Three-dimensional finite element modelling of stack pollutant emissions

In this paper we propose a finite element method approach formodelling the air quality in a local scale over complex terrain. The area of interest is up to tens of kilometres and it includes pollutant sources. The proposed methodology involves the generation of an adaptive tetrahedral mesh, the computation of an ambient wind field, the inclusion of the plume rise effect in the wind field, and the simulation of transport and reaction of pollutants. The methodology is used to simulate a fictitious pollution episode in La Palma island (Canary Island, Spain).Peer ReviewedPostprint (published version

Simulating large emitters using CMAQ and a local scale finite element model: analysis of the surroundings of Barcelona

In this work, we present a novel approach to simulate large emitters in the microscale. The main idea is to combine a nested grid approach and a finite element model to simulate the subgrid scale. The nested grid system consists of the mesoscale meteorological model WRF-ARW, the Air Emission Model of Meteosim (AEMM), and the air quality model CMAQ. The subgrid scale is simulated using an adaptive, Eulerian, non-steady finite element model. The results from the nested grid simulation are used as initial and boundary conditions in the subgrid model, making this approach one-way. A simulation has been carried out in the surroundings of Barcelona, where an important contributor to the sulphur dioxide levels is considered. The simulations were carried out for one episode with high levels of sulphur dioxide. The time period of the simulation was 48 hours with a 24-hour spin-up.Peer ReviewedPostprint (author's final draft

Simulating large emitters using CMAQ and a local scale finite element model: analysis in the surroundings of Barcelona

In this work, we compare two state of the art models to simulate large emitters in the local scale. The area of study is in the surroundings of Barcelona, where an important contributor to the SO2 levels is considered. The first modelling system uses the mesoscale meteorological model WRF-ARW, the Air Emission Model of Meteosim, AEMM, and the air quality model CMAQ. The second model is a one way nesting of the results from the first system in a subgrid Finite Element model; the results from the CMAQ simulation are used as initial and boundary conditions. The simulations have been carried out for one episode with high levels of SO2. The time period of the simulations is of 48h with a 24h spin-up.Postprint (published version

Air pollution modelling using a graphics processing unit with CUDA

The Graphics Processing Unit (GPU) is a powerful tool for parallel computing. In the past years the performance and capabilities of GPUs have increased, and the Compute Unified Device Architecture (CUDA) - a parallel computing architecture - has been developed by NVIDIA to utilize this performance in general purpose computations. Here we show for the first time a possible application of GPU for environmental studies serving as a basement for decision making strategies. A stochastic Lagrangian particle model has been developed on CUDA to estimate the transport and the transformation of the radionuclides from a single point source during an accidental release. Our results show that parallel implementation achieves typical acceleration values in the order of 80-120 times compared to CPU using a single-threaded implementation on a 2.33 GHz desktop computer. Only very small differences have been found between the results obtained from GPU and CPU simulations, which are comparable with the effect of stochastic transport phenomena in atmosphere. The relatively high speedup with no additional costs to maintain this parallel architecture could result in a wide usage of GPU for diversified environmental applications in the near future.Comment: 5 figure

Development and evaluation of models for assessing geochemical pollution sources with multiple reactive chemical species for sustainable use of aquifer systems: source characterization and monitoring network design

Michael designed a groundwater flow and reactive transport optimization model. He applied this model to characterize contaminant sources in Australia's first large scale uranium mine site in the Northern Territory. He identified the contamination sources to the groundwater system in the area. His findings will assist planning actions and steps needed to implement the mitigation strategy of this contaminated aquifer

Local scale air quality model system for diagnostic and forecasting simulations using the finite element method

Air pollution is an important topic with a great social impact; it is related with public health, environment and ecology, and climate change. Scientists have developed several models in the last thirty years, and regional air quality operational systems are used routinely by governments and agencies. Efforts have also been done to simulate the air quality in the local scale; main models are Gaussian and Puff models, that are based on a Lagrangian approach. In contrast with these models, in this thesis we have developed a system using an Eulerian approach. This model is specifically designed for regions with complex orography where the Lagrangian models have problems computing the trajectory of the particles. This model can be used for diagnostic or prediction simulations. Air quality operational systems depend on the orography, meteorological data, and emission data. Air quality models use processors to incorporate these data into the model. The data can come from numerical weather prediction systems, experimental data, or databases. In this thesis we have developed processors, specifically designed for the local scale, to incorporate these data into our system. To incorporate the orography, we have developed a mesh generation algorithm suitable for complex terrain discretization; it also allows to insert layers that can match the regional models. A wind field model has also been used; it can interpolate a three-dimensional wind field from some station measurements using a log-linear vertical wind profile, or can interpolate it from a numerical weather prediction system. Once an interpolated wind field is computed, a mass-consistent model is applied to ensure null divergence and impermeability in the terrain. The wind field is modified to take into account the injection of the pollutants into the atmosphere. Briggs studied the trajectory of the plume rise giving some empirical equations that will be used in our model. Briggs' equations describe the trajectory in a plane; our model will modify this trajectory adapting it to the ambient wind field. This modification allows the plume rise to surround the mountains or channel into the valleys. The transport and reaction of pollutants in the atmosphere is then computed using an splitting method, so the transport and the chemical reactions are computed independently. To solve the transport of pollutants we have used a finite element method stabilized using least squares. The chemical reaction is simulated using simplified models such as RIVAD, or more complex ones such as CB05. To obtain more accurate results we have used adaptation. An error indicator has been used to adapt the mesh to the solution. To adapt the mesh to the concentration distribution of all the species is very demanding, for this reason we have used a multimesh method where every chemical specie has its own mesh where we solve the transport and the chemical reactions are simulated in a common mesh. The system developed in this thesis has diagnostic and forecasting capabilities. For this reason we present two different applications. The first one is a diagnostic application in La Palma island (Spain), where wind measurements are given, and SO2 and NO2 emissions from a stack are considered. The topography of the island is real, from a digital elevation model, but the wind field measurements, and the stack location and emissions, are simulated. The second application is a forecasting application data from the CMAQ benchmark test. It is located in the surrounding of Pineville Kentucky. In this application we have used all the data from CMAQ and the chemical reaction model CB05.La contaminació atmosfèrica té gran impacte social; està relacionada ambla salut pública, l'ecologia, el medi ambient i el canvi climàtic. En els últims trenta anys, els científics han desenvolupat diversos models que els governs i les agències mediambientals utilitzen diàriament. També s'han fet esforços per simular la qualitat de l'aire en l'escala local. Els models principals són els models Gaussians i Puff, que es basen en una descripció Lagrangiana. En contrast amb aquests models, en aquesta tesi s'ha desenvolupat un sistema que utilitza una descripció Euleriana. Aquest model està dissenyat específicament per a les regions amb topografia complexa on els models Lagrangians tenen problemes calculant la trajectòria de les partícules. El model presentat en aquesta tesi pot ser utilitzat tant pel diagnòstic com per la predicció. Els sistemes operatius utilitzats actualment depenen de l'orografia, de dades meteorològiques i de dades d'emissió. Per tal d'incorporar aquestes dades, els models de qualitat de l'aire han desenvolupat diferents preprocessadors. Les dades poden venir dels sistemes numèrics de predicció meteorològics, de dades experimentals o de bases de dades. En aquesta tesi hem desenvolupat preprocessadors dissenyats específicament per a l'àmbit local, per tal d'incorporar aquestes dades al nostre sistema. Per incorporar l'orografia, hem desenvolupat un algoritme de generació de malles adequat per terreny complex; l'algoritme també ens permet inserir capes que poden coincidir amb la dels models regionals. S'ha desenvolupat un model de càlcul de camp de vent; a partir de les dades s'interpola un camp de vent tridimensional fent servir un perfil log-lineal vertical del vent, o s'interpola a partir dels resultats d'un sistema de predicció meteorològica. Quan s'ha calculat el vent interpolat, es fa servir un model de massa consistent per obtenir un camp de vent definitiu on s'ha imposat divergència zero i impermeabilitat del terreny. El camp de vent s'ha de modificar per tenir en compte la injecció dels contaminants a l'atmosfera. Briggs va estudiar la trajectòria de l'elevació de la ploma i va trobar equacions empíriques que utilitzarem en el nostre model. Les equacions de Briggs descriuen la trajectòria de la ploma en un pla vertical; el nostre model modificarà aquesta trajectòria adaptant-la al camp de vent ambiental. Aquesta modificació permet que l'elevació de la ploma rodegi les muntanyes o s'acanali a les valls. El transport i la reacció de contaminants a l'atmosfera es calcula utilitzant un mètode de "splitting", de manera que el transport i la reacció química es calculen de forma independent. Per resoldre el transport de contaminants, hem utilitzat el mètode d'elements finits estabilitzat amb mínims quadrats. La reacció química es simula mitjançant models simplificats com el model RIVAD, o més complexes com el CB05. Per obtenir resultats més precisos hem adaptat la malla a la solució utilitzant un indicador d'error. Haver d'adaptar la malla a la distribució de la concentració de totes les espècies contaminants és molt exigent i per aquest motiu hem utilitzat un mètode "multimesh" on cada espècie química té la seva pròpia malla on resolem el transport i les reaccions químiques es simulen en una malla comú. El sistema desenvolupat en aquesta tesi té capacitats de diagnòstic i pronòstic. Per aquesta raó es presenten dues aplicacions diferents. La primera és una aplicació de diagnòstic a l'illa de la Palma (Espanya), on es disposa de mesures de vent, i de les emissions de SO2 i NO2 d'una xemeneia. La topografia de l'illa és real, a partir d'un model digital del terreny, però les dades del camp de vent, la ubicació de la xemeneia i el valor de les emissions són simulades. La segona aplicació és una aplicació de predicció fent servir els resultats del benchmark del CMAQ. Es simula una zona a Pineville Kentucky. En aquesta aplicació hem utilitzat totes les dades del CMAQ i el model químic CB05

A multi-mesh adaptive scheme for air quality modeling with the finite element method

A multi-mesh adaptive scheme for convection-diffusion-reaction problems is presented. The proposal is applied to air quality modeling, especifically to the simulation of a pollutant punctual emissions. The performance of the proposal is analyzed with different nonlinear reaction models, including the photochemical model CB05 implmented within the Comunity Multiscale Air Quality model, which involves sixty-two species and very different characteristic reaction times. The problem is solved with splitting of transport and reaction processes. This allows to discretize the species in distinct computational meshes, adapted to the distribution of the error indicator of each case. A common reference mesh is used for all species and during all problem evolution. A remeshing technique based on imposing the volume of new elements is used to define and update the computational meshes. An error indicator well suited for problems involving large variation of the unknowns is used. A single-mesh strategy, with remeshing adapted to the most demanding specie in each part of the domain, is used for comparison. The results of the examples presented show that the accuracy of single and multi-mesh strategies are similar. Instead, computational cost of multi-mesh is lower than single-mesh in most cases. Reduction increases with the number of species and the number of plumes. An example of a punctual emissor in a three-dimensional domain, with realistic values of CB05 components, is presented.Peer ReviewedPostprint (published version

Advances in Modeling of Fluid Dynamics

This book contains twelve chapters detailing significant advances and applications in fluid dynamics modeling with focus on biomedical, bioengineering, chemical, civil and environmental engineering, aeronautics, astronautics, and automotive. We hope this book can be a useful resource to scientists and engineers who are interested in fundamentals and applications of fluid dynamics