To see the other types of publications on this topic, follow the link: Steady condition.
Dissertations / Theses on the topic 'Steady condition'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Steady condition.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Binjuwair, Saud. "Characterisation of flow structures inside an engine cylinder under steady state condition." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12536.
Full textAbstract:
The in-cylinder flow of internal combustion (IC) engines, formed during the intake stroke, is one of the most important factors that affect the quality of air-fuel mixture and combustion. The inducted airflow through the inlet valve is primarily influenced by the intake port design, intake valve design, valve lift and valve timing. Such parameters have a significant influence on the generation and development of in-cylinder flow motion. In most combustion systems the swirl and tumble motions are used to aid the air-fuel mixing with the subsequent decay of these bulk flow motions generating increased turbulence levels which then enhance the combustion processes in terms of rate of chemical reactions and combustion stability. Air motion formed inside the engine cylinder is three-dimensional, transient, highly turbulent and includes a wide spectrum of length and time scales. The significance of in-cylinder flow structures is mainly reflected in large eddy formation and its subsequent break down into turbulence kinetic energy. Analysis of the large scale and flow motions within an internal combustion engine are of significance for the improvement of engine performance. A first approximation of these flow structures can be obtained by steady state analysis of the in-cylinder flow with fixed valve lifts and pressure drops. Substantial advances in both experimental methods and numerical simulations provide useful research tools for better understanding of the effects of rotational air motion on engine performance. This study presents results from experimental and numerical simulations of in-cylinder flow structures under steady state conditions. Although steady state flow problem still includes complex three-dimensional geometries with high turbulence intensities and rotation separation, it is significantly less complex than the transient problem. Therefore, preliminary verifications are usually performed on steady state flow rig. For example, numerical investigation under steady state condition can be considered as a precondition for the feasibility of calculations of real engine cylinder flow. Particle Image Velocimetry (PIV) technique is used in the experimental investigations of the in-cylinder flow structures. The experiments have been conducted on an engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and different inlet valve configurations at two pressure drops, 250mm and 635mm of H2O that correlate with engine speeds of 2500 and 4000 RPM respectively. From the 2-D in-cylinder flow measurements, a tumbling vortex analysis is carried out for six planes parallel to the cylinder axis. In addition, a swirl flow analysis is carried out for one horizontal plane perpendicular to the cylinder axis at half bore downstream from the cylinder head (44mm). Numerically, modelling of the in-cylinder flow is proving to be a key part of successful combustion simulation. The numerical simulations require an accurate representation of turbulence and initial conditions. This Thesis deals with numerical investigation of the in-cylinder flow structures under steady state conditions utilizing the finite-volume CFD package, STAR CCM+. Two turbulence models were examined to simulate the turbulent flow structure namely, Realizable k-ε and Reynolds Stress Turbulence Model, RSM. Three densities of generated mesh, which is polyhedral type, are examined. The three-dimensional numerical investigation has been conducted on the same engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and both valves are opened configuration at two pressure drops 250mm and 635mm of H2O that is equivalent to engine speeds of 2500 and 4000 RPM respectively. The nature and modelling of the flow structure together with discussions on the influence of the pressure drop and valve lift parameters on the flow structures are presented and discussed. The experimental results show the advantage of using the planar technique (PIV) for investigating the complete flow structures developed inside the cylinder. It also highlighted areas where improvements need to be made to enhance the quality of the collected data in the vertical plane measurements. Based on the comparison between the two turbulence models, the RSM model results show larger velocity values of about 15% to 47% than those of the Realizable k-ε model for the whole regions. The computational results were validated through qualitative and quantitative comparisons with the PIV data obtained from the current investigation and published LDA data on both horizontal and vertical cross sections. The calculated correlation coefficient, which is above 0.6, indicated that a reasonable prediction accuracy for the RSM model. This verifies that the numerical simulation with the RSM model is a useful tool to analyse turbulent flows in complex engine geometries where anisotropic turbulence is created.
2
Fajardo, Peña Pablo. "Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow." Doctoral thesis, Universitat Politècnica de València, 2012. http://hdl.handle.net/10251/16878.
Full textAbstract:
The increasing use of turbochargers is leading to an outstanding research to understand the internal flow in turbomachines. In this frame, computational fluid dynamics (CFD) is one of the tools that can be applied to contribute to the analysis of the fluid-dynamic processes occurring in a turbine. The objective of this thesis is the development of a methodology for performing simulations of radial turbomachinery optimizing the available computational resources. This methodology is used for the characterization of a vaned-nozzle turbine under steady and pulsating flow conditions.
An important effort has been devoted in adjusting the case configuration to maximize the accuracy achievable with a certain computational cost. Concerning the cell size, a local mesh independence analysis is proposed as a procedure to optimize the distribution of cells in the domain, thus allowing to use a finer mesh in the most suitable places. Particularly important in turbomachinery simulations is the influence of the approach for simulating rotor motion. In this thesis two models have been compared: multiple reference frame and sliding mesh. The differences obtained using both methods were found to be significant in off-design regions. Steady flow CFD results have been validated against global measurements taken on a gas-stand.
The modeling of a turbine, installed either on a turbocharger test rig or an engine, requires the calculation of the flow in the ducts composing the system. Those ducts could be simulated assuming a one-dimensional (1D) approximation, and thus reducing the computational cost. In this frame of ideas, two CFD boundary conditions have been developed. The first one allows performing coupled 1D-3D simulations, communicating the flow variables from each domain through the boundary. The second boundary condition is based in a new formulation for a stand-alone anechoic end, which intends to represent the flow behavior of an infinite duct.
Finally, the turbine was simulatFajardo Peña, P. (2012). Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16878
Palancia
3
Zimmerman, Martin. "Chování EHD mazacího filmu při náhlých změnách rychlosti a zatížení." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-233979.
Full textAbstract:
This dissertation is focused on experimental study of lubricant film behavior under transient conditions. For real machine parts such as gears, roller bearings and cam mechanism the operating conditions such as speed, load and radius of curvature of rubbing surfaces are vary during the working cycle. Change in operating conditions may pose an increased risk of the lubricating film breakdown. Direct contact of rubbing surfaces at the time of the lubricating film breakdown causes an increase in friction and wear. The high-speed CMOS camera was used to record the dynamic changes in lubricating film thickness during the experiment. The optical interferometry method has been used for reverse reconstruction of lubricating film thickness of the recorded interferograms. It was confirmed that the operating parameters have a major impact on the formation of lubricant film and its thickness and a certain combination of boundary conditions can cause lubricating film rupture. The obtained results showed, that modified topography of the rubbing surfaces can help to increase the lubrication film thickness especially in critical phases of working cycle.
4
Petit, Maxime. "Residency and trafficking of ILC2 in steady steate and th2 induced inflammatory conditions." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7095.
Full textAbstract:
Les ILC2s sont retrouvées au niveau des muqueuses comme les poumons et l’intestin, ainsi que dans divers ganglions et organes liés au métabolisme comme les tissus adipeux (ATs). Elles jouent un rôle important dans l’induction des réponses immunitaires de type Th2 comme équivalents innées dans lymphocytes Th2. Elles sont activées par des alarmines (IL-25 et IL-33) et des activateurs environnementaux (allergènes, métabolites et neuromédiateurs). Les ILC2s sécrètent des cytokines de type Th2 permettant de recruter et d’activer des cellules myéloïdes, d’augmenter la production de mucus et la contraction musculaire, ainsi que d’initier la réparation et le renouvellement des tissus. Cependant, une activation non contrôlée des ILC2s participe au développement de maladies chroniques. Les ILCs sont généralement considérées comme des cellules résidentes. Cependant, plusieurs études ont suggéré que la migration pourrait être un processus important pour la maturation des capacités effectrices. La circulation des ILCs reste peu documentée, et aucun mécanisme n’est pour l’instant capable d’expliquer le renouvellement des ILC2s pour agir dans de nombreux tissus suite à une stimulation. Nous avons montré que des quantités significatives d’ILC2s matures et immatures peuvent être collectées dans la lymphe du canal thoracique de souris canulées durant plusieurs heures. Les ILC2s circulantes forment 3 groupes distincts avec des expressions de molécules d’adhésion et récepteurs de migration spécifiques. Nos expériences de transferts cellulaires montrent que ces groupes spécifiques de molécules exprimées sont liés à des tropismes particuliers pour l’intestin, les poumons ou les ATs. Pour analyser le comportement des ILC2s dans un contexte de réponse de type Th2, nous avons injecter les cytokines IL-25 et IL-33 et étudié la lymphe de ces souris. La stimulation à l’IL-33 augmente le nombre de cellules ILC2s circulants dans la lymphe. Les différents groupes d’ILC2s montrent des réponses différentes à l’IL-33. Ainsi, les ILC2s migrants vers l’intestin sont majoritairement prolifératives tandis que le groupe migrant vers les poumons et les ATs secrètent de l’IL-5, de l’IL-13 et de l’Areg. Cela suggère que les ILC2s migrants de façon spécifique possèdent une empreinte fonctionnelle. Nous confirmons les fonctions des groupes d’ILC2s circulants en utilisant des modèles plus physiologiques mimant des réactions allergiques et des infections parasitaires (stimulation par la papaïne et le succinate). Les migrations vers l’intestin et les poumons jouent un rôle primordial dans l’induction de réponse de type Th2 par sécrétion d’IL-5 et d’IL-13, et à l’initiation de la réparation tissulaire par production d’Areg. De façon intéressante, les ILC2s migrants vers les poumons participent au renouvellement des populations résidentes participant principalement à la production d’Areg. Finalement, nous caractérisons un rôle important du trafic des ILC2s à différents temps suivant l’infection par Nippostrongulus brasiliensis, confirmant la fonction des ILC2s migrantesILC2s are found in mucosal tissues as lung and intestine, in lymph nodes, and in metabolic tissues such as the adipose tissues. They play important role in maintaining or inducing type-2 immune responses as innate equivalent of Th2 lymphocytes. They are activated by alarmins (IL-25 and IL-33) and by external activators (allergens, metabolites and neuromediators). ILC2s are secreting type-2 cytokines to facilitate the activation of other cells and to induce an important repair program. Their activation allows large type of events as diverse as myeloid cells recruitment and activation, mucus production, muscle contractility and tissue repair. They have key role in lung and adipose tissue development and maintain their homeostasis by early responding against parasitic pathogens. Abnormal activation of ILC2s is also participating to chronic diseases.ILCs are mostly considered as resident cells. However, different studies suggested that migration could be important for the maturation of their effector capacities and to correctly target the injured tissue. Circulation and trafficking of ILC subsets is still unclear. No mechanism is yet available to explain the turnover of ILC2s and how they can act in many tissues following stimuli.We found that large numbers of mature and immature ILC2s could be collected in the thoracic duct lymph of mice perfused over several hours, showing that ILC2s are in fact actively circulating through the hemo-lymphatic circuit. Furthermore, circulating mature ILC2s could be separated into three distinct subsets depending on their pattern of receptor and adhesion molecule expression. Cell transfer experiments proved that specific patterns are representative of specific tropism for gut, lung and adipose tissues.To analyse ILC2 behaviour in the context of a type-2 response, we injected IL-25 and IL-33 before lymph collection. IL-33 stimulation largely enhanced the number of circulating ILC2s in the lymph. These different ILC2 tissue targeted subsets responded differently to IL-33. Specifically, gut-trafficking ILC2s were mainly stimulated to proliferate whereas lung and adipose tissue subsets were stimulated to produce IL-13, IL-5 and Areg. This suggests that, in ILC2s, specific tissue targeting is associated with already imprinted functions while transiting through the hemo-lymphatic system. We confirmed these functions of circulating ILC2 subsets in more physiological context by mimicking allergy and helminth infection (stimulation by papain and succinate) where specific migration to lungs and intestine play important roles in mounting the type-2 response by IL-5/IL-13 secretion, and also initiating tissue repair by Areg production. Interestingly, we showed that lung migrating ILC2s participated to resident pool renewal that main function is Areg production. Finally, we characterized important trafficking of ILC2 at different stages of Nippostrongulus brasiliensis infection, confirming the functional relevance of ILC2 trafficking
5
Ahmed, Kamel Abd El-Salam Attia. "Automobile cornering behaviour under steady and non-steady state conditions." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329475.
Full text
6
Larsson, Roland. "Elastohydrodynamic lubrication under non-steady conditions." Doctoral thesis, Luleå tekniska universitet, Maskinelement, 1996. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18564.
Full textAbstract:
The six papers presented in this thesis consider the effects on elastohydrodynamic lubrication (ehl) of non-steady conditions. The vast majority of ehl investigations, both experiemental and theoretical, utilise steady state conditions, i.e. constant load, velocity, geometry and temperature. The lubricant is, however, in conditions that are far from those of steady state. Many components operate with varying load, velocity and geometry. Some examples are gears, rolling element bearings, cams and follower mechanisms and reciprocating seals. To predict the operation of these components it is necessary to consider the transient effects. The theory of elastohydrodynamic lubrication under non-steady conditions is presented in this thesis and applied to some practical cases. Papers A and B deal with the simulation of the lubrication in the contact between an impacting ball and a lubricated surface. These investigations give understanding of lubrication under impact loading and also fundamental understanding of the dynamics of an ehl contact. Paper C is an experimental investigation of the impacting ball problem. The deformation of the surfaces in the contact region is studied for different combinations of lubricant viscosities and impact velocities. Paper D and E deal with the breakdown mechanisms of a lubricant film. It is shown that lubricant film failure occurs at high sliding velocities if the load is non-stationary. This contradicts elastohydrodynamic theory since increasing sliding velocity implies increasing entrainment of lubricant and thus thicker lubricant film and less risk for failure. It is, however, shown in Paper E that starvation can be the reason why film failure occurs even if the conjunction is lubricated by a thick layer of lubricant. Paper F is a transient simulation of a meshing involute spur gear. Film thickness, pressure, friction and subsurface stresses are computed at different positions along the line of action. Two different sets of lubricant properties are used, the first oneGodkänd; 1996; 20070219 (rola)
7
Nguyen, Vinh Q. "A Numerical Study of Burgers' Equation With Robin Boundary Conditions." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31285.
Full textAbstract:
This thesis examines the numerical solution to Burgers' equation on a finite spatial domain with various boundary conditions. We first conduct experiments to confirm the numerical solutions observed by other researchers for Neumann boundary conditions. Then we consider the case where the non-homogeneous Robin boundary conditions approach non-homogeneous Neumann conditions. Finally we numerically approximate the steady state solutions to Burgers' equation with both the homogeneous and non-homogeneous Robin boundary conditions.Master of Science
8
Mikhaylenko, Maxim A. "Development and Application of the Boundary Singularity Method to the Problems of Hydrodynamic and Viscous Interaction." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1442423671.
Full text
9
Jiménez, Piedrahita Martín Emilio. "Interpreting DGT measurements beyond steady-state and perfect-sink conditions." Doctoral thesis, Universitat de Lleida, 2017. http://hdl.handle.net/10803/405372.
Full textAbstract:
La tècnica "Diffusive Gradients in Thin Films" (DGT) permet estudiar la disponibilitat de contaminants o nutrients en aigües a partir de la seva acumulació en dispositius DGT, que acumulen els analits objectiu durant un període conegut de temps. En aquesta tesi es desenvolupen models fisicoquímics que tenen en compte el transport i les reaccions químiques de les espècies presents per a la interpretació de les acumulacions. Es dedica especial atenció als efectes electrostàtics que sorgeixen a baixa força iònica (en el rang típic de valors d'aigües dolces) entre cations metàl•lics o complexos carregats i els setis de resina. La influència de l'acumulació territorial en el disc de resina i la dependència de les constants de velocitat cinètica amb la força iònica son fenòmens que es consideren explícitament. Es desenvolupa també una eina de simulació basada en la resolució de les equacions de Nernst-Plack per a reproduïr les acumulacions experimentals de Mg i Mn, així com per a comprovar l'exactitud d'algunes expressions analítiques aproximades que es presenten. També es consideren situacions en les quals els efectes d'equilibri i competició són rellevants.Diffusive Gradients in Thin Films (DGT) technique allows studies of the availability of chemicals in waters by the deployment of DGT devices, which accumulate the target analytes for a known period of time. Physico-chemical models that consider the reactions and transport of species inside the device for the interpretation of the accumulations are developed in this thesis. Special attention is devoted to the electrostatic effects arising at low ionic strength (in the typical range of freshwaters) between metal cations or charged complexes and the resin sites. Influence of territorial binding in the resin disc and dependence of the kinetic rate constants on the ionic strength is explicitly considered. A simulation tool based on solving the Nernst-Plack equations is developped to reproduce the experimental aumulations of Mg and Mn, as well as to check the accuracy of some approximate analytical expressions here reported. Cases where the effective capacity or competition effects are relevant are also considered in this work.
La técnica analítica llamada Diffusive Gradients in Thin Films (DGT) permite estudiar la disponibilidad de contaminantes y nutrientes en aguas. Los dispositivos DGT se depositan en el medio para que acumulen el analito durante un período de tiempo determinado. En esta tesis se desarrollan modelos fisicoquímicos que consideran las reacciones y el transporte de especies dentro del dispositivo para la interpretación de las acumulaciones. Se presta especial atención a los efectos electrostáticos que se producen entre cationes metálicos o complejos cargados y los sitios de resina, para fuerzas iónicas en el rango de las aguas dulces. Se considera explícitamente la influencia del enlace territorial en el disco de resina y la dependencia de las constantes cinéticas de asociación y disociación con la fuerza iónica. Se desarrolla una herramienta de simulación basada en la resolución de las ecuaciones de Nernst-Plack para reproducir las acumulaciones experimentales de Mg y Mn, así como para comprobar la exactitud de algunas expresiones analíticas aproximadas presentadas en este trabajo. También se consideran situaciones en las cuales los efectos de equilibrio y competición son relevantes.
10
Bennetts, Tony Andrew. "Local scour around bridge piers under steady and unsteady flow conditions." Thesis, University of Hertfordshire, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394076.
Full text
11
Couture, Chad. "Steady States and Stability of the Bistable Reaction-Diffusion Equation on Bounded Intervals." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37110.
Full textAbstract:
Reaction-diffusion equations have been used to study various phenomena across different fields. These equations can be posed on the whole real line, or on a subinterval, depending on the situation being studied. For finite intervals, we also impose diverse boundary conditions on the system. In the present thesis, we solely focus on the bistable reaction-diffusion equation while working on a bounded interval of the form $[0,L]$ ($L>0$). Furthermore, we consider both mixed and no-flux boundary conditions, where we extend the former to Dirichlet boundary conditions once our analysis of that system is complete. We first use phase-plane analysis to set up our initial investigation of both systems. This gives us an integral describing the transit time of orbits within the phase-plane. This allows us to determine the bifurcation diagram of both systems. We then transform the integral to ease numerical calculations. Finally, we determine the stability of the steady states of each system.
12
McGenity, Philip Martin. "Studies of the Fischer-Tropsch reaction in steady state and transient conditions." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252650.
Full text
13
Ballukja, Erjon. "Power Quality Analysis in DC/DC Converters under Steady State and Transient Conditions." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
The modern electric power systems are going through significant changes because of continuous increasing demand of electric power. Further, a growing number of renewable energy systems that directly deliver DC power jointly considered with the advance in DC technology allows a more efficient and affordable use of energy. Furthermore, a rising use of DC systems and microgrids in a wide number of applications has motivated the study of Power Quality (PQ). The concept of power quality in DC systems and microgrids brings many challenges and the aim of this thesis is to understand the delivered power quality in DC microgrid systems. In this thesis, the effects of low frequency range (0-2 kHz) conducted emissions on power quality from a microgrid based DC/DC converter under steady state and transient loading conditions represent the main purpose of this work. Indeed, for a DC distribution network there is a lack of standards and guidelines concerning power quality issues and acceptable levels of conducted disturbances in the aforementioned frequency range. Consequently, the objective of this thesis is to quantify adequate power quality indices for DC systems or networks with connected loads such as Low Frequency Sinusoidal Disturbance (% LFSD) and Amplitude Probability Distribution (APD) indices.
14
Date, James Charles. "Performance prediction of high lift rudders operating under steady and periodic flow conditions." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390722.
Full text
15
Anderson, Mark Jule Jr. "Cooperative Behavior in Driven Lattice Systems with Shifted Periodic Boundary Conditions." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30606.
Full textAbstract:
We explore the nature of driven stochastic lattice systems with non-periodic boundary conditions. The systems consist of particle and holes which move by exchanges of nearest neighbor particle-hole pairs. These exchanges are controlled by the energetics associated with an internal Hamiltonian, an external drive and a stochastic coupling to a heat reservoir. The effect of the drive is to bias particle-hole exchanges along the field in such a way that a particle current can be established. Hard-core volume constraints limit the occupation of only one particle (hole) per lattice site. For certain regimes of the overall particle density and temperature, a system displays a homogeneous disordered phase. We investigate cooperative behavior in this phase by using two-point spatial correlation functions and structure factors. By varying the particle density and the temperature, the system orders into a phase separated state, consisting of particle-rich and particle-poor regions. The temperature and density for the co-existence state depend on the boundary conditions. By using Monte Carlo simulations, we establish co-existence curves for systems with shifted periodic boundary conditions.Ph. D.
16
Dave, Parth Pranavbhai. "Numerical simulation of blood flow in arterial stenosis under steady and pulsatile flow conditions." Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/3949.
Full textAbstract:
Cardiovascular diseases (CVDs) are among the leading causes of death in the world. In
this study, an attempt was made to model the flow dynamics of blood in abnormally narrowed
artery. Finite volume solver FLUENT was used for the analysis with the aim of understanding
the consequences of increasing the degree of stenosis using a two-equation turbulence model.
The compliant nature of the artery was neglected, and Newtonian behavior of the blood flow was
assumed for the larger arteries. Steady-flow simulations with 75% area reductions were used to
establish the validity of the current models by employing the standard and transitional variant of
the k turbulence models. Subsequently, it was found that transitional k model was
suitable for the low Reynolds number internal flows associated with the transition to turbulence,
although only a minor departure in terms of the turbulence intensity peak was observed.
Unsteady blood flow was introduced by employing a sinusoidal pulsatile waveform at the
inlet. The pulsatile nature of the blood flow was investigated in the range of the constriction ratio
from 60% to 90%, with an inlet-specified pulse. It was hypothesized that the severity of the
stenosis played a major role in the initiation of the turbulence, since no major turbulence was
reported for the 60% and 75% area reductions, while increasing the constriction ratio of 90%
significantly altered the flow dynamics and triggered the transition to turbulence much earlier
than anticipated. The outcome of current numerical efforts was expressed in terms of wall shear
stress, a hemodynamically relevant parameter.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
17
Ledgard, Louise Joyce. "Macrostructural and microstructural evolution during unidirectional solidification of aluminium alloys under steady state conditions." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385219.
Full text
18
Mu, Cheng. "Robust active vibration control of flexible rotor-bearing systems under steady and transient conditions." Thesis, University of Bath, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387119.
Full text
19
Qiao, Jun. "Diesel engine modelling under steady and transient conditions using a transputer-based concurrent computer." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/27160.
Full textAbstract:
The work presented describes the development of an interactive model to simulate a direct injection diesel engine under both steady and transient conditions, based on the application of concurrent process computing methods. Starting with the modelling of the engine under steady operating conditions, in which induction, injection, air entrainment, fuel air mixing, combustion, emission and mechanical friction processes are considered, the fuel pump, governor, engine crankshaft and external load dynamics are also investigated to model the transient behaviour of the engine and its associated load.
20
Palathamveed, Naqash. "Acoustic behavior of intake manifolds under tip-in and steady flow conditions an experimental investigation /." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1199738161.
Full text
21
Hartsock, Tanner. "Magma evolution, P-T conditions and volatile degassing of a steady-state volcano: Yasur, Vanuatu." Thesis, University of Iowa, 2019. https://ir.uiowa.edu/etd/6757.
Full textAbstract:
Yasur is an active scoria cone volcano in the Siwi Caldera on the island of Tanna, Vanuatu, in the South Pacific. This volcano has been erupting continuously for the last 800 years and is the latest manifestation of episodic volcanic activity in this area dating back to the late Pliocene. Yasur eruptions consist of intermittent Strombolian-style explosions of pyroclastic debris with emissions of volatiles such as SO₂, HCl and HF. Other than CO2 and H2O, the most abundant gas emitted from Yasur is sulfur, and plume monitoring has confirmed the volcano as one of the largest point sources of sulfur on the planet with an average flux of 600-1400 tons/day. Fluorine poses a chronic environmental health risk on Tanna, so understanding long-term exposure rates as well as periodic increases in volcanic intensity will help to better quantify its risk. In this study we gauge compositional variation of magma using fresh pyroclastic bombs collected over a 3-month period from August to November, 2016. Our results suggest long-term broad compositional stability in both the whole-rock and groundmass glass and minerals. Our results show slight variation in volatile phases in both olivine-hosted melt inclusions and groundmass glass over an intensively sampled 3-month period, which suggests that the plumbing beneath Yasur harbors an open-system degassing environment. Volcanic eruptions are usually driven by magma mixing, however, our results show no compositional variation in phenocrysts. We show that Yasur is an excellent example of an inefficiently degassed volcano, and that volcanic activity is controlled by volatile flux. We also use cotectic compositional data to calculate pressure and temperature conditions within the magma chamber and assess fluxes of volatiles from the magma using melt inclusion analyses for S and Cl. Our study places new bounds on the vertical extent of the magma chamber and suggests differentiation from a basaltic trachyandesite at depths of up to 12 km.
22
Casey, David Michael. "Characterization of Transition to Turbulence for Blood in an Eccentric Stenosis Under Steady Flow Conditions." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1418066674.
Full text
23
DelVecchio, Micah. "The Use of Conditional Convergence Between Economies to Estimate Steady State Incomes Within Economies." Thesis, Colorado State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3635596.
Full textAbstract:
This dissertation introduces a panel data method to estimate country-specific steady state levels of output in an augmented Solow growth model. The use of panel data permits the estimation of a country-specific effect which can explain the surprising result that many developing economies are above their steady states. These empirical results also confirm that the augmented Solow model can explain the present cross-country income divergence of developed and developing economies. Another application finds evidence that the post-Soviet economies began their transition toward markets with initial conditions of overcapitalization. Finally, when the results are sufficient, there is also the possibility of describing an entire period of growth and gaining insights into future periods. This is shown with the OECD economies.
In Islam (1995), panel data is first used to estimate the parameters of the Solow growth model. The following year, Cho and Graham (1996) published a small paper which illustrates a simple way to compute steady state levels of per capita income by using the results of cross-sectional convergence tests. This dissertation simply combines these two methods with the result that the interpretations are more satisfying. In sum, we find that countries can begin a period of development above or below their steady states and that countries converging from above should be considered to be overcapitalized. This implies that development through investment can only succeed when there is convergence from below the steady state. Above the steady state, total factor productivity is too low to sustain the relatively high levels of capital.
The organization of the dissertation is linear with an introduction preceding the second chapter's literature review and the development of a theoretical and empirical model in the third chapter. The applications of the method then follow. Chapter 4 uses a worldwide sample to compare the result to other work and to show that this fundamental model of growth theory can explain the observed increasing levels of international inequality. Chapter 5 takes a look at the transition economies. In addition to finding evidence of overcapitalization, this dissertation finds a positive correlation between growth and the privatization of small business under transition. Additionally, there is a negative impact of price liberalization under the conditions of repressed inflation experienced by many Soviet-era planned economies. Chapter 6 uses a sample of OECD economies to obtain a significant deterministic, technological growth rate. This is possible because the countries are similar enough to make the assumption that they have the same growth rate more realistic. This enables an understanding of steady states after the initial period and leading into the most contemporaneous period of the sample.
Keywords: macroeconomic analyses of economic development; institutions and growth; measurement of economic growth; cross-country output convergence; models with panel data; government policy; socialist systems and transitional economies: political economy, property rights; socialist institutions and their transitions
24
Loth, Francis. "Velocity and wall shear measurements inside a vascular graft model under steady and pulsatile flow conditions." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15907.
Full text
25
Liu, Dai. "Combustion and emissions of an automotive diesel engine using biodiesel fuels under steady and start conditions." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5797/.
Full textAbstract:
Biodiesels have been proved to reduce the smoke and THC emissions by many researchers. The demands of biodiesel are increasing all over the world. Various feedstocks of biodiesel have been used in different countries and regions. The blend ratio of biodiesel in petrol station is also varies. Therefore, more calibration works have been done for the car manufacturers. In first part this research, the combustion characteristics and emissions of using biodiesels from different feedstocks with different blend ratio was studied by experimental works. Statistical analysis indicated the correlation between emissions and fuel properties. Then, a smoke index, containing Reynolds Number of fuel spray, cetane number and gross heat value of combustion, was created and showed a significant linear relationship with the smoke emissions. The effects of engine loads and EGR rates on the relationship were also discussed. The second part of this research was focused on the cold start with using biodiesel blends. The tests were conducted in a wide range of the temperatures (from -20°C to 90°C). Results showed that the methyl ester biodiesel reduced the PM during the acceleration period of the start at 20°C conditions. As ambient temperature decreased, using of biodiesel shows an increased emissions of PM and THC. The chemical compositions of particle emissions with using biodiesel blends at cold start were identified by a 20-GC/MS and the results also confirmed this trend.
26
Zaker, Nazanin. "Population Dynamics In Patchy Landscapes: Steady States and Pattern Formation." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42279.
Full textAbstract:
Many biological populations reside in increasingly fragmented landscapes, which arise
from human activities and natural causes. Landscape characteristics may change
abruptly in space and create sharp transitions (interfaces) in landscape quality. How patchy landscape affects ecosystem diversity and stability depends, among other
things, on how individuals move through the landscape. Individuals adjust their
movement behaviour to local habitat quality and show preferences for some habitat
types over others. In this dissertation, we focus on how landscape composition and
the movement behaviour at an interface between habitat patches of different quality
affects the steady states of a single species and a predator-prey system.
First, we consider a model for population dynamics in a habitat consisting of two homogeneous one-dimensional patches in a coupled ecological reaction-diffusion
equation. Several recent publications by other authors explored how individual movement behaviour affects population-level dynamics in a framework of reaction-diffusion systems that are coupled through discontinuous boundary conditions. The movement between patches is incorporated into the interface conditions. While most of those works are based on linear analysis, we study positive steady states of the nonlinear equations. We establish the existence, uniqueness and global asymptotic stability of the steady state, and we classify their qualitative shape depending on movement behaviour. We clarify the role of nonrandom movement in this context, and we apply our analysis to a previous result where it was shown that a randomly diffusing population in a continuously varying habitat can exceed the carrying capacity at steady state. In particular, we apply our results to study the question of why and
under which conditions the total population abundance at steady state may exceed
the total carrying capacity of the landscape.
Secondly, we model population dynamics with a predator-prey system in a coupled
ecological reaction-diffusion equation in a heterogeneous landscape to study Turing
patterns that emerge from diffusion-driven instability (DDI). We derive the DDI
conditions, which consist of necessary and sufficient conditions for initiation of spatial
patterns in a one-dimensional homogeneous landscape. We use a finite difference
scheme method to numerically explore the general conditions using the May model, and we present numerical simulations to illustrate our results. Then we extend our
studies on Turing-pattern formation by considering a predator-prey system on an infinite patchy periodic landscape. The movement between patches is incorporated into the interface conditions that link the reaction-diffusion equations between patches.
We use a homogenization technique to obtain an analytically tractable approximate
model and determine Turing-pattern formation conditions. We use numerical simulations to present our results from this approximation method for this model. With
this tool, we then explore how differential movement and habitat preference of both
species in this model (prey and predator) affect DDI.
27
Helle, Steve. "A respirometric investigation of the activated sludge treatment of BKME during steady state and transient operating conditions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0013/NQ38893.pdf.
Full text
28
Mukondiwa, Steady. "Sulphur dioxide capture under fluidised bed combustion conditions using dolomite and coal ash as sorbents / Steady Mukondiwa." Thesis, North-West University, 2007. http://hdl.handle.net/10394/1570.
Full text
29
Palfreyman, Dean Daniel. "Aerodynamics of a a mixed flow turbocharger turbine under steady and pulse flow conditions : a numerical study." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417077.
Full text
30
Bin, Wan Salim Wan. "Study of externally waste-gated turbine performance under steady and pulsating inlet conditions for improved turbocharger matching." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25287.
Full textAbstract:
The demand for drastic reduction in CO2 emission among road vehicles has seen downsizing becoming a megatrend in modern engine developments due to its benefits in reducing throttling loss and improvement in engine efficiency. In light of this, turbocharging is seen as one of the key enabling technologies and therefore carries along with it an ever-increasing challenge in terms of system-matching as the device is required to operate in ranges never encountered before. The increasing reliance on 1-D engine performance simulation tools calls for more accurate representation of the turbocharger model. The present study assessed the turbocharger turbine maps for use in commercial 1-D gas dynamics engine code from several aspects, namely the width of the map and the representation of turbine unsteady performance in the virtual environment. Furthermore, the present work assessed the performance of turbine under waste-gated operations. For this, an experimental work has been carried out on a bespoke waste-gated turbine layout over a wide range of operating conditions. The performance of the radial turbine under steady inlet conditions was evaluated for different waste-gate openings, at various points along several speed-lines. Then the unsteady tests saw the turbine performance evaluated at various sets of pulse frequencies, turbine loadings and waste-gate openings. Analysis of this study include the impact of turbine map width on the turbine performance modelling in a commercial 1-D gas dynamics engine simulation software and subsequently the prediction of the engine’s performance. This simulation work is carried out based on an actual heavily downsized gasoline engine with a series super-turbocharging system. The study also examined the method of incorporating the effects of turbine unsteady performance under waste-gated and non-waste-gated conditions in the performance maps used in 1-D code and evaluate its impact on the engine performance prediction. The outcome of the study aims at providing a deeper understanding on the unsteady performance of a turbocharger turbine which will lead to improved turbocharger-engine matching methods in the future.
31
Mailloux, James Thomas. "Design Evaluation of a Duplex Circular Wet Well Pumping Station Under Steady State and Dynamic Operating Conditions." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/471.
Full textAbstract:
Duplex Circular Wet Well (DCWW) lifting pump stations are utilized for pumping clear and solid-bearing liquid. Understanding the effect of design criteria on pump performance is important to minimize maintenance costs and maximize efficiency. There are currently no known full-scale laboratory studies that have been performed to investigate the overall design of DCWWs. The objective of the research was to evaluate the impact of various design criteria, such as internal geometry and operating conditions on the performance of DCWW pump stations and provide documentation and recommendations which will be used to augment the current Hydraulic Institute/American National Standard for Pump Intake Design (ANSI/HI 9.8-1998), (HI) guidelines. The research was conducted in two phases; Phase 1 consisted of performing a comparative analysis of the basic flow patterns within the wet well by means of Computational Fluid Dynamics (CFD), Phase 2 consisted of performing detailed evaluations of various design aspects on pump performance using a full-scale Physical Model constructed for the research. The CFD research provided indications regarding potential performance problems that may occur due to poor flow patterns and potential pump suction swirl, while the physical research provided a basis for determining the relative advantages of different designs. The physical research included the evaluation of general flow patterns, free-surface and subsurface vortices, air entrainment and pump suction swirl. Measurement of the steady state swirl within the pump showed unacceptable performance in accordance with the HI acceptance criteria. Swirl data collected under real-world dynamic operating conditions showed that the pump typically did not experience the adverse conditions indicated at steady state. Normal (symmetrical) pump orientation resulted in more favorable operation in terms of pump swirl and ingestion of entrained air than a coplanar (inline) condition. A minimum water elevation was established to minimize air-entrainment and swirl entering the pumps, reducing possible effects such as cavitation and vibration of the pump impeller. Air-core subsurface vortices were present under the pumps, requiring pump-cones to be installed. The collection of real-time dynamic data will allow design engineers to better understand actual pump performance under normal cycling and clean-out modes, reducing the operating time under unfavorable conditions and overall maintenance requirements.
32
Ferdowsi, Milad. "Methane biofiltration in the absence and presence of ethanol vapors under steady state and transient state conditions." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/10536.
Full textAbstract:
Les émissions de méthane (CH[indice inférieur 4]), gaz à effet de serre provoquant le réchauffement climatique doivent être contrôlées. Les biofiltres peuvent être utilisés pour atteindre cet objectif. Les émissions de CH[indice inférieur 4] issues des industries agroalimentaires ou du traitement des eaux peuvent être accompagnées de vapeurs d’alcool. La présence simultanée de CH[indice inférieur 4], polluant à limitation par transfert de masse et d’alcool, polluant à limitation cinétique dans un mélange gazeux peut induire des limitations dans le biofiltre. L’objectif principal de cette recherche est l’évaluation des limitations dans un biofiltre traitant le CH[indice inférieur 4] en présence ou en absence de vapeur d’alcool en régime permanent ou transitoire. Dans un premier temps, une revue de littérature s’est penchée sur les limitations basées sur le transfert de masse et la cinétique lors de l’enlèvement de polluants organiques dans un biofiltre. Par la suite, l’élimination du CH[indice inférieur 4] a été effectuée dans un biofiltre afin d’évaluer l’influence de la concentration à l’entrée du biofiltre sur la performance du biofiltre. Une capacité d’élimination maximale de 45 g [indice supérieur -3] h[indice supérieur -1] a été obtenue pour une charge à l’entrée de 87 g [indice supérieur -3] h[indice supérieur -1] du biofiltre. Le biofiltre a toléré des charges par à-coups de CH[indice inférieur 4] de même que des privations de CH[indice inférieur 4] et de nutriments. Par conséquent, les comportements en régimes permanent et transitoire d’élimination du CH[indice inférieur 4] en présence de vapeurs d’éthanol ont été étudiés dans un biofiltre ayant un lit filtrant inorganique sous des temps de résidence en fût vide (EBRT) de 6, 3 et 1.5 minutes. L’ajout d’éthanol sur 3 cycles a été effectué en fonction des 3 EBRTs. Un EBRT de 6 min correspondant à des charges à l’entrée de CH4 et d’éthanol de 4.5 et de 132 g [indice supérieur -3] h[indice supérieur -1] a induit des limitations mineures en ce qui a trait à l’enlèvement du CH[indice inférieur 4] et de l’éthanol. En régime transitoire, la période de récupération après les 3 cycles a nécessité 10 à 25 jours. Ce délai est relié à la présence d’éthanol dans le lixiviat. Dans un dernier temps, deux biofiltres ayant un garnissage de pierres et un garnissage mixte ont été comparés pour l’enlèvement du CH[indice inférieur 4] et de l’éthanol présents dans un mélange gazeux en régime permanent. La section inférieure du biofiltre a permis l’élimination totale de l’éthanol. De plus, lors de l’élimination totale de l’éthanol dans la section inférieure du biofiltre, la production de dioxyde de carbone (CO[indice inférieur 2]) dépasse 16 g[indice supérieur -3] h[indice supérieur -1], pour des charges à l’entrée de CH[indice inférieur 4] et d’éthanol de 11 et 13 g m[indice supérieur -3] h[indice supérieur -1] respectivement. Par ailleurs, une concentration en éthanol dans le lixiviat excédant 2500 géthanol m[indice supérieur -3] lixiviat a été obtenue. Les biofiltres ont démontré une flexibilité pour des charges par à-coups d’éthanol suivies de périodes de carence. Le principal inconvénient du biofiltre à lit de pierres par rapport au biofiltre mixte est une perte de charge élevée dans la section inférieure du biofiltre. Une période de carence est un excellent moyen de contrer la perte de charge.Abstract : Since methane (CH[subscript 4]) is a greenhouse gas with hazardous effects for global warming, every effort should be made to reduced methane emissions. Biofilters are potential candidates for CH[subscript 4] removal. In food and beverage industries as well as ethanol refineries, the feed of the biofilter might be a mixture of CH[subscript 4] emissions from wastewater treatment unit and ethanol emissions from other units. The presence of CH[subscript 4] as a mass transfer limited and ethanol vapor as a kinetic limited pollutant in a mixture can produce several limitations in a biofilter. The main objective of this research is to evaluate the limitations of CH[subscript 4] biofiltration or in the presence of ethanol vapors under steady and transient state conditions. First, a literature review was provided on mass transfer and kinetic limited organic pollutants removal in biofilters and the related limitations. Subsequently, the CH[subscript 4] elimination was assessed in a biofilter in order to evaluate the effect of CH[subscript 4] inlet concentration in the range of 1000 to 13000 ppmv and a gas flow rate of 3 L min[supercript -1] on the biofilter performance. A maximum CH[subscript 4] elimination capacity (ECmax) of 45 g m[superscript -3] h[superscript -1] was obtained for a CH[subscript 4] inlet load (IL) of 87 g m[superscript -3] h[superscript -1]. The biofilter tolerated CH[subscript 4] shock loads as well as different types of CH[subscript 4] and nutrient starvations. Subsequently, the steady state and dynamic behaviors of CH[subscript 4] elimination in the presence of ethanol vapor was studied in an inorganic bed biofilter with empty bed residence times (EBRTs) of 6, 3 and 1.5 min. Ethanol addition was performed in 3 cycles based on the EBRTs. An EBRT of 6 min with corresponding CH[subscript 4] and ethanol inlet loads of 132 and 4.5 gpollutant m[superscript -3] h[superscript -1] respectively, caused the least limitations for the simultaneous removal of CH[subscript 4] and ethanol in the biofilter. According to dynamic behavior of the biofilter, the recovery time after the three cycles took from 10 to 25 days. The delayed biofilter recovery was linked to the presence of ethanol in the liquid effluent. Finally, a stone-based bed and a hybrid packing biofilter were compared for CH[subscript 4] and ethanol removal in a mixture under steady and transient state conditions. Ethanol was completely removed in the bottom sections of both biofilters. A large carbon dioxide (CO[subscript 2]) production rate exceeding 18 g m[superscript -3] h[superscript -1] occurred in the bottom sections for CH[subscript 4] and ethanol inlet loads of 11 and 13 g m[superscript -3] h[superscript -1] respectively. In addition, an ethanol concentration in the leachate exceeding 2500 gethanol m[superscript -3] leachate was obtained for both biofilters. The biofilters were flexible to an ethanol shock load followed by a starvation period. The main drawback of the stone based bed biofilter compared to the hybrid packing biofilter was an excess pressure drop in the bottom section. Starvation was found an effective strategy for reducing the pressure drop.
33
Ніценко, Володимир Вікторович. "Підвищення показників ефективності функціонування релейного захисту збірних шин розподільчих установок." Thesis, Запорізький національний технічний університет, 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/34557.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук (доктора філософії) зі спеціальності 05.14.02 – Електричні станції, мережі і системи. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018.
Дисертація присвячена розв'язанню актуальної науково-прикладної задачі у галузі релейного захисту елементів електроенергетичних систем, що полягає у підвищенні ефективності дії релейного захисту збірних шин розподільчих установок. У роботі вдосконалено метод диференційно-фазного захисту шин, згідно з яким алгоритм порівняння фаз струмів застосовано у якості єдиного засобу забезпечення абсолютно селективної дії захисту в аварійних режимах, та запроваджено групу неконфігурованих параметричних уставок захисту, що сприяє зниженню ймовірності його неселективної дії через допущені персоналом помилки, а також, за рахунок оптимізації умов пуску та спрацювання захисту, підвищується їх успішність за внутрішніх коротких замикань, що дозволяє відмовитись від застосування окремого високочутливого органу захисту. Для поліпшення експлуатаційних характеристик та усунення режимних обмежень застосування пристроїв релейного захисту шин вдосконалено метод компенсації кутових похибок насичених трансформаторів струму у диференційно-фазному захисті шин в частині забезпечення подовження логічних імпульсів напруги, сформованих із напівхвиль спотворених струмів. Обрано робочі уставки параметрів налаштування диференційно-фазного захисту шин, а саме кута блокування ±φбл=900 та рівня формування імпульсів ±ір=(40-50)%·Іамп, за яких забезпечуватиметься його надійна та селективна дія в аварійних режимах. Проведено математичне і імітаційне моделювання поведінки диференційно-фазного захисту шин та лабораторні досліди його макетного зразку, що дозволило підтвердити адекватність розробленої моделі захисту, ефективність її алгоритмів та правильність обраних робочих уставок. Виконано аналіз техніко-економічних показників застосування диференційно-фазного захисту шин, на підставі якого визначені його переваги у порівнянні з пристроями диференційного струмового захисту шин та оцінені показники економічної ефективності його впровадження та експлуатації.Dissertation for a candidate degree (PhD) in Engineering Sciences of the speciality 05.14.02 – Electric power stations, networks and systems. – National technical university "Kharkiv polytechnic institute", Kharkiv, 2018. The dissertation is devoted to the solution of the actual scientific and practical problem in the field of relay protection of electric power systems elements, which is to increase the efficiency of relay busbar protection of switchgears. In this work, the method of phasedifferential busbar protection has been improved, according to which the currents phases comparison algorithm is applied as the sole means of providing absolutely selective protection in emergency conditions, and a group of non-configured parametric settings is introduced that reduces the probability of its non-selective operation through mistakes made by the personnel, as well as due to optimization start and trip conditions of protection operation, its performance increases at internal faults, which allows to refuse the application a high-sensitive protection relay. In order to improve the performance and eliminate the regime limitation of the use of relay protection devices, the method of compensating angular errors of saturated current transformers in the phase-differential busbar protection in the part of ensuring the extension of logic voltage impulses formed from half-waves of distorted currents is improved. The working parameters of the phase-differential busbar protection have been selected, namely the blocking angle is 900 and the impulse formation level is (40-50)%·Іamp, which will ensure its reliable and selective operation in emergency conditions. The mathematical and simulation modeling of the phasedifferential protection behavior and laboratory experiments of its model was carried out, which allowed to confirm the adequacy of the developed model of protection, the efficiency of its algorithms and the correctness of the selected working settings. There were completed analysis of technical and economic indicators of the phase-differential busbar protection using, on the basis of which were determined its advantages compared with the devices of differential busbar protection and approximate estimates of the economic efficiency of its implementation and operation.
34
Van, Rooyen J. A. "Performance trends of an air-colled steam condenser under windy conditions /." Link to the online version, 2007. http://hdl.handle.net/10019/481.
Full text
35
Gall, M. "Study of SCR using Cu-Zeolite catalysts on a light-duty diesel engine under steady state and transient conditions." Thesis, Coventry University, 2015. http://curve.coventry.ac.uk/open/items/b4b020c3-aa97-435f-9bcc-746d63253cc3/1.
Full textAbstract:
The recognition of the negative impact of NOx resulted in increasingly tighter automotive emission regulations. Companies are under pressure to develop methods, which can meet the legislative demands. After treatment solutions, and especially Selective Catalytic Reduction, became the focus of research and have shown so far promising results. However, more in depth understanding of the SCR process under different conditions is needed. This thesis describes an investigation of the SCR performance using gas and urea injections under steady state and transient conditions undertaken on a light duty diesel engine using a 1D exhaust system designed for uniform flow across the catalyst. Under steady state conditions, the SCR performance was examined for low and high temperature conditions. Ammonia was supplied either as 5% ammonia gas or in form of urea injection. The engine was operating at 1500 rpm and 6 and 8 bar BMEP to provide an exhaust gas temperature of 210 °C and 265 °C respectively. Also, the effect of SCR brick length on the NOx conversion was investigated using SCR catalysts of length 30, 45 and 75 mm. To measure the influence of NO2:NOx ratio on the SCR performance, different sizes of standard DOC were used. NH3:NOx dosage levels included; α~0.5 - deficient ammonia, α~1.0 - stoichiometric ammonia, α~1.25 - excess ammonia. Gas emissions were measured before and after the SCR catalysts with a Horiba FTIR analyser during steady state and long transient tests. It was found that conditions such as temperature and NO2:NOx had the biggest impact on the SCR performance. During the steady state engine conditions, at α~1.0 ammonia dosing and NO2:NOx ratio of 0, only 17% of NO was converted in the first 30 mm of the SCR brick length. The conversion was improved at high temperature (263 °C) to 31%. A fast response CLD analyser was used during short transient testing to sample emissions with a high resolution. The short transient test with standard 0.5 and 1 DOC, and fixed ammonia dosing, showed that NOx conversion was reduced during the ramp event due to deficient ammonia and a drop in the supplied NO2:NOx ratio. During urea injection experiments, urea was injected either through an oblique pipe arrangement with a mixer device placed downstream or directly into a mixing can. In this case the mixer device was replaced with a straight pipe. A 75mm SCR was fitted and to ensure that supplied NO2:NOx ratio was zero, a palladium only DOC was used post a DPF. It was found that a large proportion of urea decomposition and hydrolysis was occurring on the surface of the SCR catalyst. Comparing NOx performance between urea injection and ammonia gas dosing experiment, more NO was converted for a given NH3:NOx ratio when ammonia was supplied in the form of gas. That was true for low and high temperature tests. For most studies, a long 10 degree diffuser was used in front of the SCR to provide uniform gas distribution across the catalyst. In addition SCR performance was investigated with a 180 degree sudden expansion diffuser in order to measure the influence of temperature and velocity profiles. During this study, a 45 mm SCR catalyst was used to provide a moderate amount of NO conversion and ammonia slip. The results showed that the flow and temperature distribution upstream of the SCR catalyst will have an effect on the NOx conversion, and that gas velocity has bigger impact on NOx conversion than gas temperature.
36
Tesfa, Belachew Chekene. "Investigations into the performance and emission characteristics of a biodiesel fuelled CI engine under steady and transient operating conditions." Thesis, University of Huddersfield, 2011. http://eprints.hud.ac.uk/id/eprint/11072/.
Full textAbstract:
The stringent emission laws, the depletion of petroleum reserves and the relation of fuels with politics have forced the world to find alternatives to fossil fuels. Biodiesel is one of the biofuels which is renewable and environmentally friendly and can be used in diesel engines with little or no modifications. For the last two decades, many researchers have reported extensive work on the performance and emission characteristics of engines running with biodiesel during steady state operation. However, there are numbers of knowledge gaps that have been identified which include limited information on biodiesel physio-chemical properties and their effects on combustion behaviour and performance and emission characteristics of the engine. In this study after an exhaustive literature review, the following four research areas have been identified and investigated extensively using available numerical and experimental means. The initial focus was to investigate the most important properties of biodiesel such as density, viscosity and lower heating value using experimental and numerical techniques. The effects of biodiesel blend content on the physical properties were analysed. For each property, prediction models were developed and compared with current models available in literature. New density and viscosity prediction models were developed by considering the combined effect of biodiesel content and temperature. All the empirical models have showed a fair degree of accuracy in estimating the physical properties of biodiesel in comparison to the experimental results. Finally, the effects of density and viscosity on the fuel supply system were investigated. This system includes the fuel filter, fuel pump and the engine combustion chamber in which air-fuel mixing behaviour was studied numerically. These models can be used to understand the effects of changes in the physical properties of the fuel on the fuel supply system. In addition, the fuel supply system analysis can be carried out during the design stage of fuel pump, fuel filter and injection system. The second research objective was the investigation into a CI engine’s combustion characteristics as well as performance and emissions characteristics under both the steady and transient conditions when fuelled with biodiesel blends. The effects of biodiesel content on the CI engine’s in-cylinder pressure, brake specific fuel consumption, thermal efficiency and emissions (CO2, NOx, CO, THC) were evaluated based on experimental results. It has been seen that the CI engine running with the biodiesel resulted in acceptable engine performance as well as reduction in main emissions (except NOx). Following this study, a detailed analysis on the transient performance and emission output of the CI engine has been carried out. During this analysis, the emission changing rate is investigated during speed transient and torque transition stages. Further to this, a transient emission prediction model has been developed using associated steady and transient emission data. The model has been shown to predict the transient emission reasonably accurately. The third research objective was to develop a method for on-line measurement of NOx emission. For this purpose the in-cylinder pressure generated within a CI engine has been measured experimentally along with mass air flow and these parameters have been used in the development of a NOx prediction model. This model has been validated using experimental data obtained from a NOx emission analyzer. The predicted data obtained from NOx prediction model has been compared with measured data and has shown that the deviation is within acceptable range. The final research objective was to develop a simple, reliable and low-cost novel method to reduce the NOx emission of the CI engine when using biodiesel blends. A potential solution to this problem has been found to be in the form of direct water injection which has shown to be capable to reduce NOx emission. Using a water injection technique, the performance and emission(NOx and CO) characteristics of a CI engine fuelled with biodiesel has been investigated at varying water injection flow rates. Intake manifold water injection reduces NOx emission by up to 40% over the entire operating range without compromising the performance characteristics of the CI engine
37
Poczka, Christopher M. R. "Investigation of operational conditions of steam traps through acoustic emission." Thesis, University of Sussex, 2012. http://sro.sussex.ac.uk/id/eprint/7654/.
Full text
38
Ніценко, Володимир Вікторович. "Підвищення показників ефективності функціонування релейного захисту збірних шин розподільчих установок." Thesis, НТУ "ХПІ", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/34554.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук (доктора філософії) зі спеціальності 05.14.02 – Електричні станції, мережі і системи. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2018.
Дисертація присвячена розв'язанню актуальної науково-прикладної задачі у галузі релейного захисту елементів електроенергетичних систем, що полягає у підвищенні ефективності дії релейного захисту збірних шин розподільчих установок. У роботі вдосконалено метод диференційно-фазного захисту шин, згідно з яким алгоритм порівняння фаз струмів застосовано у якості єдиного засобу забезпечення абсолютно селективної дії захисту в аварійних режимах, та запроваджено групу неконфігурованих параметричних уставок захисту, що сприяє зниженню ймовірності його неселективної дії через допущені персоналом помилки, а також, за рахунок оптимізації умов пуску та спрацювання захисту, підвищується їх успішність за внутрішніх коротких замикань, що дозволяє відмовитись від застосування окремого високочутливого органу захисту. Для поліпшення експлуатаційних характеристик та усунення режимних обмежень застосування пристроїв релейного захисту шин вдосконалено метод компенсації кутових похибок насичених трансформаторів струму у диференційно-фазному захисті шин в частині забезпечення подовження логічних імпульсів напруги, сформованих із напівхвиль спотворених струмів. Обрано робочі уставки параметрів налаштування диференційно-фазного захисту шин, а саме кута блокування ±φбл=900 та рівня формування імпульсів ±ір=(40-50)%·Іамп, за яких забезпечуватиметься його надійна та селективна дія в аварійних режимах. Проведено математичне і імітаційне моделювання поведінки диференційно-фазного захисту шин та лабораторні досліди його макетного зразку, що дозволило підтвердити адекватність розробленої моделі захисту, ефективність її алгоритмів та правильність обраних робочих уставок. Виконано аналіз техніко-економічних показників застосування диференційно-фазного захисту шин, на підставі якого визначені його переваги у порівнянні з пристроями диференційного струмового захисту шин та оцінені показники економічної ефективності його впровадження та експлуатації.Dissertation for a candidate degree (PhD) in Engineering Sciences of the speciality 05.14.02 – Electric power stations, networks and systems. – National technical university "Kharkiv polytechnic institute", Kharkiv, 2018. The dissertation is devoted to the solution of the actual scientific and practical problem in the field of relay protection of electric power systems elements, which is to increase the efficiency of relay busbar protection of switchgears. In this work, the method of phasedifferential busbar protection has been improved, according to which the currents phases comparison algorithm is applied as the sole means of providing absolutely selective protection in emergency conditions, and a group of non-configured parametric settings is introduced that reduces the probability of its non-selective operation through mistakes made by the personnel, as well as due to optimization start and trip conditions of protection operation, its performance increases at internal faults, which allows to refuse the application a high-sensitive protection relay. In order to improve the performance and eliminate the regime limitation of the use of relay protection devices, the method of compensating angular errors of saturated current transformers in the phase-differential busbar protection in the part of ensuring the extension of logic voltage impulses formed from half-waves of distorted currents is improved. The working parameters of the phase-differential busbar protection have been selected, namely the blocking angle is 900 and the impulse formation level is (40-50)%·Іamp, which will ensure its reliable and selective operation in emergency conditions. The mathematical and simulation modeling of the phasedifferential protection behavior and laboratory experiments of its model was carried out, which allowed to confirm the adequacy of the developed model of protection, the efficiency of its algorithms and the correctness of the selected working settings. There were completed analysis of technical and economic indicators of the phase-differential busbar protection using, on the basis of which were determined its advantages compared with the devices of differential busbar protection and approximate estimates of the economic efficiency of its implementation and operation.
39
Zhang, Luying. "Rotating instability on steam turbine blades at part-load conditions." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:cf8ecad1-0fd2-49b7-8e28-6d00c62c173e.
Full textAbstract:
A computational study aimed at improving the understanding of rotating instability in the LP steam turbine last stage working under low flow rate conditions is described in this thesis. A numerical simulation framework has been developed to investigate into the instability flow field. Two LP model turbine stages are studied under various flow rate conditions. By using the 2D simulations as reference and comparing the results to those of the 3D simulations, the basic physical mechanism of rotating instability is analysed. The pressure ratio characteristics across the rotor row tip are found to be crucial to the inception of rotating instability. The captured instability demonstrates a 2D mechanism based on the circumferential variation of unsteady separation flow in the rotor row. The 3D tip clearance flow is found not a necessary cause of the instability onset. Several influential parameters on the instability flow are also investigated by a set of detailed studies on different turbine configurations. The results show that the instability flow pattern and characteristics can be altered by the gap distance between the stator and rotor row, the rotor blading and the stator row stagger angle. Some flow control approaches are proposed based on the observations, which may also serve as design reference. The tip region 3D vortex flow upstream to the rotor row is also captured by the simulations under low flow rate conditions. Its appearance is found to be able to suppress the inception of rotating instability by disrupting the interaction between the rotor separation flow and the incoming flow. Finally, some recommendations for further work are proposed.
40
Lee, Charles Sim Jem. "An ex-situ study of polymer electrolyte membrane fuel cell gas diffusion layer durability under steady-state and freezing conditions." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/31663.
Full textAbstract:
Polymer electrolyte membrane fuel cells (PEMFCs) are being developed to meet the lifetime
requirements expected in commercial applications. While the effect of the gas diffusion layer (GDL) on
performance has been studied, little is known of the impact of GDL materials and designs on PEMFC
durability. Successful development of durable components such as the GDL is essential to achieving
PEMFC system requirements for commercial applications.
In this study, GDL compressive strain under steady-state and freezing conditions, and the effects of
freezing conditions on GDL properties of electrical resistivity, bending stiffness, air permeability, surface
contact angle, porosity and water vapor diffusion were studied. A GDL was aged ex-situ and its
characteristics were evaluated as a function of aging time.
GDL strain was measured to occur under steady-state aging conditions (80 °C and 200 psi). A maximum
strain of 0.98 % was measured over 1500 hours of aging time. Increasing temperature to 120 °C or
applied load to 400 psi resulted in maximum strains of 2.0 % and 1.5 %, respectively. Water phase
transition during freezing conditions (54 freeze-thaw cycles between -35 and 20 °C) had no effect on GDL
strain.
No change in in-plane electrical resistivity, bending stiffness, surface contact angle, porosity and water
vapor diffusion, through 50 consecutive freeze-thaw cycles between -35 and 20 °C, was measured. An
increase in in-plane and through-plane air permeability (18 and 80 % respectively) was attributed to
material loss during permeability measurements. Ex-situ tests showed that convective air flow can cause
material loss, resulting in increased permeability and further convection. The GDL was shown to be
much more resilient to material loss in the absence of water phase transitions.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
41
Johnson, Stephen E. "Response of mat conditions and flakeboard properties to steam- injection variables." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03242009-040404/.
Full text
42
Van, Rooyen J. A. "Performance trends of an air-cooled steam condenser under windy conditions." Thesis, Stellenbosch : University of Stellenbosch, 2007. http://hdl.handle.net/10019.1/1629.
Full textAbstract:
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007.Air-cooled steam condensers (ACSC’s) are increasingly employed to reject heat in modern power plants. Unfortunately these cooling systems become less effective under windy conditions and when ambient temperatures are high. A better understanding of the fundamental airflow patterns about and through such air-cooled condensers is essential if their performance is to be improved under these conditions. For known flow patterns, improved fan designs are possible and flow distortions can be reduced by means of extended surfaces or skirts, windwalls and screens. Spray cooling of the inlet air or the addition of an evaporative cooling system can also be considered for improving performance under extreme conditions. The present numerical study models the air flow field about and through an air-cooled steam condenser under windy conditions. The performance of the fans is modeled with the aid of a novel numerical approach known as the “actuator disc model”. Distorted airflow patterns that significantly reduce fan performance in certain areas and recirculatory flows that entrain hot plume air are found to be the reasons for poor ACSC performance. It is found that the reduction in fan performance is the main reason for the poor ACSC performance while recirculation of hot plume air only reduces performance by a small amount. Significant improvements in ACSC performance are possible under these conditions if a cost effective skirt is added to the periphery of the ACSC while the installation of a screen under the ACSC has very little effect.
43
Hoffmann, Franziska Marie [Verfasser]. "Distribution and interactions of pulmonary phagocytes in the murine lung under steady-state conditions and after allergen challenge / Franziska Marie Hoffmann." Lübeck : Zentrale Hochschulbibliothek Lübeck, 2017. http://d-nb.info/1149417862/34.
Full text
44
Louw, Francois G. "Performance trends of a large air-cooled steam condenser during windy conditions." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6593.
Full text
45
Owen, Michael Trevor Foxwell. "A numerical investigation of air-cooled steam condenser performance under windy conditions." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4101.
Full textAbstract:
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: This study is aimed at the development of an efficient and reliable method of evaluating the performance of an air-cooled steam condenser (ACSC) under windy conditions, using computational fluid dynamics (CFD). A two-step modelling approach is employed as a result of computational limitations. The numerical ACSC model developed in this study makes use of the pressure jump fan model, amongst other approximations, in an attempt to minimize the computational expense of the performance evaluation. The accuracy of the numerical model is verified through a comparison of the numerical results to test data collected during full scale tests carried out on an operational ACSC. Good correlation is achieved between the numerical results and test data. Further verification is carried out through a comparison to previous numerical work. Satisfactory convergence is achieved for the most part and the few discrepancies in the results are explained. The effect of wind on ACSC performance at El Dorado Power Plant (Nevada, USA) is investigated and it is found that reduced fan performance due to distorted flow at the inlet of the upstream fans is the primary contributor to the reduction in performance associated with increased wind speed in this case. An attempt is subsequently made to identify effective wind effect mitigation measures. To this end the effects of wind screens, solid walkways and increasing the fan power are investigated. It is found that the installation of an appropriate wind screen configuration provides a useful means of reducing the negative effects of wind on ACSC performance and an improved wind screen configuration is suggested for El Dorado. Solid walkways are also shown to be beneficial to ACSC performance under windy conditions. It is further found that ACSC performance increases with walkway width but that the installation of excessively wide walkways is not justifiable. Finally, increasing the fan power during periods of unfavourable ambient conditions is shown to have limited benefit in this case. The model developed in this study has the potential to allow for the evaluation of large ACSC installations and provides a reliable platform from which further investigations into improving ACSC performance under windy conditions can be carried out.
AFRIKAANSE OPSOMMING: Hierdie studie is daarop gemik om die ontwikkeling van 'n geskikte en betroubare metode van evaluering van die verrigting van ’n lugverkoelde stoom-kondensator (air-cooled steam condenser, ACSC) onder winderige toestande, met behulp van numeriese vloei-dinamika. ’n Twee-stap modelleringsbenadering is aangewend as gevolg van rekenaar beperkings. Die numeriese ACSC-model wat in hierdie studie ontwikkel is, maak gebruik van die druksprong waaier model, asook ander benaderings, in ’n poging om die berekeningskoste van die verrigting-evaluering te verminder. Die akkuraatheid van die numeriese model is bevestig deur middel van ’n vergelyking van die numeriese resultate met toetsdata ingesamel tydens die volskaal toetse uitgevoer op ’n operasionele ACSC. Goeie korrelasie is bereik tussen die numeriese resultate en toetsdata. Verdere bevestiging is uitgevoer deur middel van ’n vergelyking met vorige numeriese werk. Bevredigende konvergensie is in die algemeen bereik en die paar verskille in die resultate word verduidelik. Die effek van wind op ACSC verrigting by El Dorado Power Plant (Nevada, VSA) is ondersoek, en daar is bevind dat verlaagde waaierverrigting, as gevolg van vervormde vloei by die inlaat van die stroomop waaiers, die primêre bydraer is tot die afname in ACSC werkverrigting geassosieer met verhoogde windsnelheid in hierdie geval. ’n Poging word dan aangewend om effektiewe wind-effek velagingsmaatreëls te identifiseer. Windskerms, soliede wandelvlakke en die verhoging van die waaierkrag word gevolglik ondersoek. Daar is bevind dat die installasie van ’n toepaslike windskerm-opset ’n nuttige middel tot ’n vermindering van die negatiewe effekte van wind op ACSC verrigting bied, en ’n verbeterde windskerm opset is voorgestel vir El Dorado. Soliede wandelvlakke word ook aanbeveel as voordelig vir ACSC verrigting onder winderige toestande. Dit is verder bevind dat die ACSC prestasie verhoog met wandelvlak breedte, maar dat die installasie van ’n te ruim wandelvlak nie regverdigbaar is nie. Ten slotte, word bewys dat die verhoging van die waaierkrag tydens periodes van ongunstige omgewingsomstandighede ’n beperkte voordeel in hierdie geval het. Die model wat ontwikkel is in hierdie studie het die potensiaal om voorsiening te maak vir die evaluering van groot ACSC- installasies en bied ’n betroubare platform vanwaar verdere ondersoeke tot die verbetering van ACSC verrigting onder winderige toestande uitgevoer kan word.
46
Siddique, Mansoor. "The effects of noncondensable gases on steam condensation under forced convection conditions." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13219.
Full text
47
Hasanein, Hisham A. (Hisham Abdel-Moneim). "Steam condensation in the presence of noncondensable gases under forced convection conditions." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28075.
Full text
48
Ferré, Paul Andrew Ty. "Design and analysis of time domain reflectometry probes for measuring water content and bulk electrical conductivity under steady and transient flow conditions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22200.pdf.
Full text
49
Vyčítal, Václav. "Ustálený chod a zkratové poměry v síti 110 kV E.ON napájené z transformovny Sokolnice." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221345.
Full textAbstract:
This thesis can be divided into five main parts. The first part deals with theoretical analysis of power flow calculation in power network during steady state condition. Load flow calculation is presented here as a linear and nonlinear problem. Newton iteration method is proposed for solving power flow as nonlinear problem. The second part of this thesis deals with the analysis of short-circuit calculation in accordance with valid International Standard IEC 60909. The equivalent voltage source method is adopted in case of the short-circuit calculation. For the calculation of unbalanced short-circuit currents, the symmetrical components method is also presented. The last three parts of this paper are focused on calculations of power flow and short-circuit conditions in power grid Sokolnice. So in the third part is the description of nodal area Sokolnice with its substations and the calculation of load flow and short-circuit conditions for two different power supply options. For each supply option is also considered an abnormal (fault) grid condition. (overall there are solved four different options) The fourth part of this thesis deals with the result analysis and also the results of different power supply options are compared. In the last part there are presented necessary technical improvements for fault-free operation of power grid Sokolnice based on the result of power flow and short-circuit conditions in that grid.
50
Dehbi, Abdelouahab A. (Abdelouahab Abdoun). "The effects of noncondensable gases on steam condensation under turbulent natural convection conditions." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13905.
Full text