Offshore wind energy production is increasing rapidly and optimising the design of support structures has the potential to significantly reduce steel and costs. Jacket structures are commonly selected for deeper waters, and the design of these structures is primarily influenced by the fatigue performance of the tubular joints. The fatigue resistance of these joints can typically be evaluated using different stress assessment methods, each associated with a corresponding S-N curve. While the Hot Spot Stress (HSS) approach is commonly used for design purposes, the Effective Notch Stress (ENS) approach offers higher accuracy by taking into account the stress concentration originating from the weld profile. Consequently, the ENS approach has the potential to provide less conservative fatigue life estimations, leading to the reduction of steel and costs. However, the application to and research of the ENS approach for tubular joints is limited. Therefore, the objective of this thesis is to investigate the application of the ENS approach on a tubular joint. The research was divided into three parts, including an investigation on the required FE mesh, a study on sub-modeling of the ENS approach and a comparative analysis on the fatigue life predictions between the HSS and ENS approaches.

The FE mesh required for the ENS approach was evaluated on a cruciform joint according to the DNV-RP-C203 validation methodology and the Stress Concentration Factors (SCFs) values obtained for different mesh configurations were compared. Two mesh variants were developed, and different element sizes in the notch were evaluated. The results show that with a maximum element size in the notch equal to 0.39 mm, according to DNV, unacceptable SCF errors are obtained of -4% and 4%. Furthermore, with a maximum notch element size of 0.25 mm, according to IIW, SCF errors of -0.3% and -2.2% were obtained, indicating that accurate results can be obtained but are not guaranteed. Additionally, the accuracy of the mesh was found to be primarily influenced by the number of nodes surrounding the notch, rather than the size of the elements in the notch.

The accuracy of sub-modeling for the ENS approach on a tubular T-joint was evaluated by varying global modeling choices and sub-model sizes. The accuracy was measured by comparing sub-modeling stress results against those from a global T-joint FE model with the ENS approach applied. The results show that a global model composed of 3D elements with a weld profile that corresponds to the sub-model is recommended. Simplifying the global model by excluding the weld profile or using 2D elements has been found to provide inconsistent and inaccurate results. Moreover, a sub-model of the weld area with a size as small as 1.67 degrees of the brace radial angle has been found to provide consistent results. Thereby, sub-modeling reduces the required mesh size by a factor of 15, compared to the global modeling approach. Additionally, a rather surprising maximum principal stress error of approximately -6% was observed as a result of sub-modeling for all varied load types and sub-model sizes.

A comparative study between the HSS and the ENS approach was conducted for the computed fatigues of a tubular T-joint. Various FE models were composed for the T-joint subjected to different load cases, and equivalent SCFs were computed by introducing a correction factor based on the S-N curves of both approaches. The results show that the ENS approach provides a lower computed fatigue life over the HSS approach when applied to a tubular joint. This discrepancy is attributed to the FAT225 S-N curve, used for the ENS approach, which is not tailored for tubular joints but for welded straight plates. For the HSS approach, the choice of element type (2D vs 3D) and the inclusion of a weld profile have a significant effect on the stress distribution and the resulting fatigue life prediction. It was found that a model consisting of 3D elements with the inclusion of a weld profile yields the longest computed fatigue life for a tubular joint.

To conclude, the application of the ENS approach was investigated for a tubular joint, by evaluating the mesh sensitivity, examining the accuracy of sub-modeling and comparing the computed fatigue lives with those from the HSS approach. Further research is recommended to improve the computational efficiency of the ENS mesh and to achieve a deeper understanding of the -6% error found by sub-modeling. Additionally, the development of an S-N curve tailored for tubular joints is suggested to improve the accuracy of the ENS approach for this type of joint.
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Over the last years, the urge to reduce the world’s air pollutants is rapidly growing. New possibilities in order to replace fossil fuels have been explored and one of them is the usage of green hydrogen. The Argentinian, North Patagonian, province of Río Negro, has a great potential to generate green hydrogen on a large scale, due to the available natural resources. Therefore, the province is ambitious to contribute in the developing worldwide sustainable energy market by producing and exporting green hydrogen.
Argentina is located at a large distance from the expected green hydrogen sales market in Europe and Asia. In order to reach competitiveness with respect to other future hydrogen ports, the use of a Free-Trade Zone (FTZ) is considered. This is a delimited territory within a country in which tax benefits can be enjoyed. The Province of Río Negro is considering three different locations for a potential green hydrogen export port:

- Punta Colorada Muelle, is an old iron ore export port that is out of operation since 2016. It is located within a FTZ. The deteriorated dry bulk jetty could potentially be reused by accommodating the liquid bulk loading infrastructure.

- Punta Colorada South, is a location roughly one kilometre south of old iron ore export port and is also located within a FTZ.

- Puerto Lobos, is located on the border of the provinces of Río Negro and Chubut. It has potentially favourable bathymetric and hydrodynamic characteristics.

The following main research question is formed:
”Which location between Punta Colorada Muelle, Punta Colorada South and Puerto Lobos is the most suitable for a potential hydrogen export port in Río Negro?”
A conceptual qualitative Multi-Criteria Analysis is executed to compare the locations. In order to complete this analysis, firstly the hydrogen export port requirements and criteria are defined. Subsequently, primary and secondary data is collected. The primary data consists out of fieldwork surveys, including a topographic analysis, a hydraulic analysis and a structural analysis. The structural analysis is completed solely on the existing jetty at Punta Colorada Muelle, in order to create an understanding of the current state of the jetty. Furthermore, interviews are conducted with the director of the Maritime and Fluvial Research Center (CIEMF), the executive director of investment agency of the Government of Río Negro, and an ex-employee of the previous mining company at Punta Colorada Muelle. Secondary data on all locations is gathered through literature studies and presented documents from stakeholders.

With data from the field survey several detailed maps are made. A bathymetry map shows the sea bed profile from Punta Colorada Muelle until Punta Pórfido. A topographic map shows the ground level elevation for Punta Colorada Muelle. An interactive map of the jetty is made which contains all the gathered photographs of the structural components and indicates their level of corrosiveness. Next to that the stakeholders are displayed in a power-interest diagram.

Due to the limited information and the quality of the information that was gathered at Puerto Lobos no fair comparison between the locations can be made. Both locations at Punta Colorada have potential to construct a green hydrogen export port. The jetty at Punta Colorada Muelle has the potential to be used in the short-term if it is restored. Punta Colorada South has the advantage that potential future port operations will not depend on dated infrastructure. Next tot that there is no interference with the iron ore port authority. Puerto Lobos has the disadvantage that there is no FTZ and that is situated adjecent to a marine protected area.

To properly compare all three locations, bathymetric and aerial surveys that were completed at the Punta Colorada locations will need to be repeated at Puerto Lobos. To create a more definitive conclusion on any location, additional research like a CPT and an in depth analysis of the structural capacity of the jetty is required.

From the bathymetric surveys another potentially interesting location was found in Punto Pórfido. It is recommended this location is researched further.

Three alternative scenarios for phasing the port construction and operation are presented. These scenarios differ in permanent, temporary or no use of the current jetty at all. ... Read more