Modular Floating Structures (MFS) have emerged as an innovative alternative for sustainable offshore urban development, providing a response to the multifaceted challenges posed by coastal urban expansion: significant urban growth and coastal migration, increasing sea-level rise exposure and land scarcity. This thesis presents a geographically oriented exploration of the global technical and motivation potential of MFS – in maximum achievable suitable area, offshore population and material demand -, integrating technical, environmental, and demographic factors through a comprehensive GIS analysis. The methodology of this analysis involves the following key steps: 1) Establishing the Service Limit State (SLS) technical potential map by considering the natural constraints bathymetry, average wave energy, average wind speed, and hurricane risk; 2) establishing the Ultimate Limit State (ULS) technical potential map based on the SLS map and the extreme value constraints 100-year return significant wave height and 100-year return wind velocity; 3) establishing the ocean planning technical potential based on the ULS map and integrating the ocean planning constraints marine protected areas and shipping routes; 4) establishing the motivation potential maps, which are based on the outcomes of steps 1, 2, and 3 and the proximity to a coastal city as a key motivation factor; 5) evaluating additional motivation layers to reveal where potential driving forces are for floating urban development within local contexts. The maps lead to first estimates of maximum suitable area and offshore population, guiding calculations for required materials in floating breakwaters, proposed as reused end-of-life (EOL) ships, and MFS substructures. This thesis uncovers several insights. The use of Geographical Information Systems (GIS) in this field enables the exploration of the technical potential of offshore urban development, offering first estimations for total area, offshore population, and material use (specifically EOL ships and steel). On a global scale, about 84000 km2 are suitable for MFS implementation, potentially accommodating up to 1.6 billion people. These results demonstrate the potential to contribute significantly to climate-adaptive housing capacity. If the entire technical potential were to be realized the global demand for EOL ships would be approximately 261000, a demand significantly exceeding the current in-use global merchant fleet by nearly threefold. The global steel demand for the construction of the MFS substructures would be 26 billion tons, a vast amount that exceeds the annual global steel demand by about 20 times. These vast numbers may significantly impact the ship-breaking industry and global steel flows. These insights provide valuable perspectives on MFS implementation, holding the potential to significantly contribute to climate-adaptive housing capacity, however raising critical questions about sustainable material consumption and production. This research unfolds new possibilities in the field of sustainable offshore urban development and serves as a launchpad for further large scale exploration and analysis in this dynamic area of research. Future research could further assess the sustainability of offshore urban development, building upon the findings of this thesis. Potential areas of investigation include for example comparing material requirements for MFS substructures to those of land-based building substructures or conducting micro, meso or macro-scale scenario-based Material Flow Analysis (MFA) to evaluate the influence on the global steel flow and ship-breaking industry, using the technical potential estimates presented in this thesis on local and global scale as a foundational reference.

Coastal communities around the world are facing significant challenges such as erosion, flooding, and storm surges. These issues highlight the need for nature-based coastal management solutions that can help mitigate the negative impacts of these events. Coastbusters Consortium developed such a solution in the North Sea. This solution is a system that utilizes a bivalve long line approach, where blue mussels are allowed to grow and eventually attach to the seabed, forming a reef structure that can help induce natural accretion of sand, attenuate storm waves, and reinforce the foreshore against coastal erosion. This reef structure can help to enhance coastal protection and reduce the impacts of these significant challenges on coastal communities. To enhance the current long line system, it is imperative to develop numerical models that can accurately predict the forces acting on the slender cylinders in current and waves. One approach to this is to use the Morison equation, which accounts for both drag and inertia force. However, there is a lack of understanding regarding the drag and inertia coefficients in the literature that are used in the Morison equation. To address this issue, the present research conducts three experiments on a 3D-printed model of a dropper line, at a one-to-one scale, in a towing and wave tank. To treat the dropper line as a cylinder, a characteristic diameter is used. The 3D model is developed based on a thorough evaluation of the existing dropper lines at De Panne. These experiments aim to determine the drag and inertia coefficients for the dropper line in different steady and oscillatory flows, which can aid in the design of more efficient and effective bivalve aquaculture systems and integration into numerical models. To determine the drag coefficient of the current towing experiments were conducted and forced oscillations and waves experiments were conducted to determine the drag and inertia coefficient in waves. The parameters used were based on the current and wave regimes at De Panne, and were expressed in terms of Reynolds and Keulegan-Carpenter numbers. The results showed that for continuous current, the drag coefficient of a dropper line containing blue mussels was determined to be $C_D$ = 1.2 for Reynolds numbers between $3.0*10^4$ and $1.0 *10^5$. In oscillatory flow, the drag coefficient varied between $C_D$ = 2.3 - 3.5, and the inertia coefficient varied between $C_M$ = 1 - 2.5 for Keulegan-Carpenter numbers between KC = 5 - 28. The experiments conducted in this study included evaluations of the characteristic diameter and shape of the dropper line. Results also showed that a difference existed between the coefficients obtained from the forced oscillation and wave experiments. Possible explanations for this difference were investigated, including free surface effects and flow differences. The results obtained from this study can be applied to the design of bivalve aquaculture systems and their integration into numerical models. These findings contribute to improving the efficiency and effectiveness of nature-based coastal management strategies for mitigating the effects of erosion, flooding, and storm surges on coastal communities. Further research is needed to fully understand the complex dynamics of the bivalve long line system and its interactions with the coastal environment.