1,721,088 research outputs found
On the optimal tuning of individual pitch control for horizontal-axis wind turbines
Full text linkIndividual pitch control has proved capable of reducing loads on the blades and shaft of a horizontal-axis wind turbine, at the price of a potentially substantial increase in actuator activity. With accurate tuning of the control parameters, the overall performance can be satisfactorily balanced, but a manual tuning procedure often proves unbearably costly and the solution found may be far from optimal. This study tries to explore the feasibility of an optimal approach to the problem of tuning of individual pitch control, by mapping reasonable cost functions with respect to some parameters of interest in control design. The analysis is carried out by considering a possible individual pitch control implementation, tested in a virtual environment on a realistic testbed. The merit functions are also analyzed visually, in order to easily understand the effects of the various design parameters on the positions and quality of the respective optima. In a later stage, results of complete optimization runs are presented, and the approach is critically discussed
An optimal approach to the preliminary design of small hybrid-electric aircraft
Full text linkHybrid-electric propulsion is an interesting alternative for the light aviation market, carrying the advantages of electric propulsion in terms of lower noise and pollutive emissions in terminal maneuvers, while not renouncing to the flight performance – especially range – typical to conventional propulsion, based on hydrocarbon fuel. Some difficulty in the spreading of this new technology in light aviation may be ascribed to the lack of consolidated techniques to preliminary design hybrid-electric aircraft, complicating the negotiation of specifications and making design choices difficult. This is also the effect of a notable increase in the number of design variables needed to describe the hybrid-electric power-train, which include characteristics of both its thermal and electric parts, with respect to conventionally powered aircraft. The present paper presents a methodology to efficiently cope with this design problem. The procedure is based on an optimal approach where take-off weight is minimized, and constraints are included to assure meeting the mission performance requirements while not exceeding any technological limit. The paper recalls at first some simple mathematical models, allowing to translate flight performance requirements into constraints on the power-train. Then the proposed optimal design approach is thoroughly presented at a theoretical level. Finally, an example design of a hybrid-electric motor-glider is shown, where the optimal design tool is used both to find a baseline solution and to investigate the sensitivity of that design point with respect to constraints due to performance requirements and technological specifications
An integrated approach to the preliminary weight sizing of small electric aircraft
Full text linkElectric propulsion has received attention in aviation as witnessed by studies in hybrid designs and by the production of aircraft with support electric motors to be used in limited parts of the mission with ancillary roles. Until the recent past, the main limit to a wider adoption of electric propulsion, which besides having a lower environmental impact with respect to internal combustion engines (ICE) in terms of noise and emissions, can also improve reliability and on-board comfort, was the need for mass and volume-inefficient battery packs as devices for energy storage. However, thanks to the level of technology now reached by batteries, it is becoming possible to design and build electrically propelled aircraft at least in the category of light or general aviation. Due to the relative novelty of this technology, only few examples of similar aircraft exist today, mainly modifications of more traditional concepts, and thinking of a completely new electric aircraft is made difficult by the lack of a consolidated design framework, differently from the case of traditional ICE-powered models. This paper tries to cope with some basic aspects typical to electrically propelled aircraft, to the aim of setting up a stable and reliable preliminary sizing procedure allowing designers and aircraft companies to quickly size up and compare all-electric designs. To this aim, a statistical analysis of the basic characteristics of existing aircraft is presented first, showing a good correlation level between some of them. Next a method for the preliminary sizing of weights is shown, obtained starting from a more usual step-by-step procedure typically adopted for ICE-propelled aircraft. Due to the peculiar characteristics of electrically powered aircraft, the new procedure involves an integrated use of the case-specific mission profile and sizing matrix. The validity of the proposed procedure is testified by example analyses on two realistic designs of lightweight aircraft
Estimation of Wind Misalignment and Vertical Shear from Blade Loads
Full text linkThis paper describes the formulation and verification of a novel observer of wind parameters. The general idea behind the proposed approach is to consider the wind turbine rotor as an anemometer. In fact, the rotor responds to varying wind conditions; by properly interpreting this response, one can indirectly measure some desired wind characteristics, as for example yaw and shear, as described here.Measurements of wind conditions obtained this way are not affected by the usual disturbances of existing sensors, for example when installed in the nacelle or in the rotor wake. Furthermore, the approach provides rotor-equivalent quantities, and not the typical point information provided by wind vanes, anemometers or other similar sensors, whose information might be too local for large rotors.The proposed method is here formulated for the observation of wind direction and vertical shear. The new observer is demonstrated first in a comprehensive simulation study using high-fidelity aeroservoelastic models, and then experimentally using an aeroelastically-scaled wind tunnel model
Validation of a Wind Misalignment Observer Using Field Test Data
Full text linkA previously described observer of wind misalignment is validated using field test data collected on the NREL CART3 wind turbine. The observer uses blade root bending moment 1P harmonics, computed using the transformation of Coleman and Feingold, to infer the rotor-equivalent relative wind direction. The observation model parameters are determined by a least squares fitting using recorded blade loads and met-mast measured wind direction and speed; a random sample consensus (RANSAC) algorithm is used to robustify the parameter estimation procedure while detecting outliers in the experimental samples. The observer is validated using an independent verification data set: recorded blade bending loads are fed to the observer and the estimated wind misalignment is compared to both the one provided by the met-mast vanes, assumed as the ground truth, and by an on-board nacelle-mounted wind vane. Results show that the rotor-equivalent wind misalignment estimates provided by the proposed observer are well correlated in the low frequency spectrum with the met-mast reference, and in general are in much better accordance with it than the on-board wind vane measurements
- …
