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

The coupling between heel and the loads in the horizontal plane is usually neglected in manoeuvrability studies. However, the heel–sway and heel–yaw coupling can play an important role in potentially unsafe conditions, such as in a following sea. In these conditions, small fast vessels experience dynamic instabilities which threaten their ability to maintain a straight course. In this study, the coupling between the static heel and the sway force and yaw moment was investigated for a high-speed craft. The objective of this work is to understand the effect of heel on the manoeuvring in following waves, and to predict this effect by means of numerical tools for different combinations of wave characteristics and vessel speeds. A dedicated captive model test campaign was conducted to evaluate the manoeuvring loads in sway and yaw when the craft has a heel angle in following regular waves. The tests were performed in the towing tank of Delft University of Technology. The heel-induced loads depend strongly on the longitudinal position of the vessel in the wave, and they significantly differ from the heel-induced loads in calm water at the respective speed. The data carried out in the model tests were used to describe empirically the heel-induced loads for several combinations of ship speeds and wave characteristics. This empirical description was meant to correct a 3D potential flow boundary element method (BEM), with the objective of being able to predict these loads on a wide range of conditions. The corrected 3D BEM was used to simulate the behaviour of the high-speed craft in following regular waves. This analysis showed that the heel-induced loads have the effect of stabilizing the ship to the inception of dynamic instabilities in the following sea.@en

Flettner rotors are nowadays becoming a widespread solution for wind-assisted propulsion. To increase the fuel savings of the ship on which they are installed, multiple devices are typically used. However, in the performance estimate of these hybrid ships, it is currently assumed that Flettner rotors operate independently, regardless of the number of devices employed and their relative position on the ship's deck. The present investigation deals with a wind-tunnel experimental campaign aimed at understanding the aerodynamic interaction effects on the performance of two similar Flettner rotors. The study indicates that the aerodynamic performance of the two Flettner rotors is affected by their interaction, and, generally, this is most noticeable when the devices are set closer to each other and when they are aligned with the wind direction. It is demonstrated that, depending on the apparent wind direction, the layout of the Flettner rotors on the ship's deck has a remarked influence on the driving and heeling force coefficients of the entire rig. Lastly, the velocity ratio is found to play a key role in the determination of how the interaction affects the Flettner rotor aerodynamic performance.

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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 0^ᵒ, 6^ᵒ, and 9^ᵒ. 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.

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Experiments on a large-scale Flettner rotor were carried out in the boundary-layer test section of Politecnico di Milano wind tunnel. The rotating cylinder used in the experimental campaign (referred to as Delft Rotor) had a diameter of 1.0 m and span of 3.73 m. The Delft Rotor was equipped with two purpose-built force balances and two different systems to measure the pressure on the rotor’s outer skin. The goal of the experiments was to study the influence of different Reynolds numbers on the aerodynamic forces generated by the spinning cylinder. The highest Reynolds number achieved during the experiments was.

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The Flettner rotor is attracting increasing attention as a viable technology for wind-assisted ship propulsion. Nonetheless, the influence of the Reynolds number on the aerodynamic performance of rotating cylinders is still unclear and under debate. The present study deals with a series of wind-tunnel experiments on a large-scale Flettner rotor in which the forces and pressures acting on the cylinder were measured for Reynolds numbers as large as Re=1.0⋅10 ⁶ . The rotating cylinder used in the experimental campaign had a diameter of 1.0 m and span of 3.73 m. The results indicate that the lift coefficient is only affected by the Reynolds number in the critical flow region and below velocity ratio k=2.5. Conversely, in the velocity ratio range 1<k≤2.5, the drag coefficient is markedly influenced by the Reynolds number over the entire range of flow conditions analyzed. The power coefficient scales with the cube of the tangential velocity and it appears to be insensitive to the Reynolds number or whether the cylinder is spun in an air stream or in still air.

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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.

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The manoeuvring characteristics of high speed craft are greatly influenced by the hydrodynamic loads generated by the asymmetrical underwater hull shape when the vessel heels. In order to provide an insight into this aspect of the manoeuvring of high speed craft, captive model experiments were conducted in the model towing tank at the Delft University of Technology. The experiments were divided in two main phases. In the first phase, the heel-sway, heel-yaw coupled linear coefficients and hydrodynamic heel moment were measured using static heeled model measurements over a range of speeds. The second stage of the experiments examined the influence of different running trim attitudes on the values of the manoeuvring coefficients. The results from three running trim conditions were compared.@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

In the present paper the development of the Delft Systematic Deadrise Series (DSDS) is described. The DSDS has been under development for decades by now and consists of a large family of systematically varied hard chine planing monohulls, based on the original research by Clement and Blount, which have all been tested in the same speed range, changing the same parameters and using the same experimental set up. The rationale behind the DSDS is highlighted. The DSDS contains up to now some 24 different models in 350 different conditions all tested in the same speed range between Fn∇ = 0.75 and Fn∇ = 3.0. Recently there has been a new extension to the DSDS with the inclusion of more measurements on hulls with twisted bottom and rocker in the aft ship. These results are presented in this paper. In addition detailed access is facilitated to all the hull geometries used into the DSDS and to all the raw measurement data obtained during the tests by means of free access to a dedicated website.@en

In order to provide an insight into the manoeuvring of high speed crafts, an experimental study was undertaken at the towing tank of Delft University of Technology, using a rescue vessel of the Royal Netherlands Sea Rescue Institution (KNRM). @en

In recent years wind-assisted propulsion for commercial ships has gained an increasing interest as valuable alternative to reduce fuel pollutant emissions. However, the development of feasible and commercially viable wind propulsion systems to partially (or fully) propel a ship is nowadays hindered by the difficulties of modelling the complicated aerodynamic and hydrodynamic aspects involved. From an aerodynamic point of view, it appears that one of the main challenges of predicting the performance of a wind-assisted ship, is to properly evaluate the interaction effects that occur between the various wind propulsion systems mounted on the deck of the ship. This research deals with the validation of a simple and quick-to-use aerodynamic model that is capable of evaluating such effects, i.e. upwash, downwash and wake, occurring between two generic propulsion systems placed at any given relative position on the ship's deck. The wind propulsion systems might assume any given angle of attack; the flow can be attached as well as separated. Such aerodynamic model, that was first presented in [1], consists of the horseshoe vortex method modified with semi-empirical formulas to take into account the effects of viscosity. First, the results provided by the aerodynamic model were compared with results obtained by using more sophisticated tools, i.e. a CFD body force model and RANS CFD. Then, experimental validation was carried out by means of dedicated wind-tunnel tests. It can be concluded that, despite the simplicity of the aerodynamic model employed, it proved to give reasonable results when compared to more sophisticated tools and to experimental data. REFERENCES [1] K. Roncin and J.M. Kobus, “Dynamic simulation of two sailing boats in match racing”, Sports Engineering , Vol. 7, pp. 139-152, (2004).@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

Development of a Performance Prediction Program for Commercial Ships@en