Simulation des phénomènes de dégradation d'éléments de construction

Builders have always been concerned about the durability of construction materials and building components. Nowadays, powerful information technology tools offer an opportunity to approach the complexity of aging phenomena in an innovative way. This thesis presents a method and a simulation model designed to predict the aging of multi-layer building components. Integrated into a software tool, they take into account the nature and intensity of the external agents acting on a component. The tool creates possibilities for a variety of applications : it can guide users towards the most appropriate and durable construction systems, it can be helpful in decision making for building maintenance and it can provide service-life information for life-cycle analysis (LCA). The work is based on research undertaken between 1990 and 1997 by the Expert Service from the Construction and Conservation Laboratory (LCC) at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in collaboration with the ARIA-laboratory of the Ecole Nationale Supérieure d'Architecture de Lyon (UMR CNRS n°694 MAP, Hervé Lequay) for the development of the Assistance to Maintenance of Buildings tool (AMB). The goal of the present work was to continue and extend the previous investigations. In a first step, the tool has been analysed and recreated within the Delphi development environment. New parameter recorder modules and graphical analysing modules have been added for better simulation monitoring and visualisation of chain reactions due to degradation processes. The model has also been adapted to allow stochastic simulation with the Monte-Carlo Method. This part of the research permits bringing out the structure of the simulation method's various aspects and concepts and working out its detailed description. In the report, global aspects of the prediction method are presented first. Basic concepts and principles, such as stress actions, material performance and element functions, are described. In a second part, the design of the computer model is presented. The aim is to show how the general concepts of the method can find an application. Various stress agents and specific material performances that participate in the aging process and lead to a decrease in performance are highlighted. Aging is simulated by the interaction between the materials and agents over time. Definitions of the failure criteria for a given building component are made by identification of its functions and assigning performance limits values. Two chapters are dedicated to the detailed description of the different stress agents and performances used in the model. These are followed by a selection of case studies that shows the working of the simulation and illustrates the various types of results that can be obtained. The conclusions reiterate that the prediction of construction material aging is a wide and complex subject. To be able to make not only qualitative but also quantitative durability predictions, further research must be undertaken in different domains. This is necessary in order to collect existing knowledge and to obtain missing information. As the presented method and model can easily integrate new data as it becomes available, they could play the role of a development platform for future investigations. This would allow a progressive increase in the reliability of the predictions.

Development and application of a numerical simulation system to evaluate the impact of anthropogenic heat fluxes on urban boundary layer climate

Andrea Krpo

Increasing economic development, and growing population, generated during the last decades a very important growth of cities. Urban regions include nowadays more than half of the global population and, by 2030, this proportion is forecasted to increase to three quarters. A consequent more and more extensive use of natural resources, together with increasing anthropogenic activities such as emissions from traffic and factories, or heating from air-conditioning facilities, modify local climate in many different ways, leading to a progressive degradation of life quality in urban areas. Taking these facts into account, there is nowadays a real need for efficient urban planning guidelines and sustainability policies in order to improve life quality in urban areas. Different points should be considered including urban warming, air pollution, human health, economic, and cooling energy needs. The present work goes in this direction, aiming at developing a simulation system for the study of the complex interactions between buildings and the atmosphere. The system of equations describing atmospheric flows is highly non linear and it is common to employ numerical techniques in order to solve them. Moreover, the representation of urban canopy climate, and related air pollution problems, requiree taking the interaction between urban scale (tens of kilometers), and mesoscale (hundreds of kilometers) processes into account. At first, starting from previous studies, a mesoscale meteorological model has been developed as part of this work. Urban induced processes have been considered by implementing inside the model a detailed urban parameterization scheme developed in a previous work. The scheme is able to capture different urban processes, and reproduces the effects of cities in a more accurate way than traditional methods usually used in mesoscale models. However, the heat generated in buildings, and the way this heat is exchanged with the exterior, was not explicitly resolved. In particular, recent studies indicated that anthropogenic heat from air-conditioning facilities can play an important role and should be taken into account for more complete urban climate studies. To this purpose, a Building Energy Model (BEM) has been developed, and coupled to the Urban Canopy Parameterisation (UCP). This building model takes into account the diffusion of heat through walls, roofs, and floors, the natural ventilation, the generation of heat from occupants and equipments, and the consumption of energy through air conditioning systems. Comparisons with other programs indicate that BEM is able to accurately simulate the basic heat transfer phenomena, and to reproduce the heat fluxes exchanged between buildings and the atmosphere. In a second part of the work, the simulation system composed by the Mesoscale Model (MM), UCP, and BEM is tested with respect to one, and two-dimensional configurations. In particular, the impact of BEM on the meteorological variables is analyzed, as well as the efficiency of different urban warming countermeasures, and cooling energy demands control strategies. Two-dimensional results are then utilized as guidance for the application of MM-UCP-BEM over the realistic configuration including the city of Basel and the surrounding areas. At first, comparisons of urban and rural simulated temperatures with measures provided by the BUBBLE project (Basel Urban Boundary Layer Experiment), have shown that the model could reasonably well reproduce the variations in outdoor air temperature. In a second time, the simulations considered for the two-dimensional configuration are applied to the case of Basel. Numerical results confirm that anthropogenic fluxes from air-conditioning facilities can have a non negligent impact on the urban meteorology. Typically, they modify the outdoor temperature and increase the Urban Heat Island (UHI) phenomenon. In the last part of the study, the applicability of the model in performing urban warming countermeasures, and cooling energy demands control strategies, is evaluated. In this purpose in mind, a sensitivity analysis is carried out indicating that appropriate physical properties of built materials, efficient air-conditioning systems, and the application of simple energy saving policies, can lead to very important cooling energy savings. In general, the application of BEM inside the UCP allows computing the heat released into the atmosphere by air-conditioning facilities, as well as the corresponding feedbacks produced on the different meteorological variables. It also increases the capability of the urban parameterisation to provide more detailed studies of urban warming countermeasures, and cooling energy demands in real cities.

EPFL2009

Object-oriented approach for dynamic system modelling and simulation

Adel Besrour

Software engineering always cares to provide solutions for building applications as close as possible to what they should be, according to the requirements and the final users needs. Systems behavior simulation is a very common application to virtually reproduce and often predict the real-world behavior. Simulation is one of the most operational research tool in a large variety of engineering and scientific domains: Transport, telecommunication, medicine, chemical processes, physics, etc. The complexity of such application is relative to the increasing complexity of the systems. In this context, it is relevant to bring together different tools and formalisms such as markovian chain, Petri nets, etc., to improve the existent approaches and so to answer the simulations performances needs. The principle objective of this thesis is to bring together techniques from software engineering and safety engineering in order to improve the state of the art of modeling and simulation of dynamic systems in the industrial context. In addressing this objective, this work initially involves defining the essential limitations of the used formalisms, methods and tools regarding from one hand the software engineering modeling and simulation techniques and from the other hand the existent risk analysis methodologies. This work is conducted with respect to the problem of danger identification, considering the context of the complex systems behavior and their interaction with the human operator. In software engineering, it is well known that Petri/high-level nets have attractive characteristics to be used in systems simulation and behavior prediction such as the natural graphical representation, and their well-defined semantic. They are well-suited for the description of complex situations with concurrency (interleaving and true concurrency depending on the underlying semantics), conflict and confusion. However, the absence of structuring capabilities has been one of the main criticisms raised against Petri nets/high-level nets. Thus, there have been many attempts to introduce structuring principles in nets of this kind [BCM88] [Kie89] [JR91]. The attractive characteristics of Petri/high-level nets have prompted researchers to enrich these formalisms with object-oriented features. CO-OPN (Concurrent Object-Oriented Petri Net) approach, brings together the power of both Petri/high-level nets and object-orientation techniques, it has been devised so as to offer an adequate framework for the specification and design of large scale concurrent system [BG91]. CO-OPN, as a powerful modeling tool, has been used in a limited way to simulate systems. This work aims to provide a CO-OPN extension to allow a more realistic systems' simulation. Actually, its simulator semantic uses to be a suitable approach for modeling near closed systems and software components, because they need to loose coupling with external world. But, when we model more realistic problems like industrial processes, where human interaction is a relevant event, this approach is not sufficient to catch all system activity attributes. Moreover, the CO-OPN interpretation process does not allow interaction with the object internal states. This work provides a new solution to overcome CO-OPN simulation limitations and a set of prototypes to assist dynamic systems simulations. Furthermore, this work has been conducted in a Risk Analysis (RA) context, a domain where computer-based simulations research are of utmost interest. Actually, classical approaches used to address complex workplace hazard in a limited way, using checklists or sequence models. Moreover, the use of single oriented methods, such as AEA (man-oriented), FMEA (machine oriented) or HAZOP (process oriented), is not satisfactory to overcome the increasing sophistication of industrial processes. The automation of a part of the analysis process as well as the multiple-oriented approach allowed by dynamic modeling may indeed enhance significantly the analysis completeness and reduce the time analyzing time. This work, based on Object Oriented Petri net formalism (CO-OPN), propose an alternative multi-oriented approach where existent methods limitations have been criticized to develop a dynamic model, MORM (Man-machine Occupational Risk Modeling). A real industrial system (metal wire making process) has been specified to implement the different approach steps (system identification, model application, system simulation, system analysis).

EPFL2005

A Collaborative Workflow to Automate the Design, Analysis, and Construction of Integrally-Attached Timber Plate Structures

Pierre Latteur, Aryan Rezaei Rad, Nicolas Henry P Rogeau, Petras Vestartas, Yves Weinand

This paper introduces a computational framework that fosters collaboration between architects, engineers, and contractors by bridging the gap between architectural design, structural analysis, and digital construction. The present research is oriented toward the formulation of an automatic design-to-construction pipeline for Integrally-Attached Timber Plate Structures (IATPS). This construction system is based on assembling timber panels through the sole interlocking of wood-wood connections inspired by traditional Japanese joinery. Prior research focused on developing distinct computational workflows and dealt with the automation of 3D modelling, numerical simulation, fabrication, and assembly separately. In the current study, a single and interactive design tool is presented. Its versatility is demonstrated through two case studies, as well as the assembly of a physical prototype with a robotic arm. Results indicate that efficiency in terms of data flow and stakeholder synergy is considerably increased. The proposed approach contributes to the†Sustainable Development Goal (SDG) 11 by facilitating the collaborative design of sustainable timber structures. Besides, the research also contributes to SDG 9 as it paves the way for sustainable industrialisation of the timber construction sector through streamlined digital fabrication and robotic assembly processes. This reduces manufacturing time and associated costs while leveraging richer design possibilities.