Transitional dispersive scenarios driven by mesoscale flows on complex terrain under strong dry convective conditions

By experimentation and modelling, this paper analyses the atmospheric dispersion of the SO<sub>2</sub> emissions from a power plant on complex terrain under strong convective conditions, describing the main dispersion features as an ensemble of "stationary dispersive scenarios" and reformulating some "classical" dispersive concepts to deal with the systematically monitored summer dispersive scenarios in inland Spain. The results and discussions presented arise from a statistically representative study of the physical processes associated with the multimodal distribution of pollutants aloft and around a 343-m-tall chimney under strong dry convective conditions in the Iberian Peninsula. This paper analyses the importance of the identification and physical implications of transitional periods for air quality applications. The indetermination of a transversal plume to the preferred transport direction during these transitional periods implies a small (or null) physical significance of the classical definition of horizontal standard deviation of the concentration distribution

Multi-touch 3D Exploratory Analysis of Ocean Flow Models

Modern ocean flow simulations are generating increasingly complex, multi-layer 3D ocean flow models. However, most researchers are still using traditional 2D visualizations to visualize these models one slice at a time. Properly designed 3D visualization tools can be highly effective for revealing the complex, dynamic flow patterns and structures present in these models. However, the transition from visualizing ocean flow patterns in 2D to 3D presents many challenges, including occlusion and depth ambiguity. Further complications arise from the interaction methods required to navigate, explore, and interact with these 3D datasets. We present a system that employs a combination of stereoscopic rendering, to best reveal and illustrate 3D structures and patterns, and multi-touch interaction, to allow for natural and efficient navigation and manipulation within the 3D environment. Exploratory visual analysis is facilitated through the use of a highly-interactive toolset which leverages a smart particle system. Multi-touch gestures allow users to quickly position dye emitting tools within the 3D model. Finally, we illustrate the potential applications of our system through examples of real world significance

The use of impulse response tracer experiments in horizontal subsurface flow constructed wetland development

A research proposal submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2016In the past three decades there has been an increased interest in constructed wetlands (CW) and their effectiveness in treating water. The hydraulic efficiency of a CW can be determined by using chemical reactor theory to develop residence time distribution (RTD) parameters such as effective volume (Veff), normalized variance (σ2) and mean residence time (τm). Five experiments were conducted to study the effects on these RTD parameters in a CW by using a glass pilot-scale laboratory rig and varying the inlet-outlet positions. The rig made use of a glass tank 250x250x500mm filled with clear superabsorbent polymer balls as a packing. The clear tank and balls made it possible for the flow to be observed when a FWT red impulse tracer dye was inserted into the system. The flow was photographed at specific time intervals for visual analysis and comparison. . The visual results showed the formation of a hull-shaped velocity profile in all the experiments. The RTD was obtained by collecting tracer samples at specific outlet positions during the course of each experiment. The five inlet-outlet configurations RTD parameters results showed; a straight flow path from a single inlet to outlet yielded the lease desirable hydraulic performance with dead volumes contributing to up to 67% of the CW. An increase in the number of outlets and changing the direction of flow diagonally showed up to a 96% improvement to the effective volume of the system could be achieved when compared with single inline inlet-outlet flow. The best result was achieved by combining the visual and RTD data to make changes to the rigs geometry in order to eliminate dead zones and yielded up to a 148% improvement in the effective volume of the system when compared with single inline inlet-outlet flow. A well designed CW with respect to inlet-outlet position can result in reduced land requirements and construction costs by minimizing the dead volume and improving hydraulic efficiency.MT201

Numerical methods and tangible interfaces for pollutant dispersion simulation

Dissertação apresentada para obtenção do Grau de Doutor em Engenharia do Ambiente, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaThe first main objective of this thesis is to reduce numerical errors in advection-diffusion modelling. This is accomplished by presenting DisPar methods, a class of numerical schemes for advection-diffusion or transport problems, based on a particle displacement distribution for Markov processes. The development and analyses of explicit and implicit DisPar formulations applied to one and two dimensional uniform grids are presented. The first explicit method, called DisPar-1, is based on the development of a discrete probability distribution for a particle displacement, whose numerical values are evaluated by analysing average and variance. These two statistical parameters depend on the physical conditions (velocity, dispersion coefficients and flows). The second explicit method,DisPar-k, is an extension of the previous one and it is developed for one and two dimensions. Besides average and variance, this method is also based on a specific number of particle displacement moments. These moments are obtained by the relation between the advection-diffusion and the Fokker-Planck equation, assuming a Gaussian distribution for the particle displacement distribution. The number of particle displacement moments directly affects the spatial accuracy of the method, and it is possible to achieve good results for pure-advection situations. The comparison with other methods showed that the main DisPar disadvantage is the presence of oscillations in the vicinity of step concentration profiles. However, the models that avoid those oscillations generally require complex and expensive computational techniques, and do not perform so well as DisPar in Gaussian plume transport. The application of the 2-D DisPar to the Tagus estuary demonstrates the model capacity of representing mass transport under complex flows. Finally, an implicit version of DisPar is also developed and tested in linear conditions, and similar results were obtained in terms of truncation error and particle transport methods. The second main objective of this thesis, to contribute to modelling cost reduction, is accomplished by presenting TangiTable, a tangible interface for pollutant dispersion simulation composed by a personal computer, a camera, a video projector and a table. In this system, a virtual environment is projected on the table, where the users place objects representing infrastructures that affect the water of an existent river and the air quality. The environment and the pollution dispersion along the river are then projected on the table. TangiTable usability was tested in a public exhibition and the feedback was very positive. Future uses include public participation and collaborative work applications.Fundação para a Ciência e Tecnologia - scholarship contract BD/5064/2001 and the research contract MGS/33998/99-0

A Framework To Model Complex Systems Via Distributed Simulation: A Case Study Of The Virtual Test Bed Simulation System Using the High Level Architecture

As the size, complexity, and functionality of systems we need to model and simulate con-tinue to increase, benefits such as interoperability and reusability enabled by distributed discrete-event simulation are becoming extremely important in many disciplines, not only military but also many engineering disciplines such as distributed manufacturing, supply chain management, and enterprise engineering, etc. In this dissertation we propose a distributed simulation framework for the development of modeling and the simulation of complex systems. The framework is based on the interoperability of a simulation system enabled by distributed simulation and the gateways which enable Com-mercial Off-the-Shelf (COTS) simulation packages to interconnect to the distributed simulation engine. In the case study of modeling Virtual Test Bed (VTB), the framework has been designed as a distributed simulation to facilitate the integrated execution of different simulations, (shuttle process model, Monte Carlo model, Delay and Scrub Model) each of which is addressing differ-ent mission components as well as other non-simulation applications (Weather Expert System and Virtual Range). Although these models were developed independently and at various times, the original purposes have been seamlessly integrated, and interact with each other through Run-time Infrastructure (RTI) to simulate shuttle launch related processes. This study found that with the framework the defining properties of complex systems - interaction and emergence are realized and that the software life cycle models (including the spiral model and prototyping) can be used as metaphors to manage the complexity of modeling and simulation of the system. The system of systems (a complex system is intrinsically a system of systems ) continuously evolves to accomplish its goals, during the evolution subsystems co-ordinate with one another and adapt with environmental factors such as policies, requirements, and objectives. In the case study we first demonstrate how the legacy models developed in COTS simulation languages/packages and non-simulation tools can be integrated to address a compli-cated system of systems. We then describe the techniques that can be used to display the state of remote federates in a local federate in the High Level Architecture (HLA) based distributed simulation using COTS simulation packages

Interactions Between Downslope Flows and a Developing Cold-Air Pool

Downslope flows and regions of enhanced cooling have important impacts on society and the environment. Parameterisation of these often subgrid-scale phenomena in numerical models requires a sound understanding of the underlying physical processes, which has been the overarching aim of this work. A numerical model has been used to characterise the development of a region of enhanced cooling in an idealised alpine valley with width and depth of order 10 and 1 km, respectively, under stable, decoupled, poorly-drained conditions. A focus of this work has been to remove the uncertainty surrounding the forcing mechanisms behind the development of regions of enhanced cooling. The average valley-atmosphere cooling has been found to be almost equally partitioned between radiative and dynamics effects. Complex interactions between the downslope flows and the region of enhanced cooling have been quantified for the first time. For example, relatively large variations in the downslope flows are generally restricted to the region of enhanced cooling and cannot solely be attributed to the analytical model of [McNider, 1982a]. These flow variations generally coincide with return flows above the downslope flows, where a thin region of unstable air occurs, as well as coinciding with elongated downslope flow structures. The impact of these interactions on the dispersion of passive pollutants has been investigated. For example, pollutants are generally trapped within the region of enhanced cooling. The concentration of pollutants within the region of enhanced cooling, emitted over the lower half of the slopes, increase as the emission source moves away from the ground-based inversion that expands from the bottom of the valley. The concentration of pollutants within the region of enhanced cooling is very similar when varying the location of the emission source over the top half of the valley slopes. This work includes a test of the effects of varying the horizontal numerical grid resolution on average valley-atmosphere temperature changes

Modeling contaminant transport and fate and subsequent impacts on ecosystems

Assessing risks associated with the release of metals into the environment and managing remedial activities requires simulation tools that depict speciation and risk with accurate mechanistic models and well-defined transport parameters. Such tools need to address the following processes: (1) aqueous speciation, (2) distribution mechanisms, (3) transport, and (4) ecological risk. The primary objective of this research is to develop a simulation tool that accounts for these processes. Speciation in the aqueous phase can be assessed with geochemical equilibrium models, such as MINEQL+. Furthermore, metal distribution can be addressed mechanistically. Studies with Pb sorption to amorphous aluminum (HAG), iron (HFO), and manganese (HMO) oxides, as well as oxide coatings, demonstrated that intraparticle diffusion is the rate-limiting mechanism in the sorption process, where best-fit surface diffusivities ranged from 10-18 to 10-15 cm2 s-1 Intraparticle surface diffusion was incorporated into the Groundwater Modeling System (GMS) to accurately simulate metal contaminant mobility where oxides are present. In the model development, the parabolic concentration layer approximation and the operator split technique were used to solve the microscopic diffusion equation coupled with macroscopic advection and dispersion. The resulting model was employed for simulating Sr90 mobility at the U.S. Department of Energy (DOE) Hanford Site. The Sr90 plume is observed to be migrating out of the 100-N area extending into other areas of the Hanford Site and beyond. Once bioavailability is understood, static or dynamic ecological risk assessments can be conducted. Employing the ERA model, a static ecological risk assessment for exposure to depleted uranium (DU) at Aberdeen and Yuma Proving Grounds (APG and YPG) revealed that a reduction in plant root weight is considered likely to occur. For most terrestrial animals at YPG, the predicted DU dose is less than that which would result in a decrease in offspring. However, for the lesser long-nosed bat, reproductive effects are expected to occur through the reduction in size and weight of offspring. At APG, based on very limited data, it is predicted that uranium uptake will not likely affect survival of terrestrial animals and aquatic species. In model validation, sampling of pocket mice, kangaroo rat, white-throated woodrat, deer, and milfoil showed that body burden concentrations fall into the distributions simulated at both sites. This static risk assessment provides a solid background for applying the dynamic approach. Overall, this research contributes to a holistic approach in developing accurate mechanistic models for simulating metal contaminant mobility and bioavailability in subsurface environments

A KDE-based random walk method for modeling reactive transport with complex kinetics in porous media

This is the peer reviewed version of the following article: Sole-Mari, G., Fernàndez-Garcia, D., Rodríguez-Escales, P., & Sanchez-Vila, X. (2017). A KDE-based random walk method for modeling reactive transport with complex kinetics in porous media. Water Resources Research, 53, 9019–9039, which has been published in final form at https://doi.org/10.1002/2017WR021064. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.In recent years, a large body of the literature has been devoted to study reactive transport of solutes in porous media based on pure Lagrangian formulations. Such approaches have also been extended to accommodate second-order bimolecular reactions, in which the reaction rate is proportional to the concentrations of the reactants. Rather, in some cases, chemical reactions involving two reactants follow more complicated rate laws. Some examples are (1) reaction rate laws written in terms of powers of concentrations, (2) redox reactions incorporating a limiting term (e.g., Michaelis-Menten), or (3) any reaction where the activity coefficients vary with the concentration of the reactants, just to name a few. We provide a methodology to account for complex kinetic bimolecular reactions in a fully Lagrangian framework where each particle represents a fraction of the total mass of a specific solute. The method, built as an extension to the second-order case, is based on the concept of optimal Kernel Density Estimator, which allows the concentrations to be written in terms of particle locations, hence transferring the concept of reaction rate to that of particle location distribution. By doing so, we can update the probability of particles reacting without the need to fully reconstruct the concentration maps. The performance and convergence of the method is tested for several illustrative examples that simulate the Advection-Dispersion-Reaction Equation in a 1-D homogeneous column. Finally, a 2-D application example is presented evaluating the need of fully describing non-bilinear chemical kinetics in a randomly heterogeneous porous medium.Peer ReviewedPostprint (published version

A KDE-based random walk method for modeling reactive transport with complex kinetics in porous media

In recent years, a large body of the literature has been devoted to study reactive transport of solutes in porous media based on pure Lagrangian formulations. Such approaches have also been extended to accommodate second‐order bimolecular reactions, in which the reaction rate is proportional to the concentrations of the reactants. Rather, in some cases, chemical reactions involving two reactants follow more complicated rate laws. Some examples are (1) reaction rate laws written in terms of powers of concentrations, (2) redox reactions incorporating a limiting term (e.g., Michaelis‐Menten), or (3) any reaction where the activity coefficients vary with the concentration of the reactants, just to name a few. We provide a methodology to account for complex kinetic bimolecular reactions in a fully Lagrangian framework where each particle represents a fraction of the total mass of a specific solute. The method, built as an extension to the second‐order case, is based on the concept of optimal Kernel Density Estimator, which allows the concentrations to be written in terms of particle locations, hence transferring the concept of reaction rate to that of particle location distribution. By doing so, we can update the probability of particles reacting without the need to fully reconstruct the concentration maps. The performance and convergence of the method is tested for several illustrative examples that simulate the Advection‐Dispersion‐Reaction Equation in a 1‐D homogeneous column. Finally, a 2‐D application example is presented evaluating the need of fully describing non‐bilinear chemical kinetics in a randomly heterogeneous porous medium