SwePub - sökning: AMNE:(TEKNIK OCH TEKNOLOGIER) ...

Numrering	Referens	Omslagsbild	Hitta
1.	Proceedings of the 2010 Winter Simulation Conference 2010 Samlingsverk (redaktörskap) (refereegranskat)
2.	Mihaescu, Mihai (författare) Computational Aeroacoustics Based on Large Eddy Simulation and Acoustic Analogies 2005 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.
3.	Gerlee, Philip, 1980, et al. (författare) Scientific Models : Red Atoms, White Lies and Black Boxes in a Yellow Book 2016 Bok (övrigt vetenskapligt/konstnärligt)abstract A zebrafish, the hull of a miniature ship, a mathematical equation and a food chain - what do these things have in common? They are examples of models used by scientists to isolate and study particular aspects of the world around us. This book begins by introducing the concept of a scientific model from an intuitive perspective, drawing parallels to mental models and artistic representations. It then recounts the history of modelling from the 16th century up until the present day. The iterative process of model building is described and discussed in the context of complex models with high predictive accuracy versus simpler models that provide more of a conceptual understanding. To illustrate the diversity of opinions within the scientific community, we also present the results of an interview study, in which ten scientists from different disciplines describe their views on modelling and how models feature in their work. Lastly, it includes a number of worked examples that span different modelling approaches and techniques. It provides a comprehensive introduction to scientific models and shows how models are constructed and used in modern science. It also addresses the approach to, and the culture surrounding modelling in different scientific disciplines. It serves as an inspiration for model building and also facilitates interdisciplinary collaborations by showing how models are used in different scientific fields. The book is aimed primarily at students in the sciences and engineering, as well as students at teacher training colleges but will also appeal to interested readers wanting to get an overview of scientific modelling in general and different modelling approaches in particular.
4.	Gerlee, Philip, 1980, et al. (författare) Scientific Models 2016 Bok (övrigt vetenskapligt/konstnärligt)abstract A zebrafish, the hull of a miniature ship, a mathematical equation and a food chain - what do these things have in common? They are examples of models used by scientists to isolate and study particular aspects of the world around us. This book begins by introducing the concept of a scientific model from an intuitive perspective, drawing parallels to mental models and artistic representations. It then recounts the history of modelling from the 16th century up until the present day. The iterative process of model building is described and discussed in the context of complex models with high predictive accuracy versus simpler models that provide more of a conceptual understanding. To illustrate the diversity of opinions within the scientific community, we also present the results of an interview study, in which ten scientists from different disciplines describe their views on modelling and how models feature in their work. Lastly, it includes a number of worked examples that span different modelling approaches and techniques. It provides a comprehensive introduction to scientific models and shows how models are constructed and used in modern science. It also addresses the approach to, and the culture surrounding modelling in different scientific disciplines. It serves as an inspiration for model building and also facilitates interdisciplinary collaborations by showing how models are used in different scientific fields. The book is aimed primarily at students in the sciences and engineering, as well as students at teacher training colleges but will also appeal to interested readers wanting to get an overview of scientific modelling in general and different modelling approaches in particular.
5.	Okda, Sherif, et al. (författare) Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section 2020 Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5 Tidskriftsartikel (refereegranskat)abstract Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
6.	Nybacka, Mikael, et al. (författare) Project: CASTT - Centre for Automotive Systems Technologies and Testing 2007 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.
7.	Wadekar, Sandip, 1989 (författare) Large-Eddy Simulation of Gasoline Fuel Spray Injection at Ultra-High Injection Pressures 2021 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Gasoline direct injection is a state-of-the-art technique that reduces hydrocarbon and particulate emissions. However, further improvement is needed to meet current as well as future emission regulations. A prominent solution is to increase the fuel injection pressure which allows faster fuel droplet atomization, quick evaporation and improves fuel-air mixture formation under realistic engine conditions. In this work, the gasoline fuel injection process at ultra-high injection pressures ranging from 200 to 1500 bar was analyzed using numerical models. In particular, the Large-Eddy Simulation (LES) method, with the standard Smagorinsky turbulence model, was utilized using the Eulerian formulation for the continuous phase. The discrete droplet phase was treated using a Lagrangian formulation together with spray sub-models. In the first part of study, spray was injected into an initially quiescent constant volume chamber using two different nozzle hole shape geometries: divergent and convergent. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on spray development. The calibrated models were then used to investigate the impact of ultra-high injection pressures on mean droplet sizes, droplet size distribution, spray-induced large-scale eddies and entrainment rate. The results showed that, at ultra-high injection pressures, the mean droplet sizes were significantly reduced and the droplets achieving very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate were better for the divergent-shaped injector, and considerably larger at higher injection pressures compared to lower ones. In the second part of the study, four consecutive full-cycle cold flow LES simulations were carried out to generate realistic turbulence inside the engine cylinder. The first three cycles were ignored, with the fourth cycle being used to model the injection of the fuel using the divergent-shaped injector only (which was found to be better in the previous part of this study) at different injection pressures. In addition to the continuous gas phase (Eulerian) and the dispersed liquid (Lagrangian), the liquid film feature (Finite-Area) was used to model the impingement of fuel spray on the engine walls and subsequent liquid film formation. The simulation results were used to evaluate spray-induced turbulence, fuel-air mixing efficiency and the amount of liquid mass deposited on the walls. The limitation of the high-pressure injection technique with respect to liquid film formation was optimized using a start of injection (SOI) sweep. Overall results showed that the mixing efficiency increased at high injection pressure and that SOI should occur between early injection and late injection to optimize the amount of mass being deposited on the engine walls.
8.	Lejon, Marcus, 1986, et al. (författare) Multidisciplinary Design of a Three Stage High Speed Booster 2017 Ingår i: ASME Turbo Expo 2017: Turbine Technical Conference and Exposition. - : ASME Press. ; 2B-2017 Konferensbidrag (refereegranskat)abstract The paper describes a multidisciplinary conceptual design of an axial compressor, targeting a three stage, high speed, high efficiency booster with a design pressure ratio of 2.8. The paper is outlined in a step wise manner starting from basic aircraft and engine thrust requirements, establishing the definition of the high speed booster interface points and its location in the engine. Thereafter, the aerodynamic 1D/2D design is carried out using the commercial throughflow tool SC90C. A number of design aspects are described, and the steps necessary to arrive at the final design are outlined. The SC90C based design is then carried over to a CFD based conceptual design tool AxCent, in which a first profiling is carried out based on a multiple circular arc blade definition. The design obtained at this point is referred to as the VINK compressor. The first stage of the compressor is then optimized using an in-house optimization tool, where the objective functions are evaluated from detailed CFD calculations. The design is improved in terms of efficiency and in terms of meeting the design criteria put on the stage in the earlier design phases. Finally, some aeromechanical design aspects of the first stage are considered. The geometry and inlet boundary conditions of the compressor are shared with the turbomachinery community on a public server. This is intended to be used as a test case for further optimization and analysis.
9.	Van der Kelen, Christophe, 1986-, et al. (författare) Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Glass Wool 2010 Rapport (övrigt vetenskapligt/konstnärligt)abstract The air flow resistivity of nine adjacent glass wool samples is measured and estimated using a previously published method. The samples are extracted from a large slab of glass wool material. Identifying the full flow resistivity tensors for nine adjacent cubic glass wool samples allows for an estimation of the spatial distribution of normal and planar flow resistivity throughout the measured material. The average density of the samples tested is 27.8 kg/m3. The estimated flow resistivity tensors are validated by comparison to uni-directional measurements on cylindrical samples, extracted from the cubic glass wool samples tested. Furthermore, the uni-directional measurement method is studied, providing useful insights on the effect of sample thickness on the measured flow resistivity for an anisotropic material.
10.	Van der Kelen, Christophe, 1986-, et al. (författare) Measurement and Inverse Estimation of the Full Anisotropic Flow Resistivity Tensor of Melamine Foam 2010 Rapport (övrigt vetenskapligt/konstnärligt)abstract The flow resistivity tensor, which is the inverse of the viscous per- meability tensor, is one of the most important material properties for the acoustic performance of open cell foams used in acoustic treatments. Due to the manufacturing processes, these foams are most often geomet- rically anisotropic on a microscopic scale. For such a materials there is a need for improved characterisation methods, and this paper discusses the estimation of the flow resistivity tensor of Melamine samples using a methodology which is an improvement of a method previously published by Go ̈ransson et al. The validity of the new method is in addition ver- ified for a wider range of anisotropy. Measurements are performed on cubic Melamine samples, and the resulting 3D flow resistivity tensors are presented. The anisotropic flow resistivity tensors are validated by com- parison to measurements performed on uni-directional cylindrical samples extracted from the previously measured cubic samples. The results sug- gest that there is a relation between the direction of highest flow resistivity, and the rise direction of the material.
11.	Dyverfeldt, Petter, 1980-, et al. (författare) Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI 2006 Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 56:4, s. 850-858 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.
12.	Mathematical Modeling of Wave phenomena : 2nd Conference on Mathematical Modelling of Wave Phenomena, Växjö, Sweden, 14 – 19 August 2005 2006 Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract This conference illuminates and benefits from relations between different types of waves, i.e., quantum physics methods in classical wave modeling. The proceedings are intended for researchers and graduate students in fundamental as well as applied sciences. The preface classifies and summarizes the conference giving relations between the papers.
13.	Hansen, Kjetil Falkenberg, 1972-, et al. (författare) Analysis of a genuine scratch performance 2004 Ingår i: Lecture Notes in Computer Science. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 0302-9743 .- 1611-3349. - 9783540210726 ; 2915, s. 477-478, s. 519-528 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.
14.	Cervantes, Michel, et al. (författare) Interdisciplinary research in full-scale hydropower machines at Porjus, Jokkmokk, Sweden 2005 Ingår i: International Water Power and Dam Construction. - 0306-400X. ; 57:12, s. 40-44 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
15.	Etikyala, Sreelekha, 1991 (författare) Particulate Formation in GDI Engines 2022 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The need to comply with stringent emission regulations while improving fuel economy and reducing criteria pollutant emissions from transportation presents a major challenge in the design of gasoline Direct Injection (DI) engines because of the adverse effects of ultrafine Particulate Number (PN) emissions on human health and other environmental concerns. With upcoming advances in vehicle electrification, it may be the case that electric vehicles completely replace all current vehicles powered by internal combustion engines ensuring zero emissions. In the meantime, Gasoline Direct Injection (GDI) engines have become the primary mode of transportation using gasoline as they offer better fuel economy while also providing low CO2 emissions. However, GDI engines tend to produce relatively high PN emissions when compared to conventional Port Fuel Injection (PFI) engines, largely because of challenges associated with in-cylinder liquid fuel injection. Cold-starts, transients, and high load operation generate a disproportionate share of PN emissions from GDI engines over a certification cycle. The mechanisms of PN formation during these stages must therefore be understood to identify solutions that reduce overall PN emissions in order to comply with increasingly strict emissions standards. This work presents experimental studies on particulate emissions from a naturally aspirated single cylinder metal gasoline engine run in a homogeneous configuration. The engine was adapted to enable operation in both DI and PFI modes. In PFI mode, injection was performed through a custom inlet manifold about 50 cm from the cylinder head to maximize the homogeneity of the fuel-air mixture. The metal head was eventually modified by incorporating an endoscope that made it possible to visualize the combustion process inside the cylinder. The experimental campaigns were structured to systematically isolate and clarify PN formation mechanisms. Tests were initially performed in steady state mode to obtain preliminary insights and to screen operating conditions before conducting transient tests. Particulate emissions were measured and correlated with the images obtained through endoscope visualization where possible. Key objectives of these studies were to find ways of reducing PN formation by increasing combustion stability. It was found that by avoiding conditions that cause wall wetting with liquid fuel, PN emissions can be substantially reduced during both steady state operation and transients. Warming the coolant and injecting fuel at later timings reduced PN emissions during warmup and cold transient conditions. Additionally, experiments using fuel blends with different oxygenate contents showed that the chemical composition of the fuel strongly influences particulate formation under steady state and transient conditions, and that this effect is load-dependent. Overall, the results obtained in this work indicate that wall wetting is the dominant cause of particulate formation inside the cylinder and that fuel-wall interactions involving the piston, cylinder walls, and valves during fuel injection account for a significant proportion of PN emissions in the engine raw exhaust.
16.	Li, Xiaojian, 1991, et al. (författare) Installation effects on engine design 2020 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
17.	Tillig, Fabian, 1984, et al. (författare) Design, operation and analysis of wind-assisted cargo ships 2020 Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 211:1, s. 1-23 Tidskriftsartikel (refereegranskat)abstract This study presents a novel approach to analytically capture aero- and hydrodynamic interaction effects on wind-assisted ships. Low aspect ratio wing theory is applied and modified to be used for the prediction of lift and drag forces of hulls sailing at drift angles. Aerodynamic interaction effects are captured by analytically solving the Navier-Stokes equation for incompressible, potential flow. The developed methods are implemented to a 4 degrees-of-freedom performance prediction model called “ShipCLEAN”, including a newly developed method for rpm control of Flettner rotors on a ship to maximize fuel savings. The accuracy of the model is proven by model- and full-scale verification. To present the variability of the model, two case study ships, a tanker and a RoRo, are equipped with a total of 11 different arrangements of Flettner rotors. The fuel savings and payback times are assessed using realistic weather from ships traveling on a Pacific Ocean route (tanker) and Baltic Sea route (RoRo). The results verify the importance of using a 4 degrees-of-freedom ship performance model, aero- and hydrodynamic interaction and the importance of controlling the rpm of each rotor individually. Fuel savings of 30% are achieved for the tanker, and 14% are achieved for the RoRo.
18.	Kyprianidis, Konstantinos, 1984, et al. (författare) Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine 2014 Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 136:1 Tidskriftsartikel (refereegranskat)abstract The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at midcruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
19.	Thulin, Oskar, 1987, et al. (författare) First and Second Law Analysis of Radical Intercooling Concepts 2018 Ingår i: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10 Tidskriftsartikel (refereegranskat)abstract An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (HEX) (intercooler (IC)) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g., a secondary cycle (SC), moving with the aircraft. Afterward, the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e., nacelle surfaces, to reject the core heat and contributes to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio (BPR) turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a HEX in the bypass (BP) duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered HEXs and SC, is made. A striking strength of the present analysis is the assessment of the component-level irreversibility rate and its contribution to the overall aero-engine losses.
20.	Thulin, Oskar, 1987 (författare) On the Analysis of Energy Efficient Aircraft Engines 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Aero engine performance analysis is highly multidimensional using various measures of component performance such as turbomachinery and mechanical efficiencies, and pressure loss coefficients. Using conventional performance analysis, relying on only the laws of thermodynamics, it is possible to understand how the performance parameters affect the component performance, but it is difficult to directly compare the magnitude of various loss sources. A comprehensive framework has been detailed to analyze aero engine loss sources in one common currency. As the common currency yields a measure of the lost work potential in every component, it is used to relate the component performance to the system performance. The theory includes a more detailed layout of all the terms that apply to a propulsion unit than presented before. The framework is here adopted to real gases to be used in state of the art performance codes. Additionally, the framework is further developed to enable detailed studies of two radical intercooling concepts that either rejects the core heat in the outer nacelle surfaces or uses the core heat for powering of a secondary cycle. The theory is also extended upon by presenting the installed rational efficiency, a true measure of the propulsion subsystem performance, including the installation effects of the propulsion subsystem as it adds weight and drag that needs to be compensated for in the performance assessment.
21.	Zheng, Miaomiao, et al. (författare) Polymer-Shelled Ultrasound Contrast Agents with controlled size and polydispersity. 2011 Ingår i: Nanomedicine: Nanotechnology, Biology & Medicine. Konferensbidrag (refereegranskat)abstract Ultrasound imaging techniques can be greatly improved by the use of ultrasound contrast agents (UCAs). Gas bubbles encapsulated into biocompatible polymer shell are of particular interest of this work. Shell of the bubbles produced from Poly-Vinyl-Alcohol (PVA) offers considerable chemical versatility and stability. However, questions regarding the size and polydispersity of the microbubbles must be further investigated. The ideal UCAs should not obstruct the blood flow in pulmonary capillaries which diameter is less than 10 μm. From the technical perspective UCAs should modify the acoustic properties of a region of interest, by increasing backscattered efficiency. In order to enhance the ultrasound response UCAs should be engineered with narrow size distribution. In the present work PVA-shelled UCAs with controlled size and polydispersity is manufactured under varied parameters of the manufacturing protocol. It was observed that temperature of the surrounding atmosphere has major effect on the size of the UCAs, while polydispersity is regulated by geometry and speed of the disperser. Finally, the acoustic response of these microbubbles is tested using developed ultrasound test rig. The enhancement of the backscattered power of about 25 dB from a suspension of the microbubbles is observed at 5 MHz ultrasound frequency. Keeping in mind that in clinical practice ultrasound scatter from the blood is of about 30 dB weaker than scatter from surrounding tissue, introduction of novel PVA microbubbles will potentially improve diagnosis of the cardiovascular patients.
22.	Shankar, Vijay, et al. (författare) An Automatic Method for Optimizing Venturi Shape in Cavitation Flows 2017 Ingår i: Proceedings of the 4<sup>th</sup> International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT'17). - : Avestia Publishing. ; 2017 Konferensbidrag (refereegranskat)abstract In order to lower the energy consumption of the fibrillation stage for the pulp and paper industry, a new technology need to be innovated and developed. The current research work deals with a new innovative concept based on creating cavitation in the pulp flow. A venturi nozzle is designed and optimized, where hydrodynamic cavitation is achieved by the so called Venturi effect. This paper focuses on the development of an automatic method for venturi shape optimization. The process of cavitation is hard to control and can cause high mechanical wear, therefore an optimization study of the venturi shape is performed with two main objectives. Firstly, to achieve cavitation that is sustained for as long as possible downstream and secondly to avoid cavitation at the walls. The developed method is a type of two-level optimization based on neural networks and evolutionary optimization. A number of simulations are executed and the optimization is then performed on a solver approximation instead of the real solver, which considerably reduces computation time. The obtained results show the optimal venturi configuration and the relative importance of each shape parameter. The optimal configuration is a clear improvement of the baseline configuration and an improvement also compared to all of the tested samples, thereby validating the optimization method.
23.	Ström, Henrik, 1981, et al. (författare) Behaviour and stability of the two-fluid model for fine-scale simulations of bubbly flow in nuclear reactors 2015 Ingår i: International Journal of Chemical Reactor Engineering. - : Walter de Gruyter GmbH. - 1542-6580 .- 2194-5748. ; 13:4, s. 449-459 Tidskriftsartikel (refereegranskat)abstract In the present work, we formulate a simplistic two-fluid model for bubbly steam-water flow existing between fuel pins in nuclear fuel assemblies. Numerical simulations are performed in periodic 2D domains of varying sizes. The appearance of a non-uniform volume fraction field in the form of meso-scales is investigated and shown to be varying with the bubble loading and the domain size, as well as with the numerical algorithm employed. These findings highlight the difficulties involved in interpreting the occurrence of instabilities in two-fluid simulations of gas-liquid flows, where physical and unphysical instabilities are prone to be confounded. The results obtained in this work therefore contribute to a rigorous foundation in on-going efforts to derive a consistent meso-scale formulation of the traditional two-fluid model for multiphase flows in nuclear reactors.
24.	Grishenkov, Dmitry, 1983-, et al. (författare) Acoustic properties of polymer-shelled ultrasound contrast agents. Bulk volume vs. microcapillary 2009 Ingår i: 16th International Congress on Sound and Vibration 2009, ICSV 2009. - Krakow. - 9781615677368 ; , s. 2515-2522 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.
25.	Fu, Qilin, et al. (författare) Anti-vibration Engineering in Internal Turning Using a Carbon Nanocomposite Damping Coating Produced by PECVD Process 2014 Ingår i: Journal of materials engineering and performance (Print). - : Springer-Verlag New York. - 1059-9495 .- 1544-1024. ; 23:2, s. 506-517 Tidskriftsartikel (refereegranskat)abstract Machining dynamic stability has been enhanced through a damping coating based on a novel carbon-based nanocomposite material. The coating was synthesized using a plasma enhanced chemical vapor deposition method, and deposited on to the round-shank boring bar used for internal turning and tested during machining. Comparisons between an uncoated and a coated boring bar were carried out at 0.25 mm and 0.5 mm depth of cut using a five times length to diameter ratio overhang, which are typical conditions known to generate detrimental mechanical vibrations. From sound pressure measurement it was found that the measured absolute sound level during process could be reduced by about 90% when using the tool coated with damping layer. Surface roughness measurements of the processed workpiece showed decreased Ra values from approximately 3-6 mu m to less than 2 mu m (and in 50% of the cases < 1 mu m) when comparing an uncoated standard tool with its coated counterpart. Moreover, it was found that the addition of an anti-vibration coating did not adversely affect other tool properties, such as rigidity and modularity.
26.	Johansson, Anders, 1985, et al. (författare) Experimental Investigation of the Influence of Boost on Combustion and Particulate Emissions in Optical and Metal SGDI-Engines Operated in Stratified Mode 2016 Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 9:2, s. 807-818 Tidskriftsartikel (refereegranskat)abstract Boosting and stratified operation can be used to increase the fuel efficiency of modern gasoline direct-injected (GDI) engines. In modern downsized GDI engines, boosting is standard to achieve a high power output. However, boosted GDI-engines have mostly been operated in homogenous mode and little is known about the effects of operating a boosted GDI-engine in stratified mode.This study employed optical and metal engines to examine how boosting influences combustion and particulate emission formation in a spray-guided GDI (SGDI), single cylinder research engine. The setup of the optical and metal engines was identical except the optical engine allowed optical access through the piston and cylinder liner.The engines were operated in steady state mode at five different engine operating points representing various loads and speeds. The engines were boosted with compressed air and operated at three levels of boost, as well as atmospheric pressure for comparison. The fuel used was market gasoline (95 RON) blended with 10% ethanol. The spark plug and injector were mounted in parallel with the intake valves. The gas motion induced by the engine head was primarily tumble motion with a small amount of swirl.Results on particulate emissions indicated that nucleation mode particulates increased with increasing boost. In contrast, agglomeration mode particulates decreased with increasing boost pressure. The combustion was found to consist of a yellow flame in the center of the combustion chamber and a pre-mixed blue flame in the perimeter. The optical studies indicated that the flame area decreased with increasing boost.
27.	Tinnsten, Mats, et al. (författare) Optimization of acoustic response 1999 Ingår i: Structural Optimization. - 0934-4373. ; 18:1, s. 36-47 Tidskriftsartikel (refereegranskat)abstract The expression 'acoustic optimization' can be applied to numerous different disciplines within the field of acoustics. From seismic waves, sound in the atmosphere through bioacoustic, psychoacoustics, and room and theater acoustics over shock and vibration in mechanical structures. This paper deals with the latter. Sound generated by vibrating structures is often called noise which is to be minimized. However, not all vibrating structures produce noise, for example the violin is also a vibrating structure that in most people's opinion produces sound called music. In the case of the violin, great effort is made not to minimize but to optimize the sound, i.e. to get the 'right' sound out of the structure. Acoustic optimization within this discipline involves automatic changes of structural design variables to obtain minimum or specified sound in specified regions inside or outside the structure. Examples of problem formulations and some theoretical considerations in the field of acoustic optimization in connection with vibrating mechanical structures will be pointed out. Four simple test cases are included as numerical examples of the method proposed.
28.	Carlson, Rolf, et al. (författare) Cross-Cultural Perception of Discourse Phenomena 2009 Ingår i: INTERSPEECH 2009. - BAIXAS : ISCA-INST SPEECH COMMUNICATION ASSOC. ; , s. 1723-1726 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.
29.	Ottersten, Martin, 1981, et al. (författare) Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan 2022 Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12 Tidskriftsartikel (refereegranskat)abstract In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.
30.	Hadadpour, Ahmad (författare) Spray combustion with multiple-injection in modern engine conditions 2020 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Combustion of fuel in diesel engines emits substances harmful to the environment such as soot. These emissions can be reduced by either in-cylinder treatments or after-treatments. One of the common in-cylinder treatments is multiple-injection, which divides a single fuel injection to multiple smaller injections. There are many open questions on the physical processes of the ignition, combustion and emissions of diesel spray flame with multiple injections. The current PhD project aims at studying these processes using large-eddy simulations (LES) and strives to answer some of the open questions. To develop a fast and robust LES tool for this study, a new method is formulated for spray combustion simulation. This method is developed based on the flamelet-generated manifold (FGM) method and the Eulerian stochastic fields (ESF) method. The new ESF/FGM method relaxes some of the substantial assumptions in conventional FGM, while it still keeps the computational costs at a reasonable level for engineering applications. Additionally in this work, a new reaction progress variable for FGM models is proposed by using local oxygen consumption, and the advantages and limitations of this progress variable are explored. Spray-A from Engine Combustion Network (ECN) which is designed to mimic modern engine conditions is chosen as the baseline case for simulations. In this case, liquid n-dodecane, which is a diesel surrogate, is injected into a high-pressure constant-volume vessel. The comparison of simulation results with experimental measurements shows that the ESF/FGM method with the new progress variable can predict the spray combustion characteristics such as ignition delay time, ignition location, lift-off length, pressure rise and thermochemical structure of the spray flame, accurately. After validation of simulation results against experimental measurements, the new ESF/FGM and other available turbulence-combustion simulation tools are applied to simulate multiple-injection spray combustion. Different multiple-injection strategies are investigated by systematically changing the injection timing. The effects of applying each strategy on the ignition, combustion, mixing and emissions are investigated. The results show that in split-injection and post-injection strategies the major physical reason for reduction of soot is better air entrainment and lower local equivalence ratio. It is shown that increasing the dwell time and retarding it toward the end of injection can enhance this effect. On the contrary, for the pre-injection strategies, shortening the ignition delay time of the main injection reduces its pre-mixing and increases its soot formation. In these strategies, the high-temperature region from the pre-injection combustion can increase soot oxidation of the main injection fuel, only if this region is not cooled down as a result of air entrainment during dwell time. Therefore, in such cases shortening the dwell time decreases net soot emissions.
31.	Li, Xiaojian, 1991, et al. (författare) A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles 2020 Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19 Tidskriftsartikel (refereegranskat)abstract Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
32.	Pieringer, Astrid, 1979, et al. (författare) Investigation of railway curve squeal using a combination of frequency- and time-domain models 2016 Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451 Konferensbidrag (refereegranskat)abstract Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
33.	Alenius, Emma, 1983- (författare) CFD of Duct Acoustics for Turbocharger Applications 2010 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. In this work the main focus is the turbocharger compressor and a discussion of turbocharger acoustics and earlier work within the area is presented, giving an insight into its sound generating mechanisms and the damping effect it has on pressure pulses, i.e. incoming waves. However, despite the fact that turbo-charging was developed during the first part of the 20th century, there is not much research results available within the area of centrifugal compressor acoustics. To improve the understanding of the acoustics of engine duct components, methods based on compressible Large Eddy Simulation (LES) are explored. With these methods it is possible to capture both the complex flow, with sound generating mechanisms, and acoustic - flow interactions. It is also possible to get a detailed insight into some phenomena by access to variables and/or areas where it is difficult to perform measurements. In order to develop these methods the linear scattering of low frequency waves by an orifice plate have been studied, using an acoustic two-port model. This simple geometry was chosen since the flow has several of the characteristics seen in a compressor, like unsteady separation, vortex generation and shock waves at high Mach numbers. Furthermore the orifice plate is in itself interesting in engine applications, where constrictions are present in the ducts. The results have been compared to measurements with good agreement and the sensitivity to different parameters has been studied, showing an expected dependence on inlet Mach number and difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the short times series available in LES. During the development of new engines the industry uses 1D engine CFD tools. These tools are developed to give performance data, but sometimes also the acoustic pulsations are studied. The duct components are modelled and the turbocharger is often modelled with a map, representing its fluid mechanical properties measured under steady state conditions. An aim in this work has been to study the limitations of the models available in the commercial software GT-Power. The scattering of incoming waves was simulated and the results were compared to measurements, showing a large discrepancy for the compressor and a significant discrepancy for the orifice plate.
34.	Arlov, Dragana (författare) Numerical study of flows related to aerated stirred tanks 2007 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.
35.	Bergström, Christer (författare) Numerical Modelling of Fuel Sprays 1999 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The way the fuel is introduced into the combustion chamber is one of the most important parameters for the power output and the generation of emissions in the combustion of liquid fuels. The interaction beween the turbulent gas flow field and the liquid fuel droplets, the vaporisation of them and the mixing of the gaseous fuel with the ambient air that are vital parameters in the combustion process. The use of numerical calculations is an important tool to better understand these complex interacting phenomena. This thesis reports on the numerical modelling of fuel sprays in non-reacting cases using an own developed spray module. The spray module uses the stochastic parcel method to represent the spray. The module was made in such manner that it could by coupled with different gas flow solver. Results obtained from four different gas flow solver are presented in the thesis, including the use of two different kinds of turbulence models. In the first part the spray module is coupled with a k-epsilon based 2-D cylindrical gas flow solver. A thorough sensitivity analysis was performed on the spray and gas flow solver parameters, such as grid size dependence and sensitivity to initial values of k-epsilon. The results of the spray module were also compared to results from other spray codes, e.g. the well known KIVA code. In the second part of this thesis the spray was injected into a turbulent and fully developed crossflow studied. The spray module was attached to a LES (Large Eddy Simulation) based flow solvers enabling the study of the complex structures and time dependent phenomena involved in spray in crossflows. It was found that the spray performs an oscillatory motion and that the Strouhal number in the wake was about 0.1. Different spray breakup models were evaluated by comparing with experimental results.
36.	Boij, Susann, et al. (författare) Scattering and absorption of sound at flow duct expansions 2006 Ingår i: Journal of sound and vibration. - : Elsevier. ; 289:3, s. 577-594 Tidskriftsartikel (refereegranskat)
37.	Cuppoletti, Daniel, et al. (författare) The Response of Supersonic Jet Noise Components to Fluidic Injection Parameters 2013 Ingår i: 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, May 27-29, 2013. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134 ; , s. 188- Konferensbidrag (refereegranskat)
38.	Elnady, T., et al. (författare) Validation of an Inverse Semi-Analytical Technique to Educe Liner Impedance 2009 Ingår i: AIAA Journal. - : American Institute of Aeronautics and Astronautics (AIAA). - 0001-1452 .- 1533-385X. ; 47:12, s. 2836-2844 Tidskriftsartikel (refereegranskat)abstract In this paper, the acoustic impedance of a liner is educed by a novel semi-analytical inverse technique. The liner sample is placed flush with the solid walls in a rectangular duct with grazing flow. The technique uses complex acoustic pressure measured at four positions at the wall of the duct, upstream and downstream of the lined section, and educes the impedance with a mode-matching method. Previous studies neglected grazing flow nonuniformity and the pressure discontinuity that appears at the liner-wall boundary caused by the discontinuity of the acoustic particle velocity into the wall. In the present paper, the mode-matching formulation is rederived in terms of pressure instead of velocity potential which is found to be more numerically stable. Moreover, the proposed methodology is validated with benchmark data from an experiment performed by NASA. First, the ability of the code to reproduce the pressure field for a given impedance is tested. Second, the ability to educe the correct impedance for a given pressure distribution is tested. The results of the mode-matching code are in very good agreement with the experimental data. The effect of shear flow is investigated and it can be concluded that the assumption of uniform flow is appropriate for the chosen liner, duct size, and frequency range of interest.
39.	Gullbrand, Jessica (författare) Large Eddy Simulation of Turbulent Flows in Combustor Related Geometries 1999 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Numerical simulations using Large Eddy Simulation (LES) are applied to turbulent swirling flow fields. The swirling motion is often introduced into combustors to act as flame holders or enhance the mixing between species. Different turbulence models capture the swirling motion more or less accurately. LES is well suited for understanding details of swirling flows. It resolves all the large scales in the flow field and only the small scales have to be modeled. The small unresolved scales are the Subgrid Scales (SGS) and the model must take into account the interaction between the small scales and their influence on the resolved scales. In order to separate the effects from the SGS models and the numerical scheme, the problem must be well resolved and be of high order. SGS models have been applied, investigated and compared in swirling flow fields. Four SGS models are considered: an implicit, a stress similarity, a dynamic divergence and an exact differential model. The implicit model uses no SGS model. For the stress similarity model, similar behaviour between the resolved and unresolved stresses is assumed. The model parameter in the dynamic divergence model are depending upon both space and time and it is recalculated during the whole simulation. If a particular form of differential filter function is applied, an explicit expression of the SGS stress tensor can be received. This is the exact differential model. In the simulations, the stress similarity model is shown to have the largest effect on the results. Otherwise, the SGS models only show minor effects on both mean velocities and turbulence intensities. A high order Cartesian grid method have been proposed and employed in the simulations. Cartesian grids have features that are very suitable for LES. The grid generation is simple and fast, it does not require a lot of computational storage and the discretized governing equations can be easily extended to higher orders. The drawback of Cartesian grids is that it does not represent complex geometries correctly. The boundary conditions can be misplaced by as much as a cell size and this reduces the order of the solution. A high order wall treatment is proposed to handle the low order wall problem and it is incorporated into the Cartesian grid method. The high order Cartesian grid method is shown to maintain the order of the discretization.
40.	Göransson, Peter (författare) Numerical Modelling of Dynamics of Light Porous Materials 1998 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Porous materials are among the most commonly used materials for noise and vibration reduction in modern transportation vehicles. To design, industrially relevant, weight and cost effective noise and vibration measures, there is a need for general prediction models capable of representing the elasto-acoustic behaviour of such materials. The objective of the present work, is to contribute to the modelling of the inherent fluid-structure interaction phenomena related to porous materials. The modelling approach chosen allows for solution of problems having multiple layers of materials with complicated geometrical shapes and including effects of different boundary conditions along the interfaces to other fluid and solid materials. To solve general three dimensional dynamic problems involving porous materials, a finite element formulation of Biot's equations, describing the fluid-structure interaction in porous materials is proposed. The resulting discrete equation systems, including coupling matrices to other fluid and solid materials, have symmetric matrices and are thus readily implemented into standard finite element software packages. Effects of viscous dissipation, thermal interaction, solid frame disspation and inertial coupling are taken into account. In addition, a finite element formulation of a simplified equivalent fluid model for low stiffness porous materials is proposed.
41.	Hafsteinsson, Haukur, 1984, et al. (författare) Supersonic Jet Excitation using Flapping Injection 2013 Ingår i: American Physical Society, Division of Fluid Dynamics 66th Annual Meeting, November 24–26, 2013 Pittsburgh, Pennsylvania. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Supersonic jet noise reduction is important for high speed military aircraft. Lower acoustic levels would reduce structural fatigue leading to longer lifetime of the jet aircraft. It is not solely structural aspects which are of importance, health issues of the pilot and the airfield personnel are also very important, as high acoustic levels may result in severe hearing damage. It remains a major challenge to reduce the overall noise levels of the aircraft, where the supersonic exhaust is the main noise source for near ground operation. Fluidic injection into the supersonic jet at the nozzle exhaust has been shown as a promising method for noise reduction. It has been shown to speed up the mixing process of the main jet, hence reducing the kinetic energy level of the jet and the power of the total acoustic radiation. Furthermore, the interaction mechanism between the fluidic injection and the shock structure in the jet exhaust plays a crucial role in the total noise radia- tion. In this study, LES is used to investigate the change in flow structures of a supersonic (M=1.56) jet from a converging-diverging nozzle. Six fluidic actuators, evenly distributed around the nozzle exit, inject air in a radial direction towards the main flow axis with a total mass flow ratio of 3%. Steady injection is compared with flapping injection. With flapping injection turned on, the injection angle of each injector is varied sinusoidally in the nozzle exit plane and the variation is the same for all injectors. This fluid dynamics video is submitted to the APS DFD Gallery of Fluid Motion 2013 at the 66 the Annual Meeting of the American Physical Society, Division of Fluid Dynamics (24-26 November, Pittsburgh, PA, USA).
42.	Hafsteinsson, Haukur, 1984, et al. (författare) Supersonic Jet Noise Reduction Using Steady Injection and Flapping Injection 2013 Ingår i: 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, May 27-29, 2013. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134 ; , s. 140- Konferensbidrag (refereegranskat)
43.	Held, Jörgen (författare) Large Eddy Simulations of Separated Compressible Flows around Wing Sections 1999 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis concerns numerical calculations of compressible separated flows, with and without shocks, around wing sections using Large Eddy Simulations (LES). The considered geometries are the NACA 0012 wing section and the ONERA AT15A wing section. Compressible separated flows around wing sections are of considerable interest, for engineering and scientific reasons, since they involve transition, near-wall turbulence and separation. At transonic speed the interaction between shock and the viscous boundary layer is of interest. If the shock is strong enough shock induced separation occurs. Using Reynolds Averaged Navier-Stokes Simulations (RANS) one has to know in advance where transition to turbulence occurs. The RANS turbulence models also include a set of model parameters which have to be set a priori. This is not the case for dynamic LES-formulation since the model parameters are computed during the simulation utilising the information in the resolved flow field. An explicit filter is used to extract this information. A filter derived on a mathematical basis is presented as well as a new dynamic model where the divergence of the subgrid-scale (SGS) terms are modelled rather than the SGS-terms themselves. In this way only three model parameters are needed for the momentum equations and still anisotropy effects can be accounted for. A novel idea how to treat filtering close to a shock is presented. In LES the large scale flow field is resolved both in time and space and the computational time is significant. To obtain results in acceptable time computations using Parallel Virtual Machine (PVM) have been conducted. The important role of the numerical viscosity as an implicit model in LES is demonstrated. The development of streamwise vortices is shown to be strongly dependent of the spanwise distance of the computational domain.
44.	Hiselius, Per (författare) Acoustical properties of earplugs 2005 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract In this study an experimental setup for measurements of high impedance objects in ducts, yielding the acoustical Two-Port properties of the object, is applied to earplugs. A frequently used experimental setup for measuring objective acoustical properties of earplugs is that of artificial ears. Great effort is spent on duplicating the human ear. The acoustical properties of the earplug are thought to be given by the insertion loss. Such a setup, however, gives a ratio of the "response of a system" to that of "another system". The actual properties of the earplug are thereby embedded in a complicated artificial response. A novel approach, presented here, is to use a simple setup. Given the sound pressure level on both sides of the earplug for two sufficiently different termination impedances, the Two-Port properties can be assessed. First, a setup is used where the earplugs are fitted in a cylinder. Second, a setup based on molds of the ear canals of a real person is used. For six types of earplugs, the acoustical properties are assessed and numerically coupled to a model of the ear in order to predict the insertion loss. The predicted attenuation is compared to subjective (REAT) attenuation. In addition, experimental Two-Port data is used to model the acoustical behavior of three fundamentally different types of earplugs. It is shown that simple lumped models suffice to describe the acoustical behavior of the earplugs. Furthermore, it is shown that the measurement setup can be advantageously used to assess the acoustical properties of an arbitrary acoustical partition for a wide frequency range.
45.	Johansson, Ann-Charlotte (författare) Drum sound from floor coverings - objective and subjective assessment 2005 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Drum sound is the sound produced when an object, such as a foot, hits the flooring in the room in which the receiving ear is located. Drum sound has attracted interest in recent years, particularly due to an increased use of thin floating floor constructions, such as veneer or laminate flooring, which can produce loud and sharp walking sound. A prediction model of the subjective response, in a paired comparison test, to drum sound based on differences in objective measurements is developed. The difference in 10-percentile loudness, N10, between two stimuli is shown to predict the subjective perceived disturbance better than, for example, A-weighted sound pressure level. A difference of about 8% in N10 resulted in 50% of the assessors noticing a difference. A comparison of different existing approaches to analysing the result from a paired comparison test is made. The main focus is set on the basic models by Thurstone-Mosteller and Bradley-Terry and extensions of these concerning ties. Procedures for testing if the responses and calculated ranking values are statistically different are presented. The advantages and disadvantages of these methods are discussed. These methods are illustrated with examples from tests on drum sound from floor coverings. A branch norm has been established for measuring drum sound on laminate floor coverings. The norm evaluates the subjective perception of the drum sound's loudness using the ISO tapping machine. A round-robin study of the norm is reported along with the results of a paired comparison listening test using the same floor coverings. General aspects of evaluation measures, tapping machines, test environments, etc., that need to be considered when measuring drum sound on various floor coverings are discussed. It is concluded that loudness as measured according to ISO 532B correlates the best with the subjective perception of the drum sound's loudness. The tapping machine can be used to excite hard floor coverings to produce the drum sound, but should be used with caution in studying low-level drum sounds due to the tapping machine's inherent mechanical noise.
46.	Karlsson, Mikael, et al. (författare) The Herschel-Quincke tube : The attenuation conditions and their sensitivity to mean flow 2008 Ingår i: Journal of the Acoustical Society of America. - : American Institute of Physics (AIP). - 0001-4966 .- 1520-8524. ; 124:2, s. 723-732 Tidskriftsartikel (refereegranskat)abstract The classic Herschel-Quincke tube is a parallel connection of two ducts yielding multiple noise attenuation maxima via destructive interference. This problem has been discussed to different degrees by a number of authors over the years. This study returns to the basics of the system for the purpose of furthering the understanding of the conditions necessary for noise attenuation and especially their sensitivity to mean flow. First, the transmission loss for an N-duct system with mean flow and arbitrary conditions of state in the different ducts is derived. Next, the two types of conditions yielding the attenuation maxima are studied. In addition to a discussion of the underlying physics, generic expressions for frequencies at which maximum attenuation occur are presented. Experiments without mean flow generally show good agreement with theory based on straight duct elements. However, more detailed models may be required for accurate simulations in the presence of mean flow. A simple model compensating for the losses associated with bends is shown to improve the results significantly for the geometry studied.
47.	Kodakadath Premachandran, Rammohan, et al. (författare) Comparison of Spectral Properties of the Vibration Signal and Line Pressure Signal of DTH Drill 2016 Ingår i: 23rd International Congress on Sound and Vibration 2016 (ICSV 23): From Ancient to Modern Acoustics, Publisher: Curran Associates, Inc.. - : Curran Associates, Inc.. - 9781510827165 - 9789609922623 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Quantifying and Monitoring of drilling performance are becoming exceedingly important in the case of Down the Hole drilling. Various economic, environmental and safety constraints are driving the drilling process to become more efficient. To make a robust system that would enable the performance/condition monitoring of the drilling, we must understand how different properties like different line pressure etc. respond to various drilling conditions and what information can they provide regarding the Drilling Performance. A comparison of different properties like spectral properties, of the vibration signals and Pressure signals under known conditions would enable better understanding of the drilling system and the physics behind the process. A comparison is made between the Spectral properties of the vibrational signals obtained from remote locations on the drill rig and pressure signals that provide the feed and holdback forces to the drill string and a correlation between their characteristics and patterns under good and bad drilling conditions have been made. A simplified model of the system is simulated and results are compared with the patterns obtained from analyzing the Vibration signals.
48.	Kyprianidis, Konstantinos, et al. (författare) Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform 2008 Ingår i: Aeronautical Journal. - 0001-9240. ; 112:1129, s. 161-169 Tidskriftsartikel (refereegranskat)abstract This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.
49.	Kyprianidis, Konstantinos, et al. (författare) Multi-disciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine 2013 Ingår i: <em><em>Proc. ASME</em>.</em> 55133; Volume 2: Aircraft Engine; Coal, Biomass and Alternative Fuels; Cycle Innovations, V002T07A027. GT2013-95474. - 9780791855133 Konferensbidrag (refereegranskat)abstract Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. Thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyse the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption.With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio just below 1.2 at hot-day top of climb conditions. At ISA mid-cruise conditions a specific thrust of 86m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 55% and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines.The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. Analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor account for losses in the bypass duct and jet pipe, whilst a relatively detailed engine performance model such as the one utilised in this study does.Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberised-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilised to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
50.	Lagö, Thomas L (författare) A Novel Signal Model and Estimation Method for Acoustic Doppler Current Meters 1999 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis deals with the process of estimating underwater current from the backscattering signal transmitted from an ultrasonic transducer. The narrowband sinusoidal burst signal is Doppler-shifted due to the current, and this information is converted into current. The traditional mathematical model for this Doppler process is based on the assumption that the backscattering time signal is Gaussian, due to the Rayleigh backscattering amplitude with random phase. This is based on the assumption that the backscattering is due to many randomly distributed bubbles with about equal size. It is reasonable to question whether this assumption holds for real life signals. Therefore, part of the work discussed in this thesis has concentrated on looking at real life data, and has investigated whether the Gaussian assumption holds for the background noise and the Doppler signal received. It has been found that this is not generally the case. Thus, a different mathematical model has been sought which describes the Doppler signal in a more realistic way. Such a model has been developed, and is presented. When studying the work of other researchers, it has been noticed that some of the more recent modeling work relies on elaborate mathematics, but does not contribute much to the understanding of the physics, nor the effects on the estimation process. Again, and this is emphasized, the aim has been to develop a simple signal model and a simple estimation method that performs well. The latter is important since the complexity of the system needs to be low. This is because systems are often battery operated and a long battery life is needed as the systems are positioned out in the water. The new mathematical model for the backscattering signal is subsequently used to test different estimator approaches, and to investigate their behavior for different types of complexity in the Doppler signal. A new estimator, the Symmiktos Method™ estimator, has been developed, which is a non-linear estimation method. The estimator performance is compared with the covariance method, which is based on the Gaussian model assumption. The Symmiktos Method™ is based on a more complex Doppler signal model. The result is that the Symmiktos Method™ is more robust to changes in the signal complexity. Also, the method is quick and easy to implement, an important factor in real-life use. Otherwise the method becomes a theoretical method with very little practical use, and this has not been the intention with this work. The work should be viewed as a practical approach to solving a difficult signal processing application problem, where cost, size, simplicity and performance are very important for the end result. A large data set from four locations, Trubaduren, Almagrundet, Fladen and Ma-Wan, Hongkong has been collected. This data base was used when performing elaborate statistical analyses like ANOVA, higher order moments, histograms and normal probability plots. Classical signal processing has been performed as well as non-linear filtering using Multiple Peak Count Analysis, MPCA. The latter is presented in both a 2D and a 3D format. Different estimation methods are compared, including the Symmiktos Method™.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "AMNE:(TEKNIK OCH TEKNOLOGIER) AMNE:(Maskinteknik) AMNE:(Strömningsmekanik och akustik) "

Avgränsa träffmängd

År