IOP Groups
Ropes, Cables and Chains: Theory and Applications
23 September 2004
Professor Matthew Cartmell
Department of Mechanical Engineering, University of Glasgow
The Momentum Exchange Tether has gone through a continuous cycle of invention and re-invention since Tsiolkovsky's proposal of 1895 for a space elevator based on a hanging cable system. The Motorised Momentum Exchange Tether was proposed in 1996 by the author, and originally came from a separate line of enquiry to that of space vehicle propulsion. The propulsion system under investigation now comprises a symmetrical double-payloaded propulsion side based on two identical tether-tube sub-spans, spun up by a centrally located drive motor reacting against similar, stator located, tethers acting as counter-inertias. The system has been shown to be capable of significantly higher performance than hanging or librating tether configurations, and has been included on ESA's project Aurora as a possible competitor in future propulsion technology for interplanetary freight exchange between Earth and Mars. This presentation will summarise some of the dynamical modelling completed to date, in terms of practical designs and realistic performance expectations. Some burgeoning control issues will also be summarised.
Dr Jack Hale
School of Mechanical and Systems Engineering, University of Newcastle upon Tyne
The Latest Measurement Techniques on High Speed Roller Chains
The paper describes the problems involved in measuring the load in rapidly moving roller chains and the solutions that have been developed to overcome them. Loading of chains is a combination of a number of factors. Besides the direct load that transmits torque from input to output shaft, there is a cyclic loading due to “polygonal action” as the chain engages and disengages with the sprockets, centrifugal loading around the sprockets and vibration, particularly in any long unsupported spans. It is shown that the true dynamic load cannot be measured except by means of instruments mounted directly on the chain links. The problems with this type of measurement are described, together with attempts to solve them. It is shown that, although the more recent attempts have shown some success, none is entirely suitable for use with high speed timing chains. Chain dynamic load measurement is now available on a commercial basis. The current state of the technology is presented for heavy and light chains systems respectively.
Dr Stefan Kaczmarczyk
School of Applied Sciences, University College Northampton
Resonance Phenomena in Tension Member Systems with Time-Varying Characteristics
The dynamic characteristics of axially moving tension members such as ropes and cables in various vertical transport installations are of a time-variant nature. Their length variation results in slow variation of the natural frequencies rendering the entire system non-stationary. Since moving slender continua are inherently non-linear, the dynamic response of such systems is qualitatively different from the response which would occur if the characteristics were stationary, with transient resonance and modal interaction phenomena taking place. This presentation will discuss various models and techniques for the prediction of these dynamic phenomena. The effectiveness of these techniques will be demonstrated using numerical examples describing the dynamic behaviour of ropes and cables in typical vertical transport installations.
Dr John Macdonald
Earthquake Engineering Research Centre, University of Bristol
Dynamic Cable-Deck Interaction of Cable-Stayed Bridges
Cable-stayed bridges are now the most common form of construction for spans from 200m up to approximately 1km. However, vibration problems of both the bridge decks and the inclined cables are surprisingly common. Furthermore, since the natural frequencies of deck and cable vibrations are in the same frequency range, they interact dynamically. Various types of interaction can occur, including occurrence of combined cable and deck linear modes, effects of cable wind loads on the overall bridge response, and potentially serious non-linear interactions for specific frequency ratios. These interactions have been investigated using numerical, analytical and physical models, and through full-scale measurements on the Second Severn Crossing.
Mr Michael Pohle
Datwyler AG
Elevator Flat Travelling Cables and Compensation Weight
Travelling cables supply the elevator car with electrical energy and connected the car with the control unit. Therefore, this cable has a fundamental impact on the function of the elevator. Various requirements need to be met. A high mechanical stress and excellent electrical performance must be achieved. Such requirements can be fulfilled by especially developed materials, an extensive know how in construction and a very accurate production. Based on this knowledge a compensation system for high rise elevators has been designed. This compensation weight provides similar advantages to the flat travelling cables.
Mr Rory Smith
ThyssenKrupp Elevator Corporation
Elevator Suspension Ropes Constructed of Aramid Fibers
In the spring of 2000 ThyssenKrupp Elevator North America formed a team to develop a Kevlar rope. The team discovered the failure modes of Kevlar; developed ways to overcome these obstacles, and ultimately developed a functional rope. The project evolved from the development of a rope to a Kevlar suspension system. The elements include rope, traction sheaves, deflector sheaves, terminations, and nondestructive testing means. The first commercial lift installation using Kevlar rope was commissioned in the spring of 2003. The research process, failure modes, rope design, rope characteristics, and design of the suspension system components are explained.
Professor Robin Tucker
Department of Physics, University of Lancaster
Cosserat Methods and the Fluid-Structure Interaction in Cable Stayed Bridges
A review will be given of the application of Cosserat approximations with emphasis on the dynamical behaviour of undersea marine risers responding to vortex induced vibration and the motion of cables in cable stayed bridges that are excited to vibrate in light-wind rain conditions. In the latter the motion of the cable section is coupled with the motion of a mobile rivulet on its surface via aerodynamic fluid-structure interactions. These complex interactions are modelled in two distinct ways and the resulting cable motions compared. The first employs an approximation that permits the use of data extrapolated from wind-tunnel measurements. The second approaches the aerodynamic interaction in terms of a sub-critical vortex description. Such mathematical modelling offers a useful means to understand how marine risers respond to under-sea currents and how rain-wind induced vibrations of stay cables can arise and persist in terms of more realistic approaches than have been considered before in the literature.
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