Conception et évaluation d'un prototype de simulation de la morphogenèse urbaine par agents vecteurs multi-échelles

The research work of this PhD thesis was carried out in the context of an interdisciplinary project related to the study of urban morphogenesis. A team composed of architects and engineers specialized in GIS technologies have worked together in this project during three years, sharing their knowledge in order to understand and simulate the evolution of the urban environment of cities. The fundamental hypothesis that conducted this research is that the city can be seen as a self-organizing system governed by a set of morphogenesis rules, which can for example, determine the location of new architectural programs and induce the city's organization, from local to global scales. Architectural programs themselves are supposed to determine city's development. In this PhD thesis a simulation prototype of the urban growth based on the use of multi-agents systems was carried out. This prototype is a computer tool that allows the analysis and representation of the growth of the built environment. Nowadays, the ability to understand and simulate urban evolution proves to be essential in order to control the evolution of a city in a sustainable development view. Furthermore, this tool should facilitate the understanding and decision-making of those concerned with problems related to urban development. The urban system has been modeled as a set of space objects, such as buildings and networks, which interact between themselves. These interactions are carried out at different levels, from local to global scales, being controlled by behavioral rules or laws of growth. The result of their interaction can be figures or emergent phenomena represented at several scales. The approach using multi-agents vector systems was chosen in order to model a geographical complex system like a city, which integrates a vectorial modeling of space. Hence, each spatial agent does not possess a limit of form and size. The interest of using multi-agents vector systems also lies in their ability to manage various models of individuals, from simple entities to more complex ones. Thus, various levels of representation, such as individuals and groups of individuals, can be managed, which is not easily feasible, for example, with cellular agents. The development platform used is GeOxygene (Java computer programming language), which is an open-source platform developed at IGN (Institut Géographique National, France), by COGIT laboratory. This platform provides several GIS functions, allowing the development and implementation of the prototype here presented. An interaction model between agents was defined and the type of scenarios of each of these interactions was detailed. A set of methods and associated classes was developed. Agent's architecture was conceived in order to allow manipulation (sending, receiving and treatment) of exchanged messages. In order to show the relevance of the multi-agent multi-scale methodology, examples of buildings creation in a case study zone were carried out. Using the multi-scale vector simulation prototype here presented, the development of cities can be computed in a very innovative way. However, the developed prototype still lacks some accuracy, mostly due to the fact that the specified laws adopted for simulation do not reflect the whole reality, which is obviously much more complex to traduce. We have not yet validated the model for other cities – nevertheless, the model could already be used as a decision support tool, particularly as a planning support instrument for architects and urban planners. With regards to future work this prototype shall be integrated in a global approach of urban simulation, allowing the analysis of environmental risks, demographic and economic growth and transports simulation at different scales of analysis and 2D/3D visualization output, such as district and city.

Densité et logement collectif

Nicolas Bassand

As a measurement, built density (coefficient of land surface to be built and total floor space) has been the object of numerous researches on urban morphology and architectural forms during the twentieth century. However, for the last ten years, its sensory and qualitative dimension seems to be particularly valued: the perceived density. In multi-unit housing, dense, innovating and compact forms show a significant change of architectural and urban conception. In fact, project practices seem to have been marked by three major changes. Firstly, the importance of the precept of sustainable development, attempting at reducing urban sprawl. Secondly, the increased interest in urban values and the idea of "building a city within a city". Lastly, the current asserted need to redefine density: on one hand, new means are being researched to control it, on the other hand there is a widening of its definition due to the main impulse of architects and researchers. Within this framework, it is illuminating to reconsider the multiple disciplines using this term, as well as the distinct spatial scales tackled in this notion and changes in its use through time. However, focusing only on built density, the present research concentrates on the architectural and urban framework, also known as physical density. It is measured by a density figure but is also qualified by the perception of density. We propose as preliminary approach, an examination of this perceived density in fields where it is more frequently used, such as literature, painting and music. Another important notion of this research requires definition: architectural and urban innovation. Standing out from pure invention, this type of innovation consists essentially in a reinterpretation of previous architectural and urban productions worth naming "retro-innovation". Despite a housing program dependent on past models reluctant to rapid and important changes, radical innovations do occur, though more seldomly. Several ''moments'' of the collective housing architectural history allow for an updating of the different stakes manifested in the density – innovation relationship. Density perception plays a large role in a particular problem emerging from these two notions in contemporary Switzerland. The issue is how encouraging people coming back to the urban centers by proposing larger apartments with more square meters and urban architecture composed of numerous and various spaces, but protecting them at the same time from too close a proximity between neighboring housing and from environmental nuisances. The state of the art brings to light the enormous influence of the researcher and anthropologist Amos Rapoport on perceived density starting with his article, "Towards a Redefinition of Density", published in 1975. For more than thirty years now, architects, psychologists, city planners and geographers refer to this work when defining this notion in their respective fields. As a consequence, it nourishes several reflections in this research. Following these various observations, we propose the analysis of fourteen contemporary multi-unit buildings. They represent the current urban stakes at play and show the architectural and urban conception facing the double requirement of density: to insure a high enough floor area ratio (measured density) and to qualify the housing density (perceived density). In parallel, this research determines if this conception, unique to dense multi-unit housing, tends to modify architectural practice. In the first phase, we examine seven rectangular housing units, in which the width of the building is significant, and seven courtyard buildings in order to examine the exterior spaces contained by the building's volumes. In the second phase, we focus our attention on the wall expression of the fourteen buildings. In this way, these distinct analyses offer three new definitions of the perceived density expressing conception aspects particularly significant for understanding the architecture and urbanity of these dense multi-unit buildings. As a fundamental knowledge, it is shown that density, within the corpus, orientates the architects project's mode. The frequent reinterpretation of paradigmatic dense lodgings is one of the most striking proof of this conceptual change searching for innovations in the register of collective housing. So, in the density of depth, introversion and anonymity on the exterior seems to encourage distinct individualized space within the building as common domestic spheres only opened towards the inside of the apartment. In several cases, the usual urban and public spaces are integrated into the private interior of the apartments as if to domesticate a certain urbanity. In the density of the void, the proposed introversion of semi-public courtyards seems to help maintaining a larger sense of community in these multi-unit buildings. Altogether, it demonstrates a particular capacity to produce small cities within the city, at the same time independent and linked to the city. Finally, through the analysis of wall density, the exterior materiality and expression, dynamic or static, monumental at times, present a decidedly urban architecture enhancing a compact city in quest of new inhabitants.

EPFL2009

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

What will the cities of tomorrow look like? This is a crucial question because in the four and a half billion years of its existence, the Earth has never been so threatened, as it is today. Since 2008 half of the world's population has lived in towns – more than 70% in rich nations. Three quarters of CO2 emissions are produced in towns, 75% of the world's energy is consumed in towns. The battle for our climate, for the continuation of our species and all other life, will be largely waged in cities. Will it be possible to create the ideal ecological town? The objective of this study is to compare actual and theoretical urban forms in order to explore the diverse effects of daylighting and solar potential on densely built-up sites. Indeed, the search for ideal solar orientations has been a persistent problem from the 19th century until the beginning of the 20th. Even today, for all our scientific knowledge and empirical experience of solar energy, making the correct choice has still not crossed the boundary from an enigmatic, tricky art into the field of an exact science. As a first step, six existing urban sites in Switzerland and Brazil, as well as two projects in the United Kingdom, a few generic models and a utopian city, were modelled and analyzed. The goal was not merely the construction of new, exemplary districts but also the transformation of existing towns. The findings have been used to assess the potential of façades and roofs located in urban areas for active and passive solar heating, photovoltaic electricity generation and daylighting. The results obtained from these different case studies revealed large variations of the potential for solar energy collection on the buildings' façades and roofs. Ideally, these investigations are expected to help architects and town planners understand how to optimise solar collection on buildings design. In addition, a study was made of the Contemporary City of Three Million Inhabitants created by Le Corbusier. According to the latter, the Contemporary City could increase the urban capacity and at the same time improve the urban environment and the efficiency of the city. Therefore the present study extracted the solar potential of this utopian city in order to assess Le Corbusier's propositions. Since 1922, Le Corbusier's studies have influenced architects and town-planners in their choice of orientations and urban forms: it was therefore crucial to discover if this reliance on Le Corbusier was justified. Solar irradiation and illuminance values obtained through numerical simulations form the core part of the method. The method adopted for the entire set of computer simulations consisted in modelling — via a computer-aided drawing piece of software, namely AutoCAD — the digital model of each building or group of buildings prior to exporting them to an urban performance analysis software (PPF/RADIANCE software package). Spatial distributions of solar irradiation and daylight fluxes over the overall building façades and roofs were calculated using ray-tracing simulation techniques to determine the appropriate placement of different solar technologies (passive and active solar, photovoltaic and daylighting). Performance indicators were used to assess the solar utilisation potential of the urban sites (e.g. statistics of sky view factors and daylight factors) in order to determine the optimal solar strategies for a given urban context. In addition, various works and sun-related recommendations that have appeared mainly since the end of the nineteenth century, together with the various scientific models and software tools pertaining to this topic, are presented in this study.

EPFL2010

Méthodologie de gestion durable des ressources du sous-sol urbain

Pascal Blunier

The world is becoming more and more urban. During the last fifty years, the population in Swiss cities has grown from 45% to 70% of the total population. This change is characterised by urban sprawl and by an increase in the consumption of resources, particularly those coming from rural areas. This evolution is not compatible with the principles of sustainable development. To solve this problem, new urban policies are being developed. They favour development within the urbanised areas and reduced use of exogenous resources. The urban underground contains resources – space, geomaterials, groundwater and geothermal energy – which can efficiently support such policies. This project analyses how these resources have been exploited until now and how they could be used with sustainability in mind. The use of underground resources was analysed in five cities : Mexico, Paris, Helsinki, Tokyo and Montreal. It appears that, although resources participate in the urban metabolism, there is an important lack of planning and coordination in their use. Developments follow a sectional approach where the resources are considered independently, and only at the scale of a given construction project. As a consequence, conflicts occur between uses and resources are wasted. An understanding of the urban underground as a system was developed with the aim of preventing conflicts and promoting synergies. To this effect, the way in which resources interact was considered attentively. Situations in which interactions occur were described and analysed and compatibility conditions were suggested. A methodology was elaborated to evaluate the resource potential of an urban underground. It aims at considering the resources and the interactions between their uses from the beginning of the process of urban planning. The methodology is based on the use of Geographical Information Systems and 3-D modelling of geological and hydrogeological conditions. It aims at reversing the current paradigm, that proceeds from the needs to the resources, into an approach based on resources to satisfy the needs. Spatial information was exploited to determine indicators and maps of potentiality and of restrictions. The derived results will help support decision making by planners and policy makers who seek to better exploit the resources from the urban underground. The methodology was tested and applied on a case study : Geneva. The developed approach allows more efficiency in the use of urban underground resources, it can help prevent conflicts between uses and develop synergies. When integrated in the urban planning process, it highlights new opportunities and helps to develop projects that take into account the physical conditions of the underground.

EPFL2009

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

EPFL2010

Densité et logement collectif

Nicolas Bassand

EPFL2009

Méthodologie de gestion durable des ressources du sous-sol urbain

Pascal Blunier

EPFL2009