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Investigation of complex multirotor aerodynamic phenomena via wind tunnel experimentation is becoming extremely important with the rapid progress in advanced distributed propulsion VTOL concepts. Much of this experimentation is being performed in large, highly advanced tunnels. However, the proliferation of this class of vehicles extends to small aircraft used by small businesses, universities, and hobbyists without ready access to this level of test facility. Therefore, there is a need to investigate whether multirotor vehicles can be adequately tested in smaller wind tunnel facilities. A test rig for a 2.82-pound quadcopter was developed to perform powered testing in the Cal Poly Aerospace Department’s Low Speed Wind Tunnel, equipped with a 3-foot tall by 4-foot wide test section. The results were compared to data from similar tests performed in the U.S. Army 7-by 10-ft Wind Tunnel at NASA Ames. The two data sets did not show close agreement in absolute terms but demonstrated similar trends. Due to measurement uncertainties, the contribution of wind tunnel interference effects to this discrepancy in measurements was not able to be properly quantified, but is likely a major contributor. Flow visualization results demonstrated that tunnel interference effects can likely be minimized by testing at high tunnel speeds with the vehicle pitched 10-degrees or more downward. Suggestions towards avoiding the pitfalls inherent to multirotor wind tunnel testing are provided. Additionally, a modified form of the conventional lift-to-drag ratio is presented as a metric of electric multirotor aerodynamic efficiency.

The vortex particle method (VPM) is a mesh-free approach to computational fluid dynamics (CFD) solving the Navier-Stokes equations in their velocity-vorticity form. The VPM uses a Lagrangian scheme, which not only avoids the hurdles of mesh generation, but it also conserves vortical structures over long distances with minimal numerical dissipation while being orders of magnitude faster than conventional mesh-based CFD. However, VPM is known to be numerically unstable when vortical structures break down close to the turbulent regime. In this study, we reformulate the VPM as a large eddy simulation (LES) in a scheme that is numerically stable, without increasing its computational cost. A new set of VPM governing equations are derived from the LES-filtered Navier-Stokes equations. The new equations reinforce conservation of mass and angular momentum by reshaping the vortex elements subject to vortex stretching. In addition to the VPM reformulation, a new anisotropic dynamic model of subfilter-scale (SFS) vortex stretching is developed. This SFS model is well suited for turbulent flows with coherent vortical structures where the predominant cascade mechanism is vortex stretching. Extensive validation is presented, asserting the scheme comprised of the reformulated VPM and SFS model as a meshless LES that accurately resolves large-scale features of turbulent flow. Advection, viscous diffusion, and vortex stretching are validated through simulation of isolated and leapfrogging vortex rings. Mean and fluctuating components of turbulent flow are validated through simulation of a turbulent round jet, in which Reynolds stresses are resolved directly and compared to experimental measurements. Finally, the computational efficiency of the scheme is showcased in the simulation of an aircraft rotor in hover, showing our meshless LES to be 100x faster than a mesh-based LES with similar fidelity. The ability to accurately and rapidly assess unsteady interactional aerodynamics is a shortcoming and bottleneck in the design of various next-generation aerospace systems: from electric vertical takeoff and landing (eVTOL) aircraft to airborne wind energy and wind farms. For instance, current models used in preliminary design fail to predict and assess configurations that may lead to the wake of a rotor impinging on another rotor or a wing during an eVTOL transition maneuver. In the second part of this dissertation, we address this shortcoming as we present a variable-fidelity CFD framework based on the reformulated VPM for simulating complex interactional aerodynamics. We further develop our meshless LES scheme to include rotors and wings in the computational domain through actuator models. A novel, vorticity-based, actuator surface model (ASM) is developed for wings, which is suitable for rotor-wing interactions when a wake impinges on the surface of a wing. This ASM imposes the no-flow-through condition at the airfoil centerline by calculating the circulation that meets this condition and by immersing the associated vorticity following a pressure-like distribution. Extensive validation of rotor-rotor and rotor-wing interactions predicted with our LES is presented, simulating two side-by-side rotors in hover, a tailplane with tip-mounted propellers, and a wing with propellers mounted mid-span. To conclude, the capabilities of the framework are showcased through the simulation of a multirotor tiltwing vehicle. The vehicle is simulated mid maneuver as it transitions from powered lift to wing-borne flight, featuring rotors with variable RPM and variable pitch, tilting of wings and rotors, and significant rotor-rotor and rotor-wing interactions from hover to cruise. Thus, the reformulated VPM provides aircraft designers with a high-fidelity LES tool that is orders of magnitude faster than mesh-based CFD, while also featuring variable-fidelity capabilities.

The aim of this thesis is to advance the control and estimation schemes for multirotors, and more specifically the Aerial Robotic Worker, in order to progress towards the necessary control and estimation performance for robust control, cooperation and collaboration. Towards this envisioned aim, this Licentiate thesis will present the following main research contributions: a) a singularity-free attitude controller for the attitude problem has been established, that does not have the inherent drawbacks of Euler angle or Direction Cosine Matrix based approaches, b) a generalized estimation scheme for attitude, position and parameter estimation will be presented that has the merit of low computational footprint, while it is robust towards magnetic disturbances and able to identify key parameters in the model of an Aerial Robotic Worker, c) an method for estimating the induced vibration frequencies on the multirotor’s frame, and the respective amplitudes, that relies on notch filtering for attenuating the induced vibrations, and d) a theoretical establishment, as well as an experimental development and evaluation of a variable pitch propeller model to add additional degrees of freedom and increase the robustness of an Aerial Robotic Worker. In the first part of this thesis the main contributions of the previous research approaches will be highlighted, while in the second part of the thesis the corresponding and in full detail articles will be presented.

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Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2018-11-26T20:27:20Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Joel Zubek.pdf: 7864320 bytes, checksum: f2e6f06e6ec1c27abd616c5e845d97f8 (MD5) / Made available in DSpace on 2018-11-26T20:27:20Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Joel Zubek.pdf: 7864320 bytes, checksum: f2e6f06e6ec1c27abd616c5e845d97f8 (MD5) Previous issue date: 2018-08-10 / Entre os principais problemas relacionados à conservação ambiental em áreas agrícolas está a degradação dos solos por meio da erosão hídrica que ocasiona a remoção das camadas mais férteis de solo e o transporte de partículas de solo para as partes mais baixas do relevo, o que contribui para o assoreamento dos recursos hídricos. Portanto, o presente estudo teve como objetivo diagnosticar processos erosivos em uma área de produção agrícola localizada na Fazenda Escola Capão da Onça – FESCON – UEPG, mediante análise de dados obtidos por Sistema de Navegação Global por Satélite (Global Navigation Satellite System - GNSS) e Aeronaves Remotamente Pilotadas (Remotely Piloted Aircraft - RPA). Para a realização do trabalho foi implantada uma grade regular com pontos de 45 x 45 metros de distância, totalizando 140 pontos em uma área de aproximadamente 26 hectares. Foram realizados georreferenciamento dos pontos da grade regular por meio de receptores de sinal GNSS Geodésico pós-processado e a coleta de atributos do solo (textura do solo). Os dados de textura do solo levantados na grade regular proporcionaram gerar modelos para o cálculo do fator de erodibilidade do solo para área de estudo. Com os valores altimétricos das coordenadas levantadas nos pontos da grade regular foi possível avaliar a precisão vertical de Modelos Numéricos do Terreno - MNT gerados por meio de dados obtidos com RPA. Foram avaliados os modelos gerados com dados obtidos por meio de equipamentos de RPA de asa fixa e multirotor com a distribuição de diferentes números de pontos de controle e sem pontos de controle. Mediante a análise estatística aplicada em relação entre a dispersão das diferenças altimétricas geradas nos MNT e os pontos da grade regular usados como referência, o MNT gerado com os dados de RPA asa fixa com pontos de controle apresentou o melhor resultado. Diante da constatação do melhor MNT foi modelado o fator topográfico para a área de estudo. A utilização de Sistema de Informação Geográfica - SIG proporcionou integrar todos os dados em um único ambiente computacional; gerar modelos por meio de interpolação; analisar a precisão dos modelos; implementar as equações para o cálculo dos fatores de erodibilidade e topográfico e também a Equação Universal de Perda de Solo Revisada (Revised Universal Soil Loss Equation – RUSLE); além das representações das informações. O resultado obtido com o modelo gerado mediante o cálculo da RUSLE apresentou a estimativa que mais de 70 % da área de estudo está com baixa suscetibilidade à erosão ou ligeira perda de solo. O restante da área de estudo apresentou perda de solos acima de 10 tonelada/ha.ano, indicando média e alta suscetibilidade à erosão. / Among the major problems related to environmental conservation in agricultural areas is soil degradation through water erosion, which causes the removal of the most fertile soil layers and the transport of soil particles to the lower parts of the relief, which contributes to the silting up of water resources. Therefore, the present study aimed to diagnose erosive processes in an area of agricultural production located at Fazenda Escola Capão da Onça - FESCON - UEPG, by analyzing data obtained by the Global Navigation Satellite System (GNSS) and Remotely Piloted Aircraft (RPA).For the accomplishment of the work a regular grid with points of 45 x 45 meters of distance was implanted, totaling 140 points in an area of approximately 26 hectares. Georeferencing of the regular grid points was carried out by means of post-processed GNSS signal receivers and the soil attributes collection (soil texture). The soil texture data collected in the regular grid provided the model for calculating the soil erodibility factor for the study area. With the altimetric values of the coordinates raised at the points of the regular grid it was possible to evaluate the vertical accuracy of Numerical Terrain Models generated through data obtained with RPA. The models generated with data obtained by means of fixed-wing and multirotor RPA equipment with the distribution of different numbers of control points and without control points were evaluated. by means of the statistical analysis applied in relation between the dispersion of the altimetric differences generated in the Numerical Terrain Model and the points of the regular grid used as reference, the Numerical Terrain Model generated with the fixed wing RPA data with control points presented the best result. In view of the finding of the best NTM, the topographic factor was modeled for the study area. The use of Geographic Information System GIS provided to integrate all the data in a unique computational environment; generate models through interpolation; analyze the accuracy of the models; implement the equations for the calculation of the erodibility and topographic factors and also the Revised Universal Soil Loss Equation (RUSLE); beyond the representations of the information. The result obtained with the model generated by RUSLE calculation showed that more than 70% of the study area is low susceptibility to erosion or slight soil loss. The rest of the study area presented soil loss above 10 ton / ha.year, indicating medium and high susceptibility to erosion.

The interest of drones in all forms has exploded in the recent years. The development of multirotor vehicles such as quadcopters and octocopters, has reached a point where they are cheap and versatile enough to start becoming a part of everyday life. It is clear to say that the future applications seem limitless. This thesis goes through the steps of development, modelling and control design of an octocopter system. The developed octocopter builds on a concept of using the mini computer Raspberry Pi together with the code generation functionality of Matlab/Simulink. The mathematical modelling of the octocopter includes the thrust and torques generated by the propellers, added with gyroscopic torque. These are combined with the aerodynamic effects caused by incoming air. The importance of modelling the later mentioned effects has increased with the demand of precise controlled extreme manoeuvres. A full state feedback based hybrid controller scheme is designed against a linearized model, which makes use of the motor dynamics. The controllers show good performance in simulations and are approved for flight tests, which are conducted on two separate occasions. The octocopter makes two successful flights, proving that the concept can be applied on multirotor vehicles. However, there is a miss-match between the mathematical model and the physical octocopter, leaving questions for future work.

In this thesis two methods were developed for precise maritime landing of an autonomous multirotor aircraft based on real-time kinematic (RTK) Global Navigation Satellite System (GNSS). The first method called RTK-localized method (RLM) uses RTK GNSS measurements to localize a sea vessel and execute the landing. RLM was demonstrated outdoors in hardware and landed on a physically simulated boat called a mock-boat with an average landing error of 9.7 cm. The mock-boat was actuated to have boat-like motion and a forward velocity of ~2 m/s. This method showed that accurate landing is possible with RTK GNSS as the primary means of localizing a sea vessel. The localization was unaided by non-GNSS sensors or an estimator, but lacked full attitude estimation and measurement smoothing. The second method was called RTK-Estimation Method (REM) and provides a more complete and robust solution, particularly at sea. It includes a base (landing pad) estimator to fuse RTK GNSS measurements with a dynamic model of a sea vessel. In contrast to RLM, the estimator provides full attitude estimation and measurement smoothing. The base estimator consists of an EKF in conjunction with a complimentary filter and estimates the relative position, attitude, and velocity of a moving target using RTK GNSS and inertial measurements alone. REM was demonstrated outdoors in hardware for 18 flight tests. The same mock-boat from RLM was used as a substitute for a sea vessel, and the boat motion varied between tests. These dynamics were recorded and performances were compared. The rate of success was high given moderate mock-boat motion and degraded with more aggressive motion. Tests were conducted with forward velocities from 0 to 3 m/s and moderate to high wave like motion. Over all tests for REM, the multirotor landed with an average accuracy of 12.7 cm. The methods described depart from common methods given that the only sensors involved for tracking the sea vessel were RTK GNSS receivers and inertial measurement units. Most current methods rely on computer vision, and can fail in poor lighting conditions, in the presence of ocean spray, and other scenarios. The given solutions do not fail under such conditions. The multirotor was equipped with a standard off-the-shelf autopilot, PX4, and the methods function with common control and estimation schemes. The two methods are capable of landing on relatively small landing pads, on the order of 1 m by 1 m, at sea using measurements from satellites thousands of kilometers away.

Eftersom användningen av små UAV:s (Unmanned Aerial Vehicles) fortsätter att öka, harbullret från deras framdrivningssystem blivit ett ökande problem. Denna rapport är resultatetav ett masterprojekt med målet att utveckla en framdrivningsmetod med låga bullernivåerför små UAV:s.Projektet startade med en informationssökning där målet var att hitta information ombullerkällor i nuvarande system samt information om de fundamentala sätten på vilket luftflödekan skapas.När informationssökningen var färdig, genererades ett stort antal olika koncept. Konceptetsom författarna ansåg ha mest potential, var en propeller med en ny metod för passivkontroll av gränsskiktet. Konceptet har ett luftintag nära rotationscentrum. Efter att luftenhar kommit in i detta luftintag, leds den genom interna kanaler och accelereras radiellt utåtpå grund av centrifugalkraften. Luften sprutas sedan ut genom en slits nära framkantenpropellerbladets lågtryckssida. Denna ström av luft färdas över propellerbladet och sugsin genom en slits nära vingens bakkant. Därefter sprutas luften ut genom ett utlopp närapropellerbladets spets.Tanken är att den beskrivna metoden ska fördröja eller förhindra avlösning. Detta skullepotentiellt möjliggöra högre lyftkraft vid lägre rotationshastigheter, vilket därigenom potentielltsänker bullernivåerna. Förenklade modeller av det valda konceptet har utvecklats ochanalyserats med hjälp av CFD (Computational Fluid Dynamics) och jämförts med simuleringarav en referensmodell utan gränsskiktskontroll. Resultaten indikerar att flödet ikonceptmodellen strömmar genom kanalerna och över propellerbladet som det var tänkt.Lyftkraften och effektiviteten ökade med 4.3 % respektive 1.9 %, jämfört med referensmodellen,vid samma rotationshastighet. Den möjliga minskningen av rotationshastigheten pågrund av ökningen i lyftkraft resulterar i en minskning av bullernivån med 0.9 dB. Detbör noteras att resultaten från simuleringarna bör ses med försiktighet och att ytterligarearbete måste göras innan några definitiva slutsatser kan dras beträffande potentiella prestandaökningarav konceptet jämfört med en konventionell propeller. / As the use of small UAVs (Unmanned Aerial Vehicles) keeps increasing, the noise emittedfrom their propulsion systems have become an increasing issue. This report is the resultof a master thesis project with the aim of developing a propulsion method with low noiseemissions for small UAVs.The project started with a background study, where the aim was to find informationabout sources of noise in current systems and information about the fundamental ways inwhich air flow can be created.When the background study was finished, a large number of different concepts were generated.The concept that the authors considered having the most potential, was a propellerwith a new method for passive circulation control. The concept has an air intake close tothe rotational center. After air has entered this inlet it is led through internal channels andis accelerated radially outwards due to centrifugal forces. The air is then ejected through aslot close to the leading edge on the low pressure side on the propeller blade. This stream ofair travels over the propeller blade and is the sucked in through a slot close to the trailingedge. After this, the air is ejected through an outlet close to the propeller blades tip.The idea is that the method described should delay or prevent boundary layer separation.This would potentially allow for higher thrust at lower rotational speeds, thus potentiallylowering the noise emissions. Simplified models of the chosen concept have been developedand analyzed using CFD (Computational Fluid Dynamics) and compared to simulations ofa baseline model with no circulation control. The results indicate that the fluid flow in theconcept model flows through the channels and over the propeller blade, as intended. Thethrust and efficiency were increased by 4.3 % and 1.9 % respectively, compared to the baselinemodel, at the same rotational speed. The possible reduction of the rotational speed due tothe increase in thrust, results in a reduction of the noise level by 0.9 dB. It should be notedthat the results from the simulations should be viewed with caution and the that furtherwork needs to be done before any clear conclusions can be drawn regarding the potentialperformance increase of the concept compared to a conventional propeller.

Though multirotor unmanned aerial vehicles (UAVs) have become widely used during the past decade, challenges in autonomy have prevented their widespread use when moving vehicles act as their base stations. Emerging use cases, including maritime surveillance, package delivery and convoy support, require UAVs to autonomously operate in this scenario. This thesis presents improved solutions to both the state estimation and control problems that must be solved to enable robust, autonomous landing of multirotor UAVs onto moving vehicles.Current state-of-the-art UAV landing systems depend on the detection of visual fiducial markers placed on the landing target vehicle. However, in challenging conditions, such as poor lighting, occlusion, or extreme motion, these fiducial markers may be undected for significant periods of time. This thesis demonstrates a state estimation algorithm that tracks and estimates the locations of unknown visual features on the target vehicle. Experimental results show that this method significantly improves the estimation of the state of the target vehicle while the fiducial marker is not detected.This thesis also describes an improved control scheme that enables a multirotor UAV to accurately track a time-dependent trajectory. Rooted in Lie theory, this controller computes the optimal control signal based on an error-state formulation of the UAV dynamics. Simulation and hardware experiments of this control scheme show its accuracy and computational efficiency, making it a viable solution for use in a robust landing system.