Multi-body hydrodynamics featuring mutual interaction and contact between rigid or flexible floating bodies is an active area of research for complex marine engineering devices. An example refers to offshore supply vessels, where it is important to consider operations in close proximity of other vessels or structures, e.g. the landing manoeuvre of the vessel at an offshore foundation (Luo-Theilen and Rung 2017). Other examples, which are subject to significant hydrodynamic interaction forces, are the simulation of ship collisions (Rudan and Volari´c 2016) and the collision between ice floes and an ice-cruising vessel (Janßen et al. 2017). Particularly due to safety reasons, it is essential to know and to understand the flow field around moving bodies, the arising hydrodynamic forces and the resulting body behaviour within decisive marine operations already in the design process. While not all aspects can be captured economically within analytical or experimental examinations, numerical simulations are meanwhile established as a reliable design tool. Due to the continuous technological progress of numerical hard- and software, computational fluid dynamics (CFD) nowadays provides the opportunity to investigate complex marine procedures prior to critical incidences. Especially viscous CFD methods give an extensive insight into the occurring physical phenomena. Industrial viscous flow simulations often follow a finite-volume approach. However, fluid dynamic simulations of multiple floating bodies, which feature large relative motion, are still challenging using these grid-based Eulerian methods. In this regard, overset-grid methods offer a versatile approach. They simplify the grid generation by using modular grid components and at the same time often improve the grid quality. The technique comes at the expense of (a) an elaborate priority management and cell blanking for regions covered by multiple grids, (b) a challenging interpolation-based coupling between disjunct grids and (c) complex dynamic load balancing efforts for parallel applications. All these algorithmic challenges require efficient search algorithms used to manage the grid connectivity (Hadži´c 2006, Löhner 2008, Brunswig and Rung 2013). Many industrial CFD applications are based on unstructured-grid finite-volume methods and employ a co-located, cell-centred variable arrangement. A common implicit approach to couple multiple unstructured three-dimensional grids in a cell-centred scheme is to interpolate neighbouring field values onto the partner grids, which creates an implicit link between the grids on the level of the equation system. Since an interpolation-based coupling procedure is restricted to local information, it is insufficient to guarantee that the global sum of the mass fluxes across the overlapping interfaces vanishes. A simple example refers to the exterior surface of a foreground 1 1 Introduction grid, which is fully embedded in the interior of a background grid, cf. the schematic representation on the left-hand side of Figure 1.1. The arrangement implies that the sum of the mass fluxes along the exterior boundary of the foreground grid must vanish, which cannot be guaranteed by an interpolation-based grid coupling without dedicated corrections. Consequently, such overset-grid approaches violate the inherent mass conservation of finite-volume methods. This issue is of significance for both the global mass balance of the entire simulation as well as the local balance of each domain. In this context, the blanked area within the background domain yields additional boundary fluxes (displayed on the right-hand side of Figure 1.1) which also contribute to the mass balance. Due to the fact that incompressible finite-volume methods directly use the mass defect when solving for the pressure, severe pressure fluctuations can be provoked. Figureweiterlesen