Any city is made up of a very large number of interior spaces (the habitat), mostly pasted to each other, and this set is both placed on the ground and separated from the surrounding atmosphere by an envelope composed of unconnected parts (urban blocks). This envelope cannot be hermetic (it must allow air renewal), but it must be sufficiently closed to ensure temperature differences between the inside and the outside, in order to guarantee a minimum of comfort for the inhabitants. If favorable differences (that is to say: it is cooler in summer and warmer in winter inside than outside) are obtained, at least partially, simply by the shape of the city and the adequate planning of the materials of its envelope, then the city can be considered sustainable from an energy point of view. Especially, the digital mock-up of a city must therefore consist of a geometry including the thickness of the envelope, by means of a volumetric mesh that allows a precise evaluation of the thermal conduction through the walls, floors, and roofs of buildings. This necessarily implies a computation carried out by finite elements and includes, in addition, a precise evaluation of the radiative exchanges in long waves. Solar input, convection, and other phenomena involved can be considered boundary conditions. Since the interior and exterior skins of the buildings have already been identified, the same model can be used, at no additional cost, for other calculations based on ray tracing, such as that of sound and light fields. On the other hand, present photographic cameras—possibly equipped with filters to select one of the components of short waves—ultraviolet, visible, near-infrared—now make it possible to obtain very high-definition images. Thermal cameras are also making progress. Acoustic cameras have emerged, and aeraulic cameras, based on Schlieren techniques, are in development. We can therefore capture ever more precise images of the different physical fields interfering with the city, and we can simulate comparable images on the computer. The urban digital twin is the place where these different images can be compared, with the same boundary conditions. Thus, the measurements make it possible to calibrate the simulations, which can subsequently be used alone to evaluate, with sufficient reliability, different renovation, or urban growing scenarios. It is the tool that the urban planners of the past—from Haussmann to Le Corbusier—would not have dared to dream of, and which will allow our contemporaries to project the sustainable city of the twenty-first century, everywhere in the world, by methodically taking into account the characteristics of each climate, as well as the needs of ever-increasing inhabitants.

A Physics-Based Urban Digital Twin for Designing and Renovating Sustainable Cities

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发表日期：

2025年

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Benoit Beckers

摘要

Any city is made up of a very large number of interior spaces (the habitat), mostly pasted to each other, and this set is both placed on the ground and separated from the surrounding atmosphere by an envelope composed of unconnected parts (urban blocks). This envelope cannot be hermetic (it must allow air renewal), but it must be sufficiently closed to ensure temperature differences between the inside and the outside, in order to guarantee a minimum of comfort for the inhabitants. If favorable differences (that is to say: it is cooler in summer and warmer in winter inside than outside) are obtained, at least partially, simply by the shape of the city and the adequate planning of the materials of its envelope, then the city can be considered sustainable from an energy point of view. Especially, the digital mock-up of a city must therefore consist of a geometry including the thickness of the envelope, by means of a volumetric mesh that allows a precise evaluation of the thermal conduction through the walls, floors, and roofs of buildings. This necessarily implies a computation carried out by finite elements and includes, in addition, a precise evaluation of the radiative exchanges in long waves. Solar input, convection, and other phenomena involved can be considered boundary conditions. Since the interior and exterior skins of the buildings have already been identified, the same model can be used, at no additional cost, for other calculations based on ray tracing, such as that of sound and light fields. On the other hand, present photographic cameras—possibly equipped with filters to select one of the components of short waves—ultraviolet, visible, near-infrared—now make it possible to obtain very high-definition images. Thermal cameras are also making progress. Acoustic cameras have emerged, and aeraulic cameras, based on Schlieren techniques, are in development. We can therefore capture ever more precise images of the different physical fields interfering with the city, and we can simulate comparable images on the computer. The urban digital twin is the place where these different images can be compared, with the same boundary conditions. Thus, the measurements make it possible to calibrate the simulations, which can subsequently be used alone to evaluate, with sufficient reliability, different renovation, or urban growing scenarios. It is the tool that the urban planners of the past—from Haussmann to Le Corbusier—would not have dared to dream of, and which will allow our contemporaries to project the sustainable city of the twenty-first century, everywhere in the world, by methodically taking into account the characteristics of each climate, as well as the needs of ever-increasing inhabitants.