Category Archives: Engineering

Sounds of the city

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cornerRegular readers of this blog will know that I spent a relaxing day painting railings a few weeks ago [see post entitled ‘Engineering archaeology‘ on July 23rd, 2014].  A day or so later, I went out with my pail of whitewash to paint the walls of the light-well that the railings protect.  ‘The summer world was bright and fresh, and brimming with life’ but unlike Tom Sawyer I was not looking for Jim to do my white-washing for me.  I was looking forward to another therapeutic session painting the walls at the front of our house.  It was an interesting standing in the light-well facing the wall, un-noticed by most passers-by.  We live on a city street close to tourist attractions and there is a constant stream of coaches and taxis stopping to drop-off and pick-up tourists. I have written about the noise insulation in our house before [see Noise Transfer on April 13th, 2013] which means that we don’t notice the constant growl of diesel engines outside but I did while I was painting.  However, there were other sounds in the city.  The voices of pedestrians  deep in conversation as they passed by on the pavement just above my head.  I recognised Chinese, French, Italian and English but there were many different languages that I didn’t recognise.  There were young children asking parents questions as they walked down the street.  For a while I could hear cathedral bells.  When there was a pause in the traffic then it was possible to hear the cooing of pigeons, a neighbour’s radio or television and an ever-present idling diesel engine which I discovered was an ice-cream van dispensing a constant trickle of black soot and an occasional ice-cream.  It is curious that as a society we tolerant high levels of noise pollution at tourist attractions, especially ones that are meant to be places of calm and contemplation. Most tourists are, almost by definition, on holiday seeking relaxation and a lowering of stress levels – how much more pleasant would it be to glide to your destination in a silent electric coach or taxi?

We have the technology to provide such a service [see Are electric cars back? on May 28th, 2014]. Yes, it requires some investment by tour operators and taxi firms in hybrid or electric vehicles and by the city council in re-charging facilities. Induction charging stations at tourist attractions would allow vehicles to recharge while dropping off and picking up passengers. The technology is available and has been used by buses in Genoa and Turin for more than a decade.  So a little bit a regulatory pressure and investment from city councils acting together could create a calmer, quieter and cleaner environment for everyone.

Can we look forward to solar-powered ice-cream vans?

Sources: Thank you to Richard for reminding me about Tom Sawyer.

Engineering archaeology

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Last week I spent a relaxing day painting the old railings in front of our house. Since I am not a painter and decorator by trade the end result is not perfect but they look much better in shiny black than two-tone rust and matt black.   One of the fleurs de lis on our railings had been knocked off when either we moved in or the previous occupiers moved out.  It’s a way of life being an engineer, so the shape of the failure surface on the broken railing was bugging me while I was painting the rest.  You would expect wrought iron railings to be ductile, i.e. to deform significantly prior to fracture, and to have a high tensile strength.  Wrought iron’s properties are derived from its very low carbon content (less than 0.25%) and the presence of fibrous slag impurities (typically about 2%), which almost make it a composite material.  It was historically used for railings and gates.  However, my broken railing had exhibited almost no deformation prior to fracture, i.e. it was a brittle failure, and the fleur de lis had broken in half on impact with the stone flags.  So on one of the rainy days last week, when I couldn’t paint outside, I did a little bit of historical research and discovered that in the late 1790s and early 1800s, which is when our house was built, cast iron started to be used for railings.  Cast iron has a high carbon content, typically 2 to 4%, and also contains silicon at between 1 and 3% by weight.  Cast iron is brittle, i.e. it shows almost no deformation prior to fracture, so the failure surface tends be to flat and smooth just like in my fleur de lis.

This seems like a nice interdisciplinary, if not everyday, engineering example.  It would be vandalism to go around breaking iron railings in front of old buildings.  So, if you want Everyday Engineering Examples of ductile and brittle behaviour, then visit a junk shop and buy an old china dinner plate and a set of cutlery.  The ceramic of the china plate is brittle and will fracture without deformation – have some fun and break one!  The stainless steel of the fork and spoon is ductile and can be easily bent, i.e. it is easy to introduce large deformation, in this case permanent or plastic deformation, prior to failure.  In fact you will probably have to bend the fork back and forth repeatedly before it will snap with each bending action introducing additional damage.

The more curious will be wondering why some materials are ductile and others brittle.  The answer is associated with their microstructures, which in turn is dependent on their constituents, as hinted above.  However, I am not going to venture into material science to explain the details.  I have probably already given materials scientists enough to complain about because my Everyday Engineering Examples are not directly analogous at the microstructural level to wrought iron and cast iron but they are more fun.

Sources: http://www3.westminster.gov.uk/spgs/publications/Railings.pdf

Conflict Resolution

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conflict pyramidEngineers need to be experts in resolving conflicts…

Every man-made device that moves required energy to make it and uses energy when it moves. Heavier devices have greater inertia than small ones and hence more energy is needed to set them in motion – think about peddling an old-fashioned steel-framed bike compared to a modern alloy one. So, designing for sustainability requires engineers to minimise the quantity of raw materials and energy used to manufacture a device AND to minimize its weight if the device moves as part of its function.

Now, here comes the conflict.

Sustainability also implies that devices should have a long, maintenance-free service life so that resources used in maintenance and replacement are minimized. Service life is usually limited by fatigue and, or wear and the probability of these failure mechanisms occurring can be reduced by lowering stress levels. However, stress is inversely proportional to cross-section area and so can be reduced by adding material, i.e. increasing the mass of the device which will also increase its inertia, or resistance to motion. The probability of failure can be reduced by using stronger, more sophisticated materials that are lightweight and almost always more expensive, e.g. composites. Customers also want performance and additional expense might be acceptable if it is accompanied by additional performance – some people will pay for a carbon-fibre frame for their bicycle. Elegant engineering design requires resolution of the conflict between cost, safety and reliability, performance and sustainability.

This is why engineers are trained in conflict resolution or as it is more commonly known: problem-solving.

Are electric cars back?

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roadchaosDid you know that before Henry Ford developed the Model T Ford motorcar, the nearly 40% of automobiles on US roads were electric vehicles? I think we will be heading back in this direction if we are to have any hope of achieving reductions in carbon dioxide emissions. The implications for the national electricity grid of a major shift to plug-in cars would be very serious and has been the subject of several recent studies including a third year undergraduate dissertation that I have been supervising and from which came the opening factoid.

It is relatively easy, through not without obstacles, to envision a shift to all-electric cars; after all there are several models on the market now. However, an all-electric aircraft seems further in the future, if only because of the weight of the batteries required. Engineers would talk about the energy density, i.e. the amount of energy that can be extracted from a kilogram of kerosene compared to a kilogram battery. However, perhaps the future is not far away because the New Scientist reported earlier in the month [3rd May, 2014] that Airbus had completed the test flight of an electric plane, the E-fan. It is a two-seater plane with a pair of 65 kilogram lithium battery packs driving a pair of 30 kilowatt motors attached to the fans. The E-fan will cruise at 185 kilometres per hour and flies for an hour. Relative to a modern computer jet, this performance is similar to the early plug-in cars relative to their internal-combustion-engined rivals. But, it is an indication of bigger things to come. In the meantime, if you want an E-fan then a new division of Airbus called Voltair will be producing them by 2017.

I mentioned undergraduate dissertations because they have filled a sizeable chunk of my waking hours for a few weeks. This is an annual ritual in the UK during May when final-year undergraduate students are busy submitting and defending their dissertations. I had a pile of twelve dissertations to read and assess. Eight of them belonged to students that I have supervising in weekly one-to-one meetings since last October and the remainder were dissertations for which I was the assessor. All of the students that I supervised were studying either Mechanical or Aerospace Engineering and so the topics of their projects were associated mainly with energy and, or transportation. Some of these projects are provided by engineering companies (those with an asterisk in the list below), which guarantees their topicality and relevance, while others spin-out from my interests and research activities. So many of the topics in the list below will come as no surprise to regular readers of this blog.

Dissertation projects supervised during 2013-14:

Investigation into a redesign of graphite re-entrant seals for a nuclear power station*

Conceptual design for a carbon sequestration system for automobiles

Recommendations for achieving a low carbon airline industry

Strain-based defect analysis of industrial pipe-work*

Investigation of random frequency excitation of an aerospace body panel

Assessment of preload control of threaded fasteners in motorcycle production*

Recommendations for technology-based approaches to reduced ecological footprints

Investigation of low carbon power for plug-in electric vehicles