353 research outputs found

    Numerical simulation of Newtonian/non-Newtonian multiphase flows : deformation and collision of droplets

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    The complex nature of multiphase flows, particularly in the presence of non-Newtonian rheologies in the phases, limits the applicability of theoretical analysis of physical equations as well as setting up laboratory experiments. As a result, Computational Fluid Dynamics (CFD) techniques are essential tools to study these problems. Despite the advances in numerical simulation techniques in this field in the past decade, the applicability of these approaches are limited by challenges appearing in specific applications, and particular consideration must be taken into account for each of these problems. The present thesis aims at three-dimensional numerical solution of Newtonian/non-Newtonian multiphase flow problems in the context of finite-volume discretization approach with applications in different natural and industrial processes. This thesis is organized in five chapters. The first chapter aims at providing an introduction to the motivation behind this work. We also present some application of the context of this thesis in industrial processes, followed by a small introductory on the CTTC research group, objectives and the outline of the thesis. The core of this thesis lays within chapters two, three and four. In chapter 2, using a conservative level-set method, three-dimensional direct numerical simulation of binary droplets collision is performed. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This approach demonstrates to be numerically efficient and accurate compared with experimental data, with a significant save-up on computational costs in three-dimensional cases. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes where very good agreement is seen. Besides, for all the cases studied in this chapter, a detailed study of the energy budgets are provided. In chapter 3, the physics of a single droplet subjected to shear flow is studied in details, with a primary focus on the effect of viscosity on walls critical confinement ratio. First, we highly validate the ability of the numerical tools on capturing the correct physics of droplet deformation. This chapter continues by three-dimensional DNS study of subcritical (steady-state) and supercritical (breakup) deformations of the droplet for a wide range of walls confinement in different viscosity ratios. The results indicate the existence of two steady-state regions in a viscosity ratio-walls confinement ratio graph, which are separated by a breakup region. Overall, these achievements indicate a promising potential of the current approach for simulating droplet deformation and breakup, in applications of dispersion science and mixing processes. In chapter 4, with the help of experience gained in the previous chapters, a finite-volume based conservative level-set method is used to numerically solve the non-Newtonian multiphase flow problems. One set of governing equations is written for the whole domain where different rheological properties may appear. Main challenging areas of numerical simulation of multiphase non-Newtonian fluids, including tracking of the interface, mass conservation of the phases, small timestep problems encountered by non-Newtonian fluids, numerical instabilities regarding the high Weissenberg Number Problem (HWNP), instabilities encouraged by low solvent to polymer viscosity ratio in viscoelastic fluids and instabilities encountered by surface tensions are discussed and proper numerical treatments are provided in the proposed method. The numerical method is validated for different types of non-Newtonian fluids, e.g. shear-thinning, shear-thickening and viscoelastic fluids using structured and unstructured meshes, where the extracted results are compared against analytical, numerical and experimental data available in the literature.La naturaleza compleja de los flujos multifásicos, particularmente en presencia de reologías no newtonianas, limita la aplicabilidad del análisis teórico de ecuaciones físicas y también de los experimentos de laboratorio. Por lo tanto, las técnicas de dinámica de fluidos computacional (CFD) son esenciales para estudiar estos problemas. A pesar de los avances en las técnicas de simulación numérica en esta área durante la última década, la aplicabilidad de estos enfoques está limitada por los desafíos que aparecen en las aplicaciones específicas, y se debe considerar de forma particular cada uno de estos problemas. La presente tesis tiene como objetivo la solución numérica tridimensional de los problemas de flujo multifase newtoniano / no newtoniano en el contexto del enfoque de discretización de volúmenes finitos con aplicaciones en diferentes procesos naturales e industriales. Esta tesis está organizada en cinco capítulos. El primer capítulo proporciona una introducción y la motivación de este trabajo. También presentamos alguna aplicación de esta tesis en procesos industriales, seguida de una corta introducción al grupo de investigación del CTTC, los objetivos y el resumen de la tesis. En el capítulo 2, utilizando un método CLS, se realiza una simulación numérica directa (DNS) tridimensional de colisión de gotitas binarias. Se introduce un nuevo enfoque de estabilización de lamella para resolver numéricamente la capa delgada de fluido ("lamella") que aparece durante muchos regímenes de colisión. Este enfoque demuestra ser numéricamente eficiente y preciso en comparación con los datos experimentales, con una importante reducción de costos computacionales en casos tridimensionales. Las herramientas numéricas introducidas se validan y verifican con diferentes resultados experimentales para diferentes casos de colisión en los que se observa un muy buen acuerdo. Además, para todos los casos estudiados en este capítulo, se proporciona un estudio detallado de los balances de energía. En el capítulo 3, se estudia en detalle la física de una sola gota sometida a flujo de cizallamiento, con un enfoque principal en el efecto de la viscosidad en el confinamiento crítico de las paredes. Primero, validamos la capacidad de las herramientas numéricas para capturar la física correcta de la deformación de las gotitas. Este capítulo continúa con el estudio tridimensional DNS de las deformaciones subcríticas (estado estable) y supercríticas (ruptura) de la gota para un amplio rango de confinamiento de paredes en diferentes relaciones de viscosidad. Los resultados indican la existencia de dos regiones de estado estable en un gráfico de una relación de confinamiento de las paredes y la viscosidad, que están separados por una región de ruptura. En general, estos logros indican un potencial importante del enfoque actual para simular la deformación y ruptura de las gotitas, en aplicaciones de la ciencia de la dispersión y los procesos de mezcla. En el capítulo 4, con la ayuda de la experiencia adquirida en los capítulos anteriores, se utiliza un método CLS de volumen finito para resolver numéricamente los problemas de flujo multifase no newtonianos. Las principales áreas desafiantes de la simulación numérica de fluidos multifásicos no newtonianos incluso el seguimiento de la interfaz, la conservación de masa de las fases, los problemas de pequeños paso de tiempo encontrados por los fluidos no newtonianos, las inestabilidades numéricas relacionadas con el problema del alto número de Weissenberg (HWNP), inestabilidades fomentadas por una baja relación de viscosidad de disolvente a polímero en fluidos viscoelásticos y las inestabilidades encontradas por las tensiones superficiales son discutidos y se proporcionan tratamientos numéricos adecuados para el método propuesto. El método numérico se valida para diferentes tipos de fluidos no newtonianos, utilizando diluyentes de cizallamiento, espesamiento de cizallamiento y fluidos viscoelásticos utilizando mallas estructuradas y no estructuradas, donde los resultados extraídos se comparan con los datos analíticos, numéricos y experimentales disponibles en la literatura.Postprint (published version

    Numerical simulation of Newtonian/non-Newtonian multiphase flows : deformation and collision of droplets

    Get PDF
    The complex nature of multiphase flows, particularly in the presence of non-Newtonian rheologies in the phases, limits the applicability of theoretical analysis of physical equations as well as setting up laboratory experiments. As a result, Computational Fluid Dynamics (CFD) techniques are essential tools to study these problems. Despite the advances in numerical simulation techniques in this field in the past decade, the applicability of these approaches are limited by challenges appearing in specific applications, and particular consideration must be taken into account for each of these problems. The present thesis aims at three-dimensional numerical solution of Newtonian/non-Newtonian multiphase flow problems in the context of finite-volume discretization approach with applications in different natural and industrial processes. This thesis is organized in five chapters. The first chapter aims at providing an introduction to the motivation behind this work. We also present some application of the context of this thesis in industrial processes, followed by a small introductory on the CTTC research group, objectives and the outline of the thesis. The core of this thesis lays within chapters two, three and four. In chapter 2, using a conservative level-set method, three-dimensional direct numerical simulation of binary droplets collision is performed. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This approach demonstrates to be numerically efficient and accurate compared with experimental data, with a significant save-up on computational costs in three-dimensional cases. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes where very good agreement is seen. Besides, for all the cases studied in this chapter, a detailed study of the energy budgets are provided. In chapter 3, the physics of a single droplet subjected to shear flow is studied in details, with a primary focus on the effect of viscosity on walls critical confinement ratio. First, we highly validate the ability of the numerical tools on capturing the correct physics of droplet deformation. This chapter continues by three-dimensional DNS study of subcritical (steady-state) and supercritical (breakup) deformations of the droplet for a wide range of walls confinement in different viscosity ratios. The results indicate the existence of two steady-state regions in a viscosity ratio-walls confinement ratio graph, which are separated by a breakup region. Overall, these achievements indicate a promising potential of the current approach for simulating droplet deformation and breakup, in applications of dispersion science and mixing processes. In chapter 4, with the help of experience gained in the previous chapters, a finite-volume based conservative level-set method is used to numerically solve the non-Newtonian multiphase flow problems. One set of governing equations is written for the whole domain where different rheological properties may appear. Main challenging areas of numerical simulation of multiphase non-Newtonian fluids, including tracking of the interface, mass conservation of the phases, small timestep problems encountered by non-Newtonian fluids, numerical instabilities regarding the high Weissenberg Number Problem (HWNP), instabilities encouraged by low solvent to polymer viscosity ratio in viscoelastic fluids and instabilities encountered by surface tensions are discussed and proper numerical treatments are provided in the proposed method. The numerical method is validated for different types of non-Newtonian fluids, e.g. shear-thinning, shear-thickening and viscoelastic fluids using structured and unstructured meshes, where the extracted results are compared against analytical, numerical and experimental data available in the literature.La naturaleza compleja de los flujos multifásicos, particularmente en presencia de reologías no newtonianas, limita la aplicabilidad del análisis teórico de ecuaciones físicas y también de los experimentos de laboratorio. Por lo tanto, las técnicas de dinámica de fluidos computacional (CFD) son esenciales para estudiar estos problemas. A pesar de los avances en las técnicas de simulación numérica en esta área durante la última década, la aplicabilidad de estos enfoques está limitada por los desafíos que aparecen en las aplicaciones específicas, y se debe considerar de forma particular cada uno de estos problemas. La presente tesis tiene como objetivo la solución numérica tridimensional de los problemas de flujo multifase newtoniano / no newtoniano en el contexto del enfoque de discretización de volúmenes finitos con aplicaciones en diferentes procesos naturales e industriales. Esta tesis está organizada en cinco capítulos. El primer capítulo proporciona una introducción y la motivación de este trabajo. También presentamos alguna aplicación de esta tesis en procesos industriales, seguida de una corta introducción al grupo de investigación del CTTC, los objetivos y el resumen de la tesis. En el capítulo 2, utilizando un método CLS, se realiza una simulación numérica directa (DNS) tridimensional de colisión de gotitas binarias. Se introduce un nuevo enfoque de estabilización de lamella para resolver numéricamente la capa delgada de fluido ("lamella") que aparece durante muchos regímenes de colisión. Este enfoque demuestra ser numéricamente eficiente y preciso en comparación con los datos experimentales, con una importante reducción de costos computacionales en casos tridimensionales. Las herramientas numéricas introducidas se validan y verifican con diferentes resultados experimentales para diferentes casos de colisión en los que se observa un muy buen acuerdo. Además, para todos los casos estudiados en este capítulo, se proporciona un estudio detallado de los balances de energía. En el capítulo 3, se estudia en detalle la física de una sola gota sometida a flujo de cizallamiento, con un enfoque principal en el efecto de la viscosidad en el confinamiento crítico de las paredes. Primero, validamos la capacidad de las herramientas numéricas para capturar la física correcta de la deformación de las gotitas. Este capítulo continúa con el estudio tridimensional DNS de las deformaciones subcríticas (estado estable) y supercríticas (ruptura) de la gota para un amplio rango de confinamiento de paredes en diferentes relaciones de viscosidad. Los resultados indican la existencia de dos regiones de estado estable en un gráfico de una relación de confinamiento de las paredes y la viscosidad, que están separados por una región de ruptura. En general, estos logros indican un potencial importante del enfoque actual para simular la deformación y ruptura de las gotitas, en aplicaciones de la ciencia de la dispersión y los procesos de mezcla. En el capítulo 4, con la ayuda de la experiencia adquirida en los capítulos anteriores, se utiliza un método CLS de volumen finito para resolver numéricamente los problemas de flujo multifase no newtonianos. Las principales áreas desafiantes de la simulación numérica de fluidos multifásicos no newtonianos incluso el seguimiento de la interfaz, la conservación de masa de las fases, los problemas de pequeños paso de tiempo encontrados por los fluidos no newtonianos, las inestabilidades numéricas relacionadas con el problema del alto número de Weissenberg (HWNP), inestabilidades fomentadas por una baja relación de viscosidad de disolvente a polímero en fluidos viscoelásticos y las inestabilidades encontradas por las tensiones superficiales son discutidos y se proporcionan tratamientos numéricos adecuados para el método propuesto. El método numérico se valida para diferentes tipos de fluidos no newtonianos, utilizando diluyentes de cizallamiento, espesamiento de cizallamiento y fluidos viscoelásticos utilizando mallas estructuradas y no estructuradas, donde los resultados extraídos se comparan con los datos analíticos, numéricos y experimentales disponibles en la literatura

    Identifying Key Factors Associated with High Risk Asthma Patients to Reduce the Cost of Health Resources Utilization

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    Asthma is associated with frequent use of primary health services and places a burden on the United States economy. Identifying key factors associated with increased cost of asthma is an essential step to improve practices of asthma management. The aim of this study was to identify factors associated with over utilization of primary health services and increased cost via claims data and to explore the effectiveness of case management program in reducing overall asthma related cost. Claims data analysis for Medicaid insured asthma patients in Louisiana was conducted. Asthma patients were identified using their ICD-9 and ICD-10 codes, forward variable selection was used to identify significant factors in the regression model with total cost as the dependent variable, multivariate regression was used to identify patients’ factors associated with frequent utilization of primary health services, and finally, a T-test was used to compare the difference in cost over time for case managed and non-case managed patients. Cost of four claims categories was significant to the total cost variable: primary physician visits, pharmacy prescriptions, emergency room visits and urgent care clinics visits. Median income and enrollment in case management were significant in predicting number of emergency room visits. Patients who had higher income were more likely to utilize urgent care clinics. As a side finding, this study built a prediction model for total cost, the linear regression model accuracy was compared to neural networks and the proposed threshold point in which neural network outperforms the regression model is around 6,000 data points. Patients with a history of utilization of certain health services are more likely to need case management for better health outcomes and controlled cost. future work is to perform analysis on a larger scale and include more patients related factors to identify a more holistic definition of high-risk patients

    Confrontation to Humiliation Complex Causing the Violence, Crime, Uncivilized, Non-Citizenship and Extremism by Positive Education and Cognitions

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    The individual is the initial unit of society. So, building positive society begins within positive characters of its individuals. The education of the individual must be from a childhood in a positive way, and learn to define goals clearly (presence of clear life goals) and know the meaning in life (Presence and Search for Meaning in Life) and the creation of a purpose in life. This develops a positive, conscious and social personality in the individual who forms society and the world.The absence of positivity, purpose in life and/or meaning in life in individual plays a role in the creation of sadism, negative-sadomasochism personality disorder, barbarism, crime, brutality and extremism among Man who seeks behind the creation of war and destruction and savoring the pains of girls, young people, women and children as Syrian War.Man is not extremist, oblique and criminal by the innate. But, family, parents and their psychological aspect, friends, schools, universities, environmental and media make this oblique and criminal Man. In addition, education of the Civilized Man in life is made to develop his Negative Thought instead of develop his Positive Thought. The result is quite catastrophic. People are most of the time unable to live intensely a happy moment so much they are inhibited from all that is positive. So, Man becomes oblique and criminal by his environment.Crime, uncivilized and extremism have an impact on local communities all over the world. Environmental and their risk factors such as economic difficulties, no activity and no job, negative emotions (disillusioned, resentment, emptiness, boredom, loneliness, or feeling lost and abandoned, no clear purpose in life and no life's meaning, etc.), absence of coping skills to withstand life stressors, psychological and cognitive development, and ability to make prudent decisions lead acceptance of violent extremist ideologies as crime, uncivilized, violence and extremism.Good citizenship, crime, uncivilized, extremism and violence extremism are the important social issues that might be affected by patterns of thinking (positive or negative) in individuals, institutions, and communities. Positive thinking is as a way for developing good citizenship behavior and confronts the crime, uncivilized, abuse and extremism.Positive thinking about oneself would lead to positive thinking about society; hence develop the link between individuals and their environmental and society by using the positive thinking. So, the RPPT (Repetitions Phrases of Positive Thoughts) can be an effective tool for promoting positive thinking and so building positive identity and positive expectation.Therefore, practicing RPPT, as an educational tool for positive thinking, reinforces positive thoughts which lead the citizenship for better future and a better community. TRPPT (Treatment of Repeating Phrases of Positive Thoughts) contributes in building personal resilience and positive sense of identity that are essential components to prevent violent extremism

    A molecular dynamics study on the effects of wall-fluid interaction strength and fluid density on thermal resistance of graphene/argon interface

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    Molecular dynamics simulations of Argon flow confined between two parallel graphene sheets are carried out to investigate the effects of some parameters on heat transfer and thermal properties. These parameters include wall-fluid interaction strength and fluid density where for constant wall temperature simulations, we show that these two parameters have influence on near-wall fluid density. As a result, the heat transfer at wall-fluid interfaces and thus through Argon molecules across the domain will change. To analyze the results, the density and temperature profiles and two other parameters including temperature gradient of the bulk of Argon molecules and the Kapitza length are considered. The Kapitza length represents the thermal resistance at liquid-solid interface. According to the results, the increase of wall-fluidinteraction strength leads to greater number of Argon molecules near the walls and consequently, the Kapitza length decreases and an enhancement is observed in temperature gradient and the slope of temperature profile. Furthermore, higher values of fluid density cause that the thermal resistance at wall-fluid interactions increases. Therefore, greater temperature jumps are observed in temperature profiles

    Numerical simulation of non-newtonian fluid-structure interaction problems

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    This thesis represents a numerical method to solve fluid-structure interaction (FSI) prob- lems where the fluid exhibits a non-Newtonian behavior. Oldroyd-B constitutive equa- tions is used to model Viscoelastic fluid and Generalized Newtonian Fluids are used to model Shear-thinning/Shear-thickening fluids. For FSI solution, a semi-implicit partitioned method is used which separates the fluid pressure term and strongly couples it to the struc- ture, while the remaining fluid terms are only weakly coupled. Numerical tests provides information regarding the physical behaviour of the fluid and structural response of the elastic domain in non-Newtonian fluid-structure interaction problem

    Susceptibility and resistance status of dengue vectors towards selected pyrethroids in Kota Bharu, Kelantan

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    In Malaysia, Aedes sp. plays a significant role in the transmissions of vector-borne diseases such as dengue, chikungunya, and Zika. Regular usage of household insecticide products and occasional fogging events mainly in residential areas have raised an issue on the Aedes susceptibility status against insecticides. The objective of the study was to evaluate the susceptibility and resistance status of Aedes sp. mosquitoes against pyrethroids in Panji, Kota Bharu, Kelantan. A total of 100 F1 generations of adult female Aedes sp. were tested following WHO bioassay guidelines against permethrin 0.75% and lambda-cyhalothrin 0.05%. In addition, PCR analysis at the specific alleles of F1534C and V1016G of the tested mosquitoes were carried out to determine the presence of kdr mutations. Determination of the Aedes mosquito composition at the sampling areas was also done. From the results obtained, Ae. albopictus was found at both localities; Panji, Kota Bharu and Kubang Kerian whereas Ae. aegypti can only be found in Panji, Kota Bharu. The population of Ae. aegypti in the Panji area was highly resistant against all insecticides tested (type I pyrethroid permethrin 0.75%, 18.41±1.74 & type II pyrethroid lambda-cyhalothrin 0.05%, 14.58±9.45). On the other hand, Ae. albopictus was moderately resistant against type II pyrethroid lambda-cyhalothrin 0.05% (93.82±3.01). However Ae. albopictus showed to be highly resistant against type I pyrethroid, permethrin 0.75% (87.79±2.76). The Kubang Kerian Ae. albopictus population was susceptible against lambda-cyhalothrin 0.05% (98.97±1.03) and resistant against permethrin 0.75% (90.72±3.01). From the PCR analysis, the population of Ae. albopictus in Kubang Kerian showed two different genotype groups, F/C1534 and susceptible F/F1534 genotypes. On the other hand, both genotype groups of F/C1534 and resistant C/C1534 were detected in the mosquito population of Ae. aegypti and Ae. albopictus in Panji, Kota Bharu respectively. While all Ae. aegypti samples showed the V/V1016 genotype. Based on this study, both the bioassay and the PCR analysis showed that the Aedes sp. population had developed resistance against the insecticides tested. However, a study on allele frequency to confirm the role of the kdr mutations as well as a study on metabolic resistance are needed towards the Aedes mosquito resistance against pyrethroid insecticide in the population

    Structural, Microstructural, Electrical Properties of Lanthanum doped-Bismuth Titanate Ceramics Prepared by Low Temperature Combustion Synthesis

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    In this work, lanthanum doped-bismuth titanate with different contents were successfully prepared by low-temperature combustion synthesis, and subsequently, sintered at 1000 oC for 3 hours. Their structural, microstructural and electrical were systematically studied. It was found that the structural distortion of orthorhombic structure tends to transforms to a tetragonal with the increase in La content.This change is most probably due to relaxations of orthorhombic distortion and octahedral tilting because of the difference in the ionic radius of Bi3+ and La3+. Upon increasing of La content, the grain size remarkable decreases resulted in uniform grain size with better relative density. Thus, the electrical properties of La doping were greatly improved in comparison to pure sample

    TWISTED BUILDINGS: CONCEPTS AND APPROACHES

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    With the emerging of new technologies, the look for more sustainable towers appears. Through designing twisted towers, an aerodynamic and energy efficient structure can be made to reduce materials and wind loads towards it. By definition, a twisted building is one that has gradually rotating floor plates along its height. The problem here rises due to the risk of structural failure and lack of load transfer and unorganized interior function. Thus, this research aims to detect the design solutions used to execute the twisted buildings achieving stability, safety, and withstanding climatic effects. In order to accomplish the mentioned aim, the research will start with a literature review, desk research, highlighting previous readings solving the problem. Qualitative research will be conducted based on academic articles and the case study of projects such as Dubai’s Infinity Tower by SOM and the second tallest building in Saudi Arabia, the Diamond Tower in Jeddah

    Three-dimensional direct numerical simulation (dns) Of taylor bubbles rising in non-Newtonian environments

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    Three-dimensional numerical simulation of Taylor gas bubbles as primary unites of slug flow patterns rising in non-Newtonian environments is performed in the context of Direct Numerical Simulation (DNS) of the governing equations, where the whole physics of fluid motions will be taken into account. State-of-the-art numerical tools are proposed to tackle the numerical challenges in the DNS study of this problem. E.g. a coupled level-set volume-of-fluid (CLSVOF) interface capturing method is used to solve the topological changes of the interface. Physical formulations are integrated with moving-mesh (MM) technique to decrease the computational cost of 3D simulations and adaptivemesh-refinement (AMR) technique to increase the local accuracy around the interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. To the best of the authors’ knowledge, this is the first work dealing with three-dimensional direct numerical simulation of Taylor bubbles rising in non-Newtonian environments.Postprint (published version
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