| 1. |
- Mihaescu, Mihai
(författare)
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Computational Aeroacoustics Based on Large Eddy Simulation and Acoustic Analogies
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis presents a numerical method developed by the author and its applications for computing the generated sound by an unsteady flow field and its propagation. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation and propagation. It is assumed that the flow variables can be decomposed into semi-compressible / incompressible components and inviscid, irrotational acoustic components. The present method is based on Large Eddy Simulation (LES) to compute the turbulent flow and an approach based on an inhomogeneous wave equation to compute the radiated acoustic field. In this way one can avoid the necessity for a very large computational effort associated with direct simulation of the near- and specially far- field sound generated by a turbulent flow. The governing equations are written in the form of a non-homogeneous wave equation for the acoustic fluctuation with acoustic sources on the right-hand side. The thesis includes the details of the coupling between the flow solver and the acoustic one, as well as the results for test cases employed to validate the numerical algorithm and the implemented boundary conditions. The method has been successfully applied to compute the near- and far- acoustic fields generated by various unsteady flows such as a round hot turbulent jet ejected from a pipe close to a solid boundary, coaxial turbulent non-isothermal jets (separate exhaust system), or the flow around a wind-turbine.
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| 2. |
- Nybacka, Mikael, et al.
(författare)
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Project: CASTT - Centre for Automotive Systems Technologies and Testing
- 2007
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Annan publikation (populärvet., debatt m.m.)abstract
- Through the Centre for Automotive Systems Technologies and Testing, Luleå University of Technology aims to first of all support automotive winter testing in Northern Sweden. This means to support the local automotive test entrepreneurs and through them their customers: the car manufacturers and their suppliers. To succeed in this task, the center relies on the university's areas of leading research and most importantly on the cooperation between those areas.
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| 3. |
- Dyverfeldt, Petter, 1980-, et al.
(författare)
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Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI
- 2006
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 56:4, s. 850-858
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent flow, characterized by velocity fluctuations, is a contributing factor to the pathogenesis of several cardiovascular diseases. A clinical noninvasive tool for assessing turbulence is lacking, however. It is well known that the occurrence of multiple spin velocities within a voxel during the influence of a magnetic gradient moment causes signal loss in phase-contrast magnetic resonance imaging (PC-MRI). In this paper a mathematical derivation of an expression for computing the standard deviation (SD) of the blood flow velocity distribution within a voxel is presented. The SD is obtained from the magnitude of PC-MRI signals acquired with different first gradient moments. By exploiting the relation between the SD and turbulence intensity (TI), this method allows for quantitative studies of turbulence. For validation, the TI in an in vitro flow phantom was quantified, and the results compared favorably with previously published laser Doppler anemometry (LDA) results. This method has the potential to become an important tool for the noninvasive assessment of turbulence in the arterial tree.
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| 4. |
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| 5. |
- Hansen, Kjetil Falkenberg, 1972-, et al.
(författare)
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Analysis of a genuine scratch performance
- 2004
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Ingår i: Lecture Notes in Computer Science. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 0302-9743 .- 1611-3349. - 9783540210726 ; 2915, s. 477-478, s. 519-528
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Tidskriftsartikel (refereegranskat)abstract
- The art form of manipulating vinyl records done by disc jockeys (DJs) is called scratching, and has become very popular since its start in the seventies. Since then turntables are commonly used as expressive musical instruments in several musical genres. This phenomenon has had a serious impact on the instrument-making industry, as the sales of turntables and related equipment have boosted. Despite of this, the acoustics of scratching has been barely studied until now. In this paper, we illustrate the complexity of scratching by measuring the gestures of one DJ during a performance. The analysis of these measurements is important to consider in the design of a scratch model.
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| 6. |
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| 7. |
- Grishenkov, Dmitry, 1983-, et al.
(författare)
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Acoustic properties of polymer-shelled ultrasound contrast agents. Bulk volume vs. microcapillary
- 2009
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Ingår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009. - Krakow. - 9781615677368 ; , s. 2515-2522
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Konferensbidrag (refereegranskat)abstract
- The focus of contrast-enhanced ultrasound research has developed beyond detecting the blood pool to new areas such as perfusion imaging, drug and gene therapy, and targeted imaging. Polymer-shelled microbubbles are proposed as a new generation of ultrasound contrast agents (UCAs) which fulfil the requirements of these applications. With a shelf-life of several months and possibility to conjugate pharmacological molecules to their surface, these UCAs will allow not only to enhance the contrast of ultrasound images, but also to function as carriers of drugs to be delivered locally. In this study, the results of an experimental investigation of three types of UCAs stabilized by thick poly vinyl alcohol (PVA) shell are presented. These UCAs are synthesized from a PVA aqueous solution under varied pH values and temperature. The UCAs differ from each other in their average diameter, shell thickness and polydispersity. Knowledge of the peak negative pressure at which the solid shell fractures is paramount for a proper use of UCAs. Therefore, the dependence of this quantity on temperature and number of cycles in the incident pulse is examined. Much of the blood volume resides in the microcirculation, with capillaries playing a particularly important role in patho-physiology and drug delivery. In this sense in vitro characterization of the UCAs oscillation was moved from bulk volume to the capillary scale, where tissue-bubble interaction takes place. The main conclusion to be drawn from these results is that the shell of the UCAs begin to fracture at values of mechanical index (MI) approved for clinical applications. The fatigue, i.e. the accumulation of damage within the shell of the UCAs, is found to play an important role in fracturing the shell. Finally adhesion of the UCAs to the elastic wall is studied and correlated with estimates of the shell’s visco-elastic constants. Open questions arising from this comparison are briefly discussed.
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| 8. |
- Carlson, Rolf, et al.
(författare)
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Cross-Cultural Perception of Discourse Phenomena
- 2009
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Ingår i: INTERSPEECH 2009. - BAIXAS : ISCA-INST SPEECH COMMUNICATION ASSOC. ; , s. 1723-1726
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Konferensbidrag (refereegranskat)abstract
- We discuss perception studies of two low level indicators of discourse phenomena by Swedish. Japanese, and Chinese native speakers. Subjects were asked to identify upcoming prosodic boundaries and disfluencies in Swedish spontaneous speech. We hypothesize that speakers of prosodically unrelated languages should be less able to predict upcoming phrase boundaries but potentially better able to identify disfluencies, since indicators of disfluency are more likely to depend upon lexical, as well as acoustic information. However, surprisingly, we found that both phenomena were fairly well recognized by native and non-native speakers, with, however, some possible interference from word tones for the Chinese subjects.
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| 9. |
- Arlov, Dragana
(författare)
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Numerical study of flows related to aerated stirred tanks
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall purpose with this work is to investigate the bubbly flow in a aerated stirred tank using numerical simulations. Aerated stirred tanks are commonly used in chemical processes for producing for example insulin and antibiotics. The main requirement of these tanks, is to provide an optimal environment for the microorganisms found inside, with homogeneous mixing of air. The flow in a aerated stirred tank is complex and turbulent with stagnation points, swirling motion and recirculation zones. Introducing bubbles in this environment creates a wide range of bubble sizes. For the aerated stirred tank, Large Eddy Simulation (LES) is used for the continuous phase and the two-way coupled Eulerian-Lagrangian model for the dispersed phase. A break-up and coalescence model has been incorporated. Since the bubbles inside a bioreactors are many and with a wide range of sizes as well as largely varying inter-droplet distance, the underlying assumptions of the model can have significant error. However, the approach offers computational efficiency and allows one to include bubble breakup and coalescence models. The moving blades, representing the rotating impeller, is modeled by using the Volume of Solid (VOS) model. The averaged radial and tangential liquid velocities decreased with increasing gas volume fraction. Additionally, for the axial velocities the gas redirected the radial jet upwards and the symmetry of the ring vortices vanished. Although, low gas flow rate, the periodicity from the impeller is decreased and interfere with the creation of the trailing vortex pair behind the impeller. Including bubble break-up and coalescence model in the aerated stirred tank, induces small spherical bubbles. For large bubbles, shapes become important and can be modeled using the Volume of Fluid (VOF) model. Numerical simulations has been performed for deformable air-bubbles in a straight channel. Bubble features such as aspect ratio, equivalent diameter, velocity and path are compared against experimental data obtained by using shadow-graph technique. The VOF model is capable to predict the different bubble features and shows a promising future for studying the detailed interaction between the different phases inside a bioreactor. The limitations of the Eulerian-Lagrangian model arises when the inter-particle distance is small. From the simulations of Lattice Boltzmann Method (LBM), both drag- and lift-coefficients were obtained for cases with strong particle-particle (so called four-way) interaction. A novel approach of handling large spherical bubbles combined with the Eulerian-Lagrangian model in the Large Eddy Simulation (LES) framework, has been developed and utilized.
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