| 1. |
- Andersson, Anton, et al.
(author)
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Design of a Foiling Optimist
- 2018
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In: Journal of Sailboat Technology. ; 2018, s. 1-24
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Journal article (peer-reviewed)abstract
- Because of the successful application of hydrofoils on the America's Cup catamarans in the past two campaigns the interest in foiling sailing craft has boosted. Foils have been fitted to a large number of yachts with great success, ranging from dinghies to ocean racers. An interesting question is whether one of the slowest racing boats in the world, the Optimist dinghy, can foil, and if so, at what minimum wind speed. The present paper presents a comprehensive design campaign to answer the two questions. The campaign includes a newly developed Velocity Prediction Program (VPP) for foiling/non-foiling conditions, a wind tunnel test of sail aerodynamics, a towing tank test of hull hydrodynamics and a large number of numerical predictions of foil characteristics. An optimum foil configuration is developed and towing tank tested with satisfactory results. The final proof of the concept is a successful on the water test with stable foiling at a speed of 12 knots.
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| 2. |
- Andersson, A, et al.
(author)
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The Foiling Optimist
- 2017
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In: The Proceedings of the 4th International Conference on Innovation in High Performance Sailing Yachts, Lorient, France, 28-30 June 2017.. ; , s. 19-30
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Conference paper (peer-reviewed)
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| 3. |
- Ekström, David, et al.
(author)
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Optimization of the Internal Structure and Shape of a 470 Dinghy Centerboard
- 2020
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In: Proceedings (MDPI). - Basel Switzerland : MDPI. - 2504-3900. ; 49:1
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Conference paper (peer-reviewed)abstract
- The purpose of this paper is to design an improved centerboard for the Olympic 470 sailing dinghy sailing upwind. The design is improved by introducing a composite design that makes the centerboard twist to windward when sailing upwind, thereby reducing the angle of attack of the hull. The results show that a beneficial twist up to 1.5° is possible to achieve without compromising the centerboard strength. According to our estimates, by utilizing the improved design it is possible to obtain a gain of up to 9 s per race in a world cup race.
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| 4. |
- Marimon Giovannetti, Laura, et al.
(author)
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Multi-wing sails interaction effects
- 2022
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In: SNAME 24th Chesapeake Sailing Yacht Symposium, CSYS 2022. - : The Society of Naval Architects and Marine Engineers.
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Conference paper (peer-reviewed)abstract
- The effects of multiple wings interacting and the change in efficiency due to those effects as well as optimal sheeting angles are becoming an important area of study with the advent of wind-propelled ships for goods transport. This research presents a first analysis of wind tunnel tests carried out at the University of Southampton R.J. Mitchell wind tunnel where three wings are subject to turbulent flow with Reynolds number in excess of 1 million. A range of possible variations of ship heading and apparent wind angles are tested taking into consideration the blockage effects and the geometrical characteristics of the working section. The forces and moments are captured on each individual wing as well as in the overall wind tunnel balance with 6-components dynamometers. Furthermore, pressure sensors and PIV data are recorded during the tests to provide the experimental campaign with results that can validate both qualitatively and quantitatively the numerical tools developed to aid the design stage of wind propelled vessels.
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| 5. |
- Persson, Adam, 1991, et al.
(author)
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A time-domain model for unsteady upwind sail aerodynamics using the indicial response method
- 2024
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In: Ocean Engineering. - 0029-8018 .- 1873-5258. ; 299
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Journal article (peer-reviewed)abstract
- For the design of sailing vessels, the use of Dynamic Velocity Prediction Programs is expanding, as naval architects start to consider the effects of waves and varying wind conditions in order to design faster, safer and more efficient vessels. Many models that predict the unsteady hydrodynamic response are available, but for sail aerodynamics, few models have been presented, and the quasi-steady assumption is instead commonly used. The aim of this paper is to develop a time-domain model for unsteady sail aerodynamics that can handle arbitrary motions and requires only limited input. The proposed model is based on the Indicial Response Method, with specific adaptations to handle the additional complexity of sail aerodynamics. The model's predictive performance is evaluated against URANS CFD results for several cases of increasing complexity. This includes a 3D upwind sail plan subjected to pitching motion, where comparisons are also made with the common quasi-steady (Q-S) assumption. Compared to this, the proposed model delivers significantly better predictions for the amplitude of lift, thrust and sideforce. However, the drag amplitude is over-predicted by the model, and as a result, there is a significant misprediction of thrust phase. While there is a need to improve the prediction of unsteady drag, this paper shows that the model represents a significant improvement over the Q-S assumption, for unsteady performance prediction on timescales shorter than the wave period.
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| 6. |
- Persson, Adam, 1991, et al.
(author)
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An improved procedure for strongly coupled prediction of sailing yacht performance
- 2020
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In: InnovSail 2020 Proceedings. ; 6:1, s. 133-
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Conference paper (peer-reviewed)abstract
- In this paper, an improved procedure for strongly coupled prediction of sailing yacht performance is developed. The procedure uses 3D RANS CFD to compute the hydrodynamic forces. When coupled to a rigid body motion solver and a sail force model, along with a rudder control algorithm, this allows sailing yacht performance to be predicted within CFD software. The procedure provides faster convergence when compared to previously published methods. The grid motion scheme, partially using overset grid techniques, means that correct alignment between the free surface and the background grid is ensured even at large heel angles. The capabilities are demonstrated with performance predictions for the SYRF 14 m yacht, at one true wind speed, over a range of true wind angles, with one up- and one downwind sailset. The results are compared to predictions from the ORC-VPP for a yacht with similar main particulars.
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| 7. |
- Persson, Adam, 1991, et al.
(author)
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CFD prediction of steady and unsteady upwind sail aerodynamics
- 2017
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In: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 141, s. 543-554
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Journal article (peer-reviewed)abstract
- In this paper, RANS CFD simulations of steady and unsteady upwind sail aerodynamics are verified and validated against wind tunnel experiments previously performed at Politecnico di Milano. Experimental data is presented, and the experimental results are analysed to estimate repeatability. Blockage effects caused by tunnel boundary layers and measurement equipment are estimated using detailed CFD simulations, allowing such effects to be accounted for. A verification procedure is performed, resulting in very low numerical uncertainties.The force predictions are then validated for both steady and unsteady conditions. The steady results show verygood agreement, with a maximum error of 3.1%. For the unsteady conditions, good agreement is found for theforce mean values, whilst the prediction of force amplitudes is less satisfactory.
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| 8. |
- Persson, Adam, 1991
(author)
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Dynamic effects on yacht sails and rudders
- 2019
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Licentiate thesis (other academic/artistic)abstract
- In search of increased performance, modern sailing vessels are becoming more and more complex, introducing additional challenges in the design process. The dynamic behaviour of the vessel is of great importance to safe and efficient operation and thus needs to be accounted for when evaluating the performance. To accomplish this, the forces acting on the vessel in dynamic conditions must be predicted and evaluated. The purpose of this thesis is to develop methods to predict the forces acting on sails and rudders in dynamic conditions. RANS CFD is used to predict upwind sail aerodynamic forces. A comprehensive study of the numerical setup, physical modelling and uncertainties in the CFD solutions is presented. The spatial discretisation uncertainty is shown to be low for steady conditions, and the forces are well predicted. For dynamic conditions, mean values are predicted with reasonable accuracy. However, the instantaneous quantities show more scatter and a higher comparison error. Following careful analysis of the numerical simulations and experimental procedures, possible error sources are identified. For example, in the post-processing of experimental measurements, added mass forces had been removed incorrectly. For the numerical simulations, poor performance of the turbulence model may explain the error. The dynamic characteristics of rudders for the Finn dinghy are investigated using full-scale towing tank tests. Considerable differences in both performance and handling are revealed. Also, the study highlights challenges faced when performing experimental testing of dynamic effects, such as the introduction of artificial constraints. The prediction of dynamic effects introduces additional uncertainties, regardless of whether experimental or numerical techniques are utilized, that need to be carefully controlled. Further studies are proposed to investigate these.
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| 9. |
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| 10. |
- Persson, Adam, 1991, et al.
(author)
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Performance evaluation and ranking of 7 rudders for the Finn dinghy
- 2018
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In: Journal of Sailing Technology. - 2475-370X. ; 3:1, s. 1-
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Journal article (peer-reviewed)abstract
- As a follow up to the Olympic Games, commercially available Finn dinghy rudders were tested to determine their hydrodynamic performance. Seven rudders were tested, out of the nine different rudder models that were measured for competition at the 2016 Olympic Games, thus representing a large portion of the rudders used by sailors. The remaining two rudder models could not be tested, since they are of semi-custom or custom design or manufacture. Each rudder was tested in seven different conditions, selected to cover a wide range of sailing conditions. The testing revealed considerable differences, both in performance and handling.
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| 11. |
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| 12. |
- Pietrzak, Michal, 1987-, et al.
(author)
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Ghrelin decreases sensitivity to negative feedback and increases prediction-error related caudate activity in humans, a randomized controlled trial
- 2024
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In: Neuropsychopharmacology. - : Springer Science+Business Media B.V.. - 0893-133X .- 1740-634X. ; 49, s. 1042-1049
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Journal article (peer-reviewed)abstract
- The stomach-derived hormone ghrelin plays not only a role in feeding, starvation, and survival, but it has been suggested to also be involved in the stress response, in neuropsychiatric conditions, and in alcohol and drug use disorders. Mechanisms related to reward processing might mediate ghrelin's broader effects on complex behaviors, as indicated by animal studies and mostly correlative human studies. Here, using a within-subject double-blind placebo-controlled design with intravenous ghrelin infusion in healthy volunteers (n = 30), we tested whether ghrelin alters sensitivity to reward and punishment in a reward learning task. Parameters were derived from a computational model of participants' task behavior. The reversal learning task with monetary rewards was performed during functional brain imaging to investigate ghrelin effects on brain signals related to reward prediction errors. Compared to placebo, ghrelin decreased punishment sensitivity (t = -2.448, p = 0.021), while reward sensitivity was unaltered (t = 0.8, p = 0.43). We furthermore found increased prediction-error related activity in the dorsal striatum during ghrelin administration (region of interest analysis: t-values >= 4.21, p-values <= 0.044). Our results support a role for ghrelin in reward processing that extends beyond food-related rewards. Reduced sensitivity to negative outcomes and increased processing of prediction errors may be beneficial for food foraging when hungry but could also relate to increased risk taking and impulsivity in the broader context of addictive behaviors.
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| 13. |
- Prabahar, N. S. S., et al.
(author)
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Split-flaps for increased heel stability of t-foil configurations
- 2021
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In: 7th High Performance Yacht Design Conference, HPYD 2021. - : The Royal Institution of Naval Architects.
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Conference paper (peer-reviewed)abstract
- Horizontal T-foils allow for maximum lift generation within a given span. However, for T-foils, the lift force acts in the symmetry plane of the boat, thereby producing no righting moment. It results in a lack of transverse stability during foil-borne sailing. In this project, we propose a system, where the height-regulating flap on the trailing edge of the foil is split into a port and a starboard flap, whose angle is adjusted proportionally to the heel. Such a system generates and scales the righting moment based on the heel angle, making the boat easier to balance. The effectiveness of this system is studied for a custom-made double-handed skiff using a dynamic velocity prediction program (DVPP), especially in the take-off phase. It is shown that the split flap system generates a larger righting moment for the foiling boat than for the non-foiling one at boat speeds above 3 m/s.. The improved stability comes at a cost of additional induced resistance and this effect is computed by CFD. It is shown, using the DVPP, that the increased resistance, slows down the boat at the lowest wind speeds, but above 2.5 m/s true wind, the split flap boat is as fast as the boat with a single flap around the racecourse. Due to the higher stability, less depowering of the sails is required, and that compensates for the increased resistance.
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| 14. |
- Saporito, Antonio, et al.
(author)
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A New Systematic Series of Foil Sections with Parallel Sides
- 2020
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In: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 8:9
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Journal article (peer-reviewed)abstract
- Parallel-sided foil sections are used for centerboards and rudders in sailing dinghy classes and also for struts placed in a fluid flow. The objective of this work is to create a systematic series of parallel-sided sections to be used under different conditions, with an emphasis on the sailing dinghies 470, 420 and Optimist. The loss, and surprisingly the gain, in performance relative to 4-digit NACA sections are also investigated. A 2D Reynolds-averaged Navier–Stokes solver is used with the k-! SST turbulence model and the gamma transition criterion. A verification study is carried out based on four grids of systematically varied density, and results compared with experimental data on a NACA 64-006 section. The parallel-sided sections are modeled with rational Bézier curves whose geometrical parameters permit to link the shape of the profile to physical variables, which are systematically varied. Three Reynolds numbers and two angles of attack are investigated. Systematic plots show the influence of the trailing edge angle and nose radius for the different section families, and the optimum combination is presented in a table. Physical explanations of the trends, and of the exceptions, are given in the paper, using flow visualizations as well as pressure and friction plots.
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| 15. |
- Saravana Prabahar, Nimal Sudhan, et al.
(author)
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Split-Flaps – a Way to Improve the Heel Stability of T-Foil Supported Craft
- 2022
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In: Journal of Sailing Technology. - : The Society of Naval Architects and Marine Engineers. - 2475-370X. ; 7:1, s. 1-30
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Journal article (peer-reviewed)abstract
- Horizontal T-foils allow for maximum lift generation within a given span. However, the lift force on a T-foil acts on the symmetry plane of the hull, thereby producing no righting moment. It results in a lack of transverse stability during foil-borne sailing. In this paper, we propose a system, where the height-regulating flap on the trailing edge of the foil is split into a port and a starboard part, whose deflection angles are adjusted to shift the centre of effort of the lift force. Similar to the ailerons which help in steering aircraft, the split-flaps produce an additional righting moment for stabilizing the boat. The improved stability comes, however, at a cost of additional induced resistance. To investigate the performance of the split-flap system a new Dynamic Velocity Prediction Program (DVPP) is developed. Since it is very important for the performance evaluation of the proposed system it is described in some detail in the paper. A complicated effect to model in the DVPP is the flow in the slot between the two flaps and the induced resistance due to the generated vorticity. Therefore, a detailed CFD investigation is carried out to validate a model for the resistance due to the slot effect. Two applications of the split-flap system: an Automated Heel Stability System (AHSS) and a manual offset system for performance increase are studied using a DVPP for a custom-made double-handed skiff. It is shown that the AHSS system can assist the sailors while stabilizing the boat during unsteady wind conditions. The manual offset enables the sailors to adjust the difference between the deflection angles of the two flaps while sailing, thus creating a righting moment whenever required. Such a system would be an advantage whilst sailing with a windward heel. Due to the additional righting moment from the manual offset system, the sails could be less depowered by the sailors resulting in a faster boat despite the additional induced resistance. It is shown in the paper that the control systems for the ride height and the heel stability need to be decoupled. The paper ends with a description of a mechanical system that satisfies this requirement.
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| 16. |
- Stadler, Michael, et al.
(author)
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A Customised Finn Dinghy Rudder for Optimal Olympic Performance
- 2020
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In: Proceedings (MDPI). - Basel Switzerland : MDPI. - 2504-3900. ; 49:1
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Conference paper (peer-reviewed)abstract
- Because of the long history of the Finn Dinghy sailing class, the difference between a gold medal and a mediocre result often comes down to personal mistakes of the sailor, or to who has the most optimised equipment. Regarding the latter, the Finn class rules permit certain design variations of the hull, mast, sail and rudder. In the current contribution, we describe a method for developing a customised rudder system aimed at optimal performance during the Tokyo 2020 Olympics. Based on hydrodynamic analysis of existing rudder designs, an improved rudder geometry was developed. Based on the concept geometry, the rudder and tiller were structurally designed and manufactured to achieve high stiffness and sufficient strength, while respecting the minimum mass requirements as specified by the rules.
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| 17. |
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