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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.
21

Structural characteristics of various types of helically wound cables in bending

Khan, Sajjad W. January 2013 (has links)
The primary aim of this research was to investigate the bending behaviour of helically wound steel cables of various types (i.e. normal spiral strands, sheathed spiral strands and locked coil cables) in the presence of friction and to propose more efficient computational models for their analysis under combined tension and bending. The proposed model fully takes into account interwire contact forces both in the radial direction (point contact between wires in different layers) and hoop direction (line contact within the wires in the same layer). Extensive theoretical parametric studies have been undertaken on a variety of cable constructions covering a wide range of geometrical and material parameters. Explicit formulations have been developed for the smooth transition of the bending stiffness from no-slip to full slip regimes, as a function of cable curvature. Based on these formulations, it is now possible to calculate the relative displacements of the wires, as well as the tensile, bending and hoop stresses in the individual wires of the cable. Furthermore, bending stiffness of the cable is shown to decrease by a factor of 2 to 16, depending upon the friction coefficient between wires and the type of cable construction. Wherever possible, the theoretical results have been compared with experimental results from the available literature and are found in very good agreement with them. A simple method for the determination of the bending stiffness of large diameter multi-layered cable has been developed. The simplified method is further shown to provide estimates of the bending stiffness which are very close to those calculated by the original theory, allowing hand calculations for an easier use in industry. The proposed formulations have been extended to cater for the effects of external hydrostatic pressure on sheathed spiral strands in deep water applications. These forces are shown to have a great influence on the pattern of interwire contact forces and hence the interlayer slippage between the wires in the strand. Numerical results have been obtained and analysed for three different 127 mm diameter strands with lay angles of 12°, 18° and 24° respectively, experiencing a wide range of external hydrostatic pressures of 0 to 2,000 metres. The significant increase in normal contact force between wires is shown to suppress the slippage of wires in the cable. However, the no-slip and full slip values of the effective bending stiffness of the cable is shown to be independent of the level of hydrostatic pressure. A theoretical model is also proposed for estimating wire kinematics, pattern of interwire slippage, contact forces as well as the flexural rigidity of locked coil cables with outer layers made of shaped wires. In order to validate this model, numerical results are reported for two different locked coil cables. It is shown that the shaped wires in the outer layers of locked coil cables play an important role in the distribution of contact forces, slip initiation and cable unwinding.
22

Mostový jeřáb jednonosníkový / Bridge crane one-girder

Chroust, Martin January 2018 (has links)
The focus of this thesis is the construction of a single girder overhead crane. The goal is to render a crane construction according to preset parameters. The parameters include a lifting power of 8,000 kg, a 10,000 mm reach, a 2,400 mm wheelbase and a stroke of 8,000 mm. The thesis includes brief theoretical research focused on overhead cranes, their various types and description of their main components. Brief description of chosen parameters for the construction itself follows. The description of chosen parameters includes calculations of strain acting during operation, technical and stability parameters, essential for the construction. All calculations were made with regard to valid Czech technical standards and specialized literature which focuses on the construction of cranes and their parts. Finally, the thesis is extended by the required technical drawings.
23

Vliv silničních záchytných systémů na počet a druh dopravních nehod / Impact of type road restraint systems on number and type of accidents

Šťastná, Barbora January 2013 (has links)
The aim of the master´s thesis is to analyze the types of road restraint systems, a description of testing road restraint systems and the use of wire rope safety fence in the Czech Republic and abroad. In addition, there is an analysis on the highway of R48 in the section Nový Jičín – Příbor and assessed in terms of the number and type of accidents in connection with wire rope safety fence.
24

Modellierung und Simulation der Beanspruchung von Zugsträngen aus Stahllitze für Zahnriemen / Load modelling and simulation of steelcords for timing belts

Witt, Robert 11 September 2008 (has links) (PDF)
In dieser Arbeit wird das Verhalten von gewickelten Seilen aus Stahllitze unter Zug- und Biegebelastung mit Hilfe der Methode der Finiten Elemente untersucht. Ausgehend von dem Modell einer einfachen Litze mit einem Kern- und sechs Außendrähten erfolgt eine ausführliche Analyse der Spannungsverteilung sowohl bei rein axialer Belastung als auch bei Biegung über eine Seilscheibe. Darauf aufbauend wird das Simulationsmodell schrittweise um komplexere Seilkonstruktionen bis hin zu zweifachen Verseilungen erweitert. Daran schließt sich die Untersuchung der inneren Belastungen bei Einbettung in ein Elastomer an, wie dies bei Zugsträngen in Riemengetrieben der Fall ist, sowie der spezifischen Einflüsse der Verzahnung auf die Seilbeanspruchung bei Zahnriemengetrieben. Des weiteren wird eine Möglichkeit der Validierung der Modelle vorgestellt, die ein experimentelles Ermitteln der Relativverschiebungen der Filamente auch im Inneren des Seils zulässt. Abschließend folgen Richtlinien zur Auslegung von Zugsträngen in Zahnriemen sowie Vorschläge, die in dieser Arbeit gewonnenen Ergebnisse in eine zukünftige Verschleißtheorie einfließen zu lassen. / This work examines the behaviour of steel cords under tensile loading and bending by the Method of Finite Elements (FEM). Beginning with a simple strand consisting of one centre and six outer wires a detailed analysis of the stress distribution is made for pure strain as well as for bending over a sheave. Based on this examination the model is extended step by step towards complex cord constructions. The investigation of cables embedded in an elastomer follows, especially the influence of a tooth profile of timing belts on the load inside the cable. Furthermore, a possible validation method for the model is presented. In conclusion directives are given for steel cord design in timing belts and suggestions are made to use the results in a wear model in the future.
25

Modellierung und Simulation der Beanspruchung von Zugsträngen aus Stahllitze für Zahnriemen

Witt, Robert 16 November 2007 (has links)
In dieser Arbeit wird das Verhalten von gewickelten Seilen aus Stahllitze unter Zug- und Biegebelastung mit Hilfe der Methode der Finiten Elemente untersucht. Ausgehend von dem Modell einer einfachen Litze mit einem Kern- und sechs Außendrähten erfolgt eine ausführliche Analyse der Spannungsverteilung sowohl bei rein axialer Belastung als auch bei Biegung über eine Seilscheibe. Darauf aufbauend wird das Simulationsmodell schrittweise um komplexere Seilkonstruktionen bis hin zu zweifachen Verseilungen erweitert. Daran schließt sich die Untersuchung der inneren Belastungen bei Einbettung in ein Elastomer an, wie dies bei Zugsträngen in Riemengetrieben der Fall ist, sowie der spezifischen Einflüsse der Verzahnung auf die Seilbeanspruchung bei Zahnriemengetrieben. Des weiteren wird eine Möglichkeit der Validierung der Modelle vorgestellt, die ein experimentelles Ermitteln der Relativverschiebungen der Filamente auch im Inneren des Seils zulässt. Abschließend folgen Richtlinien zur Auslegung von Zugsträngen in Zahnriemen sowie Vorschläge, die in dieser Arbeit gewonnenen Ergebnisse in eine zukünftige Verschleißtheorie einfließen zu lassen. / This work examines the behaviour of steel cords under tensile loading and bending by the Method of Finite Elements (FEM). Beginning with a simple strand consisting of one centre and six outer wires a detailed analysis of the stress distribution is made for pure strain as well as for bending over a sheave. Based on this examination the model is extended step by step towards complex cord constructions. The investigation of cables embedded in an elastomer follows, especially the influence of a tooth profile of timing belts on the load inside the cable. Furthermore, a possible validation method for the model is presented. In conclusion directives are given for steel cord design in timing belts and suggestions are made to use the results in a wear model in the future.

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