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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Estudio y análisis de las membranas flexibles como elemento de soporte para la estabilización de taludes y laderas de suelos y/o materiales sueltos.

Castro Fresno, Daniel 28 March 2001 (has links)
Los taludes recién construidos presentan un aspecto adecuado y una superficie regular y estable, pero por diversos agentes se erosionan rápidamente. Una técnica a utilizar para la estabilización y control de la erosión es el empleo de mallas arriostradas al terreno mediante anclajes. Esto facilita la revegetación, la integración paisajística y un bajo impacto medioambiental. Los resultados han sido dos modelos físico-matemáticos para el diseño de dos sistemas flexibles antierosión y de estabilización superficial de desmontes. En el primero, la membrana se encuentra arriostrada a la ladera mediante anclajes en líneas horizontales y al tresbolillo (Modelo Puntual). En el segundo, la malla transmite esfuerzos a elementos de arriostre y estos a la cabeza de los anclajes (Modelo Bidireccional). Para validar los modelos, se diseñaron tres instalaciones para las membranas flexibles, objeto de patente. Para este tipo de sistemas está indicado el uso de membranas flexibles anisótropas. Estos sistemas evitan la erosión del talud, recogen presiones ejercidas por este y las transmiten a la parte estable del anclaje. / Newly built slopes show a good aspect and a regular and stable surface, but for different agents quickly erode. One technique to use for the stabilization and control of erosion is the use of meshes braced to the ground through anchors. This facilitates revegetation, landscape integration, and a low environmental impact. The resuls of the study are two physical-mathematic models for the design of two flexible anti-erosion systems and for the excavation surface stabilization. In the first, the mesh is braced to the slope through anchors in horizontal lines and staggered (Punctual Model). In the second, the mesh transmits stresses to bracing elements and these to the anchors heads (Bidirectional Model). To validate the models, three installations for the flexible membranes were designed, the object of patents. For this type of systems, the use of flexible anisotropic membranes is indicated. These systems avoid slope erosion, gather the pressures exerted by it and transmit them to the anchor stable part.
72

Entwicklung von standardisierten Prozessbausteinen für seilunterstützte Rettungs- und Bergeprozesse

Herold, Katrin 12 October 2007 (has links) (PDF)
Die derzeitigen Probleme bei der Planung, Durchführung und Überwachung des seilunterstützten Rettens und Bergens entstehen durch die hohen Anforderungen an die Rettungsteams und die erforderlichen kurzen Ablaufzeiten. Einerseits sind die • Güte der Qualifikation der Rettungsteams und der Ausbilder, • Angemessenheit der Ausrüstung der Rettungsteams, • tatsächliche Arbeitssicherheit der Prozesse für alle beteiligten Personen, • tatsächliche Prozesssicherheit unterteilt nach technischer und menschlicher Zuverlässigkeit derzeit nicht ausreichend bewertbar, und andererseits sind die technologischen Abläufe mit ihren Gefährdungs- und Gestaltungspotentialen nur einem kleinen Kreis von Fachleuten bekannt. Dieses Erfahrungswissen gilt es, für alle Anwender zu erschließen. Betrachtet man nun die große Methodenvielfalt der seilunterstützten Rettungs- und Bergeverfahren, die auftretenden Fehler bei Übungen und die Unsicherheit der Planer und überwachenden Personen dieser Verfahren bezüglich der Gefährdungen der Rettungsteams und der zu rettenden bzw. zu bergenden Personen, so zeigen sich Probleme in der Prozessgestaltung. In dieser Arbeit wird, aufbauend auf die Standardisierung der Fertigungsverfahren, ein Baukasten-System mit standardisierten Prozessbausteinen und einem Ablaufalgorithmus zur Anwendung entwickelt, mit der die Aufbau- und Ablauforganisation der Rettungsprozesse beschrieben werden kann. Für die derzeit typischen Rettungs- und Bergeprozesse wurden Standardprozesse entwickelt und in ihren Gültigkeitsbereichen definiert. Der Baustein-Katalog, bestehend aus 127 Prozessbausteinen, ist an der Professur Arbeitswissenschaft der TU Chemnitz erhältlich.
73

Drinking Water Quality Monitoring

Kilungo, Aminata Peter January 2013 (has links)
This dissertation involves two different studies. The first concerns the real-time detection of microbial contamination in drinking water using intrinsic fluorescence of the microorganisms. The prototype, “Blinky”, uses LEDs that emit light at 365nm, 590nm, and 635nm for ultraviolet, amber, and red light, respectively. At 365 nm, the cellular components excited include reduced pyridine nucleotides (RPNs), flavins, and cytochromes to distinguish viable bacteria; at 590 nm, the cellular components excited include cytochromes for non-viable bacteria; at 635 nm, the cellular components excited include calcium dipicolinic acid (DPA) for spores. By using these three different wavelengths, the prototype can differentiate between viable and non-viable organisms and also has the potential to detect spores. The aim of this study was to improve the detection limit by modifying the design of the instrument and to establish the detection limit of viable and non-viable bacteria and spores. The instrument was modified by replacing existing LEDs with LEDs that had 50% more intensity. Two additional LEDs were added for amber and red light, bringing the total to four LEDs for each. The LEDs were also positioned closer to the photomultiplier tube so as to increase sensitivity. For UV, only two LEDs were used as previous. The detection limit of the viable bacteria was ~50 live bacteria/L. No change in the intrinsic fluorescence below the concentration of ~10⁸ dead bacteria/L was observed. The results for spore measurements suggested that most of the spores had germinated before or during the measurements and could not be detected. The instrument was successful in detection of viable bacteria and also differentiating viable and non-viable bacteria. The instrument was not successful in detection of spores. The second study was designed to assess the water quality of well construction in southeastern Tanzania. Three designs were tested: Msabi rope pump (lined borehole and covered), an open well converted into a closed well (uncovered well into a covered and lined well), and an open well (uncovered and may or may not be lined). The study looked at the microbial and chemical water quality, as well as turbidity. The survey included 97 water collection points, 94 wells and three rivers. For microbial analysis, heterotrophic plate count (HPC), total coliforms and E. coli tests were performed. Fifteen of these wells were further analyzed for microflora and diversity for wells comparison purposes, using culture methods, followed by polymerase chain reaction (PCR) and genome sequencing. Ten wells out of the fifteen were analyzed for calcium (water hardiness), potassium, nitrates, nitrites, chloride, fluoride, bromide, sulfate, iron, and arsenic. Two water collection points were also selected for organic compound analysis (gasoline components). All samples tested positive for coliforms. Two samples tested positive for Escherichia coli for the lined borehole (Msabi rope pump) and four samples from closed wells. All open wells tested positive for E. coli. There was more microbial diversity in open wells than the closed wells and Msabi rope pumps. Potential bacterial pathogens were detected in seven wells out of the fifteen examined. The wells that tested positive were one Msabi rope pump, one closed well; the rest were from open water sources. Open wells had high turbidity followed by closed wells. Msabi rope pumps had low turbidity comparing to the two wells designs. No traces of gasoline components were detected in any of the water sources. One well out of ten had high amounts of nitrates-nitrogen (> 10 mg/L). The results of this study showed that the Msabi rope pumps performed comparably to the closed wells in terms of microbial quality but performed better with regard to turbidity. The open wells performed poorly in terms of microbial water quality as well and turbidity. There was a statistical difference in HPC, total coliforms, E.coli numbers and turbidity between open wells, closed wells and the Msabi rope pumps. However, there was no statistical difference in HPC, total coliforms and E.coli numbers between the closed wells and Msabi rope pumps. Msabi rope pumps performed better in turbidity
74

Deskripce kvadrupedálního lokomočního diagonálního vzoru při specifické sportovní lokomoci (šplh, chůze, shyb) / Description quadrupedal locomotion diagonal pattern in specific sport activity (rope climbing, walking, pull-up)

Bačáková, Radka January 2013 (has links)
Tittle: Description quadrupedal locomotion diagonal pattern in specific sport activity (rope climbing, walking, pull-up) Aim of work: The aim is to find a description kvadrupedal locomotion diagonal pattern with rope climbing and its motion pattern compared with the motion pattern of walking and pull-up. Methods: This work is descriptively-association study with quantitative and qualitative analysis. The dates were measured by surface electromyography and 2-D video-analysis. Results: Alternating activation of upper extremities (rope climbing without the lower extremities), we proved that the movement supporting lower extremities is quadruped locomotion diagonal pattern. Symmetric work of upper extremities (pull-up) is not in response at lower extremities quadruped locomotion diagonal pattern. Key words: Electromyography (EMG), quadruped, diagonal pattern, rope climbing, pull-up, walking
75

A novel mooring tether for highly dynamic offshore applications

Parish, David Nigel January 2015 (has links)
The mooring of vessels and other floating bodies at sea, such as offshore platforms has necessitated the development of specialised moorings technology. The marine renewable energy (MRE) sector is now at a stage in its development whereby floating devices are adding new challenges to the moorings industries. Floating MRE devices are smaller than, for instance offshore platforms, and are usually targeted for deployment in highly energetic environments. The extreme conditions and the highly dynamic response of an MRE device present challenges in terms of peak loading within the mooring system itself and load transfer to the floating body. Compliant mooring systems provide advantages by reducing the peak loads and fibre ropes are an important asset in achieving such compliance. However, the extent to which existing fibre ropes can safely extend axially to provide compliance is insufficient and is strongly associated to the minimum breaking load (MBL) of the rope. A novel fibre rope mooring tether is presented here that provides advantages over existing ropes. The tether employs a hollow fibre rope containing an elastomeric core, this mechanism de-coupling the extension properties from the strength of the line. The load path is carried through the polyester rope which is terminated conventionally by eye splices, thus minimising any new risks to reliability. Very low axial stiffness is achieved and is shown to be selectable within limits. For comparison, the prototype tether’s MBL of 222 kN is assigned to polyester and Nylon reference ropes. The axial stiifness of these ropes are 590 kN and 463 kN respectively when measured by a secant between the origin and 30% MBL; the novel tether displays an axial stiffness of 72 kN by the same method. This enables the novel tether to achieve more than two and a half times the extension of a comparable Nylon rope in its working range. Numerical modelling of a moored installation demonstrates a threefold reduction in peak load magnitude compared to the existing Nylon rope solution. The tether exhibits two distinct stages of extension, the first having very low axial stiffness. It is demonstrated that the extent of this soft phase can be selected by design and that this might add another useful element of control to moorings design work.
76

Řízení vírového proudění v sací troubě vodní turbíny / Flow control in a hydraulic turbine draft tube

Litera, Jiří January 2017 (has links)
Hydraulic energy is one of the most important sources in the world for electricity production. Nowadays the trend is to limit the production of the electricity from fossil fuels and to protect the environment. The main idea is to use more renewable energy sources such as wind and solar energy. Unfortunately, these alternative sources are strongly dependent on current weather conditions, which causes the instability of the electrical grid. Luckily pumped storage and hydraulic power plants provide the solution. However, it requires an extension of the operating range of the hydraulic machines. For that reason, the water turbines now operate over and extended range of regimes, that can be quite far from the best efficiency point. Hence two types of unstable two-phase flows in the Francis turbine draft tube occur: part load overload. This diploma’s thesis is focused on the Francis turbine operating at the part load. During part load conditions the helical vortex rope is being developed in the draft tube, it causes pressure pulsation and it can lead to the hydro-acoustic resonance, which damages the elements of the power plant. The aim is to eliminate the pulsation by jet control of the swirling flow in the draft tube. In the diploma’s thesis, various approaches to jet control of the flow in conical diffuser are tested using the computational fluid dynamics.
77

CFD simulace vírové struktury v sací troubě Francisovy turbíny (Francis-99) při pod-optimálním provozu - srovnání s měřením / CFD simulation of vortex structure in the Francis turbine draft tube at part load operating point - comparison with measurements

Neděla, Jiří January 2019 (has links)
This master's thesis deals with simulation of vortex structure which is created in the draft tube of Francis turbine, at part load flow conditions. The main objective is to get the most accurate results from the calculations, using the student license of Ansys Fluent 19.1. The results from the calculations are compared with the experiment under the Francis-99 project. Mainlly in terms of dynamic properties of vortex rope – aplitude and frequency of pressure pulsations. Additionaly the time-averaged velocity profiles are compared. I used the test-case provided by NTNU – Norwegian University of Science and Technology under the Francis-99 workshop series.
78

Vliv otevření difuzoru na dynamické vlastnosti spirální vírové struktury / Influence of difuser's opening angle on the dynamic properties of spiral vortex structure

Hazucha, Jan January 2019 (has links)
This master’s thesis deals with CFD simulation of spiral vortex structure in the diffuser of swirl generator. The objective of the thesis is to evaluate influence of change in diffuser opening angle on frequency and amplitude of pressure pulsation. All results are compared in charts which shows courses of frequencies and amplitudes along the diffuser. Two different turbulence models and several types of mesh were tested
79

Vírový cop při nadoptimálním průtoku Francisovou turbínou / Vortex rope for overload operation of Francis turbine

Kozák, Jiří January 2013 (has links)
This master's thesis deals with CFD simulation of vortex rope in the elbow draft tube for overload operation of Francis turbine. The main objective of the thesis is to compare results of the CFD simulations of the original elbow draft tube with a derived straight cone draft tube considering volume and the shape of the cavitation region and dynamic flow characteristic. Results of the 3D simulations are also compared with axi-symmetric simulations, which reduce demands for computing time and power.
80

Study of the Dissipation in Spiraling Vortical Structures / Study of the Dissipation in Spiraling Vortical Structures

Štefan, David January 2015 (has links)
This work deals with study of swirling flows where the spiral vortical structure appears. The main relation is to flow seen in the draft tube cone of hydraulic turbines operated out of the design point (i.e. best efficiency point). In this cases large coherent vortex structure (vortex rope) appears and consequently high pressure pulsations are propagated to the whole machine system leading to possible restriction of turbine operation. This flow features are consequence of flow instability called vortex breakdown in case of Francis turbine operated at part load (flow rate lower than optimal one). The present study is carried out using simplified device of swirl generator in order to access similar flow conditions as can be found in real hydraulic turbines. Both the dynamic and dissipation effect of spiral vortex breakdown are investigated. The first part of thesis deals with spiral form of vortex breakdown. The experimentally measured velocity profiles (LDA) and wall static pressures are correlated with numerical simulations carried out using open-source CFD package OpenFOAM 2.2.2. The high speed camera recording of cavitating vortex core is used to obtain image ensemble for further post-processing. The dissipation effect of spiral vortex structure is in detail discussed based on computed flow fields. The second part of thesis is dedicated to the application of POD decomposition to the study of spatio-temporal features of spiral vortex dynamics. Firstly the POD is applied to the both the experimentally obtained image ensemble of cavitating vortex and numerically computed static pressure fields. Secondly the comprehensive analysis of spiral vortex mitigation effect by the axial water jet is analyzed. The collaborative study employing the swirl generator apparatus designed by the researchers from Politehnica University of Timisoara in Romania is performed and changes in spatio-temporal vortex dynamic are studied. In this study the numerical data (in a form of three-dimensional pressure and velocity fields) are obtained using commercial CFD software ANSYS Fluent R14.

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