Predicting Water Quality Distribution of Lakes through Linking Remote Sensing–Based Monitoring and Machine Learning Simulation

The present study links monitoring and simulation models to predict water quality distribution in lakes using an optimized neural network and remote sensing data processing. Two data driven models were developed. First, a monitoring model was established that is able to convert spectral images to TDS distribution. Moreover, a simulation model was developed to generate a TDS distribution map for unseen scenarios for which no spectral images are available. Outputs of the monitoring model were applied as the observations for training the simulation model. The Nash–Sutcliffe model efficiency coefficient (NSE) was utilized in the system performance measurement of the models. Based on the results in the case study, the monitoring model was sufficiently robust to convert the operational land imager spectral bands of Landsat 8 to the TDS distribution map. The NSE was more than 0.6 for the monitoring model, which confirms the predictive skills of the model. Furthermore, the simulation model was highly reliable in generating the TDS distribution map of the lakes. Three tests were carried out to demonstrate the reliability of the model. When comparing the results of the monitoring model and simulation model, an NSE of more than 0.6 was found for all the tests. It is recommendable to apply the proposed method instead of conventional hydrodynamic models that might be highly time consuming for simulating water quality parameters distribution in lakes. Low computational complexity is the main advantage of the proposed method

Multiscale modelling of the primary breakup of liquid jets

The primary breakup of liquid jets is a major step in many technical and industrial processes, from fuel injection to spray cooling, from ink-jet printing to surface treatment and from spray drying to medical sprays. However, due to the small length scales involved, which determine the size of entrained droplet, a fully resolved numerical simulation of industrial applications is still unfeasible. In this work a numerical model for the coarse-grid simulation of turbulent liquid jet disintegration and primary atomization is developed based on an Eulerian-Lagrangian coupling. To picture the unresolved droplet formation near the liquid jet interface in the case of coarse grids we considered a theoretical model to describe the unresolved flow instabilities leading to turbulent breakup. The generated droplets are then represented by an Eulerian-Lagrangian hybrid concept. On the one hand, we used a volume of fluid method (VOF) to characterize the global spreading and the initiation of droplet formation; one the other hand, Lagrangian droplets are released at the liquid-gas interface according to the theoretical sub-grid model balancing consolidating and disruptive energies. The dynamics of the generated droplets are modelled using Lagrangian particle tracking (LPT). A numerical coupling between the Eulerian and Lagrangian frameworks is then established via source terms in conservation equations. The presented methodology was tested through sets of validation studies using different test cases and empirical correlations from the literature. As a more sophisticated validation study, the results of an in-house phase-Doppler anemometry (PDA) experiment were used to test the simulation results of three liquid jets at high Reynolds numbers. The droplet properties, such as size distribution, Sauter mean diameter (SMD) and velocity distributions obtained from the simulations are compared with experiment at various streamwise locations with very good agreement. Finally, the proposed multiscale Eulerian-Lagrangian methodology is further adopted to be used for numerical simulations of the general flow behaviour, jet breakup and surface porosity formation in high pressure die casting process.Der Zerfall von flüssigen Freistrahlen ist von großer Wichtigkeit in vielen technischen und industriellen Prozessen. Diese Prozesse reichen von Dieseleinspritzung, über Sprühkühlung, Sprühtrocknen und Tintenstrahldruckern bis zum Hochdruckformfüllen von Aluminium. Da der Strahlzerfall auf sehr kleinen Längenskalen, die die Größe der sich vom Strahl lösenden Tröpfchen bestimmen, stattfindet, ist eine hoch aufgelöste numerische Simulation von industriellen Anwendungen mit heutigen Rechenkapazitäten nicht möglich. In dieser Arbeit wurde ein numerisches Modell entwickelt, dass die "grobe" Simulation des turbulenten Strahlzerfalls durch Zerwellen und Zerstäuben ermöglicht. Dies wurde durch die Kopplung eines Lagrangen Tröpfchenmodells mit einem Eulerschen Kontinuumsmodells erreicht. Um nun die kleinskalige Ablösung von Tröpfchen vom Freistrahl unter der Verwendung von groben Rechengittern zu beschreiben, wurde ein theoretisches Modell entwickelt, dass die Instabilität der Strahloberfläche beschreibt. Während der Freistrahl mit Hilfe der Volume of Fluid (VOF) Methode (Eulersche Beschreibung) modelliert wurde, wurden die Trajektorien der sich vom Strahl lösenden Tröpfchen mittels eines Lagrangen Verfahrens bestimmt. Der Massenverlust des Freistrahl durch die Tröpfchen wurde mittels Quelltermen realisiert. Die in dieser Arbeit entwickelte Methode wurde einerseits unter Verwendung von experimentellen Daten aus der Literatur und empirischen Korrelationen validiert. Anderseits wurden in-house Experimente, die mit Hilfe eines Phasen-Doppler Anemometers (PDA) die Tröpfchengrößenverteilung und Tröpfchengeschwindigkeiten bereitstellten, zur Validierung herangezogen. Die numerischen Ergebnisse zeigen hier sehr gute Übereinstimmung mit der experimentellen Daten, obwohl der Strahlzerfall selbst nicht durch das Rechengitter aufgelöst wird. Abschließend wurde das hier vorgestellte Modell auf das Hochdruckformfüllen von flüssigem Aluminium angewendet. Die numerischen Ergebnisse geben hier Aufschluss über den Strahlzerfall während des Gießprozesses und dessen Einfluss auf die Oberflächenporosität des finalen Produktes.eingereicht von Mahdi Saeedipour MSc.Zusammenfassung in deutscher SpracheUniversität Linz, Dissertation, 2017OeBB(VLID)193199

Large eddy simulation of turbulent interfacial flows using Approximate Deconvolution Model

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LES‐VOF simulation of turbulent interfacial flow in the continuous casting mold

Slag entrainment during continuous casting process is a multiscale problem strongly dependent on the molten metal flow in the mold. Large-scale flow structures in the mold interact with the slag layer at the top of the meniscus, and small-scale liquid structures in the form of slag droplets may be entrained into the solidifying metal. In this work a large eddy simulation - volume of fluid (LES-VOF) approach is applied to investigate the unsteady flow interaction with the metal-slag-air interface including the interface instability, deformation of the slag layer and its entrainment into the molten metal. A benchmark experiment was designed to investigate the flow field in the proximity of a liquid-liquid interface for validation purposes. The experiment uses water and paraffinum liquidum to model the combination of liquid steel and the slag layer. While the entrainment of oil droplets can be visualized via shadowgraphy the flow field was measured via particle image velocimetry PIV. In combination, these two methods allow a qualitative and quantitative comparison of the unsteady flow characteristics with the CFD results. The measurement data at different inflow conditions have been used to validate the simulation results. We compare the global flow characteristics and mean velocity of submerged entry nozzle jet upon injection to the mold. Furthermore, the statistics of turbulence including velocity fluctuations and turbulent kinetic energy are used to investigate the unsteady jet interaction with the slag layer as well as liquid-liquid interface dynamics. The comparison of CFD results and experimental data reveals fairly good agreement both quantitatively and qualitatively

Sensitivity of approximate deconvolution model parameters in a posteriori LES of interfacial turbulence

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Towards a general stuctural subgrid modeling approach for turbulent multiphase flows

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Progress in Applied CFD. Selected papers from 10th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries

Slag entrainment during continuous casting process is a multiscale problem strongly dependent on the molten metal flow in the mold. Large-scale flow structures in the mold interact with the slag layer at the top of the meniscus, and small-scale liquid structures in the form of slag droplets may be entrained into the solidifying metal. In this work a large eddy simulation - volume of fluid (LES-VOF) approach is applied to investigate the unsteady flow interaction with the metal-slag-air interface including the interface instability, deformation of the slag layer and its entrainment into the molten metal. A benchmark experiment was designed to investigate the flow field in the proximity of a liquid-liquid interface for validation purposes. The experiment uses water and paraffinum liquidum to model the combination of liquid steel and the slag layer. While the entrainment of oil droplets can be visualized via shadowgraphy the flow field was measured via particle image velocimetry PIV. In combination, these two methods allow a qualitative and quantitative comparison of the unsteady flow characteristics with the CFD results. The measurement data at different inflow conditions have been used to validate the simulation results. We compare the global flow characteristics and mean velocity of submerged entry nozzle jet upon injection to the mold. Furthermore, the statistics of turbulence including velocity fluctuations and turbulent kinetic energy are used to investigate the unsteady jet interaction with the slag layer as well as liquid-liquid interface dynamics. The comparison of CFD results and experimental data reveals fairly good agreement both quantitatively and qualitatively.publishedVersio

Toward a fully resolved volume of fluid simulation of the phase inversion problem

International audienceAbstract This paper presents an enstrophy-resolved simulation of the phase inversion problem using the volume of fluid (VOF) method. This well-known benchmark for modeling multiphase flows features a buoyancy-driven unsteady motion of a light fluid into a heavy one followed by several large- and small-scale interfacial processes such as deformation, ligament formation, interface breakup, and coalescence. A fully resolved description of such flow is advantageous for a priori and a posteriori evaluations when developing new subgrid-scale closure models for large eddy simulation of two-phase flows. However, most of the previous attempts in performing the direct numerical simulation of this problem have been unsuccessful to reach grid-independent high-order flow statistics such as enstrophy. The key contribution of this paper lies in proposing a new converging configuration for this problem by reducing the Reynolds and Weber numbers. The new setup reaches grid convergence for all the flow characteristics on a $$512^3$$ 512 3 grid. Particularly, the enstrophy which has always revealed a grid-dependent behavior in all the previous studies converges for the proposed setup. Also, we analyze the temporal evolution of interfacial structures including the statistics of the total interfacial area during the process on different grid resolutions. First, no convergence on the interfacial area is observed and the possible reasons for lack of convergence are discussed. The potential remedies are investigated through a comprehensive parameter study. The findings highlight that (i) the enstrophy always converges for these moderate Re and We numbers, and (ii) the convergence of the total interfacial area is sensitive to the choice of initial and wall boundary conditions. Then, a new setup based on this sensitivity analysis is proposed that succeeded in full convergence for enstrophy and a partial convergence for the total interfacial area. The numerical simulations were carried out using the VOF solvers of OpenFOAM with a comparison between the algebraic and geometric schemes. Besides, the convergence of size distribution of dispersed structures is investigated. The present study provides insight into the possible directions toward a DNS of phase inversion problem with all the flow and interfacial structures resolved, which is essential for the future development of multiphase flow models

Drug dosage for microneedle-based transdermal drug delivery systems utilizing evaporation-induced droplet transport

We present a setup for directed loading of standard microneedle arrays for transdermal drug delivery with the respective therapeutic agent. The necessity to dose medical drugs according to their particular utilization requires an exact volumetric measure of the particular drug, which is usually provided as a liquid. This is achieved by arranging a metallic plate above the array featuring a set of holes aligned with the microneedles underneath. The plate is coated with a superhydrophobic layer. To initiate the filling, droplets are deposited on said holes, where the volume needs to be above the desired load for an individual needle, but the exact dosage is not required. Evaporation of these sessile droplets, after some time, leads to the falling of the droplets through the microfluidic plate, delivering an exact amount of liquid drug to the needles underneath. The proposed setup is easy to implement and parallelize, assisting in the task of accurate and high throughput coating of microneedle-based transdermal drug delivery devices.(VLID)435213