scholarly journals Development of a THMC code for bentonites in COMSOL Multiphysics

2020 ◽  
Vol 195 ◽  
pp. 04002
Author(s):  
Ángel Yustres ◽  
Rubén López-Vizcaíno ◽  
Virginia Cabrera ◽  
Vicente Navarro
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Numerical Models ◽  
Swelling Pressure ◽  
Double Porosity ◽  
Comsol Multiphysics ◽  
Chemical Potentials ◽  
Definition Of ◽  
High Degree ◽  
First Time

The proposed use of active clays for the isolation of radioactive wastes in deep geological repositories has been followed by a deeper understanding of this type of soils. This increased knowledge has led to the need for both conceptual and numerical models capable of capturing the main trends in behaviour and the different couplings between different physical-chemical phenomena. In addition, the model must have a high degree of flexibility that enables it to accommodate future developments or new relevant phenomena. This work presents a numerical THMC code developed entirely on the COMSOL Multiphysics numerical implementation platform, which provides the required adaptability. This model includes, for the first time in this environment, a reactive transport model in unsaturated porous media for a relevant geochemical system (consistent with the MX-80 bentonite) together with a THM model based on a double porosity approach. The chemical potentials of water and solutes are used for the definition of thermodynamic equilibria between both porosity levels. Trends in the behaviour of a bentonite sample under oedometric conditions are satisfactorily simulated in response to a process of saturation and change in salinity conditions. Variations in swelling pressure, porosity distribution or dissolution/precipitation of the main accessory minerals are analysed and explained by means of the proposed conceptual model.

scholarly journals Numerical Models of Subsurface Flow Constructed Wetlands: Review and Future Development

2020 ◽  
Vol 12 (8) ◽  
pp. 3498
Author(s):  
Chunbo Yuan ◽  
Ting Huang ◽  
Xiaohong Zhao ◽  
Yaqian Zhao
Keyword(s):  
Constructed Wetlands ◽  
Reactive Transport ◽  
Transport Model ◽  
Numerical Models ◽  
Degradation Process ◽  
Research Direction ◽  
Future Research ◽  
Comprehensive Model ◽  
Advantages And Disadvantages ◽  
Model Complex

Numerical model as a simulation tool was used to describe the pollutants transformation and degradation process in constructed wetlands (CWs). It can help provide insight into the “black box” and increase the understanding of the complex processes in CWs. In the last few decades, several process-based numerical models were developed to depict the pollutants removal processes in CWs, which include biochemical model, hydraulic model, reactive-transport model, plants model, clogging model, and coupling model combining two or more sub-models. However, there was a long way to go before fully understanding the decontamination mechanisms of CWs. On the one hand, single or a composite model coupling a small number of sub-models cannot fully reveal the decontamination processes. On the other hand, a comprehensive model including all sub-models of current cognition involves numerous parameters, most of which are interaction and cannot quantitatively determined, thus making the model complex and leading to diffuse interaction. Therefore, in order to describe the reaction processes in CWs more accurately, it is expected that all parameters should be quantified as far as possible in the future model. This study aims to provide a review of the numerical models of CWs and to reveal mechanism of decontamination. Based on the advantages and disadvantages of existing models, the study presented the improvement method and future research direction: (1) new detection/monitoring technique or computing method to quantitatively assess the parameters in CWs models, (2) correcting the simulation errors caused by the assumption of Activated Sludge Models (ASMs) and developing a complete biofilm reaction sub-model, (3) simplification of the comprehensive model, and (4) need of emerging pollutants modeling.

scholarly journals M4EKR, Multiphysics for ElectroKinetic Remediation of Polluted Soils

2020 ◽  
Vol 195 ◽  
pp. 02003
Author(s):  
Ángel Yustres ◽  
Rubén López-Vizcaíno ◽  
Virginia Cabrera ◽  
Vicente Navarro
Keyword(s):  
Reactive Transport ◽  
Natural Waters ◽  
Transport Model ◽  
Numerical Models ◽  
Electrokinetic Remediation ◽  
Natural Soil ◽  
Algebraic Equations ◽  
Advective Flow ◽  
Partially Saturated Soils ◽  
2,4 Dichlorophenoxyacetic Acid

Electrokinetic soil remediation (EKR) is one of the most promising techniques for decontamination of low permeability soils, in which the most classical techniques have been found to be less efficient. However, its practical application on a real scale has been rather limited since the phenomena involved in these processes are very complex. For this reason, it is essential to use numerical models that allow us to know the main trends in the behaviour of soils and natural waters subjected to EKR processes. This study presents the numerical model M4EKR (Multiphysics for ElectroKinetic Remediation). The M4EKR module is a reactive transport model for partially saturated soils that allows reproducing the transport of species due to electroosmosis, electromigration, diffusion and advective flow. The model was completely implemented in COMSOL Multiphysics, a partial differential equation solver. The system of differential and algebraic equations to solve the chemical and transport problem was fully defined by the authors, and they were solved by the M4EKR module in COMSOL (monolithic approach). The scope of the model is illustrated by simulating an EKR process of a natural soil and porewater contaminated with a polar pesticide: 2,4-Dichlorophenoxyacetic acid. For simplicity, the M4EKR version used in this study does not include gas transport, it does not consider the deformability of the soil and it is assumed the processes occur under isothermal conditions.

Spent fuel alteration model integrating processes of different time-scales

MRS Advances ◽  
2020 ◽  
Vol 5 (3-4) ◽  
pp. 159-166
Author(s):  
O. Riba ◽  
E. Coene ◽  
O. Silva ◽  
L. Duro
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Beta Radiation ◽  
Comsol Multiphysics ◽  
Water Radiolysis ◽  
Spent Fuel ◽  
Subsequent Reduction ◽  
Reactive Transport Model ◽  
Safety Assessments ◽  
Different Time Scales

ABSTRACTA 1D reactive transport model has been implemented in iCP (interface COMSOL Multiphysics and PhreeqC) to assess the corrosion of Spent Fuel (SF), considered as homogeneous UO2(am,hyd) doped with Pd. The model couples: i) generation of water radiolysis species by alpha and beta radiation considering the complete water radiolysis system with the kinetic reactions involving: H+, OH-, O2, H2O2, H2, HO2-, HO2·, O·, O-, O2-, H·, ·OH and e- ii) processes occurring in the spent fuel surface: oxidative dissolution reactions of UO2(am,hyd) and subsequent reduction of oxidized fuel, considering H2 activation by Pd, and iii) corrosion of Fe(s) in oxic and anoxic conditions. Process i) has been implemented in COMSOL and processes ii) and iii) have been implemented in PHREEQC with their kinetic constants being calibrated with different sets of experimental data published in the open literature. The model yields a UO2(am,hyd) dissolution rates similar to the values selected in safety assessments.

scholarly journals Portolankarten – Aufnahme und Abbildung

2021 ◽  
Vol 71 (3) ◽  
pp. 195-206
Author(s):  
Peter Mesenburg
Keyword(s):  
Data Base ◽  
Coastal Structures ◽  
Map Projection ◽  
Support Points ◽  
Construct Maps ◽  
Ancient Times ◽  
The Subject ◽  
Definition Of ◽  
High Degree ◽  
First Time

AbstractMaps are flat images of the earth‘s surface. The basis and prerequisite for their production is the relative spatial definition of the map content on the earth‘s surface, and this is usually done in the context of surveying recording processes. The particular accuracy of the portolan charts, which have passed on since the thirteenth century, suggests that these were also created on the basis of specific measurements, although details of their creation have not yet been clarified. Questions about the data base and especially about the projection of the maps have been the subject of scientific research for over 100 years (Kretschmer 1909; Campbell 2021). Here, for the first time, a method is presented that makes it possible to construct maps of the Mediterranean with simple aids (compasses and ruler) in such a way that they correspond to the accuracy and other properties of the portolan charts. A map projection is used for which there are no mapping equations, but at most a mapping description. As a surveying basis for the mapping, distances are used that have been determined with a high degree of probability since ancient times. Triangles are constructed from these lines and transferred directly to the plane without any reduction in the image. The result is a geometrically unambiguous field of support points of known ports. The missing coastal structures can be supplemented after the construction of the field of support points on the basis of traditional coastal descriptions (Portolani/Periploi).

Influence of the filter properties in the diffusive transport of ions through a bentonite. Sensitivity analysis

2021 ◽  
Author(s):  
Virginia Cabrera ◽  
Rubén López-Vizcaíno ◽  
Ángel Yustres ◽  
Vicente Navarro
Keyword(s):  
Sensitivity Analysis ◽  
Reactive Transport ◽  
Spent Nuclear Fuel ◽  
Transport Model ◽  
Task Force ◽  
Chemical Species ◽  
Double Porosity ◽  
Point Of View ◽  
Compacted Bentonite ◽  
Infiltration Tests

<p>The deep geological repository concept for spent nuclear fuel considers many safety elements. Among them, compacted bentonite has been selected as the primary engineering barrier between the encapsulated radioactive waste and the host rock. Thermo-hydro-mechanical behaviour of this material has been studied in detail from an experimental and numerical point of view. Furthermore, the study of chemical behaviour has become very important, both for the evaluation of the transport of species through the clay matrix and for the evaluation of their coupling to other physico-chemical phenomena.</p><p>Generally, to conduct these types of studies, infiltration tests through compacted bentonite columns are carried out using an experimental setup composed of common parts: (i) porewater and infiltration water reservoirs, (ii) pumping devices and (iii) a confined sample of bentonite. The infiltration/output solutions are injected/extracted through filters positioned in the top/bottom of the sample. The results obtained in these tests are strongly influenced by the properties of these filters. For this reason, it is very important how the chemical species and the fluid are transported in the filters to correctly interpret the experimental observations. The study presented in this work is framed in this context, in which a numerical sensitivity analysis of the transport properties and size of the filters has been conducted. For this purpose, a reactive transport model for bentonites (assuming this material as a double porosity media) formulated by the authors and fully implemented in the multiphysics platform, COMSOL, has been used to simulate a cation exchange-infiltration test in MX-80 bentonite defined in the “Chemical session” of the Task Force on Engineered Barrier Systems (EBS) organised by SKB AB. The results obtained depend on the tortuosity, porosity and thickness of the filters. These parameters have been estimated for the correct interpretation of the selected test.</p>

scholarly journals Numerical modelling in the coastal aquifer between Burlamacca Canal and Bufalina Ditch, southern Versilia (Tuscany, Italy)

2015 ◽  
Vol 4 (1) ◽  
Author(s):  
Gioia Bravini ◽  
Matia Menichini ◽  
Marco Doveri
Keyword(s):  
Flow Model ◽  
Transport Model ◽  
Numerical Models ◽  
Salt Water ◽  
Monitoring Network ◽  
Transient State ◽  
Salt Water Intrusion ◽  
Visual Modflow ◽  
Hydrogeological Model ◽  
Definition Of

Groundwater numerical models are necessary instruments for management of water resources and for their protection, both in terms of quantity and quality. In this paper we present a study on an area located along the southern coastline of Versilia (Viareggio,LU) affected by marine intrusion. The main purpose of this work was to create a mathematical flow model based on a conceptual hydrogeological model defined by a multidisciplinary approach. For the realization of the numerical model the ModFlow code and the graphic interface Visual ModFlow was used. The procedure for defining the mathematical model involves a series of steps such as horizontal and vertical discretization of the space, the definition of the initial and boundary conditions, the assignment of the hydraulic properties of the cells and, finally, the definitions of external perturbations to the system (recharge, evapotranspiration, drainage and pumping wells). Implementation, development and calibration of the numerical flow model was performed both in steady and transient state. Both models were calibrated using the manual “trial and error adjustment” method using heads measurements. Moreover the model results gathered in transient state simulation were compared with the data continuously recorded by a piezometer of the monitoring network of the Regional Hydrological Service. There is a good correlation between the measured data and those calculated by the model which then turns out to be sufficiently representative and provides a solid basis for the development of a transport model that could be useful to control and manage the phenomenon of the salt water intrusion.

Genetic Diversity of Basil (Ocimum spp. - Lamiaceae) Based on RAPD Markers and Volatile Oil Constituents

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 492f-493
Author(s):  
Roberto F. Vieira ◽  
James E. Simon ◽  
Peter Goldsbrough ◽  
Antonio Figueira
Keyword(s):  
Genetic Diversity ◽  
Molecular Markers ◽  
Rapd Markers ◽  
Volatile Oil ◽  
Essential Oil Composition ◽  
Oil Composition ◽  
Traditional Medicines ◽  
The Tropics ◽  
High Degree ◽  
First Time

Essential oils extracted from basil (Ocimum spp.) by steam distillation are used to flavor foods, oral products, in fragrances, and in traditional medicines. The genus Ocimum contains around 30 species native to the tropics and subtropics, with some species naturalized and/or cultivated in temperate areas. Interand intraspecific hybridization have created significant confusion in the botanical systematics of this genus. Taxonomy of basil (O. basilicum) is also complicated by the existence of numerous varieties, cultivars, and chemotypes within the species that do not differ significantly in morphology. In this study we are using RAPD markers and volatile oil composition to characterize the genetic diversity among the most economically important Ocimum species. We hypothesize that the genetic similarity revealed by molecular markers will more accurately reflect the morphological and chemical differences in Ocimum than essential oil composition per se. Preliminary research using five Ocimum species, four undetermined species, and eight varieties of O. basilicum (a total of 19 accessions) generated 107 polymorphic fragments amplified with 19 primers. RAPDs are able to discriminate between Ocimum species, but show a high degree of similarity between O. basilicum varieties. The genetic distance between nine species and among 55 accessions within the species O. americanum, O. basilicum, O. campechianum, O. × citriodorum, O. gratissimum, O. kilimandscharium, O. minimum, O. selloi, and O. tenuiflorum will be analyzed by matrix of similarity and compared to the volatile oil profile. This research will for the first time apply molecular markers to characterize the genetic diversity of Ocimum associate with volatile oil constituent.

scholarly journals Can one use Earth’s magnetic axial dipole field intensity to predict reversals?

2020 ◽  
Author(s):  
K Gwirtz ◽  
M Morzfeld ◽  
A Fournier ◽  
G Hulot
Keyword(s):  
Magnetic Field ◽  
Numerical Models ◽  
Dipole Field ◽  
Axial Dipole ◽  
Intensity Threshold ◽  
Magnetic Dipole Field ◽  
Model Hierarchy ◽  
Definition Of ◽  
Virtual Axial Dipole Moment ◽  
Prediction Strategy

Summary We study predictions of reversals of Earth’s axial magnetic dipole field that are based solely on the dipole’s intensity. The prediction strategy is, roughly, that once the dipole intensity drops below a threshold, then the field will continue to decrease and a reversal (or a major excursion) will occur. We first present a rigorous definition of an intensity threshold-based prediction strategy and then describe a mathematical and numerical framework to investigate its validity and robustness in view of the data being limited. We apply threshold-based predictions to a hierarchy of numerical models, ranging from simple scalar models to 3D geodynamos. We find that the skill of threshold-based predictions varies across the model hierarchy. The differences in skill can be explained by differences in how reversals occur: if the field decreases towards a reversal slowly (in a sense made precise in this paper), the skill is high, and if the field decreases quickly, the skill is low. Such a property could be used as an additional criterion to identify which models qualify as Earth-like. Applying threshold-based predictions to Virtual Axial Dipole Moment (VADM) paleomagnetic reconstructions (PADM2M and Sint-2000) covering the last two million years, reveals a moderate skill of threshold-based predictions for Earth’s dynamo. Besides all of their limitations, threshold-based predictions suggests that no reversal is to be expected within the next 10 kyr. Most importantly, however, we show that considering an intensity threshold for identifying upcoming reversals is intrinsically limited by the dynamic behavior of Earth’s magnetic field.

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