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A continuum–discrete multiscale methodology using machine learning for thermal analysis of granular media
No full textThis work presents a data-driven continuum–discrete multiscale methodology to simulate heat transfer through granular materials. The two scales are hierarchically coupled, where the effective thermal conductivity tensor required by the continuous method at the macroscale is obtained from offline microscale analyses. A set of granular media samples is created through the Discrete Element Method (DEM) to relate microstructure properties with thermal conductivity. The protocol for generating these Representative Volume Elements (RVEs) and homogenizing the microscale response is presented and validated by assessing the representativeness of the granular assemblies. The study found that two local properties, the porosity and the fabric of the material, are sufficient to accurately estimate a representative thermal conductivity tensor. The created dimensionless database of microscale results is used for training a surrogate model based on machine learning. In this way, effective thermal conductivity tensors that accurately reflect the local microstructure can be efficiently predicted from the surrogate model by taking the microstructural properties as inputs. The proposed multiscale methodology enables us to solve heat problems in granular media using a continuum approach with accuracy comparable to a pure discrete computational method but at significantly reduced computational cost
L’impacte i el desenvolupament ordenat de l’economia col.laborativa com a un fenòmen econòmicament determinant.
No full textEix 3: La musculatura del sistema empresarial català
L’impacte i el desenvolupament ordenat de l’economia col.laborativa com a un fenòmen econòmicament determinant.
Abstract
L’economia col.laborativa, redefinida com a economia de plataformes és un fenomen emergent que utilitza la tecnologia i l’entorn digital per proporcionar serveis atractius i/o productes desintermediant i disrumpint l’statu quo de moltes indústries, inclús creant-ne de noves.
Cada any s’inverteixen milers de milions d’euros en aquesta nova economia arreu del món fent créixer el fenomen i expandint-lo de forma exponencial. Catalunya és seu d'algunes d’aquestes empreses, tant startups de producció pròpia com scaleups d’origen internacional donant pas així a un nou sector d’activitat econòmica lligat a les noves tecnologies digitals.
La velocitat amb què el sector tecnològic i digital en l’àmbit de l’economia de plataformes evoluciona els seus models de negoci i la seva implementació per part dels usuaris planteja un gran repte tant de seguiment i comprensió com de predicció i prevenció a temps dels seu impacte. Hem estat testimonis de com els perjudicis que el desconeixement, el destemps o la manca d’adequació a la regulació existent poden afectar a un sector enguany tan determinant. Amb l’objectiu d’evitar aquests desajustos i de permetre un desenvolupament de l’economia de plataformes sostenible, racional i beneficiós per Catalunya i els seus ciutadans i ciutadanes, és imperiós conèixer el sector, les seves necessitats, els seus actors principals i les tendències que cal tenir en compte.
 
Impact of saturated granular masses against rigid obstacles: the role of fluid compressibility and front inclination
Get PDFIn recent years, the impact of saturated granular flows against rigid obstacles has been studied by using different numerical approaches. The very low compressibility of water causes numerical instabilities when impact problems are simulated. In this work, a sensitivity analysis has been done by using a Material Point Method code to assess the influence of fluid compressibility and front inclination on numerical results. When the mass front is inclined, fluid bulk modulus does not significantly affect the solution and can be reduced to speed up the computations and reduce spurious numerical oscillations
On the Usage of PANS for the CFD Simulation of Wind Turbines
Get PDFWith the rapid evolution of o↵shore wind energy, engineering tools are crucial to catalyze technological developments and increase their maturity, therefore leading to lower costs. Complex turbine-turbine interactions require a good knowledge of the physics of the flow on, around and down/upstream of each turbine, which can be provided using high-fidelity CFD simulations. Turbulence models play a critical role on this matter and an adequate balance between accuracy and computational e ort is necessary. While RANS approaches are quite e cient, LES should provide the most accurate result. Yet, even nowadays, LES blade-resolved simulations are still computationally prohibitive for industrial purposes. A middle-ground exists in SRS formulations, such as hybrid ones as DDES, or bridging ones such as PANS. In the present work emphasis is placed on PANS, since numerical and modelling errors can be studied and quantified independently, as opposite to other SRS approaches. Using as a benchmark the UNAFLOWwindturbine, it is found that traditional RANS and DDES turbulence formulations are able to predict integral forces, but partially fail in capturing wake mixing. Nevertheless, PANS, while enabling the user to select the ratio of turbulent quantities modelled, is not able to properly capture the integral forces due to premature separation in the blades. Several causes are discussed, including insu cient mesh refinement in the near-wall region and lack of turbulent content of the numerical inlet, preventing laminar to turbulent flow transition. Future work should focus on inlet synthetic turbulence generation, in line with existent literature, in order to improve the shortcomings faced in properly resolving the near-wall flow
Adaptive Refinement Techniques using Multiresolution Wave Propagation Simulations Guided by Inherent Convergence Indicators
Get PDFThe multiresolution finite wavelet domain method has been meticulously studied in wave propagation simulations. The multiresolution procedure always starts with the coarse solution, and then finer solutions can be superimposed on the coarse solution, until convergence is achieved. Based on remarkable observations on the multiple resolution components of the method, a residual-based convergence indicator that reveals convergence at the coarse solution is developed. This convergence metric is rapidly applicable and straightforward and can also divulge the spatial and temporal ranges/domains that the already obtained solution needs to be enhanced. In that way, an automatic adaptive refinement technique is proposed for the local enrichment of the solution, only in the specific grid points and time-steps that it is needed. A numerical case study regarding wave propagation in an inhomogeneous rod manifests the effectiveness and accuracy of the proposed automatic refinement methodology, as also the performance of the suggested convergence indicator
A Hybrid Hexahedral Solid-shell Element with Self-equilibrated Stresses for the Geometrically Nonlinear Static Analysis of Composite Laminated Structures
Get PDFHybrid nite elements with self-equilibrated assumed stresses have proven to pro vide several advantages for analysing shell structures. They guarantee high performance when using coarse meshes and accurately represent the stress eld. Additionally, they do not require assumptions about the displacement eld within the element domain, and the integration is ef ciently performed only along their contours. This work exploits those advantages to develop a solid-shell nite element for the geometrically nonlinear static analysis of composite laminated structures. In particular, an eight-node nite element, which has 24 displacement variables and 18 stress parameters, is developed. The displacement eld is described only by translations, eliminating the need for complex nite rotation treatments in large displacement problems. A Total Lagrangian formulation is used with the Green-Lagrange strain tensor and the second Piola-Kirchho stress tensor. Thickness locking is cured using an assumed natural strain formu lation for the transversal normal stress, and the assumed stress eld eliminates shear locking. Then, for the analysis of linear-elastic problems, no domain integration is needed, and all the element operators are obtained by line integrals. The resulting formulation is e cient and allows for easy implementation. Computed numerical results show the accuracy and robustness of the presented element when used for both the linear elastic static and geometrically nonlinear elastic static analysis of composite laminated shell structures
Modeling small scale processes in Antarctic sea ice
Get PDFThe Antarctic sea ice, which undergoes annual freezing and melting, plays a signif icant role in the global climate cycle. Adverse environmental conditions in the Southern Ocean influence the extent and amount of ice in the Marginal Ice Zones (MIZ), the BioGeo- Chemical (BGC) cycles, and their interconnected relationships. The ’Pancake’ floes are a composition of porous sea ice matrix with interstitial brine, nutrients, and biological com- munities inside the pores. To realistically model these multi-phasic and multi-component coupled processes, the extended Theory of Porous Media (eTPM) is used to develop mod- els capable of simulating the different seasonal variations. All critical variables like salinity, ice volume fraction, and tem perature, among others, are considered and have their equations of state. The phase transition phenomenon is approached through a micro-macro linking scheme. A Phase- field solidification model coupled with salinity is used to model the micro-scale freezing processes and up-scaled to the macro scale eTPM model. This allows for modeling the salt trapped inside the pores. For the biological part, a BGC flux model for sea ice is also set up to simulate the algal species present in the sea ice matrix. Processes like photosynthesis are dependent on temperature and salinity, and are derived through an ODE-PDE coupling with the eTPM model. Academic sim ulations and results are presented as validation for the mathematical model. These high-fidelity models will eventually lead to their incorporation into large-scale global climate models
