abstract: This thesis focuses on studying the interaction between floating objects and an air-water flow system driven by gravity. The system consists of an inclined channel in which a gravity driven two phase flow carries a series of floating solid objects downstream. Numerical simulations of such a system requires the solution of not only the basic Navier-Stokes equation but also dynamic interaction between the solid body and the two-phase flow. In particular, this requires embedding of dynamic mesh within the two-phase flow. A computational fluid dynamics solver, ANSYS fluent, is used to solve this problem. Also, the individual components for these simulations are already available in the solver, few examples exist in which all are combined. A series of simulations are performed by varying the key parameters, including density of floating objects and mass flow rate at the inlet. The motion of the floating objects in those simulations are analyzed to determine the stability of the coupled flow-solid system. The simulations are successfully performed over a broad range of parametric values. The numerical framework developed in this study can potentially be used in applications, especially in assisting the design of similar gravity driven systems for transportation in manufacturing processes. In a small number of the simulations, two kinds of numerically instability are observed. One is characterized by a sudden vertical acceleration of the floating object due to a strong imbalance of the force acting on the body, which occurs when the mass flow of water is weak. The other is characterized by a sudden vertical movement of air-water interface, which occurs when two floating objects become too close together. These new types of numerical instability deserve future studies and clarifications. This study is performed only for a 2-D system. Extension of the numerical framework to a full 3-D setting is recommended as future work. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2018

Abstract   Background The sea levels have risen about 10 cm since 1993 and will continue to rise due to global warming along with the expected increase in population. The rise will decrease the available landmass for settlements and raw material production. The increasing population needs to fit in an increasingly smaller area on a planet covering 30 % of the earth's surface, the rest is water. The covered area will increase as the ice caps covering the poles melts due to global warming. One solution to settle this increasing population would be on man-made floating islands on the sea around already established major cities. This would create an artificial increase in available dwelling space for people to live without covering more of the decreasing land. Stockholm tiny house expo is an organization that wishes to build a self-sustaining floating island in the Stockholm archipelago.   Objectives The objectives of this thesis are to analyze already present structures and how they have solved problems regarding anchoring permanent floating structures. From these, a few solutions will be presented regarding how a yet-to-be-built, man-made island could be securely anchored in Stockholm’s archipelago. In addition to anchoring, there exists a conceptualized desire to rotate the island to extract as much solar energy over the duration of the day. By rotating the island in sync with the sun, the efficiency of the solar cells will increase by decreasing the solar incident angle when striking the photo-voltaic throughout the day. This is one small step towards creating a larger island aimed to become a symbol for the EU: s sustainable development goals. Finally, different solutions will be presented allowing the island to be securely anchored while still being able to rotate.    Methods Design thinking was the method of choice because of the creative and innovative aspects of the project. Design thinking provides inspiration and ideas from already present technology to be gathered and compared to each other. The iterative nature of design thinking aided in discovering ideas while problems occurred. Information gathering was conducted through mainly tech- and trend-watching since existing technology on the market can be modified to suit the problem. Solutions and products in markets adjacent to maritime technologies were explored to gain broader inspiration in accomplishing rotation of the island. Interviews were conducted with the customers to gather enough information for the need-finding as well as using personas. Design decisions were supported by Pugh and Quality Function Deployment (QFD) matrices.    Results The results proposed three potential solutions to rotate the island with one proven insufficient after a deeper investigation. The two remaining solutions were believed to be sufficiently capable of withstanding the forces acting upon the island from the wind and waves. The second concept presented rotates the island through a gearbox situated in the island's center of mass. This solution requires the island to be rigidly anchored, so the rotation has something to push against. The final concept utilizes as many off-the-shelf components as possible and creates a rotational torque with traditional outboard boat motors. This solution is anchored with ropes or chains and traditional anchors used for houseboats or floating bridges.     Conclusions. The conclusion is that the rotation should be avoided since the benefit of aiming the solar panels towards the sun does not outweigh the energy costs of rotating the whole island. Instead, the focus should be on either rotating the solar panels individually or storing the energy gathered during the day. If the rotation is still desired, the traditional boat motors would be the choice based on reliable products and technology existing in today's market and their ability to counteract the forces caused by the wind.