Models de qualitat d'aigua als rius: aplicació i tendències futures

Després de vint anys de desenvolupament intens i les recents primeres aplicacions als rius catalans, escau de participar a la present etapa de reflexió iniciada per diversos estudiosos sobre les aportacions dels models de qualitat de les aigües als rius, llurs avantatges i dificultats de realització , així corn les perspectives de noves aplicacions

Symmetry-preserving discretisation methods for magnetohydrodynamics

In this work, the symmetry-preserving method [1, 2, 3] is extended to include magnetohydrodynamic effects, using the collocated grid arrangement of Ni et al. [4, 5]. The electromagnetic part is solved explicitly using the induction-less approximation and an electric potential Poisson equation. The proposed solver is implemented in OpenFOAM and tested for accuracy and stability, and compared to the method of Ni et al. [4, 5]. A new benchmark case using a Taylor-Green vortex in a transverse magnetic field is used, for which kinetic energy budget terms are compared to the analytical solutions. Finally, Hunt’s case is used to compare flow profiles to the analytical solutions. Influence of the spatial discretisation on accuracy and stability is also examined by solving both cases on meshes with variable degrees of distortion. The symmetry-preserving method showed accuracy on Cartesian meshes and stability even on extremely distorted meshes, whereas the method of Ni et al. [4, 5] showed less accurate conservation of current density and was not able to produce stable solutions on the extremely distorted meshes.This project is part of the RIS3CAT-FEDER, FusionCAT project (001- P-001722) of Generalitat de Catalunya and the RETOtwin project (PDC2021-120970-I00) of Ministerio de Economía y Competitividad, Spain. J.A.H. is supported by the predoctoral grant FI 2022 (2022 FI B1 00204) of the Catalan Agency for Management of University and Research Grants (AGAUR).Peer ReviewedPostprint (published version

A General Method to Compute Numerical Dispersion Error

This article presents a new methodology to compute numerical dispersion error. The analysis here presented is not restricted to uniform structured meshes nor linear discrete operators as it does not rely on sinusoids to compute the associated error. When using uniform meshes, the results obtained with the present method collapse onto the obtained with the classic one via an easy change of basis. If non-uniform meshes are used, a new kind of results are obtained which shed some light onto the role stretching has on dispersion error.This work has been financially supported by the Ministerio de Economía y Competitividad, Spain (No. ENE2017-88697-R). J.R.P. is supported by a FI-DGR 2015 predoctoral contract financed by Generalitat de Catalunya, Spain.Peer ReviewedPostprint (published version

A simple optimization approach for the insulation thickness distribution in household refrigerators

Determination of the optimal insulation thickness is of great relevance in many thermal engineering applications. In this paper, a simple optimization strategy based on the Lagrange multipliers is presented. The optimal set of thicknesses is analytically found for different constraints and objective functions of interest for the refrigeration industry. Namely, the minimization of heat losses in a single compartment with fixed internal and external volumes and the optimal configuration for a prescribed energy efficiency index. Then, these two basic problems are extended for configurations with two compartments, e.g. domestic refrigerators-freezers, and for configurations with vacuum insulation panels. Optimization problems for realistic configurations show the great potential of the proposed methodology for industrial refrigeration applications.Postprint (author's final draft

Evaluation of enhanced gray area mitigation approaches based on jet aeroacoustics

An investigation of various eddy viscosity models for accurate scale-resolving simulation of aerodynamics and aeroacoustics of a turbulent jet is presented. The models are considered from the perspective of solving the so-called gray area problem. This problem is related to nonphysical delay in the transition from Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) in hybrid RANS–LES approaches such as detached eddy simulation (DES) when applied to shear-layer flows. The performance of recently developed dynamic adapting subgrid length scales ([Formula: see text], [Formula: see text], and [Formula: see text]) and subgrid LES models ([Formula: see text] and S3QR) separately and together is demonstrated. The object of the investigation is an immersed subsonic turbulent jet. The simulations are carried out on a set of refining meshes using two different scale-resolving numerical algorithms with basic and higher-accuracy schemes on unstructured meshes. The evaluation of various eddy-viscosity models within the DES approach is mostly focused on the analysis of far-field noise. The study has clearly demonstrated the importance of both a numerical scheme and a subgrid turbulence model. The results show that some of the considered techniques provide the necessary accuracy to predict the noise generated by a turbulent jet. The features of the considered approaches are identified and discussed. Recommendations are formulated for the choice of the LES model and subgrid length scale for this kind of problem.The work of Jesús Ruano, F. Xavier Trias, and Joaquim Rigola has been financially supported by the project RETOtwin (PDC2021- 120970-I00) funded by MCIN/AEI/10.13039/501100011033 and European Union Next Generation European Union / Plan de Recuperación, Transformación y Resiliencia (EU/PRTR). The work of Alexey P. Duben and Andrey V. Gorobets was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (Theme No. 122041100137-4). NOISEtte computations were carried out using the equipment of the shared research facilities of high performance computing (HPC) computing resources at Lomonosov Moscow State University, the computing resources of the federal collective usage center Complex for Simulation and Data Processing for Mega-science Facilities at National Research Centre (NRC) “Kurchatov Institute” (http://ckp.nrcki.ru/), and the hybrid supercomputer K60 installed in the Supercomputer Centre of Collective Usage of Keldysh Institute of Applied Mathematics of Russian Academy of Sciences (KIAM RAS). The authors thankfully acknowledge these institutions.Peer ReviewedPostprint (published version

Issues in System Boundary Definition for Substance Flow Analysis: The Case of Nitrogen Cycle Management in Catalonia

The great complexity of the nitrogen cycle, including anthropogenic contributions, makes it necessary to carry out local studies, which allow us to identify the specific cause-effect links in a particular society. Models of local societies that are based on methods such as Substance Flow Analysis (SFA), which study and characterise the performance of metabolic exchanges between human society and the environment, are a useful tools for directing local policy towards sustainable management of the nitrogen cycle. In this paper, the selection of geographical boundaries for SFA application is discussed. Data availability and accuracy, and the possibility of linking the results with instructions for decision making, are critical aspects for proper scale selection. The experience obtained in the construction of the model for Catalonia is used to draw attention to the difficulties found in regional studies

Benvinguda i presentació

Acte de benvinguda i presentació de la XII International Summer School on the Environment (ISSE 2012), celebrat a la Universitat de Girona del 3 al 7 de setembre de 201

Tècniques avançades per la mitigació de la zona grisa en simulacions DES i els seus efectes en l'espectre acústic del jet circular

The research dedicated to the investigation of different gray-area mitigation approaches towards accurate aerodynamics and aeroacoustics is presented. The recent modifications of hybrid RANS-LES DDES approach based on combinations of new adapting subgrid length scales (~ !, SLA and lsq) and LES models ( and S3QR) are considered. The object of investigation is an immersed subsonic turbulent jet. The simulations are carried out on a set of refining meshes using two different scale-resolving numerical algorithms realized in the compressible codes NOISEtte and OpenFOAM. The evaluation of different approaches is focused on the analysis of far field noise. The results show that all the considered techniques provide appropriate accuracy to predict the noise generated by the turbulent jet. The study clearly demonstrated the importance of both numerical scheme and subgrid turbulence model. The peculiarities of considered approaches are revealed and discussed.A.D. was supported by Moscow Center for Fundamental and Applied Mathematics, Agreement with the Ministry of Science and Higher Education of the Russian Federation, No. 075-15-2019-1623. The NOISEtte computations were carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University and the computing resources of the federal collective usage center Complex for Simulation and Data Processing for Mega-science Facilities at NRC ”Kurchatov Institute” (http://ckp.nrcki.ru/). J.Ru. was supported by a FI-DGR 2015 predoctoral contract financed by Generalitat de Catalunya, Spain. J.Ru. and F.X.T. have been financially supported by the Ministerio de Economía y Competitividad, Spain (No. ENE2017-88697-R). J.Ru., F.X.T. and J.Ri. are also supported by the Clean Sky 2 Joint Undertaking. ANTIFOD project (Grant ID 821352).Peer ReviewedPostprint (published version