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Organische Halbleiterbauelemente sind eine vielversprechende Technologie, die das Spektrum der optoelektronischen Halbleiterbauelemente erweitert und etablierte Technologien basierend auf anorganischen Halbleitermaterialien ersetzen kann. Für Display- und Beleuchtungsanwendungen werden sie z. B. als organische Leuchtdioden oder Transistoren verwendet. Eine entscheidende Eigenschaft organischer Halbleitermaterialien ist, dass die Ladungstransporteigenschaften stark von der Temperatur im Bauelement beeinflusst werden. Insbesondere nimmt die elektrische Leitfähigkeit mit der Temperatur zu, so dass Selbsterhitzungseffekte, einen großen Einfluss auf die Leistung der Bauelemente haben. Mit steigender Temperatur nimmt die elektrische Leitfähigkeit zu, was wiederum zu größeren Strömen führt. Dies führt jedoch zu noch höheren Temperaturen aufgrund von Joulescher Wärme oder Rekombinationswärme. Eine positive Rückkopplung liegt vor. Im schlimmsten Fall führt dieses Verhalten zum thermischen Durchgehen und zur Zerstörung des Bauteils. Aber auch ohne thermisches Durchgehen führen Selbsterhitzungseffekte zu interessanten nichtlinearen Phänomenen in organischen Bauelementen, wie z. B. die S-förmige Beziehung zwischen Strom und Spannung. In Regionen mit negativem differentiellen Widerstand führt eine Verringerung der Spannung über dem Bauelement zu einem Anstieg des Stroms durch das Bauelement. Diese Arbeit soll einen Beitrag zur mathematischen Modellierung, Analysis und numerischen Simulation von organischen Bauteilen leisten. Insbesondere wird das komplizierte Zusammenspiel zwischen dem Fluss von Ladungsträgern (Elektronen und Löchern) und Wärme diskutiert. Die zugrundeliegenden Modellgleichungen sind Thermistor- und Energie-Drift-Diffusion-Systeme. Die numerische Diskretisierung mit robusten hybriden Finite-Elemente-/Finite-Volumen-Methoden und Pfadverfolgungstechniken zur Erfassung der in Experimenten beobachteten S-förmigen Strom-Spannungs-Charakteristiken wird vorgestellt., Organic semiconductor devices are a promising technology to extend the range of optoelectronic semiconductor devices and to some extent replace established technologies based on inorganic semiconductor materials. For display and lighting applications, they are used as organic light-emitting diodes (OLEDs) or transistors. One crucial property of organic semiconductor materials is that charge-transport properties are heavily influenced by the temperature in the device. In particular, the electrical conductivity increases with temperature, such that self-heating effects caused by the high electric fields and strong recombination have a potent impact on the performance of devices. With increasing temperature, the electrical conductivity rises, which in turn leads to larger currents. This, however, results in even higher temperatures due to Joule or recombination heat, leading to a feedback loop. In the worst case, this loop leads to thermal runaway and the complete destruction of the device. However, even without thermal runaway, self-heating effects give rise to interesting nonlinear phenomena in organic devices, like the S-shaped relation between current and voltage resulting in regions where a decrease in voltage across the device results in an increase in current through it, commonly denoted as regions of negative differential resistance. This thesis aims to contribute to the mathematical modeling, analysis, and numerical simulation of organic semiconductor devices. In particular, the complicated interplay between the flow of charge carriers (electrons and holes) and heat is discussed. The underlying model equations are of thermistor and energy-drift-diffusion type. Moreover, the numerical approximation using robust hybrid finite-element/finite-volume methods and path-following techniques for capturing the S-shaped current-voltage characteristics observed in experiments are discussed.

[EN] The integration of a cargo UAV into the non-segregated airspace is studied in this thesis in terms of its normal and emergency operating regimes. Several algorithms have been developed in order to ensure that the Rules of the Air concerning the cruise flight phase are followed. The UAV mission consists of flying over a path generated between a given set of waypoints and avoiding collision with intruders respecting the Rules of the Air. Path planning and path-following algorithms are based on simple approaches which result in guidance command performance limitations. In particular, Dubins curves approach has been used to obtain the flyable paths, hence discontinuous guidance commands are demanded. Path-following approach is based on Pure Pursuit guidance, therefore the guidance commands are generated by this algorithm and affected by the path planning phase. A decision making algorithm has been developed to manage the UAV operations. This decision making algorithm requires information about the number of intruders, hence a conflict detection algorithm has been programmed as well. This together with the type of intruder, which is determined based on its velocity, determines the required manoeuvre to ensure the separation with the intruders while flying along the given waypoints. Simulations have shown that the safety distance is maintained for distinct types of intruders and different types of approaches in the case of single conflicts. Multiple conflicts resolution can be solved, but an improvement of this approach should be developed

[ES] El objetivo del presente Trabajo de Fin de Grado es la revisión de diferente algoritmos de seguimiento de ruta para multirrotores. Este proyecto comenzará introduciendo brevemente el crecimiento e importancia que han tenido los UAVs en los últimos años, proliferando el uso comercial de multirrotores entre los que destaca el "quadrotor". Tras esto, proseguiremos explicando a gran escala los aspectos más destacados en la dinámica y cinemática de los multirrotores: posibles sistemas de coordenadas, posibles movimientos, fuerzas y momentos que intervienen, el control. Una vez entrados en este tema, se procederá a la revisión de cuatro sistemas de control en algoritmos de seguimiento de ruta para UAVs, comparando las ventajas y desventajas de cada metodología. Por último, se implentará una simulación basada en uno de los algoritmos en Simulink, Matlab. A partir de esta simulación, se implementarán diferentes rutas (paths) y se comentarán los resultados., [EN] The objective of the present Independent Study is the review of path-following algorithms for multirotors, including a small experimentation. This study will first start briefly introducing the growth and importance of UAVs in the recent years, spreding the commercial use of the multirotors. The idea of a path-following algorithm will also be covered, and its application on multirotors. Then, the project will continue explaining the highlighted aspects in the dynamics and kinematics of a multirotors: coordinate systems, motions, acting forces and moments. Once covered this topic, the review of four path-following algorithms will be performed. Advantages and disadvantages of these tecniques will be explained and compared. Lastly, a small experimentation based on one of the explained path-following algorithms will be executed. This experimentation will be implemented in a simulation environment in Simulink. Couple of cases will be simulated and the corresponding results will be discussed.

This paper presents an effective autonomous follow-the-leader strategy for Azimuthal Stern Drive vessels. The control logic has been investigated from a theoretical point of view. A line-of-sight algorithm is exploited to ensure yaw-check ability, while a speed-check feature is implemented to track the velocity of the target along the path. For this purpose, a linearised manoeuvrability model for azimuthal drive surface vessels is presented. A model-based control synthesis is proposed to ensure the stability of the closed-loop system and robust PID controllers are designed by using Linear Matrix Inequalities technique. The control strategy has been successively validated in two steps, initially by using simulation techniques, and then experimentally using an outdoor scenario with model scale tugs. The path planning, navigation, guidance and control modules are studied, detailed, and digitally implemented on-board of the model scale tugs. The models are supplied with GNSS+INS navigation system. Low-level management and control of Azimuthals angles and shaft revolutions is implemented on-board. High-level decen-tralised path planning, guidance, and control sequence evaluation are dealt with at a remote ground station. In particular, the presented follow-the-leader strategy meets the most generic needs of platooning convoys, and, in the specific instance, of Escort convoy tugs. The operative profile of the latter concerns long-lasting and routine chases with the continuous demand of tuning heading and speed to track the target vessels, until the rare occurrence of an emergency event. In a realistic scenario, the proposed control system would be beneficial for the tug master’s lucidity and alertness, while reducing avoidable risks. At the end of the paper, the results of the experimental campaign are shown to demonstrate the effectiveness of the proposed control logic., Transport Engineering and Logistics

The actual performance of model-based path-following methods for unmanned aerial vehicles (UAVs) shows considerable dependence on the wind knowledge and on the fidelity of the dynamic model used for design. This study analyzes and demonstrates the performance of an adaptive vector field (VF) control law which can compensate for the lack of knowledge of the wind vector and for the presence of unmodeled course angle dynamics. Extensive simulation experiments, calibrated on a commercial fixed-wing UAV and proven to be realistic, show that the new VF method can better cope with uncertainties than its standard version. In fact, while the standard VF approach works perfectly for ideal first-order course angle dynamics (and perfect knowledge of the wind vector), its performance degrades in the presence of unknown wind or unmodeled course angle dynamics. On the other hand, the estimation mechanism of the proposed adaptive VF effectively compensates for wind uncertainty and unmodeled dynamics, sensibly reducing the path-following error as compared to the standard VF., Accepted Author Manuscript, Team Bart De Schutter, Ship Design, Production and Operations

A Fenchel dualization scheme for the one-step time-discretized contact problem of quasi-static elasto-plasticity with combined kinematic-isotropic hardening is considered. The associated path is induced by a coupled Moreau-Yosida / Tichonov regularization of the dual problem. The sequence of solutions to the regularized problems is shown to converge strongly to the optimal displacement- stress-strain triple of the original elasto-plastic contact problem in the space-continuous setting. This property relies on the density of the intersection of certain convex sets which is shown as well. It is also argued that the mappings associated with the resulting problems are Newton- or slantly differentiable. Consequently, each regularized subsystem can be solved mesh-independently at a local superlinear rate of convergence. For efficiency purposes, an inexact path-following approach is proposed and a numerical validation of the theoretical results is given., Peer Reviewed

The main contributions of this work are applications of robust control and analysis methods to complex engineering systems, namely, small fixed-wing unmanned aircraft systems (UAS). Multiple path-following controllers for a small fixed-wing Telemaster UAS are presented, including a linear parameter-varying (LPV) controller scheduled over path curvature. The controllers are synthesized based on a lumped path-following and UAS dynamic system, effectively combining the six degree-of-freedom aircraft dynamics with established parallel transport frame virtual vehicle dynamics. The robustness and performance of these controllers are tested in a rigorous MATLAB simulation environment that includes steady winds, turbulence, measurement noise, and delays. After being synthesized off-line, the controllers allow the aircraft to follow prescribed geometrically defined paths bounded by a maximum curvature. The controllers presented within are found to be robust to the disturbances and uncertainties in the simulation environment. A robust analysis framework for mathematical validation of flight control systems is also presented. The framework is specifically developed for the complete uncertainty characterization, quantification, and analysis of small fixed-wing UAS. The analytical approach presented within is based on integral quadratic constraint (IQC) analysis methods and uses linear fractional transformations (LFTs) on uncertainties to represent system models. The IQC approach can handle a wide range of uncertainties, including static and dynamic, linear time-invariant and linear time-varying perturbations. While IQC-based uncertainty analysis has a sound theoretical foundation, it has thus far mostly been applied to academic examples, and there are major challenges when it comes to applying this approach to complex engineering systems, such as UAS. The difficulty mainly lies in appropriately characterizing and quantifying the uncertainties such that the resulting uncertain m

Path-following splitting and semismooth Newton methods for solv- ing a class of problems related to elasto-plastic material deformations are pro- posed, analyzed and tested numerically. While the splitting techniques result in alternating minimization schemes, which are typically linearly convergent, the proposed Moreau-Yosida regularization based semismooth Newton tech- nique and an associated lifting step yield local superlinear convergence in func- tion space. The lifting step accounts for the fact that the operator associated with the linear system in the Newton iteration need not be boundedly invert- ible (uniformly along the iterates). For devising an efficient update strategy for the path-following parameter regularity properties of the path are studied and utilized within an inexact path-following scheme for all approaches. The paper ends by a report on numerical tests of the different approaches., Peer Reviewed

This article describes a novel add-on for powered wheelchairs that is composed of a gaze-driven control system and a navigation support system. The add-on was tested by three users. All of the users were individuals with severe disabilities and no possibility of moving independently. The system is an add-on to a standard power wheelchair and can be customized for different levels of support according to the cognitive level, motor control, perceptual skills, and specific needs of the user. The primary aim of this study was to test the functionality and safety of the system in the user's home environment. The secondary aim was to evaluate whether access to a gaze-driven powered wheelchair with navigation support is perceived as meaningful in terms of independence and participation. The results show that the system has the potential to provide safe, independent indoor mobility and that the users perceive doing so as fun, meaningful, and a way to reduce dependency on others. Independent mobility has numerous benefits in addition to psychological and emotional well-being. By observing users' actions, caregivers and healthcare professionals can assess the individual's capabilities, which was not previously possible. Rehabilitation can be better adapted to the individual's specific needs, and driving a wheelchair independently can be a valuable, motivating training tool.

A priori estimates of the length of the primal-dual path resulting from a Moreau--Yosida approximation of the feasible set for state constrained optimal control problems are derived. These bounds depend on the regularity of the state and the dimension of the problem. Numerical results indicate that the bounds are indeed sharp and are typically attained in cases where the active set consists of isolated active points. Further conditions on the multiplier approximation are identified which guarantee higher convergence rates for the feasibility violation due to the Moreau--Yosida approximation process. Numerical experiments show again that the results are sharp and accurately predict the convergence behavior.

Thin-walled structures, when properly designed, possess a high strength-to-weight and stiffness-to-weight ratio, and therefore are used as the primary components in some weight critical structural applications, such as aerospace and marine engineering. These structures are prone to be limited in their load carrying capability by buckling, while staying in the linear elastic range of the material. Buckling of thinwalled structures is an inherently nonlinear phenomena. When the material stays within its linear elastic range, the source of the nonlinearity is purely geometric. Thus, the analysis of nonlinear response of structures, especially thin-walled structures which are buckling sensitive, is important for determining their load carrying capability. For this reason, structural geometric nonlinearities are increasingly taken into account in engineering design. Nowadays, with the expanding computational power of modern computers nonlinear finite element analysis using commercial software is becoming the standard technique used to obtain the nonlinear response of complex structures, however, the repeated analyses that are needed in the design phase are still computationally intensive, in terms of the computation time required to run large models, even for modern computers. For this reason, reduced order techniques that reduce the problem size are attractive whenever repetitive analyses are required, such as in design optimization. Research on reduced order modeling of the nonlinear response of structures has attracted much attention from researchers. Some analytic techniques constitute very powerful tools for reducing the number of degrees of freedom (DOFs) in a nonlinear system, such as the Rayleigh-Ritz techniques and perturbation techniques. These two reduced basis techniques can be implemented in both analytical and numerical contexts, and due to the modeling versatility of the finite element method (FEM), most researchers prefer to reconstruct them within the FE, Aerospace Structures and Computational Mechanics, Aerospace Engineering

This paper discusses the evaluation of quasi-static equilibrium solutions for inflatable space membrane structures. A Mooney-Rivlin hyper-elastic material model, with variable constitutive constants, is considered. A compressible weightless medium is used to introduce within the membrane a one-parametric over-pressure loading compared to an ambient pressure. Analytical instability results are shown for a spherical and derived for a cylindrical case. These are compared to numerical simulations based on a flat linearly interpolated triangular space membrane element. Path-following procedures are used to find generalized equilibrium paths, with different parameterizations. Numerical examples show that the methods developed can give information on the stability of the membranes, but that the medium and means for introducing the internal pressure are of importance for the interpretation of stability., QC 20120910

In the multi-billion dollar motion control industry, systems are often required to traverse along a geometric path, where the speed at which the path is traversed is not pre-determined. Such path-following tasks involve competing control objectives of maximising accuracy while minimising traversal time.Existing trajectory planning routines optimise the path speed with respect to some of these objectives. However, trajectory planning is conducted in an open loop fashion, relying on trajectory tracking controllers to achieve the desired motion. Meanwhile, closed-loop path-following control schemes do not explicitly consider the control objectives. This thesis investigates the development of closed-loop path-following control schemes based on minimisation of a cost function within a receding horizon structure. The cost function is selected to reflect the desired objectives such as minimising traversal time, and is minimised subject to the system constraints. The receding horizon formulation allows for feedback to be taken into account at each sample, in contrast to open loop trajectory planning. A receding horizon path-following control scheme is first developed with the intention of achieving time-optimal path-following. The controller is designed to advance along the path as far as possible within a finite horizon while staying exactly on the path and honouring the constraints. The conditions under which the receding horizon approach replicates the time-optimal path-following solution are identified for second order differentially flat systems. In particular, it is shown that minimum-time path-following is achieved when the horizon is sufficiently long. Subsequently, a contouring control scheme for biaxial systems based on a similar framework is developed where the exact path-following constraint is relaxed in favour of penalising contouring error in the finite horizon cost function, which reflects the trade-off between competing control objectives of contouring accu

This paper discusses the evaluation of quasi-static equilibrium solutions for inflatable space membrane structures, such as balloons. A flat linearly interpolated triangular element is used for simulations, with a Mooney-Rivlin hyper-elastic material model, with variable constitutive constants. A compressible medium is used to introduce a one-parametric over-pressure loading within the membrane. Complex path-following procedures are used to find generalized equilibrium paths, with different parameterizations. Numerical examples show that the methods developed can give information on the stability of the structures, but that the medium and means for introducing the internal pressure is of importance for the interpretation of stability., QC 20140910

We highlight an essential difference between path-following and reference-tracking for nonminimum phase systems. It is well known that in the reference-tracking, for nonminimum phase systems, there exists a fundamental performance limitation in terms of a lower bound on the L-2-norm of the tracking error, even when the control effort is free. We show that this is not the case for the less stringent path-following problem, where the control objective is to force the output to follow a geometric path without a timing law assigned to it. Furthermore, the same is true even when an additional desired speed assignment is imposed.