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mysteries of mechanics, and consequently of scientific and technical knowledge, through the analysis of numerical simulation, the objective of Jean-François Sigrist, engineer and industrial researcher, is this: to rectify the mysteries created around the contributions of cutting-edge technological dynamics to contemporary research and to remind us that citizens have a certain power – that of the power of words that express choices – over scientists, experts and decision-makers.

      It is indeed with a mixture of cynicism and disbelief that many often react to statements about algorithms, for example, focusing media attention. Some talk about them in order to dominate the “ignorant”, others argue against seizing this mode of knowledge and conceptual construction by claiming its abstraction from the lived world and the last would like to push the “backward” to become “intelligent” by teaching them what they should know, based on this too ordinary sharing of the organization of the social world.

It is clear that these three modes of approaching a hierarchical relationship between knowledge (scientific and technological) and people are based on the same presupposition: on the one hand there are “those who know” and on the other hand “the ignorant”. From the first to the second, the darkness of routine and superstition is invoked, which legitimizes their dominant position and their relationship with rulers.

      Jean-François Sigrist’s first concern is not to affirm doctrinally the validity of contemporary scientific and technological knowledge and approaches. Nor does he seek to maintain a classificatory pedagogical model, exposing only raw knowledge to those willing to learn. He encourages those who are ready to embark on the adventure to seek to understand what this knowledge means, taking into account the context in which it is advanced and the fictions with which they are confronted: cinema, drawing, painting, photography, etc. By facilitating the encounter with the uses of scientific and technological knowledge – objects used daily, simulation for industrial applications – within the culture of time, he interrupts the automatism of the social machine of knowledge that constantly divides the world between those who are “informed” or “cultivated” and those who are “behind”.

      In this respect, the spirit of this book is entirely woven from the relationships between the description of the mathematical and physical world as understood by knowledge and techniques and the deciphering of the specific cultural meanings that can be attributed to them. These meanings then refer less to games of optimism or pessimism or to functions of accompanying the educational order, or even to catastrophist speeches or a cautious morality of the slightest evil, than to the double exercise of the effort of scientific culture and the taking of political sides, to the benefit of all of society.

      Christian RUBY

      Philosopher

      Introduction

      A Technology at the Service of Humans

      In this second volume, we continue our discovery of numerical simulation technology, understood in a broad sense as a tool for carrying out virtual experiments. In the first volume, we have shown how the idea of representing a given entity in an abstract way is realized: a model made up of equations and/or data allows us to predict its evolution or behavior in different situations. Taking the example of mechanics in general, we first discussed various possible uses of simulation in the industrial sector and recalled its strategic nature. We then extended our presentation to other applications that require or perform simulations, such as artificial intelligence, which aims to simulate, in the sense of reproducing, certain human cognitive abilities. We concluded the presentation by questioning the meaning that numerical simulation can take and the techniques it helps to develop or whose advances it incorporates.

      The objective of this second volume is to provide some concrete answers to these questions by illustrating different fields of application of numerical modeling. Without claiming to be exhaustive in any way, we thus propose an overview of some of its uses in agriculture, the shipbuilding and aeronautics industry, earth and universe sciences, meteorology and climatology, energies, the human body and finally, we discuss the use of models covering certain activities of individuals, alone or in communities.

      This second volume, consisting of seven chapters, presents various contributions from researchers and engineers working in French laboratories, centers of expertise or industrial groups using numerical modeling to support their research and/or design work. Please note that any uncited quotations are taken from personal interwiews. We choose examples in these areas by showing how these digital techniques benefit humans, without avoiding the question of their use for other purposes.

Faced with the difficulty of drawing clear boundaries between knowledge and skills, and between techniques, we have chosen to emphasize, with the variety of examples proposed, the links they maintain and the way in which digital technology contributes to changing scientific practices.

      1

      Agriculture

      In 1916, Chicago, Bill was a worker employed in a foundry. Following an altercation, he fled the city, accompanied by his girlfriend Abby and his sister Linda. He found refuge in Texas where wheat was harvested from huge arable areas and a favorable climate allowed him to grow it. Hired as a seasonal worker by a wealthy farmer suffering from an incurable disease, Bill pushed Abby to give in to his employer’s advances. A calculation to get out of poverty? Set in a bourgeois house drowned in an almost endless expanse of wheat, inspired by the paintings of the American painter Andrew Wyeth (1917–2009), Days of Heaven (1978) recounts a psychological drama [MAL 78]. The contemplative camera of its author, the American filmmaker Terence Malik, also depicts the blazing sun of long working days, the power of harvesting machines and the hazards of harvests, stormy bad weather or locust invasion, which become a tragedy subject to the whims of the sky – whose unpredictability symbolizes that of human passion?

      Controlled and perfected for more than 10,000 years, as attested to by remains from ancient Egypt (Figure 1.1), agriculture remains a survival challenge for a humanity facing climate change in the 21st Century even though it is capable of changing its practices.

      Figure 1.1. Cereal harvest, Tomb of Menna, Sheikh Abd el-Gournah Necropolis, Egypt

       (source: 10,000 Meisterwerke der Malerei, The Yorck Project)

1.1. Feeding the world

      Agriculture is also at the center of current ecological concerns and strategic issues, particularly those of state food sovereignty, to which simulation techniques provide answers. Today, the world’s cultivated land covers more than 50 million km² (Figure 1.2): this area is about three times that of Russia, the largest country in the world with 17 million km².

      Figure 1.2. Allocation of land areas for food production (source: Our World in Data/https://ourworldindata.org/yields-and-land-use-in-agriculture). For a color version of this figure, see www.iste.co.uk/sigrist/simulation2.zip

      COMMENT ON FIGURE 1.2.– Only 30% of the total area of our planet is covered by land, 70% of which is considered habitable (about 100 million km2). Humans use about half of it for agriculture, and less than one-tenth for urban infrastructure. More than three-quarters of the agricultural land is used for animal husbandry, combining land allocated to pasture and feed production (these aggregate data obviously do not reflect disparities between countries).

      The

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