Velocity Prediction Program Research Articles

VPP-Driven Sail and Foil Trim Optimization for the Olympic NACRA 17 Foiling Catamaran

Abstract. The Nacra-17 catamaran is currently the only type of multihull that participates in the Olympic Games. It features semi-L-shaped daggerboards, allowing the boat to foil. For maximizing boat speed, the sailors have to cope with a large set of trimming parameters. Boat speed depends on sail trim, but additional trim parameters also have a strong impact on boat speed: the rake of the daggerboard and the rudder, the platform trim and heel angle and the rudder angle. The project described here tries to assist the sailors in finding an optimized set of trim parameters. This is done with the help of a proprietary velocity prediction program, which - besides solving for equilibrium of all forces acting on the boat - searches for the set of daggerboard and rudder rake, rudder angle, heel angle and platform trim, for which performance yields a maximum. The paper describes the method as well as some of the results.

Development of a 6-DOF Dynamic Velocity Prediction Program for offshore racing yachts

Thanks to high lift-to-drag ratios, hydrofoils are of great interest for high-speed vessels. Modern sailing yachts fitted with foils have thus reached impressively high speeds on the water. But this hydrodynamic efficiency is achieved at the expense of stability. Accurate tradeoffs are therefore needed to ensure both performance and safety. While usual Velocity Prediction Programs (VPPs) are inadequate to assess dynamic stability, the varying nature of the offshore racing environment further complicates the task.Dynamic simulation in the time-domain is thus necessary to help architects assess their designs. This paper presents a system-based numerical tool which aims at predicting the dynamic behavior of offshore sailing yachts. A 6 degrees of freedom (DOF) algorithm is used, calculating loads as a superposition of several components (hull, appendage, sails). Part of them are computed at runtime while the others use pre-computed dataset, allowing a good compromise between efficiency and flexibility.Three 6DOF simulations of an existing offshore trimaran (a maneuver, unsteady wind conditions and quartering seas) are presented. They underline the interest of dynamic studies, demonstrating how important the yacht state history is to the understanding of her instantaneous behavior and showing that dynamic simulations open a different field of optimization than VPPs.

Application of System-based Modelling and Simplified-FSI to a Foiling Open 60 Monohull

The increasing number of foiling yachts in offshore and inshore races has driven engineers and researchers to significantly improve the current modelling methods to face new design challenges such as flight analysis and control (Heppel, 2015). Following the publication of the AC75 Class Rules for the 36th America's Cup (RNZYS, 2018) and since the brand new Open 60 Class yachts are all equipped with hydrofoils, the presented study will propose a system-based modelling coupled with a simplified FSI (fluid-structure interaction) method that leads to better understand the dynamic behavior of monohulls with deformable hydrofoils. The aim of the presented paper is to establish an innovative approach to assess appendage behavior in a dynamic VPP (velocity prediction program). For that purpose, dynamic computations are based on a 6DOF mathematical model derived from the general non-linear maneuvering equations (Horel, 2016). The force model is expressed as the superposition of 7 major force components expressed at the center of gravity of the yacht: gravity, hydrostatic, maneuvering, damping, propulsion, control and wave. As test cases, course keeping simulations are performed on an Open 60 yacht with control loops to simulate the sail trimmer, helmsman and foil trimmer when finding the optimal foil settings is needed. In first hand, IMOCA's polar diagrams are used as reference. In calm water and in waves, the influence of foil's shapes and stiffness (non-deformable, realistic, flexible) on the global behavior of the yacht is presented.

Maneuver Simulation and Optimization for AC50 Class

The stability and the dynamic behavior are integral parts of designing hydrofoil supported sailing vessels, such as the America's Cup (AC) 50 class. The foil design and the control systems have an important influence on the performance and stability of the vessel. Both foil and control system design also drive the maneuverability of the vessel and determine maneuvering procedures. The AC50 class requirements lead to complex foil control systems and the maneuvering procedures become sophisticated and multifaceted. Sailing and maintaining AC50 class yachts is a complex, expensive and time-consuming task. A dynamic velocity prediction program (DVPP) for the AC50 is therefore developed to assess the dynamic stability of different foil configurations and to simulate and optimize maneuvers. The goal 143 is to evaluate certain design ideas and maneuvering procedures with this simulator so that sailing time on the water can be saved. The paper describes the principal concepts of developing an AC50 model in the DVPP FSEquilibrium. The force components acting on the yacht are defined based on physical principles, computational fluid dynamics (CFD) simulations and experimental investigations. The control systems for adjusting the aero- and hydrodynamic surfaces are modeled. Controllers are utilized to simulate the human behavior of performing sailing tasks. Maneuvers are then defined as sequences of crew actions and crew behaviors. In the paper examples of utilizing the DVPP in preparation for the 35th America's Cup in Bermuda are described. The DVPP is for example used to investigate the effect of different boat set-ups on stability and handling during maneuvers. With the sailing team, maneuver procedures are developed and tested. Procedures such as dagger board and rudder elevator movement and crew position are investigated and evaluated to minimize the distance lost during tacking and gybing. The DVPP is also employed for trajectory optimization during maneuvers.

Velocity Prediction of Wing-Sailed Hydrofoiling Catamarans

Abstract. The paper presents a Velocity Prediction Program for hydrofoiling catamarans with solid wing sails. Starting from a description of the mechanical model, suitable models are identified for the forces that act on the boat components. The study is deliberately limited to means for restricted methods where computational resources and budgets are limited. Enhanced lifting line approaches are described for the wingsail and appendages. Windage is calculated from force coefficients and dynamic pressure while hull resistance is determined by means of a potential flow solver. The description of the implementation is followed by the presentation of the results. An approach for processing of measurement data is shown in preparation to compare measured and predicted performance. Good agreement was found for upwind conditions whereas varying differences are found for most of the remaining wind angles. Finally, some of the challenges encountered during the study are discussed.

Design of a Foiling Optimist

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.

Sailing yacht performance prediction based on coupled CFD and rigid body dynamics in 6 degrees of freedom

Traditional Velocity Prediction Programs (VPPs) for sailing yachts rely on empirical relations, while modern techniques include CFD. Normally a multi-dimensional matrix of CFD results is pre-computed and forces and moments obtained by interpolation during a VPP execution. A more exact technique is to use the CFD code itself as a VPP, i.e. to simultaneously integrate the flow and rigid body equations in time. In the present paper a technique of this coupled type is introduced.An initial guess is required for speed and attitude, and by time integration in six degrees of freedom this guess is corrected to a steady state solution. Three phases are identified. First the attitude is kept constant over a period of time to stabilize the flow. Thereafter the different degrees of freedom are released successively and the rudder activated to achieve yaw balance. Finally, in the converged phase, the net forces and moments are zero in all degrees of freedom and the results reported.The performance prediction is carried out for a dinghy and a large high-performance racing yacht. Convergence of all variables is demonstrated and the results used for finding the optimum speed to windward and downwind. Details of the numerical setup are reported.

Development of a Sailing-Specific Pose Capture Method To Measure Dynamic Sailor Loadings

Research into the dynamics of sailing vessels, most notably yachts, has led to the development of sophisticated models including the unsteady aero and hydrodynamics and even sailor's tactics. However, the time-varying loadings caused by a sailor's motions have typically been neglected in velocity prediction programs (VPPs). When applied to the assessment of sailing dinghy performance, the position and motions of the crew are significant but impractical to measure mechanically. A sailing-specific pose capture method to determine the sailor loadings using orientation sensors and a model of the sailor's mass distribution is presented. The accuracy of the hiking moment estimate was evaluated using laboratory-based measurements. The estimated hiking moment exhibits excellent dynamic tracking of the measured moment. The method is used to measure on-water hiking moment for the first time and the results are discussed. The proposed method provides a platform to analyze and model how sailor-generated forces interact with the sailboat to affect boat speed. This can be used alongside realistic modelling of the wind and wave loadings to extend existing time-domain dynamic velocity prediction programs (DVPPs). This opens a new area of sailing research as the human can now be modelled to respond to force perturbations.

Performance prediction for sailing dinghies

This study describes the development of an approach for performance prediction for a sailing dinghy. Key modelling issues addressed include sail depowering for sailing dinghies which cannot reef; effect of crew physique on sailing performance, components of hydrodynamic and aerodynamic drag, decoupling of heel angle from heeling moment, and the importance of yaw moment equilibrium.In order to illustrate the approaches described, a customised velocity prediction program (VPP) is developed for a Laser dinghy. Results show excellent agreement with measured data for upwind sailing, and correctly predict some phenomena observed in practice. Some discrepancies are found in downwind conditions, but it is speculated that this may be related at least in part to the sailing conditions in which the measured data was gathered.The effect of crew weight is studied by comparing time deltas for crews of different physique relative to a baseline 80kg sailor. Results show relatively high sensitivity of the performance around a race course to the weight of the crew, with a 10kg change contributing to time deltas of more than 60s relative to the baseline sailor over a race of one hour duration at the extremes of the wind speed range examined.

Prediction of velocity and attitude of a yacht sailing upwind by computational fluid dynamics

One of the most important factors in sailing yacht design is accurate velocity prediction. Velocity prediction programs (VPP's) are widely used to predict velocity of sailing yachts. VPP's, which are primarily based on experimental data and experience of long years, however suffer limitations when applied in realistic conditions. Thus, in the present study, a high fidelity velocity prediction method using computational fluid dynamics (CFD) was proposed. Using the developed method, velocity and attitude of a 30 feet sloop yacht, which was developed by Korea Research Institute of Ship and Ocean (KRISO) and termed KORDY30, were predicted in upwind sailing condition.

Assessing Human-Fluid-Structure Interaction for the International Moth

The International Moth is an ultra-lightweight foiling dinghy class. Foil deflections and dynamic sailor-induced motions are identified as two key areas relating to foiling moth performance that are currently ignored in Velocity Prediction Programs (VPP). The impact of foil deflections is assessed by measuring the tip deflection and twist deformation of a T-foil from an International Moth. The full field deformation due to an applied load is measured using Digital Image Correlation (DIC). The foil's structural properties can then be determined based on the measured structural response. The deformations are then calculated for an estimated steady sailing force distribution on the T-foil and their impact on performance is evaluated. To investigate the impact of dynamic sailor motions a system is developed that allows a sailor's dynamic pose to be captured when out on the water by determining the orientations of key body segments using inertial sensors. It is validated against measured hiking moments and is demonstrated to work out on the water whilst sailing. Both these studies pave the way towards developing a Dynamic VPP for the international Moth, which can include unsteady human and foil interactions.

Numerical Prediction of the Best Heel and Trim of a Laser Dinghy

As the Laser Olympic dinghy is one of the highest-level sail racing classes in the world, there is an interest in obtaining physical facts around the experience that already exist. For this reason, a numerical investigation has been carried out to find the best heel and trim angles in upwind sailing. Flat water is assumed. The core of the work is a newly developed Inverse Velocity Prediction Program (IVPP) that computes the required wind speed for a given boat speed. Input to the program is both available towing tank data and CFD results. By keeping speed constant interpolation is avoided in the very non-linear resistance-speed relation, reducing considerably the required number of CFD computations. Another reduction is obtained by a special technique for avoiding interpolation in leeway. Systematic CFD computations are carried out to find the optimum trim versus heel at the speeds 2, 3, 4, 5 knots. Using this relation the required wind speed at the four boat speeds can be expressed as a function of heel only. The heel angle corresponding to the smallest wind speed is the best. Knowing this, and the corresponding optimum trim, the position of the sailor is computed. It turns out that the predicted best positions correspond well with practical experience. However, the results highlight the benefit of a small heel in higher winds, which often is regarded as undesired by sailors.

풍상 범주 중인 세일링 요트의 자세를 고려한 속도 추정 방법

One of the most important factors in sailing yacht design is an accurate velocity prediction. Velocity prediction programs (VPPs) are widely used to predict velocity of sailing yachts. VPPs, which are primarily based on experimental data and experience of long years, suffer limitations applied in realistic conditions. Thus, in the present study, a high fidelity velocity prediction method using the computational fluid dynamics (CFD) is proposed. Using the developed method, velocity and motion of a 30 feet sloop yacht, which was developed by Korea Research Institute of Ship and Ocean (KRISO) and termed KORDY30, were predicted in upwind sailing condition.

On risk attitude and optimal yacht racing tactics

When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a stochastic routing problem. The objective of this problem is to maximise the probability of reaching the next mark ahead of all the other competitors. This paper describes some numerical experiments that explore the effect of the skipper׳s risk attitude on their policy when match racing another boat. The tidal current at any location is assumed to be negligible, while the wind direction is modelled by a Markov chain. Boat performance in different wind conditions is defined by the output of a velocity prediction program, and we assume a known speed loss for tacking and gybing. We compare strategies that minimise the average time to sail the leg with those that seek to maximise the probability of winning, and show that by adopting different attitudes to risk when leading or trailing the competitor, a skipper can improve their chances of winning.

Recent Advances in Sailing Yacht Aerodynamics

The analysis of sailing yacht aerodynamics has changed dramatically over the last 15 years and has enabled significant advances in performance prediction. For instance, the growth of computational fluid dynamics has significantly changed the way high-performance sails are designed. Three-dimensional mathematical models of fully rigged sail plans and the visualization of the turbulent unsteady flow pattern around them are now quite common, whereas ten years ago such a simulation would have been very rare and 20 years ago it would have been impossible. The parallel development of optimization techniques has resulted in new sail and yacht design methods. Changes in the experimental techniques have been as dramatic as in the numerical techniques. The introduction of the twisted flow device, the real-time velocity prediction program, and the most recent pressure measurements have allowed a step change in the potentialities of experimental sail aerodynamics. This paper aims to review the recent advances in sail aerodynamics and to highlight potential research areas for future work.

Development and Preliminary Experimental Validation of a Wind- and Solar-Powered Autonomous Surface Vehicle

The design and initial testing of a wind- and solar-powered (WASP) autonomous surface vehicle (ASV) are presented. The concept vehicle is a 4.2-m length overall monohull keelboat powered by a rigid wing sail with a 5-m span. It is designed to operate in 7-10 km of wind and a maximum sea state of 2. Specific attention is placed on the aerodynamic, hydrodynamic, and systems integration aspects of the design. Rigid wing sails are shown to have superior performance to conventional cloth sails for use on ASVs owing to their higher aerodynamic efficiency and robustness. The manual design process involved in selection of the airfoil cross section for the wing sail and the resulting aerodynamic performance predictions are presented. Through mathematical derivation, the optimal angle for switching the sail configuration from an upwind/crosswind lift-generating mode to a downwind drag-generating mode is found to be 135 . To simplify implementation of the control system when operating in the lift-generating sailing mode, a control scheme that decouples heading and speed control by simply setting the wing sail to an angle of attack of 10 and independently controlling heading was used. The simulation results from a velocity prediction program (VPP) used to verify the feasibility of this control approach are presented. Initial field trials of the vehicle using the control approach with autonomous wing control and manual rudder control are presented. It is shown that the measured boat speeds and wind speed/directions are within the range of values expected from the VPP. Temperatures recorded in a thermal plume during the field trials of the ASV are shown as a function of global positioning system (GPS) location and time.

Mechanics of a rowing stroke: Surge speed variations of a single scull

A generic model of a rowing craft is presented and used to identify the mechanics of the rowing stroke that give rise to variations in the speed of a rowing shell, together with the causes and locations of maximum and minimum shell speeds through the stroke. The model is implemented computationally in a velocity prediction program which uses readily available measured data for the input and simulates the motion of the athlete using a seven-body-segment model. The rowing model is derived to avoid limitations that arise from the quasi-steady application of steady state data to the unsteady flow around the oar blades and includes hydrodynamic and aerodynamic resistance models. Propulsive drive forces arise as a result of the difference between the gate and handle forces due to the lever action of the oar. The surge motion is dominated by the inertial forces arising as a result of the athlete's motion within the craft which are much larger in magnitude than the drive forces. The minimum surge speed occurs midway through the drive phase. Two distinct maxima in the surge speed occur: one at the end of the drive as the athlete comes to rest at the end of the stroke, and one during the recovery as the athlete's seat attains the maximum speed backwards relative to the craft. The relative magnitudes of these peaks are mainly determined by the ratio of the drive time to the recovery time.

A hybrid numerical method to develop America’s Cup yacht appendages

A method aimed at the development of an America’s Cup racing yacht bulb is developed and validated against experimental data. The method relies heavily on Reynolds Averaged Navier Stokes computational fluid dynamics (CFD) and also factors in gravitational and aerodynamics effects through the use of a Velocity Prediction Program. Initial extensive use of towing tank results is made to be able to validate the CFD solution and thus develop a solid ground for predictive work. Then, in order to narrow down the focus on bulb developments, decoupled hypotheses are made on the influence of the hull and free surface wave. The development of a detailed performance analysis chart of a known base bulb allows the use of a relatively small series of CFD simulations together with physical hypotheses to assess any given bulb performance relative to the known base. The discussion of the results on a specific development highlights the promises and limitations of the method; final full scale results are discussed and analysed as well.

English

Considerable progress has been made in the development of Velocity Prediction Programs (VPPs) suitable for analysis of racing yacht performance. In addition, investigations on yacht dynamics (i.e. optimal tacking procedure) are now available. While these tools will no doubt be further refined and computations speeded up, there is also a need to assess the performance of the yacht's helmsman and crew. The scope of the present study is the prediction of the performances of a yacht-crew system as a whole, by deriving numerical models for human behaviour alongside with those referred to the physics of yacht motion. The latter issue, the mechanical side of the problem, is analysed by solving yacht equations of motions in the time domain; crew inputs in terms of yacht steering and sail trim are considered. The yacht-crew system can sail a racecourse in an arbitrary wind pattern, according to strategic rules and given decision making schemata.

30피트급 요트의 선형개발 및 성능추정

An overview of 30 feet sailing yacht design is presented, with an emphasis on the factors contributing to start-up popularization. After prescribing the configurations of the purposed yacht, the design of the hull form with a rudder and a keel, are schematically described. Also the determinations of the dimensions of the sail and rig are performed. Finally this paper is associated with the state-of-the-art of calculating sailing yacht performance as this is performed in velocity prediction program (VPP). The VPP results shows a typical shape of a sailing yacht and the designed yacht has the best performance at 120 degree angle of true wind with 20 knots.