Large-diameter monobucket foundations are a promising alternative for offshore wind turbines in cases where monopiles are not suitable. However, during installation, the induced underpressure leads to compressive stresses in the thin-walled shell, making these structures susceptible to buckling. This is further amplified by the need for slender designs to remain cost efficient. This study investigates an alternative monobucket geometry in which the cylindrical shell is replaced by a segmented configuration composed of multiple curved sections. Two concepts are studied: the Outward Segmented Bucket (OSB) and the Inward Segmented Bucket (ISB). These geometries either increase local curvature or fundamentally alter the load application, both with the aim of improving buckling resistance.

A two-step finite element approach is applied, consisting of Linear Buckling Analysis (LBA) and Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA). The results show that segmented geometries achieve significantly higher buckling capacities, compared with a conventional cylindrical design. For OSB configurations, this improvement is driven by the increased local curvature, for which a clear relationship with the limit pressure is observed. In contrast, ISB configurations exhibit a different failure mechanism, where buckling is governed by local instabilities at segment edges due to stress concentrations, rather than global buckling. Furthermore, the results show that the buckling limit strongly depends on the eigenmode used as an imperfection, and that higher-order modes should also be taken into account. The improved buckling performance allows for substantial reductions in required shell thickness, demonstrating clear material and thus cost savings.

For the installation of suction pile jackets, a new installation method initiated by SPT Offshore could extend the allowable size for suction pile jackets used as foundations for offshore wind turbines. This method involves installing the suction piles separately from the jacket frame. First, the suction piles are installed on the seabed. Then, the jacket frame is placed on top of the suction piles, and the piles and the frame are connected. The installation of the suction piles in the seabed requires a certain level of precision to ensure a proper connection with the jacket frame. This can be achieved by introducing an installation tool called the suction pile installation template (SPIT). The goal of this thesis is to take the first steps towards realizing the SPIT installation method by designing the suction pile installation template and identifying key design challenges for the SPIT.
To bound the scope of the research, assumptions are made regarding the installation vessel, foundation dimensions, jacket-pile connection, and site specifications based on a case study and the resources of DEME. To design the SPIT, the use of the SPIT is analysed, considering a wide range of design options. The most significant inputs to the analysis are the limitations of the installation vessel and operational efficiency. Next, the changes to the suction pile and jacket frame are examined. The selected grout connection between the suction pile and the jacket frame creates a jacket frame similar to a standard pin pile jacket. The suction pile requires a stub on top of the top-plate. An optimization study is conducted to determine the size of the stub. These two analyses provide the general design requirements for the SPIT, which is then checked for structural strength, installation tolerance of the suction piles and lift capacity. The checks are based on industry standard codes.
Analysis shows that the hydrodynamic loading on the suction piles induces the largest loads on the SPIT. However, if the suction piles are incorrectly placed in the seabed, the interaction between the soil and the suction piles could result in even larger loads on the SPIT. The models used in this thesis should provide conservative estimates. In future research, the analysis of hydrodynamic loading, geotechnical analysis, and dynamic response of the SPIT should be verified and justified using more sophisticated models and/or simulation software.
The results from this thesis indicate that the proposed design of the SPIT provides a solution to extent the installation of SPJ for OWT. The research identifies four key design challenges. Each challenge indicates solvable obstacles to the design of the SPIT. Based on the results, the estimated total weight of the SPIT is 240mt. DEME's installation vessel, the Orion, has sufficient lift capacity to perform the installation and deck-space to perform up to 13 installations in one trip.