O objetivo deste trabalho é investigar o controle ativo de vibração em uma pá inteligente de helicóptero. O desenvolvimento de materiais inteligentes para trabalharem como sensores e atuadores apresentam uma nova alternativa no controle de vibração. A pá de helicóptero é modelada pelo método dos elementos finitos, considerando os movimentos de batimento, flexão no plano de rotação, estiramento axial e torção. O modelo da pá considera também ângulo de torção geométrica, não coincidência entre os eixos, elástico e do centro de gravidade das seções transversais e material isotrópico. O modelo matemático é desenvolvido, e nele é incorporado atuadores piezelétricos distribuídos ao longo da envergadura da pá. O controle ativo de vibração é baseado no controle individual da pá na condição de vôo pairado. As matrizes de elementos finitos são obtidas pelo método de energia e um procedimento de linearização é aplicado às equações resultantes. O carregamento aerodinâmico linearizado é calculado para a condição de vôo pairado e a representação no espaço de estados é usada para o projeto de um controlador. Usou-se a técnica de atribuição da autoestrutura por realimentação de saída no modelo de ordem reduzida, resultado da aplicação do método da expansão por frações parciais. As simulações do modelo em malha aberta e fechada, exibiu boas qualidades de resposta, o que mostra que o controle ativo é uma boa alternativa para a redução de vibrações em helicópteros. / The objective of this work is to investigate the performance of a smart helicopter blade. Developments on smart materials for both sensing and/or actuation have provided a novel alternative in vibration control. The helicopter blade is modeled by the finite element method, considering the motions of flapping, lead-lagging, axial stretching, and torsion. The blade model also considers a pretwist angle, offset between mass and elastic axes, and isotropic material. The helicopter blade mathematical model allows the incorporation of piezoelectric actuators distributed along the blade span. The active vibration control is based on the premise of individual blade control and the investigation is carried out for hovering flight condition the finite element matrices are obtained by energy methods and a linearization procedure is applied to the resulting expressions. The linearized aerodynamic loading is calculated for hover and the state-space approach is used to design the control law. The eigenstructure assignment by output feedback is used in the blade-reduced model resulting from the application of the expansion method by partial fractions. The simulations for open and closed-loop systems are presented, having exhibited good response qualities, which shows that output feedback is a good alternative for smart helicopter blade vibration attenuation.

L’objectif principal du travail de recherche présenté dans ce mémoire est l’amélioration de la sécurité et les performances du vol des mini drones soumis à des perturbations atmosphériques. Pour ce faire, un couplage entre un estimateur ensembliste à erreurs bornées et une stratégie de guidage pilotage est mise en œuvre. L’estimateur ensembliste a été utilisé pour restituer l’état du modèle dynamique du drone en présence de perturbations et de bruits de mesure supposés bornés. L’utilisation de ces techniques avait pour objet tout d’abord de détecter l’occurrence d’une perturbation atmosphérique par estimation de l’état du drone puis d’estimer l’amplitude et la direction du vent agissant sur le véhicule. Des expérimentations dans le générateur de rafale B20 à Lille ont été ainsi présentées afin de valider ces approches et d’évaluer leurs performances. La stratégie de guidage pilotage développée favorise le déplacement du véhicule dans une direction qui tient compte de l’évolution de la perturbation atmosphérique et du prochain point de passage désigné au véhicule. Cette loi de guidage est basée sue la loi de guidage par navigation proportionnelle et a été adaptée pour tenir compte des perturbations dans le déplacement du véhicule. Les résultats obtenus montrent qu’il est possible d’améliorer la sécurité du vol des mini-drones en présence de perturbations atmosphériques transversales, en modifiant en ligne la trajectoire. / The principal objective of this thesis is to enhance the safety of flight for small UAVs in presence of atmospheric perturbation. The approach suggested here consists in coupling a bounded–error estimation method with a new guidance strategy. The bounded error estimation has been used to estimate the states of the dynamical systems corrupted by perturbations and measurement noises, assumed to remain bounded. The method has been first used to detect the occurrence of a wind gust and afterwards to characterize the amplitude and direction of the wind acting on the vehicle Experiments in the B20 gust generator are also presented to validate these approaches and evaluate their performance. The developed guidance strategy provides the vehicle with a direction that takes into account the atmospheric perturbation and the next waypoint position. The guidance law is designed by using proportional navigation guidance that has been adapted to take the perturbations into account. The results presented in this thesis show that it is possible to improve the flight safety in a perturbed environement using the combination of the two methods.

Despite the high cost of memory and CPU time required to resolve the boundary layer, a viscous unstructured grid solver has many advantages over a structured grid solver such as the convenience in automated grid generation and shock or vortex capturing by solution adaption. Since the geometry and flow phenomenon of a helicopter are very complex, unstructured grid-based methods are well-suited to model properly the rotor-fuselage interaction than the structured grid solver. In present study, an unstructured Cartesian grid solver is developed on the basis of the existing solver, NASCART-GT. Instead of cut-cell approach, immersed boundary approach is applied with ghost cell boundary condition, which increases the accuracy and minimizes unphysical fluctuations of the flow properties. The standard k-epsilon model by Launder and Spalding is employed for the turbulence modeling, and a new wall function approach is devised for the unstructured Cartesian grid solver. It is quite challenging and has never done before to apply wall function approach to immersed Cartesian grid. The difficulty lies in the inability to acquire smooth variation of y+ in the desired range due to the non-body-fitted cells near the solid wall. The wall function boundary condition developed in this work yields stable and reasonable solution within the accuracy of the turbulence model. The grid efficiency is also improved with respect to the conventional method. The turbulence modeling is validated and the efficiency of the developed boundary condition is tested in 2-D flow field around a flat plate, NACA0012 airfoil, axisymmetric hemispheroid, and rotorcraft applications. For rotor modeling, an actuator disk model is chosen, since it is efficient and is widely verified in the study of the rotor-fuselage interaction. This model considers the rotor as an infinitely thin disk, which carries pressure jump across the disk and allows flow to pass through it. The full three dimensional calculations of Euler and RANS equations are performed for the GT rotor model and ROBIN configuration to test implemented actuator disk model along with the developed turbulence modeling. Finally, the characteristics of the rotor-fuselage interaction are investigated by comparing the numerical solutions with the experiments.

The thesis presents a framework for integrating models, simulation, and experimental data to diagnose incipient failure modes and prognosticate the remaining useful life of critical components, with an application to the main transmission of a helicopter. Although the helicopter example is used to illustrate the methodology presented, by appropriately adapting modules, the architecture can be applied to a variety of similar engineering systems. Models of the kind referenced are commonly referred to in the literature as physical or physics-based models. Such models utilize a mathematical description of some of the natural laws that govern system behaviors. The methodology presented considers separately the aspects of diagnosis and prognosis of engineering systems, but a similar generic framework is proposed for both. The methodology is tested and validated through comparison of results to data from experiments carried out on helicopters in operation and a test cell employing a prototypical helicopter gearbox. Two kinds of experiments have been used. The first one retrieved vibration data from several healthy and faulted aircraft transmissions in operation. The second is a seeded-fault damage-progression test providing gearbox vibration data and ground truth data of increasing crack lengths. For both kinds of experiments, vibration data were collected through a number of accelerometers mounted on the frame of the transmission gearbox. The applied architecture consists of modules with such key elements as the modeling of vibration signatures, extraction of descriptive vibratory features, finite element analysis of a gearbox component, and characterization of fracture progression. Contributions of the thesis include: (1) generic model-based fault diagnosis and failure prognosis methodologies, readily applicable to a dynamic large-scale mechanical system; (2) the characterization of the vibration signals of a class of complex rotary systems through model-based techniques; (3) a reverse engineering approach for fault identification using simulated vibration data; (4) the utilization of models of a faulted planetary gear transmission to classify descriptive system parameters either as fault-sensitive or fault-insensitive; and (5) guidelines for the integration of the model-based diagnosis and prognosis architectures into prognostic algorithms aimed at determining the remaining useful life of failing components.

<p>Den senaste trenden inom flygvapenindustrin är utveckling av obemannade farkoster. Den svenska vapenindustrikoncernen Saab AB följer denna trend i och med den stundande introduktionen av företagets obemannade helikopter Skeldar V-150. Som ett led i vidareutvecklingen av detta system finns planer på att även lansera en marin variant, kallad Skeldar M. Tanken med denna marina variant är att möjliggöra fullständigt autonoma starter och landningar från fartyg. För att kunna genomföra detta på ett tryggt sätt även i hårt väder krävs att helikoptern hålls säkrad på fartygsdäcket såväl innan start som efter landning.</p><p>Uppgiften för detta arbete har varit att ta fram koncept för hur ett sådant säkringssystem skulle kunna se ut. För att ta fram idéer för dessa koncept har en flitigt brukad produktutvecklingsmetod använts. Metoden innebär att en kravspecifikation tas fram utifrån kundens behov. Med stöd av den genereras sedan ett antal produktkoncept genom kreativt tänkande och analyser av hur andra löser samma problem. Koncepten jämförs sedan utefter hur väl de uppfyller kundens behov och de bästa idéerna kan på så sätt väljas ut och vidareutvecklas.</p><p>De koncept som tagits fram i detta arbete har sträckt sig från enklare idéer där kardborrmaterial används för att säkra helikoptern, till system som mäter in helikopterns position relativt fartyget och justerar sitt eget läge därefter. Totalt framkom nio grundidéer och sammanlagt tolv varianter på antiglidsystem. I samråd med personer inblandade i Skeldar-projektet valdes sedermera tre av koncepten ut för att vidareutvecklas ytterligare, en lösning där helikoptern vinschas ner på däck, en annan där kardborrlås används för att säkra den och en tredje där sugkoppar håller Skeldar fast.</p><p>Med hänsyn tagen till bland annat svårigheter att implementera en vinschlösning ombord på såväl Skeldar som fartygen valdes denna lösning slutligen bort. Svårigheterna bottnar framför allt i utrymmesbrist och problem med automatisk sammankoppling av helikopter och fartyg. De koncept som rekommenderas i detta arbete blir därför ett av systemen med kardborrlås eller sugkoppar.</p> / <p>The latest trend within the air force industry is development of unmanned aerial vehicles. The Swedish defense industry group Saab AB is following this trend by means of the introduction of their unmanned helicopter Skeldar V-150. As part of the further development of this system Saab has plans on introducing a marine version of the system, called Skeldar M. One of the purposes of this version is to enable completely autonomous take-offs and landings from ships. To be able to complete this in a safe manner in harsh conditions the helicopter needs to be secured to the deck before take-off as well as after landing.</p><p>The purpose of this thesis has been to develop a concept for keeping Skeldar secured on deck. To establish ideas for these concepts a common method for product development has been used. The method involves acquiring customer needs and from these needs establish a list of demands on the product itself. A set of product concepts are then generated by means of creative thinking and competitor analysis. After that the concepts are compared based on how well they meet the demands put upon them and the best ideas get picked out and further developed.</p><p>The concepts developed in this thesis stretch from simple ideas where hook and loop fasteners are used to secure the helicopter to more advanced ones where the helicopter’s position relative to the ship is measured and the system adjust to this position. All in all nine basic ideas were developed and a total of twelve versions on securing systems. In consultation with people involved in the Skeldar project, three of the concepts were chosen for further development, one concept where the helicopter was winched to the deck, a second where hook and loop fasteners were used to secure it and finally one where vacuum grippers keeps Skeldar on deck.</p><p>With difficulties of implementing a winch system onboard Skeldar as well as on board the ships taken into account, this solution was dropped. This was primarly due to lack of space and difficulties solving an automatic connection between helicopter and ship. The concepts recommended in this thesis will therefore be one of the systems where hook and loop fasteners or vacuum grippers are used.</p>

Den senaste trenden inom flygvapenindustrin är utveckling av obemannade farkoster. Den svenska vapenindustrikoncernen Saab AB följer denna trend i och med den stundande introduktionen av företagets obemannade helikopter Skeldar V-150. Som ett led i vidareutvecklingen av detta system finns planer på att även lansera en marin variant, kallad Skeldar M. Tanken med denna marina variant är att möjliggöra fullständigt autonoma starter och landningar från fartyg. För att kunna genomföra detta på ett tryggt sätt även i hårt väder krävs att helikoptern hålls säkrad på fartygsdäcket såväl innan start som efter landning. Uppgiften för detta arbete har varit att ta fram koncept för hur ett sådant säkringssystem skulle kunna se ut. För att ta fram idéer för dessa koncept har en flitigt brukad produktutvecklingsmetod använts. Metoden innebär att en kravspecifikation tas fram utifrån kundens behov. Med stöd av den genereras sedan ett antal produktkoncept genom kreativt tänkande och analyser av hur andra löser samma problem. Koncepten jämförs sedan utefter hur väl de uppfyller kundens behov och de bästa idéerna kan på så sätt väljas ut och vidareutvecklas. De koncept som tagits fram i detta arbete har sträckt sig från enklare idéer där kardborrmaterial används för att säkra helikoptern, till system som mäter in helikopterns position relativt fartyget och justerar sitt eget läge därefter. Totalt framkom nio grundidéer och sammanlagt tolv varianter på antiglidsystem. I samråd med personer inblandade i Skeldar-projektet valdes sedermera tre av koncepten ut för att vidareutvecklas ytterligare, en lösning där helikoptern vinschas ner på däck, en annan där kardborrlås används för att säkra den och en tredje där sugkoppar håller Skeldar fast. Med hänsyn tagen till bland annat svårigheter att implementera en vinschlösning ombord på såväl Skeldar som fartygen valdes denna lösning slutligen bort. Svårigheterna bottnar framför allt i utrymmesbrist och problem med automatisk sammankoppling av helikopter och fartyg. De koncept som rekommenderas i detta arbete blir därför ett av systemen med kardborrlås eller sugkoppar. / The latest trend within the air force industry is development of unmanned aerial vehicles. The Swedish defense industry group Saab AB is following this trend by means of the introduction of their unmanned helicopter Skeldar V-150. As part of the further development of this system Saab has plans on introducing a marine version of the system, called Skeldar M. One of the purposes of this version is to enable completely autonomous take-offs and landings from ships. To be able to complete this in a safe manner in harsh conditions the helicopter needs to be secured to the deck before take-off as well as after landing. The purpose of this thesis has been to develop a concept for keeping Skeldar secured on deck. To establish ideas for these concepts a common method for product development has been used. The method involves acquiring customer needs and from these needs establish a list of demands on the product itself. A set of product concepts are then generated by means of creative thinking and competitor analysis. After that the concepts are compared based on how well they meet the demands put upon them and the best ideas get picked out and further developed. The concepts developed in this thesis stretch from simple ideas where hook and loop fasteners are used to secure the helicopter to more advanced ones where the helicopter’s position relative to the ship is measured and the system adjust to this position. All in all nine basic ideas were developed and a total of twelve versions on securing systems. In consultation with people involved in the Skeldar project, three of the concepts were chosen for further development, one concept where the helicopter was winched to the deck, a second where hook and loop fasteners were used to secure it and finally one where vacuum grippers keeps Skeldar on deck. With difficulties of implementing a winch system onboard Skeldar as well as on board the ships taken into account, this solution was dropped. This was primarly due to lack of space and difficulties solving an automatic connection between helicopter and ship. The concepts recommended in this thesis will therefore be one of the systems where hook and loop fasteners or vacuum grippers are used.

New helicopter rotor designs are desired that offer increased efficiency, reduced vibration, and reduced noise. This problem is multidisciplinary, requiring knowledge of structural dynamics, aerodynamics, and aeroacoustics. Rotor optimization requires achieving multiple, often conflicting objectives. There is no longer a single optimum but rather an optimal trade-off space, the Pareto Frontier. Rotor Designers in industry need methods that allow the most accurate simulation tools available to search for Pareto designs. Computer simulation and optimization of rotors have been advanced by the development of "comprehensive" rotorcraft analysis tools. These tools perform aeroelastic analysis using Computational Structural Dynamics (CSD). Though useful in optimization, these tools lack built-in high fidelity aerodynamic models. The most accurate rotor simulations utilize Computational Fluid Dynamics (CFD) coupled to the CSD of a comprehensive code, but are generally considered too time consuming where numerous simulations are required like rotor optimization. An approach is needed where high fidelity CFD/CSD simulation can be routinely used in design optimization. This thesis documents the development of physics based rotor simulation frameworks. A low fidelity model uses a comprehensive code with simplified aerodynamics. A high fidelity model uses a parallel processor capable CFD/CSD methodology. Both frameworks include an aeroacoustic simulation for prediction of noise. A synergistic process is developed that uses both frameworks together to build approximate models of important high fidelity metrics as functions of certain design variables. To test this process, a 4-bladed hingeless rotor model is used as a baseline. The design variables investigated include tip geometry and spanwise twist. Approximation models are built for high fidelity metrics related to rotor efficiency and vibration. Optimization using the approximation models found the designs having maximum rotor efficiency and minimum vibration. Various Pareto generation methods are used to find frontier designs between these two anchor designs. The Pareto anchors are tested in the high fidelity simulation and shown to be good designs, providing evidence that the process has merit. Ultimately, this process can be utilized by industry rotor designers with their existing tools to bring high fidelity analysis into the preliminary design stage of rotors.

<p>This dissertation investigates the optimal aerodynamic performance and design of conventional and coaxial helicopters in hover and forward flight using conventional and higher harmonic blade pitch control. First, we describe a method for determining the blade geometry, azimuthal blade pitch inputs, optimal shaft angle (rotor angle of attack), and division of propulsive and lifting forces among the components that minimize the total power for a given forward flight condition. The optimal design problem is cast as a variational statement that is discretized using a vortex lattice wake to model inviscid forces, combined with two-dimensional drag polars to model profile losses. The resulting nonlinear constrained optimization problem is solved via Newton iteration. We investigate the optimal design of a compound vehicle in forward flight comprised of a coaxial rotor system, a propeller, and optionally, a fixed wing. We show that higher harmonic control substantially reduces required power, and that both rotor and propeller efficiencies play an important role in determining the optimal shaft angle, which in turn affects the optimal design of each component. Second, we present a variational approach for determining the optimal (minimum power) torque-balanced coaxial hovering rotor using Blade Element Momentum Theory including swirl. We show that the optimal hovering coaxial rotor generates only a small percentage of its total thrust on the portion of the lower rotor operating in the upper rotor's contracted wake, resulting in an optimal design with very different upper and lower rotor twist and chord distributions. We also show that the swirl component of induced velocity has a relatively small effect on rotor performance at the disk loadings typical of helicopter rotors. Third, we describe a more refined model of the wake of a hovering conventional or coaxial rotor. We approximate the rotor or coaxial rotors as actuator disks (though not necessarily uniformly loaded) and the wake as contracting cylindrical vortex sheets that we represent as discrete vortex rings. We assume the system is axisymmetric and steady in time, and solve for the wake position that results in all vortex sheets being aligned with the streamlines of the flow field via Newton iteration. We show that the singularity that occurs where the vortex sheet terminates at the edge of the actuator disk is resolved through the formation of a 45 degree logarithmic spiral in hover, which results in a non-uniform inflow, particularly near the edge of the disk where the flow is entirely reversed, as originally hypothesized by previous authors. We also quantify the mutual interference of coaxial actuator disks of various axial spacing. Finally, we combine our forward flight optimization procedure and the Blade Element Momentum Theory hover optimization to form a variational approach to the multipoint aerodynamic design optimization of conventional and coaxial helicopter rotors. The resulting nonlinear constrained optimization problem may be used to map the Pareto frontier, i.e., the set of rotor designs for which it is not possible to improve upon the performance in one flight condition without degrading performance in the other. We show that for both conventional and coaxial rotors analyzed in hover and high speed flight, a substantial tradeoff in performance must be made between the two flight conditions. Finally, computational results demonstrate that higher harmonic control is able to improve the Pareto efficiency for both conventional and coaxial rotors.</p> / Dissertation

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This thesis presents the design and implementation of all the subsystems required to perform precision autonomous helicopter landings within a low-cost framework. To obtain high-accuracy state estimates during the landing phase a vision-based approach, with a downwards facing camera on the helicopter and a known landing target, was used. An e cient monocular-view pose estimation algorithm was developed to determine the helicopter's relative position and attitude during the landing phase. This algorithm was analysed and compared to existing algorithms in terms of sensitivity, robustness and runtime. An augmented kinematic state estimator was developed to combine measurements from low-cost GPS and inertial measurement units with the high accuracy measurements from the camera system. High-level guidance algorithms, capable of performing waypoint navigation and autonomous landings, were developed. A visual position and attitude measurement (VPAM) node was designed and built to perform the pose estimation and execute the associated algorithms. To increase the node's throughput, a compression scheme is used between the image sensor and the processor to reduce the amount of data that needs to be processed. This reduces processing requirements and allows the entire system to remain on-board with no reliance on radio links. The functionality of the VPAM node was con rmed through a number of practical tests. The node is able to provide measurements of su cient accuracy for the subsequent systems in the autonomous landing system. The functionality of the full system was con rmed in a software environment, as well as through testing using a visually augmented hardware-in-the-loop environment. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwikkeling van die substelsels wat vir akkurate outonome helikopter landings benodig word. 'n Onderliggende doel was om al die ontwikkeling binne 'n lae-koste raamwerk te voltooi. Hoe-akkuraatheid toestande word benodig om akkurate landings te verseker. Hierdie metings is verkry deur middel van 'n optiese stelsel, bestaande uit 'n kamera gemonteer op die helikopter en 'n bekende landingsteiken, te ontwikkel. 'n Doeltreffende mono-visie posisie-en-orientasie algoritme is ontwikkel om die helikopter se posisie en orientasie, relatief tot die landingsteiken, te bepaal. Hierdie algoritme is deeglik ondersoek en vergelyk met bestaande algoritmes in terme van sensitiwiteit, robuustheid en uitvoertyd. 'n Optimale kinematiese toestandswaarnemer, wat metings van GPS en inersiele sensore kombineer met die metings van die optiese stelsel, is ontwikkel en deur simulasie bevestig. Hoe-vlak leidingsalgoritmes is ontwikkel wat die helikopter in staat stel om punt-tot-punt navigasie en die landingsprosedure uit te voer. 'n Visuele posisie-en-orientasie meetnodus is ontwikkel om die mono-visie posisie-en orientasie algoritmes uit te voer. Om die deurset te verhoog is 'n saampersingsalgoritme gebruik wat die hoeveelheid data wat verwerk moet word, te verminder. Dit het die benodigde verwerkingskrag verminder, wat verseker het dat alle verwerking op aanboord stelsels kan geskied. Die meetnodus en mono-visie algoritmes is deur middel van praktiese toetse bevestig en is in staat om metings van voldoende akkuraatheid aan die outonome landingstelsel te verskaf. Die werking van die volledige stelsel is, deur simulasies in 'n sagteware en hardeware-indie- lus omgewing, bevestig.

Syftet med studien har varit att ur ett militärtekniskt överlevnadsperspektiv ta fram underlag över vilken verkansförmåga helikopter 16 behöver under ett transportuppdrag, i en nationell insats där hotet utgörs av mekaniserat infanteri. Studien har genomförts som en kvalitativ studie med ett visst kvantitativt inslag och baseras på data och fakta hämtad ur öppen litteratur samt genom intervjuer av uppdragsspecialister med erfarenhet och kunskap inom dörrskytte. Till hjälp har metodverktyget A´WOT-analys använts, vilken är en hybrid till SWOT-analysen. Syftet med A´WOT-analysen är att skilja ut de faktorer som behövs för verkan från helikopter 16 mot en definierad motståndare. Det samlade resultatet och sammanfattningen av studien är att helikopter 16 verkansförmåga behöver en omfattande uppgradering, om uppdrag som egen taktisk enhet skall kunna genomföras i en hotmiljö som utgörs av en kvalificerad motståndare. / The purpose of the study has been to investigate, from a military technical survival perspective, the effectiveness of helicopter 16 during a transport mission, in a national effort where the threat consists of a qualified opponent. The study has been conducted as a qualitative study with a certain quantitative element and based on data and facts obtained from open literature as well as interviews by mission specialists with experience and knowledge from door gunnery. As a help, the method tool A'WOT analysis have been used, which is a hybrid to the SWOT analysis. The purpose of the A'WOT analysis is to distinguish important factors for the effect from helicopter 16 against a defined opponent. The overall result and summary of the study is that helicopter 16 action ability needs a proper upgrade if assignments as a tactical unit can be carried out in a hot environment dictated by a qualified opponent.