Sail Structure Research Articles

Aerodynamic Analysis of Rigid Wing Sail Based on CFD Simulation for the Design of High-Performance Unmanned Sailboats

The utilization of unmanned sailboats as a burgeoning instrument for ocean exploration and monitoring is steadily rising. In this study, a dual sail configuration is put forth to augment the sailboats’ proficiency in its wind-catching ability and adapt to the harsh environment of the sea. This proposition is based on a thorough investigation of sail aerodynamics. The symmetric rigid wing sails NACA 0020 and NACA 0016 are selected for use as the mainsail and trailing wing sail, respectively, after considering the operational environment of unmanned sailboats. The wing sail structure is modeled using SolidWorks, and computational fluid dynamics (CFD) simulations are conducted using ANSYS Fluent 2022R1 software to evaluate the aerodynamic performance of the sails. Key aerodynamic parameters, including lift, drag, lift coefficient, drag coefficient, and thrust coefficient, are obtained under different angles of attack. Furthermore, the effects of mainsail aspect ratios, mainsail taper ratios, and the positional relationship between the mainsail and trailing sail on performance are analyzed to determine the optimal structure. The thrust provided by the sail to the boat is mainly generated by the decomposition of lift, and the lift coefficient is used to measure the efficiency of an object in generating lift in the air. The proposed sail structure demonstrates a 37.1% improvement in the peak lift coefficient compared to traditional flexible sails and exhibits strong propulsion capability, indicating its potential for widespread application in the marine field.

Analysis of Dynamic Characteristics of Rotor Sail Using a 4DOF Rotor Model and Finite Element Model

The interest in wind-assisted ship propulsions (WASPs) is increasing to improve fuel efficiency and to reduce greenhouse gas emissions in ships. A rotor sail, one of the typical WASPs, can provide auxiliary propulsive force by rotating a cylinder-shaped structure based on the Magnus effect. However, due to its huge rotating structure, a meticulous evaluation of the influence on the ship structure and dynamical stability of the rotating structure should be conducted in the design stage. In this respect, an analysis of the rotating structure for a 30 m height and 3 m diameter rotor sail was conducted in this study. First, a 4DOF (four-degree-of-freedom) model was derived to simplify the dynamics of the rotor sail. Using the 4DOF model, natural frequencies for four low-order modes of the rotor sail were calculated, and frequency responses at support points were predicted. Next, a comparison and validation with the finite element model of the rotor sail were carried out. For the 1st and 2nd natural frequencies, a difference of approximately 0.3 Hz was observed between the 4DOF model and the finite element model, confirming the effectiveness of the 4DOF model for low-order modes. In analysis with changes in the bearing supporting stiffnesses, it was verified that lower support bearings have a significant impact on rotor dynamics compared to upper support bearings. Vibration response at the upper support was also confirmed through frequency response analysis caused by imbalance at Thom disk and mid-plate. Additionally, when estimating the eccentricity of the Thom disk as imbalance, a limit of eccentricity error could be set as 24 mm. The presented modeling procedures and analysis results can be references during early design stage of a novel rotor sail structure.

A wind‐electric hybrid polar roaming robot: Design, modeling, and experiments

AbstractThe background observation of the polar region is used to develop the requirements with regard to low carbon and no pollution for scientific research. Polar robots have certain advantages over human beings, but their long‐term residence still faces the problems of energy supply and autonomous control. To solve this problem, a hybrid wind‐ and electricity‐driven polar roaming robot is presented and includes the consideration of low carbon and energy savings. It innovatively uses wind energy as the main driving force and is assisted by electric energy, which is used when wind energy is not sufficiently available. In the ideal scenario, compared with traditional pure electric‐driven robots, it can save up to approximately 3/4 of energy. In this paper, the design principle is described, then the sail structure and some innovative mechanisms of the robot are designed, and the theoretical analysis and simulation of the mechanisms are carried out. The innovative mechanism enables good motion control under wind and electric drives, as well as the switching of the drive modes. Of particular importance, the aerodynamic performance of the sail structure is analyzed, and the optimal control scheme for sailing the robot is proposed. Then, a prototype of the polar robot is developed, the structure rationality and principle feasibility of which are verified in experiments, and the energy‐saving effect is confirmed by calculation.

Product design innovation based on the functional characteristics of the eight-masted windmill

To catch and research the functional characteristics of the eight-masted vertical windmill and its automatic readjustment of sail angle in the Lixia River area of northern Jiangsu Province, to permit this intangible cultural heritage a new practical meaning in modern tourism through the innovative design of the sail structure of the eight-masted windmill, and to come up with a portable folding windmill product suitable for outdoor sports enthusiasts. Firstly, we spell out the history of the eight-masted windmill and its “trotting horse lamp” structure through literature research and draw the working principle of the eight-masted windmill in operation, and combine the eight-masted windmill with power generation device by converting wind energy into electricity. The design direction was to design a lightweight, breeze start, and stable power output windmill generator; secondly, the sketch of the windmill main shaft structure and scheme were selected, and the integrated form of the fan blade and the mast was selected as the sketch scheme; finally, the model experiment of the prototype of the folding scheme was conducted, and the absolute pressure difference between blades was analyzed by hydrodynamics to determine that the windmill can be used to generate electricity. After verifying its feasibility, the portable folding generator was modeled in 3D by MCAD, and make a physical model of the generator was made in a reduced scale of 1:2.5. Through the innovative design of the eight-masted windmill, it is made to serve the production life of modern society.

Electrothermally Driven Reconfiguration of Microrobotic Beam Structures for the ChipSail System

Solar sailing enables efficient propellant-free attitude adjustment and orbital maneuvers of solar sail spacecraft with high area-to-mass ratios. However, the heavy supporting mass for large solar sails inevitably leads to low area-to-mass ratios. Inspired by chip-scale satellites, a chip-scale solar sail system named ChipSail, consisting of microrobotic solar sails and a chip-scale satellite, was proposed in this work. The structural design and reconfigurable mechanisms of an electrothermally driven microrobotic solar sail made of Al\Ni50Ti50 bilayer beams were introduced, and the theoretical model of its electro-thermo-mechanical behaviors was established. The analytical solutions to the out-of-plane deformation of the solar sail structure appeared to be in good agreement with the finite element analysis (FEA) results. A representative prototype of such solar sail structures was fabricated on silicon wafers using surface and bulk microfabrication, followed by an in-situ experiment of its reconfigurable property under controlled electrothermal actuation. The experimental results demonstrated significant electro-thermo-mechanical deformation of such microrobotic bilayer solar sails, showing great potential in the development of the ChipSail system. Analytical solutions to the electro-thermo-mechanical model, as well as the fabrication process and characterization techniques, provided a rapid performance evaluation and optimization of such microrobotic bilayer solar sails for the ChipSail.

Finite element modeling of fluid-structure interaction of an elastic 2D flag in harmonic viscous fluid flow and an elastic 3D sail structure in stationary viscous fluid flow (concised version)

Finite element modeling of fluid-structure interaction of an elastic 2D flag in harmonic viscous fluid flow and an elastic 3D sail structure in stationary viscous fluid flow (concised version)

Deployment simulation of a scalable planar gossamer space structure based on Miura-ori pattern

Miura-ori is a rigid origami structure utilized in the packaging of deployable solar panels for use in space or in the folding of maps. It's pattern can largely reduce the membrane stress and improve the work efficiency. Inspired by origami structures, we numerically and experimentally studied a scalable solar sail structure. As an improvement of the existing membrane simulations, a variable Poisson's ratio model considering the wrinkling effect of the membrane was introduced. We focused on a quadrant shape and studied how its geometry parameters and initial imperfections affect the membrane mechanical behavior. We also designed and fabricated a pantographic mechanism as an origami membrane actuator. In addition, design protocols of deployment applied to a scalable gossamer structure were proposed.

Structural dynamic responses of a stripped solar sail subjected to solar radiation pressure

The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural efficiency. In this paper, the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in sequence. Considering the coupling effects between booms and membrane strips, an exact and semi-analytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is established. The case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic response. Larger prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic response. Increasing thickness of the boom will benefit to stability of the sail and reduce the resonant amplitudes. This proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail.

Modeling of solar sail surface oscillations during interplanetary flight

The purpose of this work is to study the influence of solar sail surface oscillations on the motion of a spacecraft performing an interplanetary flight. The solar sail is a propulsion system, creating thrust due to the pressure of sunlight. The article consists of three parts. The first part focuses on the wave equation applied to this problem. The equation for oscillations is derived for various cases of sail loading, and various types of its design. Also, we derived a formula for the thrust produced by the solar sail. In the second part, the problem of oscillations of the sail structure is solved and its thrust is estimated. Solar sail thrust depends both on the shape of the sail, and on its distance from the Sun. In the third part, the interplanetary flight is modeled taking into account these factors.

Rigid–flexible coupled dynamics analysis for solar sails

The coupled orbit, attitude, and structural dynamics are established for the sailcraft with sliding mass, which is modeled as the Euler beam and merely experiences the pitch motion. The von Karman’s nonlinear strain–displacement relation and Kelvin–Voigt model are adopted to consider the geometric nonlinearity and damping of the structure, respectively. The torques generated by the gravity gradient of the two-body sailcraft, the center-of-mass (cm) and center-of-pressure (cp) offset, the motion of the sliding mass, and the coupled attitude-vibration motion are deduced in detail, respectively. The dynamics responses influenced by the flexibility of the sail structure are examined by analyzing the simulation results for the dynamics models with (m1) and without (m2) the geometric nonlinearity and the rigid-body model (m3), respectively. The pitch responses and corresponding torques are calculated and compared for various cases adopting a range of velocities and initial positions of the sliding mass to see how the pitch motion is affected by the parameters. The transient and steady-state dynamics responses are also identified in the simulation cases. It is suggested that the full nonlinear model should be adopted for the sailcraft in long duration missions and the restricted position of the sliding mass could be selected elaborately to utilize the resultant torque by the gravitational and cm/cp torques.

Finite Element Modeling and Motion Planning of an Adaptive Elastic Wingsail

A systematic motion planning methodology for elastomechanic structures is introduced using a combination of flatness based feedforward control and state feedback control. The concept is applied to a so-called wingsail for yachts, this structure can be described as a complex flexible structure based on two curved carbon sail areas with embedded actuators allowing to generate deflections to accomplish an adaptive sail structure. Due to the complexity of the structure the finite element method (FEM) is applied to determine the equations of motion (EOMs) in terms of a high dimensional system of ordinary differential equations (ODEs). The usage of model order reduction by means of modal truncation leads to a design system of feasible dimension and also directly represents a suitable form for the determination of the flatness-based state and input parametrization. This yields an efficient approach for motion planning and feedforward control, which is amended by a state feedback controller to address model uncertainties or disturbances. Simulation results illustrate the performance of the presented two-degrees-of-freedom control approach.

Effect of Imidazolium-Based Surface-Active Ionic Liquids on the Orientation of Liquid Crystals at Various Fluid/Liquid Crystal Interfaces.

A series of imidazolium-based surface-active ionic liquids (IM-SAILs), viz., single-chained IM-SAILs, 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br, n = 12, 14, 16), 1-dodecyl-3-methylimidazolium salicylate ([C12mim]Sal), 1-dodecyl-3-methylimidazolium 3-hydroxy-2-naphthoate ([C12mim]HNC), 1-dodecyl-3-methylimidazolium cinnamate ([C12mim]CA), 1-dodecyl-3-methylimidazolium para-hydroxy-cinnamate ([C12mim]PCA), gemini IM-SAIL, and 1,2-bis(3-dodecylimidazolium-1-yl)ethane bromide ([C12-2-C12im]Br2), along with three short-chained ionic liquids (ILs) [ethylammonium nitrate (EAN), propylammonium nitrate (PAN), and butylammonium nitrate (BAN)] were synthesized and applied to nematic liquid crystal (LC)/fluid interfaces. First, we evaluated the influence of the length and number of aliphatic chains as well as the counterion in the IM-SAIL structures on the anchoring of LCs at the aqueous/LC interface. It was observed that the threshold concentration of [Cnmim]Br (n = 12, 14, 16) decreased with the increase in aliphatic chain length. And double-chained [C12-2-C12im]Br2 has a far lower threshold concentration than single-chained [C12mim]Br. But the alteration of counterions (e.g., Br- and aromatic counterions) scarcely affected the anchoring of LCs at the interface. Second, we investigated the alignment of LCs at the diverse IL/LC interfaces in the presence of IM-SAILs. It is found that the variations in both aliphatic chain length and number can remarkably change the trigger points of the orientational transition of LCs at the EAN/LC interface. Specifically, with a slight increase in the alkyl chain length of short-chained ILs, as the fluid medium, the orientation of LCs varied tremendously at the IL/LC interface. Therefore, the higher threshold concentration of IM-SAILs and the corresponding greater stability in the optical appearance of LCs at the EAN/LC interface compared to that of the aqueous/LC interface can be ascribed to the discrepancy in the microstructure of water and IL. Finally, we verified that the volume ratio of H2O to EAN could more dramatically affect the alignment of LCs than the change in IM-SAIL concentration in aqueous solution. This work first illustrated the impact of SAIL structure on the LCs orientation at the aqueous/LC, IL/LC, and H2O-IL mixture/LC interfaces, which will inspire us to obtain a stabilized molecular alignment of LCs at the IL/LC interfaces and to further design novel functionalized SAIL molecules for various chemical and biological applications.

Structural Dynamics and Attitude Control of a Solar Sail Using Tip Vanes

This paper delves into the structural and attitude dynamics of a cord-mat square solar sail being controlled by two-degree-of-freedom tip-vane actuation. The paper’s main goal is to simulate and analyze the behavior of a solar sail under a tip-vane attitude control scheme using a geometrically nonlinear elastic finite element method model of the sail. The controller/structural interaction is of particular interest, as the control solution of the two-degree-of-freedom tip-vane actuation is based on a flat, inflexible sail. The sail structure is further augmented by a wrinkling model for handling the membranes under negative strain. The model is further augmented by the disturbance forces produced by the reflective sail membrane itself. A combined, dynamic simulation of all of the aforementioned are performed to analyze the performance of the control system as a whole.

Degradation of metallic surfaces under space conditions, with particular emphasis on Hydrogen recombination processes

The widespread use of metallic structures in space technology brings risk of degradation which occurs under space conditions. New types of materials dedicated for space applications, that have been developed in the last decade, are in majority not well tested for different space mission scenarios. Very little is known how material degradation may affect the stability and functionality of space vehicles and devices during long term space missions.Our aim is to predict how the solar wind and electromagnetic radiation degrade metallic structures. Therefore both experimental and theoretical studies of material degradation under space conditions have been performed. The studies are accomplished at German Aerospace Center (DLR) in Bremen (Germany) and University of Zielona Góra (Poland).The paper presents the results of the theoretical part of those studies. It is proposed that metal bubbles filled with Hydrogen molecular gas, resulting from recombination of the metal free electrons and the solar protons, are formed on the irradiated surfaces. A thermodynamic model of bubble formation has been developed. We study the creation process of H2-bubbles as function of, inter alia, the metal temperature, proton dose and energy. Our model has been verified by irradiation experiments completed at the DLR facility in Bremen.Consequences of the bubble formation are changes of the physical and thermo-optical properties of such degraded metals. We show that a high surface density of bubbles (up to 108cm-2) with a typical bubble diameter of ∼0.4μm will cause a significant increase of the metallic surface roughness. This may have serious consequences to any space mission.Changes in the thermo-optical properties of metallic foils are especially important for the solar sail propulsion technology because its efficiency depends on the effective momentum transfer from the solar photons onto the sail structure. This transfer is proportional to the reflectivity of a sail. Therefore, the propulsion abilities of sail material will be affected by the growing population of the molecular Hydrogen bubbles on metallic foil surfaces.

Sail Structure Design and Stability Calculation for Sail-assisted Ships

Ship sail-assisting is a kind of integrated technology involved in fluent dynamic analysis, sail structure design, sail rotation control, ship stability and maneuverability. This paper systematically introduces several aspects of sail-assisting technology. The paper firstly introduces sail type selection and experimental results of arc sail models. Thrust force coefficient, drifting force coefficient, lifting force coefficient, resistance coefficient and rotating torque coefficient of the sail model are discussed and optimal sail rotated angle is calculated in the paper. A control mechanism and the material of sail structure are designed for the sail operation of a ocean-going bulk carrier. Based on stability requirements of ocean-going ships, this paper proposes a stability criterion for sail-assisted ships and suggests a calculation method of stability parameter for the requirements. Comments and recommendations are finally discussed for the further application of the sail onboard ship.

Nonlinear static analysis-based thrust for solar sail

An accurate thrust model is extremely important for the navigation and space mission of solar sails. The thrust is deeply affected by the deformation of the highly flexible structure. Thus, in this paper, the exact thrust models for two-point and infinite-point-connected sails are presented by calculating the static deformations for the sail support beam structure with geometrical nonlinearity based on the assumption that the deformation of the sail film coincides with the support beam. And the film is merely regarded as the structure that transfers the solar radiation pressure force to the support beam. The nonlinear finite element model of the support beam with the Von-Karman’s nonlinear strain–displacement relationships is obtained. Then the Newton iteration method is used to calculate the large deformation of the sail structure. The thrust-modification methods are proposed for the two-connected sail. The deformation of the two-point-connected sail is larger than the infinite-point-connected sail, and the thrust loss of the two-point-connected sail is larger than the infinite-point-connected sail by nonlinear static calculations. Some suggestions are given based on the calculation results and relevant analysis. The thrust model should be verified and modified by in-flight data in the future.

Statics Analysis on Sail Structure for Ocean-Going Ships

It is becoming a trend to achieve the purpose of energy conservation and emissions reduction that application of sailing navigation technology in large ocean-going ships. Two kinds of three-dimensional models of sail are presented in this paper, and they are made to do a structural calculation under the action of gravity with the ANSYS simulation software. Then the deflection of the sail under the action of gravity load and the distribution of its stress is concluded. A more reasonable design of sail structure can be selected.

Dynamics and Control of a Flexible Solar Sail

Solar sail can merely make use of solar radiation pressure (SRP) force as the thrust for space missions. The attitude dynamics is obtained for the highly flexible solar sail with control vanes, sliding masses, and a gimbaled control boom. The vibration equations are derived considering the geometric nonlinearity of the sail structure subjected to the forces generated by the control vanes, solar radiation pressure (SRP), and sliding masses. Then the dynamic models for attitude/vibration controller design and dynamic simulation are obtained, respectively. The linear quadratic regulator (LQR) based and optimal proportional-integral (PI) based controllers are designed for the coupled attitude/vibration models with constant disturbance torques caused by the center-of-mass (cm)/center-of-pressure (cp) offset, respectively. It can be concluded from the theoretical analysis and simulation results that the optimal PI based controller performs better than the LQR based controller from the view of eliminating the steady-state errors. The responses with and without the geometrical nonlinearity are performed, and the differences are observed and analyzed. And some suggestions are also presented.

Spin-stabilized solar sail for displaced solar orbits

An optical force model is used to investigate the stability of a flat spinning solar sail in a displaced solar orbit. The solar sail can be stabilized in the orbit by design of the spinning rate and the sail structure. The orbital and attitude dynamics are studied separately. The orbit is stable as the sail attitude keeps fixed with respect to the sunlight, as does that of a perfectly reflecting solar sail. The attitude is stable as long as the spin angular velocity is much larger than the orbital angular velocity. The stability of the individual components cannot guarantee the stability of the entire system since the orbit and attitude interact with each other. Therefore, the coupled dynamics of the orbit and attitude are used to study the overall stability; the results show that the coupled system is also stable. It should be noted that the orbit and attitude are critically not asymptotically stable. The analysis only provides the necessary conditions for stability because a linearization is performed. To numerically verify the nonlinear stability of the true nonlinear system, the dynamical equations are simulated for a time that is longer than the mission life.

Healed Fractures in the Neural Spines of an Associated Skeleton of Dimetrodon: Implications for Dorsal Sail Morphology and Function

Hyperelongate neural spines forming a prominent dorsal “sail” are known in eight genera distributed between two families of pelycosaurian-grade synapsids. Although the function(s) of the sail remain disputed, most researchers assume that resilient soft tissue stretched between the elongate neural spines, extending to the distal tips. Hypotheses to explain the purpose of the sail have included thermoregulation (Romer & Price, 1940; Bramwell & Fellgett, 1973; Haack, 1986; Tracy et al., 1986; Bennett, 1996; Florides et al., 1999) and sexual selection (Tomkins et al., 2010). In this paper, we analyze the natural pathologies found in the neural spines of a very large pelycosaur, Dimetrodon giganhomogenes, as a natural experiment: What would ensue in the event of sail breakage and what does that tell us about sail structure, development, maintenance, and the orientation of the sail?A series of seven associated neural spines from fmnh UC 1134 demonstrate subtle though distinctly abnormal rugosities, a sign most often indicative of a well-healed hard callus of bone fracture. Microstructural examination revealed surprising facts: not only did the abnormal bone areas prove NOT to be fracture hard callus, but the abnormal tissue reflected underlying material failure resulting from slippage between adjacent lamellae of bone. Moreover, the characteristic cranial and caudal orientation of the deep longitudinal grooves contributing to the classic dimetrodont figure-8 spine cross section was rapidly reestablished in vivo by a combination of osteoclastic resorption and additional lamellar deposition of bone to regain the “correct” pre-injury orientation, underscoring the architectural importance of the dumbbell shape in resisting lateral bending. This bone disruption and repair occurred at least five seasons before death, which explains the well-healed external appearance of the lesions. The absence of vascular communicating canals casts doubt on the widely held hypothesis that these grooves contained blood vessels that supplied a thermoregulatory sail. Furthermore, the distal morphology of spines in more complete specimens, including the type fmnh UC 112 and omnh 01727, suggests that the dorsal margin of the sail was located well proximal to the tips of the elongate neural spines. The cross-sectional architecture of the spines suggests a further hypothesis: that the proximal portion of the sail may have also functioned as an energy storage device, facilitating fast locomotion in this top predator.