Tornado simulations in the visual effects industry have always been an interesting problem. Developing tools to provide more control over such effects is an important and challenging task. Current methods to achieve these effects use either particle systems or fluid simulation. Particle systems give a lot of control over the simulation but do not take into account the fluid characteristics of tornadoes. The other method which involves fluid simulation models the fluid behavior accurately but does not give control over the simulation. In this thesis, a novel method to model tornado behavior is presented. A tool based on this method was also created. The method proposed in this thesis uses a hybrid approach that combines the flexibility of particle systems while producing interesting swirling motions inherent in the fluids. The main focus of the research is on providing easy-to-use controls for art directors to help them achieve the desired look of the simulation effectively. A variety of controls is provided which include the overall shape, path, rotation, debris, surface, swirling motion, and interaction with the environment. The implementation was done in Houdini, which is a 3D animation software whose node based system allows an algorithmic approach to the problem and integrates well with the current tools. The tool allows the user to create animations that reflect the visual characteristics of real tornadoes. The usefulness of the tool was evaluated among participants who had some experience in 3D animation software. The results from the simulation and evaluation feedback reveal that the tool successfully allowed the users to create tornadoes of their choice efficiently.

In the past few decades, many people spent a lot of time and used many different ways, which includes analytic method, numerical method, and experimental observations for investigating the flow around circular cylinder problem. Eventually, the purpose of these investigations is to determinate the force acting on the cylinder and which is very useful and important for marine and hydraulic engineering. Essentially, it can be divided into three circumstances, (i) the flow around a fixed cylinder, (ii) the flow around a rotating cylinder, (iii) the flow around a moving cylinder. The first two conditions have already been will discussed. Consequently, besides analyzing the first two conditions and comparing with reference papers, the purpose of this present is discussing the variation of the flow field and the force acting on the cylinder by using finite difference method. Because of the considerable quantity of computation, using parallel computing for this model to speedup the numerical process is also one of the issues of the present.

A novel numerical method solves the VIScous Vorticity Equation (VISVE) in 3D in order to model the Leading Edge Vortex (LEV) of propellers is proposed and implemented in this dissertation. The spatial concentration of the vorticity is exploited in the method, which is designed to be spatially compact and numerically efficient, in the meantime, capable of modeling complicated vorticity/solid boundary interaction in 2D and 3D. The numerical model can work as a viscous correction on top of the traditional Boundary Element Method (BEM) results. The proposed method is first applied in the case of a 2D hydrofoil at high angle of attack. The results are correlated with those from Navier-Stokes (N-S) simulation. The method is then used to model the LEV and tip vortex of a 3D swept wing. The results of the 3D simulation show great similarity to those from N-S. In the end, the method is applied in the case of propellers at low advance ratios. All the essential flow characteristics (LEV and tip vortex) are predicted. The objective of this dissertation is not developing a mathematically equivalent numerical method to the full-blown Reynolds-Averaged Navier-Stokes (RANS) solver, but inventing an accurate and computationally efficient tool to model the effects of the LEV on the propeller performance for engineering's purpose. / text

Sloshing phenomena could seriously damage tank structures and reduce its lifetime. On the one hand, studies directly recommend the use of baffles to solve these problems, nevertheless on the other hand the existence of small tanks or plastic tanks without baffles confuse and complicate the case. The first aim in this thesis is to clarify the necessity of baffles for a particular diesel tank L120 H-Generation in Volvo front loaders. Then, the second aim is to improve the existing design. Four configurations are proposed and checked independently. Experiments in the lab, FEM static stresses analyses and vibrational simulations are done in order to fulfill the requirements. The conclusion of this thesis is that the dissipation of energy is highly recommended, so having an oblique baffle with holes could be a good way to reduce the sloshing and extend the lifetime of the tank.

Os ciclones secundários são sistemas que ainda não são bem definidos e, assim, são fenômenos de difícil previsibilidade, necessitando de mais estudos para identificar os sinais que disparam seu desenvolvimento. Neste estudo realizou-se um levantamento climatológico e estudo numérico de ciclogênese secundária no sudoeste do Oceano Atlântico Sul com o objetivo de obter informações sobre a atuação destes sistemas e entender os processos dinâmicos envolvidos no seu desenvolvimento. Para o período entre 1980 e 2010, a climatologia mostra que uma média de 3,9 sistemas secundários se forma por ano no Oceano Atlântico Sul. Estes sistemas ocorrem com maior e menor frequência nos meses frios e quentes, respectivamente. Dois tipos distintos de ciclones secundários foram encontrados. TIPO1 que se forma a leste e na região da frente quente do ciclone primário. Estes sistemas se desenvolvem sob advecção quente nos baixos níveis e pouca influência de anomalias de vorticidade potencial (VP) de altos níveis; TIPO2 se desenvolve a oeste/noroeste do ciclone primário onde predomina forte advecção fria em baixos níveis. No entanto, fluxos de calor e umidade intensos contribuem para aquecer a baixa troposfera e em altos níveis são forçados por anomalias de VP. Simulações numéricas com o modelo Weather Research and Forecasting (WRF) indicam os fluxos de calor sensível e latente na superfície como mecanismos de intensificação dos ciclones secundários TIPO1 e TIPO2, sendo o fluxo de calor latente mais importante no abaixamento de pressão destes sistemas. Os experimentos numéricos mostram que o ciclone do TIPO2 não se desenvolve na ausência de anomalia de VP, enquanto que o TIPO1 se desenvolve mais fraco e atrasado no tempo. A análise por separação de fatores indica que a anomalia de VP e algum outro mecanismo não relacionado aos fatores avaliados nas simulações tiveram papel disparador no ciclone do TIPO1, enquanto a interação da anomalia de VP com os fluxos de superfície atuou como intensificador. No TIPO2, o desenvolvimento ocorreu unicamente pela atuação da anomalia de VP, a qual também agiu como um intensificador juntamente com os fluxos de calor e umidade, bem como os processos de interação entre estes dois fatores. / Secondary cyclones are systems that are not well defined yet and they are difficult to predict, requiring further studies to identify the signals that trigger their development. In this study we carried out a climatology and numerical study of secondary cyclogenesis over the southwestern South Atlantic Ocean in order to obtain information about these systems and understand the dynamic processes involved in its development. The climatology for the period 1980-2010 shows that an average of 3.9 secondary systems per year develops in the southwestern South Atlantic Ocean. These systems occur with more and less frequency in the colder and warmer months, respectively. Two distinct types of secondary cyclones were found. TYPE1 forms eastward and over the warm front region of the primary cyclone. These systems develop due to warm advection at lower levels and relatively weak influence of potential vorticity (PV) anomalies at upper levels. TYPE2 develops westward/northwestward of the primary cyclone where strong cold advection predominates at lower levels. However, in this type, the lower troposphere is heated due to intense heat and moisture fluxes and at upper levels it is forced by PV anomalies. Numerical simulations using the Weather Research and Forecasting model (WRF) indicate that the sensible and latent heat fluxes on surface act as intensification mechanisms for both TYPE1 and TYPE2 secondary cyclones and that the latent heat flux influences more on decreasing the pressure in these systems. The numerical experiments show that the cyclone TYPE2 does not develop in the absence of PV anomalies, while the TYPE1 does, but it is relatively weaker and delayed in time. Factors separation analysis indicates that the PV anomaly and some other mechanism unrelated to the factors evaluated in the simulations have a triggering role in the development of the secondary cyclone TYPE1, while the interaction of PV anomaly with surface fluxes acted to intensify the cyclone. The TYPE2 development occurred solely due to PV anomaly, which also acted to intensifying together with heat/moisture fluxes on surface as well as the interaction processes of these two factors.

We consider the two-dimensional Navier-Stokes equation on the (possibly) asymmetric torus, D_δ = [0,2𝜋δ] × [0,2𝜋], both with and without stochastic forcing. Absent external force, the vorticity is known to reach a rest state of zero. There exists at least three so called "quasi-stationary states" which attract nearby solutions at rates faster than the global decay rate. The system evolves toward one of these three qualitatively different transient states for long times while the system overall tends toward the final rest state. We develop a finite-dimensional model of the associated deterministic vorticity equation to show how the selection of the dominant quasi-stationary state depends on the aspect ratio of the domain, given by δ. This is followed by formal analysis of the problem as a perturbation from the symmetric domain. Once the selection mechanism for the deterministic model is characterized, stochastic forcing is added to the reduced system. Numerical analysis shows the dominant quasi-stationary state is consistent with what is seen in the deterministic setting. Finally through multiscale averaging methods, the leading order dynamics of the stochastically forced finite-dimensional model for δ close to one is studied. As a result we formally obtain leading order asymptotics of statistics of interest, including the selection mechanism.

The Himalayan orogen provides a natural laboratory to test models of orogenic development due to large-scale continental collision. The Greater Himalayan Series (GHS), a lithotectonic unit continuous along the entire length of the belt, comprises the metamorphic core of the Himalayan orogen and underlies the highest topography. GHS rocks are exposed as a moderately north-dipping slab bounded below by the Main Central Thrust (MCT) and above by the South Tibetan Detachment System (STDS) of normal faults. Coeval reverse- and normal-sense motion on the crustal-scale MCT and STDS ductile shear zones allows the GHS to be modeled as an extruded wedge or channel of mid-crustal material. Due to this unique tectonic setting, the deformation path of rocks within the bounding shear zones and throughout the core of the GHS profoundly influences the efficiency of extrusion and exhumation processes. Attempts to quantify GHS deformation and metamorphic evolution have provided significant insight into Himalayan orogenic development, but these structural and petrologic studies are often conducted in isolation. Penetrative deformation fabrics developed under mid-upper amphibolite facies conditions within the GHS argue that deformation and metamorphism were coupled, and this should be considered in studies aimed at quantifying GHS teconometamorphic evolution. This work focuses on two projects related to the coupled deformation, thermal and metamorphic evolution during extrusion and exhumation of the GHS, focused on the lower and upper margins of the slab. A detailed examination of the P--T history of a schist collected from within the MCT zone of the Sutlej River, NW India, provides insight into the path experienced by these rocks as they traveled through the crust in response to the extreme shortening related to India-Asia collision. Combined forward thermodynamic and diffusion modeling indicates compositional zoning preserved in garnet has remained unmodified since growth and can be related directly to the P--T--X evolution of rocks from this zone. Classic porphyroblast--matrix relationships coupled with the above models provide a structural framework within which to interpret the microstructures and provide additional constraints on the relative timing of metamorphic and deformation events. A combined microstructural and quartz petrofabric study of rocks from the highest structural levels of the GHS in the Zanskar region was completed. This work provides the first quantitative estimate of temperatures attending normal-sense shearing along the Zanskar Shear Zone, the westernmost strand of the STDS. Results indicate penetrative top-N (extensional) deformation occurred at elevated temperatures and resulted in the telescoping of isothermal surfaces present during shearing and extrusion of GHS rocks. Simple geometric models invoking heterogeneous simple shear parallel to the overlying detachment require dip-slip displacement magnitudes on the order of 15--40 km, identical to estimates derived from nearby barometric analyses. Finally, focus is given to the rotational behavior of rigid inclusions suspended in a flowing viscous matrix from a theoretical perspective. Predictions of clast rotational behavior have been used to construct several kinematic vorticity estimation techniques that have become widely adopted for quantitative studies of naturally deformed rocks. Despite the popularity of the techniques, however, basic questions regarding clast-based analyses remain open. Therefore a numerical model was constructed and a systematic investigation of 2- and 3D clasts suspended in steady and non-steady plane-strain flows was undertaken to determine likely sources of error and the intrinsic strengths and limitations of the techniques. / Ph. D.

No description available.

An accurate and efficient numerical method for Compressible Vorticity Confinement (CVC) was developed. The methodology follows from Steinhoff's vorticity confinement approach that was developed for incompressible flows. In this research, the extension of this approach to compressible flows has been developed by adding a vorticity confinement term as a "body force" into the governing compressible flow equations. This vorticity confinement term tends to cancel the numerical dissipative errors inherently related to the numerical discretization in regions of strong vorticity gradients. The accuracy, reliability, efficiency and robustness of this method were investigated using two methods. One approach is directly applying the CVC method to several real engineering problems involving complex vortex structures and assessing the accuracy by comparison with existing experimental data and with other computational techniques. Examples considered include supersonic conical flows over delta wings, shock-bubble and shock-vortex interactions, the turbulent flow around a square cylinder and the turbulent flow past a surface-mounted 3D cube in a channel floor. A second approach for evaluating the effectiveness of the CVC method is by solving simplified "model problems" and comparing with exact solutions. Problems that we have considered are a two-dimensional supersonic shear layer, flow over a flat plate and a two-dimensional vortex moving in a uniform stream. The effectiveness of the compressible confinement method for flows with shock waves and vortices was evaluated on several complex flow applications. The supersonic flow over a delta wing at high angle of attack produces a leeward vortex separated from the wing and cross flow, as well as bow shock waves. The vorticity confinement solutions compare very favorably with experimental data and with other calculations performed on dense, locally refined grids. Other cases evaluated include isolated shock-bubble and shock-vortex interactions. The resulting complex, unsteady flow structures compare very favorably with experimental data and computations using higher-order methods and highly adaptive meshes. Two cases involving massive flow separation were considered. First the two-dimensional flow over a square cylinder was considered. The CVC method was applied to this problem using the confinement term added to the inviscid formulation, but with the no-slip condition enforced. This produced an unsteady separated flow that agreed well with experimental data and existing LES and RANS calculations. The next case described is the flow over a cubic protuberance on the floor of a channel. This flow field has a very complex flow structure involving a horseshoe vortex, a primary separation vortex and secondary corner vortices. The computational flow structures and velocity profiles were in good agreement with time-averaged values of the experimental data and with LES simulations, even though the confinement approach utilized more than a factor of 50 fewer cells (about 20,000 compared to over 1 million). In order to better understand the applicability and limitations of the vorticity confinement, particularly the compressible formulation, we have considered several simple model problems. Classical accuracy has been evaluated using a supersonic shear layer problem computed on several grids and over a range of values of confinement parameter. The flow over a flat plate was utilized to study how vorticity confinement can serve as a crude turbulent boundary layer model. Then we utilized numerical experiments with a single vortex in order to evaluate a number of consistency issues related to the numerical implementation of compressible confinement. / Ph. D.

The performance of the heart after a valve replacement operation will greatly depend on the flow character downstream the mitral valve thus a better understanding of the flow character is essential. Most in vitro studies of the flow downstream of a MHV have been conducted with the valve in the aortic position. Researchers reported detailed measurements most of which were obtained by Laser Doppler Velocimetry (LDV) in rigid models of the aorta. Digital Particle Image Velocimetry (DPIV) has also been utilized to reveal intricate patterns of interacting shed vortices downstream of the aortic valve. The orientation of the valves may considerably affect the flow development and slight difference may produce significant differences in the ventricular flow fields. Two orientations, respectively anatomical and anti-anatomical, of the St. Jude Medical (SJM) bileaflet valve are presented and compared with the SJM Biocor porcine valve, which served to more closely represent the natural valve. In this effort, we employ a powerful tool to monitor the velocity field in a flexible, transparent LV and study the evolution of large eddies and turbulence through a complete cardiovascular cycle. Both time average and instantaneous results of velocity, vorticity, and turbulent kinetic energy distributions are presented. The presence and location of vortical structures were deduced as well as the level of coherence of these structures. The presence of three distinct flow patterns were identified, by the location of vortical structures and level of coherence, for the three configurations corresponding to significant differences in the turbulence level distribution inside the LV. / Master of Science