The human upper airways embrace the source of phonation and affect the modulation of the voice, which is of vital importance for communication. Moreover, unwanted sounds may be generated in the upper airways due to elastic, collapsible parts that are susceptible to flow-induced vibration and resonance. The sound resulting from fluid-structure interaction in the upper respiratory tract, commonly known as snoring, can be an important indicator for underlying breathing disorders, such as obstructive sleep apnea (OSA). The scope of this work is the assessment of acoustic sources and the conditions for sound being produced in the upper airways in healthy and diseased state. For the study of the vocal tract under phonation, both low- and high-order numerical methods are applied and the obtained results are compared to experimental data from collaborators. The geometries of the vocal tract are based on magnetic resonance imaging (MRI) data for the different vowel pronunciations under voiced speech of a healthy male subject. Unsteady, direct compressible flow simulations using a finite volume solver are carried out for the computation of the pressure fluctuations and the associated distribution of frequency peaks as a result of the modulation through the static vocal tract. The peaks of the envelope of the far-field Fourier spectrum, which are characterising the spoken tone, are extracted and compared to the Helmholtz eigenfrequencies of the airway volume. The effect of variations of vocal fold closure, fundamental frequency, and vocal tract length on the computed acoustic signal is investigated. Thus, an estimation of the impact of vocal disorders on the ability of vowel production is attempted. A particular advantage of the presented approach is the attainment of time-resolved pressure and velocity fields of the flow, which allows for analysis of the coherent structures at the level of the vocal fold constriction, responsible for sound output during unvoiced speech. Furthermore, fluid-structure interaction simulations are performed for the study of the influence of critical parameters, such as Reynolds number of the flow or elasticity of the structure, on the onset of oscillations for a simplified model. The acoustic sources involved in the generation of the dominant frequencies of tissue vibrations are identified by application of an acoustic analogy. The obtained results of this work contribute to the development of a computational tool that assists physicians in the assessment of the airway function and the effectiveness of treatment plans prior to their application. / <p>QC 20170413</p>

The presence of solid rigid particles alters the global transport and rheological properties of the mixture in complex (and often unpredictable) ways. In recent years a few studies have been devoted to investigating the behavior of dense suspensions in the turbulent/inertial regime with the majority of theses analyses limited to mono-disperse rigid neutrally-buoyant spheres. However, one interesting parameter that is rarely studied for particles with high inertia is the particle shape. Spheroidal particles introduce an anisotropy, e.g. a tendency to orient in a certain direction, which can affect the bulk behavior of a suspension in an unexpected ways. The main focus of this study is therefore to investigate the behavior of spheroidal particles and their effect on turbulent/inertial flows. We perform fully resolved simulations of particulate flows with spherical/spheroidal particles, using an efficient/accurate numerical approach that enables us to simulate thousands of particles with high resolutions in order to capture all the fluid-solid interactions. Several conclusions are drawn from this study that reveal the importance of particle's shape effect on the behaviour of a suspension e.g. spheroidal particles tend to cluster while sedimenting. This phenomenon is observed in this work for both particles with high inertia, sedimenting in a quiescent fluid and inertialess particles (point-like tracer prolates) settling in homogenous isotropic turbulence. The mechanisms for clustering is indeed different between these two situations, however, it is the shape of particles that governs these mechanisms, as clustering is not observed for spherical particles. Another striking finding of this work is drag reduction in particulate turbulent channel flow with rigid oblate particles. Again this drag reduction is absent for spherical particles, which instead increase the drag with respect to single-phase turbulence. / <p>QC 20170328</p>

For an accurate prediction of the low and medium frequency surface vibration and sound radiation behaviour of porous layered systems, there is a need to improve the means of estimating their elastic and acoustic properties. The underlying reasons for this are many and of varying origin, one prominent being a poor knowledge of the geometric anisotropy of the cell microstructure in the manufactured porous materials. Another one being, the characteristic feature of such materials i.e. that their density, elasticity and dissipative properties are highly dependent upon the manufacturing process techniques and settings used. In the case of free form moulding, the geometry of the cells and the dimensions of the struts are influenced by the rise and injection flow directions and also by the effect of gravity, elongating the cells. In addition the influence of the boundaries of the mould also introduces variations in the properties of the foam block produced. Despite these complications, the need to predict and, in the end, optimise the acoustic performance of these materials, either as isolated components or as part of a multi-layer arrangement, is growing. It is driven by the increasing demands for an acoustic performance in balance with the costs, a focus which serves to increase the need for modelling their behaviour in general and the above mentioned, inherent, anisotropy in particular. The current work is focussing on the experimental part of the characterisation of the material properties which is needed in order to correctly represent the anisotropy in numerical simulation models. A hybrid approach based on a combination of experimental deformation and strain field mapping, and physically based porous material acoustic Finite Element (FE) simulation modelling, is under development which ultimately will provide the anisotropic elastic coefficients and acoustic properties of the porous layered system. The first step, involving new testing methods, is discussed here and demonstrated for a soft foam. In addition investigations using laser vibrometers combined with finite element modelling of the Panphonics G1 multi-layered panel elements are also discussed. Variations in the mounting conditions, including globally acting restraints, are evaluated through dynamic measurements and acoustic interaction with the surrounding acoustic field. Results from investigations into different changes of the panel design parameters in order to improve the effectiveness in the low frequency range are presented. / QC 20101115

In this thesis, vibration based techniques for detection of localised surface damages in multistage gearboxes are presented and evaluated. A modern vehicle gearbox is a complex system and the number of potential errors is large. For instance, surface damages can be caused by rough handling during assembly. Large savings can be made in the production industry by assuring the quality of products such as gearboxes. An automated quality test as a final step in the production line is one way to achieve this. A brief review of available methods for vibration based condition monitoring of gearboxes is given in the opening summary. In the appended papers, a selection of these methods is used to design signal processing procedures for detection of localised surface damages in gearboxes. The procedures include the Synchronous signal averaging technique (SSAT), residual calculation, filtering with a prediction error filter (PEF) based on an AR-model and the use of crest factor and kurtosis as state features. The procedures are fully automatic and require no manual input during calibration or testing. This makes them easy to adapt to new test objects. A numerical model, generating simulated gearbox vibration signals, is used to systematically evaluate the proposed procedures. The model originates from an existing model which is extended to include contributions from several gear stages as well as measurement noise. This enables simulation of difficulties likely to arise in quality testing such as varying background noise and modulation due to test rig misalignment. Without the numerical model, the evaluation would require extensive measure-ments. The numerical model is experimentally validated by comparing the simulated vibration signals to signals measured of a real gearbox. In the experimental part of the study, vibration data is collected with accelerometers while the gearbox is running in an industrial test rig. In addition to the healthy condition, conditions including three different surface damage sizes are also considered. The numerical and the experimental analysis show that the presented procedures are able to detect localised surface damages at an early stage. Previous studies of similar procedures have focused on gear crack detection and overall condition monitoring. The procedures can handle varying back-ground noise and reasonable modulation changes due to misalignment. The results show that the choice of sensor position and operating conditions during measure-ments has a significant impact on the efficiency of the fault detection procedures. A localised surface damage excites resonances in the transfer path between the gear mesh and the accelerometer. These resonances amplify the defect signal. The results indicate that it is favourable to choose a speed at which the resonant defect signals are well separated from the gear meshing harmonics in the order domain. This knowledge is of great importance when it comes to quality testing. When a quality test procedure is being developed, it is often possible to choose the operating conditions and sensor positions. It can in fact be more important to choose proper operating conditions than to apply an optimal signal processing procedure. / QC 20101124

Traffic is a major source of green house gases. The transport field stands for 32 % of the energy consumption and 28 % of the total CO2 emissions, where road transports alone causes 84 % of these figures. The energy consumed by a car traveling at constant speed, is due to engine ineffiency, internal friction, and the energy needed to overcome resisting forces such as aerodynamic drag and rolling resistance.Rolling resistance plays a rather large role when it comes to fuel economy. An improvement in rolling resistance of 10 % can yield fuel consumption improvements ranging from 0.5 to 1.5 % for passenger cars and light trucks and 1.5 to 3 % for heavy trucks. The objective of this thesis is to estimate the power consumption in the tyres. To do this a car tyre is modeled with waveguide finite elements. A non-linear contact model is used to calculate the contact forces as the tyre is rolling on a rough road. The contact forces combined with the response of the tyre is used to estimate the input power to the tyre structure, which determines a significant part of the rolling resistance. The tyre model accounts for: the curvature, the geometry of the cross-section, the pre-stress due to inflation pressure, the anisotropic material properties and the rigid body properties of the rim. The model is based on design data. The motion of the tyre belt and side wall is described with quadratic anisotropic, deep shell elements that includes pre-stress and the motion of the tread on top of the tyre by quadratic, Lagrange type, homogenous, isotropic two dimensional elements. To validate the tyre model, mobility measurements and an experimental modal analysis has been made. The model agrees very well with point mobility measurements up to roughly 250 Hz. The eigenfrequency prediction is within five percent for most of the identified modes. The estimated damping is a bit too low especially for the antisymmetric modes. Above 500 Hz there is an error ranging from 1.5 dB up to 3.5 dB for the squared amplitude of the point mobility. The non proportional damping used in the model is based on an ad hoc curve fitting procedure against measured mobilities. The contact force predictions, made by the division of applied acoustics, Chalmers University of Technology, are based on a non-linear contact model in which the tyre structure is described by its flexibility matrix. Topographies of the surface are scanned, the tread pattern is accounted for, and then the tyre is ’rolled’ over it. The contact forces are inserted into the tyre model and the response is calculated. The dissipated power is then calculated through the injected power and the power dissipated within each element. Results are promising compared to literature and measurements. / <p>QC 20101112</p>

No description available.

Renewable energy has been demonstrated to be an efficient energy production technique worldwide. Due to the geographical location of Sweden, running water has been used as a widely accessible and clean renewable source of energy for power production. The hydro-turbines are designed to operate at the best efficiency point (BEP); however, recent varying energy demands have prompted hydro-turbines to serve as grid stabilizers in energy production and to operate far from the BEP. Thus, the turbine's flexible operation is essential to satisfy grid requirements consistently.  The working conditions of the turbines vary from lower and higher load to shut-down and startup, which cause several unresolved problems. For instance, a low load on the turbine induces the formation of a rotating vortex rope (RVR) in the draft tube section, causing pressure variations and risking turbine performance due to the possibility of resonance. Furthermore, the turbine’s operation during startup and shut-down generates a significant number of uncontrolled vortices, which can cause wear and shorten the turbine's lifetime. Despite the experimental measurements conducted to address the issues associated with off-design operating conditions, some issues are still unsolved, and additional measurements are needed to obtain more details. For instance, pressure sensors have been used widely in several locations to determine the pressure pulses caused by instabilities, but they are limited to the flow information on one point on the walls and cannot reveal additional details about the positions far from the wall. Although numerical simulations can be beneficial to provide more detailed information, they lack thorough initial conditions that accurate experiments can only offer.  The current study first reviews several velocity measuring methods used to assess the performance of the propeller and Kaplan turbine. The literature study includes several velocity measuring techniques, including flow visualization in various sections of the turbine and LDV measurements. It reviews the advantages and disadvantages of several approaches and explains the benefits of particle image velocimetry (PIV) over other methods. PIV has been demonstrated to be a more thorough approach capable of providing 2D and 3D velocity profiles in various turbine areas; nevertheless, implementing this technology is challenging. In addition, 2D-2C and 2D-3C PIV tests were performed on the draft tube of a down-scale propeller turbine at the BEP and part load (PL). The goal of this study was to ensure a trusty mean velocity profile in the conical section of the draft tube. As a result, an uncertainty analysis of the acquired mean velocity profiles is conducted and reported. The results indicate that compared to BEP, a more extended measurement period is required to get accurate mean velocity profiles for all velocity components due to the presence of the RVR with a periodic nature in PL.

Experiments and computational simulations have been performed as part of a larger project to instil trust in computational methods for design of hydraulics flows in spillways. Presented in this licenciate is one manuscript and two conference papers. The first conference paper details experiments done at Älvkarleby of a multiple outlet spillway model with an inlet channel specifically designed to contain interesting hydraulic features. The results indicate that simulations agree well with experiments. In the second conference paper acoustic doppler velocimetry measurements (ADV) were done and compared to simulations of a racetrack flume with a fish passageway at Älvkarleby. The results showed agreement but due to inlet conditions of the experiment some discrepancies were noticed. The manuscript presents experiments of a wider range of flow in the experimental flume of the first conference paper, with additional ADV measurements. Preliminary conclusions are that discrepancies can be due to inlet conditions. A short summary of further work is included.

In present thesis, the Lagrangian particle based method Smoothed ParticleHydrodynamics (SPH) is used to model two-dimensional problems associated with hydropower applications such as dam break evolution and hydraulic jumps. In the SPHmethod, the fluid domain is represented by a set of non-connected particles which possess individual material properties such as mass, density, velocity, position and pressure. Besides representing the problem domain and acting as information carriers the particles also act as the computational frame for the field function approximations. As the particles move with the fluid the material properties changes over time due to interaction with neighbouring particles. The adaptive nature of the SPH-method together with the nonconnectivity between the particles results in a method that is able to handle very large deformations as is the case for highly disordered free-surface flows such as hydraulic jumps.The dam break case was used as a model validation test case where the response of different parameter settings was explored. The SPH spatial resolution and the choice of artificial viscosity (a term in the momentum equation) constants had a major impact on the results. Increasing the spatial resolution increased the number of flow features resolved and setting the constants equal to unity resulted in a highly viscous and unphysical solution.Following the parameter study, the work focused on SPH simulations of hydraulic jumps. A hydraulic jump is a rapid transition from supercritical flow to subcritical flow characterized by the development of large scale turbulence, surface waves, spray, energy dissipation and considerable air entrainment. Several features of the jump were explored using the SPH method and good agreement with theory and experiments was obtained for e.g. the conjugate depth and the mean free surface elevation in the roller section. However, the free surface fluctuation frequencies were over predicted and the model could not capture the decay of fluctuations in the horizontal direction.

Hydropower is a versatile renewable source of power generation able to change rapidly operating conditions. Hydropower plants may today work over a larger operating range than designed for due to the introduction of renewable sources of energy and the deregulation of the electricity market. Such operating conditions may involve large stresses and losses due to complex unsteady and transient flow phenomena, which have to be taken into account under design or refurbishment phase. The use of computational fluid dynamics (CFD) in the design and refurbishment process is becoming increasingly popular due to its flexibility, detailed flow description and cost-effectiveness comparing to model testing used since a century in the development of turbines. However, issues have still to be resolved due to the combined flow physics involved in hydropower machines such as partly separated flow at curved surfaces, vortices, unsteadiness, swirl flow, strong adverse pressure gradients, convoluted geometry as well as numerical artefacts. Therefore, experimental data in such complicated systems are required to validate numerical simulations and develop more accurate models.The first part of this thesis is a numerical investigation of the three-dimensional flow of the axial Hölleforsen model spiral casing and distributor, where the influence of the penstock on the flow is analysed using different turbulence models and inlet boundary conditions. Comparisons with experimental results indicate the importance of the penstock to perform accurate simulation in the present case. Therefore, detailed inlet boundary conditions are necessary to simulate accurately the spiral casing flows if the penstock is not included in the simulation.The second part of the thesis focuses on an experimental investigation of an axial hydropower turbine model known as Porjus U9. The measurements are part of a project aiming to investigate experimentally the flow in different regions of the machine to build a data bank in order to validate numerical simulations and study scale-up efficiency between model and prototype, since the corresponding prototype is available for similar experiments. The investigation was performed at 3 different working points: part load, best efficiency point and high load. The inlet flow of the spiral casing as well as some sections in the spiral casing and draft tube are investigated with a two components laser Doppler anemometer (LDA). To improve the signal quality and measurement accuracy refractive index matching optical box was mounted on the circular pipe of the spiral casing inlet. LDA result of the mean velocities and corresponding RMS are presented to investigate the flow before the runner and at the inlet of the spiral casing, since the flow is influenced by the existence of a bend before the inlet. The results of the draft tube measurements are also presented. Good quality data are obtained for initial boundary conditions at the inlet of the casing and drafttube cone to perform numerical simulations.