Wind tunnel CFD simulation by using OpenFOAM

Aerodynamics and fluid dynamics are used in many fields, such as aerospace, marine, and oil & gas. All these industries require precise results from experiments, tests, and simulations. This is because it is connected to considerable risks and losses. However, getting a perfectly correct answer in a fluid dynamic world is impossible. So, an approximation is used to solve unsolvable equations. This led people to simulate and test with CFD and wind tunnels. A wind tunnel is a test machine to test the fluid flow over the minimized object and expect how it will be in the real world. To test it in the real world, the size of the product is too huge and very expensive. Therefore, wind tunnel testing is essential. This dissertation it was verifying CFD conducted processes by using Openfoam for the new wind tunnel at Universitetet i Stavanger. First, the log law of the wall was verified. This process was confirmed without any model inside the wind tunnel. After this verification, grid optimization and wall distance effect were done to reduce errors and check for any corrections. Pressure distribution, velocity distribution, and drag coefficient were used as criterion properties to check any difference in each case. The mesh size did not have any significant effect on the results. However, the wall distance affected the results because of the wall interference. Finally, support interference was carried out. Support interference is also one of the significant factors that can affect the result, as well as wall interference. These interferences are the most significant differences between the natural world and the wind tunnel. The existence of the supports behind the test model interrupted the vortex creation. Also boundary layer along the supports affected the pressure distribution. All these factors influenced the drag coefficient of the disk model. As a result, the drag coefficient decreased by 3%. This is because of the location of the supports. The supports must locate far away from the model so it does not affect the vortex formation

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Department of Materials Science EngineeringNanoparticle usually refers to the particle which is ranging from one to one-hundred nm. They have unique properties which can???t be seen in bulk materials; high surface to volume ratio, quantum size effect, surface plasmon resonance and so on. Among nanocrystals, magnetic nanoparticles are hot topics because of their wide usages for application such as catalysis, nano-medicine, electromagnetic wave absorption, bio-sensors and data storage. In the first part of the paper, I briefly introduced overall description of magnetic nanoparticles including magnetism, properties, synthetic method. Iron cobalt(FeCo) nanoparticles are one of important magnetic nanoparticles because of their large values of permeability and saturation magnetization. So, they can be used in wide range of application. So, there have been many researches to synthesize FeCo nanoparticles. Nevertheless, synthesis of oxygen-free monodisperse FeCo nanoparticles remains challenging. In this paper, the new synthetic method synthesizing of FeCo nanoparticles is introduced. During synthesis, hydrogen gas was directly injected throughout the reaction time, leading to the reduction of oxygen part of the nanoparticles. I also synthesized size and shaped controlled FeCo nanoparticles by controlling the amount and ratio of oleic acid and oleylamine. I also fabricated magnetic nanoparticles and edge-oxidized graphene (EOG) nanocomposites. Graphene has also attracted considerable attention from a number of different research areas, because it has great potential for a wide usages in application like catalyst, optoelectronic materials, sensors. There are many attempts to fabricate nanoparticles/graphene composites by EDC coupling, in-situ fabrication and so on. In this paper, I synthesized magnetic nanoparticles and EOG composite. EOG has carboxylic acid and hydroxyl functionalities only at the edge of it. So, it has great dispensability on water and better electrical properties than graphene oxide, expecting the superior properties to graphene oxide. I synthesized the composite using two methods; One is EDC coupling and the other is using electrostatic interaction. In second method, the surface of FeCo nanoparticles are exchanged organic ligands into inorganic ligands to give the negative surface charge, while PEI-coated graphene oxide has positive charge. I fabricated FeCo nanoparticles and EOG hybrid materials through electrostatic interaction.ope

Topological Twisting of Multiple M2-brane Theory

Bagger-Lambert-Gustavsson theory with infinite dimensional gauge group has been suggested to describe M5-brane as a condensation of multiple M2-branes. Here we perform a topological twisting of the Bagger-Lambert-Gustavsson theory. The original SO(8) R-symmetry is broken to SO(3)XSO(5), where the former may be interpreted as a diagonal subgroup of the Euclidean M5-brane world-volume symmetry SO(6), while the latter is the isometry of the transverse five directions. Accordingly the resulting action contains an one-form and five scalars as for the bosonic dynamical fields. We further lift the action to a generic curved three manifold. In order to make sure the genuine topological invariance, we construct an off-shell formalism such that the scalar supersymmetry transformations are nilpotent strictly off-shell and independent of the metric of the three manifold. The one loop partition function around a trivial background yields the Ray-Singer torsion. The BPS equation involves an M2-brane charge density given by a Nambu-Goto action defined in an internal three-manifold.Comment: 20 pages, no figure; Refs added, minor improvement, to appear in JHE

Convergence and non-convergence in a nonlocal gradient flow

We study the asymptotic convergence of solutions of $\partial_t u=-f(u)+\int f(u)$, a nonlocal differential equation that is formally a gradient flow in a constant-mass subspace of $L^2$ arising from simplified models of phase transitions. In case the solution takes finitely many values, we provide a new proof of stabilization that uses a {\L}ojasiewicz-type gradient inequality near a degenerate curve of equilibria. Solutions with infinitely many values in general need not converge to equilibrium, however, which we demonstrate by providing counterexamples for piecewise linear and cubic functions $f$. Curiously, the exponential rate of convergence in the finite-value case can jump from order $O(1)$ to arbitrarily small values upon perturbation of parameters.Comment: 31 pages, 2 figure

Designing a new battery system using NaCl aqueous solution as cathode

Department of Energy Engineering(Battery Science and Technology)The importance of Electrical Energy Storage (EES) for integration with renewable sources has increased gradually in accordance with rising environmental concerns and energy demands. Although research and development in EES technologies has been progressing, some challenges, such as improved performances, cost, location, etc., still remain before they can be successful. The cost-competition is expected to significantly affect the broad market penetration of EES. The eco-friendly seawater battery, employing seawater to a cathode material, is cost-effective, thus addressing the cost issue. As a seawater cathode provides Na ions of the energy source continuously and finally, a seawater battery can have high energy density despite having low salt (NaCl) concentration (~0.46 M). That is to say, it should be located near the ocean. In addition, renewable sources, possibly integrated with the seawater battery, are limited owing to the locational constraint. Herein, a rechargeable saltwater battery is proposed for the first time, which utilizes NaCl aqueous solution as an active material while it has typically served as electrolyte to conduct ions, in batteries or electrolysis. Using cheap and safe saltwater as catholyte allows the battery to be located anywhere, and also offers a significant reduction in production costs which is one of the requisitions for large-scale EES systems. In addition, changing salt levels in water enables the control of the working potential of the cell and energy density (up to 423 Wh/kg at 6 M NaCl). This ultimately provides the flexibilities of the saltwater battery for different applications. The cell design and components (e.g. change of material components) significantly affected its electrochemical performances. Thus, this research also focused on designing the new cell and the key components (a solid electrolyte and a carbon-based cathode electrode) to test saltwater cathode. The electrochemical mechanism and performances were therefore investigated. In addition, some catalysts were applied to improve cell performances. Lastly, a cost analysis of a saltwater battery was examined, by comparing it to other batteries, to demonstrate its feasibility as a next-generation EES technology.ope

A Nonperturbative Test of M2-Brane Theory

We discuss non-perturbative effects in the ABJM model due to monopole instantons. We begin by constructing the instanton solutions in the $U(2)\times U(2)$ model, explicitly, and computing the Euclidean action. The Wick-rotated Lagrangian is complex and its BPS monopole instantons are found to be a delicate version of the usual 't Hooft-Polyakov monopole solutions. They are generically 1/3 BPS but become 1/2 BPS at special locus in the moduli space of two M2-branes, yet each instanton carries eight fermionic zero modes, regardless of the vacuum choice. The low energy effective action induced by monopole instantons are quartic order in derivatives. The resulting vertices are nonperturbative in $1/k$, as expected, but are rational functions of the vacuum moduli. We also analyze the system of two M2-branes in the supergravity framework and compute the higher order interactions via 11-dimensional supergraviton exchange. The comparison of the two shows that the instanton vertices are precisely reproduced by this M2-brane picture, supporting the proposal that the ABJM model describes multiple M2-branes.Comment: 40 pages, 1 figure, references update

Experiences of International Students in Practicum and Internship Courses: A Consensus Qualitative Research

This qualitative study explores the practicum and/or internship experiences of international students in counseling. Based on the foundation of phenomenological research, this study uses a consensual qualitative research method. Semi-structured interview questionnaires asked ten participants regarding their experiences of practica and/or internships (including their fears, challenges, and support from training programs). Results revealed that the fears and challenges that international students face during the practicum and/or internship training primarily stemmed from their language barrier and/or a lack of understanding of the American counseling system. Our findings indicated that providing practical information, such as sites, the American counseling system, insurance, and cultures, in addition to ensuring that supervisors and faculty members increase in multicultural competency and sensitivity about international students, would improve international students’ preparation for their practica and/or internships