Sail Shape Research Articles

Te Laa o Lata of Taumako: Gauging the performance of an ancient Polynesian sail

Voyaging canoes were the vehicles of ancient Pacific exploration, settlement and interactions. However, we know little about the ocean-going performance of those vessels. This account of Taumako (Duff Islands) voyaging technology draws on 20 years of collaborative research initiated by Koloso Kaveia, the late paramount chief of Taumako, during which a new generation learned to build and sail voyaging canoes using only ancient materials, methods, designs and tool types. Recent researchers have tested models of bifurcate tipped sail shapes in wind tunnels. The shapes they used, which appear similar to what Taumakoans call Te Laa o Lata, demonstrated outstanding efficiency compared to others. But one researcher noticed that a more flexibly tipped model performed better than a rigid model. Historical, cultural, technical and operational information about the proportions and the built-in flexibility and plasticity of the design, materials and rig of real Te Laa o Lata suggest that there is much more to learn about their performance. If a model of Te Laa o Lata is to be tested in a wind tunnel it must be shape-shifting and proportionally correct. It also should be rigged to allow it to align and adjust itself in the ways that it actually does at sea. Furthermore, the role of the mostly submarine hull and buoyant outrigger on sail and vessel performance should be measured in a tow tank. But since Taumakoans are still building and sailing Vaka o Lata (ancient Polynesian voyaging vessels) using centuries-old designs, materials and methods, it is still possible to measure the aerodynamic performance of Te Laa o Lata and the hydrodynamic performance of the overall vessel at sea, as well as to more fully understand how the vessel works and how it is sailed under various conditions and for various purposes.

Real-time flying shape detection of yacht sails based on strain measurements

The flying shape detection of boat sails whilst racing may offer valuable insight into the sail design and performance. This paper describes a monitoring system based on fiber optic strain gauge sensors used to reconstruct in real time the form of a sail. For this purpose, a developed and implemented algorithm converts strain measurements into curvatures and integrates those in order to identify the sail deformed shape and the most significant parameters used in its characterization. Experimental studies are carried out in laboratory to validate this concept using a glass-fiber-reinforced polymer (GFRP) pultruded profile and fiber Bragg grating (FBG) sensors fixed and deformed on a calibrated board reproducing common configurations of the sail shape. It is shown that 5 instrumented sections along the beam using 10 FBG sensors are required to evaluate the profile of deformed sails, leading to maximum errors in the estimations of the sail parameters lower than 5%.

On the stability of a space vehicle riding on an intense laser beam

The Breakthrough Starshot Initiative is suggested to develop the concept of propelling a nanoscale spacecraft by the radiation pressure of an intense laser beam. In this project, the nanocraft is a gram‐scale robotic spacecraft comprising two main parts: StarChip and Lightsail. To achieve the goal of the project, it is necessary to solve a number of scientific problems. One of these tasks is to make sure that the nanocraft position and orientation inside the intense laser beam column are stable. The nanocraft driven by intense laser beam pressure acting on its Lightsail is sensitive to the torques and lateral forces reacting on the surface of the sail. These forces influence the orientation and lateral displacement of the spacecraft, thus affecting its dynamics. If unstable, the nanocraft might be expelled from the area of laser beam. In choosing the models for nanocraft stability studies, we are using several assumptions: (i) configuration of nanocraft is treated as a rigid body; (ii) flat or concave shape of circular sail; and (iii) mirror reflection of laser beam from surface of the Lightsail. We found conditions of position stability for spherical and conical shapes of the sail. The simplest stable configurations require the StarChip to be removed from the sail to make the distance to the center of mass of the nanocraft bigger than the curvature radius of the sail. Stability criteria do not require the spinning of the nanocraft. A flat sail is never stable. Copyright © 2016 John Wiley & Sons, Ltd.

A THREE-DIMENSIONAL INVERSE METHOD FOR THE DESIGN OF SAILS

This paper investigates an inverse process for the design of yacht sails. The method is described and then applied to the design of optimal sails for a specific yacht. The proposed inverse method generates the three-dimensional shapes of a headsail and mainsail from prescribed loading (i.e. differential pressure) distributions, accounts for the effect of the sea surface, and also simulates the twist and shear of the incoming flow. The uncoupled iterative routine solves a sequence of analysis steps so that the sail shapes are deformed in such a way that their updated loading distributions converge to the specified target distributions. During each iteration equations derived from two-dimensional Thin Aerofoil Theory, calculate a geometry correction from the difference between the current and target loading distributions. This correction is applied to the sail geometry, and a vortex lattice method code calculates the updated three-dimensional differential pressure distributions, which are again compared to the target distributions. Usually only five iterations are required to converge to sail shapes that have the target loading distributions. The inverse method has been validated by inverting the traditional way of analysing sails, i.e. a set of sails with known geometry has been analysed and the loading distributions on the headsail and mainsail were calculated. These distributions were then used as an input for the inverse code. It was found that the difference in camber between the original sails and the calculated geometry is less than 0.01% of camber at the mid-span of the sails. The second part of the paper presents two methods for the design of optimal sails for a yacht. One of the methods uses the more traditional analysis approach, while the other employs the inverse method described in this paper. The optimisation is performed for a Transpac 52 yacht in 12 knots (6.5 m/s) of true wind speed to obtain the best velocity made good. Results from both methods are presented and discussed and it is found that the results in terms of boat speed are similar although the trims differ slightly. However, the new inverse method is approximately nine times faster than the traditional analysis approach.

Thrust vectoring of an electric solar wind sail with a realistic sail shape

The shape of a rotating electric solar wind sail under the centrifugal force and solar wind dynamic pressure is modeled to address the sail attitude maintenance and thrust vectoring. The sail rig assumes centrifugally stretched main tethers that extend radially outward from the spacecraft in the sail spin plane. Furthermore, the tips of the main tethers host remote units that are connected by auxiliary tethers at the sail rim. Here, we derive the equation of main tether shape and present both a numerical solution and an analytical approximation for the shape as parametrized both by the ratio of the electric sail force to the centrifugal force and the sail orientation with respect to the solar wind direction. The resulting shape is such that near the spacecraft, the roots of the main tethers form a cone, whereas towards the rim, this coning is flattened by the centrifugal force, and the sail is coplanar with the sail spin plane. Our approximation for the sail shape is parametrized only by the tether root coning angle and the main tether length. Using the approximate shape, we obtain the torque and thrust of the electric sail force applied to the sail. As a result, the amplitude of the tether voltage modulation required for the maintenance of the sail attitude is given as a torque-free solution. The amplitude is smaller than that previously obtained for a rigid single tether resembling a spherical pendulum. This implies that less thrusting margin is required for the maintenance of the sail attitude. For a given voltage modulation, the thrust vectoring is then considered in terms of the radial and transverse thrust components.

Inviscid approach for upwind sails aerodynamics. How far can we go?

This work presents a full-scale experimental study of a yacht rig and sails in real upwind sailing conditions and a comparison with Fluid Structure Interaction (FSI) simulations with the ARAVANTI model (Finite Element Method for the structure and Vortex Lattice Method for the fluid). A specific on-board instrumentation system simultaneously measures loads in the rig and sails, sailing data (wind, boat attitude and speed) and the shape of sails in real navigation conditions (flying shape). Flying shape parameters are extracted using the camera-based VSPARS system to characterize the effects of sail trims and to be compared with the results of the simulation. The potential flow solver gives fast and accurate predictions of both the flying shape and the loads in the rig in most conditions. The inviscid approach, commonly used in the early stage of design, must be checked, as in particular cases where the sails are heavily loaded, flow separation is significant and results from a potential flow solver are inaccurate. A new version of the model including the heel angle as an additional degree of freedom in the structural solver enables to detect when the inviscid flow approach overestimates the aerodynamic load. This upgrade improves the utility and reliability of the inviscid flow approach which remains relevant at the early stages of design as it is much more cost-effective than RANS models.

AERODYNAMIC FORCE DEDUCTION ON YACHT SAILS USING PRESSURE AND SHAPE MEASUREMENTS IN REAL TIME

This paper describes a method of deducing aerodynamic force components produced by individual sails. This is achieved by measuring the pressure distribution at a number of discrete locations over the sail and extrapolating these measurements into a distribution across the entire sail surface. The sail shape is measured using the camera-based VSPARS system and the force distribution over the sail surface is then determined. Wind tunnel tests have been conducted to validate the accuracy of the model. Full scale testing has been undertaken to investigate how aerodynamic effects of trimming sails affect yacht performance.

Interaction between water and wind as a driver of passive dispersal in mangroves.

Although knowledge on dispersal patterns is essential for predicting long-term population dynamics, critical information on the modalities of passive dispersal and potential interactions between vectors is often missing. Here, we use mangrove propagules with a wide variety of morphologies to investigate the interaction between water and wind as a driver of passive dispersal. We imposed 16 combinations of wind and hydrodynamic conditions in a flume tank, using propagules of six important mangrove species (and genera), resulting in a set of dispersal morphologies that covers most variation present in mangrove propagules worldwide. Additionally, we discussed the broader implications of the outcome of this flume study on the potential of long distance dispersal for mangrove propagules in nature, applying a conceptual model to a natural mangrove system in Gazi Bay (Kenya). Overall, the effect of wind on dispersal depended on propagule density (g l-1). The low-density Heritiera littoralis propagules were most affected by wind, while the high-density vertically floating propagules of Ceriops tagal and Bruguiera gymnorrhiza were least affected. Avicennia marina, and horizontally floating Rhizophora mucronata and C. tagal propagules behaved similarly. Morphological propagule traits, such as the dorsal sail of H. littoralis, explained another part of the interspecific differences. Within species, differences in dispersal velocities can be explained by differences in density and for H. littoralis also by variations in the shape of the dorsal sail. Our conceptual model illustrates that different propagule types have a different likelihood of reaching the open ocean depending on prevailing water and wind currents. Results suggest that in open water, propagule traits (density, morphology, and floating orientation) appear to determine the effect of water and wind currents on dispersal dynamics. This has important implications for inter- and intraspecific variation in dispersal patterns and the likelihood of reaching suitable habitat patches within a propagule's viable period.

Experimental investigation of asymmetric spinnaker aerodynamics using pressure and sail shape measurements

An innovative method combining simultaneous on-water pressure and sail shape measurements for determining aerodynamic forces produced by sails is described and used on Stewart 34 and J80 Class yachts flying asymmetric spinnakers. Data were recorded in light and medium winds in order to check the reliability, accuracy and repeatability of the system. Results showed similar trends to the published literature. The accuracy of the system was investigated by wind tunnel tests, with determination of the entire sail shape from the stripe images recorded by the camera-based (VSPARS) system, and was found to be relatively good. Generally the pressure distributions show a leading edge suction peak, occurring at 5 to 10% of the chord length, followed by a pressure recovery and then a suction increase due to the sail curvature, with finally a reduction in suction near the trailing edge. The drive force coefficient measured on the Stewart 34 is lower than for the J80 because of a non-optimal sail shape due to light winds. On a reaching course, the standard deviation of the pressure signals was largest near the luff, reducing in the stream-wise direction, while it was high on the entire sail section when sailing on a running course.

The work achieved with the sail dynamometer boat “Fujin”, and the role of full scale tests as the bridge between model tests and CFD

The work achieved with the sail dynamometer boat Fujin was reported. At first, the sail shapes and performance for upwind conditions were measured in steady sailing conditions. The results were compared with the numerical calculations. The database of three-dimensional coordinates of the sail shapes was also tabulated with the aerodynamic coefficients. The sail shape database provides a good benchmark for the validation of sail CFD in full scale level. Then, the aerodynamic force variation during tacking maneuvers was measured by Fujin, and a new simulation model of tacking maneuver was proposed. The simulated results showed good agreement with the measured data. Finally, the scale effect problem of wind tunnel tests was discussed. Wind Tunnel tests using model sails are performed at the region of critical Reynolds number. Therefore, the wind tunnel test had to be performed very carefully. On the other hand, the full scale tests using a sail dynamometer boat are free from scale effect problems and appear more promising.

Fluid-structure interaction analysis of deformation of sail of 30-foot yacht

Most yacht sails are made of thin fabric, and they have a cambered shape to generate lift force; however, their shape can be easily deformed by wind pressure. Deformation of the sail shape changes the flow characteristics over the sail, which in turn further deforms the sail shape. Therefore, fluid-structure interaction (FSI) analysis is applied for the precise evaluation or optimization of the sail design. In this study, fluid flow analyses are performed for the main sail of a 30-foot yacht, and the results are applied to loading conditions for structural analyses. By applying the supporting forces from the rig, such as the mast and boom-end outhaul, as boundary conditions for structural analysis, the deformed sail shape is identified. Both the flow analyses and the structural analyses are iteratively carried out for the deformed sail shape. A comparison of the flow characteristics and surface pressures over the deformed sail shape with those over the initial shape shows that a considerable difference exists between the two and that FSI analysis is suitable for application to sail design.

Fluid-structure interaction analysis of deformation of sail of 30-foot yacht

Most yacht sails are made of thin fabric, and they have a cambered shape to generate lift force; however, their shape can be easily deformed by wind pressure. Deformation of the sail shape changes the flow characteristics over the sail, which in turn further deforms the sail shape. Therefore, fluid-structure interaction (FSI) analysis is applied for the precise evaluation or optimization of the sail design. In this study, fluid flow analyses are performed for the main sail of a 30-foot yacht, and the results are applied to loading conditions for structural analyses. By applying the supporting forces from the rig, such as the mast and boom-end outhaul, as boundary conditions for structural analysis, the deformed sail shape is identified. Both the flow analyses and the structural analyses are iteratively carried out for the deformed sail shape. A comparison of the flow characteristics and surface pressures over the deformed sail shape with those over the initial shape shows that a considerable difference exists between the two and that FSI analysis is suitable for application to sail design.

단순형태 세일의 변형에 대한 유체-구조 연성 해석

Since most of yacht sails are made of thin fabric, they form cambered sail shape that can efficiently generate lift power by aerodynamic interaction and by external force delivered from supporting structures such as mast and boom. When the incident flow and external force alter in terms of volume or condition, the shape of sail also change. This deformation in shape has impact on the peripheral flow and aerodynamic interaction of the sail, and thus it is related to the deformation of the sail in shape again. Therefore, the precise optimization of aerodynamic performance of sail requires fluid-structure interaction (FSI) analysis. In this study, the simplified sail without camber was under experiment for one-way FSI that uses the result of flow analysis to the structural analysis as load condition in an attempt to fluid-structure interaction phenomenon. To confirm the validity of the analytical methods and the reliability of numerical computation, the difference in deformation by the number of finite element was compared. This study reproduced the boundary conditions that sail could have by rigs such as mast and boom and looked into the deformation of sail. Sail has non-linear deformation such as wrinkles because it is made of a thin fabric material. Thus non-linear structural analysis was conducted and the results were compared with those of analysis on elastic material.

Odbudowa miasta Roztok po II wojnie światowej

The reconstruction of the city of Rostock after World War IIOne can distinguish three periods in the urban planning and housing industry in the Soviet occupation zone, which also reflect architectural trends in Rostock: 1) in the years 1945–1950 – the construction industry inspired by the style of “New Objectivity”; 2) in the years 1950–1957 – the reconstruction of city centres in the style of “national tradition” (in Rostock it was Gothic art) following the Soviet model (with trunk lines, parade squares and city landmarks); 3) industrial housing industry (“wielka płyta” / panelák – blocks of fl ats constructed of pre-fabricated concrete): “cheaper, better, more beautiful” with reference to the style of the “New Objectivity”, constructing dormitory-towns with panelak (prefab) blocks of flats. The so-called Bildzeichenarchitektur (the architect Hermann Henselmann) constitutes a special architectural form, the example of which are such buildings as: the tower block for the University in Leipzig in the form of an open book, the fine tower block of the VEB Carl Zeiss enterprise in Jena in the shape of a telescope, the tower block in the shape of a large sail in Rostock (the project was not completed). The housing industry had priority over urban planning.

Capturing Sail Shape in A Wind Tunnel Environment

AbstractValidation is an important part of computer‐based numerical modelling and can be very difficult to achieve. Comparisons with results from practical trials are often used; in this research, photogrammetry has proved to be an excellent method of creating a benchmark model from experimental results against which the computer generated numerical model can be compared. The wind tunnel experimental environment is challenging with practical limitations imposed by space and airflow capabilities. There are few documented cases where stereo‐photogrammetry has been used in wind tunnel sail modelling and the results from this research have shown it has played a prominent role in validating an innovative method of modelling fluid–structure interaction. This paper presents the photogrammetric work undertaken to validate a fluid–structure interaction (FSI) solution by measuring the shape of a close reaching asymmetric spinnaker in a wind tunnel at The University of Nottingham. There is particular focus on the data capture in the wind tunnel and the photogrammetric analysis.

요트세일의 형상계측 기법 연구

In this study, we introduced image processing technic to measure shape variations of general bodies and applied it to the flexible yacht sail. Shape measurements of simple bodies sails were carried out and results showed that technic can be a reliable method to measure shape variations of the flexible yacht sail. The sail shape variation of 30ft sloop type yacht sail is measured on different sailing conditions. As velocity and direction of wind are increased, trailing edges in the upper part of the sail become more open than the lower part of the sail which are not changed. So it is confirmed that the shape measurement of a sail shape depending on a sailing condition is possible to use image processing scheme.

分離カメラ画像の陰影によるIKAROSの膜面形状推定

IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the world's first solar sail demonstration spacecraft. It was launched in May 2010 and has 14-m-square solar sail. Solar sail is a propulsion system which accelerates the spacecraft with the solar radiation pressure, and its performance is largely affected by its unevenness. In order to recover a shape of the sail in the space, pictures of IKAROS taken in the space with cameras separated from the main body are used because of its structural complexity. There are two types of image analysis method and in this paper shape from shading method, in which the brightness of pixels is focused on, is adopted. Since there are some causes of image degradation and they are difficult to model, some cases are verified to know the detail characteristics. This paper presents the approach for analyzing the pictures to obtain the shape of IKAROS sail, and compares the result with the one of another image analysis method and flight data of the attitude motion.

A fictitious domain method for the numerical two-dimensional simulation of potential flows past sails

This paper deals with the mathematical and numerical analysis of a simplified two-dimensional model for the interaction between the wind and a sail. The wind is modeled as a steady irrotational plane flow past the sail, satisfying the Kutta-Joukowski condition. This condition guarantees that the flow is not singular at the trailing edge of the sail. Although for the present analysis the position of the sail is taken as data, the final aim of this research is to develop tools to compute the sail shape under the aerodynamic pressure exerted by the wind. This is the reason why we propose a fictitious domain formulation of the problem, involving the wind velocity stream function and a Lagrange multiplier; the latter allows computing the force density exerted by the wind on the sail. The Kutta-Joukowski condition is imposed in integral form as an additional constraint. The resulting problem is proved to be well posed under mild assumptions. For the numerical solution, we propose a finite element method based on piecewise linear continuous elements to approximate the stream function and piecewise constant ones for the Lagrange multiplier. Error estimates are proved for both quantities and a couple of numerical tests confirming the theoretical results are reported. Finally the method is used to determine the sail shape under the action of the wind. © EDP Sciences, SMAI, 2011.

Database of sail shapes versus sail performance and validation of numerical calculations for the upwind condition

A database of full-scale three-dimensional sail shapes is presented with the aerodynamic coefficients for the upwind condition of International Measurement System (IMS) type sails. Three-dimensional shape data are used for the input of numerical calculations and the results are compared with the measured sail performance. The sail shapes and performance were measured using sail dynamometer boat Fujin. This is a boat of 10.3-m length overall in which load cells and CCD cameras were installed to simultaneously measure the sail forces and shapes. At the same time, the sailing conditions of the boat, e.g., boat speed, heel angle, wind speed, and wind angle, were measured. The sail configurations tested were: mainsail with 130% jib, mainsail with 75% jib, and mainsail alone. Sail shapes were measured at several vertical positions for the shape parameters defined by: chord length, maximum draft, maximum draft position, entry angle at the luff, and exit angle at the leech, all of which finally yield three-dimensional coordinates of the sail geometry. The tabulated shape data, along with aerodynamic coefficients, are presented in this article. In addition, numerical flow simulations were performed for the measured sail shapes and the sailing conditions to investigate the capability and limitations of the methods through detailed comparison with the measurements. Two numerical methods were used: a vortex lattice method (VLM) and a Reynolds-averaged Navier–Stokes (RANS)-based computational fluid dynamics method. The sail shape database, in association with the numerical results, provides a good benchmark for the sail performance analysis of the upwind condition of IMS type sails.

Development of Deployment System for Small Size Solar Sail Mission

The Japan Aerospace Exploration Agency (JAXA) is studying the feasibility of using the solar power sail as a new propulsion engine for deep space exploration missions. In this paper, the sail shape and equipment layout for missions utilizing small-sized solar power sails are proposed. The two-stage deployment method of the sail is also proposed. The sail need to be deployed statically at the first stage, and two types of deployment mechanisms are introduced. On the other hand the second stage of the deployment can be performed dynamically, and the oscillating motion of the membrane is converged by tethers connecting the membrane to the main body. The deployment motions are analyzed by numerical simulations using multi-particle models in order to verify the deployment. They are compared with the results calculated by finite element method models. The numerical simulation results are discussed from the technological viewpoint of the sail deployment dynamics and mechanisms.