# Modelling and reality

How are you? Have you been able to cope with the lockdown? Are you still able to work? We are constantly urged to maintain contact using technology and to look after our mental health. However, not all communication needs new technology. A good old-fashioned letter or email, if time is taken in thoughtful composition, can still be of benefit. What better than to share your views, experiences and hopes with people who are in the same profession and who can appreciate the context. This is the time to take advantage of BINDT and share your worries, fears, hopes and ideas by sending them in. You may be surprised to see the response, discover that you are not alone and realise that you can influence the future of NDT.

For months we have been hearing a lot about flattening the curve and reducing the ‘R number’ as a prerequisite for relaxing the lockdown. The mantra in the UK is that we have followed the science, meaning that a particular mathematical model for predicting how the coronavirus pandemic would spread was being used to influence policy. At the beginning of April, there was discussion in the media about the reliance on this single model and the need for alternatives so that policy decisions could be supported or challenged.

When considering models, a particular exchange from a 1970s television show always comes to my mind. I did not actually see the programme, but those who did had a habit of repeating the various scenarios presented, so I am familiar with many of them. I am referring to Ripping Yarns, written by Sir Michael Palin and Terry Jones. In the pilot episode, Tomkinson is keen to escape from boarding school. In one of his attempts, he joins the model boat club and builds a full-size icebreaker. This annoys the teacher, who tells him that if it is made to full size it is not a model: it is an actual icebreaker! Inverting this gives us the basic premise of models and mathematical models in particular: they are models and not reality.

Models are built using assumptions and the discussion around the coronavirus model is based on the validity of the assumptions. Coronavirus is a new disease and, if the assumptions in the model are based on one prevalent years ago, they may not be fully applicable. At the beginning of April, a newspaper article reported that the Royal Society was looking to bring in experts from different fields to build new transmission models to provide confirmation or otherwise. In a subsequent discussion on the television about coronavirus modelling, a professor told us to ignore the beginnings of the curve but to look at the trend of the slope. This highlights the fact that the model is not reality but an approximation, which can be used to indicate how things may be and how they may change going forward.

Within the NDT profession, mathematical modelling was slow to develop, owing to the computational power required to produce representative models. In more recent times this has changed and there are well-known commercial models that have found widespread use. However, with the increased availability of models, there is a danger that they are used inappropriately. Just as access to CAD software does not immediately turn people into skilled engineering drawing practitioners, there is a requirement for knowledge of both the model and the actual practice before the benefits can be realised.

The modelling of the spread of the coronavirus, and its discussion in the media, has given us some key reminders applicable to NDT: a mathematical model is only as good as the assumptions that it is based on; we can only know how good a model is by validating it against real data; and even when models are in use, the only way to discover the reality is to perform testing to collect real data. That is why NDT is important. The only way to know the current state of a component or a piece of plant, and to check for errors in design, manufacture and operation, is to inspect and test it.

Please note that the views expressed in this column are the author’s own personal ramblings for the purpose of encouraging discussion within NDT News. They do not represent the views of Jacobs or BINDT.

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Fax: +44 (0)1604 438301; Email: ndtnews@bindt.org or email Bernard McGrath direct at bernard.mcgrath1@jacobs.com