True Wind Research Articles

Wingsail performance in unsteady atmospheric surface layer winds

The performance of wind propulsion systems is evaluated in unsteady inhomogeneous winds with tools that are routinely used to predict the performance of wind turbines and which give access to the unsteady aerodynamic forces acting on the wingsail. A rigid wingsail exposed to a realistic atmospheric surface layer wind is used as a testbed. For this case, we show that standard deviations of the aerodynamic driving force are larger than 15%–20% of the mean values when the true wind velocity is larger than the ship speed. We also show that the mean aerodynamic driving forces computed by averaging the unsteady driving forces are only slightly smaller than the ones computed on the mean wind despite the strongly nonlinear dependence of the unsteady forces on the wind velocity and direction.

The effect of current on the course and speed of a sailing ship

A feature of the movement of a sailing ship is that its speed depends not only on the strength of the wind, but also on the course of the ship in relation to the wind. This dependence is graphically reflected in its polar. A special feature of the movement of a sailing ship in a current is the influence of this current itself on the wind acting on the sails. The specifics of choosing the course of a sailing ship on a current, taking into account this influence, are considered. The accepted terminology is clarified and new terminology is proposed in the names of the winds involved in the creation of the apparent wind acting on the sails. The correct view of the speed triangle is shown to determine the true wind in the presence of wind drift of the vessel. A technique is proposed for determining the course and speed of a sailing ship in a current using its polar.

Метод оперативной корректуры спутниковой гидрометеорологической информации в районе плавания судна с помощью подспутниковых измерений

The problem of assessing the state of the sea surface by combining satellite and ship measurements is considered. Information about the strength and direction of the wind at the sea surface is important to ensure safe navigation and planning of vessel transit routes. It is of key importance for weather forecasting and excitement. Wind data is traditionally obtained from passing ships and buoys. Ship data covers only limited areas of the World Ocean and is received unevenly, buoy data is highly sparse, which makes it impossible to obtain an adequate picture of the distribution of atmospheric currents. The use of remote sensing satellites has made it possible to increase the density of measurements of wind speed and direction by orders of magnitude, and the relevance of the data obtained. However, satellite measurements can be distorted. In particular, the influence of atmospheric precipitation (rain) can give a two-fold error in measuring wind speed. Strong and weak winds also create problems: in strong winds, the measured data underestimate the true wind speed, in weak winds they overestimate. A method for correcting satellite data on wind speed and direction is proposed. The essence of the method is to use subsatellite ship measurements in conjunction with satellite information. Knowing the weather data measured locally (from the ship), it is possible to calculate regression parameters for correcting satellite data. By applying regressions with calculated parameters to satellite images in the water area, it is possible to obtain more accurate weather data in the area of the vessel's route. The results of calculations based on real satellite and on-board data in the waters of the Sea of Okhotsk are presented. A polynomial of the second degree is taken as a regression function. It is shown that the correction using subsatellite ship measurements more accurately characterizes the wave than the data directly received from the satellite.

Tackling Modern Sailing Challenges with a CFD-based Dynamic VPP

A dynamic Velocity Prediction Program (VPP) integrated in a Computational Fluid Dynamics (CFD) code is described. Aerodynamic forces are obtained either through empirical coefficients or interpolated from aerodynamics matrices. These aerodynamic forces are then input to the hydrodynamics CFD solver, which solves both the flow and the motions of the boat, resulting in a closely coupled VPP. For a given True Wind Angle and True Wind Speed a sail power parameter is optimised to obtain the best possible boat speed within heel angle constraints. This approach allows naval architects to swiftly and precisely compare several yacht designs in real sailing configurations using only a few CFD computations. Several advanced features recently added to this program are covered in this paper including convergence criteria, automatic grid refinement, foil fluid-structure interaction, multiple aerodynamics models and rudder control. Results obtained from our CFD VPP on a 40-feet fast-cruising yacht demonstrates promising agreement with other existing VPP polars, affirming the accuracy and reliability of our approach. The CFD VPP presented was also successfully applied to an IMOCA, a 60-feet racing yacht.

Acquisition and integration of differential pressure measurements on sails for boat performances improvement

In this paper, we integrated within a specifically developed acquisition system, denoted as Oceanus, the measurements from a differential pressure sensor between the two sides of a sail (windward and leeward sides); experiments have been performed using a light jib sail of a 35 feet cruising-racing yacht. We analyzed the correlation between such a signal and other standard signals usually present on board such as boat speed, intensity and direction of apparent or real wind; moreover, data from Inertial Measurement Units are handled. We also considered the Target Data, which depend on the actual point of sail, and the discrepancy between measured data and the predicted Targets is monitored as an error in terms of the true wind angle and boat velocity. In this way, the trimmer/helmsman can monitor the differential sail pressure together with Target data and decide to reduce the error with a correction in how sails are trimmed, rather than in how the boat is steered to achieve an improvement of boat performances. The resulting telemetry system represents an effective low cost solution, which is affordable even for amateur yachtsmen.

A novel wind comfort evaluation method for different airflows by considering dynamic characteristics of wind direction and velocity

The dynamic velocity characteristics of wind have been studied over the past several decades. However, there was a lack of consideration for the incoming flow directions. Besides, the comfort assessment studies mainly focused on thermal comfort from the mechanism of heat transfer instead of wind comfort from the mechanism of tactile stimuli. This study carried out a mixed indoor and outdoor experiment. The indoor experiment was conducted with a room temperature of 29 °C and a relative humidity of 50%, which closely resembled the outdoor environmental conditions. Totally 17 healthy subjects dressed at 0.36 clo and being sedentary were exposed to five kinds of airflow during the experiment. According to the results, outdoor true natural wind was more preferred than directly supplied wind. This paper also proposed a novel wind comfort (WC) model by considering various air parameters. The model relied on tactile stimuli, which were the reflections of wind pressure fluctuations and could be affected by changes in velocity and direction of airflows. Based on these two dynamic characteristics, four wind perceptions, including wind intensity vote (WIV), velocity variation sense (VVS), direction variation sense (DVS) and overall enveloping sense (OES) were introduced and linearly regressed. The findings revealed that not only velocity but also the direction could affect the wind comfort evaluation. This paper will hopefully provide a better understanding of impacts of incoming flow directions on comfort and further rethink a novel route of dynamic wind environment imitation for future indoor environments.

A study of the characteristics of dynamic incoming flow directions of different airflows and their influence on wind comfort

Studies on the dynamic characteristics and comfort evaluation of natural and mechanical wind have been extensively conducted over the past two decades. However, in these contributions, varying wind directions were not considered. In this study, we systematically analysed different airflows from the perspective of the wind azimuth by using statistical analysis, power spectral analysis, wavelet analysis and chaos analysis. Several concepts are newly defined, such as the wind azimuth fluctuation rate (WAFR), the wind azimuth power spectral exponent (βa value) and the dimensionless parameter of the phase space curve (δa value). The results show that the standard deviations (SDs) of the wind azimuth, WAFR, and βa values of typical natural wind are typically larger than those of mechanical wind, while the δa value is lower. The differences in the direction characteristics between natural and mechanical wind highly agree with those in the velocity characteristics. To determine how the direction influences wind comfort, seventeen human subjects were invited to participate in a mixed experiment and exposed to five types of airflow. The results show that true natural wind was preferred, which may be due to the frequently changing direction. The findings also reveal that both the velocity and direction characteristics significantly influence wind comfort evaluations. By understanding the dynamic wind direction characteristics of airflows, this paper may provide new insights into further studies on characteristics, comfort assessments and the application of dynamic wind field in indoor built environments.

Prescribed performance LOS guidance-based dynamic surface path following control of unmanned sailboats

The unmanned sailboat path following control problem with model uncertainties and unknown external disturbances is addressed. Firstly, different sailing strategies are set for the sailboat under three different wind fields in nature for its vulnerability to the true wind field so that the sailboat can complete the path-following task under different wind directions. Secondly, a barrier Lyapunov function with prescribed performance is used to limit position errors and heading errors of the unmanned sailboat within prescribed constraints. A radial-based function neural network technique is then introduced to approximate model uncertainties. Then an adaptive law is introduced to estimate an upper bound on the sum of the external environmental disturbances and neural network approximation errors. A path-following control scheme for the unmanned sailboat is proposed by the backstepping method and combined with the dynamic surface control technique. Finally, stability analysis is performed by Liapunov functions, demonstrating that the proposed control method can guarantee that all error signals in the closed-loop system are semi-global uniform ultimate bounded and that the prescribed performance constraints are not violated. Finally, the effectiveness of the scheme is demonstrated by simulation.

Алгоритм управления движением колесного судна при ветровом воздействии

The article highlights the study of the influence of wind parameters and operating modes of the propulsion plant on the quality indicators of motion control of the vessel with a paddle type propulsion and steering system. The dynamics of the vessel motion is considered on the basis of a mathematical model of a paddle vessel. Wind action has a significant impact on the dynamic characteristics of the vessel due to its design features: flat bottom, shallow draft, large windage. The effect of apparent and true wind with both constant and variable wind parameters and operating modes of the propulsion plant is analyzed. Conclusions are drawn about the limits of the vessel controllability for various parameters of motion and wind action. The operability area of the vessel control system is constructed depending on the direction and speed of the wind. It is noted that a change in the speed of the vessel leads to a change in the parameters of the apparent wind, which in turn affects the dynamics of the vessel. To compensate for the effect of wind changes there is proposed an algorithm for changing the speed of the vessel while keeping a given optimal trajectory under wind impact. The algorithm is designed subject to the control of the ratio of the rotational speed of the propeller wheels, without taking into account the impact of the thruster. A computer simulation of the ship’s movement was performed with a changing speed of movement and different parameters of the wind effect, taking into account the proposed algorithm. The proposed control algorithm makes it possible to compensate for the effect of apparent wind in transient operating modes of the propulsion plant, to ensure movement along a given trajectory and to improve the accuracy of ship control.

Wind-Assisted Ship Propulsion: Matching Flettner Rotors with Diesel Engines and Controllable Pitch Propellers

The harvesting of wind energy and its transformation into a thrust force for ship propulsion are gaining in popularity due to the expected benefit in fuel consumption and emission reductions. To exploit these benefits, a proper matching between the conventional diesel engine-screw propeller propulsion plant and the wind-assisted plant is key. This paper aims to present a method and a code for the preliminary sizing of a ship propulsion plant based on a diesel engine, a controllable pitch propeller, and one or more Flettner rotors. A mathematical model describing the behaviour of the rotor in terms of propulsive thrust and power is proposed. The rotor model has been integrated into an existing diesel propulsion model in order to evaluate the ship’s fuel consumption. The ship’s propulsion model is written in a parametric form with respect to the following design parameters: ship dimensions and resistance-speed curve, propeller diameter, engine power, rotor geometry, and true wind conditions. The methodology helps in evaluating the engine–propeller working points and eventually the total ship propulsive power, including the power required to spin the rotor. It provides a way to compare wind-assisted propulsive solutions in terms of fuel consumption and CO2 emissions. A 3000-ton Ro-Ro/Pax ferry has been selected as a case study. Results on the parametric analysis of rotor dimensions and propeller pitch optimization are presented.

Uncertainty in the Mobile Observation of Wind

Air quality and greenhouse gas sampling from mobile platforms enables local to regional analyses of pollutant exposure, atmospheric chemistry, and emission sources. Simultaneous meteorological observations, particularly wind speed and direction, are often used to interpret measurements and construct emission fluxes. However, the wind arising from a moving platform contributes to the observed wind speed and direction, and this artifact requires adequate removal to best apply wind observations. Here, we calculate the theoretical limitations to the measurement of wind from a moving vehicle, assess the accompanying uncertainty, and apply these methods to an example transect across a plume of methane. The angle of the wind relative to the moving vehicle is a crucial determinant of the ability to distinguish a true wind and defines its uncertainty. Unlike a stationary wind measurement, the wind speed and direction contain complementary information that broadens the capability of the mobile anemometer. We find that the isolation of a true wind depends on the anemometer wind speed accuracy for true winds moving with or against the vehicle, while the anemometer directional accuracy is more important for crosswinds, such as is experienced when observing across a plume. The uncertainty in estimated wind speed has similar geometry, but the uncertainty in estimating true wind direction is the opposite: the accuracy of measured wind speed most greatly impacts crosswind direction. Exact values are determined by the specific accuracy limitations of the anemometer and vehicle speed, and the geometrical distributions vary. As a result, the characteristics of each mobile lab setup should be assessed individually to best inform meteorological analyses and observation route planning.

Minimum Time Sailing Boat Path Algorithm

An iterative procedure to solve the nonlinear problem of fastest-path sailing vessel routing in an environment with variable winds and currents is proposed. In the routing of a sailing vessel, the primary control variable is the pointing (heading) of the vessel (assuming that the sails are chosen and trimmed optimally). Sailing vessel routing is highly nonlinear when considering environmental factors, such as winds and currents, and the behavior of the boat, given the weather conditions (i.e., polar diagrams that predict how fast one can sail, given the vessel's pointing relative to the true wind and the wind speed). The key algorithmic contribution of this article is a fastest-path algorithm for graphs with nonconvex edge costs that depend on weather, current, and boat polars. An illustrative scenario, with idealized weather attributes, and a real-world scenario, with parameters generated by numerical weather and current prediction models, are simulated and tested to compare the proposed algorithm against open-source routing software validated by active sailors. Preliminary results from the simulation setups tested are as follows: 1) the proposed sailing boat path algorithm is comparable to the open-source software available; and 2) exploiting the often unused but significant impactor of surface currents and incorporating leeway into sailing boat path planning enables higher fidelity guidance and faster (i.e., shorter time) routes, in comparing against the freely available baseline.

System Economy Improvement and Risk Shortening by Fuel Cell-UPFC Placement in a Wind-Combined System

It is important to understand the features of an integrated renewable energy power system, especially for deregulated systems. The greatest obstacle to assimilating renewable energy generators with the existing electrical system is their unpredictability. Because wind energy is inconsistent, incorporating it into an established power system necessitates more planning. The effects of wind farm (WF) incorporation with fuel cells and a unified power flow controller (UPFC) on electric losses, voltage profile, generating price, and the economics of the system in a deregulated power market are examined in this paper. An impact analysis of integrating wind farms into controlled and uncontrolled situations is conducted. At two randomly selected locations in India, the real-time statistics of the actual wind speed (AWS) and forecasted wind speed (FWS) were merged for this study. The surplus charge rate and deficit charge rate are intended to evaluate the imbalance cost which is arising from the difference between anticipated and true wind speeds to determine the economics of the system. Customers are always trying to find electricity that is reliable, inexpensive, and efficient due to the reconfiguration of the power system. As a consequence, the security limitations of the system may be surpassed or might function beyond the safety limit, which is undesirable. In the last section, heuristic algorithms, such as sequential quadratic programming (SQP), artificial bee colony algorithms (ABC), and moth-flame optimization algorithms (MFO), are employed to analyze economic risk. In the real-time energy market, it also covers how the fuel cells and UPFC are utilized to rectify the WF integration’s deviation. Economic risk evaluation approaches include value-at-risk (VaR) and conditional value-at-risk (CVaR). A modified IEEE 30-bus test system is used throughout the whole project.

Development and characterization of a passive, bio-inspired flow-tracking sensor

The effective natural transport of seeds in turbulent atmospheric flows is found across a myriad of shapes and sizes. However, to develop a sensitive passive sensor required for large-scale (in situ) flow tracking measurements, systems suffer from inertial lag due to the increased size and mass needed for optical visibility, or by carrying a sensor payload, such as an inertial measurement unit (IMU). While IMU-based flow sensing is promising for beyond visual line-of-sight applications, the size and mass of the sensor platform results in reduced flow fidelity and, hence, measurement error. Thus, to extract otherwise inaccessible flow information, a flow-physics-based tracer correction is developed through the application of a low-order unsteady aerodynamic model, inspired by the added-mass concept. The technique is evaluated using a sensor equipped with an IMU and magnetometer. A spherical sensor platform, selected for its symmetric geometry, was subject to two canonical test cases including an axial gust as well as the vortex shedding generated behind a cylinder. Using the measured sensor velocity and acceleration as inputs, an energized-mass-based dynamic model is used to back-calculate the instantaneous flow velocity from the sensor measurements. The sensor is also tracked optically via a high-speed camera while collecting the inertial data onboard. For the 1D test case (axial gust), the true (local) wind speed was estimated from the energized-mass-based model and validated against particle image velocimetry measurements, exhibiting good agreement with a maximum error of 10%. For the cylinder wake (second test case), the model-based correction enabled the extraction of the velocity oscillation amplitude and vortex-shedding frequency, which would have otherwise been inaccessible. The results of this study suggest that inertial (i.e. large and heavy) IMU-based flow sensors are viable for the extraction of Lagrangian tracking at large atmospheric scales and within highly-transient (turbulent) environments when coupled with a robust dynamic model for inertial correction.

WIND LOAD EVALUATION OF ROOF PHOTOVOLTAIC PANELS LOADED IN THE BOUNDARY LAYER WIND TUNNEL

Nowadays, more and more solar panel devices are mounted on the roofs. In some particular situations, the assessment of a structure in a higher energetic efficiency category (passive/active houses) may lead to the case of covering the entire roof with a system of photovoltaic panels. In these circumstances, an experimental study for testing the structural behaviour of the roof is mandatory to accurately estimate the true wind load. In this paper is presented an experimental setup based on two configurations of roofs, both made with photovoltaic panel systems, which are tested to wind actions. To maximize precision, the roof scaled models were designed in 3D modelling software and printed using a 3D printer. After the models were printed, they were instrumented with strain-gauge pressure sensors and prepared for the wind load tests.

The sailing performance of ancient Polynesian canoes and the early settlement of East Polynesia

ABSTRACTScholarly estimates and opinions of the sailing performance of ancient Pacific canoes vary widely. This paper measures performance by testing real sails in a wind tunnel and hulls in a towing tank. The sails were three East Polynesian Oceanic spritsails of late eighteenth century type, held by the British Museum, collected from New Zealand, Tahiti and Hawaii/Marquesas, which conform to the first historical records. Also tested was a hypothetical generic ancestral sail, and the Māori sail was tested in different ways to accommodate different views. Tests of hull form found that upwind sailing performance improved as underwater hull profile changed from U‐shape to V‐shape and some archaeological hulls can be assigned to this scale. Velocity prediction programs (VPPs) were calculated for a range of different canoes and simulated voyages by the fourteenth century AD archaeological canoe (waka) found at Anaweka, New Zealand retraced real voyages made by the experimental Polynesian replica canoe Hōkūle'a between 1980 and 2000, in the same recorded weather. Both canoes could average speeds of up to four knots and sail upwind at 75° to the true wind angle (TWA), as proposed by Lewis and Finney. The paper identifies a package of technological innovations involved in the settlement of East Polynesia following the “long pause” in Pacific settlement in West Polynesia. Two innovations previously suggested by linguistics were the Oceanic spritsail and the double canoe, and a third was the development of complex composite planked hulls and V‐shaped underwater hull forms. East Polynesian canoes were capable of two‐way voyaging and some migrations were planned, as in the case of New Zealand.

Fuzzy sliding mode power control for wind power generation systems connected to the grid

In recent years we have witnessed a real increase in the production of wind turbines and wind farm installations around the world, in order to improve this own energy, several studies have focused on the interest of controlling the active and reactive power of the system. Wind power, and at the same time on the quality of the energy produced and its connection in order to ingest suitable electrical energy into the distribution network. This article studies a new control technology to meet the various constraints in the field. The objective for work is to develop and study the sliding mode control method applied to a wind power system based on doubly fed induction generation (DFIG), as well as an optimization using the fuzzy logic technique. Ensuring the stability of the system is one of the objectives of using the Lyapunov nonlinear technique in the sliding mode control strategy which will be applied to the two converters (machine side and network side). The proposed solution was to validate a simulation on MATLAB/Simulink, tracking test (true wind speed) and also the robustness of the system.

Towards a general design evaluation tool: The development and validation of a VPP for autonomous sailing monohulls

Sailing speed performance is a crucial indicator that significantly affects the trafficability, efficiency, and tracking capability of autonomous sailing monohulls during marine science missions. Considering that the design of the hull and keel of an autonomous sailing monohull is usually a task-orientated and creative process, estimating speed performance by traditional velocity prediction programs (VPPs) based on empirical formulas and gradient solvers will lead to errors. This paper proposes a generalized VPP for helping designers assess the speed performance of their autonomous sailing monohulls. We designed an enhanced genetic algorithm (GA) solver to help the VPP converge quickly without a priori performance estimation. Furthermore, we propose an innovative neighbourhood information-based optimization (NIBO) strategy to accelerate and refine the solutions using adjacent states (external conditions with the same true wind speed (TWS) or true wind angle (TWA)) instead of culminating prediction by solving each state independently. We provide an application of the proposed VPP on our prototype as an example. Moreover, the numerical and experimental results show that the proposed VPP can serve as a practical design evaluation tool, especially in the early stages of design.

On the quality of RS41 radiosonde descent data

Abstract. Radiosonde descent profiles have been available from tens of stations for several years now – mainly from Vaisala RS41 radiosondes. They have been compared with the ascent profiles, with ECMWF short-range forecasts and with co-located radio occultation retrievals. Over this time, our understanding of the data has grown, and the comparison has also shed some light on radiosonde ascent data. The fall rate is very variable and is an important factor, with high fall rates being associated with temperature biases, especially at higher altitudes. Ascent winds are affected by pendulum motion; on average, descent winds are less affected by pendulum motion and are smoother. It is plausible that the true wind variability in the vertical lies between that shown by ascent and descent profiles. This discrepancy indicates the need for reference wind measurements. With current processing, the best results are for radiosondes with parachutes and pressure sensors. Some of the wind, temperature and humidity data are now assimilated in the ECMWF forecast system.

Adaptive Learning for Maximum Takeoff Efficiency of High-Speed Sailboats

This paper presents an optimal takeoff maneuver for an AC75 foiling sailboat competing in the America's Cup. The innovative sailboat design introduces extra degrees of freedom and articulations in the boat that result in nonlinear, high-dimensional, and unstable dynamics. The optimal maneuvers were achieved by exploring out-of-the-box solutions through adaptive control and optimization. We used a high-fidelity sailboat simulator for the data generation process and an adaptive control approach (Jacobian Learning (JL)) to optimize the sailing maneuver. Takeoff is a dynamic sailboat maneuver that involves transitioning the boat from a low-speed in-water status (displacement mode) to a high-speed out-of-water status (foiling mode) via actuation of the sailboat's inputs. We optimized the time for the boat's transitions from displacement mode to foiling mode while maximizing the projection of the velocity (Velocity Made Good (VMG)) in the desired target direction (True Wind Angle (TWA)). Furthermore, we optimized the sailboat's upwind steady-state performance (closed-haul VMG) for varying sailing directions (TWA) and used the optimal TWA to formulate the takeoff. The optimal solution is subject to physical/actuator constraints and the ones enforced to ensure the feasibility of the maneuvers by humans (sailors). The optimal takeoff achieved an average VMG of 7.42 m/s. This maneuver serves as a performance benchmark for the sailors and provides insightful information about the underlying dynamics of the boat.