Higher Institute on Territorial Systems for Innovation
PORTO Publications Open Repository TOrinoNot a member yet
91193 research outputs found
Sort by
Molecular junctions for thermal transport between graphene nanoribbons: Covalent bonding vs. interdigitated chains
No full textAn efficient data exchange mechanism for chained network functions
No full textThanks to the increasing success of virtualization technologies and processing capabilities of computing devices, the deployment of virtual network functions is evolving towards a unified approach aiming at concentrating a huge amount of such functions within a limited number of commodity servers. To keep pace with this trend, a key issue to address is the definition of a secure and efficient way to move data between the different virtualized environments hosting the functions and a centralized component that builds the function chains within a single server. This paper proposes an efficient algorithm that realizes this vision and that, by exploiting the peculiarities of this application domain, is more efficient than classical solutions. The algorithm that manages the data exchanges is validated by performing a formal verification of its main safety and security properties, and an extensive functional and performance evaluation is presented
Prediction, experimental results and analysis of the ITER TF insert coil quench propagation tests, using the 4C code
No full textThe ITER Toroidal Field Insert (TFI) coil is a single-layer Nb3Sn solenoid tested in 2016-2017 at the National Institutes for Quantum and Radiological Science and Technology (former JAEA) in Naka, Japan. The TFI, the last in a series of ITER insert coils, was tested in operating conditions relevant for the actual ITER TF coils, inserting it in the borehole of the Central Solenoid Model Coil, which provided the background magnetic field. In this paper, we consider the five quench propagation tests that were performed using one or two inductive heaters (IHs) as drivers; out of these, three used just one IH but increasing delay times, up to 7.5 s, between the quench detection and the TFI current dump. The results of the 4C code prediction of the quench propagation up to the current dump are presented first, based on simulations performed before the tests. We then describe the experimental results, showing good reproducibility. Finally, we compare the 4C code predictions with the measurements, confirming the 4C code capability to accurately predict the quench propagation, the evolution of total and local voltages, as well as of the hot spot temperature. To the best of our knowledge, such a predictive validation exercise is performed here for the first time for the quench of a Nb3Sn coil. Discrepancies between prediction and measurement are found in the evolution of the jacket temperatures, in the He pressurization and quench acceleration in the late phase of the transient before the dump, as well as in the early evolution of the inlet and outlet He mass flow rate. Based on the lessons learned in the predictive exercise, the model is then modified to try and improve a posteriori (i.e. in interpretive, as opposed to predictive mode) the agreement between simulation and experiment
Orthogonal polynomials in badly shaped polygonal elements for the Virtual Element Method
No full textIn this paper we propose a modified construction for the polynomial basis on polygons used in the Virtual Element Method (VEM). This construction is alternative to the usual monomial basis used in the classical construction of the VEM and is designed in order to improve numerical stability. For badly shaped elements the construction of the projection matrices required for assembling the local coefficients of the linear system within the VEM discretization of Partial Differential Equations can result very ill conditioned. The proposed approach can be easily implemented within an existing VEM code in order to reduce the possible ill conditioning of the elemental projection matrices. Numerical results applied to an hydro-geological flow simulation that often produces very badly shaped elements show a clear improvement of the quality of the numerical solution, confirming the viability of the approach. The method can be conveniently combined with a classical implementation of the VEM and applied element-wise, thus requiring a rather moderate additional numerical cost
Solar-assisted integrated biogas solid oxide fuel cell (SOFC) installation in wastewater treatment plant: Energy and economic analysis
No full textA unique cogeneration system integrating a biogas fed Solid Oxide Fuel Cell (SOFC) and a Concentrating Solar Thermal (CST) system for a reference Waste Water Treatment Plant (WWTP) in Italy is proposed. Biogas - which is locally in the WWTP from the anaerobic digestion (AD) of the collected sludge - can be used to produce electricity using SOFC power modules. The thermal power recovered from the SOFC exhaust stream is used to meet part of the digester thermal load. However, the rest heat loads are provided by using the integration with the CST system and an auxiliary boiler. Energy analysis is performed to determine the effect of using the solar heating system on the system performance. Also, the economic performance is evaluated through a cash-flow analysis and the calculation of the Levelized cost of electricity (LCOE). It is observed that installing 300 m2, 700 m2, 1100 m2 of solar collectors could cover 8%, 18% and 30% of total digester heat load, respectively. Results show an overall beneficial effect of the solar installation, both from an energy and economic standpoint of view. For all the scenarios analyzed, the LCOE is lower than the grid electricity price and, with increasing solar integration, the value is further reduced showing that, despite the investment return time, the electricity production during the entire system lifetime is competitive against grid electricity prices
Multilayered plate elements accounting for refined theories and node-dependent kinematics
No full textAn axiomatic/asymptotic evaluation of best theories for isotropic metallic and functionally graded plates employing non-polynomic functions
No full textThis paper presents Best Theory Diagrams (BTDs) constructed from various non-polynomial terms to identify best plate theories for metallic and functionally graded plates. The BTD is a curve that provides the minimum number of unknown variables necessary to obtain a given accuracy or the best accuracy given by a given number of unknown variables. The plate theories that belong to the BTD have been obtained using the Axiomatic/Asymptotic Method (AAM). The different plate theories reported are implemented by using the Carrera Unified Formulation (CUF). Navier-type solutions have been obtained for the case of simply supported plates loaded by a bisinusoidal transverse pressure with different length-to-thickness ratios. The BTDs built from non-polynomial functions are compared with BTDs using Maclaurin expansions. The results suggest that the plate models obtained from the BTD using nonpolynomial terms can improve the accuracy obtained from Maclaurin expansions for a given number of unknown variables of the displacement field
Thermal transmittance in graphene based networks for polymer matrix composites
No full textGraphene nanoribbons (GNRs) can be added as fillers in polymer matrix composites for enhancing their thermo-mechanical properties. In the present study, we focus on the effect of chemical and geometrical characteristics of GNRs on the thermal conduction properties of composite materials. Configurations consisting of single and triple GNRs are here considered as representative building blocks of larger filler networks. In particular, GNRs with different length, relative orientation and number of cross-linkers are investigated. Based on results obtained by Reverse Non-equilibrium Molecular Dynamics simulations, we report correlations relating thermal conductivity and thermal boundary resistance of GNRs with their geometrical and chemical characteristics. These effects in turn affect the overall thermal transmittance of graphene based networks. In the broader context of effective medium theory, such results could be beneficial to predict the thermal transport properties of devices made of polymer matrix composites, which currently find application in energy, automotive, aerospace, electronics, sporting goods, and infrastructure industries
Fabrication of nanofiltration membranes via stepwise assembly of oligoamide on alumina supports: Effect of number of reaction cycles on membrane properties
No full textRobust and Efficient Globally-Asynchronous Locally-Synchronous (GALS) digital design
No full textProcess and operating condition variability creates a huge problem for current and future digital integrated circuits, because it forces them to operate at a speed, voltage and hence power and energy consumption which is very far from the optimum. System on Chip (SoC) architectures are born to meet some of the microelectronic trends. A single integrated chip contains an entire system with one or more central processors, several other chip-set, memories, and interfaces. The bottleneck of this approach are the interconnections between the various components. A global asynchronous communication is particularly suitable for this purpose because it removes most of the variable delays of the synchronous operation. At the same time, there is always the need to optimize the speed or power consumption of the computation and the Razor approach has been built for this purpose (trying to go below the synchronous safe operation). So the goal of my work was to implement a new Globally-Asynchronous Locally-Synchronous (GALS) architecture that combines Safe Razor modules connected by flexible asynchronous communication channels. In such architecture, both computation and communication are executed without the margins required by the synchronous worst-case methodology achieving better performance. The thesis makes two contributions to the state of the art: 1. Safe-Razor: a metastability-robust adaptive clocking inside each synchronous GALS module. 2. M-of-N PID code: an efficient Delay-Insensitive (DI) protocol for the asynchronous communication between the GALS module