Sail Design Research Articles

Efficient jib-mainsail fluid-structure interaction modelling – Validations with semi-rigid sails experiments

The present work takes place in the framework of the “Jib Sea” project. The main purpose of the project is to develop a new sail design made of articulated composite panels, for large merchant ships. The French laboratory “ENSTA Bretagne, IRDL” is involved in this industrial project for its expertise on fluid-structure interactions modelling. A fast and robust approach to model fluid-structure interactions for yacht sails is presented. Specifically, interaction effects between the jib and the mainsail are considered in the flow model presented. This is achieved using the lifting-line theory combined with a discrete vortex method, involving distributions of lumped-vortex elements along sail sections. The flow model is coupled with a finite element analysis of the structure, using shell elements for the modelling of sail membranes, beam stringers for battens modelling and a quasi-static resolution based on a dynamic backward Euler scheme. The flow model based on the Lifting-Line Theory is presently validated by a commercial software tools using the Unsteady Reynolds-Average Navier-Stokes equations. Numerical comparisons with experiments are conducted on a 50 m2 composite mainsail prototype and a conventional jib, built and hoisted on an onshore balestron rig. Measurements, such as strain gauges or cable tensions, are synchronized with a wind sensor. These data collected together enable both global and local numerical-experimental comparisons for forces and moments, providing a validation of the proposed fluid-structure interactions modelling of ship sails. A good match between experimental and numerical modelling is observed on local comparisons as relative differences are all less than 25% for TWA∈[−20;20] and TWS<10 kn. Global comparison results exhibit validations with experiments for |TWA|<10 deg and TWS<10 kn, where numerical-experimental relative differences are less than 10%.

An integrated simulation system for operating solar sail spacecraft

An integrated simulation system for solar sail spacecraft with individually controllable elements (SSICE) is investigated in this paper, including the modelling of power management, thermal control, attitude control, umbra prediction, and orbit prediction subsystems. Considering the self-control and reactivity subsystems, an agent based method is applied to develop the subsystem models. Each subsystem is an individual agent component, which manages itself autonomously and reacts to the requirements from other agents. To reduce computing burden on a specified computer and improve the suitability and flexibility of the integrated simulation system, a distributed framework is employed in the system by deploying agent components on different computers. The data transmission among agents is based on the transmission control protocol/Internet protocol (TCP/IP). A practical example of sun pointing is used to test the operating effect of the integrated system and the working condition of subsystems. The simulation results verify that the integrated system has higher sun pointing accuracy, quicker dynamical response to variations of the lighting, attitude and temperature and fewer computing resources with effective and accurate subsystems. The integrated system proposed in this paper can be applied to solar sail design, operation, and mission planning.

Improving the Downwind Sail Design Process by Means of a Novel FSI Approach

The process of designing a sail can be a challenging task because of the difficulties in predicting the real aerodynamic performance. This is especially true in the case of downwind sails, where the evaluation of the real shapes and aerodynamic forces can be very complex because of turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical methods are very useful and reliable tools to investigate sail performances, and their use, also as a result of the exponential growth of computational resources at a very low cost, is spreading more and more, even in not highly competitive fields. This paper presents a new methodology to support sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind sails. The proposed method is parametric and automated and allows for investigating multiple kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is presented as a case study. Based on the numerical results obtained, an analytical formulation for calculating the sail corner loads has been also proposed. The novel proposed methodology could represent a promising approach to allow for the widespread and effective use of numerical methods in the design and manufacturing of yacht sails.

Inverse Design of Diffractive Relativistic Meta‐Sails via Multi‐Objective Optimization

AbstractPhotonic propulsion of light sails using the radiation pressure of an intense laser beam is a promising route to achieve relativistic velocities for deep space exploration. A successful photonic design of such relativistic sails requires efficient acceleration and maintaining stability of the beam‐riding across a Doppler‐broadened propulsion band due to considerable red‐shift of the wavelength in the frame of the moving sail. While efficient acceleration of the sail requires maximizing the optical force along the beam propagation direction, the stability degree of the sail depends on the magnitude of lateral forces in the transverse plane of the beam. This establishes a trade‐off between these two requirements which calls for their synergistic engineering. In this work, an evolutionary multi‐objective optimization technique for the inverse design of diffractive relativistic meta‐sails with a genetic pixelated geometry is adopted. The goal is to identify a set of Pareto optimal solutions which provides the designer with an intuitive understanding of the ultimate trade‐off between acceleration and stability degree of the sail in a vast design space, and allows for a well‐informed decision on the best design given the requirements for the acceleration time and distance as well as the tolerance with respect to mispointings and misalignments.

CONFIGURATION SELECTION AND ANALYSIS OF A SUPERSTRUCTURE SOLAR SAIL

Solar sail propulsion is one of the most innovative spaceship propulsion system which make use of the radiation pressure in space. The continuous supply of radiation pressure means the ship has infinite propellant reserve. Theoretically, the solar sail keeps accelerating to gain high velocities due to this continuous supply of radiation pressure, therefore this system is ideal for interstellar exploration. As there are numerous developments going on this field of study, it is important to have a generalized sail design that can be used for further developments. This paper gives the configuration selection of the sail along with calculations and analysis to develop a superstructure solar sail, which is theoretically ideal for interstellar exploration and for future engineering

Modeling and analysis of a fully passive swinging sail wind turbine

AbstractWind energy has been an attractive renewable energy source, and in recent decades, highly efficient horizontal axis wind turbines have been developed and successfully deployed. However, alternative designs for wind energy conversion have also been proposed. In previous studies, a novel swing sail design for wind energy harvesting was proposed and analyzed. This turbine harvests energy by pitching a sail, causing a mast to swing, which in turn drives a flywheel in a rectified rotational motion. The rotating flywheel is then used to drive an electric generator. The designed turbine was originally semiactive, while in the present study, the fully passive version of the turbine was proposed, and its performance was examined. The turbine consists of an oscillating sail attached to a reciprocally moving mast via a torsion spring, and the wind‐driven oscillatory motion is transformed into the rotational motion of a flywheel using a ratchet. Furthermore, a dry‐friction dynamometer was utilized as a simple way of extracting energy. The dynamical equations of the turbine were derived and were used to analyze the time response of the turbine. In the model, the correlations for the aerodynamic lift and drag forces for a flat plate were utilized. The results were validated using the computation fluid dynamics (CFD) simulation. The effects of various dynamical and geometric parameters of the turbine on the generated power and the turbine performance were also investigated.

Multi-Fidelity Surrogate Models for VPP Aerodynamic Input Data

Predicting the performance of a sail design is important for optimising the performance of a yacht, and Velocity Prediction Programs (VPPs) are commonly used for this purpose. The aerodynamic force data for a VPP is often calculated using Computational Fluid Dynamics (CFD) models, but these can be computationally expensive. A full VPP analysis for sail design is therefore usually restricted to high-budget design projects or research activities and is not practical for many industry projects. This work presents a method to reduce the computational cost of creating lift and drag force coefficient curves for input into a VPP using both multi-fidelity kriging surrogate modelling and data from existing sail designs. This method is shown to reduce the number of CFD simulations required for a desired accuracy when compared to a single-fidelity model. A maximum reduction in the required computational effort of 57% was achieved for model-scale symmetric spinnaker sails. For the same number of simulations, the accuracy of the model predictions was improved by up to 72% for scale-symmetric spinnaker sails, and 90% for asymmetric spinnakers.

Electro-thermo-mechanical modelling of micro solar sails of chip scale spacecraft in space

This paper presents a novel design of micro solar sails for emerging lightweight chip scale spacecraft based on flexible electronic circuits. To acquire large deformation, the micro solar sails were designed to be bilayer beams that were able to be electro-thermally actuated by Joule heating. The concept design of the solar sail with high area-to-mass ratios allowed the solar sailing system, named as ChipSail, for efficient orbital transfer and attitude adjustment. The principle of solar sailing with ChipSail was illustrated, and the thickness of the two metals for the bilayer sails should be no more than 1 µm, so as to achieve the efficient solar sailing. Then, the fabrication and characterization of such bilayer microstructures for solar sails were introduced briefly. After that, the electro-thermal analysis of such solar sails deployed on the low earth orbit was carried out, and it was found that the balanced temperature of the sails under the effect of solar radiation and thermal reemission of the sails was 315.31 K, followed by electro-thermal modelling of the sails under the Joule heating. A nonlinear second order differential equation was derived, which allowed rapid prediction of the thermal distribution across the sail. Equivalence of the bilayer solar sail to a width-changing 980 µm long bilayer beam was proposed and validated by finite element analysis. Finally, the thermo-mechanical model on the bilayer sail was then established and solved numerically. Results showed that the maximum bending angle could reach to 94.05o by applying a voltage of 0.05 V across the sail. The electro-thermo-mechanical model laid a solid foundation for dynamic control of the configuration of the ChipSail for efficient orbital transfer and attitude adjustment in space.

Monocular 3D reconstruction of sail flying shape using passive markers

We present a method to recover the 3D flying shape of a sail using passive markers. In the navigation and naval architecture domain, retrieving the sail shape may be of immense value to confirm or contest simulation results, and to aid the design of new optimal sails. Our acquisition setup is very simple and low-cost, as it is only necessary to fix a series of printable markers on the sail and register the flying shape in real sailing conditions from a side vessel with a single camera. We reconstruct the average sail shape during an interval where the sailor maintains the sail as stable as possible. The average is further improved by a Bundle Adjustment algorithm. We tested our method in a real sailing scenario and present promising results. Quantitatively, we show the precision in regards to the reconstructed markers area and the reprojected points. Qualitatively, we present feedback from domain experts who evaluated our results and confirmed the usefulness and quality of the reconstructed shape.

Shape and Spacing Effects on Curvy Twin Sail for Autonomous Sailing Drone

There is a growing interest this paper for ocean sensing where autonomous vehicles can play an essential role in assisting engineers, researchers, and scientists with environmental monitoring and collecting oceanographic data. This study was conducted to develop a rigid sail for the autonomous sailing drone. Our study aims to numerically analyze the aerodynamic characteristics of curvy twin sail and compare it with wing sail. Because racing regulations limit the sail shape, only the two-dimensional geometry (2D) was open for an optimization. Therefore, the first objective was to identify the aerodynamic performance of such curvy twin sails. The secondary objective was to estimate the effect of the sail’s spacing and shapes. A viscous Navier-Stokes flow solver was used for the numerical aerodynamic analysis. The 2D aerodynamic investigation is a preliminary evaluation. The results indicated that the curvy twin sail designs have improved lift, drag, and driving force coefficient compared to the wing sails. The spacing between the port and starboard sails of curvy twin sail was an important parameter. The spacing is 0.035 L, 0.07 L, and 0.14 L shows the lift coefficient reduction because of dramatically stall effect, while flow separation is improved with spacing is 0.21 L, 0.28 L, and 0.35 L. Significantly, the spacing 0.28 L shows the maximum high pressure at the lower area and the small low pressure area at leading edges. Therefore, the highest lift was generated.

A novel design and thermal analysis of micro solar sails for solar sailing with chip scale spacecraft

The past few decades have seen many meaningful trials on development of solar sail spacecraft with high area-to-mass ratios and thus allowing efficient, propellant-free photon propulsion. However, the restriction to bending stiffness of thin solar films has proven to be an obstacle for building solar sails with high area-to-mass ratios. This paper presents a novel design of micro solar sails for emerging lightweight chip scale spacecraft based on flexible electronics. A representative concept design of the chip scale solar sail spacecraft with area-to-mass ratios over 100 m2/kg is proposed, which enables efficient orbital transfer and attitude adjustment. To acquire large deformation for adjustment of forces, the micro solar sails consisting of bilayer beams are actuated by Joule heating. Electro-thermal analysis on the sails after deployed into space should be the prioritized and fundamental problem for following evaluation of deflection and thus change of solar radiation pressure on the reflective sails. Solar radiation, thermal reemission, and Joule heating are incorporated into the electro-thermal model for such solar sails deployed in geospace. A nonlinear second order differential equation is derived, which is solved numerically for temperature distribution across the sail. The proposed electro-thermal model is validated by finite element analysis and lays a solid foundation for the thermo-mechanical modelling, as well as flight modelling, of the chip scale spacecraft with such micro solar sails.

Temperature increase on folded solar sail membranes

All currently considered solar sail designs require the deployment of a thin reflective membrane. This membrane is stowed using some folding technique and sometimes coiled onto a spool. The temperature of the deployed sail membrane is a critical aspect for solar sail design. Depending on the geometry of the imprinted folding lines, sunlight may be reflected inside folding lines which would locally increase the temperature of the membrane. The analysis presented here aims for a quantification of that temperature increase. Microscope images of a 7.5μm thick polyimide membrane reveal the geometry of folding lines for different tensioning states. In addition, the opening of folding lines are analysed with a finite-element beam model. After the determination of the geometry as a function of the tensioning state, it is analysed how many reflections may appear in a folding line depending on its opening angle for a sail that is oriented perpendicular to the Sun. Two cases are investigated, deep space and low-Earth orbit. It is shown that, even for small tensioning states, the membrane geometry does not allow more than only two reflections. Depending on the material, this can cause a slight temperature increase that also depends on the investigated case (deep space or low-Earth orbit).

DragSail systems for satellite deorbit and targeted reentry

The safe disposal of spacecraft upon mission completion is necessary to preserve the utility of high-value orbits. Small satellite launches to low Earth orbit and plans for large commercial constellations for global internet service have the potential to exacerbate the orbital debris problem. A dragsail provides an efficient method for accelerating deorbit following the completion of a satellite's operational mission. Unlike propulsive deorbit approaches that require an active host satellite, the passive deorbit approach offered by dragsails does not require a functional host, and dragsails can offer mass savings for deorbit relative to chemical propulsion. Previous dragsail systems have employed flat square sails, which tend to tumble due to atmospheric and solar pressure perturbations. In this paper, a square pyramid geometry for the drag sail is evaluated. The pyramid geometry offers the benefit of passive aerodynamic stability about the maximum drag attitude. Through a six degree-of-freedom simulation, the passive aerodynamic stability provided by the square pyramid geometry is shown, and the deorbit performance of the square pyramid geometry is benchmarked against a typical square sail design. Uncontrolled satellite reentry results in large entry corridor uncertainties, with the range of possible re-entry trajectories often extending over multiple orbits and spanning groundtrack swaths that encompass large portions of the globe. To reduce this uncertainty, dragsails can be applied to achieve targeted reentry capability. The change in ballistic coefficient provided by sail deployment can be used as a control parameter to initiate reentry from a very low orbit, thereby reducing the uncertainty in the reentry corridor and the surface impact footprint. The ability to control the reentry corridor to within a fraction of an orbit reduces the impact of satellite reentry on the air traffic control system and can be used to constrain the probability of debris impact in populated areas. In this work, parametric studies show the efficacy of targeted reentry using dragsail deployment as a control parameter.

Influence of optical parameters on a solar sail motion

Detailed dynamic modeling of a solar sail requires recording of solar radiation pressure influence. A photon-solar sail is determined by the thrust value and the direction. We define the solar sail’s reflectivity depending on the film materials, the sail design and temperature, the thickness of multiple layers, and degradation factor, with a reasonable degree of accuracy. Thus, this work is devoted to the identification of optical characteristics of thin multilayer films in space flight conditions, i.e. to finding its reflectance, absorbance, and transmittance. In particular, the paper asks whether the solar sail simulates by a mathematical model of the optical characteristics of a multilayer epitaxial thin film. The temperature change effect and optical properties of solar sail degradation are considered as well. Solar sail flight from Earth to Mercury is designed as a simulation of the flight change in optical parameters.

Light-induced propulsion of graphene-on-grid sails in microgravity

Light sailing is the only existing in-space propulsion technology that could allow us to visit other star systems in a human lifespan. In order to best harness radiation pressure, light sails need to be highly reflective, lightweight and mechanically robust. This is traditionally achieved by the use of nanometer-thin reflective layers supported by a micrometer-thick substrate that endows them with the necessary sturdiness. This combination usually results in a sail mass that is too high to be efficiently used for extrasolar exploration. Here, we propose a potentially scalable sail design that combines a hollow substrate with an atomically-thin 2D material which, thanks to its ultimately low surface density, allows reducing the mass contribution of the substrate. To demonstrate the potential of such sails, we have studied the laser-induced displacement of graphene-on-copper sails in vacuum and in microgravity. In these conditions, 0.25 mg samples are accelerated by using lasers of different wavelengths (450 and 655 nm) and power (0.1–1 W). The measured thrust is one order of magnitude larger than the theoretical calculations for radiation pressure alone. This calls for further theoretical studies and attracts interest on graphene as light-sail material.

Гравитационное буксирование астероидов космическими аппаратами с солнечным парусом в качестве движительной установки

The paper considers the possibility of changing the orbit of potentially dangerous aste-roids using a gravity tractor. The concept of using spacecrafts equipped with a solar sail for gravitational towing is described. The analysis of this type spacecraft effectiveness is carried out on the example of changing the orbit of the Apophis asteroid. Software and mathematical support for modeling the joint motion of the asteroid-spacecraft system has been developed. The model was used to assess the impact of spacecraft with design features on the asteroid’s orbit over a long period of time. Several variants of the spacecraft configuration with different weight and sail design are considered. A comparative analysis of the results of using solar sail vehicles with similar vehicles using low-thrust jet engines is carried out.

Анализ управляемого движения исследовательского космического аппарата с солнечным парусом

The paper considers guided motion of a research spacecraft with a frame-type solar sail. When scheduled turns of the solar sail are performed, disturbing forces appear, the characteristics of which depend on the solar sail design. It is necessary to take into account the design features of the solar sail to analyze the controlled motion of the spacecraft. A finite element model of a frame-type solar sail spacecraft construction is developed. A mathematical model of motion in the combined helio-centric coordinate system is described. Local-optimal control laws of orbit elements maintenance and correction are formulated. The software developed for simulating the motion of a spacecraft with a solar sail in the heliocentric coordinate system is used in this study. The analysis of the data obtained during motion simulation demonstrates the feasibility of using the solar sail technology for interplanetary flights.

Solar sailing technology challenges

Solar sailing technology has been demonstrated in the space environment over the past decade, in Earth orbit and on an interplanetary trajectory. These technology demonstration missions, along with a forty-year history of conceptual studies and laboratory development, have provided a foundation for a new era of missions where solar sailing provides the necessary propulsion to achieve space science and infrastructure goals. Numerous challenges remain on the path to flagship-class missions utilizing solar sails. This paper provides a survey of the current state of the art in solar sailing technology, including a taxonomy of solar sail design. A summary of solar sailing missions is provided, along with description of the larger-scale ground test programs. A set of representative next-generation solar sailing mission concepts is then presented, to establish driving requirements for future applications. To meet the objectives for these future missions, sail areas must increase by a factor of 50–500 relative to the largest solar sail flown to date. Sail loading, sailcraft areal density, characteristic acceleration and lightness number must improve by one to two orders of magnitude. Technology advancements required to meet the future solar sailing performance needs are described, providing a technology roadmap for solar sailing capability.

Implementation of a Fluid-Structure Interaction Solver for a Spinnaker Sail

Abstract. The design of sails has always been done experimentally, and only recently simulations are starting to be used in the design process. This paper presents a solver that couples CFD and FEM in order to compute the deformed sail shape (flying shape) and the thrust it can provide. The complexity of the problem is both in the flow, which is fully turbulent and detached, and in the structure, which is deformable and free to move in all directions. Moreover, the coupling of the solvers has to be performed in a way that minimizes loss of information and accuracy. The CFD simulations have been run and validated with the commercial software FINE/Open. The results were reasonably satisfying when compared to the experimental data obtained by Viola et al. (2014). Consequently, the FEM solver has been successfully validated for some cases of which the analytical solution is known, due to lack of reference data for this specific case. Finally, the interpolation techniques have been implemented in Matlab and the fluid structure interaction solver has been run. From the results it can be argued that the design and flying shape of the sail are quite different and provide different thrusts. This results in the need for this type of analysis in the sail design and manufacturing process: considering the sail as rigid is not enough to have a correct representation of the spinnaker behavior. It is necessary to couple the CFD solver with a finite element solver able to describe the cloth deformation. This is true for all types of sails, but for downwind sails it is particularly important, due to their high deformability with respect to upwind sails.

Recent Advances in Numerical and Experimental Downwind Sail Aerodynamics

Abstract. Over the past two decades, the numerical and experimental progresses made in the field of downwind sail aerodynamics have contributed to a new understanding of their behaviour and improved designs. Contemporary advances include the numerical and experimental evidence of the leading-edge vortex, as well as greater correlation between model and full-scale testing. Nevertheless, much remains to be understood on the aerodynamics of downwind sails and their flow structures. In this paper, a detailed review of the different flow features of downwind sails, including the effect of separation bubbles and leading-edge vortices will be discussed. New experimental measurements of the flow field around a highly cambered thin circular arc geometry, representative of a bi-dimensional section of a spinnaker, will also be presented here for the first time. These results allow interpretation of some inconsistent data from past experiments and simulations, and to provide guidance for future model testing and sail design.