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Lai, Shouwen. "Duty-Cycled Wireless Sensor Networks: Wakeup Scheduling, Routing, and Broadcasting." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27333.
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In order to save energy consumption in idle states, low duty-cycled operation is widely used in Wireless Sensor Networks (WSNs), where each node periodically switches between sleeping mode and awake mode. Although efficient toward saving energy, duty-cycling causes many challenges, such as difficulty in neighbor discovery due to asynchronous wakeup/sleep scheduling, time-varying transmission latencies due to varying neighbor discovery latencies, and difficulty on multihop broadcasting due to non-simultaneous wakeup in neighborhood. This dissertation focuses on this problem space. Specifically, we focus on three co-related problems in duty-cycled WSNs: wakeup scheduling, routing and broadcasting.
We propose an asynchronous quorum-based wakeup scheduling scheme, which optimizes heterogenous energy saving ratio and achieves bounded neighbor discovery latency, without requiring time synchronization. Our solution is based on quorum system design. We propose two designs: cyclic quorum system pair (cqs-pair) and grid quorum system pair (gqs-pair). We also present fast offline construction algorithms for such designs. Our analytical and experimental results show that cqs-pair and gqs-pair achieve better trade-off between the average discovery delay and energy consumption ratio. We also study asymmetric quorum-based wakeup scheduling for two-tiered network topologies for further improving energy efficiency.
Heterogenous duty-cycling causes transmission latencies to be time-varying. Hence, the routing problem becomes more complex when the time domain must be considered for data delivery in duty-cycled WSNs. We formulate the routing problem as time-dependent Bellman-Ford problem, and use vector representation for time-varying link costs and end-to-end (E2E) distances. We present efficient algorithms for route construction and maintenance, which have bounded time and message complexities in the worst case by ameliorating with beta-synchronizer.
Multihop broadcast is complex in duty-cycled WSNs due to non simultaneous wakeup in neighborhoods. We present Hybrid-cast, an asynchronous multihop broadcast protocol, which can be applied to low duty-cycling or quorum-based duty-cycling schedules, where nodes send out a beacon message at the beginning of wakeup slots. Hybrid-cast achieves better tradeoff between broadcast latency and broadcast count compared to previous broadcast solutions. It adopts opportunistic data delivery in order to reduce the broadcast latency. Meanwhile, it reduces redundant transmission via delivery deferring and online forwarder selection. We analytically establish the upper bound of broadcast count and the broadcast latency under Hybrid-cast.
To verify the feasibility, effectiveness, and performance of our solutions for asynchronous wakeup scheduling, we developed a prototype implementation using Telosb and TinyOS 2.0 WSN platforms. We integrated our algorithms with the existing protocol stack in TinyOS, and compared them with the CSMA mechanism. Our implementation measurements illustrate the feasibility, performance trade-off, and effectiveness of the proposed solutions for low duty-cycled WSNs.Ph. D.
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Zhu, Yanmin. "Low-power event detection and wakeup scheduling in wireless sensor networks /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CSED%202007%20ZHU.
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Kumar, Santosh. "Foundations of coverage for wireless sensor networks." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1154986262.
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Shah, Devanshi. "St. Jude Medical: Enhanced MICS (eMICS)." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/377.
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Heart disease is one of the most prevalent diseases in the world. The survival chances for patients with ventricular fibrillation/ventricular tachycardia reduces significantly as time passes without treatment and even after getting timely treatment recurring episode are common. These patients can benefit from an Implantable Cardioverter Defibrillator (ICD) which can monitor heart rhythm and provide immediate treatment. Due to the ever changing physical conditions and disease progression, the ICD needs to collect diagnostic data as well as support programming by the physician. The ICD uses inductive telemetry and radio-frequency telemetry for the communication with the external devices such as a programmer or a monitor. Inductive telemetry uses less energy than RF telemetry but has a very short range of communication. In addition to inductive telemetry, the St. Jude Medical ICD supports 2.45 GHz band based asynchronized wakeup and 400 MHz MICS band based synchronized wakeup. The 2.45 GHz band based wakeup has limited wakeup range and the 400 MHz MICS based synchronized wakeup has limited availability for connection because it requires synchronization with the base station. The enhanced Medical Implant Communications Service (eMICS) algorithm is a firmware based algorithm which addresses the issues with other two wakeup schemes and provides fast, robust, and seamless wakeup. This thesis describes the design, implementation, and initial testing of eMICS algorithm on the Unity device platform in Technology Project Management (TPM) phase. The eMICS automated test tool developed at St. Jude Medical was used to test the eMICS algorithm under a controlled lab environment, typical home environment, typical hospital/clinic environment, and in the field. The project was successfully completed and transferred to Product Project Management (PPM) phase. However, the suggested duration of 60-90 seconds for sniff interval which will cause the least effect on the battery life was found unacceptable, and there is also a strong need for energy efficient hardware which draws minimal amount of current during each sniff. Therefore, St. Jude Medical is collaborating with the hardware vender to implement eMICS algorithm in the next version of hardware.
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Bjernheim, Fina. "Livsmedelsäkerhet, hästnäringens wakeup-call? : Foder och livsmedeslproduktion i konkurrens om markresurser i Stockholms län- en framtidstudie med utgångspunkt i torkan 2018." Thesis, Stockholms universitet, Kulturgeografiska institutionen, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-185595.
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Antilahy, Herimpitia Tsilavina Chrystelle. "Développement et mise en œuvre d’un mécanisme « 4D-addressing Wakeup radio » pour la réduction de la consommation d’énergie dans les réseaux de capteurs sans fil." Thesis, La Réunion, 2018. http://www.theses.fr/2018LARE0038.
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Les réseaux de capteurs sans fil qui conviennent pour vaste domaine d’applications, constituent une solution prometteuse qui répond à toute exigence de surveillance continue. L’autonomie énergétique des nœuds constitue un facteur de vulnérabilité qui influe directement leur longévité et la capacité du réseau à assurer longuement la couverture d’une zone géographique d’intérêt. La gestion de consommation énergétique représente la seule approche pour accroître la durée de vie de ces réseaux et leur conférer une autonomie raisonnable. Des solutions logicielles proposées à travers les protocoles MAC, apportent des améliorations significatives à la minimisation de la dépense énergétique des nœuds. Elles permettent de réduire les périodes d’écoute du canal qui, représente l’opération la plus coûteuse en termes d’énergie dans le fonctionnement des nœuds de capteurs sans fil. Néanmoins, se limiter à ces solutions n’est pas suffisant pour garantir une longévité acceptable. La seule méthode pour optimiser la conservation d’énergie dans les RCSFs est de mettre chaque nœud constamment en mode faible puissance et d’utiliser un mécanisme de télé-réveil à travers des signaux de réveil. Cela implique, l’utilisation de circuits de réveil de faible consommation qui assurent la surveillance de canal et qui déclenchent le réveil des nœuds uniquement à chaque fois qu’événement d’intérêt se produit. Dans ce contexte, une quantité importante de travaux ont proposés l’utilisation d’un mécanisme d’adressage (adresses MAC ou d’autres informations binaires), pour permettre aux nœuds non concernés de retourner rapidement dans son état de sommeil. Cette démarche est intéressante, mais implique toutefois une dépense énergétique non négligeable, liée à la réception et au traitement des informations d’adresse au niveau de tous les nœuds. La solution la plus efficace énergétiquement serait l’utilisation d’une autre forme d’adresse. Cette thèse s’inscrit dans le contexte de minimisation de la consommation énergétique des RCSFs par la mise en œuvre d’un adressage qui permet aux nœuds de recevoir et de traiter les signaux de réveil, sans allumer leur module de communication principal. Il s’agit pour nous de supprimer la dépense énergétique liée à l’allumage du module RF et à la réception de paquets d’adresse, en se tournant vers l’exploitation de la durée des signaux de réveils. Notre solution se repose sur les caractéristiques matérielles du microcontrôleur (IRQ, Timer/Counter) des nœuds de capteurs. Elle permet de réduire les complexités liées aux conditionnements des signaux de réveils. Notre solution est implémentée sur un réseau de petite taille. Elle est évaluée expérimentalement et ses performances énergétiques sont comparées à celles d’un schéma classique de télé-réveil sans mécanisme d’adressage et à celles d’un schéma classique basé sur le duty-cyclingWireless sensor networks that are suitable for a wide range of applications, represent a promising solution that meets any requirement for continuous monitoring. The energy autonomy of sensor nodes constitutes a vulnerability factor that directly affects their longevity and the capacity of the network to ensure long coverage of the geographical area of interest. Energy consumption management is the only way to increase the lifespan of these networks and to give them a reasonable autonomy. Software solutions proposed through MAC protocols, bring significant improvements to the minimization of the energy expenditure of sensor nodes. They reduce the idle-listening periods which represents the most expensive operation in terms of energy, in the operation of the wireless sensor nodes. However, Focusing lonely on these solutions is not enough to guarantee acceptable longevity. The only way to optimize energy conservation in the WSN is to constantly put each node in low power mode and use a wakeup mechanism through wake-up signals. This involves the use of low-power wake-up circuits that provide channel monitoring, and trigger node wake-up only whenever event of interest occurs. In this context, a significant amount of work has proposed the use of an addressing mechanism (MAC addresses or other binary informations), to allow non-concerned nodes to quickly return to their sleep state. This approach is interesting, but involves a significant energy expenditure, related to address information’s reception and processing at all nodes. The most energy efficient solution would be the use of another type of address. This thesis is part of the context of minimizing the energy consumption of the WSN, using an addressing system that allows sensor nodes to receive and process the wake-up signals, without turning on their main communication module. It is to eliminate the energy expenditure related to the RF module’s activation and the reception of address packets, by exploiting wakeup signals duration. Our solution is based on the hardware characteristics of the microcontroller (IRQ, Timer/Counter) of sensor nodes. It reduces the complexities related to wakeup signals conditioning. Our solution is implemented on a small network. Its evaluations were done experimentally and its energy performance is compared to a conventional wake-up mechanism without addressing,and a conventional scheme based on duty-cycling
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Yang, Fei. "Reliable and time-constrained communication in wireless sensor networks." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00706211.
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Wireless Sensor Networks (WSNs) are composed of a large number of battery-powered sensor nodes that have the ability to sense the physical environment, compute the obtained information and communicate using the radio interfaces. Because sensor nodes are generally deployed on a large and wild area, they are powered by embedded battery. And it is difficult to change or recharge the battery, thus to reduce the energy consumption when sensors and protocols are designed is very important and can extend the lifetime of WSNs. So sensor nodes transmit packets with a lower transmission power (e.g. OdBm). With this transmission power, a packet can only be transmitted dozens of meters away. Therefore, when a sensor detects an event, a packet is sent in a multi-hop, ad-hoc manner (without fixed infrastructure and each sensor is able to relay the packet) to the sink (specific node which gathers information and reacts to the network situation). In this thesis, we first give an elaborate state of the art of WSNs. Then the impacts of duty-cycle and unreliable links or the performances of routing layer are analyzed. Based on the analytical results, we then propose three new simple yet effective methods to construct virtual coordinates under unreliable links in WSNs. By further taking the duty-cycle and real-time constraints into consideration we propose two cross-layer forwarding protocols which can have a greater delivery ratio and satisfy the deadline requirements. In order to have protocols for the WSNs that have dynamic topology, we then propose a robust forwarding protocol which can adapt its parameters when the topology changes. At last, we conclude this thesis and give some perspectives.
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Cicatelli, Giancarlo. "Time warying wake flow characteristics behind turbine blade wakes." Doctoral thesis, Universite Libre de Bruxelles, 1998. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212070.
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Nilsson, Karl. "Numerical computations of wind turbine wakes and wake interaction." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166658.
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When wind turbines are placed in farms, wake effects reduce the overall power production. Also, turbine loads are significantly increased since turbulence levels are high within the wake flow. Therefore, when planning for a wind farm, it is imperative to have an understanding of the flow conditions in the farm in order to estimate the power losses and to optimize the durability of the turbines to be selected for the farm. The possibilities granted by numerical modeling and the development of computational capabilities give an opportunity to study these flow conditions in detail, which has been the key focus of this doctoral work. The actuator disc method is used for predicting the power production of the Lillgrund wind farm. The results of the simulations are compared to measurements from the actual wind farm, which are found to be in very good agreement. However, some uncertainties are identified in the modeling of the turbine. One of the uncertainties is that a generic rotor is used in the Lillgrund case. In order to quantify the errors resulting from this generalization three different rotor configurations are simulated in various flow conditions. Generally, it can be stated that the choice of rotor configuration is not crucial if the intention of the simulations is to compute the mean wake characteristics subject to turbulent inflow. Another uncertainty is that the turbines in the Lillgrund case were simulated without a power controller. Therefore, a power controller is implemented and used in simulations. Generally, the controller reduces the thrust of the turbines, reduces turbulence intensity and increases velocity levels in the wake flow. However, the use of a controller was observed to have a small impact on the power production. The effects of using the technique of imposing pregenerated turbulence and a prescribed boundary layer in the simulation are analyzed in order to verify its applicability in very long domains. It is observed that close to the plane of imposed turbulence, the conditions are mainly dependent on the imposed turbulence while far downstream the turbulence, regardless of its initial characteristics, is in near equilibrium with the prescribed wind shear. The actuator line method is validated using measurements of the near wake behind the MEXICO rotor. The analysis is performed by comparing position, size and circulation of the tip vortices, as well as velocity distributions in the wake flow. The simulations and measurements are generally found to be in good agreement apart from the tip vortex size, which is greatly overestimated in the simulations.QC 20150519
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Smith, David Andrew Robert. "Pertubation of vortex wakes for amelioration of the vortex wake hazard." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406670.
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Öztürk, Esma. "WAKE INDUCED POWER DEFICIT ANALYSIS ON WIND TURBINES IN FORESTED MODERATELY COMPLEX TERRAIN USING SCADA DATA." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-346639.
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Over the last few decades, wind power has shown a continuous and significant developmentin the energy market globally. Having reached a certain level in both technologyand in dimensions, the role of optimizing wind turbines as well as wind farms hasbecome an additional aspect to future development and research. Since turbine wakescan cause significant power deficits within a farm, research in this area has the potentialfor large improvements in wind farm design. A wake is described as the downstream flow behind the rotor of an operating windturbine. The two main characteristics of wakes are a velocity (momentum) deficit and anincreased turbulence level. The velocity deficit behind the upwind turbine results in apower loss of the downstream turbines, whereas the higher turbulence causes additionalloads on the downstream turbines’ structures resulting in fatigue problems. The study of wakes is a complex topic, they are influenced by an interconnection of anumber of parameters like ambient wind speed and turbulence, atmospheric stabilityconditions (stable, unstable, and neutral), the turbines’ operational characteristics, andthe terrain properties. In order to assess the power deficits affected by wake interaction between turbines,an analysis can be realized by processing SCADA data of turbines in a wind farm. The collected data is treated by a comprehensive filtration process, excluding events of icing, curtailment, faults, etc. and by grouping into different atmospheric conditions, windspeed intervals and wind speed sectors. Finally, power deficit values, as a function ofwind direction, are calculated and quantified, and thereafter analyzed to assess the wakebehavior at different conditions for different cases.In this thesis, the wake-induced power deficit has been investigated in a specificstudy case for three pairs of two neighboring turbines in a forested moderately complexterrain using SCADA data. The production losses amounted between the range of 32% to 67% for the specific site with turbine spacing around 4D. The obtained results werepartially unsatisfactory, caused by the reasons of inaccurate wind direction values due toyaw misalignment issues and challenging separation into different stability conditions. Moreover, the power deficits showed a clear reduction of losses with increasing windspeed. A conclusion regarding the differences between stable and near neutral conditionscould not be determined from the data.
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Farr, Thomas D. "The effects of atmospheric and wake turbulence on wind turbines and wind turbine wakes." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807177/.
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Wind tunnel studies using model wind turbines have been used to investigate the effects and characteristics of neutral and unstable atmospheric boundary layers on their operation and wake behaviour. Wind turbine arrays have also been arranged to observe the effect of wake interaction. Single-point two-component and two-point single-component velocity measurements have been made using laser Doppler anemometry in conjunction with cold-wire anemometry to interrogate the modelled boundary layer. The manufacture and installation of a second traverse mechanism in the wind tunnel was necessary to perform the two-point measurements, along with the development of laboratory software for control and data analysis. In order to allow for measurements of turbine performance, a current sensor was developed so that correlations could be made between velocity and torque fluctuations. Investigation of larger arrays, up to 12 turbines, required the production of additional turbines and installation and subsequent integration of the associated control systems. Measurements made in the neutral flow conditions show that there is an increasing correlation between the upstream turbulence and torque fluctuations with proximity to the turbine, especially in the wake of another turbine where the flow is rapidly evolving. Two-point velocity measurements, with a lateral separation, have shown that there is little effect of the turbine on the correlation of the flow over the rotor disc. Analysis of data from this type of measurement also shows that in an array of four aligned turbines, the spatial structures reach an equilibrium state and are of larger size after the second turbine. Furthermore, the velocity-torque correlation magnitude decreases after the first turbine, but then increases with distance through the array owing to the increased correlation over the rotor disc, although not to the level observed for the first turbine. The turbulence approaching the first turbine behaves in a frozen-flow manner, but this is not true for the second and subsequent turbines, although the idea of convection time still applies. Measurements made in the modelled unstable atmospheric boundary layer show that the length and time scales are changed in the flow, in addition to the alteration of the profiles of mean velocity and Reynolds stresses. The increased turbulence caused by the convective boundary layer increases the rate of wake deficit recovery and does not result in the same spatial structures as the neutral conditions. Temperature effects are of secondary importance with regard to wake and turbine behaviour, with the main driving force behind the performance being the increased turbulence levels.
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Aronis, Stavros. "Effective Techniques for Stateless Model Checking." Doctoral thesis, Uppsala universitet, Avdelningen för datalogi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-333541.
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Stateless model checking is a technique for testing and verifying concurrent programs, based on exploring the different ways in which operations executed by the processes of a concurrent program can be scheduled. The goal of the technique is to expose all behaviours that can be a result of scheduling non-determinism. As the number of possible schedulings is huge, however, techniques that reduce the number of schedulings that must be explored to achieve verification have been developed. Dynamic partial order reduction (DPOR) is a prominent such technique. This dissertation presents a number of improvements to dynamic partial order reduction that significantly increase the effectiveness of stateless model checking. Central among these improvements are the Source and Optimal DPOR algorithms (and the theoretical framework behind them) and a technique that allows the observability of the interference of operations to be used in dynamic partial order reduction. Each of these techniques can exponentially decrease the number of schedulings that need to be explored to verify a concurrent program. The dissertation also presents a simple bounding technique that is compatible with DPOR algorithms and effective for finding bugs in concurrent programs, if the number of schedulings is too big to make full verification possible in a reasonable amount of time, even when the improved algorithms are used. All improvements have been implemented in Concuerror, a tool for applying stateless model checking to Erlang programs. In order to increase the effectiveness of the tool, the interference of the high-level operations of the Erlang/OTP implementation is examined, classified and precisely characterized. Aspects of the implementation of the tool are also described. Finally, a use case is presented, showing how Concuerror was used to find bugs and verify key correctness properties in repair techniques for the CORFU chain replication protocol.UPMARC
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Rodenhiser, Rebecca J. "An Ultrasonic Method for Aircraft Wake Vortex Detection." Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-theses/1004.
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"This thesis documents the experimental proof of concept study for an ultrasonic method of wake vortex detection. A new acoustic technique is utilized to measure the circulation produced in the wake of lift-generating aircraft. Ultrasonic signals are transmitted in a path around the wake vortex, and are used to determine the average in-line velocity component along the acoustic path. It is shown herein that this velocity component is directly proportional to the net circulation value within the acoustic path. This is the first study to take this methodology and implement it in a realistic airport setting. This project included constructing a prototype and conducting field tests to prove the validity of this technology in a realistic environment setting. During field tests an acoustic path enclosed the vorticity shed behind one wing of a Piper PA-28 aircraft. Fourteen initial test flights were conducted in calm atmospheric conditions, and results show circulation values measured are comparable in magnitude and direction to expected circulations generated by the Piper PA-28 aircraft. Additional testing in various atmospheric conditions revealed the scope of practice for such a measurement technology. This study demonstrates the validity of the acoustic method in detecting aircraft wake vortices. Future investigations and applications utilizing this technique are discussed within."
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Giacobello, Matteo. "Wake structure of a transversely rotating sphere at moderate Reynolds numbers." Online version, 2005. http://repository.unimelb.edu.au/10187/2840.
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Over the last century, the problem of a viscous flow past a sphere has received on-going attention due to its many engineering applications. These include combustion processes, sediment transport processes and atmospheric flow problems, where the sphere serves as a good model for more general bluff body particles. In these environments, particles may be subjected to both translational and rotational velocities. The objective of this study was to investigate the effect that sphere rotation, about an axis transverse to the freestream flow, has on the characteristics or the vertical wake structure and the forces exerted on the sphere. That was achieved by solving the time-dependant, incompressible Navier Stokes equations, using a highly accurate Fourier Chebyshev spectral collation method.
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Mohd, Raizamzamani Bin Md Zain. "Aerodynamic Instabilities of Twin Cables of Cable-stayed Bridge under Wind Actions." Kyoto University, 2018. http://hdl.handle.net/2433/235072.
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Acreman, D. M. "Galaxy wakes." Thesis, University of Birmingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403583.
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Subaschandar, N. "Turbulent Near Wake Behind An Infinitely Yawed Flat Plate." Thesis, Indian Institute of Science, 1995. http://hdl.handle.net/2005/146.
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Near wake is the region of wake flow just behind the trailing edge of the body where the flow is strongly influenced by the upstream flow conditions and also perhaps by the characteristics of the body. The present work is concerned with the study of the development of turbulent near wake behind an infinitely yawed flat plate. The turbulent near wake behind an infinitely yawed flat plate is the simplest of the three-dimensional turbulent near wake flows. The present study aims at providing a set of data on the turbulent near wake behind an infinitely yawed flat plate and also at understanding the development and structure of the near wake. Detailed measurements of mean and turbulent quantities have been made using 3-hole probe, X-wire and 3-wire hotwire probes.
Further an asymptotic analysis of the two-dimensional turbulent near wake flow has been formulated for the near wake behind an infinitely yawed flat plate. The feature that the near wake which is dominated by mixing of the oncoming turbulent boundary layer retains, to a large extent, the memory of the turbulent structure of the boundary layer, has been exploited to develop this analysis. The analysis leads to three regions of the wake flow (the inner near wake, the outer near wake and the far wake) for which the governing equations are derived. The matching conditions among these regions lead to logarithmic variations in both normal and longitudinal directions in the overlapping regions surrounding the inner wake. These features are validated by the present results.
A computational study involving seven well known turbulence models was also undertaken in order to assess the performance of the existing turbulence models in the prediction of the turbulent near wake behind an infinitely yawed flat plate. In this study all the seven models are implemented into a common flow solver code, thus eliminating the influence of grid size, initial conditions and different numerical schemes while making the comparison. This study shows that the K - e model performs better than other models in predicting the near wake behind an infinitely yawed flat plate.
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Nedic, Jovan. "Fractal-generated wakes." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12632.
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This thesis aims at getting a better understanding of the properties, scalings and similarities of turbulent axisymmetric wakes, as well as possible applications that arise from the information learnt. Over the last 60 years, axisymmetric wakes have been generated using axisymmetric bodies, such as disks, spheres and bodies of revolution, and key parameters such as the drag coefficient, shedding frequency and similarity and scaling of the wake width and velocity deficit have been documented and verified by numerous experimental and numerical studies. However, in this thesis the aim is to use asymmetric wake generators to generate the axisymmetric wakes and see if this has any effect on the results. These asymmetric wake generators are made up of a square plate and a number of fractal plates, where the perimeter of the plates can be increased by as much as 16 times that of the square. As well as increasing the perimeter, the irregularity, or fractal dimension, is also increased. It is found that the drag coefficient of the fractal plates is increased to beyond the values observed for regular polygons and a theory is presented that could explain this possible change in the drag coefficient, whereby the drag coefficient is the product of the volume of the wake and the dissipation of the turbulent kinetic energy within the wake. Wake profiles were taken over a moderate downstream distance of up to 50l, where l is the characteristic length of the plates, defined as the square root of the frontal area. Using the measured integral width of the wake directly, it was found that the volume of the wake decreased with increasing fractal dimension and iteration. Using these values, the similarity and scaling of the wake was carried out and a new high local Reynolds number scaling for turbulent axisymmetric wakes was discovered and for which the data from the fractal plates fit very well. The intensity of the vortex shedding is also shown to decrease with increasing perimeter and fractal dimension and it is found that the rate at which these vortices are shed is the same for all plates if the characteristic length is used to normalise the frequency. It is also discussed how the decrease in the energy of the vortex shedding is linked to the volume of the wake. Finally, the use of fractal geometries to manipulate the wake to reduce noise is also investigated, with emphasis placed on various aspects of an aircrafts wing.
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Rigas, Georgios. "Modelling of turbulent wakes." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/26590.
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The dynamics of the turbulent three-dimensional wake generated by an axisymmetric bluff body with blunt trailing edge are experimentally and theoretically investigated at a diameter based Reynolds number of 188,000. A detailed analysis of the base pressure measurements shows that the large scale structures of the turbulent three-dimensional wake retain the structure of the laminar instabilities observed in the transitional regimes, in a statistical sense. These persisting instabilities at the turbulent regime, are associated with spatial and temporal symmetry breaking, giving rise to spatial reflectional symmetry and quasi-periodic vortex shedding. The influence of turbulence recovers the lost temporal and spatial symmetries in the long-time average. It is shown that the turbulent spatial dynamics are reproduced by a simple stochastic model the deterministic part of which accounts for the spatial symmetry breaking and gives rise to steady large scale structures through a supercritical pitchfork bifurcation, and the stochastic part modelling in a phenomenological sense the turbulent fluctuations acting on the large scale structures. The axisymmetric body wake is further investigated when axisymmetric slot-jet zero-net-mass-flux forcing is applied on the rear base. Landau-like models that capture the weakly nonlinear interaction between the global vortex shedding mode and axisymmetric forcing are derived from the phase-averaged Navier-Stokes equations. The Landau-like models describe accurately the forced response by means of measured base pressure of the global vortex shedding mode. With the present analysis it is demonstrated that the concept of weakly nonlinear global modes can be extended to a fully turbulent flow, far from the critical bifurcation Reynolds number, and a general framework for the description of systems with broken symmetries---giving rise to global dynamics---and turbulent dynamics is provided. The novel results presented here advance the understanding of the dynamics of three-dimensional turbulent wakes and pave the way for turbulence prediction and control.
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Rodrigues, Vítor André Correia Gonçalves. "Desenvolvimento de um Smart Object : Wakeme Pillow." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/14776.
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Mestrado em Comunicação MultimédiaA proliferação dos smart&objects e wearables,no dia a dia dos consumidores, tem contribuído ativamente para a mudança de hábitos e comportamentos dos mesmos, dado que estes item como objectivo o bem estar e o incentivo à mudança de determinados factores dos consumidores. Daí este estudo parte de todo o conhecimento de alguns produtos tendo o intuito de criar uma solução que por uma lado possa enriquecer a experiência, oferecendo eficiência e por outro a capacidade de personalização do despertar. A investigação começa numa fase inicial por analisar a problemática relacionada com a temática e em estudo, realizando uma revisão bibliográfica de forma a compreender o contexto da temática abordada bem como reunir algumas características e especificidades de produtos disponíveis no mercado. O estudo empírico parte da realização de entrevistas a utilizadores e a um inquérito online, de forma a compreender as expectativas de funcionalidades para um novo produto mas por outro lado garantindo que as características mais utilizadas atualmente estejam integradas. O desenvolvimento do protótipo, uma almofada, envolve-o Utilizador em todas as fases cruciais da construção do mesmo, garantindo desta forma que o smart&object desenvolvido, cumpre com os requisitos de quem o vai utilizar. Com os resultados obtidos, demonstram se as potencialidades desta solução, mas sobretudo criam se várias oportunidades relevantes não só para o melhoramento do protótipo actual mas também diferentes áreas de investigação que não foram abordados neste estudo. !
The proliferation of smart objects and wearable’s, in the daily lives of consumers, has actively contributed to the changing habits and behaviors, as these aims the welfare and encourage them to move certain factors consumers. Hence this study part of all knowledge of some products with the aim of creating a solution that on the one hand can enrich the experience, offering efficiency and the other hand, improve the customization of awakening. The investigation begins at an early stage by analyzing the problems related to the topic under study, conducting a literature Review in order to understand the theme of context addressed and gather some product features and specifics available. The empirical study of conducting user interviews and an online questionnaire in order to understand the expectations of features! for a new product but on the other hand ensuring that the most used features are now integrated. The development of the prototype, a cushion, involves the user in all key stages of the construction of it, thus ensuring that the smart object developed, complies with the requirements of those who will use. With the results, we show the potential of this solution, but above al! it creates several important opportunities not only to improve the current prototype but also different research areas that were not covered in this study.
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Onur, Cagla. "Acoustic Tracking Of Ship Wakes." Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615656/index.pdf.
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Theories about ship wake structure, bubble dynamics, acoustic propagation through bubble clouds, backscattering and target strength of bubble clouds have been investigated and related Matlab simulations have been carried on. Research has been carried on algorithms for ship wake acoustic detection and tracking. Particle filter method has been simulated with Matlab for target tracking using wake echo measurements. Simulation results are promising.
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Rind, Elad. "Turbulent wakes in turbulent streams." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/193955/.
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Direct numerical simulation and wind tunnel experiments have been used to study the effects of free-stream turbulence on axisymmetric wakes. In both cases the wake was introduced to various turbulent streams having various levels of turbulence intensity and length scales. It was found that the presence of the free-stream turbulence changes the wake’s decay rate and does not allow self-similarity to occur (unless maybe very far downstream and way beyond the current measurements reached). Also, the free-stream turbulence was found to be causing a significant transformation in the turbulence structure inside the wake, where the latter was found to be gradually evolving towards the former. Last, the fact that the two approaches were modelling two different problems led to some differences in their results emphasising the importance of the flow structure around the wake generating body in shaping the far wake region.
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Parslew, Ben. "Simulating avian wingbeats and wakes." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/simulating-avian-wingbeats-and-wakes(038035c2-fe9e-4104-92dc-544579c7011b).html.
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Analytical models of avian flight have previously been used to predict mechanical and metabolic power consumption during cruise. These models are limited, in that they neglect details of wing kinematics, and model power by assuming a fixed or rotary wing (actuator disk) weight support mechanism. Theoretical methods that incorporate wing kinematics potentially offer more accurate predictions of power consumption by calculating instantaneous aerodynamic loads on the wing. However, the success of these models inherently depends on the availability and accuracy of experimental kinematic data. The predictive simulation approach offers an alternative strategy, whereby kinematics are neither neglected nor measured experimentally, but calculated as part of the solution procedure. This thesis describes the development of a predictive tool for simulating avian wingbeat kinematics and wakes. The tool is designed in a modular format, in order to be extensible for future research in the biomechanics community. The primary simulation module is an inverse dynamic avian wing model that predicts aerodynamic forces and mechanical power consumption for given wing kinematics. The model is constructed from previous experimental studies of avian wing biomechanics. Wing motion is defined through joint kinematic time histories, and aerodynamic forces are predicted using blade element momentum theory. Mechanical power consumption at the shoulder joint is derived from both aerodynamic and inertial torque components associated with the shoulder joint rotation rate. An optimisation module is developed to determine wing kinematics that generate aerodynamic loads for propulsion and weight support in given flight conditions, while minimising mechanical power consumption. For minimum power cruise, optimisation reveals numerous local minima solutions that exhibit large variations in wing kinematics. Validation of the model against wind tunnel data shows that optimised solutions capture qualitative trends in wing kinematics with varying cruise speed. Sensitivity analyses show that the model outputs are most affected by the defined maximum lift coefficient and wing length, whereby perturbations in these parameters lead to significant changes in the predicted amount of upstroke wing retraction. Optimised solutions for allometrically scaled bird models show only small differences in predicted advance ratio, which is consistent with field study observations. Accelerating and climbing flight solutions also show similar qualitative trends in wing kinematics to experimental measurements, including a reduction in stroke plane inclination for increasing acceleration or climb angle. The model predicts that both climb angle and climb speed should be greater for birds with more available instantaneous mechanical power. Simulations of the wake using a discrete vortex model capture fundamental features of the wake geometry that have been observed experimentally. Reconstruction of the velocity field shows that this method overpredicts induced velocity in retracting-wing wakes, and should therefore only be applied to extended-wing phases of an avian wingbeat.
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Beard, Christopher Aaron. "Wake." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955111/.
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Preface: A consideration of the New Sincerity movement in contemporary American poetics in the work of Tao Lin, Matt Hart, and Dorothea Lasky. Creative work: A three section book of poetry exploring elegy, form, and the intersection of strangeness and domesticity.
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Shea, Timothy David. "Wake /." Available to subscribers only, 2008. http://proquest.umi.com/pqdweb?did=1559850851&sid=16&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Zúñiga, Inestroza Manuel Alejandro. "Influência da turbulência atmosférica na esteira aerodinâmica de turbinas eólicas : estudo experimental em túnel de vento." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/165631.
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Aerogeradores, ou turbinas eólicas, são máquinas instaladas em grandes parques eólicos que convertem a energia cinética do vento em energia elétrica. A definição da separação e da interação entre máquinas é um fator fundamental de análise durante a fase de projeto, pois os chamados efeitos de esteira podem inviabilizar o desenvolvimento de um parque eólico. Em geral, a esteira de um aerogerador está caracterizada por um significativo déficit de velocidade e uma intensificação dos níveis de turbulência, o que ocasiona a diminuição da eficiência aerodinâmica e a redução da vida útil das máquinas localizadas a sotavento. Embora existam diferentes pesquisas destinadas à compreensão e previsão dos efeitos de esteira, o problema permanece como uma questão desafiadora que exige a adoção de ferramentas de alta precisão para sua identificação. Este trabalho apresenta uma metodologia experimental em túnel de vento, para a caracterização e avaliação do campo de escoamento na esteira aerodinâmica de um modelo reduzido, sob diferentes condições de escoamento incidente. Especificamente, investiga-se a influência da turbulência atmosférica para quatro perfis de escoamento: i) uniforme-suave; ii) uniforme-turbulento; iii) lei potencial com expoente α = 0,11; iv) lei potencial com expoente α = 0,23. Todos os casos foram conduzidos sob condições de estratificação neutra, e foi utilizado anemômetro de fio-quente para efetivar as medições dos perfis de velocidade média e intensidade da turbulência, em diferentes posições da esteira. Os resultados mostraram diferenças substanciais no comportamento dos perfis de esteira, em função dos níveis de turbulência incidente. Particularmente, observou-se que o incremento da turbulência atmosférica reduz o déficit de velocidade e promove uma maior mistura turbulenta, o que acelera a dissipação dos efeitos de esteira. Assim, a metodologia experimental em túnel de vento evidencia-se como uma importante ferramenta de análise que possibilita amplo espectro para a investigação, precisão e confiabilidade de projetos eólicos.Wind turbines are machines installed in large wind farms to convert the wind's kinetic energy into electrical power. For an optimal wind farm siting, it is necessary to take into account the interaction between wind turbine wakes. In general, wake effects are associated with velocity deficit and enhanced turbulence intensity. This may reduce the aerodynamic efficiency and lifetime of downwind turbines, making the project unfeasible. Several experimental and numerical studies have been conducted to unravel the behavior of wind turbine wakes under different inflow conditions. However, current wind farm siting tools are incapable of accurately predicting and assessing its effects. This document presents an experimental methodology in the wind tunnel to survey the influence of the atmospheric turbulence on the wake flow field of a wind turbine model. Specifically, four different flow conditions were investigated: i) uniform-laminar; ii) uniform-turbulent; iii) power law exponent α = 0.11; iv) power law exponent α = 0.23. All cases were developed under neutrally stratified conditions. Hot-wire anemometry was used to obtain high-resolution measurements of the mean velocity and turbulence intensity profiles at different downwind positions. Results show that different turbulence intensity levels of the incoming flow lead to substantial differences in the spatial distribution of the wakes. Particularly, higher ambient turbulence promotes a faster wake recovery and lower velocity deficit. In conclusion, the use of wind tunnel experiments is a trustworthy alternative that brings precision and reliability to wind projects.
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Haffner, Yann. "Manipulation of Three-Dimensional Turbulent Wakes for Aerodynamic Drag Reduction Mechanics of bluff body drag reduction during trnasient near wake reversals Unsteady Coanda Effect and Drag Reduction of a Turbulent Wake Manipulation of Three-Dimensional Asymmetries of a Turbulent Wake for Drag Reduction Large-Scale Asymmetries of a Turbulent Wake: Insights and Closed-Loop Control for Drag Reduction." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0006.
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Une combinaison de moyens passifs et actifs de contrôle d'écoulement est utilisée pour réduire la traînée aérodynamique produite par le sillage turbulent d'une géométrie simplifiée de véhicule à culot droit. Ces sillages sont caractérisés par deux aspects principaux : une traînée de pression importante liée à la séparation massive de l'écoulement, et des asymétries à grande échelle. Ces dernières, se manifestant sous forme de dynamique bimodale ou de brisure de symétrie permanente, contribuent pour environ 10% de la traînée de pression. L'étude des basculements de sillage transitoires en dynamique bimodale s'opérant au travers d'états symétriques du sillage permet d'isoler le mécanisme responsable de l'augmentation de traînée des états à brisure de symétrie. Une interaction et un couplage entre l'écoulement de recirculation issu d'un côté et la couche cisaillée opposée propre aux états à brisure de symétrie déclenche et amplifie les instabilités de couche cisaillée, ce qui conduit à une augmentation de l'écoulement d'entraînement et de la traînée. Il est montré que ce mécanisme est caractéristique des sillages de corps à culot droit.Une stratégie de contrôle actif de l'écoulement combinant des jets pulsés émis tangentiellement aux bords de fuite et de surfaces courbées miniatures affleurantes est utilisée pour réduire la traînée de pression de la géométrie. Le recollement de l'écoulement sur les surfaces courbées résulte en un rétreint fluidique du sillage se traduisant par une réduction de trainée jusqu'à 12%, indépendamment de l'asymétrie initiale du sillage, et est notablement influencé par l'échelle de temps caractéristique de l'instationnarité du forçage. Une combinaison minutieuse entre l'échelle de temps du forçage et la taille caractéristique des surfaces courbées permet d'exploiter tout le potentiel de réduction de traînée de cet effet Coanda instationnaire comme le montre un modèle simple d'écoulement permettant la mise en évidence de lois d'échelles caractérisant le phénomène. De plus, un forçage localisé selon certaines arêtes seulement permet d'interagir avec les asymétries à grande échelle du sillage et impacte de manière très différente la traînée selon l'équilibre su sillage non-forcé. La symétrisation du sillage résultant d'un forçage asymétrique permet une réduction de traînée d'environ 7% à coup énergétique réduit. Des éléments clefs sont donnés concernant l'adaptation de la localisation du contrôle pour une réduction de traînée en présence de différentes asymétries du sillage. Comme le changement d'équilibre global du sillage résulte de changements géométriques et d'écoulement mineurs, des stratégies de contrôle adaptives et robustes sont essentielles pour les applications dans l'industrie automobileCombination of passive and active flow control are used to experimentally reduce the aerodynamic drag produced by the turbulent wake past a simplified vehicle geometry with a blunt base. Such wakes are characterized by two main features: important pressure drag linked to the massive flow separation, and large-scale asymmetries. The latter,manifesting as bi-modal dynamics or permanent symmetry-breaking, are shown to contribute for around 10% of the pressure drag. The study of the transient wake reversais occurring in bi-modal dynamics though symmetric states enables to isolate the flow mechanism responsible for increased drag in symmetry-breaking states. An interaction and coupling between the recirculating flow from one side and the shear-layer from opposite side peculiar to symmetry-breaking states triggers shear-layer instabilities and their amplification leading to increased flow entrainment and drag.This mechanism is shown to be characteristic of the wakes of blunt bodies.An active flow control strategy combining tangential pulsed jets along the trailing-edges and small flush-mounted curved surfaces is used to reduce the pressure drag of the geometry. The flow reattachment and separation on thecurved surfaces results in a fluidic boat-tailing of the wake leading to drag reductions up to 12%, independently of the unforced large-scale asymmetry of the wake, and is noticeably influenced by the time-scale of unsteadiness of the forcing. Careful combination between forcing time-scale and size of the curved surfaces is needed to achieve ail thepotential of this unsteady Coanda effect in drag reduction as shown from a simple flow model providing scaling laws of the phenomenon. The model provided allows for an extension of the flow control mechanism to separated flows moregenerally. Furthermore, forcing along only selected edges enables to interact with the large-scale wake asymmetries and has very different impact on the drag depending on the unforced wake equilibrium. Symmetrisation of the wake through asymmetric forcing leads to 7% drag reduction at a reduced energetic cost. Key ingredients are provided to adapt forcing strategies for drag reduction in presence of various wake asymmetries. As global wake equilibrium changes result from minor geometric and flow conditions changes, adaptive and robust flow control strategies are essential for industrial automotive applications
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Zagorski, Marcus. "And drown the wakeful anguish of the soul." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/MQ43989.pdf.
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Paolizzo, Fabio. "VIVO : a wakeful instrument for collective musical embodiment." Thesis, University of Kent, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633665.
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A new category of music-related software is proposed, implemented and tested through creative practice. "Wakeful" musical instruments are those whose interaction listeners may understand as musical. The term "wakeful" means here "sign -bearing", in relation to the potential of computers and human beings to interact in terms of exchange of signs. Wakeful instruments may empower the users' capacity for the interpretation of digital music in terms of agency, cognition and communication. These users may experience a phenomenon of collective musical embodiment, producing a shared form of intelligence, extended and mediated by the computer, in music. VIVO is a computer-based interactive instrument of this type, whose development is part of the research . It represents salience of action in terms of energy and features video tracking for mapping quantity of motion to specific subranges of audio plug-ins parameters, dynamically. It includes an editor for stochastic scores and a single graphic interface to control any plug-in, while monitoring the users' and software agents' activity. The present case studies cross-confirm the results by an analysis of the users' and listeners' experiences and verbalisations and by an . identification of the musical coherence in the content, which the program generated.
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Nessler, Chase A. "Characterization of Internal Wake Generator at Low Reynolds Number with a Linear Cascade of Low Pressure Turbine Blades." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1270749309.
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Medici, Davide. "Wind turbine wakes : controland vortex shedding." Licentiate thesis, KTH, Mechanics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-361.
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Wind tunnel studies of the wake behind a model wind turbine have been made in order to get a better understanding of wake development as well as the possibility to predict the power output from downstream turbines working in the wake of an upstream one. Both two-component hot-wire anemometry as well as particle image velocimetry (PIV) have been used to map the flow field. All three velocity components were measured both for the turbine rotor normal to the oncoming flow as well as with the turbine inclined to the free stream direction (the yaw angle was varied from 0 to 30 degrees). The measurements showed, as expected, a wake rotation in the opposite direction to that of the turbine. A yawed turbine is found to clearly deflect the wake flow to the side showing the potential of controlling the wake position by yawing the turbine. The power output of a yawed turbine was found to vary nearly as the square of the cosine of the yaw angle. The possibility to use active wake control by yawing an upstream turbine was evaluated and was shown to have a potential to increase the power output significantly for certain configurations. An unexpected feature of the flow was that spectra from the time signals showed the appearance of a low frequency fluctuation both in the wake and in the flow outside. This fluctuation was found both with and without free stream turbulence and also with a yawed turbine. The non-dimensional frequency (Strouhal number) was independent of the free-stream velocity and turbulence level but increases with the yaw angle. However the low frequency fluctuations were only observed when the tip speed ratio (or equivalently the drag coefficient) was high. This is in agreement with the idea that the turbine shed structures as a bluff body. It is hypothesized that the observed meandering of wakes in field measurements is due to this shedding.
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Williams, Patrick Richard Giles. "Transition to turbulence in cylinder wakes." Thesis, University of Warwick, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487916.
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The laminar to turbulent transition of a circular cylinder wake was investigated experimentally, examining a range of features leading to an aperiodic three-dimensional structure and a possible mechanism causing the route to turbulence was postulated. Following the analysis of the Stuart-Landau equations defining a Hopf bifurcation at the primary instability, a new relationship between the Strouhal number (St) and the Reynolds number (Re) was formed, providing agreement with a range of equations defined experimentally. The St-Re relationship was examined for a range of mechanisms modifying the cylinder's end termination and a variation in the free-stream turbulence level. It was ascertained that the end termination had a direct influence on the wake dynamics, producing a change in the wake structure leading to the possibility of parallel vortex shedding and also a modification of the critical Reynolds number. Following the introduction of specific boundary conditions, it was ascertained that the critical Reynolds number could be delayed to a value of 192. Although an increased level of free-stream turbulence demonstrated a reduction in the critical Reynolds number for all end conditions imposed. Within a small range of Reynolds numbers prior to transition, random wake irregularities \vere identified within the laminar velocity signal. These were ascertained to be generated from finite three-dimensional perturbations within the wake, introduced by the method of end termination and the increased level of free-stream turbulence. Following the analysis of these intermittent aperiodic bursts within the transition regime, they were demonstrated to relate to the occurrence of turbulent flow prior to transition. This produced an alternate switching between the two states relating to the hysteretic bifurcation to the mode A wake structure. A possible transition mechanism causing a route to turbulence was considered, relating to the statistics of these intermittent bursts. Leading to a proposal that the cylinder wake transition undergoes a noise induced dynamic forcing, which is consistent with on-off intermittency.
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Potylitsin, Pavel G. "Columnar vortex stability in island wakes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ53839.pdf.
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Ivanell, Stefan S. A. "Numerical computations of wind turbine wakes." Licentiate thesis, Stockholm : Royal Institute of Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-316.
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Drake, Nick. "Wakes and dynamics of galaxy clusters." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326792.
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Agoropoulos, D. "Interactions between wakes and boundary layers." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372874.
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Bereketab, Semere. "Complex Equilibrium of Laterally Curved Wakes." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35806.
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Turbulent wakes generated from an aircraft or submarine vehicles has been of main interest to researchers due to the broad band noise associated with such wakes. One such case is the noise generated by spiral vortices shed of from one blade interacting with another oncoming blade of helicopter rotor. Consequently, researchers have been trying to understand the basic physics and evolution of such wakes. Although there has been numerous studies done on plane wakes, there has been little research being done on laterally curved wakes.
Single and two-point velocity measurements were taken on a plane and laterally curved turbulent wakes to understand the evolution and effect of lateral curvature into the far wake region. The analyses provide useful information in modeling curved or spiral wakes such as turbulence field surrounding tip vortices shed from a wing. In order to achieve our objectives, the Virginia Tech 3’ x 2’ subsonic wind tunnel was used to take velocity measurements of toroidal ring model and a straight cylinder as a control case. Velocity measurements were done using four sensor hot-wire anemometers, to obtain all mean velocity, Reynolds stress, triple product components of the turbulence field. Single point, spectra and two-point measurements of the wakes were performed throughout the development into the far wake region. The single point results reveal the universality of the mean axial velocity, however the Reynolds stresses and triple products were not universal illustrating that the turbulence field has its own length and velocity scales different from that of the mean flow. The effect of lateral curvature is mainly evidenced in the early development of the curved ring wake. The turbulent energy budget reveals similar trend for both wakes and plane wake achieves approximate equilibrium. The spectra result reveals for the plane wake that self-preservation is achieved for all scales of motion, while the ring wake does not achieve such a state. While the longitudinal correlations of both wakes are similar in form, in general difference in form and orientation prevailed over all indicating the difference in the turbulent structure of both wakes. Linear stochastic estimation reveals the presence of spanwise and double-roller eddy structures in the plane wake and only spanwise eddies were detected for the ring wake.Master of Science
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Ivanell, Stefan S. A. "Numerical computations of wind turbine wakes." Doctoral thesis, Stockholm : Royal Institute of Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9916.
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Shi, Shaoping. "Large-eddy simulation of ship wakes." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2217.
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Thesis (Ph. D.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xv, 211 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 200-211).
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Boldrini, Lucia. "In Dante's wake : the Dantean poetics of 'Finnegans Wake'." Thesis, University of Leicester, 1996. http://hdl.handle.net/2381/35090.
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The thesis investigates how the theories of linguistic and literary composition of Dante's treatises and the poetics of ineffability of the Divine Comedy may be seen to provide the basis for (one of) the poetics of Joyce's Finnegans Wake. The polysemy of Joyce's last novel relies on Dante's literary-exegetical model of the four levels of meaning at the same time as it challenges it so as to show both its inadequacy for the modern literary work and, conversely, how its failings can be turned to the writer's advantage in the production of an original text. The multilingual idiom of the Wake draws from, at the same time as it reshapes, Dante's conception of the history of language and his theory of an illustrious poetic language, and the thesis shows how Joyce exploits these two aspects, turning them into a narrative framework for several episodes of the Wake and thematising their features in order to explore the function of character-roles in connection with the processes of artistic creation. Finally, Joyce's reliance on a pliable language for his evocation of the unfathomable dimension of the "nocturnal world" and of the unconscious is shown to be comparable to the poetics of ineffability that informs Dante's "vision" in the Divine Comedy. In this context, the thesis looks at such issues as silence, vowels / vocalisation, and the use of geometry to express the ineffable and / or the unspeakable. Joyce's use of Dante's works thus involves a constant reflection on the processes of writing and of literary composition as well as on the relationship between a modern writer and his sources, and the intertextual practice of the Wake is shown to be part of the "poetics in progress" that Joyce has been elaborating from his earliest to his last publication.
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Chan, Fung Chi. "Investigation of water wakes in shallow environment /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202005%20CHANFC.
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Fransson, Jens H. M. "Flow control of boundary lagers and wakes." Doctoral thesis, KTH, Mekanik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3664.
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Both experimental and theoretical studies have beenconsidered on flat plate boundary layers as well as on wakesbehind porous cylinders. The main thread in this work iscontrol, which is applied passively and actively on boundarylayers in order to inhibit or postpone transition toturbulence; and actively through the cylinder surface in orderto effect the wakecharacteristics. An experimental set-up for the generation of the asymptoticsuction boundary layer (ASBL) has been constructed. This studyis the first, ever, that report a boundary layer flow ofconstant boundary layer thickness over a distance of 2 metres.Experimental measurements in the evolution region, from theBlasius boundary layer (BBL) to the ASBL, as well as in theASBL are in excellent agreement with boundary layer analysis.The stability of the ASBL has experimentally been tested, bothto Tollmien-Schlichting waves as well as to free streamturbulence (FST), for relatively low Reynolds numbers (Re). For the former disturbances good agreement is foundfor the streamwise amplitude profiles and the phase velocitywhen compared with linear spatial stability theory. However,the energy decay factor predicted by theory is slightlyoverestimated compared to the experimental findings. The latterdisturbances are known to engender streamwise elongated regionsof high and low speeds of fluid, denoted streaks, in a BBL.This type of spanwise structures have been shown to appear inthe ASBL as well, with the same spanwise wavelength as in theBBL, despite the fact that the boundary layer thickness issubstantially reduced in the ASBL case. The spanwise wavenumberof the optimal perturbation in the ASBL has been calculated andis β = 0.53, when normalized with the displacementthickness. The spanwise scale of the streaks decreases withincreasing turbulence intensity (Tu) and approaches the scale given by optimalperturbation theory. This has been shown for the BBL case aswell. The initial energy growth of FST induced disturbances hasexperimentally been found to grow linearly as Tu2Rexin the BBL, the transitional Reynolds numberto vary as Tu-2, and the intermittency function to have a relativelywell-defined distribution, valid for all Tu. The wake behind a porous cylinder subject to continuoussuction or blowing has been studied, where amongst other thingsthe Strouhal number (St) has been shown to increase strongly with suction,namely, up to 50% for a suction rate of 2.5% of the free streamvelocity. In contrast, blowing shows a decrease ofStof around 25% for a blowing rate of 5% of the freestream velocity in the considered Reynolds number range. Keywords:Laminar-turbulent transition, asymptoticsuction boundary layer, free stream turbulence,Tollmien-Schlichting wave, stability, flow control, cylinderwake.QC 20100607
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Rødningsby, Anders. "Multitarget Multisensor Trackingin the Presence of Wakes." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for teknisk kybernetikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11913.
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TARGET tracking is an essential requirement for surveillance and control systems to interpret the environment. This environment may contain multiple targets, and the environmental information may be obtained by multiple sensors in a multitarget multisensor tracking system. In this thesis we focus on targets which, in addition to reflecting signals themselves, also have a trailing path behind them, called a wake. This wake causes additional measurements to those originating from the target. When the measurements are processed, the estimated track can be misled and sometimes lose the real target because of the wake. This problem becomes even more severe in multitarget environments where targets are operating close to each other in the presence of wakes. In this thesis a probabilistic model is developed which reflects the probability that a false measurement originates from the wake behind a target. This wake model is integrated in the probabilistic data association filter (PDAF) to improve the track continuity for tracking single targets. The modified PDAF is further extended to handle multiple targets in the presence of wakes by using a probabilistic wake model for each of the targets in the multitarget environment that has a wake behind it. These single wake models are combined to form a joint wake model which augments the joint probabilistic data association filter (JPDAF) for both coupled and decoupled filtering. The wake-originated measurements may also cause confusion in the track initiation. To prevent this problem, a clustering method is proposed based on morphological operators which allows tracks to be initialized based on two-point differencing of the cluster centroids from succeeding scans. The modified PDAF is tested on data of a real scuba diver with an open breathing system. In this case the air bubbles produced by the diver form a wake which extends far behind the diver. The experiment showed that the above modifications of the PDAF improved the track continuity significantly. Finally, a relatively extensive simulation, based on real scuba diver data, is presented. Four different multitarget multisensor tracking scenarios are simulated, considering two targets with wakes that are: 1. Crossing each other. 2. Moving in parallel to each other. 3. One following after another. 4. Meeting and then passing each other. The results of these simulation scenarios show that the presented modifications improve the tracking performance, and the probability of lost tracks is significantly reduced. The targets are observed by two sensors, and it is shown that tracks estimated in a centralized fusion configuration are better than the local tracks estimated using data from individual sensors only. It is also shown that applying the wake model to targets that do not generate a wake, yields almost no deterioration of the tracking performance.
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Blomhoff, Hedda Paulsen. "An experimental investigation of wind turbine wakes." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18412.
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In the present study the wake behind a scaled; Horizontal Axis Wind Turbine (HAWT) has been investigated. The experiments were performed at the Department of Energy and Process Engineering, at the Norwegian University of Science and Technology, NTNU. The turbine was installed in the wind tunnel at the department and measurements were performed at several distances behind the turbine to examine the development of the flow. A five-hole pitot probe was applied as measurement instrument. The instrument made it possible to calculate both size and direction of the velocity components.Through the experiments, characteristic curves of the turbine and grid measurements over the cross-section of the wind tunnel, were obtained. The power and thrust coefficients were measured against the local velocity ratio at the tip of the blade, the 'Tip Speed Ratio' (TSR). The power coefficient had a peak at TSR=5,5. The maximum value at this point was 0,45. The highest measured thrust coefficient was 1,15, achieved at TSR=10,3. During the experiments the turbine operated at optimal conditions, at the highest obtained power coefficient.Measurements behind the turbine found that the axial velocity distribution developed as expected. A significant velocity deficit was measured in the wake behind the turbine, which gradually decreased with increased distance to the turbine. Due to the presence of the hub and tower, the middle of the wake was characterized by disturbances. Moving down the wake the profile got more symmetric. The tangential profile was almost symmetric about the origin, right behind the turbine, but drifted to the left at increased distance downstream. Contribution from the tangential components were gradually reduced further down the wake.The tower shadow moved with the rotation of the wake, in clockwise direction, as a region of lower velocities than the prevailing wake. Further downstream the tower shadow merged with the surrounding wake.The rotational axis relocated in the wake behind the turbine. Downstream, measurements showed that the center of rotation moved to the left of the origin. To investigate if the tower was responsible for the experienced downshift, an additional tower was mounted to the tunnel roof, above the turbine. The additional tower created symmetry about the hub and gave a symmetric development of the flow field. Thus, it was concluded that the tower was responsible for the relocation of the rotational axis.
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Emerson, Benjamin L. "Dynamical characteristics of reacting bluff body wakes." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49073.
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Combustion instability plagues the combustion community in a wide range of applications. This un-solved problem is especially prevalent and expensive in aerospace propulsion and ground power generation. The challenges associated with understanding and predicting combustion instability lie in the flame response to the acoustic field. One of the more complicated flame response mechanisms is the velocity coupled flame response, where the flame responds dynamically to the acoustic velocity as well as the vortically induced velocity field excited by the acoustics. This vortically induced, or hydrodynamic, velocity field holds critical importance to the flame response but is computationally expensive to predict, often requiring high fidelity CFD computations. Furthermore, its behavior can be a strong function of the numerous flow parameters that change over the operability map of a combustor.
This research focuses on a nominally two dimensional bluff body combustor, which has rich hydrodynamic stability behavior with a manageable number of stability parameters. The work focuses first on experimentally characterizing the dynamical flow and flame behavior. Next, the research shifts focus toward hydrodynamic stability theory, using it to explain the physical phenomena observed in the experimental work. Additionally, the hydrodynamic stability work shows how the use of simple, model analysis can identify the important stability parameters and elucidate their governing physical roles. Finally, the research explores the forced response of the flow and flame while systematically varying the underlying hydrodynamic stability characteristics. In the case of longitudinal combustion instability of highly preheated bluff body combustors, it shows that conditions where an acoustic mode frequency equals the hydrodynamic global mode frequency are not especially dangerous from a combustion instability standpoint, and may actually have a reduced heat release response. This demonstrates the very non-intuitive role that the natural hydrodynamic flow stability plays in the forced heat release response of the flame.
For the fluid mechanics community, this work contributes to the detailed understanding of both unforced and forced bluff body combustor dynamics, and shows how each is influenced by the underlying hydrodynamics. In particular, it emphasizes the role of the density-shear layer offset, and shows how its extreme sensitivity leads to complicated flow dynamics. For the flow-combustor community as a whole, the work reviews a pre-existing method to obtain the important flow stability parameters, and demonstrates a novel way to link those parameters to the governing flow physics. For the combustion instability community, this thesis emphasizes the importance of the hydrodynamic stability characteristics of the flow, and concludes by offering a paradigm for consideration of the hydrodynamics in a combustion instability problem.
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Moroney, Gerard. "Internal wave wakes in stratified shear flows." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399177.
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Eriksson, Ola. "Numerical Computations of Wakes Behind Wind Farms." Licentiate thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-255859.
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More and larger wind farms are planned offshore. As the most suitable build sites are limited wind farms will be constructed near to each other in so called wind farm clusters. Behind the wind turbines in these farms there is a disrupted flow of air called a wake that is characterized by reduced wind speed and increased turbulence. These individual turbine wakes combine to form a farm wake that can travel a long distance. In wind farm clusters farm to farm interaction will occur, i.e. the long distance wake from one wind farm will impact the wind conditions for other farms in the surrounding area. The thesis contains numerical studies of these long distance wakes. In this study Large Eddy Simulations (LES) using an Actuator Disc method (ACD) are used. A prescribed boundary layer is used where the wind shear is introduced using body forces. The turbulence, based on the Mann model, is introduced as fluctuating body forces upstream of the farm. A neutral atmosphere is assumed. The applied method has earlier been used for studies of wake effects inside farms but not for the longer distances needed for farm to farm interaction. Numerical studies are performed to get better knowledge about the use of this model for long distance wakes. The first study compares the simulation results with measurements behind an existing farm. Three parameter studies are thereafter setup to analyze how to best use the model. The first parameter study examines numerical and physical parameters in the model. The second one looks at the extension of the domain and turbulence as well as the characteristics of the flow far downstream. The third one gathers information on the downstream development of turbulence with different combinations of wind shear and turbulence level. The impact of placing the turbines at different distances from the turbulence plane is also studied. Finally a second study of an existing wind farm is performed and compared with a mesoscale model. The model is shown to be relevant also for studies of long distance wakes. Combining LES with a mesoscale model can be of interest.
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Karlsson, Christian. "Regression Models of 3D Wakes for Propellers." Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik (from 2013), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-67785.
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In this work, regression models for the wake field entering a propeller at certain axial andnominal position have been proposed. Wakes are non-uniform flows following a body immersedin a viscous fluid. We have proposed models for the axial and tangential velocity distribution asfunctions of ship hull and propeller measures. The regression models were modelled using Fourierseries and parameter estimations based on skewed-Gaussian and sine functions. The wake fieldis an important parameter in propeller design. The regression models are based on experimentaldata provided by the Rolls-Royce Hydrodynamic Research Center in Kristinehamn. Also we havestudied the flow in the axial velocity distribution in the propeller plane using the coherent structurecoloring method. The coherent structure coloring is used to study coherent patterns by looking atfluid particle kinematics. Using this type of analysis, we observed that the velocity distributionbehaves kinematically similar in the different regions of the wake distribution, which according tothe coherent structure coloring indicate coherence.I det här arbetet, har regressionsmodeller för medströmsfältet in i en propeller vid viss axielloch nominell position utvecklats. Medströmsfältet är ojämn strömning efter en kropp nedsänkt i enviskös vätska. Vi har föreslagit modeller för axiell och tangentiell hastighetsfördelning som funktionerför fartygsskrov-och propeller-parametrar. Regressionsmodellerna modellerades med hjälpav Fourier-serier och parameterskattning baserade på skeva Gaussfördelningar och sinusfunktioner.Medströmsfältet är en viktig parameter i propeller design. Regressionsmodellerna är baserade påexperimentella data från Rolls-Royces Hydrodynamiska Forskningscenter i Kristinehamn. Vi harockså studerat flödet i axialhastighetsfördelningen i propellplanet med hjälp av den koherenta struktureringsfärgmetoden.Den koherenta struktureringsfärgmetoden används för att studera koherentamönster genom att titta på vätskepartikelkinematik. Med hjälp av denna typ av analys observeradevi att hastighetsfördelningen uppför sig kinematiskt lika i de olika regionerna i medströmsfältet,vilket enligt koherenta strukturfärgmetoden indikerar koherens.
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Costis, Christopher E. "Separation and wakes over three-dimensional bodies." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54745.
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The laminar flow over a prolate spheroid was investigated via flow visualization and Laser-Doppler Velocimetry. Experiments were conducted in a water tunnel and the flow was visualized with dyes. The measurement of three-dimensional boundary layers required a special design of the laser optics. Attention was focused in the neighborhood of three-dimensional separation.
The Vortex-Lattice method was employed to calculate the inviscid flow and the development of separated vortex sheets over a prolate spheroid. An approximate-method based on the assumption of local similarity was used to solve the boundary layer equations and calculate the line of open separation. A condition of vortex shedding along separation is proposed. The two schemes, viscous and inviscid, interact through the line of separation which is allowed to displace as the wake grows. Results are compared with flow visualization data for laminar separation and pressure data for turbulent separation.Ph. D.