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238 results on '"Rubini, Riccardo"'

1. Diagnostics of Wind Turbine by Detectivity

Author

Cocconcelli, Marco, D’Elia, Gianluca, Strozzi, Matteo, Rubini, Riccardo, Ceccarelli, Marco, Series Editor, Corves, Burkhard, Advisory Editor, Glazunov, Victor, Advisory Editor, Hernández, Alfonso, Advisory Editor, Huang, Tian, Advisory Editor, Jauregui Correa, Juan Carlos, Advisory Editor, Takeda, Yukio, Advisory Editor, Agrawal, Sunil K., Advisory Editor, Quaglia, Giuseppe, editor, Boschetti, Giovanni, editor, and Carbone, Giuseppe, editor

Published
2024
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2. Sparsification techniques for reduced order models of turbulent flows

Author

Rubini, Riccardo and Lasagna, Davide

Abstract

The complexity of scale interactions, arising from the increasing number of dynamically active flow structures, is a well-known problem for the numerical modelling of high Reynolds number flows. Without doubts, this complexity is the main obstacle to the development of computationally affordable and physically interpretable models of complex flows. This research focuses on the nonlinear energy interactions across modes in reduced order Galerkin models of turbulent flows demonstrating a novel approach to automatically identify relevant interactions. This work is motivated by the key observation that, in the dynamics of high Reynolds number flows, not all the interactions have the same contribution to the energy transfer between flow structures. With the proposed work, we aim to develop a set of techniques to systematically select the dominant interactions in Galerkin models of turbulent flows, therefore identifying dominant triadic interactions. In the present work, two different approaches have been developed. First, a regression-based approach where the relevant interactions are identified a posteriori according to their relative strength. Second, an a priori approach, where a new set of basis functions, encoding the sparsity features of the flow, is generated. The key aspect of the latter approach is that the reduced-order model obtained by Galerkin projection onto the subspace spanned by the basis has sparse matrix coefficients without the need for any a posteriori evaluation. Both approaches have been tested on a set of flow configurations of increasing complexity. Results show that both approaches can identify the subset of dominant interactions preserving their physics throughout the sparsification process. In addition, further analysis showed that the a priori sparsification method preserves better the physics of triadic interactions, resulting in a better long term time stability and, therefore, should be preferred. Looking into the future, to scale up the a priori methodology to a more complex configuration some aspects need to be further investigated such as the role of the initial guess on the uniqueness of the result and its properties.

Published
2022

3. A-priori sparsification of Galerkin-based reduced order models

Author

Rubini, Riccardo, Lasagna, Davide, and Da Ronch, Andrea

Subjects
Physics - Fluid Dynamics
Abstract

A methodology to generate sparse Galerkin models of chaotic/unsteady fluid flows containing a minimal number of active triadic interactions is proposed. The key idea is to find an appropriate set of basis functions for the projection representing elementary flow structures that interact minimally one with the other and thus result in a triadic interaction coefficient tensor with sparse structure. Interpretable and computationally efficient Galerkin models can be thus obtained, since a reduced number of triadic interactions needs to be computed to evaluate the right hand side of the model. To find the basis functions, a subspace rotation technique is used, whereby a set of Proper Orthogonal Decomposition (POD) modes is rotated into a POD subspace of larger dimension using coordinates associated to low-energy dissipative scales to alter energy paths and the structure of the triadic interaction coefficient tensor. This rotation is obtained as the solution of a non-convex optimisation problem that maximises the energy captured by the new basis, promotes sparsity and ensures long-term temporal stability of the sparse Galerkin system. We demonstrate the approach on two-dimensional lid-driven cavity flow at $Re = 2 \times 10^4$ where the motion is chaotic. We show that the procedure generates Galerkin models with a reduced set of active triadic interactions, distributed in modal space according to established knowledge of scale interactions in two-dimensional flows. This property, however, is only observed if long-term temporal stability is explicitly included in the formulation, indicating that a dynamical constraint is necessary to obtain a physically consistent sparsification.

Published
2021

4. Named Entity Recognition and Linking for Entity Extraction from Italian Civil Judgements

Author

Pozzi, Riccardo, Rubini, Riccardo, Bernasconi, Christian, Palmonari, Matteo, Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Basili, Roberto, editor, Lembo, Domenico, editor, Limongelli, Carla, editor, and Orlandini, Andrea, editor

Published
2023
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5. A European Researchers’ Night Project on Mechanical Vibrations for High School Students

Author

Cocconcelli, Marco, Fonte, Cosimo, Grosso, Pasquale, Mottola, Giovanni, Strozzi, Matteo, Rubini, Riccardo, Ceccarelli, Marco, Series Editor, Agrawal, Sunil K., Advisory Editor, Corves, Burkhard, Advisory Editor, Glazunov, Victor, Advisory Editor, Hernández, Alfonso, Advisory Editor, Huang, Tian, Advisory Editor, Jauregui Correa, Juan Carlos, Advisory Editor, Takeda, Yukio, Advisory Editor, García Prada, Juan Carlos, editor, Castejon, Cristina, editor, and Pedrero Moya, Jose Ignacio, editor

Published
2023
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6. $l_1$-based sparsification of energy interactions in two-dimensional turbulent flows

Author

Rubini, Riccardo, Lasagna, Davide, and Da Ronch, Andrea

Subjects
Physics - Fluid Dynamics
Abstract

In this paper, sparsity-promoting regression techniques are employed to automatically identify from data relevant triadic interactions between modal structures in large Galerkin-based models of two-dimensional unsteady flows. The approach produces interpretable, sparsely-connected models that reproduce the original dynamical behaviour at a much lower computational cost, as fewer triadic interactions need to be evaluated. The key feature of the approach is that dominant interactions are selected systematically from the solution of a convex optimisation problem, with a unique solution, and no a priori assumptions on the structure of scale interactions are required. We demonstrate this approach on models of two-dimensional lid-driven cavity flow at Reynolds number $Re = 2 \times 10^4$, where fluid motion is chaotic. To understand the role of the subspace utilised for the Galerkin projection on sparsity characteristics, we consider two families of models obtained from two different modal decomposition techniques. The first uses energy-optimal Proper Orthogonal Decomposition modes, while the second uses modes oscillating at a single frequency obtained from Discrete Fourier Transform of the flow snapshots. We show that, in both cases, and despite no \textit{a-priori} physical knowledge is incorporated into the approach, relevant interactions across the hierarchy of modes are identified in agreement with the expected picture of scale interactions in two-dimensional turbulence. Yet, substantial structural changes in the interaction pattern and a quantitatively different sparsity are observed. Finally, although not directly enforced in the procedure, the sparsified models have excellent long-term stability properties and correctly reproduce the spatio-temporal evolution of dominant flow structures in the cavity.

Published
2020

9. Gravity Balancing of Parallel Robots by Constant-Force Generators

Author

Mottola, Giovanni, Cocconcelli, Marco, Rubini, Riccardo, Carricato, Marco, Ceccarelli, Marco, Series Editor, Agrawal, Sunil K., Advisory Editor, Corves, Burkhard, Advisory Editor, Glazunov, Victor, Advisory Editor, Hernández, Alfonso, Advisory Editor, Huang, Tian, Advisory Editor, Jauregui Correa, Juan Carlos, Advisory Editor, Takeda, Yukio, Advisory Editor, and Arakelian, Vigen, editor

Published
2022
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10. A Structured Approach to Machine Learning Condition Monitoring

Author

Capelli, Luca, Massaccesi, Giulia, Molano, Jacopo Cavalaglio Camargo, Campo, Federico, Borghi, Davide, Rubini, Riccardo, Cocconcelli, Marco, Haddar, Mohamed, Series Editor, Bartelmus, Walter, Series Editor, Chaari, Fakher, Series Editor, Zimroz, Radoslaw, Series Editor, Chiementin, Xavier, editor, and Bolaers, Fabrice, editor

Published
2022
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13. Damage Mechanism of Surrounding Rock under Blasting Excavation of the Tunnel.

Author

Li, Yaoxin, Wang, Zhibin, Wu, Tingyao, and Rubini, Riccardo

Subjects
STRESS concentration, BLAST effect, SIMULATION software, BLASTING, COMPUTER simulation
Abstract

Based on numerical simulation software LSDYNA and field monitoring data, this paper analyzes the peak particle velocity (PPV) of rock mass at different distances from the blasting face of the roadway. At the same time, the dynamic stress concentration coefficient of surrounding rock under the action of different blasting times and the blasting damage effect of the tunnel are studied. The results show that in the tunnel blasting near the area, the PPV in the vertical direction of the tunnel is maximum in three directions; PPV decreases more slowly in the excavated zone than in the nonexcavated zone. When the explosion source is close to the roadway, the dynamic stress concentration coefficient of the blasting side and the rear side is large, so the vibration standard of surrounding rock should be strictly controlled. [ABSTRACT FROM AUTHOR]

Published
2024
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21. Comparison of Metrics for Peaks Enhancement in Variable Speed Conditions

Author

Cocconcelli, Marco, Rubini, Riccardo, Pancaldi, Fabrizio, Capdessus, Cécile, Ceccarelli, Marco, Series Editor, Hernandez, Alfonso, Editorial Board Member, Huang, Tian, Editorial Board Member, Velinsky, Steven A., Editorial Board Member, Takeda, Yukio, Editorial Board Member, Corves, Burkhard, Editorial Board Member, Carbone, Giuseppe, editor, and Gasparetto, Alessandro, editor

Published
2019
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22. Bearing Fault Model for an Independent Cart Conveyor

Author

Cocconcelli, Marco, Cavalaglio Camargo Molano, Jacopo, Rubini, Riccardo, Capelli, Luca, Borghi, Davide, Haddar, Mohamed, Series Editor, Bartelmus, Walter, Series Editor, Chaari, Fakher, Series Editor, Zimroz, Radoslaw, Series Editor, Fernandez Del Rincon, Alfonso, editor, and Viadero Rueda, Fernando, editor

Published
2019
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26. Dynamic Model of an Independent Carts System

Author

Molano, Jacopo Cavalaglio Camargo, Rossi, Stefano, Cocconcelli, Marco, Rubini, Riccardo, Ceccarelli, Marco, Series editor, Corves, Burkhard, Advisory editor, Takeda, Yukio, Advisory editor, Boschetti, Giovanni, editor, and Gasparetto, Alessandro, editor

Published
2017
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34. Effect of the gas to wall temperature ratio on the bypass transition

Author

Rubini, Riccardo, Maffulli, Roberto, and Arts, Tony

Abstract

The study of the boundary layer transition plays a fundamental role in the field of turbomachinery. The main reason is the strong influence of the transition on the flow field local parameters, such as skin friction and heat transfer, this variation is reflected on the global ones such as efficiency and heat load of the blade row. Turbulent transition models are nowadays commonly used tools in both CFD research and design practice. It is then of particular interest to understand if they are able to predict the effect of temperature on bypass transition and, in case of positive answer, the reasons of their behaviour. This becomes even more interesting as the effect of the flow aero-thermal coupling becomes prominent in the analysis of such phenomena and is typically not accounted for in the validation of turbulence models. In this work we focus our attention on two state of the art transition model that use two radically different approaches to describe transition. To isolate the effects of the temperature ratio on the transition the simulations have been performed keeping the same values of Reynolds and Mach numbers and changing the value of the wall to freestream Temperature Ratio (TR). The results of the two transition models have been compared between them as well as with experimental results. They show that both models are sensitive to TR, though a locally based (rather than correlation based) approach for transition modelling should be favoured.

Published
2024
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43. Sparsification techniques for reduced order models of turbulent flows

Author

Rubini, Riccardo. and Rubini, Riccardo.

Abstract

The complexity of scale interactions, arising from the increasing number of dynamically active flow structures, is a well-known problem for the numerical modelling of high Reynolds number flows. Without doubts, this complexity is the main obstacle to the development of computationally affordable and physically interpretable models of complex flows. This research focuses on the nonlinear energy interactions across modes in reduced order Galerkin models of turbulent flows demonstrating a novel approach to automatically identify relevant interactions. This work is motivated by the key observation that, in the dynamics of high Reynolds number flows, not all the interactions have the same contribution to the energy transfer between flow structures. With the proposed work, we aim to develop a set of techniques to systematically select the dominant interactions in Galerkin models of turbulent flows, therefore identifying dominant triadic interactions. In the present work, two different approaches have been developed. First, a regression-based approach where the relevant interactions are identified a posteriori according to their relative strength. Second, an a priori approach, where a new set of basis functions, encoding the sparsity features of the flow, is generated. The key aspect of the latter approach is that the reduced-order model obtained by Galerkin projection onto the subspace spanned by the basis has sparse matrix coefficients without the need for any a posteriori evaluation. Both approaches have been tested on a set of flow configurations of increasing complexity. Results show that both approaches can identify the subset of dominant interactions preserving their physics throughout the sparsification process. In addition, further analysis showed that the a priori sparsification method preserves better the physics of triadic interactions, resulting in a better long term time stability and, therefore, should be preferred. Looking into the future, to scale up the a

Published
2022

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