The Active Control of Structural Response (ACSR) vibration suppression system, where hydraulic actuators located between the gearbox and the fuselage are used to cancel vibration in large helicopters, has been used successfully for many years. However the power consumed by the actuators can be high, and using hydraulic actuation for smaller rotorcraft has not been seen as practical. In contrast to active vibration reduction systems, passive vibration isolation systems require no external power. Passive vibration isolation systems however have the disadvantage of being limited to working at one specific frequency which will not be acceptable as slowed rotor flight becomes more common for fuel efficiency and noise legislation reasons. In this thesis two electrically powered actuation concepts, one piezoelectric, and one electromagnetic were initially evaluated. An electrically powered actively augmented passive, or hybrid, vibration reduction system based on an electro hydrostatic actuator (EHA) concept was proposed to be developed further. This hybrid actuator will have a wider range of operating frequencies than a purely passive system, and have lower power consumption than a purely active system. The design is termed a “Resonant EHA”; in that the resonant frequency of the coupled fluid, pump and electric motor rotor inertia matches the fundamental vibration frequency. The hydraulic cylinder, fluid and pump act as a single stage gear ratio, and the. brushless electric motor’s inertia is the main resonating mass as in a Dynamic Antiresonant Vibration Isolator (DAVI) passive vibration reduction system. The electrical power is used to compensate for friction in the actuator and other losses, and if needed can shift the operating point away from the resonant frequency. Simulation results indicated that a hydraulic circuit in which the pump leakage is fed back into the low pressure line would introduce unacceptable disturbances in the flows to and from the cylinder. To eliminate the source of the disturbances, a fully integrated electric motor and pump circuit design was chosen in which the electric motor is immersed in hydraulic fluid. An EHA demonstrator was built sized for a 1.5 tonne rotorcraft. For sizing comparison purposes the frameless brushless D.C motor for each strut of 1.5 tonne rotorcraft has a rotor and stator mass of approximately 1 kg, and can produce a continuous stall torque of 2 Nm. The bidirectional pump has a displacement of 1.5 cm3/rev, the mean system pressure was taken as 90 bar, and the double ended hydraulic cylinder has a 32 mm diameter bore, and 18 mm rod. Initial test results for the proof of concept EHA showed highly significant free play with a reversal of torque direction, resulting in unacceptable loss in transmission stiffness. The free play was traced to the gear pump and a hypothesis for the origin of the free play was put forward. To avoid torque reversals the EHA was further tested with a constant offset torque bias which proved successful in restoring a sufficient stiffness to the transmission. The sizing of the electric motor and power consumed with a non-zero offset torque is greater than a torque reversing motor, which limits the immediate application of the device in the present form. Future research investigating the use of other transmission elements, such as a piston pump, to obtain a more linear stiffness is recommended. As a hybrid vibration isolation system a Root Mean Square (RMS) reduction by a factor of four and near elimination of the fundamental frequency vibrations was achieved for the frequency range of 10 to 20 hertz.

No description available.

A new active-passive approach for the control of noise radiated from a small axial fan was investigated. The approach involved the installation of an axial fan into a short duct with both passive and active noise control functions. First, a systematic methodology for the analytical modeling of finite-length ducts with multiple discontinuities was formulated. The procedure involved the modeling of a duct as a collection of simple duct sections, which were interconnected at multiple junctions. Analytical studies have shown that a short lined duct provides passive noise reduction effects through the mass-loading effect of the duct air volume at low frequencies and the sound absorption by a passive liner at high frequencies. It was also shown that active control can provide further noise attenuations at low-to-mid frequencies, thereby enhancing the overall noise control performance. Two alternate designs of active-passive noise control fan duct were considered. One was a simple non- segmented duct with a 2x2 active control and the other was an internally segmented duct with an 8x8 active control. It was indicated that the latter design possesses a significantly higher global noise control potential than the former with respect to both bandwidth and attenuation level. This was attributed to the reduction of the unwanted pressure contributions from the duct cross modes through the high frequency shifting of the associated cut-on frequencies. The experimental validation of the noise control approach was also carried out. An active-passive noise control fan duct incorporating the segmented duct design with 8x8 active control was constructed in conjunction with a hybrid feedforward-feedback control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the broadband fan noise power by the feedback control. The overall active-passive noise control characteristics were observed to be in accordance with the analytical results. / Ph. D.

Des travaux expérimentaux et théoriques ont été menés afin d’enrichir la connaissance et la compréhension du comportement en corrosion du carbure de silicium en présence de mélanges gazeux complexes à très hautes températures. A cette fin ont été mis au point deux nouvelles méthodes expérimentales basées sur le chauffage par effet Joule pour le suivi in-situ des cinétiques d’oxydation, ainsi qu’un modèle intégrant thermodynamique hétérogène et phénomènes de transport en phase gazeuse. Dans le domaine des hautes températures et des basses pressions partielles en espèces oxydantes, l’oxydation de SiC est dite « active » et se traduit par la formation de produits gazeux et la dégradation rapide du matériau associée à une cinétique limitée par le transport des espèces en phase gazeuse. Dans le domaine des basses températures et des hautes pressions partielles en espèces oxydantes, l’oxydation est dite « passive » et se traduit par la croissance d’une couche d’oxyde condensé SiO2 qui agit comme une barrière de diffusion vis-à-vis des espèces oxydantes, et dont la croissance fait intervenir une variété de phénomènes physico-chimiques qu’il a été nécessaire de découpler.Une attention particulière a été portée à l’étude de la transition entre les domaines de conditions correspondant à chacun de ces modes d’oxydation dans des mélanges simples et dans des mélanges complexes comportant deux espèces oxydantes différentes. Une analyse précise de plusieurs modèles de description théorique de cette transition active/passive a pu être réalisée en s’appuyant sur les nouveaux moyens numériques ainsi que sur les nouveaux éclairages relatifs aux mécanismes d’oxydation active et passive issus de cette étude et de la littérature. / Experimental and theoretical studies have been carried out in order to obtain further knowledge and understanding of the corrosion behavior of silicon carbide under complex gas mixtures at very high temperatures. To that purpose, two original experimental methods based on Joule-heating have been designed for the in-situ following of SiC oxidation kinetics, and a model accounting for both heterogeneous kinetics and gas-phase transport phenomena has been developed thanks to a finite volume method. At high temperatures and low oxidant partial pressure, oxidation of SiC is « active » and associated with the formation of gaseous products and high degradation rates of the original materials, the reaction being rate-determined by species transport through a gaseous boundary layer. At low temperatures and high oxidant partial pressures, oxidation is « passive » and associated with the growth of a condensed oxide scale acting as a protecting diffusion barrier. An analytical study has been conducted in order to try and isolate the effects of the various physical and chemical phenomena involved during this passive oxidation, such as different growth mechanisms, volatilization or bubble formation, and quantify how temperature and gas composition influence them.An experimental study of the active/passive transition in the oxidation of SiC has been conducted under gas mixtures including one or two different oxidant species. Numerical simulation tools as well as new insights on oxidation mechanisms were used to analyze different predictive models of the active/passive transition and evaluate and understand the differences between these theoretical results and the ones obtained experimentally.

This essay advances a libertarian theory of moral rights, which responds effectively to some serious objections that have been raised against libertarianism. I show how libertarianism can explain children’s rights to certain physical integrity and aid. I defend strong moral rights of human, pre-natal organisms, infants and children against all agents to certain non-interference with their physical integrity. I also argue that parents’ moral obligation to aid their offspring follows from a moral principle that prohibits agents to actively harm rights-bearers. Since this is the core principle of all versions of libertarianism, we gain simplicity and coherence. In chapter two, I explain my theory’s similarities and differences to a libertarian theory of moral rights advanced by Robert Nozick in his 1974 book Anarchy, State, and Utopia. I explain the structure and coherence of negative moral rights as advanced by Nozick. Then, I discuss what these negative rights are rights to, and the criteria for being a rights-bearer. In chapter three, I formulate a clear distinction between active and passive behaviour, and discuss the moral importance of foreseeing consequences of one’s active interventions. In chapter four, I claim that some pre-natal human organisms, human infants, and children, are rights-bearers. I formulate a morally relevant characterization of potentiality, and argue that possession of such potentiality is sufficient to have negative rights against all agents. In chapter five, I discuss whether potential moral subjects, in addition, have positive moral rights against all agents to means sufficient to develop into actual moral subjects. I argue that this suggestion brings some difficulties when applied to rights-conflicts. In chapter six, I argue that potential moral subjects’ rights to means necessary to develop into actual moral subjects can be defended in terms of merely negative rights. By adopting the view advanced in this chapter, we get a simple, coherent theory. It avoids the difficulties in the view advanced in chapter five, while keeping its intuitively plausible features. In chapter seven, I discuss whether the entitlement theory is contradictory and morally repugnant. I argue that my version of the entitlement theory is not.

<p>The telecommunication business has changed in Sweden during the recent years. From being a monopoly, the market has switched into a more competitive market with more competitors that offer more services. <em>TeliaSonera </em>is one of the largest telecommunication providers in Sweden. <em>TeliaSonera </em>is a co-operation between the companies <em>Telia</em>, which was one of the leading telecommunication companies in Sweden, and the Finnish counterpart <em>Sonera</em>. At the present time of this thesis, they provide their customers with services like Broadband, TV, Stationary phone and Mobile phone. These services are provided both to residential and business customers.</p><p>The aim of this research project is to understand the switching behaviour of former <em>TeliaSonera </em>customers by investigating the background of the customers' motivation to switch. Through analysing the findings, the researchers will be able to make assumptions about customer switching processes.</p><p>The research has been conducted with an explorative research approach and qualitative interviewing via telephone with 22 former <em>TeliaSonera </em>customers. The questions were related to their behaviour before, while and after the switching from <em>TeliaSonera </em>to a competing provider. From the interviews, the researchers seek to get a better understanding what triggers sway customers to switch. Additionally, it is equally important to understand the switching process customers go through.</p><p>The theoretical framework is based on prior research on customer behaviour and customer relationship management in the field of service management and marketing. Theories as triggers, active and passive customers or suggestions like the unconscious decision-making are being discussed. Triggers are the point where the customer begins to be aware of a possible switch of services. An active customer searches for the information oneself and a passive customer often are influenced by a third party. The theory about unconscious decision-making questions if the human subconscious can make decision for customers before they are even aware of it. This theory is being applied to the collected data.</p><p>The results of the research show that there can be found two different switching paths of interviewed customers, which are generated based on the collected customer stories. The two different paths are categorised into a <em>reactional </em>and <em>situational </em>switching path and an <em>influenced </em>switching path.</p>

The telecommunication business has changed in Sweden during the recent years. From being a monopoly, the market has switched into a more competitive market with more competitors that offer more services. TeliaSonera is one of the largest telecommunication providers in Sweden. TeliaSonera is a co-operation between the companies Telia, which was one of the leading telecommunication companies in Sweden, and the Finnish counterpart Sonera. At the present time of this thesis, they provide their customers with services like Broadband, TV, Stationary phone and Mobile phone. These services are provided both to residential and business customers. The aim of this research project is to understand the switching behaviour of former TeliaSonera customers by investigating the background of the customers' motivation to switch. Through analysing the findings, the researchers will be able to make assumptions about customer switching processes. The research has been conducted with an explorative research approach and qualitative interviewing via telephone with 22 former TeliaSonera customers. The questions were related to their behaviour before, while and after the switching from TeliaSonera to a competing provider. From the interviews, the researchers seek to get a better understanding what triggers sway customers to switch. Additionally, it is equally important to understand the switching process customers go through. The theoretical framework is based on prior research on customer behaviour and customer relationship management in the field of service management and marketing. Theories as triggers, active and passive customers or suggestions like the unconscious decision-making are being discussed. Triggers are the point where the customer begins to be aware of a possible switch of services. An active customer searches for the information oneself and a passive customer often are influenced by a third party. The theory about unconscious decision-making questions if the human subconscious can make decision for customers before they are even aware of it. This theory is being applied to the collected data. The results of the research show that there can be found two different switching paths of interviewed customers, which are generated based on the collected customer stories. The two different paths are categorised into a reactional and situational switching path and an influenced switching path.

A partly new train of thought has emerged during the last few years, which claims that national conditions are of importance for company strength in relation to international competitors. National competition has stood out as one of the most important explanatory factors, and is seen as the catalyst or motor in dynamic industrial environments. The demands and pressures that evolve from competition between geographically proximate companies stimulate the innovativeness within the industry. Thus, the question about why and how dynamics of competition develop and function has not been answered in existing research. The main purpose of this study is therefore to analyse the process of competition in industries with a high degree of geographical proximity between competitors, in order to improve the understanding of the character and dynamics of competition. A general review of literature dealing with competition at industry, strategic group, and organisation level was compiled. The review gave two dimensions by which four types of competition were possible to distinguish, degree of symmetry between competitores and degree of activity in competition. To obtain an understanding for the character and dynamics of competition, it is not enough to identify different types of competition. The process through which competition is formed over time also needs to be studied. Other theoretical approaches are therefore necessary. First, the companies' competitive actions should be understood from their experience and expectations of competition. Second, the specific competitive moves that are taken by individual companies are of importance for the competition. Third, competition has to be described as a process of interaction over time. A case-study approach has been used for the gathering of data. Case-studies have been conducted within three industries that differ from each other with regard to competition. Competition in the Frontloader industry has been driven by two companies equal in both size and relative strength. The competitors in the Lining industry are,on the other hand, dissimilar, both in respect to relative strength and to the orientation of their business. The third industry, that of Hoisters, is characterised by the domination by one company. Two major results have been reached in this study. First the concept climate of competition has been coined to analyse and describe the character of the four types of competition. The following four climates of competition emerge from the analysis; climate of rivalling competion, of co-existing competition, of evolutionary competition and climate of revolutionary competition. The climates of competition differ with regard to the functional and psychological distance between competitors, the possibility to survey competition, and the actors' acceptance of current rules-of-play and role distribution. The second result of the study is a greater understanding for the dynamics within competition. By analysing the character of and change in competition over time two partly different, but interwined forces, have been detected. Competition gives rise on the one hand to different kinds of learning processes, and on the other forces competitors to innovative and creative measures. / digitalisering@umu

Fluid-structure interactions occur in many engineering and industrial applications. Such interactions may result in undesirable forces acting on the structure that may cause fatigue and degradation of the structural components. The purpose of this research is to develop a solver that simulates the fluid-structure interaction, assess tools that can be used to control the resulting motions and analyze a system that can be used to convert the structure's motion to a useful form of energy. For this purpose, we develop a code which encompasses three-dimensional numerical simulations of a flow interacting with a freely-oscillating cylinder. The solver is based on the accelerated reference frame technique (ARF), in which the momentum equations are directly coupled with the cylinder motion by adding a reference frame acceleration term; the outer boundary conditions of the flow domain are updated using the response of the cylinder. We develop active linear and nonlinear velocity feedback controllers that suppress VIV by directly controlling the cylinder's motion. We assess their effectiveness and compare their performance and required power levels to suppress the motion of the cylinder. Particularly, we determine the most effective control law that requires minimum power to achieve a desired controlled amplitude. Furthermore, we investigate, in detail, the feasibility of using a nonlinear energy sink to control the vortex-induced vibrations of a freely oscillating circular cylinder. It has been postulated that such a system, which consists of a nonlinear spring, can be used to control the motion over a wide range of frequencies. However, introducing an essential nonlinearity of the cubic order to a coupled system could lead to multiple stable solutions depending on the initial conditions, system's characteristics and parameters. Our investigation aims at determining the effects of the sink parameters on the response of the coupled system. We also investigate the extent of drag reduction that can be attained through rotational oscillations of the circular cylinder. An optimization is performed by combining the CFD solver with a global deterministic optimization algorithm. The use of this optimization tool allows for a rapid determination of the rotational amplitude and frequency domains that yield minimum drag. We also perform three-dimensional numerical simulations of an inline-vibrating cylinder over a range of amplitudes and frequencies with the objective of suppressing the lift force. We compare the amplitude-frequency response curves, levels of lift suppression, and synchronization maps for two- and three-dimensional flows. Finally, we evaluate the possibility of converting vortex-induced vibrations into a usable form of electric power. Different transduction mechanisms can be employed for converting these vibrations to electric power, including electrostatic, electromagnetic, and piezoelectric transduction. We consider the piezoelectric option because it can be used to harvest energy over a wide range of frequencies and can be easily implemented. We particularly investigate the conversion of vortex-induced vibrations to electric power under different operating conditions including the Reynolds number and load resistance. / Ph. D.

Asymmetric interactions and relationships between celebrities and followers, referred to as Parasocial Interactions (PSI) and Parasocial Relationships (PSR), respectively, have been extensively studied within the context of TV, radio and print media. However, within the Social Media (SM) ecosystem - where follower engagement and experience flow seamlessly across multiple SM tools/platforms - the nature of PSI and PSR is changing and research within this context is still nascent. Using Identity Theory and Motivational Theory, this dissertation analyses the impact active/passive engagement and compulsive use of the SM ecosystem can have in the formation of PSI and PSR. Specifically, the goal of this research is to understand how different types of engagement (passive and active) can influence parasocial relationships (friendship and love) through the mediation of cognitive and behavioural parasocial interactions. A model is proposed and validated with 294 respondents. The findings show that passive engagement in the SM ecosystem does not impact PSI/PSR while active engagement significantly impacts PSI and the consequent PSR formation. Compulsive use of the SM ecosystem strongly attenuates the relationships between PSI and PSR. Contributions and implications for both theory and practice are discussed. / Thesis / Doctor of Business Administration (DBA)