Magnetic reconnection plays an important role in the transfer of mass, energy and momentum from the solar wind to the terrestrial magnetosphere. The earliest contributions to the theory of magnetic reconnection dates from the beginning of the 1930's. However, it took until the end of the 1950's when Sweet and Parker made their first reconnection model, for the concept to reach a somewhat solid ground. During the years since then magnetic reconnection has walked through the phase of reaching mythical proportions where some researchers believed in it, and some not, to the acceptance it has today where the main issue not is whether the process happens or not, but rather the main physical properties and the implications of it. During the last fifteen years much of the research due to the rapid increase in computer capacity, treats numerical simulations of magnetic reconnection. Theoretical analysis keeps though its position as a cornerstone for the understanding of the process. But also for the base of new implemented models. Much of the theoretical work accomplished to this day has its focus on magnetic reconnection itself; applications for different conditions, and the onset of the process - something which still is under much discussion among researchers. This work focuses on the implications of magnetic reconnection in combination with the outer magnetosheath flow. The analysis treats a two-dimensional and three-dimensional case. For the 3D case, the magnetosheath plasma flow is considered to be incompressible, while we for the 2D case also treat a compressible magnetosheath plasma. Magnetic reconnection is assumed to occur in a region stretching from the sub-solar point to the north, at an arbitrary point for the 2D case, and along a line parallel to the y-axis for the 3D case. The analysis is based on the MHD equations including dissipative effects such as viscosity and resistivity, where the equations are solved approximately by the use of an ordinary perturbation expansion for large Reynolds and Lundqvist numbers. The objective of the 2D study treating an incompressible plasma flow, is to get a description of the current transition layer in combination with the outer magnetosheath and boundary layer flow. The solutions are asymptotically matched with an existing model for the magnetosheath magnetic field. For the 2D compressible case and 3D analysis, the objective is to study the development of the magnetic field and total velocity during the transition from the magnetosheath to the magnetosphere. / Godkänd; 2005; 20070116 (ysko)

In a classroom an assistive listening device (ALD) is a system of external microphones that transmit sound from a sound source directly to students' hearing aids. An ALD can be a microphone close to the mouth which transmits a voice directly to listeners' hearing aids. An ALD can also be a microphone placed centrally and used by several persons at the same time. Sound quality of a listening device can be described as sound-transmission quality where maximal quality is no difference between input and output. From a wider perspective, this output can be the perceived quality of speech where a high speech quality matches given expectations, demands and necessaries. A focus on participatory learning environment in Swedish hearing impaired classes has brought out new perspectives on ALD solutions. The purpose of the studies reported in this thesis was to develop a methodical framework for the evaluation of classroom ALDs. As a basis for the evaluation of ALD communication quality is suggested. Communication quality is an extension of the sound quality concept which emphasizes student participation and peer interaction. As a pedagogical parallel, sound quality emphasizes a more cognitive view of learning whereas communication quality emphasizes participatory learning. By using room acoustic modelling and auralization in listening tests it was possible to evaluate aspects of room acoustics, signal processing techniques, speech and masking signals, and binaural advantage. A self-assessment approach was also used and a questionnaire was developed based on the Speech, Spatial and Qualities of Hearing Scale (SSQ). The studies found that students in hearing impaired classes prefer using only their hearing aids over using an ALD. Retrieving information about the acoustic environment was important aspects. Also observed was that when comparing different ALD solutions microphone distance is of importance. Listening effort correlates with hearing loss rather than with using different technologies. Today's hearing aids offer the best communication quality but it is also apparent than ALDs are preferred by students in some situations. Determining the combination of design and ALD function which can best benefit students is needed. The methodological framework described is promising for continuous studies developing and assessing classroom ALD. / <p>Godkänd; 2007; 20070315 (ysko)</p>

This thesis concerns the development of non-contact measurement methods and analysis of rotors. The methods have been verified and applied to milling machine spindles in order to investigate the speed dependency in the milling machine spindle dynamic. The research was financed by the Swedish Agency for Innovation Systems (Vinnova). Turning operations like milling are common in the automotive and aerospace industries where large metal work pieces are reduced to a fraction of their original weight when creating complex thin structures. During these operations it is important that unwanted behaviours such as excessive tool vibrations be avoided (this is normally called "chatter"). Chatter causes poor surface finish and/or material damage and can expose machine operators to annoying and/or dangerous noise levels. In order to predict processes parameters for a chatter free milling operation, knowledge of the properties of the dynamic system are essential. Normally the system dynamics are measured during no rotation; in order to include the influence of the spin speed the system must be analysed for all spindle speeds intended for the milling operation. This can be done either by measurement or modelling. Non- contact measurement techniques are however, often based on displacement sensors which do not have the same sensitivity as velocity or acceleration based methods. To improve the sensitivity in non-contact measurements of rotors a laser Doppler Vibrometry (LDV) based method has been developed. The developed LDV method is based on the reduction of the rotor surface structure and makes it possible to use single beam LDV measurements of rotors. These types of measurements were previously considered inaccurate but now have become feasible through the use of the method described in this research. Furthermore the dynamic properties of a high-speed-milling machine spindle were studied by a contactless dynamic spindle tester (CDST) developed by SKF. The measurements were substantiated by simulations using a finite element model (FEM) which confirmed the measurement results. The CDST measurements could be performed without violating safety regulations regarding human interaction with high speed spindles through the use of a magnetic excitation method. In the measurements conducted by the CDST a speed dependency in the spindle dynamic could be detected. By performing FEM simulations the major source of this dependency could be identified. The centrifugal force of the balls in the angular contact ball bearings was shown to have the largest influence on the overall dynamics compared to the gyroscopic moment of the rotor. The study performed indicates that predictions of high-speed-milling stability must include consideration of the speed dependency in the dynamic. / Godkänd; 2006; 20070109 (haneit)

Rotary kilns are industrial furnaces that have been widely used in limestone calcination, cement industry and hazardous waste incineration for centuries. In this work a rotary kiln used for the iron ore pellet sintering process in the grate-kiln pelletizing system has been studied. In order to increase the energy efficiency, a large amount of air is supplied to the kiln through air channels connected to the cooler. This air is necessary for the coal combustion process and the heat transport to the kiln bed. However, the geometry of the kiln hood connecting the air channels and the cooler is complicated. As a consequence, the jet flame is unstable. In order to improve the performance of the jet flame it is therefore necessary to study the kiln aerodynamics to reveal the flow field. Even though it is a complicated problem containing fluid dynamics, combustion and heat and mass transfer, it can be simplified into a down-scaled cold model to make it feasible to understand the flow field both experimentally and numerically. In this work, the whole kiln is generalized as a high Reynolds number turbulent round jet interacting with asymmetric co-flows. With the aid from previous PIV measurement data of a down-scaled water model of the kiln, Computational Fluid Dynamics (CFD) simulations using the commercial code ANSYS CFX 16.0 have been pursued for two main purposes: 1) To find a turbulence model that is computationally inexpensive and able to capture the main features of the mean flow field; 2) With the turbulence model chosen in 1), to study the geometrical effect on the development of the primary jet. In Paper A, three turbulence models were employed, the standard k-epsilon model, a modified k-epsilon model with slightly higher turbulence production and the SSG Reynolds stress model. Wall functions were applied since resolving the viscous wall region was not a concern in this work. It is found that the standard k-epsilon model fit the experimental data best compared to the other two models and that all three turbulence models predict an asymmetric development of the primary jet, especially far downstream, In Paper B, again using the down-scaled kiln model, isothermal cases with four different nozzle diameters were simulated with the standard k-epsilon model. The aim is to investigate the effect of initial Reynolds number on the jet development in asymmetric co-flows from the air channels. It is found that, with increasing Reynolds number, the jet becomes shorter and the mixing between the primary jet and surrounding flow is better. A low-velocity region or external recirculation zone (ERZ) form near the kiln upper wall and shrink with increased nozzle diameter or decreased initial Reynolds number. The ERZ may stabilize the flame since it is a low-velocity region and consequently attract the jet to reside predominantly in it or in the shear layer. As a conclusion, by enlarging the jet exit diameter, the jet can be prolonged, while to a certain extent, the benefit from the ERZ would need to be sacrificed. Since the asymmetric development and the ERZ in the kiln were not studied during the previous PIV measurement campaign, more experimental studies are planned to provide more experimental evidences of the details of the flow and to lay grounds for validation of the CFD simulation results.

Many new challenges in wind energy require the use of large eddy simulation for accurate modeling of wind farm flows. However, the immense computational cost hinders its use in research and industry. The lattice Boltzmann method is the most promising candidate to date to achieve the highest level of accuracy while decreasing computational cost by orders of magnitude compared to traditional methods. In this thesis, I present further development of the lattice Boltzmann method for wind energy and compile various applications, such as industrial use, generation of training data for machine learning, and analysis of wind farm control paradigms. In order to evaluate the requirements of different industrial stakeholders, we conduct a survey among industry experts on the use of large eddy simulation and show that the run time requirements indicated by many respondents can be met with the current state of the lattice Boltzmann method. In a validation study, the lattice Boltzmann method is as accurate as traditional Navier-Stokes solvers, while reducing computational cost by one to more orders of magnitude. A convolutional neural network is trained to predict average flow velocities in the wake of a single turbine. The predictions exhibit very high accuracy at execution times similar to engineering models. The lattice Boltzmann method enables the generation of larger training sets at a feasible computational cost. A proof of concept is provided for the use of reinforcement learning to discover new, cooperative wind farm control mechanisms. In an extensive analysis of the helix approach, its physical mechanisms are elucidated and a thorough parameter study of the wake of a single turbine is provided. We also study the interaction of multiple helical wakes, providing a way to extend the approach from a pair of turbines to wind farms.

Greenhouse gases and their negative effects on climate is one of the most discussed topics around the world. Globally, fossil fuel-related emissions from process industries, transportation, and electricity generation are one of the biggest contributors to greenhouse gases. One of the prime questions asked globally is how to reduce these emissions. Plasma burners can be an answer to the question. They are entirely electric-driven burners and operate at high temperatures. Presently, the available burners are small scale due to which they are not applicable in industries. So a substantial amount of interest lies in up-scaling them. However, to begin the up-scaling process, it is fundamental to clearly understand the working of the plasma burner and the various factors that affect its operation. The present thesis explains the working of a plasma burner under different operating conditions is studied experimentally, computationally, and the obtained results are validated with theoretical data. Experimentally, the temperature measurements at the plasma torch outlet were carried out using optical spectroscopy. The velocity and structure of the plasma jet coming from the outlet were studied using a high-speed camera. The experimental measurements were carried out for varied input working gases, velocities, and powers. The computational analysis was perfomed using COMSOL multiphysics software. The primary modeling was done using the equilibrium discharge interface model (EDI) in which plasma is considered to be fully ionized and at local thermal equilibrium. But considering the drawbacks of the EDI model, further computational analysis was initiated by modeling weakly ionized plasma. Different geometries of the plasma torch, working gases, velocities, and power are analyzed computationally. Further, the experimental and computational results are validated with each other and thermodynamic equilibrium data obtained using the TEC program. Finally, this thesis promises to give an overview of the plasma torches, their working under different operating conditions, and a brief discussion about the future focusing on up-scaling the plasma burners.

The automotive industry is facing ever increasing demands for reduced emissions, and lightweight solutions are thusly required. One field that has significant potential in this regard is composite materials, which can offer a good combination of weight reduction and mechanical properties. However, the rapid development cycles in the automotive industry mean that tools for numerical modeling are necessary, both regarding manufacturing processes and prediction of mechanical properties.  The material that has been of interest for this work is Sheet Moulding Compound (SMC). SMC consists of sheets of resin and chopped fibres. When used for manufacturing the sheets are cut into appropriate size and shape. The cut sheets are then placed in a pre-heated mould. When this mould is closed, the sheets melt and the fibre-filled resin flows out and fills the mould cavity; the resin then cures and solidifies. A significant advantage of SMC compared to other composite solutions is that the process has comparatively short cycle times, which is a necessity for automotive applications. However, it is a rather complicated process to model numerically for a number of reasons, including the complex rheological properties of the charge, the often rather significant temperature gradients throughout the thickness, often complicated three-dimensional effects in the flow, and the chopped fibres present in the charge. These fibres will move and change orientation as the charge is pressed, which is a significant challenge to model properly. The first part of this work is a review and discussion of the difficulties described above, and some solutions that have been suggested. The second part concerns a suggestion for a three-dimensional flow model for the compression moulding process, which takes into account factors that have been suggested to influence the flow behavior, such as temperature distribution and shear strain rate. Some simulation results are presented along with comparison to previous experimental results, and similar flow patterns are observed serving as a qualitative validation. The third part concerns the expansion of this model to include the effects of the flow on the fibre orientation.

River flow velocity is critical information for hydraulic and hydrological applications. Monitoring flow fields in near-plant waterways and river reach has wide engineering applications insustainable hydropower generation. For instance, exploring eco-hydraulic concerns such as fish migration, pollutant transport, and river erosion and understanding river floating debris are a few examples of practical applications. Due to complicated geometry and large volumes of natural flows, the measurement task using traditional methods (e.g., velocity propellers, acoustic Doppler velocimetry, with acoustic Doppler current profilers) usually requires extensive investigative work. The measurement procedure also requires contact with waterbody, thus avoiding its use in severe flood conditions. Image analysis approach allows the measurement task to capture the surface-water velocity distribution over a large outdoor area. The main objectives of this research are to (1) evaluate the feasibility of employing multiple cameras in a single measuring system to estimate the flow surfacevelocity and (2) improve the capability to use natural floating materials in river flow observations. The properties of the camera system and particle tracking velocimetry (PTV) algorithm were investigated in a laboratory open channel flow measurement before being deployed for field measurements. The in situ camera calibration methods, which correspond to the two measurement situations, were used to mitigate the instability of the camera mechanism and camera geometry. The artificial tracer particles were deployed to seed the flows. Two photogrammetry-based PTV algorithms are presented regarding different types of employed seeding particles. The first algorithm uses the particle tracking method applied for individual particles, whereas the second algorithm employs correlation-based particle clustering tracking for clusters of small-size particles. The outcomes reveal that the method can offer a reliable and accurate assessment of 3D surface velocity. In river surface velocity measurements, flow seeding is unavoidable in some situations where the water flow is clear, and there are no occurrences of floating materials on the surface. This part of the study focuses on the application of this technique for river velocity measurements using natural surfacefloating patterns. The use of a multiple-camera system provides the ability to perform 3D measurements on the river surface, including surface velocimetry and water surface reconstruction. The pattern-based tracking approach is used to adapt the performance of image measurements on different types of naturalfloating tracers. A comparison of pattern-based tracking with particle tracking reveals that these two approaches are consistent. An analysis of the characteristics of floating patterns is performed to understand their influences on standard deviation of measured velocity. Considerations on practicing image velocimetry in river flows are also discussed.

On demand energy market and favourable government policies to encourage the usage of renewable energy have led to a dramatic increase of grid connected wind, solar, and other power in recent years. Penetration of the power above manageable limit, produced using intermittent energy sources, to meet the demand has induced instable grid operations. On the other hand, the consumers more – or – less expect to be able to draw greater or lesser amount of grid power, whensoever require, at their discretion, and they expect the grid to accommodate this flexibility. Intermittency in the power production and utilisation flexibility to the end users resulted in increased grid incidents. In order to ensure the uninterrupted grid operation one has to take the responsibility to retrieve the grid parameters within operating band before it collapses.Because of speedy and smooth response to the connected grid network, hydroelectric turbines are most frequently used to bring the grid parameters within stable operating band. In a hydro power plant variation in the parameters is detected by a governor and that governs guide vanes angular movement through servo-actuation mechanism. The guide vanes manage mass flow rate flowing to the runner, i.e., the output torque/power. The guide vanes have to react promptly in a very short time to balance the grid. Thus, most of the hydroelectric units are supposed to operate over a larger operating range irrespective of efficiency and the stability, continuous load variation, load rejections, and increased numbers of start-stop cycles.An incompetent opening/closing of the guide vanes during transients induce aperiodic pressure loading on the blade surfaces resulted in cyclic stresses and fatigue. Unexpected transients led to increased wear, shortening the runner life, increased cost of plant operation, and loss of power production. Transients cannot be stopped or avoided but the damage due to the wear and, therefore, runner life may be improved by minimising the unfavourable pressure loading in the turbine through strategic movement of the guide vanes.This motivated to carry out the investigations on hydraulic turbine during transients and study guide vanes operating strategy. The main scope of the licentiate thesis is to identify the change in operating trend of hydraulic turbines due to injection of intermittent energy to the power grid and how it is affecting the turbine operations. The first paper reviews the change in operating trend and consequences to the hydraulic turbines due to changes in the pattern of turbine operation in the recent years. After drawing conclusions from the referred literature, experimental measurements on a model Francis turbine installed at NTNU, Norway, were performed. Both types of, steady state and transient, operational conditions were investigated including pressure measurements. The second paper presents the observations and investigations of steady state measurements and the corresponding numerical simulations. The third paper presents part of the transient experimental investigations; load variations and rejections. Six transient operational conditions were investigated including time domain frequency variation and rotor-stator interaction. The largest pressure variation compared to steady state operation is obtained during load rejection. Preliminary results indicated that appropriate gate closure may minimize large pressure amplitudes in the blade cascade.

Suspensions are composed of mixtures of particles and fluid and are omnipresent in natural phenomena and in industrial processes. While hydrodynamic interactions or lubrication forces between the particles are important in the dilute regime, they become of lesser significance when the concentration is increased, and direct particle contacts become dominant in the rheological response of concentrated suspensions, particularly those close to the maximum volume fraction where the suspension ceases to flow. The mixture of particles and fluid can be seen as a fluid with effective rheological properties but also as a two-phase system wherein the fluid and particles can experience relative motion. By introducing a numerical scheme including both hydrodynamic interactions and grnularlike contacts for dense particle suspensions in overdamped linear flows, we show that contact friction is essential for having DST. Above a critical volume fraction, we observe the existence of two states: a low viscosity, contactless (hence, frictionless) state, and a high viscosity frictional shear jammed state. These two states are separated by a critical shear stress, associated with a critical shear rate where DST occurs. Potential strategies to extend the present methodology to non-spherical particles are also demonstrated and explained for very concentrated suspensions but due to the cumbersome numerical model we will present the results in the future works.