the most significant characteristics of the river and of its main tributaries, as well as its impact on the environmental sustainability and socio-economic development. Navigation and the economic contribution of the Danube River are the key issues of this work, emphasizing its importance as an international transport artery that facilitates trade and tourism, and develops the energy industry through hydropower plants. The study includes an analysis of the volume of goods transported from 2019 to 2023, as well as an analysis of the goods traffic in the busiest port on the Danube. Furthermore, climate change affects the hydrological regime of the Danube, as well as the ecosystems, economy, and energy security of the riparian countries. Main impacts include changes in the hydrological regime, increased frequency of droughts and floods, reduced water quality, deterioration of biodiversity, and disruption of the economic activities dependent on the river, such as navigation, agriculture, and hydropower production. Thus, hydrological risks and challenges are investigated, focusing on the extreme events of the last two decades and the awareness of their repercussions. In this context, the national and international institutions responsible for monitoring and managing the Danube are presented, and their role in promoting a sustainable river policy is explored. Methods and technologies are shown to be essential tools for monitoring and prediction studies. The Danube includes an extensive network of hydrometric stations that help to prevent and manage the most significant risks. Finally, a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis of the development of the hydrological studies was conducted, highlighting the potential of the river.

Reducing the added resistance in waves has become a crucial aspect of today’s ship design. The added resistance in waves is traditionally considered proportional to the square of wave height. However, this assumption is believed to be only partly valid, and further investigations are required. In the present study, experimental tests and numerical simulations were carried out to determine the added resistance in regular head waves of the DTC hull (the scale factor is 135). The numerical analysis was performed with SHIPFLOW 7.01, and the experimental campaign was carried out in the ETSIN-UPM towing tank. The investigation revealed that the added resistance in waves was not proportional to the square of the wave height, and a better correlation was obtained by changing the power of the wave weight to 1.75. Furthermore, an unexpected double resonance phenomenon on the added resistance was found at a Froude number of 0.13. The study also revealed an acceptable agreement between the numerical simulations and the experiments, except for the double resonance phenomenon.