4.3 Optical networking DWDM improves the utilisation of optical fibre for point-to-point links, but a further step in exploiting the potential of optical fibre comes from optical networking in which routeing or switching is done optically. Optical networking is in its infancy, but the concept of the optical layer based upon wavelength channels is emerging. The optical layer effectively sits below the SDH layer in the network, and provides wavelength channels from one location to another. An analogy can
5.3 Ethics and ethos: ‘does mum know?’ In Act 1 we are presented with a fairly naïve Ned, who initially believes himself to be in control. We discover he is very proud of his intellectual achievements and less concerned with money. He explains his inventions and, when he does so, he finds analogies that highlight the aesthetics of what he is designing. At a crucial point in the conversation, his brother Dan asks: ‘does mum know?’ This is a really significant point in the play because it draws in another relationship and, as I
6.11 Presenting the case 23. Is the format of presentation appropriate for the audience? 24. Is the case presented in a persuasive way overall? Hopefully, the analytical work carried out to determine costs, benefits and so on will almost
References Learning outcomes After studying this course, you should be able to: view solutions as belonging to particular categories, broadly classified as: innovation by context; innovation by practice; routine see how external factors affect engineering projects, and appreciate the range of engineering involved in meeting the basic needs of our society recognise and apply a range of problem-solving techniques from each stage of the engineering design cycle, to include the fol Conclusion This free course provided an introduction to studying Technology. It took you through a series of exercises designed to develop your approach to study and learning at a distance, and helped to improve your confidence as an independent learner. 5.7.2 Elimination of pathogens through solar disinfection The lack of safe drinking water in many developing countries has prompted research into simple methods of disinfecting small quantities of water. One such investigation at the University of Beirut in the Lebanon revealed that 99.9% of total bacteria in a water sample could be destroyed by 300 minutes exposure to direct sunlight. In effect this means that if you left a sample of water in a translucent container, a lot of the bacteria in it would be killed. Research to date has concentrat 3.3.3 Reassembling the parts As the wreckage was pulled from the river it was examined and identified, and any failures of the metal components were recognised and tagged. This was a mammoth task, given that virtually the whole bridge had fallen into the water, including all the road decks, trusses, chains and hangers, eye bars and the two towers. The parts were then reassembled and all the failed or fractured components photographed and catalogued. Over 90 per cent of the bridge components were collected together and re 3.3.2 Planning the investigation A plan was needed to determine the chain of events leading up to and during the collapse. That sequence would necessarily depend on which parts had broken first, and a fault tree would enable a plan of action in isolating the cause (or causes) of the disaster. Such a systematic approach is known as fault-tree analysis or FTA, and is part of the armoury of methods used by accident investigators. With large-scale and devastating accidents, all possibilities, however remote, need evaluation in t 3.3 The investigation The investigation took three years to complete, although critical evidence emerged within weeks of the accident. Some possibilities could be ruled out immediately. For example, there were rumours of supernatural forces at work that night, but very little solid evidence of the ‘Mothman’ emerged, either there or anywhere else. The Mothman was a demon purportedly haunting the bridge, which has supposedly appeared as a portent of similar disasters around the world. Such stories would ha 3.2 The disaster The 39-year-old Silver Bridge collapsed suddenly at about 5 p.m. on 15 December 1967 when the roadway was filled with rush-hour traffic – 37 vehicles were trapped on the roadway. The first signs of collapse were later recounted by the survivors. Many occupants of the cars on the bridge had felt it ‘quivering’ before it fell. Most witnesses had then heard ‘cracking’ or ‘popping’ noises, some saying that it sounded like a ‘shotgun blast’. After this, the bridge started d 2.6.2 Cracking of copper alloys Stainless steel is not the only metal to fall victim to SCC. One of the first discoveries of SCC occurred in India in the early part of the nineteenth century, when that country was still part of the British Empire. There was a large standing army that was always in need of live ammunition. The brass cartridge cases would occasionally split, and often at the worst possible time (when being fired), frequently causing injury to the marksman. So what caused such failures? The two factors n 2.6.1 Stress corrosion cracking in stainless-steel structures On 9 May 1985 the roof of a swimming pool at Uster near Zurich collapsed, killing 12 and injuring several others. The concrete roof had been held up by a set of stainless-steel tie bars, which were found after the accident to have cracked transversely (Figure 21). Chlorine is added at qu 2.6 Corrosion in stressed products – stress corrosion cracking (SCC) If a stress exists in a product exposed to a corrosive environment, the rate of corrosion can then increase and be extremely localised, such as at the tip of a growing crack. Furthermore, some specific chemicals are so aggressive that corrosion will occur at relatively low stress levels, such as those created during manufacture, for example. The residual stress in a component can then be enough to trigger crack growth and failure. 2.5 Corrosion processes: galvanic series A similar concept to the electrochemical series that has been used by engineers for many years is the galvanic series (one example of which is shown in Table 2: here the list should be read down the columns rather than across the rows). It ranks metals and alloys in order of reactivity or 2.3 Corrosion processes For many materials, degradation processes are simply one or a series of chemical reactions that act to erode or deteriorate the material. The deterioration of metals is a little more complex than that of non-metals because metals are electrical conductors. Local electrochemical cells freq 2.1 Introduction Structures are not always doomed to fail, but they do usually have a limited useful life. Exceptions include many of the monuments that have survived from the ancient world, such as the Great Pyramid in Egypt (Figure 11a), the Pont du Gard in southern France (Author(s): 1.3 Environmental factors I indicated earlier that many failures occur after a product has been in service for some time: such as the wear of a car tyre, or corrosion of the car body itself. It is also possible for components to fail because of a combination of a manufacturing defect with the applied loading or with the environmental conditions during use. Author(s): 1.2 Component failure We have all experienced component failures in one form or another. In many cases this is because something has reached the end of its working life due to a slow-acting failure mechanism: car tyres wear slowly and will eventually burst if not replaced; the filament in a light bulb slowly loses material until it cannot sustain the applied voltage and melts. Failures where something has been so badly designed that it cannot withstand its intended loading during normal use are rarer, but they do 1.1 Safe design This unit is about the concepts and theories that underpin the field of engineering known as Structural integrity – that is, the safe design and assessment of load-bearing structures in their entirety, including any individual components from which they may have been constructed. Aspects of structural integrity are implemented in almost every engineering design process, even if the engineer or designer does not necessarily think of it in that way. In this unit, we have separated the
