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Turbulent open channel flow, sediment erosion and sediment transport

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Book Series: Dissertationsreihe am Institut für Hydromechanik des Karlsruher Instituts für Technologie / Karlsruher Institut für Technologie (KIT), Institut für Hydromechanik ISSN: 14394111 ISBN: 9783866449008 Year: Volume: 2012,1 Pages: XXXII, 154 p. DOI: 10.5445/KSP/1000029253 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: General and Civil Engineering
Added to DOAB on : 2019-07-30 20:01:58
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This thesis aims to contribute to a better understanding of turbulent open channel flow, sediment erosion and sediment transport. The thesis provides an analysis of high-fidelity data from direct numerical simulation of (i) open channel flow over an array of fixed spheres, (ii) open channel flow with mobile eroding spheres, (iii) open channel flow with sediment transport of many mobile spheres. An immersed boundary method is used to resolve the finite-size particles.

Turbulence: Numerical Analysis, Modelling and Simulation

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ISBN: 9783038428091 9783038428107 Year: Pages: VI, 222 Language: English
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Physics (General) --- Mathematics
Added to DOAB on : 2018-05-04 10:38:08
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The problem of accurate and reliable simulation of turbulent flows is a central and intractable challenge that crosses disciplinary boundaries. As the needs for accuracy increase and the applications expand beyond flows where extensive data is available for calibration, the importance of a sound mathematical foundation that addresses the needs of practical computing increases. This Special Issue is directed at this crossroads of rigorous numerical analysis, the physics of turbulence and the practical needs of turbulent flow simulations. It seeks papers providing a broad understanding of the status of the problem considered and open problems that comprise further steps.

Gas transfer at the air-water interface in a turbulent flow environment

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Book Series: Dissertationsreihe am Institut für Hydromechanik der Universität Karlsruhe (TH) ISSN: 14394111 ISBN: 3937300740 Year: Volume: 2005,4 Pages: IX, 128 p. DOI: 10.5445/KSP/1000003544 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: General and Civil Engineering
Added to DOAB on : 2019-07-30 20:01:58
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The gas transfer process across the air-water interface in a ottom-shear-induced turbulent environment was investigated to gain improved fundamental understanding of the physical mechanisms that control the process. For this purpose, it is necessary to reveal the hydrodynamics of the flow field as well as the molecular diffusion and the turbulent transport contributions to the total flux. Therefore, detailed laboratory experiments were conducted to obtain these information.The experiments were performed in a grid-stirred tank using a combined Particle Image Velocimetry - Laser Induced Fluorescence (PIV-LIF) technique that has been developed for these near surface gas transfer measurements. The turbulence characteristics of the velocity near the interface were acquired from the PIV measurements and showed generally good agreement with the theoretical profiles from Hunt & Graham (1978). The LIF technique enabled visualization of the planar concentration fields which provided more insight into the gas transfer mechanisms. The high data resolution allowed detailed quantification of the concentration distribution within the thin aqueous boundary layer. The mean and turbulent fluctuation characteristics of the concentration could be elucidated and the molecular diffusion contribution to the total flux across the interface could be determined. With the combined PIV-LIF technique, which enables simultaneous and spatially synoptic measurements of 2D velocity and concentration fields, the turbulent mass flux term cw and also the total mass flux across the air-water interface could be quantified directly. For the first time, a particular trend can be inferred from the measured mean cw profiles. It could also be shown that the contribution of the turbulent mass flux to the total gas flux is significant. The co-spectra indicated different behavior for the cases with lower and higher turbulent Reynolds numbers.The interrelated interpretation of the obtained results suggest that the gas transfer process is controlled by a spectrum of different eddy sizes and the gas transfer at different turbulence levels can be associated to certain eddy sizes. For high turbulence levels the gas transfer should be asymptotic to the small eddy model, whereas for low turbulence level to the large eddy model. The new results of turbulent mass flux should aid as an excellent database in refining numerical models and developing more accurate models for the prediction of the transfer velocity.

Stochastische Modellierung der Bildung von Nanopartikeln in reaktiven Strömungen

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ISBN: 9783731505853 Year: Pages: XVIII, 149 p. DOI: 10.5445/KSP/1000059807 Language: GERMAN
Publisher: KIT Scientific Publishing
Subject: Chemical Engineering
Added to DOAB on : 2019-07-30 20:02:02
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Soot formation in a laminar and a turbulent diffusion flame as well as the formation of iron oxide nanoparticles in an iron pentacarbonyl doped near stoichiometric H?/O?/Ar-premixed flame have been investigated numerically. The particular modus operandi of the simulated test cases is described. In the case of the turbulent flame the impact of the turbulent closure of the single particle source terms on particle size distribution is shown.

Reactive Control of Turbulent Wall-Bounded Flows for Skin Friction Drag Reduction

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Book Series: Schriftenreihe des Instituts für Strömungsmechanik, Karlsruher Institut für Technologie ISSN: 21998868 ISBN: 9783731507666 Year: Volume: 4 Pages: IX, 193 p. DOI: 10.5445/KSP/1000080529 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: Technology (General)
Added to DOAB on : 2019-07-28 18:37:01
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The work presents an attempt to improve the understanding of reactive drag reducing control of near-wall turbulence with respect to limitations present in a realistic application scenario. The reference reactive control scheme of opposition control is studied using direct numerical simulation through the consideration of various application oriented restrictions, i.e. local control application, limited spatial and temporal resolution of the scheme, sensor noise and control elements arrangement.

Shallow turbulent wake flows: momentum and mass transfer due to large-scale coherent vortical structures

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Book Series: Dissertationsreihe am Institut für Hydromechanik der Universität Karlsruhe (TH) ISSN: 14394111 ISBN: 3937300635 Year: Volume: 2005,2 Pages: XXVI, 398 p. DOI: 10.5445/KSP/1000003453 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: General and Civil Engineering
Added to DOAB on : 2019-07-30 20:01:59
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Shallow turbulent wake flows are generated by large obstacles - like islands or headlands - introduced to shallow turbulent open-channel flows. Large-scale quasi two-dimensional vortices may shed off from an obstacle, and advect downstream in a vertical shear flow with predominantly small-scale turbulence induced by bottom friction. Experimental, analytical, and numerical techniques are employed in the present study to characterize the mean flow and turbulence properties of shallow wakes; mechanisms of generation and decay of large-scale vortical structures are clarified, as is their influence on momentum and mass transport in shallow wakes; the global and local stability of shallow wakes is analyzed and evidenced from experimental data. Part I of this work covers non-intrusive optical measurement techniques especially adapted to investigate shallow shear flows. Flow velocities and mass concentrations are obtained (i) point-wise with high spatiotemporal resolution using a combinded LDV-LIF system, and (ii) field-wise using near-surface PIV and depth-averaged PCA systems with a coupling by phase-resolved averaging. Improved algorithms for the evaluation of mass concentrations are based on hydro-optical models of the underlying fluorescence and light attenuation processes. Part II addresses the time-mean description of shallow wake flows. The stochastic description of the turbulence fields displays a characteristic spectral distribution both of kinetic energy and of mass variance, which is partially consistent with the theory of unbounded 2D turbulence at large scales, and with the theory of homogeneous 3D turbulence at small scales. An integral wake model including the effect of bottom friction is derived analytically, and is validated by experimental data. The time-mean distributions of flow velocities and of mass concentration allow to identify wake near fields and far fields with specific asymptotic wake developments. Wake stability classes are associated with local stability regions suggested by linear stability analyses. Part III elaborates the structure and dynamics of quasi-periodic wake flows and the significance of large-scale eddies. This involves a structure identification scheme to educe individual vortices, and a phase-resolved averaging procedure to decompose the flow fields into large-scale coherent and small-scale turbulent parts. A Numerical Particle Tracking technique is employed to model the mass transport and to elucidate different diffusion and dispersion effects.

Intermittency and Self-Organisation in Turbulence and Statistical Mechanics

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ISBN: 9783039211081 / 9783039211098 Year: Pages: 298 DOI: 10.3390/books978-3-03921-109-8 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Mathematics
Added to DOAB on : 2019-08-28 11:21:27
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There is overwhelming evidence, from laboratory experiments, observations, and computational studies, that coherent structures can cause intermittent transport, dramatically enhancing transport. A proper description of this intermittent phenomenon, however, is extremely difficult, requiring a new non-perturbative theory, such as statistical description. Furthermore, multi-scale interactions are responsible for inevitably complex dynamics in strongly non-equilibrium systems, a proper understanding of which remains a main challenge in classical physics. As a remarkable consequence of multi-scale interaction, a quasi-equilibrium state (the so-called self-organisation) can however be maintained. This special issue aims to present different theories of statistical mechanics to understand this challenging multiscale problem in turbulence. The 14 contributions to this Special issue focus on the various aspects of intermittency, coherent structures, self-organisation, bifurcation and nonlocality. Given the ubiquity of turbulence, the contributions cover a broad range of systems covering laboratory fluids (channel flow, the Von Kármán flow), plasmas (magnetic fusion), laser cavity, wind turbine, air flow around a high-speed train, solar wind and industrial application.

Heart Rate Variability: Clinical Applications and Interaction between HRV and Heart Rate

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Book Series: Frontiers Research Topics ISSN: 16648714 ISBN: 9782889196524 Year: Pages: 166 DOI: 10.3389/978-2-88919-652-4 Language: English
Publisher: Frontiers Media SA
Subject: Science (General) --- Physiology
Added to DOAB on : 2016-08-16 10:34:25
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Over the last decades, assessment of heart rate variability (HRV) has increased in various fields of research. HRV describes changes in heartbeat intervals, which are caused by autonomic neural regulation, i.e. by the interplay of the sympathetic and the parasympathetic nervous systems. The most frequent application of HRV is connected to cardiological issues, most importantly to the monitoring of post-myocardial infarction patients and the prediction of sudden cardiac death. Analysis of HRV is also frequently applied in relation to diabetes, renal failure, neurological and psychiatric conditions, sleep disorders, psychological phenomena such as stress, as well as drug and addiction research including alcohol and smoking. The widespread application of HRV measurements is based on the fact that they are noninvasive, easy to perform, and in general reproducible – if carried out under standardized conditions. However, the amount of parameters to be analysed is still rising. Well-established time domain and frequency domain parameters are discussed controversially when it comes to their physiological interpretation and their psychometric properties like reliability and validity, and the sensitivity to cardiovascular properties of the variety of parameters seems to be a topic for further research. Recently introduced parameters like pNNxx and new dynamic methods such as approximate entropy and detrended fluctuation analysis offer new potentials and warrant standardization. However, HRV is significantly associated with average heart rate (HR) and one can conclude that HRV actually provides information on two quantities, i.e. on HR and its variability. It is hard to determine which of these two plays a principal role in the clinical value of HRV. The association between HRV and HR is not only a physiological phenomenon but also a mathematical one which is due to non-linear (mathematical) relationship between RR interval and HR. If one normalizes HRV to its average RR interval, one may get ‘pure’ variability free from the mathematical bias. Recently, a new modification method of the association between HRV and HR has been developed which enables us to completely remove the HRV dependence on HR (even the physiological one), or conversely enhance this dependence. Such an approach allows us to explore the HR contribution to the clinical significance of HRV, i.e. whether HR or its variability plays a main role in the HRV clinical value. This Research Topic covers recent advances in the application of HRV, methodological issues, basic underlying mechanisms as well as all aspects of the interaction between HRV and HR.

Turbulence in River and Maritime Hydraulics

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ISBN: 9783038975946 Year: Pages: 296 DOI: 10.3390/books978-3-03897-595-3 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: General and Civil Engineering --- Technology (General)
Added to DOAB on : 2019-03-21 15:50:41
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Understanding of the role of turbulence in controlling transport processes is of paramount importance for the preservation and protection of aquatic ecosystems, the minimization of the deleterious consequences of anthropogenic activity, and the successful sustainable development of river and maritime areas. In this context, the present Special Issue collects 15 papers which provide a representation of the present understanding of turbulent processes and their effects in river and maritime environments. The presented collection of papers is not exhaustive, but it highlights the key priority areas and knowledge gaps in this field of research. The published papers present the state-of-the-art knowledge of complex environmental flows which are useful for researchers and practitioners. The paper contents are an overview of some recent topics of research and an exposure of the current and future challenges associated with these topics.

Keywords

breaking waves --- turbulence invariants --- laboratory experiments --- flow-through system --- tidal inlets --- residence time --- coastal lagoon --- MIKE 3 FM (HD & --- TR) --- MIKE 21 FM (HD) --- dense jet --- current flow --- velocity --- trajectory --- turbulence --- dissipation --- rivers --- meanders --- turbulence --- secondary motion --- prediction --- bedrock canyon --- ADCP --- eddy viscosity --- bed shear stress --- spatial analysis --- smoothed particle hydrodynamics models --- physical modelling --- plunging breaking waves --- vorticity --- turbulent jet --- wave–current interaction --- spectral dissipation --- bottom friction --- numerical model --- hydrodynamic model --- spectral model --- wave attenuation --- energy dissipation --- drag coefficient --- flexible vegetation --- Spartina maritima --- vegetation patch --- wake region --- submerged ratio --- SVF --- channel confluences --- junction angle --- flow deflection zone --- flow retardation zone --- flow separation zone --- numerical modelling --- PANORMUS --- jets --- waves --- turbulence --- mixing --- diffusion --- advection --- river mouth --- flow mixing --- nonlinear shallow water equations --- macrovortices --- sub-grid turbulence --- seabed friction --- flow resistance --- roughness --- gravel-bed rivers --- casting technique --- CFD --- Kelvin–Helmholtz --- billow --- lobe --- cleft --- gravity current --- surface waves --- inclined negatively buoyant jets --- regular waves --- dilution --- sea discharges --- rivers --- maritime areas --- turbulent processes

Remote Sensing of Atmospheric Conditions for Wind Energy Applications

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ISBN: 9783038979425 / 9783038979432 Year: Pages: 290 DOI: 10.3390/books978-3-03897-943-2 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Physics (General)
Added to DOAB on : 2019-06-26 08:44:06
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This Special Issue “Atmospheric Conditions for Wind Energy Applications” hosts papers on aspects of remote sensing for atmospheric conditions for wind energy applications. Wind lidar technology is presented from a theoretical view on the coherent focused Doppler lidar principles. Furthermore, wind lidar for applied use for wind turbine control, wind farm wake, and gust characterizations is presented, as well as methods to reduce uncertainty when using lidar in complex terrain. Wind lidar observations are used to validate numerical model results. Wind Doppler lidar mounted on aircraft used for observing winds in hurricane conditions and Doppler radar on the ground used for very short-term wind forecasting are presented. For the offshore environment, floating lidar data processing is presented as well as an experiment with wind-profiling lidar on a ferry for model validation. Assessments of wind resources in the coastal zone using wind-profiling lidar and global wind maps using satellite data are presented..

Keywords

detached eddy simulation --- turbulence --- Lidar --- range gate length --- wind energy resources --- QuikSCAT --- WindSAT --- ASCAT --- global ocean --- wind energy --- resource assessment --- power performance testing --- wind turbine controls --- complex flow --- Doppler lidar --- coherent Doppler lidar --- wind sensing --- single-particle --- wind gusts --- Doppler lidar --- detecting and tracking --- impact prediction --- wind energy --- atmospheric boundary layer --- wind turbine wake --- wind lidar --- turbulence --- wake modeling --- field experiments --- wind energy --- atmospheric boundary layer --- wind turbine wake --- wind lidar --- virtual lidar --- turbulence --- wake modeling --- large-eddy simulations --- tropical cyclones --- Doppler Wind Lidar --- atmospheric boundary layer --- wind structure --- wind energy --- Doppler lidar --- wind turbine controls --- lidar-assisted control (LAC) --- IEA Wind Task 32 --- coastal wind measurement --- vertical Light Detection and Ranging --- NeoWins --- fetch effect --- Hazaki Oceanographical Research Station --- empirical equation --- complex terrain --- complex flow --- lidar --- VAD --- remote sensing --- wind energy --- Doppler lidar --- NWP model --- mesoscale --- Floating Lidar System (FLS), wind resource assessment --- wind atlas --- lidar --- wind --- Doppler --- aerosol --- motion estimation --- optical flow --- cross-correlation --- wind energy --- gust prediction --- variational analysis --- Doppler radar --- five-minute ahead wind power forecasting --- probabilistic forecasting --- remote sensing forecasting --- offshore wind speed forecasting --- wind energy --- remote sensing --- Doppler wind lidar --- velocity-azimuth-display algorithm --- resource assessment --- offshore --- turbulence intensity --- Doppler wind lidar --- wind energy --- aerosol --- wind turbine --- wind farm --- wake --- control --- complex terrain --- offshore

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