In the last century, the offshore industry has installed a network of offshore pipelines in the southern North Sea. Due to decreasing oil and gas extraction in the North Sea, many pipelines of this network are becoming redundant. A potential option for the reuse of these pipelines is the transport and storage of gaseous hydrogen, which is increasingly considered as an attractive energy carrier for a fossil fuel free economy. A Shell study has shown that offshore hydrogen production located at a renewable energy source, such as an offshore wind park, can economically compete with onshore hydrogen production that uses power cables to transport the energy to shore. The offshore hydrogen production case is based on newly built pipelines. If it is technically feasible to use existing pipelines, this can contribute to making the offshore hydrogen production case more attractive. A transition from hydrocarbon transport to hydrogen transport through existing carbon steel gas pipelines changes the material behaviour of the pipeline, including a change in fatigue behaviour. Fatigue damage due to Vortex-induced vibrations (VIV) in offshore pipeline parts that are suspended above the seabed is a major challenge for oil and gas transportation in the southern North Sea. Therefore, it is of great importance to understand the change in fatigue behaviour due to the presence of gaseous hydrogen to assess the technical feasibility of hydrogen transport through the existing offshore pipelines. A fatigue analysis for a specified existing gas pipeline of the NAM in the southern North Sea has been done according to DNV Free Spanning Assessment Methodology. For this analysis, the fatigue SN-curve for carbon steel material in a hydrogen environment is required. The SN-curve is approached based on available fatigue data for carbon steel material in hydrogen and severe sour environments. It shows that hydrogen has a significant influence on the fatigue behaviour of carbon steel material. The fatigue analysis outcomes show that adjustments to the pipeline are needed to avoid a significant increase in the risk of fatigue failure in critical pipeline sections. A remediation analysis has shown that rock dumping comes out as the cheapest option. An existing time-domain numerical model that can determine the dynamic behaviour of a pipeline due to VIV is extended to perform fatigue damage calculations. The pipeline is modelled as a Euler-Bernoulli beam using the Finite Element Method. The model determines the VIV with a modal analysis in time-domain, which allows the model to include non-linear soil behaviour. The fatigue damage is determined for each pipeline element, which gives the fatigue damage distribution over the length of the pipeline. The time-domain numerical model is compared with the DNV Free Spanning Assessment Methodology and gives significantly higher fatigue lives. This suggests that the methodology that is used for the fatigue analysis is too conservative. However, there is still uncertainty about the influence of parameters predicting VIV. Further calibration of the model is required to ensure that the model outcomes correspond with target failure probabilities regarding industry standards. The general conclusion of this research is that the specified existing offshore gas pipeline of the NAM is technically suitable for the transport of hydrogen if the adjustments are conducted. Compared to newly built pipelines, hydrogen transport through existing pipelines is an attractive option due to relatively low adjustments costs.

The main goal of this project is to determine the optimal location for an OTEC installation with a minimum lifespan of 30 years off the coast of Barranquilla and to make an anchor mooring design for the floater on which this installation is located. Bluerise has identified an area near the coast of Barranquilla for which OTEC can be applied. This area is situated within Colombia’s territorial waters (within 12 nautical miles, or 22.2 kilometres), where two locations have been identified by Bluerise: Location 1: 11.2028 latitude, -75.0003 longitude, Location 2: 11.2772 latitude, -74.9208 longitude. Environmental conditions - The daily wind direction is NE-ENE. There is no clear extreme wind direction. The daily waves have a dominant Northeast direction while the extreme waves have a dominant Northern direction. The extreme waves are generated far north of Barranquilla by very high wind speeds which explains the relatively high extreme significant wave heights in the area and the relatively low extreme wind speeds. The yearly average (nautical) surface current direction at the two possible floater locations is predominantly south or southeast. The top 20 strongest current speeds in the past few decades have come from the west or southwest however and therefore these are the normative current directions. The environmental conditions are equal for both possible floater locations. A temperature difference of 20_C is reached at warm water intake and cold water intake depths of 30 and 763 meters, respectively. The depths at which a temperature difference of 22_C is reached are 36 and 1023 meters (with temperatures of 27 and 5 degrees, respectively). The influence of the Magdalena river and upwelling is concluded to be negligible. Marine traffic - The two locations with safety zones are located in a traffic-dense area. The area is getting more traffic intense in the upcoming years. However, it will not pose an immediate threat to the operation. As location 2 has slightly less traffic, it would be preferable from a safety point of view. Seawater intake- and return pipes - Assuming a cold seawater intake temperature of 5C and a warm seawater intake temperature of 27C, the intake pipe lengths become 1023 and 36 meters, respectively. Based on the equation of state, the mixed water return flow pipe length becomes 130 m. At this depth, the effects of a difference in density between the surrounding seawater and the mixed returned water are minimized. Also, the depth is outside of the euphotic zone which minimizes algae growth. If the intake water is higher than 27 degrees, the discharge temperature will have a higher temperature. Calculations with the Equation of State reveal that the warmer the discharge temperature, the lower the density of the discharge water is. Whenever the discharge temperature is higher than the output temperatures, less depth is needed in order for the discharge water to be naturally buoyant. As the intake temperature fluctuates throughout the year, it is therefore advised to design the length of the discharge pipe at 120 meters. Anchor mooring design - The proposed anchor mooring design consists of a spread-moored 4x3 taut mooring system. The lines are composed of three parts: a 50 meter chain connected to the ship, a 1290 meter fibre line part and another 150 meter chain at the end that is connected to the anchor. The floater is positioned in a 58,05 angle with respect to the north in a northeast direction. This ensures comfortable operation during daily conditions and will reduce fatigue build up. The hurricane conditions were found to be governing. The design complies with the basis of design stated in section 5.3 and with the DNV-OS-E301 code and the API Recommended Practice 2SK.