Università degli Studi eCampus

About: Università degli Studi eCampus is a education organization based out in Novedrate, Italy. It is known for research contribution in the topics: Anxiety & Planck. The organization has 124 authors who have published 538 publications receiving 21483 citations. The organization is also known as: Universita degli Studi eCampus.

Prediction of the vertical force during FSW of AZ31 magnesium alloy sheets using an artificial neural network-based model

Abstract: A multivariable empirical model based on an artificial neural network (ANN) was developed in order to predict the vertical force occurring during friction stir welding (FSW) of sheets in AZ31 magnesium alloy. To this purpose, FSW experiments were performed at different values of rotational and welding speeds, and the vertical force versus time curve was recorded during the different stages of the process by means of a dedicated sandwich dynamometer. Such results were used in the training stage of the artificial neural network-based model developed to predict vertical force versus time curves. A multi-layer feed forward ANN, using the back-propagation algorithm, consisting of the input layer with four input parameters (rotational speed, welding speed, rotational speed to welding speed ratio and processing time), two hidden layers with four neurons each, and the output layer with the vertical force as output, was built and trained. The generalization capability of the ANN was tested using a two-step procedure: in the former, the leave-one-out cross-validation method was used whilst, in the latter, curves not included in the training dataset were taken into account. The low values of the relative error and average absolute relative error, and the high correlation coefficients between predicted and experimental results have proven the excellent capability of the artificial neural network in modeling complex shape of the curve and in capturing the effect of the process parameters on the vertical force without a priori knowledge of the complex microstructural and mechanical mechanisms taking place during friction stir welding. Finally, the relationship between vertical force and processing time, at different welding and rotational speeds, was also predicted using the support vector machine algorithm and the results were compared with those given by the ANN-based model.

Time-dependent ground movements induced by shield tunneling in soft clay: a parametric study

Abstract: In this work, the effects of coupled hydromechanical (consolidation) processes associated with shield tunneling excavation in soft clays are investigated with particular attention to the prediction of ground movements at the ground surface. A series of 2d FE analyses have been carried out in parametric form in order to investigate the effects of tunnel excavation velocity relative to the soil consolidation rate and the hydraulic boundary conditions at the tunnel boundary. The shield advancement process has been simulated with a simplified procedure incorporating both volume loss and ovalization of the tunnel section. In order to investigate the relative importance of soil consolidation during the excavation process, different characteristic times for the tunnel face advancement and for the consolidation process around the tunnel have been considered, for the two limiting conditions of fully permeable liner and impervious liner. The potential damage induced by the tunnel excavation on existing structures, based on computed ground surface distortions and horizontal deformations, has been found to vary significantly with time during the consolidation process. The results of the simulations allowed to obtain useful information on the minimum tunnel face advancement speed for which the assumption of fully undrained conditions for the soil during the excavations is acceptable, as well as on the speed range for which solving the fully coupled hydromechanical problem is necessary.

Lyapunov-Based Design of a Distributed Wardrop Load-Balancing Algorithm With Application to Software-Defined Networking

Abstract: This paper presents an original discrete-time, distributed, noncooperative load-balancing algorithm, based on mean field game theory, which does not require explicit communications. The algorithm is proven to converge to an arbitrarily small neighborhood of a specific equilibrium among the loads of the providers, known as Wardrop equilibrium. Thanks to its characteristics, the algorithm is suitable for the software-defined networking (SDN) scenario, where service requests coming from the network nodes, i.e., the switches, are managed by the so-called SDN controllers, playing the role of providers. The proposed approach is aimed at dynamically balancing the requests of the switches among the SDN controllers to avoid congestion. This paper also suggests the adoption of SDN Proxies to improve the scalability of the overall SDN paradigm and presents an implementation of the algorithm in a proof-of-concept SDN scenario, which shows the effectiveness of the proposed solution with respect to the current approaches.