System

Related publications (100)

Generic Occupancy Sensor

Sélim Cédric Kamal

The goal of this project was to work on room occupancy and to provide solutions and ideas on how to detect if a room is occupied or not using generic and non expensive sensors. This is motivated by the fact that buildings account for 50% of the total energy consumption in the US and 30% of it is wasted mainly due to a bad management of light, heating, cooling and ventilation systems. Being able to know if rooms are occupied or not would then enable us to automatize these systems and make them more energy efficient. The sensors studied in the process were a CO2, relative humidity and temperature sensor, a camera, a WiFi sniffer and a PIR(Passive infrared) sensor. All of them were implemented and tested to see how they could measure occupancy. After analyzing each sensor alone we had to combine them to obtain the best possible accuracy. To do so, two methods were tried. The first using all the sensors mentioned was tested and the accuracy achieved was 93%. The second was based on the use of neural network on images provided by the camera to detect people and the accuracy was 97%.

2021

Local Vulnerabilities and Global Robustness of Coupled Dynamical Systems on Complex Networks

Melvyn Sandy Tyloo

Coupled dynamical systems are omnipresent in everyday life. In general, interactions between individual elements composing the system are captured by complex networks. The latter greatly impact the way coupled systems are functioning and evolving in time. An important task in such a context, is to identify the most fragile components of a system in a fast and efficient manner. It is also highly desirable to have bounds on the amplitude and duration of perturbations that could potentially drive the system through a transition from one equi- librium to another. A paradigmatic model of coupled dynamical system is that of oscillatory networks. In these systems, a phenomenon known as synchronization where the individual elements start to behave coherently may occur if couplings are strong enough. We propose frameworks to assess vulnerabilities of such synchronous states to external perturbations. We consider transient excursions for both small-signal response and larger perturbations that can potentially drive the system out of its initial basin of attraction. In the first part of this thesis, we investigate the robustness of complex network-coupled oscillators. We consider transient excursions following external perturbations. For ensemble averaged perturbations, quite remarkably we find that robustness of a network is given by a family of network descriptors that we called generalized Kirchhoff indices and which are defined from extensions of the resistance distance to arbitrary powers of the Laplacian matrix of the system. These indices allow an efficient and accurate assessment of the overall vulnera- bility of an oscillatory network and can be used to compare robustness of different networks. Moreover, a network can be made more robust by minimizing its Kirchhoff indices. Then for specific local perturbations, we show that local vulnerabilities are captured by generalized resistance centralities also defined from extensions of the resistance distance. Most fragile nodes are therefore identified as the least central according to resistance centralities. Based on the latter, rankings of the nodes from most to least vulnerable can be established. In summary, we find that both local vulnerabilities and global robustness are accurately evaluated with resistance centralities and Kirchhoff indices. Moreover, the framework that we define is rather general and may be useful to analyze other coupled dynamical systems. In the second part, we focus on the effect of larger perturbations that eventually lead the sys- tem to an escape from its initial basin of attraction. We consider coupled oscillators subjected to noise with various amplitudes and correlation in time. To predict desynchronization and transitions between synchronous states, we propose a simple heuristic criterion based on the distance between the initial stable fixed point and the closest saddle point. Surprisingly, we find numerically that our criterion leads to rather accurate estimates for the survival probability and first escape time. Our criterion is general and may be applied to other dynamical systems.

EPFL2020

Online Stream Mining for Condition Monitoring in Large Infrastructure Systems

Nils Robin Bouchardon

Supervisory Control and Data Acquisition (SCADA) systems are nowadays widely used in modern industry. Their utility has been proven over the past decades to supervise any automated processes. The scope of applications of such a system has been extended from industrial to infrastructure and facility processes. Classic SCADA systems offer tools to help monitoring and analyzing data from this type of systems, but the existing approaches are often limited to Data Warehousing and Reporting. The main problem of these solutions is that they are not designed to work on online mode and can be seen as batch processing on archived data. In this thesis we study how to link machine learning solutions to SCADA systems on large infrastructures. The solution we propose in this work is a complete framework with its architecture providing a ’toolkit’ with different modules to build online solutions on top of a SCADA system.

2015

A partition-free approach to transient and steady-state charge currents

We construct a non-equilibrium steady state and calculate the corresponding current for a mesoscopic Fermi system in the partition-free setting. To this end we study a small sample coupled to a finite number of semi-infinite leads. Initially, the whole system of quasi-free fermions is in a grand canonical equilibrium state. At t = 0 we turn on a potential bias on the leads and let the system evolve. We study how the charge current behaves in time and how it stabilizes itself around a steady state value, which is given by a Landauer-type formula.

2010

ENERGY STORAGE: LIQUID CH4 AND CO2 NETWORK INTEGRATION

Charles-Thomas Stern

In this project, we will study the energy storage with liquid methane linked to a CO2 network that provides heat for district heating. The generated methane enters an hybrid cycle composed of a solid oxide fuel cell and turbines to generate electricity. The goal of this project is to determine the global eciency of the system but also to optimize it with the help of softwares like Belsim Vali and Osmose. In addition, we determine its cost. At the end, we compare the global system with an equivalent one without the CO2 network integration.

2014

Towards sufficiency in housing: Agent-based model and transition scenarios

Margarita Agriantoni

Research problem: Housing is responsible for a considerable part of global resource consumption. In Switzerland, it accounts for almost one third of the country's CO2 emissions and half of the total energy demand. Thus, housing plays an important role in the transition to sustainable development. Housing has been thoroughly studied from a disciplinary perspective, e.g., economics, social sciences, psychology, engineering. However, little attention has been paid to housing as a system of interrelated actors, e.g., developers, owners, tenants and state, whose actions might be described by different disciplines. Aim: The aim of this thesis is to investigate how a change in the construction practices of property owners in combination to a more space-efficient allocation of dwellings to households and a behavioural change of tenants can achieve a substantial reduction in the environmental impact of housing. This dissertation focuses on the interrelations of housing actors, concentrating mainly on the property owners and explores which measures and to what extent can lead to a reduction of space consumption of housing.Methods: Housing is characterised by a high level of complexity, therefore a transdisciplinary approach is adopted. Firstly, the Swiss housing market and its unique attributes are studied. However, in this thesis, we study a subset of the Swiss rental housing market; it comprises two housing cooperatives: ABZ in Zurich and SCHL in Lausanne as well as the insurer and asset manager Swiss Mobiliar. Their housing stocks, of approximately 10,000 dwellings, are examined in depth and are used as a case study. Extensive data gathering allowed to create an exhaustive inventory of the building stock of the three property owners. The data on tenants was limited, thus, we conducted a tenant survey. Furthermore, a series of workshops with both tenants and property owners were organised to study their decision-making processes. A bottom-up agent-based model (ABM) is built, which portrays the case study housing system. The main actors of the rental housing market (property owners and households) are represented in the model by agents; the owner agents make decisions about their building stock and tenants, while the household agents choose a dwelling based on their needs and housing preferences. The dynamic evolution of both owners and households and the interaction between them is simulated in the model and allows the study of emergent phenomena. The present thesis attempts the assessment of the environmental impact of housing through the lens of housing sufficiency. Space consumption, in terms of dwelling surface and floor area per capita, is considered as the largest determinant of resource consumption.Results: The simulation results show that measures taken to decrease the environmental impact of housing and space consumption are inadequate if owners do not change their construction practices and households do not actively change their housing behaviour. Most measures explored in this thesis, if implemented individually, succeed in reducing the rate of increase in space consumption but fail to reverse the upward trend. A more space-efficient allocation of dwellings to households proves to have a certain effect. However, only when combined with other measures, such as the densification of the existing building stock and a change in construction practices, a significant decrease of environmental impact is observed.

EPFL2022

Tracing attacks and restoring integrity with LASCAR

Alexandre Aellig, Philippe Oechslin

We present a novel method to trace the propagation of intrusions or malicious code in networked systems. Our solution is aimed at large numbers of loosely managed workstations typical of a research environment as found in CERN. The system tags events which have a potential to become harmful. On a given machine all processes that results from the tagged event are marked with the same tag and the tag is carried on to others machines if a tagged process establishes a connection. Tag creation logs are stored in a central database. When an intrusion is detected at a later time, all machines and processes that may have lost their integrity due to this incident can easily be found. This leads to a quick and effective restoration of the system. Our implementation of the system is designed to incur very little overhead on the machines and integrates easily with many flavors of the Linux operating system on any type of hardware.

2003

System design of a geothermal sourced CO2 network in a residential district

Tobia Wyss

Many countries and cities in the world have pledged to drastically reduce their CO2 emissions during the next decades. Given the high degree of urbanization in occidental society, district energy systems present a high potential to increase the efficiency of heating and cooling systems. The present work focuses on a specific type of district network, based on CO2 as a working fluid, which allows to exchange heat through condensation and evaporation. The low distribution temperature increases the potential of heat recovery, and thus the energy and exergy efficiency of the global system. Previous studies have shown that very high efficiencies can be reach with the use of heat pumps to supply heat to the buildings, and harvesting heat from lake water. The aim of this work is to study the performance of such a system, based on a case study, the Eglantine district located near Lausanne. The focus is set at evaluating the integration of a geothermal field, as a heat source. The main research questions that will be tried to answer are: "How does the CO2 district energy network perform - energetically as well as financially - in the Eglantine district, and under which conditions does it perform better than concurrent solutions?" "What are the characteristics of a typical district that favor the choice of the CO2 district energy network technology?" The results show a very high energy and exergy performance (COPglobal of 6.1)for the CO2 network that is combined with a geothermal field, which is considerably higher than for the conventional GS-HP system (COPglobal of 4.6). The difference is principally explained by the use of a direct expansion system of CO2 into the ground. Moreover, it is shown that for different uses of the buildings there is an optimal ground temperature, or in other words an optimal borehole depth, and the other way around. This work identiffies the key parameters that the CO2 network technology can leverage to compete against modern, well performing, heat pump systems.

2019

Tribological Approach to the Watch Movements

Valentine Agnès Madeleine Magnin

Mechanical watches are complex and sensitive systems that have to maintain a faultless precision over their lifetime. However, this precision can be altered by disturbances occurring during the functioning time, such as friction, lubricant drying, or wear, leading to surface modification. Due to the significant number of contacts, and diversity of materials, geometries, motions, and lubricants, these disturbances and their consequences over time are difficult to control. To deeply understand these phenomena and limit their effect on watches precision over time, a tribological study of watch movements is necessary. The goal of this Ph.D. research is to contribute to the development of a scientific methodology to appraise friction and wear evolution over time in watch movements. To achieve this, a system approach combined with a modelling of the phenomena was used to anticipate the evolution of two critical watch components: the barrel and the escapement. Based on existing theories of lubrication, the performance of the Swiss lever escapement was appraised as a function of well defined geometrical, kinematic, and dynamic parameters. The developed formalism allowed to highlight the relevance of the radii of curvature of the escapement tooth and the anchor pallet on the effectiveness of the fluid lubrication of the Swiss lever escapement. The tribology of the barrel, a brass piece coated with a nickel sublayer and a flash of gold, was then investigated. Wear characterization of real pieces allowed to identify the relevant wear mechanisms at the barrel drum/spring contact. Friction tests were performed to reproduce the observed phenomena in controlled conditions. A predictive law was proposed to estimate the loss of power at the escapement wheel and showed that the wear of the barrel drum can significantly affect the energy efficiency of the watch. Model surfaces composed of a nickel substrate of a specific waviness profile coated with different gold thicknesses were used for further investigation on the wear mechanisms of the gold coating. A simple mechanistic model considering contact pressure, geometrical, and frictional properties was developed to predict the minimum gold thickness necessary to lubricate the system. Two different relations were proposed according to the sliding direction. These relations were used to evaluate possible improvement strategies in terms of materials properties and surface finishing. With the intention to perform further tribological studies of any contacts of a mechanical watch, a methodology was proposed. This methodology stands on three phases: analysis, modelling and application to the watch. This thesis emphasizes the need of a tribological study to better understand the tribological response of a mechanical watch. By combining reviews of literature, experimental observations, and theoretical laws, analytical models were developed to identify critical parameters, materials and design strategies for improving the tribological response of watch components.

EPFL2020

Numerical simulation of deck de-icing using energy pile systems

Aymen Achich

Geothermal energy is heat energy generated and stored in the Earth. With the awareness of the society about environmental issues, geothermal power is developing worldwide. It is cost-effective, reliable, sustainable, and environmentally friendly but has historically been extracted from the depth of the earth. Recent technological advances permits to use this energy from the shallow depth of the earth. Thanks to infrastructure foundations combined with heat pump technology, we are able to use this geothermal shallow energy. It have dramatically expanded the range and size of viable resources especially for applications such as home heating, cooling thus opening a potential for widespread exploitation. The renewable soil energy can be also used in transportation infrastructures such as the de-icing of bridges. Indeed, the icing of bridge decks in the winter is a real problem that potentially creates vehicules accidents. For example, in United states, more than 5’500’000 vehicle crashes occur per year and 23% of them are weather-related (data derived from Federal Highway Administration website). Instead of performing a mechanical de-icing combined with spraying de-icing salt, we can use geothermal energy to proceed to the de-icing by heating the bridge slab. This energy is extracted thanks to the foundations (piles) of the bridge. These foundations are used as heat exchangers to extract the heat from the ground. Snow melting system based on energy piles is a technology that combines the structural function as a foundation with geothermal energy extraction. This technology was already proposed in 1990s in Japan [35] but it is actually nearly applied. The concept is simple: during snowfall periods, hot fluid is injected inside the bridge’s deck through the pipes placed in the bridge’s slab. The heat is transmitted to the pavement and the ice melts down. The hot fluid is obtained thanks to the mechanical work of heat pumps which enhances the power extracted from the energy piles. This method overcomes the problems of prevalent methods (mechanical de-icing combined with spraying de-icing salt) which are associated with extensive corrosion of transportation infrastructure, huge amount of material consumption, and negative environmental impacts. In this technical report, we will see why such a melting system could be a good altenative to traditional de-icing methods ? How can we define the applicability and performance of such a snow melting system ? How this system could be designed and implemented in a real case ? What is the structural behaviour of a bridge deck when the system operates ? In the first chapter, we will explain the different methods used for bridge de-icing and we will focus in particular on the concept of deck de-icing using energy piles system explaining the physical phenomena of heat transfer involved in this system. In chapter 2, we will define a methodology that could determine the energy demand of a bridge deck to remove the ice in different weather conditions. Furthermore, we will investigate to what corresponds this required energy in terms of the fluid temperature injected below the pavement and in terms of the required number of energy piles. We will study the feasability of such a system through verifying whether the heat provided by energy piles will be sufficient to satisfy the energy demand. In the chapter 3, we will study a real case bridge located in the city of Jiangyin (China) where Hohai University geotechnical group is supervising the project. We will decribe first the main features of the project. Since I had the opportunity to assist to the construction phases of the bridge, we will explain in details the construction phases of the project (bridge+de-icing system). Then we will determine the thermal needs of the bridge deck considering the project data. We will conclude this report by dedicating a chapter for numerical simulations done using Comsol Multiphysics software. As a first part, a parametric analysis was performed considering the main elements forming the melting system of the bridge deck in order to understand more its thermal performance. In the next part of this chapter, a set of numerical simulations were done to compare different possible pipe layouts that can be installed on Jiangyin bridge deck. Finally, based on this real case bridge deck, we will concentrate on its structural behaviour during the de-icing process. Since the bridge was in construction during this study, iterative operations were done to optimise the efficiency of the system and predict the thermal and structural response of the bridge deck.