Last month when I was in Taiwan [see ‘Ancient Standards‘ on January 29th, 2020] , I visited Kuosheng Nuclear Power Plant which has a pair of boiling water reactors that each generate 986 MWe, or between them about 7% of Taiwan’s electricity. The power station is approaching the end of its licensed life in around 2023 after being constructed in 1978 and delivering electricity commercially for about 40 years, since the early 1980’s. There is an excellent exhibition centre at the power station that includes the life-size mock-up of the reinforcement rods in the concrete of the reactors shown in the photograph. I am used to seeing reinforcing bar, or rebar as it is known, between 6 to 12mm in diameter on building site, but I had never seen any of this diameter (about 40 to 50mm diameter) or in such a dense grid. On the other hand, we are not building any nuclear power stations in the UK at the moment so there aren’t many opportunities to see closeup the scale of structure required.
Earlier this summer, when we were walking the South West Coastal Path [see ‘The Salt Path‘ on August 14th, 2019], we frequently saw kestrels hovering above the path ahead of us. It is an enthralling sight watching them use the air currents around the cliffs to soar, hang and dive for prey. Their mastery of the air looks effortless. What you cannot see from the ground is the complex motion of their wing feathers changing the shape and texture of their wing to optimise lift and drag. The base of their flight feathers are covered by small flexible feathers called ‘coverts’ or ‘tectrix’, which in flight reduce drag by providing a smooth surface for airflow. However, at low speed, such as when hovering or landing, the coverts lift up and the change the shape and texture of the wing to prevent aerodynamic stalling. In other words, the coverts help the airflow to follow the contour of the wing, or to remain attached to the wing, and thus to generate lift. Aircraft use wing flaps on their trailing edges to achieve the same effect, i.e. to generate sufficient lift at slow speeds, but birds use a more elegant and lighter solution: coverts. Coverts are deployed passively to mitigate stalls in lower speed flight, as in the picture. When I was in the US last month [see ‘When upgrading is downgrading‘ on August 21st, 2019], one of the research reports was by Professor Aimy Wissa of the Department of Mechanical Science & Engineering at the University of Illinois Urbana-Champaign, who is working on ‘Spatially distributed passively deployable structures for stall mitigation‘ in her Bio-inspired Adaptive Morphology laboratory. She is exploring how flaps could be placed over the surface of aircraft wings to deploy in a similar way to a bird’s covert feathers and provide enhanced lift at low speeds. This would be useful for drones and other unmanned air vehicles (UAVs) that need to manoeuvre in confined spaces, for instance in cityscapes.
I must admit that I had occasionally noticed the waves of fluttering small feathers across the back of a bird’s wing but, until I listened to Aimy’s presentation, I had not realised their purpose; perhaps that lack of insight is why I specialised in structural mechanics rather than fluid mechanics with the result that I was worrying about the fatigue life of the wing flaps during her talk.
The picture is from a video available at Kestrel Hovering and Hunting in Cornwall by Paul Dinning.
The moral of this story is don’t travel with me. Last week, I wrote about my train being delayed by someone pulling the emergency handle before we got to the end of the platform in Liverpool [see ‘Stopped in Lime Street’ on June 26th, 2019]. Four days later, I was once again on a late afternoon train to London waiting for it to leave Lime Street station. This time we didn’t even get started before the train manager announced that a road vehicle had hit a bridge between Crewe and Liverpool; and, so we were being held in Liverpool for an unknown period of time. I sent a message to my family telling them about the delay and one, an engineer, replied that I was ‘hitting the low frequency failure modes on the service quality pareto’. The Pareto principle is also known as the 80/20 principle. I first encountered it when I was working at the University of Sheffield and the Vice-Chancellor, Professor Gareth Roberts, used it to describe the distribution of research output in academic departments, i.e., 80% of research was produced by 20% of the professors. In service maintenance, it is assumed that 80% of service interruptions are caused by 20% of the possible failure modes. Hence, if you can address the correct 20% of failure modes then you will prevent 80% of the service interruptions, which is an efficient use of your resources. The remaining, unaddressed failure modes are likely to occur infrequently and, hence, can be described as low frequency modes; including passengers pulling emergency handles or people driving vehicles into bridges.
How do you drive into a bridge and block the main railway lines between London and the north-west of England? Perhaps the driver was using their smart phone which was not smart enough to warn them of the impending collision with the bridge. So, there’s a new product for someone to develop: a smartphone app that connects to dashboard camera in your vehicle and warns you of impending collisions, or better still just drives the vehicle for you. Yes, I know some vehicles come with all of this installed but not everyone is driving the latest model; so, a retro-fit system should sell well and protect train passengers from unexpected delays caused by road vehicles damaging rail infrastructure.
By the way, the 14:47 to London magically became the 15:47 to London and left on time!
If you enjoyed a holiday dinner lit by candles then you might be interested to know that the majority of the light from the candle does not come from the combustion of the candle wax in the flame, but from the unburnt soot glowing in the intense heat of the flame. The combustion process generates the heat and the blue colour in the centre of the flame. However, due to the lack of sufficient oxygen, the combustion of the candle wax is incomplete and this produces particles of unburnt carbon. The unburnt carbon forms soot or graphite, but also more exotic structures of carbon atoms, such as nano-diamonds. The average candle has been estimated to produce about 1.5 million nano-diamonds per seconds, or maybe 10 billion nano-diamonds per Christmas dinner! Unfortunately, they are too small to see otherwise they would add a lot of sparkles to festive occasions.
The picture is an infrared image of a 1cm diameter candle. About 2cm of the candle height extends from the bottom of the picture and the visible flame is about 2cm high.
Helen Czerski, Storm in a Teacup: The Physics of Everyday Life, London: Penguin Random House, 2016.