Дисертації з теми "Turbulence of the environment"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Turbulence of the environment.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Turbulence of the environment".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Read, Simon. "Transition to turbulence in a turbomachinery environment." Thesis, Cranfield University, 1997. http://dspace.lib.cranfield.ac.uk/handle/1826/10509.
Повний текст джерелаАнотація:
This thesis aims to contribute to the understanding of transitional flows in
the blade boundary layers of axial compressors. Two experiments are described,
the first examining in detail the transitional boundary layer on a
simulated controlled-diffusion blade and the second surveying the mid-height
flowfield in an embedded
stage of a low-speed axial compressor. The velocity
distribution on the simulated blade is identical to the Velocity distribution on
the suction surface of the blades in the axial compressor.
At 2
Reynolds numbers and 3 levels of freestream turbulence, a single hot
wire was used to conduct a boundary layer survey on a simulated controlled-diffusion
blade.
Integral parameters of the boundary layers are explored to
dene the
length and nature of transition.
At low Reynolds number there is a separated or near separated region at the
leading edge which does not lead to turbulence. Transition covers a length of
approximately 20% of the blade chord, starting between 20% and 30% chord.
The
position of transition is strongly influenced by the level of freestream
turbulence. Most of the transition process occurs within the decelerating flow
region which exists from 20% of the chord. At high Reynolds number, a leading
edge separation bubble leads to transition within 2% of the blade chord.
Abu-Ghannam & Shaws correlation for the start and length of transition
was found to
predict the start of transition well for attached flows, but could
not be relied
upon for separated flows. It is apparent that the correlation was
not
designed for the very strong Velocity gradients in the leading edge region,
and
probably not for separated flow. _
Three flow conditions in the axial compressor were used: design speed, peak
efficiency, low Reynolds number at peak efficiency (the machine was slowed
to
one-quarter speed) and design speed near the stall. Using hot wires at
mid-height, axial and circumferential velocity and turbulence information was
obtained.
Wakes and structure within wakes are visible in the turbulence and Reynolds
stress distributions. The wakes of more than one upstream blade row are visible;
the region where two wakes intersect gives some information about interaction
between a stator blade Wake and a rotor blade boundary layer. Some
information is available about the length scale 'distribution inside and outside
wakes.
Secondary flow in the axial-circumferential plane shows motion within
wakes and a vortex in the near-stall flowfield, shed preferentially at one point
in the
blade-passing cycle.
2
Westerberg, Mats. "Managing in turbulence : an empirical study of small firms operating in a turbulent environment." Doctoral thesis, Luleå tekniska universitet, Innovation och Design, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18430.
Повний текст джерелаАнотація:
This thesis deals with how small firms, and especially their CEOs, manage their situation in times of high environmental turbulence. Eight firms have been chosen for the empirical study based on their performance and the CEO’s self-efficacy and tolerance for ambiguity. Interviews with the CEO and employees at each firm, observations, gathering of annual reports and a questionnaire are the principal means used for data collection. The results show that the CEO is very influential at all firms, regardless how the company performs. A CEO that tolerate uncertainty is better able to engage in enterprising, which seems necessary in turbulence. A CEO with high self- efficacy is generally able to control his firms destiny by having access to the appropriate resources for the task (e.g. own ability and network). However, too high self-efficacy could be a sign of dysfunctional overconfidence, where the CEO dismiss relevant information from actors around him.Godkänd; 1998; 20061120 (haneit)
3
Bosco, Carol. "The Relationship Between Environmental Turbulence, Workforce Agility and Patient Outcomes." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195013.
Повний текст джерелаАнотація:
For years heath care workers have been dealing with environmental changes which have created turbulent, complex work environments. Turbulence has been considered a negative phenomenon. However Workforce Agility may be a positive response to Environmental Turbulence. Other disciplines are familiar with the term Turbulence and Workforce Agility but there is little research available on this concept despite the impact that they may have on patient outcomes.The purpose of this research was to identify the relationship between Environmental Turbulence, Workforce Agility and Patient Outcomes through the examination of four alternative theoretical models.This research was conducted using secondary analysis of the IMPACT data set (Verran, Effken & Lamb, 2001-2004). The data were reanalyzed in order to answer different questions than the primary study. Causal modeling with path analysis and regression analysis was conducted to answer the research questions. Three questions included the use of either a moderator variable or mediator variable.The setting for the IMPACT Study was acute care hospitals in the Southwestern region of the United States. For the IMPACT study, the sample consisted of patient care units from teaching and non-teaching hospitals. Subjects consisted of staff members who were employed on the patient care units.Data collected from the Registered Nurses were used for the secondary analysis because this research was interested in looking primarily at the nursing unit. The total RN staff assigned to patient care units who responded to the questionnaires was N=454. The total number of patients who responded to the survey was N=1179.In summary, the unit characteristics that were found to be Antecedents to ET were the sub-composites of Team and Complexity. Proxy variables, Collaborative Culture Agility and Experiential Agility, were successfully formed as a composite for WFA and were tested with the primary data. No mediators or moderators were shown; however, main effects of WFA and ET did have an impact on patient outcomes.
4
Wall, Dylan Joseph. "Anisotropic Turbulence Models for Wakes in an Active Ocean Environment." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104162.
Повний текст джерелаАнотація:
A set of second-moment closure turbulence models are implemented for the study of wake evolution in an oceanic environment. The effects of density stratification are considered, and the models are validated against laboratory experiments mimicking the stratified ocean environment, and against previous experimental study of wakes subjected to a density stratification. The turbulence models are found to reproduce a number of important behaviors which differentiate stratified wakes from those in a homogeneous environment, including the appropriate decay rates in turbulence quantities, buoyant suppression of turbulence length scales, and canonical stages in wake evolution. The existence of background turbulence is considered both through the introduction of production terms to the turbulence model equations and the replication of scale-resolved simulations of wakes embedded in turbulence. It is found that the freestream turbulence causes accelerated wake growth and faster decay of wake momentum. Wakes are then simulated at a variety of Re and Fr representative of full-scale vehicles operating in an ocean environment, to downstream distances several orders of magnitude greater than existing RANS studies. The models are used to make some general predictions concerning the dependence of late-wake behavior on these parameters, and specific insights into expected behavior are gained. The wake turbulence is classified using "fossil turbulence" and stratification strength criteria from the literature. In keeping with experimentally observed behavior, the stratification is predicted to increase wake persistence. It is also predicted that, regardless of initial Re or F r, the wake turbulence quickly becomes a mixture of overturning eddies and internal waves. It is found that the high Re wakes eventually become strongly affected by the stratification, and enter the strongly-stratified or LAST regime. Additional model improvements are proposed based on the predicted late wake behavior.Doctor of Philosophy
A set of advanced turbulence models are implemented and used to study ship wakes in an oceanic environment. The flows in the ocean are subject to a density stratification due to changes in temperature and salinity; the associated effects are included in the turbulence models. The models are validated against laboratory experiments mimicking the stratified ocean environment, and against previous experimental study of wakes subjected to a density stratification. The turbulence models are found to reproduce a number of important behaviors expected under such conditions based on experimental study. Additional modifications are made to the models to include the effect of pre-existing freestream turbulence. Wakes are then simulated under conditions representative of full-scale vehicles operating in an ocean environment. The models are used to make some general predictions concerning late-wake behavior. Specific insights into expected behavior are gained. The wake turbulence is classified using ``fossil turbulence'' and stratification strength criteria from the literature. In keeping with experimentally observed behavior, the stratification is predicted to increase wake persistence. Additional model improvements are proposed based on the predicted late wake behavior.
5
Choksi, Kashyap Nalin. "A Strategic Approach to Managing Turbulence in the Normative Environment." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29508.
Повний текст джерелаАнотація:
One of the central areas of focus in organizational theory that has been of particular interest is the organization-environment interface. While various theories have made vital contributions to the study of organization-environment relations, their emphasis on organization adaptation is varied. However, research and practice have amply demonstrated that organizations do not exist in a vacuum; that if an organization is to survive and meet its goals, it has to adapt to or somehow make accommodations with its cognitive and normative environment.
This study explores the issue of an organization trying to adapt to its normative environment by deeply examining the situation of a national private nonprofit organization, with ties to the land-grant university and college system, which found itself in the midst of a turbulent environment. Specifically, the study discusses how that nonprofit was affected by this turbulence when it accepted funding from the nation's largest tobacco company to develop and implement a tobacco prevention program. The act of this nonprofit accepting funds from the tobacco corporation caused challenges in internal management, worsened relations with some of its core constituencies, and fomented discord within leading non-profit organizations. The notion of turbulence, the mechanism of isomorphism as espoused by the new institutionalists, and the role of agency was explored, supplemented by a strategic approach that included components of contracting standards that organizations could adapt to attain congruency with elements of their turbulent normative environment. In particular, this strategic approach utilized a framework borrowed from research conducted by Oliver (1991), emphasizing strategies of Defiance, Manipulation and Avoidance. What this study offers is a strategic approach to help non-profit organizations when they partner with a controversial source of funding, especially in cases where they are faced with these kinds of management dilemmas.Ph. D.
6
Genin, Franklin Marie. "Study of compressible turbulent flows in supersonic environment by large-eddy simulation." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28085.
Повний текст джерелаАнотація:
Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Menon, Suresh; Committee Member: Ruffin, Stephen; Committee Member: Sankar, Lakshmi; Committee Member: Seitzman, Jerry; Committee Member: Stoesser, Thorsten
7
Cerda, Rodrigo Andrés Miranda. "Synchronization in intermittent turbulence and spatiotemporal chaos in the solar-terrestrial environment." Instituto Nacional de Pesquisas Espaciais, 2010. http://urlib.net/sid.inpe.br/mtc-m19@80/2010/04.29.12.38.
Повний текст джерелаАнотація:
Neste trabalho de Tese analisamos a sincronização devido a interações entre escalas em observações de turbulência intermitente e em simulações numéricas de intermitência espaço-temporal em fluidos neutros e plasmas espaciais. Este estudo é feito em duas partes. Primeiro, aplicamos duas técnicas não-lineares, curtose e índice de coerência de fase, para medir o grau de não-Gaussianidade e sincronização de fase da turbulência de campo magnético intermitente observada no vento solar, na fotosfera solar e no solo, e da turbulência atmosférica intermitente observada na copa da floresta Amazônica. Depois, analisamos um modelo espacialmente estendido de ondas não-lineares em fluidos e plasmas para identificar estruturas coerentes transientes, responsáveis pela intermitência \texteit{on-off} espaço-temporal observada nas séries temporais da energia. Quantificamos o grau de sincronização de amplitude e fase usando a entropia espectral de potência e de fase no regime logo depois da transição para caos espaço-temporal. Os resultados observacionais e teóricos indicam que a sincronízação de amplitude e fase pode ser a origem da intermitência na turbulência completamente desenvolvida no ambiente solar-terrestre.In this work we analyze synchronization due to multiscale interactions in observations of intermittent turbulence and numerical simulations of spatiotemporal intermittency in neutral fluids and space plasmas. This study is carried out in two parts. First, we apply two distinct nonlinear techniques, kurtosis and phase coherence index, to measure the degree of non-Gaussianity and phase synchronization of intermittent magnetic field turbulence observed in the ambient solar wind, in the solar photosphere and in the ground, and intermittent atmospheric turbulence observed in the Amazon rain forest canopy. Next, we analyze a spatially-extended model of nonlinear waves in fluids and plasmas to identify transient coherent structures responsible for the on-off spatiotemporal intermittency observed in the time series of energy. We quantify the degree of amplitude-phase synchronization using the power-phase spectral entropy at the onset of spatiotemporal chaos. The observational and theoretical results indicate that the amplitude-phase Synchronization may be the origin of intermittency in fully-developed turbulence in the solar-terrestrial environment.
8
Elge, Murat. "Langmuir circulations in a coastal environment during CBLAST." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sept%5FElge.pdf.
Повний текст джерелаАнотація:
Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004.Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 95-99). Also available online.
9
Hillary, Richard Matthew. "Effects of turbulence and a patchy environment on the dynamics of plankton populations." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/843526/.
Повний текст джерелаАнотація:
The main aim of this project has been to investigate how turbulence and a patchy environment can affect the dynamics of plankton. In the first chapter, a brief introduction to the subject, both the methods and models we use and some of their behaviour in relation to observed phenomena, is given. In the second chapter, a reduced model for Langmuir circulations is used as a paradigm for chaotic advection of planktonic species. The patchiness of plankton due to such advection is discussed along with the effects of swimming/turbulent diffusion and how we can sometimes gain an analytical hold on the transport of organisms, using Melnikov analysis, in certain flows and we extend the results of previous work in this area. In Chapter 3, the possibility of pattern formation of swimming, spheroidal organisms in a simple, steady shear flow is investigated. In Chapter 4, the effects of turbulence and any inertial effects (buoyancy or density differences) is considered with regard to the initiation and subsequent propagation of phytoplankton blooms. The effect of a patchy environment is studied first, in Chapter 5, for the situation where we know explicitly the dynamics of the plankton. We take a spatially discrete, coupled oscillator approach to the patchy dynamics of plankton. The case where the dynamics of the patches is not known and, consequently all we might have is time series data is studied in Chapter 6. Given only measurements of the dynamics of some patchy population, we present a way of trying to deal with the patchy data in a more rigorous framework as mention of the inherently heterogeneous environments being measured is made but is mostly ignored. A method of first distinguishing independent patch dynamics from deterministically related dynamics is presented based on the algorithm first seen in Pecora et al. Given this deterministic bond between the patches we then set about creating a meta-population time series representing the collective dynamics of the population. This new time series is constructed so as to try and preserve as much of the individual dynamics as possible. Using a non-linear prediction algorithm ideally suited to possibly short data sets, we suggest this new time series can be used to improve short term predictions of general trends in the dynamics and also for the purposes of model fitting. Particular attention is given to using algorithms that can be applied to relatively short data sets, often a problem in studying time series data of ecosystems.
10
Rivas, David Roy. "Theory and simulation of electrostatic wave turbulence in the space shuttle-induced plasma environment." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/49593.
Повний текст джерела
11
Rey, Raposo Ramon. "The interplay between stellar feedback and galactic environment in molecular clouds." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/21022.
Повний текст джерелаАнотація:
In this thesis we address the problem of understanding the star formation process in giant molecular clouds in a galactic context. Most simulations of molecular clouds to date use an oversimplified set of initial conditions (turbulent spheres/boxes or colliding flows). Full galactic scale models are able to generate molecular clouds with complex morphologies and velocity fields but they fail to reproduce in detail the effects that occur at sub-pc scales (e.g. stellar feedback). Our goal is to build the bridge between these two scenarios, and to model the star formation process in molecular clouds produced in a galactic context. We extract our molecular clouds from full-scale galactic simulations, hence we need to increase the resolution by two orders of magnitude. We introduce the details of the program used to simulate molecular clouds in Chapter 2, and describe in detail the method we follow to increase the resolution of the galactic clouds. In Chapter 3 we compare our simulated galactic clouds with the more conventional approach of using turbulent spheres. We create turbulent spheres to match the virial state of three galactic clouds. We perform isothermal simulations and find that the velocity field inherited from the full-scale galactic simulations plays an important role in the star formation process. Clouds affected by strong galactic shear produce less stars compared with clouds that are compressed. We define (and test) a set of parameters to characterise the dynamical state of our clouds. To include stellar feedback in our simulations we need to introduce a cooling/heating algorithm. In Chapter 4 we analyse how the different velocity fields of our clouds change the temperature distribution even in the absence of feedback. To study the formation of molecules we need to model the chemistry of H2 in our clouds. We also add CO chemistry, and produce synthetic observations of our clouds. The effect of feedback from winds and supernovae in galactic clouds is studied in Chapter 5. We analyse the effect of winds in clouds with very different velocity fields. We find that the effect of winds is stronger in highly virialised, high star forming clouds, with clouds with weak galactic shear, compared to unbound shear-dominated clouds. The steady and continuous action of the winds appears to have a greater effect than the supernovae. In summary, the inherited properties from the galaxy have an impact on many relevant processes in star formation, influencing gravitational collapse, the formation of filamentary structures, the temperature field of the cloud, and have a considerable effect on the impact of feedback in the clouds.
12
Mason, Roger Bruce. "An investigation into how marketers cope with an environment of high complexity and turbulence, with special reference to the South African environment." Thesis, Rhodes University, 2004. http://hdl.handle.net/10962/d1003873.
Повний текст джерелаАнотація:
This study investigated relationships between marketing success, the level of external environmental complexity and turbulence, and marketing mix tactics. The literature suggested that more successful companies in simple and stable environments use stabilising marketing tactics, while more successful companies in complex and turbulent environments use destabilising tactics, regardless of industry habits, management preferences or market sector. A marketing mix model for the different environments was developed using a chaos and complexity theory perspective. The study was exploratory, using a qualitative, case study technique. Data was collected via depth interviews and document analysis from four companies in the information technology (IT) and packaging industries. These industries were identified as, respectively, the most complex and turbulent, and the simplest and most stable, South African environments. Two companies from each industry were chosen to reflect more successful and less successful companies. The more successful company in the complex/turbulent environment was found to use destabilising tactics, as did the more successful company in the simple/stable environment. Therefore, contrary to expectations, it appears that destabilising tactics contribute more to success than stabilising tactics do, regardless of the environment. It was also found, contrary to expectations, that stabilising tactics were used by both the less successful companies. The research concluded that destabilising tactics are related to more success and stabilising tactics to less success. The lack of clear differentiation between the two industries may be because the whole South African environment is complex and turbulent, because the packaging industry is not sufficiently simple and stable to differentiate it from the IT industry or because packaging industry managers perceive their industry to be complex and turbulent and act accordingly. Despite these uncertainties, the research showed the marketing mix model to be reasonably accurate for the complex/turbulent environment, and therefore of potential value to South African companies. To overcome the equivocal findings, further research is recommended in different industries, in countries with different levels of complexity and turbulence and into specific marketing mix tactics. Research into managers’ perceptions of environmental complexity and turbulence and into co-evolution of marketing tactics and external environments would also be of value.
13
Inizan, Maxime. "Turbulence-particle interactions on surfaces." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120445.
Повний текст джерелаАнотація:
Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 105-110).
The physics of adhesion and detachment of particles in ventilation ducts is important to understand and control contaminant and pathogen dispersal indoors. This thesis presents an experimental characterization of parameters which affect the resuspension of settled micro-particles and spores in a turbulent airflow channel. We examine, quantify, and analyze the role of relative humidity (RH), air temperature, particle size, and surface properties on particle detachment rate and mode. This is done using a combination of high-speed imaging in a turbulent channel where spores and particles are deposited initially followed by image-processing and particle-tracking. First, we show that ambient moisture hinders particle detachment, however, we also find that this is only true for a relative humidity higher than 60% RH. At lower air saturation, we show that, instead, another effect dominates, leading to a different mode of detachment. Instead of individual particle detachment, it is a collision dynamics leading to cluster formation that dominates the pattern of detachment of particles from surfaces. We find that collisions lead to aggregations of particles on the surface in the form of clusters of self-similar sizes. We find that the larger the cluster (above 5 particles) the more anisotropic its shape, similarly to what was observed in prior literature examining clusters of air-suspended particles in channel flows. We examined and quantified the role of initial particle surface concentration, mean air velocity, and particle surface properties on these results. Our study have implications in the control of pathogen and contaminant dispersal in confined geometries, relevant for a wide range of applications.
by Maxime Inizan.
S.M.
14
Xu, Ying. "Flow/acoustic interactions in porous media under a turbulent wind environment." Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/3510.
Повний текст джерела
15
Nguyen, Viet. "Simulation of the atmospheric behavior for the environment of a small-scale wind turbine." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/8777.
Повний текст джерелаАнотація:
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Zhongquan Zheng
This study investigates a method using computational fluid dynamics (CFD) to model low-elevation atmospheric conditions. There are three goals in this research: to analyze the wind behavior downwind from buildings and trees, to validate the accuracy of the simulations by comparing wind measurements to the simulation for a specific site, and to find a relationship between the wind speed and the power output of a small-scale wind turbine. The first goal is to define a proper CFD model for buildings and trees. The trends in the Strouhal number are found to correlate to changes in building height and the wind resistance of a tree as supported in literature, with minor differences with the addition of a tree. The second goal of this study is to model an actual low-elevation environment to compare the energy output predictions for a small-scale wind turbine versus traditional methods. The simulations are compared to on-site wind measurements at a suburban wind turbine, recorded by the rotor and two anemometers installed on the wind turbine tower. The measurements and simulations presented in this study show an improvement in the accuracy in the estimation of the energy output of a wind turbine versus using traditional methods involving high-elevation wind maps. The third goal is to provide a relationship between the wind speed and the power output of a small-scale wind turbine. To accomplish this task, system identification is implemented. The traditional auto-regressive model with exogenous input variables (ARX), its moving average counterpart (ARMAX), and the output error (OE) model are compared in this study. It is found that the transfer function provided by the ARX model most sufficiently estimates the power output of the studied wind turbine, with power output accuracies of 83%. With all three goals addressed, the feasibility of small-scale wind turbines in different low-elevation environments is assessed. In accomplishing these tasks, the siting of a small-scale wind turbine can be optimized qualitatively and quantitatively.
16
Eroglu, Ozer. "Analysis of the influence of turbulence and environmental variability on broadband acoustic coherence." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FEroglu.pdf.
Повний текст джерелаАнотація:
Thesis (M.S. in Engineering Acoustics and M.S. in Operations Research)--Naval Postgraduate School, Sept. 2004.Thesis advisor(s): Kevin B. Smith, Samuel E. Buttrey. Includes bibliographical references (p. 75). Also available online.
17
Vivoni-Gallart, Enrique Rafael 1975. "Turbulence structure of a model seagrass meadow." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/35483.
Повний текст джерелаАнотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1998.Includes bibliographical references (p. 235-239).
A laboratory study of the hydrodynamics of a seagrass meadow was conducted to investigate the effect of water depth and velocity variations during a tidal cycle on the mean and turbulent velocity fields in and above the vegetation layer. The principal goal was to characterize the turbulence structure of a depth-limited canopy, a gap that presently exists in the knowledge concerning the interaction of a unidirectional flow with an assemblage of plants. The experiments were carried out in an open channel flume with a model seagrass canopy. Proper modeling of the system for both the geometric and dynamic behavior of natural Zostera marina communities allows the results to be extrapolated to the conditions in a coastal, tidal meadow. The results also serve as an important comparative case to the characterization of turbulence within atmospheric plant canopies. The laboratory study included the measurement of the mean and turbulent velocity fields with the use of an acoustic Doppler velocimeter and a laser Doppler velocimeter. Standard turbulence parameters were evaluated including the velocity moments, the turbulence spectra. the turbulent kinetic energy budget and the quadrant distribution of the Reynolds stress. Each of these provided a means of describing the effect of submergence depth and the degree of canopy waving (monami) on the transport of momentum and mass between the canopy and its surrounding fluid environment. In addition. surface slope measurements were made with surface displacement gauges. the plant motion was quantified using video and camera images. and the canopy morphology was recorded from measurements taken from a random sampling of the model plants. The investigation showed a clear link between the shear generated eddies arising at the interface of the canopy and the surface layer and the vertical exchange of momentum. the plant motion characteristics and the turbulence time and length scales. The turbulence field within the seagrass meadow was composed of a shear-generated turbulence zone near the canopy height and a wake-generated zone near the bed In addition. a mean flow due to the pressure gradient from the water surface slope created a region of secondary maxima in the mean velocity profile near the bed. The parameter determining the seagrass turbulence structure was found to be the characteristic depth (H' h). defined such that the effective canopy height. reflects the plant deflection. Across the range of values considered for H/h. the flow characteristics showed a clear transition from a confined to an unbounded canopy flow. This transition was observed in all the principal turbulence parameters. From this analysis. a critical surface layer depth governing the transition between the two extreme canopy flow conditions was identified as half the effective canopy height. H'h = 1.50.
by Ernique Rafael Vivoni Gallart.
S.M.
18
Heimar, Markus, and Daniel Nilsson. "Survival in Chaos: A Study of Strategy Formation in a Turbulent Business Environment." Thesis, Linköping University, Department of Management and Economics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1498.
Повний текст джерелаАнотація:
Since the late 1960’s, the hydromechanical term turbulence has been a part of the business administration vocabulary, but until the late 1980’s and early 1990’s, a relatively small amount of research was dedicated to this field. These studies and more contemporary ones conclude that where the business environment is paradoxical and of fast- changing and chaotic nature, successful corporate strategies are shaped by strategic flexibility founded in high innovation rates, networks and alliances, and organisational elasticity and adaptiveness. From this perspective, the purpose of this study was to track and examine the strategy formation processes of a company operating in a turbulent context, and to contribute to an understanding of how these turbulent conditions can be managed. The study was conducted with a hermeneutic, systems- oriented, longitudinal case-study method and with a contextcontent- process perspective in which the process was the key factor. To a large extent, our conclusions coincide with those of other researchers. Forming multidimensional networks and alliances coloured by voluntary initiatives and full attention seem to be an extremely important contribution to survival in turbulent contexts. Nevertheless, it is equally important to break up and build new alliances as the initial objectives of the arrangement have expired or been reached. Furthermore, in contrast to other researchers’ observations, we conclude that high innovation rates do not necessarily lead to a greater potential to be successful in a turbulent context. The issue is instead to present a product offering flexible in itself developed and marketed by a flexible organisation. Innovation rates are decided by self-initiated and unofficial activity on part of the r&d teams and other coworkers, and management’s task is to facilitate for this corporate creativity to develop.
19
Hübner, Jens. "Buoyant plumes in a turbulent environment." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603909.
Повний текст джерелаАнотація:
This dissertation investigates how a nominally axisymmetric plume is affected by the presence of ambient turbulence. The results of this investigation are based on laboratory experiments in water. The experiments employ a saline plume released downwards into a tank of fresh water with an oscillating grid positioned near the bottom. A wide range of regimes with increasing levels of ambient turbulence is covered from a quiescent environment to the eventual break-up of the plume. Buoyancy and velocity data were obtained using fluorescent dye and particle tracking, respectively. The response of a plume to ambient turbulence is found to be twofold. The plume centreline position deviates from the perfect vertical and the plume spreading relative to that centreline position increases. Both mechanisms, plume "meandering" and "spreading", combine to create a time averaged plume image in which the plume appears wider. Sophisticated image processing techniques are developed to disentangle the two mechanisms and to quantify their respective contributions to the overall plume spreading. The turbulence-induced plume meandering scales on the ratio of the transversal velocity fluctuation of the background turbulence to the vertical mean velocity on the plume centreline. A simple extension to classical plume theory is proposed to account for the increased plume spreading via enhanced entrainment that becomes dependent on the strength of the ambient turbulence. Although in a quiescent environment the cross-sectional profiles of velocity and buoyancy are close to Gaussian in shape, the actual mechanism of plume spreading involves an inwards erosion of the Gaussian shape from the flanks of the profile by the ambient turbulence. Obviously, a simple extension to classical plume theory does not capture this qualitative change to the shape of the plume profiles. A scaling is proposed instead that links the radial extent to which the Gaussian profile is eroded by the ambient turbulence to the relative magnitudes of the fluctuating velocity in the ambient turbulence and on the centreline of a plume in a quiescent environment.
20
Hu, Wilson Kun. "Particle ejection and suspension due to isotropic turbulence." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12634.
Повний текст джерела
21
Yang, Qingjun (Judy Qingjun). "Impacts of vegetation-generated turbulence on sediment transport." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120638.
Повний текст джерелаАнотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 179-188).
Aquatic vegetated habitats, including wetlands and mangroves, are disappearing at an annual rate of 1 to 7%. These ecosystems provide habitats important to fisheries, enhance water quality by filtering nutrients from run-off, and also protect coastal regions from storm surges and waves. To mitigate the loss of these habitats, restoration projects import sediment to eroded areas. The success of the restoration depends on its ability to retain sediment; therefore restoration design requires a good understanding of sediment transport within vegetated landscapes. However, there is currently no quantitative model for sediment transport in vegetated regions, and many restoration projects have failed due to unanticipated erosion from the restored regions. The goal of this thesis is to develop a predictive model for sediment transport in regions with vegetation. First, the affect of vegetation on the critical condition when sediment start to move was explored. To identify the critical condition, an imaging system was designed to track the trajectories of individual moving grain through running water. The critical flow velocity (U[subscript crit]) above which sediment starts to move was identified from the tracked sediment trajectories for both bare (non-vegetated) and vegetated regions. The experimental results showed that for the same type of sediment, U[subscript crit] decreased with increasing vegetation solid volume fraction. This was attributed to the vegetation-generated turbulence, which induced a local, vertical, adverse pressure, or a lift force on the sediment grain, facilitating sediment transport. In contrast, the turbulent kinetic energy (k[subscript t]) was found to be roughly a constant at the critical condition for different vegetation volume fractions, suggesting that k[subscript t] is a more universal metric than T for predicting the critical condition of the sediment transport. A k[subscript t]-based model was developed to predict U[subscript crit] for channels with different vegetation solid volume fractions. The turbulence-based model successfully predicted U[subscript crit] for both bare and vegetated channels, providing a useful tool for ecologists to predict whether a vegetated landscape will erode or not. Second, the impact of vegetation on the bed load transport rate was explored. A system that allows sediment to be bypassed, a cart to distribute sediment, a method that measures the dry weight of wet sand without drying the sediment, a topography system, and an sediment trajectory imaging system were designed. The bed load transport rate (Q[subscript s],) was measured for both bare channels and channels with different vegetation solid volume fractions ([phi]) under different flow rates. At the same [tau], the measured Q[subscript s], increased with increasing [phi], suggesting that vegetation-generated turbulence, which also increased with increasing ]phi], was augmenting the bed load transport. At the same near-bed turbulent kinetic energy, k[subscript t], the Q[subscript s], measured in both bare and vegetated channels agreed within uncertainty, suggesting that k[subscript t] may be a more universal predictor of Q[subscript s] than [tau]. The Einstein-Brown [tau]-based bed load transport model was reinterpreted as a k[subscript t]-based model. The new kt-based model predicted the Q[subscript s] measurements for both bare and vegetated channels. The dependence of Q[subscript s] on k[subscript t] was explained by the statistics of individual grain motion, which showed that Q[subscript s] was predominantly controlled by the number of grains in motion, which correlated with k[subscript t]. The proposed k[subscript t]-based sediment transport model can be used to simulate large-scale landscape evolution and to help ecologists design better coastal restoration strategies. Third, the impacts of vegetation on bed-form characteristics and migration rate were studied. After the measured bed load transport rate converged to an equilibrium value, the bed topography was scanned by a laser topography system. Bed-forms with height less than 2cm were observed and characterized as ripples. For low vegetation solid volume fraction ([phi] by Qingjun Judy Yang.
Ph. D.
22
Chen, Huijuan. "Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment." Doctoral thesis, Linköpings universitet, Energisystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-106483.
Повний текст джерелаАнотація:
A well-functioning, energy-efficient ventilation system is of vital importance to offices, not only to provide the kind of comfortable, healthy indoor environment necessary for the well-being and productive work performance of occupants, but also to reduce energy use in buildings and the associated impact of CO2 emissions on the environment. To achieve these goals impinging jet ventilation has been developed as an innovative ventilation concept. In an impinging jet ventilation system, a high momentum of air jet is discharged downwards, strikes the floor and spreads over it, thus distributing the fresh air along the floor in the form of a very thin shear layer. This system retains advantages of mixing and stratification from conventional air distribution methods, while capable of overcoming their shortcomings. The aim of this thesis is to reach a thorough understanding of impinging jet ventilation for providing a good thermal environment for an office, by using Computational Fluid Dynamics (CFD) supported by detailed measurements. The full-field measurements were carried out in two test rooms located in a large enclosure giving relatively stable climate conditions. This study has been divided into three parts where the first focuses on validation of numerical investigations against measurements, the second addresses impacts of a number of design parameters on the impinging jet flow field and thermal comfort level, and the third compares ventilation performance of the impinging jet supply device with other air supply devices intended for mixing, wall confluent jets and displacement ventilation, under specific room conditions. In the first part, velocity and temperature distributions of the impinging jet flow field predicted by different turbulence models are compared with detailed measurements. Results from the non-isothermal validation studies show that the accuracy of the simulation results is to a great extent dependent on the complexity of the turbulence models, due to complicated flow phenomena related to jet impingement, such as recirculation, curvature and instability. The v2-f turbulence model shows the best performance with measurements, which is slightly better than the SST k-ω model but much better than the RNG k-ε model. The difference is assumed to be essentially related to the magnitude of turbulent kinetic energy predicted in the vicinity of the stagnation region. Results from the isothermal study show that both the SST k-ω and RNG k-ε models predict similar wall jet behaviours of the impinging jet flow. In the second part, three sets of parametric studies were carried out by using validated CFD models. The first parametric study shows that the geometry of the air supply system has the most significant impact on the flow field. The rectangular air supply device, especially the one with larger aspect ratio, provides a longer penetration distance to the room, which is suitable for industrial ventilation. The second study reveals that the interaction effect of cooling ceiling, heat sources and impinging jet ventilation results in complex flow phenomena but with a notable feature of air circulation, which consequently decreases thermal stratification in the room and increases draught discomfort at the foot level. The third study demonstrates the advantage of using response surface methodology to study simultaneous effects on changes in four parameters, i.e. shape of air supply device, jet discharge height, supply airflow rate and supply air temperature. Analysis of the flow field reveals that at a low discharge height, the shape of air supply device has a major impact on the flow pattern in the vicinity of the supply device. Correlations between the studied parameters and local thermal discomfort indices were derived. Supply airflow rates and temperatures are shown to be the most important parameter for draught and stratification discomfort, respectively. In the third part, the impinging jet supply device was shown to provide a better overall performance than other air supply devices used for mixing, wall confluent jets and displacement ventilation, with respect to thermal comfort, heat removal effectiveness, air exchange efficiency and energy-saving potential related to fan power.
23
Jabur, Nahida Ali. "Environmental turbulence and innovation durability in selected patient care units." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284172.
Повний текст джерелаАнотація:
A previously unexamined issue, innovation durability relative to perceived environmental uncertainty and nursing unit culture among staff nurses (N = 48), was investigated. The Differentiated Group Professional Practice (DGPP) in Nursing project was selected for this five-year follow-up study. Verran, Milton, Murdaugh, and Gerber developed the DGPP model in two urban hospitals and one rural hospital in Arizona in 1988. Model implementation and evaluation was completed in 1992. The theoretical model incorporated elements of contingency and learning organization theories. A descriptive correlation research design was used to explore the relationships among environmental uncertainty, nursing unit culture, innovation durability and two innovation outcomes: control over nursing practice and work satisfaction. Data were collected in October 1997 at three selected patient care units in one rural hospital. The hospital was selected because the implementation of the DGPP model was successful, and no other redesign activity was implemented between 1992 and 1997. Structured self-report scales were used to measure each of the concepts within this study. RNs' perceptions of the current nursing practices suggested that the DGPP model was in existence on the three patient care units at the time data were collected. Nursing unit culture (β = .53) was the best predictor of the DGPP model durability (R² = .28) and its subcomponents of group governance (R² = .24) and shared values (R² = .49). Group governance and innovation related behaviors showed significant individual and combined effects on RNs' perceived control over nursing practice (R² = .55). Decision making, innovation related behaviors, and group governance accounted for the variance in RNs' overall work satisfaction (R² = .50). Although perceived control over nursing practice remained unchanged over a period of 5 years, decreases were found in overall work satisfaction and satisfaction with organizational policies. The findings provided support for the conceptual model as expected with one exception, the positive correlation between DGPP model durability and perceived uncertainty in the internal environment. In summary, the findings suggested the inclusion of environmental uncertainty and nursing unit culture in studies of innovation durability and innovation outcomes.
24
Hedlöf, Carina, and Ulrika Janson. "How to cope with a turbulent environment." Thesis, Linköping University, Department of Management and Economics, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-567.
Повний текст джерелаАнотація:
Background: Due to constant changes and unpredictability in a turbulent environment, the traditional way of planning does not seem to work anymore. Therefore, new approaches to the external and internal conditions need to develop in order to cope with the environmental turbulence.
Purpose: The purpose of this thesis is to define a turbulent environment and identify how an organisation can cope with this environment. Procedure: We have developed a frame of reference mainly consisting of theories regarding a turbulent environment and change. In addition, we have selected eight guiding factors, which we have used when studying, systemising, and comparing how contemporary literature suggests that an organisation can cope with a turbulent environment.
Results: The conclusions we have come to are that with a definition of the environment as being fast-changing and of chaotic nature, where the changes are continuous, emergent, small, big or somewhere in between, and where paradoxes play an important role, it is necessary to develop an organisational structure, leadership, human resource, and corporate culture, in which the objective always is to create dynamics and to build in an acceptance of change.
25
Choi, Young-Tae. "Alliance coordination effectiveness and the performance of international strategic alliances: development of the partnership and moderating role of market environment turbulence." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1238.
Повний текст джерелаАнотація:
The purpose of this dissertation was to investigate post-international strategic alliance (ISA) formation issues, which have been neglected in the ISA literature. The specific research questions were 1) how do ISA partners develop their relationships? 2) how does this relationship development impact effective management of resources contributed by each ISA partner? and 3) how does effective resource management influence ISA performance?
Data were collected by mail and web surveys from those who were/are involved in ISA operations. Structural equation modeling using LISREL was employed to test the conceptual model and multiple regression analysis was adopted to test the moderating effects in the model. The model was modified by introducing second order factors to correctly interpret the relationships between factors and achieve a more parsimonious model.
Results indicate that alliance partnership interactions between ISA partners (i.e., reciprocity, transparency, formal and informal communication, two-way and participative communication, and cultural sensitivity) positively influenced the development of desire for joint action between them which is based on trust and commitment. Desire for joint action positively influenced alliance coordination effectiveness (ACE: integration and utilization of resources) which underlies effective resource management between ISA partners. ACE positively affected ISA performance. Market environment turbulence (i.e., host government interference and technology turbulence), however, did not have moderating effects between ACE and ISA performance.
The first question was answered by introducing alliance partnership interaction factors which influence the building of the positive relationship between ISA partners. The introduction of ACE explained how ISA partners manage the resources provided by each partner. The significant impact of ACE on ISA performance and the nonsignificant impact of the moderating variables indicate that ACE has strong impact on ISA performance that can absorb the effects of host government interference and technology turbulence in the operation of ISAs.
26
Pianezze, Joris. "Modélisation de la structure verticale de la turbulence optique en milieu naturel." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00830505.
Повний текст джерелаАнотація:
Les milieux complexes sont une source d'incertitude importante notamment lorsqu'il s'agit de développer des modèles climatique ou météorologique. Le développement de la couche limite atmosphérique à l'intérieur d'une vallée encaissée, incluant des vents de vallée et de pente, n'est, par exemple, pas résolu, ce qui a un impact considérable sur la prévision de la convection, du transport de polluants, etc... La simulation des grandes échelles de la turbulence (SGE) est un outil qui a montré sa capacité à reproduire finement les structures turbulentes dans ce type de contextes au travers des approches idéalisées. L'extension de la SGE aux milieux naturels est réalisée dans cette thèse qui s'articule en trois parties. La première partie présente les équations et les notions nécessaires à la compréhension des problèmes de turbulence dans la couche limite atmosphérique. On s'attache à décrire le cadre des lois issues de la théorie des similitudes et le cadre de la turbulence optique. La seconde partie présente des résultats issus de deux simulations idéales dans lesquelles nous comparons les résultats issus de la simulation avec d'une part les lois issues de la théorie des similitudes et d'autre part les données radar disponible lors de la campagne IHOP. L'utilisation d'un maillage raffinée près du sol permet d'améliorer les profils verticaux des champs turbulents en améliorant la prédiction des gradients à l'interface sol/atmosphère. De plus, le profil de couche limite est bien reproduit par les profils du paramètre de structure des fluctuations de l'indice de réfraction de l'air simulé si on compare avec les résultats issus du radar. Globalement, la dynamique des champs turbulents résolus par le modèle reproduise une dynamique et des ordres de grandeurs corrects conformes à nos attentes. Une fois l'évaluation du modèle effectuée, une simulation a été mise en place autour de la campagne d'observation VOTALP située dans le sud de la Suisse. Cette simulation comprend 5 domaines emboités allant de 16 kms de résolution horizontales pour le plus grand domaine à 100m pour le plus petit domaine. L'important dispositif déployé durant la campagne VOTALP située dans une vallée dans le sud de la Suisse a permis de confronter les résultats issus de la modélisation à haute résolution avec ces données d'observation. Les résultats obtenus ont, entre autre, montré que la simulation à haute résolution est un outil adapté pour l'étude des phénomènes de basses couches et notamment la turbulence optique en milieu complexe.
27
Carpman, Nicole. "Turbulence Intensity in Complex Environments and its Influence on Small Wind Turbines." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-153215.
Повний текст джерелаАнотація:
The market of wind power as a sustainable energy source is growing, both on large and small scale. Conventional large scale wind turbines normally operate in uniform areas where expected wind speeds and turbulence characteristics are well investigated and the constructional design of the wind turbines is regulated by standard classes for different external conditions. Small scale wind turbines (SWT), on the other hand, are sometimes placed in more complex environments where the turbulence conditions are rougher. A larger amount of turbulence will generate a larger amount of fatigue loadings on the construction, increasing the risk of breakdown. It is therefore of major concern to perform more measurements and further investigate the turbulence characteristics in complex environments and the effect that these will have on small wind turbine construction. Thus, turbulence is measured with sonic anemometers at two sites with complex environments; at an urban site above a rooftop in a medium sized city (Uppsala, Sweden) and above a forest in Norunda (outside Uppsala) at two heights, near the treetops (z = 33 m) defined as complex and further up (z = 97 m) defined as more uniform. The turbulence data is analyzed and the results are compared to the normal turbulence model (NTM) as it is defined for the standard SWT classes by the International Electrotechnical Commission in the International standard 61400-2: Design requirements for small wind turbines (IEC, 2006). Measurements of minute standard deviations of longitudinal wind speed (σu) and turbulence intensity (TIu) are reported, as well as the distributions of TIu and of 10 minute mean wind speeds (um) for the different sites and stabilities. The results show that the NTM represents the turbulence at 97 m height above the forest only for light wind speeds, smaller than 10 m/s, but underestimates the turbulence for higher wind speeds. It should also be noted that the data is scattered and contain a number of occasions with extreme values of σu and TIu. For wind speeds higher than 10 m/s the number of observations is limited but the majority of the observations are more extreme than the NTM. At the complex sites (near the treetops and the rooftop) the NTM clearly underestimates both the magnitude and rate of change of σu with increasing wind speed, although the observed wind speeds close to these rough surfaces are low so the conclusions are limited. Average TIu at 97 m height is 19 %, compared to 41 % close above forest and 43 % above rooftop. Mean values of TIu above forest are generally 10 % lower during stable conditions (z/L > 0.05) while above rooftop, the wind material is sparse and 95 % of the observations had stable stratification so no dependence on stability can be seen. From these results it can be concluded that the turbulence characteristics close above treetops is similar to those above rooftop, but that the NTM, as it is defined for the standard SWT classes, is not valid in these complex and urban terrains and need to be modified to correctly estimate the turbulence intensities, and consequently also the loadings, affecting small wind turbines located at these kinds of sites.Marknaden för vindkraft som en förnyelsebar energikälla växer snabbt, både stor- och småskaligt. Traditionella storskaliga vindkraftverk placeras normalt på homogena platser där vindklimatet och turbulensens karaktär är ganska väl kartlagda och konstruktionsstandarden regleras av standardklasser utifrån olika externa förhållanden. Små vindkraftverk (SWT) å andra sidan placeras ofta i mer komplex eller urban miljö där turbulensen är mer intensiv. En större andel turbulens genererar större utmattningslaster på konstruktionen vilket ökar risken att vindturbinen går sönder. Det är därför av stor vikt att utföra fler mätningar och ytterligare undersöka turbulensen i komplexa miljöer och vilken effekt den kommer ha på de små vindkraftverkens konstruktion. Med anledning av detta så har turbulensdata analyserats från mätningar med sonicanemometrar. Dels på en urban plats, ovanför ett hustak i en medelstor stad (Uppsala, Sverige). Dels vanför en skog i Norunda (utanför Uppsala) på två höjder, nära trädtopparna (33 m) som anses komplex och högre upp (97 m) som anes mer homogen. Resultaten är jämförda med den normala turbulensmodellen (NTM) så som den definieras för standard SWT klasserna av International Electrotechnical Commission i International standard 61400-2: Design requirements for small wind turbines (IEC, 2006). Mätningar av 10 minuters standardavvikelse av den longitudinella vindhastigheten (σu) och turbulensintensiteten (TIu) redovisas, liksom fördelningen av TIu och 10 minuters medelvinden (um) för olika stabilitet för de olika mätplatserna. Resultaten visar att NTM är representativ på 97 m höjd endast för låga vindhastigheter, under 10 m/s, medan modellen underskattar turbulensen för högre vindhastigheter. Det bör också noteras att spridningen är stor i data och att extrema värden av σu och TIu uppmätts vid flertalet tillfällen. För vindhastigheter över 10 m/s så är antalet mätvärden begränsade, men majoriteten av mätvärdena är högre än NTM. På de komplexa mätplatserna (nära trädtopparna och ovan hustaket) så underskattar NTM avsevärt både storleken av σu och dess förändring med ökad vindhastighet på de komplexa platserna (nära trädtopparna och ovan hustaket). Dock är de observerade vindhastigheterna låga såhär nära de skrovliga ytorna så slutsatserna är begränsade. På 97 m höjd är medelvärdet av TIu 19 %, jämfört med 41 % nära trädtopparna och 43 % ovan hustak. De är generellt 10 % lägre under stabila förhållanden (z/L > 0.05) över skog, medan ovan hustak där vindmaterialet är begränsat och 95 % av observationerna var stabilt skiktade så ses inte något stabilitetsberoende. Från dessa resultat kan slutsatserna dras att turbulensens karaktär nära trädtoppar liknar den ovan hustak, men att NTM, så som den definieras för standard SWT klasserna, inte gäller vid dessa komplexa och urbana platser och behöver modifieras för att korrekt uppskatta turbulensintensiteterna och därmed också de laster som påverkar små vindkraftverk placerade på den här typen av platser.
28
Li, Xiang-Yu. "Numerical approaches to droplet growth in atmospheric turbulence." Licentiate thesis, Stockholms universitet, Meteorologiska institutionen (MISU), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129868.
Повний текст джерелаАнотація:
The bottleneck problem of cloud droplet growth is one of the most challenging problems in cloud physics. Cloud droplet growth is neither dominated by con-densation nor gravitational collision in the size range of 15–40 μm in radius. Turbulence-generated collision has been thought to be the mechanism to bridge the size gap, i.e., the bottleneck problem. This study develops the numerical approaches to study droplet growth in atmospheric turbulence and investigates the turbulence effect on cloud droplet growth. The collision process of in-ertial particles in turbulence is strongly nonlinear, which motivates the study of two distinct numerical schemes. An Eulerian-based numerical formulation for the Smoluchowski equation in multi-dimensions and a Monte Carlo-type Lagrangian scheme have been developed to study the combined collision and condensation processes. We first investigate the accuracy and reliability of the two schemes in a purely gravitational field and then in a straining flow. Discrepancies between different schemes are most strongly exposed when con-densation and coagulation are studied separately, while their combined effects tend to result in smaller discrepancies. We find that for pure collision simulated by the Eulerian scheme, the mean particle radius slows down using finer massbins, especially for collisions caused by different terminal velocities. For the case of Lagrangian scheme, it is independent of grid resolution at early times and weakly dependent at later times. Comparing the size spectra simulated by the two schemes, we find that the agreement is excellent at early times. For pure condensation, we find that the numerical solution of condensation by the Lagrangian model is consistent with the analytical solution in early times. The Lagrangian schemes are generally found to be superior over the Eulerian one interms of computational performance. Moreover, the growth of cloud droplets in a turbulent environment is investigated as well. The agreement between the two schemes is excellent for both mean radius and size spectra, which gives us further insights into the accuracy of solving this strongly coupled nonlinear system. Turbulence broadens the size spectra of cloud droplets with increasing Reynolds number.
29
Pettersson, Kristofer, and Papaioannou Stylianos. "Corporate Social Responsibility of SMEs during Times of Turbulence : - A Case Study of Small and Medium-sized Exporters in a Changing Environment." Thesis, Linnéuniversitetet, Ekonomihögskolan, ELNU, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-20643.
Повний текст джерелаАнотація:
The increased globalization has brought increased interdependency between countries as well as markets. The 2007 financial crisis impacted companies on a global scale and the need for companies to be socially responsible has increased. Corporate social responsibility (CSR) can build reputation and lead to societal and competitive advantage, which can be especially useful for small and medium sized enterprises (SME) with limited resources. CSR has traditionally been the domain of multinational corporations and little is known about CSR in SMEs. Recent research shows mixed results of how the financial crisis has affected CSR strategies. The purpose of this study is to explore how stakeholders‟ issues and CSR strategies change during times of market turbulence and SMEs conform to the changes of the internal and external environment. This was studied through a qualitative case study of three Swedish exporting SMEs and their key stakeholders. Interviews with managing directors of the companies and key stakeholders together with secondary data constitute the gathered empirical data. Key stakeholders, key issues, legitimacy with stakeholders, company matching with the external environment and the CSR strategy, as well as changes during crisis were analyzed based on the empirical data. We found an increased need for CSR activities during times of turbulence. Two companies increased their CSR activities while one decreased the activities. The results of the study indicate that the external environment changes during times of market turbulence and companies need to adapt to the newly shaped environment. CSR activities became more important for some stakeholders during market turbulence. Companies which adapted to the changes of the external environment improved legitimacy with their stakeholders and moved toward enhancing their competitive advantage as well as improved their performance. The study contributes to the knowledge of how SME form CSR strategy as well as how this strategy is changed during times of turbulence. We found CSR strategies of the studied SMEs to be emergent and intuitive, and that CSR strategy changed in a mixed direction during the crisis. Finally, a recommendation is made based on the results. SMEs can strategically use CSR activities in order to develop a competitive advantage through differentiation by a creating societal advantage.
30
Catalan, Ros Leyre. "Analysis of human exposure at local exhaust ventilation by means of 3D air velocity measurements, tracer gas tests and controlled turbulence environment." Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-19713.
Повний текст джерелаАнотація:
Local exhaust (LE) ventilation is a ventilation technique where contaminated air is locally extracted close to the contaminant source usually with the purpose to reduce the exposure of workers to dust, fumes or vapour, which can be hazardous to their health. The performance of a LE installation depends however on many influential factors, and there is not yet an international standardized way to test LE constructions. The present study is the natural continuation of some previous studies at the University of Gävle that aimed at contributing to the establishment of such tests. The study entails full scale experimental measurements that include 3-D air velocity measurements and tracer gas tests in a controlled air turbulence environment generated through physical movements of a vertical, human-sized cylinder. These measurements were focused on human exposure, which was analysed by means of a seated human simulator for different configurations in which the exhaust flow rate, turbulence level, the exhaust hood arrangement and the measuring/injecting distance varied. The use of a sonic 3-D anemometer, that yielded both magnitude and direction of the air movement, proved very useful in analysing the generated air turbulence. As a measure of the LE performance, PNV value (Percentage of Negative Velocities) was used. This measure represents the percentage of time when the air flow at the measuring point in front of the exhaust hood is directed away from the nozzle, i.e. when the velocity component in the direction towards the exhaust hood opening is negative. Regarding the results obtained, in an otherwise undisturbed environment, measurement data showed that the natural convection from the human simulator sitting in front of the LE introduces some disturbances of the air flow in the suction region, proportional to the exhaust flow rate. However, when additional turbulence was generated through the controlled movements of the human-sized cylinder, thus creating a controlled turbulence setting, natural human convection leaded to a lower percentage of negative velocities (PNV) in comparison with the case in which human simulator was not present, especially for low exhaust air flow rates and when the exhaust hood was raised from the table. The tracer gas tests implied injection of a neutrally buoyant tracer gas through a perforated sphere placed in front of the exhaust hood. The amount of tracer gas that escaped from the suction flow was measured both in the room air and in the breathing zone. The first measurements yielded a sensitive method for measuring the capture efficiency (CE) of the exhaust hood. The CE is the percentage of injected tracer gas that is directly captured by the exhaust hood. This parameter showed that although the convection flow generated by the human simulator leads to low PNV values, it seems that the tracer gas is not actually being captured, but trapped in that convection flow. As a consequence, PNV and CE get a strong correlation, which is even more intense when injection and capture point are closer together. Hence, PNV represents a good alternative to tracer gas measurements only if the relationship between the correlation of PNV and CE with respect to the distance from the injection to the capture point is known. Finally, measurements of tracer gas in the breathing zone showed random, short and high exposures when turbulence was generated and those exposures got worse by natural human convection.
31
Renoud, Robert W. "Boundary layer response to an unsteady turbulent environment." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22931.
Повний текст джерела
32
Blackmore, Tom. "Grid generated turbulence and actuator disc representations of tidal turbines." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/361942/.
Повний текст джерела
33
Gwilliam, David J. "Separating boundary layer response to an unsteady turbulent environment." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27259.
Повний текст джерела
34
Van, Der Mescht Deon. "Mountain wave turbulence in the lee of the Hex River Mountains." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20240.
Повний текст джерелаАнотація:
Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Despite recorded mountain wave related aircraft accidents in South Africa, very little literature exists on South African mountain waves. This study discusses the results of a mountain wave study in the Hex River Mountains in the Western Cape province of South Africa. The aim of this study was to measure mountain wave turbulence on the lee side of the mountains by conducting weather balloon soundings on the upwind and lee sides of the mountains. These soundings were performed over four days in the winter and spring, with each field day representing different synoptic scale weather conditions. Lee wave rotors were detected from several of the lee wave soundings. Significant values of horizontal vorticity around a north-south axis (y-component horizontal vorticity) were detected. The instrumentation was highly sensitive and able to measure even weak up and downdraft velocities associated with the rotors. Strong downdrafts were measured some mountain waves, but no strong downdrafts were detected near rotors which occurred below the mountain waves. The two dimensional positions of balloons were only available after a considerable amount of reanalysis. If this data can be made available onsite shortly after soundings, it can be used to decide where to move launch sites to, in order to obtain optimal results.
AFRIKAANSE OPSOMMING: Ten spyte van gedokumenteerde berggolf-verwante vliegongelukke, bestaan baie min literatuur oor Suid Afrikaanse berggolwe. Hierdie tesis bespreek die resultate van ‘n berggolfstudie in die Hexrivier Berge in the Weskaap Provinsie van Suid- Afrika. Die doel van hierdie studie was om die berggolfturbulensie aan die lykant van die berge te meet deur middel van weerballonopstygings aan beide die winden lykante van die berge. Hierdie opstygings is oor ‘n tydperk van vier winter en lente dae uitgevoer, met elkeen van die dae wat verskillende sinoptiese weersomstandighede verteenwoordig het. Rotors is waargeneem in die data van verskeie ballonopstygings wat aan die lykant uitgevoer is. Beduidende waardes van horisontale vortisiteit rondom ‘n noord-suid as (y-komponent horisontale vortisiteit) is gemeet. Die instrumentasie was hoogs sensitief en kon selfs swak op- en afstrominge meet. Sterk afstrominge is waargeneem in berggolwe, maar nie in die omgewing van rotors wat onmder die berggolwe voorgekom het nie. Die twee-dimensionele posisies van ballonne was slegs na aansienlike heranaliese van die data beskikbaar. Indien hierdie data kort na opstygings beskikbaar is tydens veldwerk, kan dit help met besluite oor alternatiewe posisies waarvandaan ballonopstygings gedoen kan word ten einde optimale resultate te bekom.
35
Stewart, Robert L. III. "DECELERATING OPEN CHANNEL FLOW OVER GRAVEL: TURBULENCE STRUCTURE & SENSOR DEVELOPMENT." UKnowledge, 2014. http://uknowledge.uky.edu/ce_etds/25.
Повний текст джерелаАнотація:
This dissertation describes investigations of fully turbulent decelerating hydraulically roughbed flow over gravel and the development of technology to measure turbulence and associated sediment transport in streams. Theory is developed for predicting velocity distributions in simple uniform flow using the asymptotic invariance principle and tested using laboratory and field collected data. A mixed scale is developed that accounts for bed derived turbulent structures throughout the flows depth and is used to parameterize the external boundary’s effect on the flow for the logarithmic and outer layers. The asymptotic invariance principle and similarity analysis is conducted for the equations of motion in the outer region of decelerating flow over gravel to define equilibrium conditions for this class of flows with the velocity scale is the freestream velocity. The combination of time series and time averaged statistical analysis of turbulent flow is used to elucidate the structure of flow under decelerating conditions. Time averaged statistical measures of turbulence confirm results of others for higher Froude number approaching transcritical and time series analysis shows the effects of decelerating flow on turbulence to be frequency dependent. Wireless velocity sensors were developed and found capable of measuring time averaged velocity and able to resolve macroturbulence from time series data. A semi-theoretical model of elastic deformation of cantilever beams under hydraulic forcing was coupled with circuit theory to develop a calibration procedure for the VBS that requires only three measurement points, one of which is at zero velocity. Light based sensors are developed to estimate light attenuation in water for ecological research or estimating sediment concentration in water. A semi-theoretical scaling of light attenuation and sediment properties was developed which predicts light attenuation from sediment properties. The combination of new theory on open channel velocity, turbulent structure and field sensors for measuring turbulence and sediment offers the possibility to extend our laboratory knowledge to realistic flow situations.
36
Millard, Deborah J. "An investigation into flow in confined environments using laser doppler anemometry and computational fluid dynamics." Thesis, London South Bank University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245092.
Повний текст джерела
37
Grose, Mitchell. "Forecasting Atmospheric Turbulence Conditions From Prior Environmental Parameters Using Artificial Neural Networks: An Ensemble Study." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1619632748733788.
Повний текст джерела
38
Connell, R. J. "Unstable equilibrium : modelling waves and turbulence in water flow." Diss., Lincoln University, 2008. http://hdl.handle.net/10182/592.
Повний текст джерелаАнотація:
This thesis develops a one-dimensional version of a new data driven model of turbulence that uses the KL expansion to provide a spectral solution of the turbulent flow field based on analysis of Particle Image Velocimetry (PIV) turbulent data. The analysis derives a 2nd order random field over the whole flow domain that gives better turbulence properties in areas of non-uniform flow and where flow separates than the present models that are based on the Navier-Stokes Equations. These latter models need assumptions to decrease the number of calculations to enable them to run on present day computers or super-computers. These assumptions reduce the accuracy of these models. The improved flow field is gained at the expense of the model not being generic. Therefore the new data driven model can only be used for the flow situation of the data as the analysis shows that the kernel of the turbulent flow field of undular hydraulic jump could not be related to the surface waves, a key feature of the jump. The kernel developed has two parts, called the outer and inner parts. A comparison shows that the ratio of outer kernel to inner kernel primarily reflects the ratio of turbulent production to turbulent dissipation. The outer part, with a larger correlation length, reflects the larger structures of the flow that contain most of the turbulent energy production. The inner part reflects the smaller structures that contain most turbulent energy dissipation. The new data driven model can use a kernel with changing variance and/or regression coefficient over the domain, necessitating the use of both numerical and analytical methods. The model allows the use of a two-part regression coefficient kernel, the solution being the addition of the result from each part of the kernel. This research highlighted the need to assess the size of the structures calculated by the models based on the Navier-Stokes equations to validate these models. At present most studies use mean velocities and the turbulent fluctuations to validate a models performance. As the new data driven model gives better turbulence properties, it could be used in complicated flow situations, such as a rock groyne to give better assessment of the forces and pressures in the water flow resulting from turbulence fluctuations for the design of such structures. Further development to make the model usable includes; solving the numerical problem associated with the double kernel, reducing the number of modes required, obtaining a solution for the kernel of two-dimensional and three-dimensional flows, including the change in correlation length with time as presently the model gives instant realisations of the flow field and finally including third and fourth order statistics to improve the data driven model velocity field from having Gaussian distribution properties. As the third and fourth order statistics are Reynolds Number dependent this will enable the model to be applied to PIV data from physical scale models. In summary, this new data driven model is complementary to models based on the Navier-Stokes equations by providing better results in complicated design situations. Further research to develop the new model is viewed as an important step forward in the analysis of river control structures such as rock groynes that are prevalent on New Zealand Rivers protecting large cities.
39
Babajee, Jayson. "Detailed numerical characterization of the separation-induced transition, including bursting, in a low-pressure turbine environment." Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00984351.
Повний текст джерелаАнотація:
La turbine basse-pression est un composant essentiel d'un turboréacteur car elle entraine la soufflante qui génère la plus grande partie de la poussée dans la configuration actuelle des turboréacteurs à double flux. Dans la perspective d'accroître son rendement en termes de consommation de carburant, il y a une recherche permanente dans la réduction du nombre d'aubage (c'est-à-dire la réduction de la masse) qui implique un chargement plus élevé par aube de rotor. Cet environnement est caractérisé par un écoulement dont le nombre de Reynolds est faible ainsi qu'une large diffusion le long de la partie aval de l'extrados. Par conséquent, l'écoulement le long de cette surface est potentiellement sujet à une séparation laminaire qui, suivant le statut de la bulle de recirculation, pourrait causer une diminution de la performance aérodynamique (sillages plus larges et plus profonds). La présente thèse de doctorat se concentre sur l'investigation du phénomène de la transition induite par séparation dans les écoulements de turbines basse-pression. L'accent est mis sur les prédictions numériques basées sur une approche CFD RANS utilisant le modèle innovant de transition γ-Reθt à deux équations de transport (la première équation pour l'intermittence numérique et la seconde équation pour le nombre de Reynolds dont la longueur caractéristique est l'épaisseur de quantité de mouvement au début de transition γ-Reθt). Neuf aubes différentes de rotor de turbine basse-pression constituent une base de données de référence et couvrent les plages de fonctionnement de différents nombres de Reynolds de sortie isentropique, de nombres de Mach de sortie isentropique, d'intensités de turbulence d'entrée, avec ou sans sillage provenant d'une rangée d'aubes amont et avec deux configurations de rugosité locale. Une première analyse de cette base de données met en évidence l'effet de la séparation sur le début de la transition et sur les performances. La définition d'une corrélation a été tentée et permet de lier le taux de diffusion d'un aubage au nombre de Reynolds de sortie isentropique fia la condition de " Bursting ". Une méthodologie numérique fiable et robuste a été établie afin de prédire la transition dans le cas d'un écoulement amont uniforme. Les résultats sont en bon accord avec les mesures expérimentales même si il a été nécessaire d'adapter les conditions limites dans le but de prédire une séparation laminaire numériquement pour des aubages fortement chargés et fia fort taux de diffusion uniquement. La résolution des profils de vitesse de la couche limite permet d'obtenir une évaluation détaillée des paramètres de la topologie de l'écoulement. Cela fournit une information sur l'épaisseur de quantité de mouvement qui est le paramètre principal définissant les corrélations de transition. La technique " Chimère " des maillages recouvrants est utilisée pour faciliter la modélisation des moyens de contrôle passif pour déclencher la transition. C'est une technique appropriée pour l'implémentation de géométries simples ou plus élaborées.
40
Sinha, Nityanand. "Towards RANS Parameterization of Vertical Mixing by Langmuir Turbulence in Shallow Coastal Shelves." Thesis, University of South Florida, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3605268.
Повний текст джерелаАнотація:
Langmuir turbulence in the upper ocean is generated by the interaction between the wind-driven shear current and the Stokes drift velocity induced by surface gravity waves. In homogenous (neutrally stratified) shallow water, the largest scales of Langmuir turbulence are characterized by full-depth Langmuir circulation (LC). LC consists of parallel counter-rotating vortices aligned roughly in the direction of the wind. In shallow coastal shelves, LC has been observed engulfing the entire water column, interacting with the boundary layer and serving as an important mechanism for sediment re-suspension. In this research, large-eddy simulations (LES) of Langmuir turbulence with full-depth LC in a wind-driven shear current have revealed deviations from classical log-layer dynamics in the surface and bottom of the water column. For example, mixing due to full-depth LC induces a large wake region eroding the classical bottom (bed) log-law velocity profile. Meanwhile, near the surface, Stokes drift shear serves to intensify small scale eddies leading to enhanced mixing and disruption of the surface velocity log-law. The modified surface and bottom log-layer dynamics induced by Langmuir turbulence and full-depth LC have important implications on Reynolds-averaged Navier-Stokes simulations (RANSS) of the general coastal ocean circulation. Turbulence models in RANSS are typically calibrated under the assumption of log-layer dynamics, which could potentially be invalid during occurrence of Langmuir turbulence and associated full-depth LC. A K-Profile Parameterization (KPP) of the Reynolds shear stress in RANSS is introduced capturing the basic mechanisms by which shallow water Langmuir turbulence and full-depth LC impact the mean flow. Single water column RANS simulations with the new parameterization are presented showing good agreement with LES
41
Akan, Cigdem. "Surface Mass Transfer in Large Eddy Simulation (LES) of Langmuir Turbulence." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/3944.
Повний текст джерелаАнотація:
Over the past century the study of gas exchange rates between the atmosphere and the ocean has received increased attention because of concern about the fate of greenhouse gases such as CO2 released into the atmosphere. Of interest is the oceanic uptake of CO2 in shallow water coastal regions as biological productivity in these regions is on average about three times larger than in the open ocean. It is well-known that in the absence of breaking surface waves, the water side turbulence controls gas transfer of sparingly soluble gases such as CO2 from the air to the water. The dependence of gas transfer on wind-driven shear turbulence and convection turbulence generated by surface cooling has been investigated previously by others. However, the effect of Langmuir turbulence generated by wave-current interaction has not been investigated before. More specifically, Langmuir turbulence is generated by the interaction of the wind-driven shear current with the Stokes drift velocity induced by surface gravity waves.
In this dissertation, large-eddy simulations (LES) of wind-driven shallow water flows with Langmuir turbulence have been conducted and scalar transport and surface scalar transfer dynamics analyzed. The scalar represents the concentration of a dissolved gas such as CO2 in the water. In flows with Langmuir turbulence, the largest scales of the turbulence consist of full-depth Langmuir circulation (LC), parallel downwind-elongated, counter-rotating vortices acting as a secondary structure to the mean flow.
LES guided by the full-depth LC field measurements of Gargett & Wells (2007) shows that Langmuir turbulence plays a major role in determining scalar transport throughout the entire water column and scalar transfer at the surface. Langmuir turbulence affects scalar
transport and its surface transfer through 1. the full-depth homogenizing action of the large scale LC and 2. the near-surface vertical turbulence intensity induced by the Stokes drift velocity shear. Two key parameters controlling the extent of these two mechanisms are the dominant wavelength (λ) of the surface waves generating the turbulence and the turbulent Langmuir number, Lat , which is inversely proportional to wave forcing relative to wind forcing.
Furthermore, LES representative of the field measurements of Gargett et al. (2004) shows that Langmuir turbulence increases transfer velocity (a measure of mass transfer efficiency across the air-water interface) dramatically with respect to shear-dominated turbulence.
Finally, direct resolution of the surface mass transfer boundary layer allows for the LES to serve as a testing ground for bulk parameterizations of transfer velocity. Several wellestablished
parameterizations are tested and a new parameterization based on Stokes drift velocity shear is proposed leading to encouraging results.
42
Goettel, Michael Thomas. "Analysis of the swimming behavioral response of western blacknose dace in a turbulence modified flow field." Thesis, State University of New York at Buffalo, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1539819.
Повний текст джерелаАнотація:
Fish passage success rates through hydraulic infrastructure have been historically low due to flow field conditions that exceed the physical or behavioral capabilities of a given species. Significant efforts to design and modify hydraulic structures for enhanced passage rates have failed to achieve the desired results, with a primary reason being a poor understanding of how fish respond to complex hydraulic conditions. Many contemporary research efforts have targeted the inter-relationship between hydraulics and fish behavior in the laboratory using live fish trials in an attempt to better comprehend these interactions and ultimately provide a basis for the development of biologically-based design criteria. In this study experiments were conducted to assess the behavioral responses along swimming trajectories of western blacknose dace ( Rhinichthys obtusus) in turbulent flow conditions. The objective was to test the hypothesis that the dace would preferentially adjust their swim paths to minimize their exposure to elevated turbulent conditions. Experimental data were collected through digital imaging of dace trajectories for fish that had been released into a shallow flume and allowed to swim through turbulence enhanced flow fields. Additionally, detailed velocity measurements were collected with an acoustic Doppler velocimeter to allow the comparison of dace trajectories to flow field conditions represented by average metrics of turbulent kinetic energy and Reynolds shear stresses. Analysis of the data consisted of the quantification of the proportion of the time that a dace's swim path selected a direction toward a lower magnitude turbulence condition when such an option existed. Fish paths were also graphically compared to turbulence contour plots to qualitatively assess the presence of swim path preferences or patterns. Lastly, video footage of each trial was evaluated to qualitatively assess the presence of novel behaviors that could have implications for the swimming trajectories observed. Results indicate that the dace did not preferentially avoid turbulence at statistically significant levels under the conditions experienced in the flume; however, data do suggest that some behavior relative to turbulence was non-random. Qualitative observations of video footage suggest that non-hydraulic factors, such as the presence of conspecifics and light intensity, also influence the swim path trajectories of the western blacknose dace. Future research will require more targeted turbulent conditions, simultaneous multivariate observations and analyses that factor in non-hydraulically-based behavior and the incorporation of coupled behavioral and hydraulic data at reduced time and length scales for primary variables. It is envisioned that the results of this study can provide guidance for future studies aimed at developing biologically based design criteria for enhanced fish passage at hydraulic infrastructure.
43
Newman, Paul Lockwood. "Numerical simulation of diffusive shock acceleration in a turbulent astrophysical environment." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307793.
Повний текст джерела
44
Fairbank, Nicola. "Viral infection and predation of phytoplankton residing in a turbulent environment." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548765.
Повний текст джерела
45
Machin, Alison Isabel. "Role identity in a turbulent environment : the case of health visiting." Thesis, University of Newcastle upon Tyne, 2009. http://hdl.handle.net/10443/3972.
Повний текст джерелаАнотація:
This thesis presents a grounded theory study of UK health visitors practising in an increasingly integrated, collaborative, service user focused healthcare system. Emphasis is placed in policy on a preventative, public health approach to addressing the ongoing health needs of the population. This has provoked a national debate on the healthcare contribution of health visitors. Better use of health visiting capacity and closer alignment of the role with the collaborative public health agenda have been identified as a national priority. The theoretical framework for this study has been developed from the symbolic interactionist premise, that individuals continually reinterpret their world in the context of their social interaction with others. Data has been collected from direct observation and individual interviews. The process of constant comparative analysis has generated four interrelated data categories: professional role in action; interprofessional working; local micro systems for practice and professional role identity (core category). Three models have been developed to support the discussion of the findings. The first two make explicit the inter-relationship between the concepts identified in the data and interactive processes relating to the maintenance of identity. The third model proposes a process of interprofessional role change. It links the uniprofessional and interprofessional dimensions of practice to the core principle of valuing individuals through the maintenance of equilibrium in their professional role identity. Embedding a process for feedback on identity is identified as important. This thesis theorises that role change facilitation should enable individuals to continually renegotiate their professional role identity in the context of their practice. It also suggests that promoting a sense of collective identity within a professional group will enhance the experience of individuals involved in a collaborative role change process. The thesis concludes with a consideration of its implications for health visiting and others in the healthcare system, in seeking to maintain their role identity in a turbulent practice environment.
46
Smith, Heather Dianne. "Flow and sediment dynamics around three-dimensional structures in coastal environments." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196261689.
Повний текст джерела
47
Huang, Yongxiang. "ARBITRARY ORDER HILBERT SPECTRAL ANALYSIS DEFINITION AND APPLICATION TO FULLY DEVELOPED TURBULENCE AND ENVIRONMENTAL TIME SERIES." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2009. http://tel.archives-ouvertes.fr/tel-00439605.
Повний текст джерелаАнотація:
La Décomposition Modale Empirique (Empirical Mode Decomposition - EMD) ou la Transformation de Hilbert-Huang (HHT) est une nouvelle méthode d'analyse temps-fréquence qui est particulièrement adaptée pour des séries temporelles nonlinéaires et non stationnaires. Cette méthode a été proposée par NE. HUANG. il y a plus de dix ans. Pendant les dix dernières années, plus de 1000 articles ont appliqué cette méthode dans le cadre de diverses applications ou domaines de recherche. Dans cette thèse, nous appliquons cette méthode à des séries temporelles de turbulence, pour la première fois, et à des séries temporelles environnementales. Nous avons obtenu comme résultat le fait que la méthode EMD correspond à un banc de filtre dyadique (ou quasi-dyadique) pour la turbulence pleinement développée. Pour caractériser les propriétés intermittentes d'une série temporelle invariante d'échelle, nous avons généralisé l'analyse spectrale de Hilbert-Huang classique à des moments d'ordre arbitraire $q$, pour effectuer ce que nous avons appelé ``analyse spectrale de Hilbert d'ordre arbitraire''. Ceci fournit un nouveau cadre pour analyser l'invariance d'échelle directement dans un espace amplitude-fréquence, en estimant une intégrale marginale d'une pdf jointe $p(\omega,\mathcal{A})$ de la fréquence instantanée $\omega$ et de l'amplitude $\mathcal{A}$. Nous validons tout d'abord la méthode en analysant des séries temporelles de mouvement Brownien fractionnaire, et en analysant des séries temporelles multifractales synthétiques, en tant que modèle respectivement de processus monofractals et multifractals. Nous comparons les résultats obtenus avec la nouvelle méthode, à l'analyse classique utilisant les fonctions de structure: nous trouvons numériquement que la méthodologie utilisant l'approche de Hilbert fournit un estimateur plus précis pour le paramètre d'intermittence. Avec une hypothèse de stationarité, nous proposons un modèle analytique pour la fonction d'autocorrélation des incréments de séries temporelles de vitesse $\Delta u_{\ell}(t)$, où $\Delta u_{\ell}(t)=u(t+\ell)-u(t)$, et $\ell$ est l'incrément temporel. Dans le cadre de ce modèle, nous prouvons analytiquement que, si une loi de puissance est valide pour la série d'origine, la position minimisant la fonction d'autocorrélation de la variable d'origine est égale exactement au temps de séparation $\ell$ lorsque $\ell$ appartient à la zone invariante d'échelle. Ce modèle prédit une loi de puissance pour la valeur minimum, comportement vérifié par une simulation de mouvement Brownien fractionnaire et à partir de données expérimentales de turbulence. En introduisant une fonction cumulative pour la fonction d'autocorrélation, la contribution en échelle est alors caractérisée dans l'espace de fréquence de Fourier. Nous observons que la contribution principale à la fonction d'autocorrélation provient des grandes échelles. La même idée est appliquée à la fonction de structure d'ordre 2. Nous obtenons que celle-ci est également fortement influencée par les grandes échelles, ce qui montre que ceci n'est pas une bonne approche pour extraire les exposants invariants d'échelle d'une série temporelle lorsque les données sont caractérisées par des grandes échelles énergétiques. Nous appliquons ensuite cette méthodologie Hilbert-Huang à une base de données de turbulence homogène et presque isotrope, pour caractériser les propriétés multifractales invariantes d'échelle des série temporelles de vitesse en turbulence pleinement développée. Nous obtenons un comportement invariant d'échelle pour la pdf jointe $p(\omega,\mathcal{A})$ avec un exposant proche de la valeur de Kolmogorov. Nous estimons les exposants $\zeta(q)$ dans un espace amplitude-fréquence, pour la première fois. L'hypothèse d'isotropie est testée échelle par échelle dans l'espace amplitude-fréquence. Nous obtenons que le rapport d'isotropie généralisé décroit linéairement avec le moment $q$. Nous effectuons également l'analyse d'une série temporelle de température (scalaire passif) possédant un effet de rampe marqué (ramp-cliff). Pour ces données, l'approche traditionnelle utilisant les fonctions de structure ne fonctionne pas. Mais la nouvelle méthode développée dans cette thèse fournit un net régime invariant d'échelle jusqu'au moment $q=8$. Les exposants $\xi_{\theta}(q)-1$ sont très proches des exposants $\zeta(q)$ obtenus par l'approche des fonctions de structure pour la vitesse longitudinale. Nous nous intéressons ensuite à l'auto-similarité étendue (Extended Self Similarity - ESS) dans le cadre Hilbert-Huang. En ce qui concerne la méthode ESS, qui est devenue classique en turbulence, nous adaptons l'approche pour le cas Hilbert-Huang dans un espace de fréquence, et nous constatons que le modèle lognormal, avec un coefficient adéquat, fournit une très bonne estimation des exposants invariants d'échelle. Finalement nous appliquons la nouvelle méthodologie à des données environnementales: des débits de rivières, et des données de turbulence marine dans la zone de surf. Dans ce dernier cas, la méthode ESS permet de séparer les ondes de vent de la turbulence à petite échelle.
48
Wang, Jialin. "Building integrated wind energy." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/building-integrated-wind-energy(81978798-e68a-4189-87b0-4159b280b6e9).html.
Повний текст джерелаАнотація:
In considering methods of reducing the emission of carbon dioxide; there is a growing interest for use of wind power at domestic building in U.K. But the technology of wind turbines development in building environment is more complicated than in open areas. Small wind turbines in suburban areas have been reported as having unsatisfactory energy output, but it is not clear whether this is due to insufficient wind resource or low turbine efficiency. The aim of this research is to discover whether the wind resource in suburban areas is large enough for small wind turbines to produce a useful energy output.Historical wind data and manufacturers' turbine characteristics were used to estimate the hourly wind speed and energy output for different U.K. cities, terrain zones and turbines. It was found that for turbines at 10 m height in suburban areas and depending on city, the annual wind energy conversion efficiency ranged from about 20 to 40%, while the number of turbines required to produce the annual average electricity consumption of a UK dwelling ranged from about 6 for the smallest turbine (5.3 m² rotor area) to about 1 for the largest (35.26 m² rotor area).This analysis was based on average conditions, but the wind speed near buildings can vary considerably from one point to another. In order to predict the performance of wind turbines more accurately, the atmospheric boundary layer (ABL) of suburban areas was simulated in both CFD and wind tunnel models, and models of groups of semi-detached and terraced houses were set in this ABL. It was found that at 10 m height in the area of the houses, the turbulence intensity was too high for satisfactory operation of wind turbines (19 to 35%) while the mean velocity at different points ranged from 86 to 108% of the 10m reference velocity. At 30m height the turbulence intensity was satisfactory (less than 19 %), while the mean velocity ranged from 92 to 103 % of the 30 m reference velocity. It is concluded that for wind turbines in suburban areas, at 10 m height the wind speed is too low and the turbulence is too high for satisfactory performance, while at 30 m height the wind speed is much higher and the turbulence is low enough.
49
Crawford, Thomas Joseph. "An experimental study of the spread of buoyant water into a rotating environment." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/264526.
Повний текст джерелаАнотація:
This thesis examines previously unresolved issues regarding the fluid dynamics of the spread of buoyant water into a rotating environment. We focus in particular on the role that finite potential vorticity and background turbulence play in determining the flow properties. When water of an anomalous density enters into an oceanic basin, gravity-driven surface flows can be established as a result of the density difference. These flows are often of a sufficiently large scale that the dynamics are affected by the Coriolis force arising from the rotation of the earth. This causes the formation of a large outflow gyre near to the source which feeds into a propagating gravity current that is confined to the coast. Previous experimental work in this field has sought to simplify the problem through the use of a point source and a quiescent ambient. We extend this work to provide a better representation of the real-world flow by introducing a source of finite depth and background turbulence to the rotating ambient. This study seeks to answer three key questions that are critical to the understanding of the flow behaviour in this scenario. First, what is the effect of the finite potential vorticity of the outflow on the properties of the outflow vortex and the boundary current? Second, what role does the presence of the the outflow vortex play in determining the behaviour of the current? Third, what is the effect of background turbulence on the flow properties? To carry out the investigation, experiments were conducted in the laboratory and compared with a theoretical description of the flow. The currents are generated inside a rotating tank filled with saltwater by the continuous release of buoyant freshwater from a source structure located at the fluid surface. A horizontal source of finite depth is used to introduce finite potential vorticity into the outflow. The impact of background turbulence is examined by introducing an oscillating grid into the rotating tank. We find that the finite potential vorticity of the outflow plays an important role in determining the flow properties for sufficiently low Rossby and Froude number. As the value of these parameters is increased a zero potential vorticity model is able to capture the key elements of the flow behaviour. The outflow vortex is found to act as a time-varying source to the boundary current, with the current velocity fixed by the vortex velocity field. The vortex vorticity is seen to decrease with time, while the vortex radius continues to increase at late times despite the vortex having reached a limiting depth, which enables potential vorticity to be conserved and the current to be supplied with a non-zero velocity. Finally, the structure of the background turbulence is found to be key in determining the effect that it has on the flow properties, with different behaviours observed for three-dimensional and quasi- two-dimensional turbulence.
50
Augier, Pierre. "Turbulence en milieu stratifié, étude des mécanismes de la cascade." Phd thesis, Ecole Polytechnique X, 2011. http://tel.archives-ouvertes.fr/tel-00697245.
Повний текст джерелаАнотація:
La turbulence fortement influencée par une stratification stable en densité est étudiée expérimentalement, numériquement et théoriquement. Ce type de turbulence est rencontré dans l'atmosphère et les océans dans une gamme d'échelles intermédiaires où la force de Coriolis est négligeable. Dans une première partie, la transition à la turbulence d'un écoulement simple : une paire de tourbillons colonnaires contra-rotatifs est étudiée. Des Simulations Numériques Directes (DNS) montrent que lorsque la dissipation est suffisamment faible, deux instabilités secondaires, de cisaillement et gravitationnelle, se développent après l'instabilité zigzag. La taille caractéristique des tourbillons de Kelvin-Helmholtz est de l'ordre de l'échelle de flottabilité. Ces deux instabilités mènent à une transition à la turbulence qui présente des spectres anisotropes similaires à ceux associés à la turbulence stratifiée pleinement développée. Pour la première fois, un retour à l'isotropie est observé pour des échelles inférieures à l'échelle d'Ozmidov. Dans une deuxième partie, un écoulement pleinement turbulent forcé par plusieurs générateurs de dipoles est étudié. Les expériences aux plus grands nombres de Reynolds de flottabilité ont permis pour la première fois de quasiment atteindre le régime de turbulence fortement stratifié. Les simulations numériques forcées dans l'espace physique avec le même type de forcage ont permis de reproduire les résultats expérimentaux et de les étendre aux grands nombres de Reynolds de flottabilité. Elles révèlent que la plus grande échelle des retournements est de l'ordre de l'échelle de flottabilité. Enfin, une généralisation de la loi des 4/5 de Kolmogorov est proposée pour la turbulence stratifiée.