Biomechanics at the workplace under hypogravity conditions

The main goal of my research is to establish guidelines for workplace design based on human biomechanics: specifically sitting workplaces and handling areas in 1/6G-1/3G (Moon, Mars) conditions. Such a workplace could be used in long-term space missions in order to maximize worker performance and minimize the risks of musculoskeletal injuries.Research objective is to formalize a baseline workplace design based on best practices limited to the tasks: operating a computer, assembling/maintenance operations.Proposed steps:1) Data collection and methods definitions2) Measurement and simulation of the human fatigue in the variation of sitting postures and handling areas (identification of typical poses, 3D simulation, graph analysis)3) Optimization of the workplace design based on human biomechanics (motion capture, factor analysis, optimization) 4) Simulation of workplace design in different environments (validation methods).Scientific & technological novelty: 1) Measurement of human muscular fatigue as a function of workload in reduced gravity conditions and integration of the results into the design model2) Modeling of the biomechanics of human movements in the workplace in reduced gravity conditions;3) Developing of sitting workplace design in reduced gravity conditions - taking into account human biomechanics.This research addresses problems revealed by workplace design in confined conditions found in Earth or near-Earth facilities in extreme environments including in underwater conditions, remote & non-remote locations and Low Earth Orbit (LEO), habitat simulators. Human-centered design strategies and biomechanics issues for creating an effective workplace design for long-term missions will also be addressed. The recommendations for design, maintenance, and usage of this workplace in different gravity conditions (1G, 1/6G,1/3G) will be provided. The design optimization of such a workplaces design based on human biomechanics will be done with the help of numerical simulations and digital human modeling. Physical experiments will validate these results by means of the suspension system, underwater experiment and possible by parabolic flights. This work may have a significant impact on workplace designs for both Earth and Space projects. Keywords: biomechanics, workplace, posture, extreme environments, human-centered design, Moon/Mars exploration, comfort conditions, task performance, reduced gravity, digital human modeling, motion capture

Rate allocation and optimized decoding in inter-session network coding

Eirina Bourtsoulatze

Recent advances in data processing and communication systems have led to a continuous increase in the amount of data communicated over today’s networks. These large volumes of data pose new challenges on the current networking infrastructure that only offers a best effort mechanism for data delivery. The emergence of new distributed network architectures, such as peer-to-peer networks and wireless mesh networks, and the need for efficient data delivery mechanisms have motivated researchers to reconsider the way that information is communicated and processed in the networks. This has given rise to a new research field called network coding. The network coding paradigm departs from the traditional routing principle where information is simply relayed by the network nodes towards the destination, and introduces some intelligence in the network through coding at the intermediate nodes. This in-network data processing has been proved to substantially improve the performance of data delivery systems in terms of throughput and error resilience in networks with high path diversity. Motivated by the promising results in the network coding research, we focus in this thesis on the design of network coding algorithms for simultaneous transmission of multiple data sources in overlay networks. We investigate several problems that arise in the context of inter-session network coding, namely (i) decoding delay minimization in inter-session network coding, (ii) distributed rate allocation for inter-session network coding and (iii) correlation-aware decoding of incomplete network coded data. We start by proposing a novel framework for data delivery from multiple sources to multiple clients in an overlay wireline network, where intermediate nodes employ randomized inter-session network coding. We consider networks with high resource diversity, which creates network coding opportunities with possibly large gains in terms of throughput, delay and error robustness. However, the coding operations in the intermediate nodes must be carefully designed in order to enable efficient data delivery. We look at the problem from the decoding delay perspective and design solutions that lead to a small decoding delay at clients through proper coding and rate allocation. We cast the optimization problem as a rate allocation problem, which seeks for the coding operations that minimize the average decoding delay in the client population. We demonstrate the validity of our algorithm through simulations in representative network topologies. The results show that an effective combination of intra- and inter-session network coding based on randomized linear coding permits to reach small decoding delays and to better exploit the available network resources even in challenging network settings. Next, we design a distributed rate allocation algorithm where the users decide locally how many intra- and inter-session network coded packets should be requested from the parent nodes in order to get minimal decoding delay. The capability to take coding decisions locally with only a partial knowledge of the network statistics is of crucial importance for applications where users are organized in dynamic overlay networks. We propose a receiver-driven communication protocol that operates in two rounds. First, the users request and obtain information regarding the network conditions and packet availability in their local neighborhood. Then, every user independently optimizes the rate allocation among different possible intra- and inter-session packet combinations to be requested from its parents. We also introduce the novel concept of equivalent flows, which permits to efficiently estimate the expected number of packets that are necessary for decoding and hence to simplify the rate allocation process. Experimental results indicate that our algorithm is capable of eliminating the bottlenecks and reducing the decoding delay of users with limited resources. We further investigate the application of the proposed distributed rate allocation algorithm to the transmission of video sequences and validate the performance of our system using the NS-3 simulator. The simulation results show that the proposed rate allocation algorithm is successful in improving the quality of the delivered video compared to intra-session network coding based solutions. Finally, we investigate the problem of decoding the source information from an incomplete set of network coded data with the help of source priors in a finite algebraic field. The inability to form a complete decoding system can be often caused by transmission losses or timing constraints imposed by the application. In this case, exact reconstruction of the source data by conventional algorithms such as Gaussian elimination is not feasible; however, partial recovery of the source data may still be possible, which can be useful in applications where approximate reconstruction is informative. We use the statistical characteristics of the source data in order to perform approximate decoding. We first analyze the performance of a hypothetical maximum a posteriori decoder, which recovers the source data from an incomplete set of network coded data given the joint statistics of the sources. We derive an upper bound on the probability of erroneous source sequence decoding as a function of the system parameters. We then propose a constructive solution to the approximate decoding problem and design an iterative decoding algorithm based on message passing, which jointly considers the network coding and the correlation constraints. We illustrate the performance of our decoding algorithm through extensive simulations on synthetic and real data sets. The results demonstrate that, even by using a simple correlation model expressed as a correlation noise between pairs of sources, the original source data can be partially decoded in practice from an incomplete set of network coded symbols. Overall, this thesis addresses several important issues related to the design of efficient data delivery methods with inter-session network coding. Our novel framework for decoding delay minimization can impact the development of practical inter-session network coding algorithms that are appropriate for applications with low delay requirements. Our rate allocation algorithms are able to exploit the high resource diversity of modern networking systems and represent an effective alternative in the development of distributed communication systems. Finally, our algorithm for data recovery from incomplete network coded data using correlation priors can contribute significantly to the improvement of the delivered data quality and provide new insights towards the design of joint source and network coding algorithms.

EPFL2013

Ground to Flight Investigations of Hayabusa with Ablation Effects

Nikhil Banerji, Elise Joy Fahy, Pénélope Leyland, Valentin Marguet, Jérémy Raphaël Mora-Monteros, Daniel Potter

Thermal protection systems (TPS) are of extreme importance for the survival of space vehicles especially during superorbital re-entry to Earth. The design of thermal protection systems requires in-depth knowledge of the thermal loading experienced during a re-entry. The thermal loading data is mostly determined using ground testing and can be backed up by modelling activities including computational fluid dynamics (CFD). The verification of this data with flight data is invaluable and a recent, rare example of an opportunity for comparison was the Hayabusa asteroid sample return mission, which landed in Australia in 2010. During this re-entry a team of international scientists collected spectral data which can now be used for comparison and verification of ground test and modelling/CFD data. Ground testing of subscale models at flight equivalent hypervelocity flow conditions (8 − 12 km/s) can be performed in hypersonic impulse facilities such as the X2 expansion tunnel at The University of Queensland. A recently developed method at The University of Queensland enables heated reinforced carbon-carbon (RCC) models to be tested at temperatures repre- sentative of those experienced in flight ( 2000 − 3000 K), in addition to testing with cold-wall metallic models. Hot wall testing allows more realistic simulation of re-entry flow characteristics including important thermal surface effects (surface chemistry, catalycity) which has previously not been possible. The eilmer3 compressible flow CFD code is used extensively for simulating atmospheric re-entry vehicles at flight and laboratory conditions. Simulations of the Hayabusa aeroshell incorporate heated walls, as well as surface catalycity, to accurately model the conditions experienced by the TPS. These simulations can be coupled with SACRAM, a 1D ablation modelling code, to include the effects of ablation and recession at critical points on the model surface. Current work is investigating the effects and validity of heat flux scaling correlations applied to a range of scaled models with the Hayabusa geometry and flight equivalent flow conditions. This will be achieved through results of CFD simulations, incorporating radiation and ablation modelling, and expansion tunnel testing with hot and cold wall models. Increased understand- ing of scaling methods will allow higher fidelity heat loading data to be acquired allowing more efficient and effective design of TPS. This paper will discuss results from CFD simulations coupled with ablation modelling and modelled surface chemistry. An outline of planned experiments in the X2 expansion tunnel, including background on the RCC heating method and condition development, will also be presented.

2013

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