Identifying modular flows on multilayer networks reveals highly overlapping organization in social systems

Unveiling the community structure of networks is a powerful methodology to comprehend interconnected systems across the social and natural sciences. To identify different types of functional modules in interaction data aggregated in a single network layer, researchers have developed many powerful methods. For example, flow-based methods have proven useful for identifying modular dynamics in weighted and directed networks that capture constraints on flow in the systems they represent. However, many networked systems consist of agents or components that exhibit multiple layers of interactions. Inevitably, representing this intricate network of networks as a single aggregated network leads to information loss and may obscure the actual organization. Here we propose a method based on compression of network flows that can identify modular flows in non-aggregated multilayer networks. Our numerical experiments on synthetic networks show that the method can accurately identify modules that cannot be identified in aggregated networks or by analyzing the layers separately. We capitalize on our findings and reveal the community structure of two multilayer collaboration networks: scientists affiliated to the Pierre Auger Observatory and scientists publishing works on networks on the arXiv. Compared to conventional aggregated methods, the multilayer method reveals smaller modules with more overlap that better capture the actual organization

Development of a novel gerotor pump for lubrication systems of aeronautic engines

The technology of lubrication systems for aircrafts engines has seen significant development during the history of aeronautics and has progressed in parallel with the evolution of the engines themselves. Starting from the first, wetsump schemes derived from automotive applications, more complex systems and components have been introduced. The progressive increase of aeronautic engines’ power and speed, as well as that of the maximum operative altitude of the aircraft, have increased the lubricant flow rate required to avoid severe mechanical issues that can cause dangerous conditions for the vehicle and its users. Currently, the main focus on the development of novel lubrication pumps is aimed at reducing the pumps’ weight and envelope while maintaining, or possibly increasing, their reliability. The first two objective could be pursued by searching for novel pump types and/or increasing the pump speed in order to downsize its required capacity, but the low-pressure environment, typical of the lubrication circuits, over imposes a few, severe, limitations to avoid cavitation occurrence that decrease the effectiveness of this approach. The central aim of the presented research, performed within the program “Greening the Propulsion”, is to provide a theoretical framework to help in the development of a novel gerotor pump for the lubrication of aeronautic engines.The first step of the research involves the study of the state of the art of aeronautic engines’ lubrication systems, providing particular care to the effect that any design choice and possible operational condition may have on the lubrication pump design. Hence, the state of the art for gerotor pumps is investigated; results of this study are used, along with catalogue comparisons, to build simplified sizing tools to perform a benchmarking activity involving gerotors and other low pressure pumps type. This activity, performed to position gerotor pumps in the aeronautic engine lubrication market, is then used as a starting point to highlight the weak points of gerotors traditional design and to propose some possible solutions to enhance the pumps performances. To study the outcomes of these modifications, a rigorous theoretical framework is required; sizing and modeling criteria, based on the theory of gearing and compressible fluids, are hence detailed and used to build an Automatic Design and Simulation Framework, able to automatically design, validate and simulate a novel gerotor pump given a minimum number of geometrical and physical input parameters. This design and simulation tool is then used to evaluate the performance boost provided by the proposed variations and to optimize the gears profiles by pairing it with a multiobjective algorithm based on evolutionary strategies. Another critical component of any lubrication system is the pressure relief valve used to avoid the occurrence of dangerous conditions for the pipes integrity. A side activity involving the study of a preliminary sizing tool for pressure relief valve is hence performed. A preliminary design framework is presented and discussed, highlighting the importance of the valve discharge coefficient. To study its dependence on the valve’s geometry, a lengthy CFD simulation campaign is performed varying the poppet shape and the fluid Reynolds’ number. Results are hence discussed and used inside the design framework

Constrained Allocation Flux Balance Analysis

New experimental results on bacterial growth inspire a novel top-down approach to study cell metabolism, combining mass balance and proteomic constraints to extend and complement Flux Balance Analysis. We introduce here Constrained Allocation Flux Balance Analysis, CAFBA, in which the biosynthetic costs associated to growth are accounted for in an effective way through a single additional genome-wide constraint. Its roots lie in the experimentally observed pattern of proteome allocation for metabolic functions, allowing to bridge regulation and metabolism in a transparent way under the principle of growth-rate maximization. We provide a simple method to solve CAFBA efficiently and propose an "ensemble averaging" procedure to account for unknown protein costs. Applying this approach to modeling E. coli metabolism, we find that, as the growth rate increases, CAFBA solutions cross over from respiratory, growth-yield maximizing states (preferred at slow growth) to fermentative states with carbon overflow (preferred at fast growth). In addition, CAFBA allows for quantitatively accurate predictions on the rate of acetate excretion and growth yield based on only 3 parameters determined by empirical growth laws.Comment: 21 pages, 6 figures (main) + 33 pages, various figures and tables (supporting); for the supplementary MatLab code, see http://tinyurl.com/h763es

A Preliminary Experimental Study on the Effects of Wear on the Torsional Stiffness of Strain Wave Gears

Strain wave gears, also known as harmonic drives, are employed in a wide range of fields such as robotics and aerospace, where light weights, precision, and reliability are essential to the correct execution of the tasks. For this reason, their understanding and optimization are of high interest for both academia and industry. Previous studies have been mainly focused on investigating and modeling the working principle of strain wave gears in nominal operating conditions. On the contrary, the present paper describes the results of an experimental campaign aimed to introduce wear in gears of two different suppliers and its impact on the gear torsional stiffness. Results show how the change in the gear performance strongly depends both on the gear manufacturer and the location of wear. For the analyzed components, a damaged wave generator–flexspline interface reduces the gear stiffness up to one-fourth of its nominal value, while the non-nominal shape of the teeth jeopardizes the gearbox performance, leading up to just 4% of the nominal stiffness values, and resulting in backlash. Such data can be used to properly model the presence of wear in strain wave gears and to train data-driven diagnostics and prognostics routines to effectively detect such a fault

ISAC6+ Delivering Smarter Administration through innovation - a Benefits Realisation approach to ensuring success.

The paper describes how the Project Management discipline of benefits realisation has been applied to an EU funded E-government initiative. It explores the benefits of using this approach, the challenges to be addressed, and suggest a framework for applying the approach to other local and national e-government initiatives. One of the key project objectives is to demonstrate through the pilot that implementation of the iSAC6+ system will provide value for money by delivering the desired benefits both to government office users and citizens. The approach described here focuses on costs and benefits generated by use of the system. There are staff costs for training, support and operation, technical costs for integrating iSAC6+ in to existing systems and websites, and more significantly organisational costs for designing and implementing new procedures and working practices. Citizens too will incur costs to access and use the service. In iSAC6+ we have created a model of costs and benefits which can be applied in the short term to the pilot, and in the longer term to a much larger number of public organisations. The aim of the Benefits Realisation model is to demonstrate that iSAC6+ is capable of delivering value for money, and thus to justify the investment needed for expanding its use. Information Technology project success or failure is traditionally judged against objectives set during initial project planning. Enterprises, both public and private sector, have found this approach inadequate because long term costs and benefits do not occur until after the project has completed. Benefits Realisation emerged in the 1990s and developed two roles: a discipline for anticipating and quantifying the expected value of a project in terms of the costs and benefits which will accrue after the project itself is complete; and an over-arching project management philosophy. The paper uses the case study experience to comment upon these two different perspectives. The model developed within the project is based upon the recognised public sector costing formula, the Standard Cost model (SCM) but goes much further by integrating it into a Benefits Realisation tool which creates an audit trail from organisational strategic aims through to detailed cost measures for both quantitative and qualitative incidences

In-depth Feature Selection for PHM System’s Feasibility Study for Helicopters’ Main and Tail Rotor Actuators

As deeply complex machines subjected to heavy vibratory environment, helicopters require relative low mean time between overhaul and suffer from high maintenance cost and availability issues. So far, PHM for helicopters has been aimed at detecting the presence of structural defects in the most critical parts of the mechanical transmission conveying power from the engine to the rotor blades, but very little has been presented on other flight-critical components, such as the main and tail rotor actuators. The proposed paper is focused on preliminary diagnostics and prognostics considerations for a traditional configuration of hydraulic solution, where a tandem actuator is aided by a Stability and Command Augmentation System (SCAS) during operations. At first, the case-study is introduced and the simulation model employed for the analysis is described. Hence, two different failure modes affecting the SCAS are investigated and the physical models used to describe their progression are presented. In-depth data mining is then applied to achieve an accurate feature selection from raw data and an original way to visualize features’ performances through an accuracysensitivity plane is proposed. Lastly, a particle filtering approach is adopted for failure prognosis and its output evaluated through traditional PHM metrics to assess the algorithm effectiveness. The present research provides encouraging results regarding the opportunity of realising a PHM system for helicopters’ flight control actuators without the need of additional sensors, which could make solutions based upon the presented work feasible for both in-service and future platform

Integrated Health Monitoring for the actuation system of high-speed tilting trains

Tilting trains are designed to reach high speed on pre-existing railroads without the need of adjusting the tracks geometry or building dedicated lines; the tilting of the carbody keeps an acceptable level of comfort by limiting the lateral acceleration felt by passengers when the train runs along curved tracks with speed higher than the balance speed built into the curve geometry. As such, they are often used to reduce travel times on routes with several curves. Tilting is performed through a position-controlled actuation system which operates according to the commands received from the train control system: in the studied configuration, the torque needed to tilt the car body with respect to the bogie is provided by a series of hydraulic actuators, while the position information used to close the control loop comes from two capacitive sensors located in the front and rear part of each vehicle. Tilt angle measurement is vital for the system operation and for ensuring a safe ride; the traditional solution in case of discrepancy between the signals of the two tilt angle sensors of any vehicle is to disable the tilting function while limiting the train speed to avoid issues during changes of direction. In a similar fashion, the failure in one (or more) of the tilting actuators would result in the loss of the tilting capability and the return to a fixed configuration operating at reduced speed. It should be noticed that the negative impact of the loss of the tilting system is not limited to the faulty train, since it might affect the entire traffic schedule on the interested lines. The paper presents an integrated Health Monitoring framework that makes intelligent use of all available information thus enhancing the system availability, allowing its operation even in presence of faulty sensors and detecting the onset of failures in the actuation system. At the same time its use can facilitate maintenance organization, simplify the spare parts logistics and provide help to the traffic management. The proposed framework has been developed taking advantage of a high-fidelity model of the physical system validated through comparison with experimental mission profiles on the Lichtenfels - Saalfeld and Battipaglia - Reggio Calabria routes, which have been used by the train manufacturer to assess the performance of their tilting trains

Detection and Prognosis of Propagating Faults in Flight Control Actuators for Helicopters

Recent trend in the aeronautic industry is to introduce a novel prognostic solution for critical systems in the attempt to increase vehicle availability, reduce costs, and optimize the maintenance policy. Despite this, there is a general lack of literature about prognostics for hydraulic flight control systems, especially looking at helicopter applications. The present research was focused on a preliminary study for an integrated framework of fault detection and failure prognosis tailored for one of the most common architectures for flight control actuation. Starting from a high-fidelity dynamic model of the system, two different faults were studied and described within a dedicated simulation environment: the opening of a crack in the coils of the centering springs of the actuator and the wear of the inner seals. Both failure modes were analyzed through established models available in the literature and their evolution simulated within the model of the actuator. Hence, an in-depth feature selection process was pursued aimed at the definition of signals suitable for both diagnosis and prognosis. Results were then reported through an accuracy-sensitivity plane and used to define a prognostic routine based on particle filtering techniques. The more significant contribution of the present research was that no additional sensors are needed so that the prognostic system can be potentially implemented for in-service platforms

Preliminary study towards the definition of a PHM framework for the hydraulic system of a fly-by-wire helicopter

On-board hydraulic systems are tasked to provide a number of critical functions to ensure the in-flight operability of rotary-wings vehicles; the hydraulic system is needed to supply power to the flight control actuators and a number of other utilities, as well as to condition the hydraulic fluid, under a wide range of possible in-service conditions. Being a flight-critical system, the definition of a Prognostics and Health Management framework would provide significant advantages to the users, such as better risk mitigation and improved availability. Moreover, a significant reduction in the occurrences of unpredicted failures, one of the more known downsides of helicopters, is expected. A preliminary analysis on the effects of the inception and progression of several degradation types is the first step assess the feasibility of a PHM system for new platforms, and which failure modes are more likely to be observed. Further, since several key components are frequently provided by different suppliers to the airframer, this preliminary analysis would allow to better assess if an Integrated Vehicle Health Management approach, integrating signals coming from different components, could be beneficial. To pursue this study, a complete model of the hydraulic system for a flyby-wire helicopter has been prepared. Then, an in-depth simulation campaign was pursued with the aim of studying the interactions between different failure modes, the effects that the propagating degradations have on the system performances and which signals can be used to define a robust set of features. The paper introduces the case-study under analysis, a general configuration for fly-by-wire helicopters, presenting the most prominent peculiarities of the system and the effect of such peculiarities on the definition of health monitoring schemes. The model is then used to describe the behavior of the system under nominal and degraded conditions is introduced. Between the possible failure modes, the interaction between wear in several mechanical components and the clogging of the hydraulic lines filters was chosen as the subject of this study; motivations are provided and the degradation model described in detail. Hence, results of a wide-ranging simulation campaign are presented, where the time-domain response of the system is used to guide in the definition of a proper set of features able to characterize the selected fault cases. Selected features are presented, chosen according to significant metrics such as correlation with the simulated degradations, signal-to-noise ratio and accuracy. Two different approaches with a varying degree of integration between system signals are proposed and compared. Prognostics is then pursued through well-known particle filter algorithms. The analysis provides promising results on the capability of successfully detecting, isolating and identifying the selected fault mode; laying the foundations for further and more comprehensive studies on the subject

Design of a PHM system for electro-mechanical flight controls: a roadmap from preliminary analyses to iron-bird validation

Literature on PHM is focused on research dedicated to the definition of new algorithms to achieve better failures prognosis or earlier and more accurate fault diagnosis, but lacks of examples on the design of novel PHM frameworks and the practical issues related with their implementation. This paper describes a roadmap for the design of a novel Prognostics and Health Management system while making reference to a real-case scenario applied to electro-mechanical actuators for flight control systems