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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A Real Time Expert Control System for Helicopter Autorotation

Sunberg, Zachary Nolan 03 October 2013 (has links)
Autorotation maneuvers are required to perform a safe landing of a helicopter in cases of engine loss in a single engine vehicle and transmission or tail rotor malfunction. The rise of autonomous helicopter technology, and the pilot skill required to manually perform an autorotation, motivate the need for new autonomous autorotation control laws. Previous approaches to automatic control for this maneuver have relied on control law optimization based on a high-fidelity model of the helicopter, or have attempted to match recorded trajectories flown by an expert human pilot. In this paper, a new expert control system is proposed. The term “expert control system” is used because the system is intended to mimic the actions that a human pilot might take, does not require any iterative learning, model prediction, or optimization at runtime, and is based on an inference system that involves fuzzy logic, PID, and other conventional control techniques. The multi-stage control law drives the helicopter to a near-optimal steady-state descent and uses an estimate of the time to impact to safely flare and land the helicopter in the vast majority of flight conditions. The control law is validated using a full 6-degree-of-freedom simulation of both a full-size attack helicopter and a small hobby-class helicopter. The pro- posed control design is highly flexible and may be used to perform fully autonomous autorotation or to provide guidance to pilots during manual autorotation maneuvers.
2

Aérodynamique et contrôle de l'écoulement de jeu dans un ventilateur axial obtenu par rotomoulage. / Aerodynamic and tip clearance flow control of an axial fan obtained with rotational molding

Azzam, Tarik 18 February 2018 (has links)
Aujourd’hui, la fabrication des turbomachines est conditionnée par des normes de plus en plus restrictives. L'enjeu industriel pour les chercheurs est d'envisager des solutions optimales visant à réduire les sources de perte d'énergie, d'instabilité et du bruit, en particulier l'écoulement de jeu (débit de fuite). Des actions préliminaires ont été élaborées à Arts & Métiers ParisTech sur le rotomoulage du ventilateur axial de refroidissement d'automobile. L'idée de ce travail est d'utiliser la forme creuse induite par le rotomoulage afin de l'exploiter dans le controle de l'écoulement de jeu radial par soufflage rotatif. Pour cela, la virole comporte des trous d'injection orientés de façon à réduire simultanément le débit de fuite et le couple. Dans ce travail, trois parties ont été traité. La première concerne la réalisation du ventilateur par rotomoulage. La deuxième concerne l'étude expérimentale menée dans le banc d'essai ISO 5801. Cette étude comporte la réalisation d'un montage dédié au contrôle par soufflage rotatif, la métrologie menée pour la détermination des performances globales et la caractérisation de la vitesse axiale du sillage proche. La troisième partie traite la modélisation numérique des conditions expérimentales rentables ensuite l'extrapolation du travail vers des taux d'injection importants. Pour ce dernier, on arrive à annuler le débit de fuite avec un gain considérable du couple mettant ainsi le ventilateur en autorotation. / Nowadays, the manufacture of turbomachinery is conditioned by more and more restrictive rules. The industrial challenge for researchers has to consider optimal solutions to reduce sources of energy loss, instability and noise, particularly the tip clearance flow (leakage flow rate). Preliminary actions have been developed at Arts & ParisTech on rotational molding process used for the automobile cooling axial fan. The idea of this work is to use the hollow shape induced by rotational molding process in order to exploit it in the control of tip clearance flow through rotary steady air injection. For this, the shroud ring is composed of injection holes oriented in such away to reduce both of leakage flow rate and the torque. In this work, the thesis focuses on three parts. The first concerns the build of the fan by rotational molding process. The second concerns the experimental study carried out in the ISO 5801 test bench. This study involves the realization of drive system dedicated to rotary steady air injection, metrology for performance determination and the characterization of the near wake axial velocity. The third part deals with the numerical modeling of efficient experimental conditions, then the extrapolation of work towards high injection rates. For this latter, it is possible to cancel leakage flow rate with a considerable gain of the torque thus putting the fan in autorotation.
3

Stability and control issues associated with lightly loaded rotors autorotating in high advance ratio flight

Rigsby, James Michael 22 October 2008 (has links)
Interest in high speed rotorcraft has directed attention toward the slowed-rotor, high advance ratio compound autogyro concept. The behavior of partially unloaded rotors, autorotating at high advance ratio is not well understood and numerous technical issues must be resolved before the vehicle can be realized. The necessity for a reduction in rotor speed with increasing flight speed results in high advance ratio operation. Further, rotor speed changes also affect the rotor dynamics and the associated hub moments generated by cyclic flapping. The result is rotor characteristics that vary widely depending on advance ratio. In the present work, rotor behavior is characterized in terms of issues relevant to the control system conceptual design and the rotor impact on the intrinsic vehicle flight dynamics characteristics. In this research, non-linear models, including the rotor speed degree of freedom, were created and analyzed with FLIGHTLABTM rotorcraft modeling software. Performance analysis for rotors trimmed to autorotate with zero average hub pitching and rolling moments indicates reduced rotor thrust is achieved primarily through rotor speed reduction at lower shaft incidence angle, and imposing hub moment trim constraints results in a thrust increment sign reversal with collective pitch angle above advance ratio . Swashplate control perturbations from trim indicate an increase in control sensitivities with advance ratio, and advance ratio dependent control cross coupling. Rotor speed response to swashplate control perturbations from trim results in non-linear behavior that is advance ratio dependent, and which stems from cyclic flapping behavior at high advance ratio. Rotor control strategies were developed including the use of variable shaft incidence to achieve rotor speed control with hub moment suppression achieved through cyclic control. Flight dynamics characteristics resulting from the coupling of the rotor and airframe were predicted in flight using a baseline airframe with conventional fixed-wing controls. Results predicted by linearization of the non-linear models were compared with system identification results using the non-linear simulation as surrogate flight test data. Low frequency rotor response is shown to couple with the vehicle motion for short period and roll mode response to airframe control inputs. The rotor speed mode is shown to couple with short period and long period vehicle modes as the rotor torque balance is sensitive to vehicle speed and attitude changes.
4

The sagittal soft-tissue changes of the lower lip and chin associated with surgical maxillary impaction and consequent mandibular autorotation

Ksiezycki-Ostoya, Beata Katarzyna 17 November 2006 (has links)
Student Number : 9000040F - M Dentistry research report - Faculty of Health Sciences / This study assessed the sagittal soft-tissue changes of the lower lip and chin area in 22 patients subsequent to mandibular autorotation following surgical vertical impaction of the maxilla. A subgroup of six patients in addition had undergone advancement genioplasty procedures. Lateral cephalometric radiographs were taken immediately prior to surgery and on average 15 months following surgery. Sixteen cephalometric landmarks were identified on each radiograph and these were digitized using a Kontron Videoplan Image Analysis System to enable differences reflecting changes to be assessed. The comparison between those cases that had had maxillary elevation only and the six cases that had received additional advancement genioplasty procedures revealed statistically significant differences in relation to the proportional changes in the chin area. Therefore, when studying the soft-tissue chin changes following mandibular autorotation, these six patients were excluded from the sample. It was found that there was no significant difference in the lower lip response between the two groups and therefore when studying the lower lip changes, the two groups could be pooled. The soft-tissue changes in the chin area showed statistically and clinically significant correlations. In the horizontal plane, a ratio of 0.9:1 was found for the changes between sulcus inferior and point B, between soft-tissue pogonion and hard-tissue pogonion, and between soft-tissue gnathion and hard-tissue gnathion. In the vertical dimension, soft-tissue gnathion followed hard-tissue gnathion in a ratio of 0.9:1, whereas soft-tissue menton followed hardtissue menton in a ratio of 1:1. In the study of the lower lip response, a significant correlation with a ratio of 1:1 existed for the horizontal change in the lower lip as measured at labrale inferius relative to both lower incisor tip and lower incisor anterius. In the vertical dimension, stomion inferius followed lower incisor anterius in a ratio of 1.3:1, while labrale inferius followed lower incisor anterius in a ratio of 1.5:1. Multiple regression analyses revealed that presurgical tissue thickness exerted no influence upon the strength of the correlations between changes expressed at corresponding soft- and hard-tissue landmarks located in the lower lip and soft-tissue chin area. Based on the findings of this study, it is suggested that the soft-tissue to hard-tissue ratios may be applied to prediction tracings with enhanced confidence. As a result, the tracings will reflect a more accurate prediction of the lower lip and soft-tissue chin positions following autorotation of the mandible.
5

A Lab-Scale Experimental Framework for Studying the Phenomenon of Autorotation

Rimkus, Sigitas 15 May 2014 (has links)
While wind energy has emerged as a popular source of renewable energy, the traditional wind turbine has an inherent limitation, namely that it only generates power in the presence of sufficiently high and consistent wind speeds. As a result, wind farms are typically built in areas with a high probability of the required wind speeds, which are geographically sparse. One way of overcoming this drawback is to tap into the energy available in winds at high altitudes which are not only consistent and of high magnitude, but also globally pervasive. An airborne wind energy device based upon the phenomenon of autorotation could potentially be used to exploit the abundance of wind of energy present at high altitudes. The work in this thesis first presents our study of a tethered-airfoil system as a candidate airborne wind energy (AWE) system. A mathematical model was used to show the feasibility of energy capture and the stability of the device in a wind field. Subsequently, the research identified the principle of autorotation to be better suited for high altitude energy harvesting. To this end, the thesis first presents a theoretical basis of the principle of autorotation, which is developed from existing models in literature. The model was adapted to predict aerodynamic conditions when used for harvesting energy. Encouraging simulation results prompted the main emphasis of this thesis, namely design of an experimental framework to corroborate the theory. Several experiments were devised to determine basic performance characteristics of an autogyro rotor and the data from each experiment is presented. A lab-scale experimental setup was developed as part of this thesis. The setup, consisting of a flapping-blade autogyro rotor and sensors, was used to acquire preliminary aerodynamic performance data. It is envisioned that refinements to this setup will ultimately provide a means of directly comparing analytical and experimental data. In this regard, we provide conclusions and make comments on improvements for future experiments. / M.S.M.E. / Masters / Mechanical and Aerospace Engineering / Engineering and Computer Science / Mechanical Engineering; Mechanical Systems Track
6

An Introductory Study of The Dynamics of Autorotation for Wind Energy Harvesting

Salih, Bilal 15 May 2014 (has links)
Wind turbines have been used for decades to harvest wind energy. They are suitable only to work on close to ground, and have several drawbacks that are related to the availability of the wind and the amount of extracted power compared with the cost of construction. On the other hand, there is an abundant wind power that is available at high altitudes. The wind jet streams at high elevations 8 - 12 kms are pervasive and persistent, and can potentially produce immense wind energy. Even at moderate elevations of 4 - 5 kms, wind power densities are much higher than on ground and more consistent. Consequently, in this thesis research, we investigate the topic of harvesting energy from high altitudes. First, we provide a comprehensive review of two existing theoretical methods that are proposed for airborne wind energy harvesting, the tethered airfoil, and the static autogyro. The latter approach has inherent advantages that warrant further investigation. Autorotation is a well-known phenomenon where a rotor sustains its angular velocity and maintains significant lift in the presence of strong aerodynamic forces and torques generated by interaction with a strong wind field. Autorotation has been researched in the context of free descent of helicopters but has not been considered for energy harvesting. Existing models have mainly focused on statics analysis. In this research, we propose a simple dynamic model of the Autogyro, with the goal of ultimately realizing an Autorotation Energy System (AES). The focus of our work is to provide a preliminary dynamic analysis of autorotation, which is largely absent in current literature, to explore the possibility of using autorotation for designing a multipurpose system that can simultaneously fly at high altitudes and generate energy from the wind. The proposed preliminary dynamic model is used to generate a simulation platform, which is used to explore the autogyros rudimentary maneuvers. Extensive simulation results are provided to evaluate the dynamic performance of AES. Energy harvesting analyses and results are also presented. It is expected that the results will guide the choice of actuations and control that will be necessary for generating combined autorotation and powered flights that would be net energy generating or energy efficient. The research will be relevant for both tethered and untethered AES and could also be incorporated into multi-rotor based UAVs such as quadrotors. / M.S.M.E. / Masters / Mechanical and Aerospace Engineering / Engineering and Computer Science / Mechanical Engineering; Mechanical Systems Track
7

Etude aérodynamique de ventilateurs axiaux réversibles à performance duale compresseur/turbine élevée / Aerodynamic study of reversible axial fans with high compressor/turbine dual performance

Ortolan, Aurélie 19 October 2017 (has links)
Dans le contexte des avions plus électriques, le potentiel de récupération d'énergie de ventilateurs de refroidissement embarqués est étudié. Ces compresseurs conventionnels, utilisés uniquement au sol, fonctionnent en autorotation libre en vol. Dans cette dernière configuration, appliquer un couple donné sur l'arbre permet de récupérer de l'énergie électrique, le ventilateur fonctionne alors en autorotation chargée (mode turbine). Cependant, ces géométries conventionnelles obtiennent de faibles rendements turbine, causés par des incidences fortement négatives conduisant à des décollements massifs. Il est alors nécessaire de concevoir une machine axiale réversible capable de fonctionner de manière duale en mode compresseur et turbine, avec une performance élevée dans les deux cas. Ce nouveau concept permet de capitaliser l’équipement tout au long de la mission. Dans cette étude, l'adéquation de l'approche quatre-quadrants et du formalisme psi-phi à propos du mode dual de turbomachines est soulignée, au détriment des représentations classiques séparant les performances compresseur et turbine. Une analyse du fonctionnement du mode compresseur à l'autorotation chargée a permis de mettre en évidence les propriétés génériques des écoulements d'autorotation ainsi que ce qui fait la spécificité des machines duales. Les mécanismes de l’écoulement et les paramètres géométriques impactant la performance le long de la ligne de fonctionnement ont également été identifiés. Le concept de machine duale est validé grâce aux grands rendements obtenus en essais. Enfin, une géométrie optimisée est proposée et des recommandations liées au design de machines duales sont données. / In the more electric aircrafts context, the in-flight windmilling operation of conventional onboard axial fans is regarded as a functioning mode that enables energy recovery. Poor turbine efficiencies of classical geometries, due to massive separations, require to design a reversible machine. The latter allows a dual compressor/turbine functioning with high performances in both modes to capitalize the equipment throughout the mission. In this study, the relevance of psi-phi formalism to multi-quadrant approach is underlined. The flow analysis from compressor to load-controlled windmill enables to highlight generic properties of windmilling flows as well as dual machines specificities. The flow mechanisms and geometrical parameters impacting the performances along the operating line are also identified. Finally, an optimized dual machine design is proposed.
8

Aerodynamic Characterization of a Tethered Rotor

January 2019 (has links)
abstract: An airborne, tethered, multi-rotor wind turbine, effectively a rotorcraft kite, provides one platform for accessing the energy in high altitude winds. The craft is maintained at altitude by its rotors operating in autorotation, and its equilibrium attitude and dynamic performance are affected by the aerodynamic rotor forces, which in turn are affected by the orientation and motion of the craft. The aerodynamic performance of such rotors can vary significantly depending on orientation, influencing the efficiency of the system. This thesis analyzes the aerodynamic performance of an autorotating rotor through a range of angles of attack covering those experienced by a typical autogyro through that of a horizontal-axis wind turbine. To study the behavior of such rotors, an analytical model using the blade element theory coupled with momentum theory was developed. The model uses a rigid-rotor assumption and is nominally limited to cases of small induced inflow angle and constant induced velocity. The model allows for linear twist. In order to validate the model, several rotors -- off-the-shelf model-aircraft propellers -- were tested in a low speed wind tunnel. Custom built mounts allowed rotor angles of attack from 0 to 90 degrees in the test section, providing data for lift, drag, thrust, horizontal force, and angular velocity. Experimental results showed increasing thrust and angular velocity with rising pitch angles, whereas the in-plane horizontal force peaked and dropped after a certain value. The analytical results revealed a disagreement with the experimental trends, especially at high pitch angles. The discrepancy was attributed to the rotor operating in turbulent wake and vortex ring states at high pitch angles, where momentum theory has proven to be invalid. Also, aerodynamic design constants, which are not precisely known for the test propellers, have an underlying effect on the analytical model. The developments of the thesis suggest that a different analytical model may be needed for high rotor angles of attack. However, adding a term for resisting torque to the model gives analytical results that are similar to the experimental values. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019
9

A physics based investigation of gurney flaps for enhancement of rotorcraft flight characteristics

Min, Byung-Young 26 March 2010 (has links)
Helicopters are versatile vehicles that can vertically take off and land, hover, and perform maneuver at very low forward speeds. These characteristics make them unique for a number of civilian and military applications. However, the radial and azimuthal variation of dynamic pressure causes rotors to experience adverse phenomena such as transonic shocks and 3-D dynamic stall. Adverse interactions such as blade vortex interaction and rotor-airframe interaction may also occur. These phenomena contribute to noise and vibrations. Finally, in the event of an engine failure, rotorcraft tends to descend at high vertical velocities causing structural damage and loss of lives. A variety of techniques have been proposed for reducing the noise and vibrations. These techniques include on-board control (OBC) devices, individual blade control (IBC), and higher harmonic control (HHC). Addition of these devices adds to the weight, cost, and complexity of the rotor system, and reduces the reliability of operations. Simpler OBC concepts will greatly alleviate these drawbacks and enhance the operating envelope of vehicles. In this study, the use of Gurney flaps is explored as an OBC concept using a physics based approach. A three dimensional Navier-Stokes solver developed by the present investigator is coupled to an existing free wake model of the wake structure. The method is further enhanced for modeling of Blade-Vortex-Interactions (BVI). Loose coupling with an existing comprehensive structural dynamics analysis solver (DYMORE) is implemented for the purpose of rotor trim and modeling of aeroelastic effects. Results are presented for Gurney flaps as an OBC concept for improvements in autorotation, rotor vibration reduction, and BVI characteristics. As a representative rotor, the HART-II model rotor is used. It is found that the Gurney flap increases propulsive force in the driving region while the drag force is increased in the driven region. It is concluded that the deployable Gurney flap may improve autorotation characteristics if deployed only over the driving region. Although the net effect of the increased propulsive and drag force results in a faster descent rate when the trim state is maintained for identical thrust, it is found that permanently deployed Gurney flaps with fixed control settings may be useful in flare operations before landing by increasing thrust and lowering the descent rate. The potential of deployable Gurney flap is demonstrated for rotor vibration reduction. The 4P harmonic of the vertical vibratory load is reduced by 80% or more, while maintaining the trim state. The 4P and 8P harmonic loads are successfully suppressed simultaneously using individually controlled multi-segmented flaps. Finally, simulations aimed at BVI avoidance using deployable Gurney flaps are also presented.
10

Aerodynamics of the Maple Seed

Desenfans, Philip January 2019 (has links) (PDF)
Purpose - The paper presents a theoretical framework that describes the aerodynamics of a falling maple (Acer pseudoplatanus) seed. --- Methodology - A semi-empirical method is developed that provides a ratio stating how much longer a seed falls in air compared to freefall. The generated lift is calculated by evaluating the integral of two-dimensional airfoil elements using a preliminary falling speed. This allows for the calculation of the definitive falling speed using Blade Element Momentum Theory (BEMT); hereafter, the fall duration in air and in freefall are obtained. Furthermore, the input-variables of the calculation of lift are transformed to require only the length and width of the maple seed. Lastly, the method is applied to two calculation examples as a means of validation. --- Findings - The two example calculations gave percentual errors of 5.5% and 3.7% for the falling speed when compared to measured values. The averaged result is that a maple seed falls 9.9 times longer in air when released from 20 m; however, this result is highly dependent on geometrical parameters which can be accounted for using the constructed method. --- Research limitations - Firstly, the coefficient of lift is unknown for the shape of a maple seed. Secondly, the approximated transient state is yet to be verified by measurement. --- Originality / Value - The added value of this report lies in the reduction of simplifications compared to BEMT approaches. In this way a large amount of accuracy is achieved due to the inclusion of many geometrical parameters, even though simplicity is maintained. This has been accomplished through constructing a simple three-step method that is fundamental and essentially non-iterative.

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