This paper deals with the hydrodynamic sideforce production of a wind-assisted ship. The subject is introduced, both in physical terms, and with an overview of current and recent work. The importance of the hydrodynamic sideforce is established, before classical models are reviewed. Finally, the complications arising from diverse appendage topologies are discussed, and a theory for zero-aspect ratio lifting surfaces is discussed. The paper concludes with a short summary of ongoing work.@en

Wind propulsion for commercial ships has been identified as a key component in the energy transition for the maritime industry. The sailing hybrid ship will operate with leeway (drift) angles to produce a lateral force known as sideforce, for steady operation under sail. In this paper, experimental results for the sailing performance of ships fitted with bilge keel appendages are presented. Systematic variations in appendage height, length, and position were tested, including several special cases (multiple bilge keels). The appendage typology is shown to mitigate the strong ‘destabilizing’ yaw moment that is characteristic of wind-assisted commercial vessels and to promote the non-linear sideforce component. The working principal for bilge keels—promotion of flow separation—can be employed to specify the separation location for components of the vessel vortex wake to improve the sailing performance of the ship.@en

Wind energy as an auxiliary form of propulsion for commercial ships has again become of great interest as a possible response to volatile fuel prices and increasingly stringent environmental regulations. A well-founded performance prediction tool is a key prerequisite for the further development of this promising technology, and with the support of the European Commission and others, a group of researchers at Delft University of Technology is developing a performance prediction program for these hybrid ships. Reynolds-Averaged Navier Stokes (RANS) packages will be one of the primary tools used during the study. The advent of the numerical towing tank brings possibilities but also new challenges. The predominance of large, separated flow structures in the wake of the sailing ship, and the particular interest in the transverse force component points to a conscientious grid verification and validation study. Here, it is sufficient to achieve parity for absolute uncertainty within the larger context of the project. The ‘drift sweep’ procedure is presented with validation levels alongside computational time to demonstrate the utility of this approach in support of the derivation of empirical formulations using systemic hull form variations. Finally, a moving mesh for the rudder may be implemented in an extended drift/rudder sweep. However for this case there is no validation data presently available.@en

A Reynolds-Averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for Wind-Assisted commercial ships. The modelling challenge presented by large separated flow structures in the wake of the sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ship sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Four hull geometries were selected to represent of the Delft Wind-Assist Systematic Series. Appended cases were designed to represent a broad range of appendage topologies: Rudder, Bilge-keels, Skeg, and Barkeel. The direct validation exercise for the bare-hull case was successful, with the validation level for the sideforce equal to 9.5% (fine mesh: 9M cells). An extended validation statement is made for simulations for the entire series. This exercise was successful for leeway angles equal to 훽훽=[3표표,6표표]. The validation level (base mesh, 3M cells) for each force component is:푢푢푋푋′=12%, 푢푢푌푌′=17%, 푢푢푁푁′=10%. The validation for appended geometries was not regarded as successful, with the exception of the Rudder case. The numerical uncertainty is the dominant contribution for the validation level, motivating a proportionate refinement of the grid. Here, it is sufficient to achieve parity with other contributions to the uncertainty within the larger context of the project.@en

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper describes the simulation verification exercise, performed in support of the experimental validation presented in Part 1 of this two-part series describing the RANS-CFD method employed in this research. The predominance of large-scale separated flow structures in the wake of the sailing ship, an artefact of sideforce production necessary for sailing, points to a careful verification exercise and estimate for the numerical uncertainty to support the systematic investigation of wind-assisted ship hydromechanics and meshing guidelines within the available computer resources. Methods for CFD uncertainty quantification are defined and implemented for verification cases at leeway angles equal to 0ᵒ, 6ᵒ, and 9ᵒ. Analysis for four sets of grids with different meshing strategies and for varying time steps results in a grid definition and time step for simulation validation. Numerical uncertainty as adopted in Part 1 for validation is defined. Finally, the meshing strategy for full-scale simulation is described, as used for the production runs of the Delft Wind Assist Series.@en

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper describes the simulation verification exercise, performed in support of the experimental validation presented in Part 1 of this two-part series describing the RANS-CFD method employed in this research. The predominance of large-scale separated flow structures in the wake of the sailing ship, an artefact of sideforce production necessary for sailing, points to a careful verification exercise and estimate for the numerical uncertainty to support the systematic investigation of wind-assisted ship hydromechanics and meshing guidelines within the available computer resources. Methods for CFD uncertainty quantification are defined and implemented for verification cases at leeway angles equal to 0ᵒ, 6ᵒ, and 9ᵒ. Analysis for four sets of grids with different meshing strategies and for varying time steps results in a grid definition and time step for simulation validation. Numerical uncertainty as adopted in Part 1 for validation is defined. Finally, the meshing strategy for full-scale simulation is described, as used for the production runs of the Delft Wind Assist Series.@en

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper is Part 1 of a two-part series describing the RANS-CFD method adopted for this study. The modelling challenge presented by large separated flow structures in the wake of a sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ships sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Appended cases were designed to represent a broad range of appendage typologies: Rudder, Bilge-keels, Skeg, and Barkeel. A validation statement is made for simulations for the entire bare-hull series and for appended geometries, excepting the Bilge-keel case. The simulation method is described in Part 2, including the assessment of the numerical uncertainty.@en

In this paper, a vessel model for the performance of wind-assisted ships is combined with a routing tool to assess the fuel savings available from the installation of both one and two Flettner rotors when travelling along a Great Circle Route path. This is combined with an economic analysis to assess commercial viability for these hybrid concepts. The case study is performed in collaboration with DAMEN shipyards, who have provided a design for a wind-assist concept to sail in the Baltic Sea, that, since January 2015, is an Emission Control Area where a sulphur limit content of 0.1 % is enforced on the ship fuels. Results for this case study are presented in terms of fuel savings and payback period analysis, where the reference case is an identical ship sailing without wind propulsors. For the 5,150 dwt general cargo vessel travelling at a speed of 10 knots, average fuel savings of 2.99% were obtained in the Baltic Sea for the single Flettner scenario, and 6.11% for the double Flettner scenario. A discussion of key engineering and design constraints for these ships is included.@en

Development of a Performance Prediction Program for Commercial Ships@en