Visual Simulation of Flow

We have adopted a numerical method from computational fluid dynamics, the Lattice Boltzmann Method (LBM), for real-time simulation and visualization of flow and amorphous phenomena, such as clouds, smoke, fire, haze, dust, radioactive plumes, and air-borne biological or chemical agents. Unlike other approaches, LBM discretizes the micro-physics of local interactions and can handle very complex boundary conditions, such as deep urban canyons, curved walls, indoors, and dynamic boundaries of moving objects. Due to its discrete nature, LBM lends itself to multi-resolution approaches, and its computational pattern, which is similar to cellular automata, is easily parallelizable. We have accelerated LBM on commodity graphics processing units (GPUs), achieving real-time or even accelerated real-time on a single GPU or on a GPU cluster. We have implemented a 3D urban navigation system and applied it in New York City with real-time live sensor data. In addition to a pivotal application in simulation of airborne contaminants in urban environments, this approach will enable the development of other superior prediction simulation capabilities, computer graphics and games, and a novel technology for computational science and engineering

Large-scale cloudscapes using noise

Clouds have been of particular interest in computer graphics due to the challenge they present. Clouds are considered fuzzy objects, and need specialized algorithms to model and render realistically. Many techniques exist to model and render clouds that have had much success. This research will take existing techniques in cloud modeling and rendering and create a new technique combining those with noise. The idea is that noise can be used to model large-scale repeatable 3D cloudscapes and to be able to model such cloudscapes much more quickly than current techniques. This would be beneficial to developers of virtual universes that have very many worlds numbering in the ten to hundreds to create convincing cloudscapes on each distinct world

Cinematic Scientific Visualizations

The Hubble Space Telescope has provided the world with incredible imagery of the surrounding universe. The aesthetic quality of this imagery is limited by production resources; by creating a method to harness the highly refined detail and quality of CG elements in live-action films, we can inspire and educate at a much greater level. In this thesis, I create a rendering approach that allows camera movement around and through elements such as nebulae and galaxies, creating a more cinematic experience. The solution will also allow for reasonable scientific accuracy, visual appeal, efficiency, and extendability to other astronomical visualizations. 3D meshes are constructed and textured using telescopic images as reference. Splats are volumetrically generated using a voxelized bounding box around the mesh. Valid splats within a user specified maximum distance receive initial color and alpha values from the texture map. Probability density functions are used to create a density falloff along the edges of the object, and modifications to the RGBA values are made to achieve the desired cloud-like appearance. The data sets are rendered using a C program developed at the Space Telescope Science Institute by Dr. Frank Summers. The methodology is applied to the test cases of a nebula, star-forming region Sharpless 2-106, and a galaxy, Messier 51, or the Whirlpool Galaxy. The results of this thesis demonstrate the visual, scientific, and technical success of this solution. The code developed during this project generates the desired imagery with reasonable efficiency. A short animation moving from outside the galaxy to a close up of the nebula exhibits the flexibility in scale and camera movement. A careful balance between scientific accuracy and visual appeal were maintained through consultation with astronomers at the Space Telescope Science Institute. The favorable efficient, flexible, visual, and scientific results presented by this work make this process extendable to most other cases of nebula and galaxy visualizations

Simulation de flammes interactives en temps réel

Vidéos et images des résultats disponible à : http://www.iro.umontreal.ca/labs/infographie/theses/fatnasss/La synthèse d'une flamme animée dans un environnement 3D virtuel, reste à ce jour une tâche ardue, exigeant de judicieusement balancer réalisme et coût de calcul. Dans ce mémoire, nous présentons un ensemble de techniques pour sa simulation en temps réel tout en modélisant une interaction à des forces externes. Nous désirons minimiser son coût de calcul tout en préservant une apparence convaincante dans l'optique d'une intégration au sein de systèmes existants, n'affectant pas indûment leurs performances. Un champ de vélocité est extrait d'une simulation de ressorts et mis à profit dans le déplacement de chaînes de particules modélisant la forme de la flamme par l'entremise de la paramétrisation d'une surface NURBS. Considérant l'importance qu'ils ont sur notre perception de la combustion, nous prenons également soin de reproduire l'illumination, les ombres, et l'effet d'éblouissement qu'elle engendre.The synthesis of an open flame in a virtual 3D environment, remains to this day an arduous task, requiring a wise balance between realism and processing cost. In this M. Sc. thesis, we present a set of techniques for its simulation in real time while also modeling the interaction with external forces. Our goal is to minimize the cost while preserving a convincing appearance, thus facilitating integration of the techniques into existing systems without unduly affecting their performance. A velocity field is extracted from a spring-mass simulation which contributes to moving chains of particules that are used in modeling the flame shape through the configuration of a NURBS surface. In light of the importance they have on our perception of combustion, we also take care to duplicate the lighting, shadows and bloom the flame gives rise to

Empirical Comparison of Three Existing Methods for Simulating Embers in Computer-generated Fire

This study compares computer-generated embers using three existing methods. While there exists research related to fire propagation, flame rendering, and smoke generation, there is nothing that discusses embers. This study focuses specifically on the generation of an ember's path when it is animated. The three methods selected were the Lattice Boltzmann Model, a 3D fractal tree, and a particle system that uses third-order polynomials. The three methods were compared using three different metrics: memory requirements, time requirements (computational cost), and a subjective visual representation. A different method performed best in each of the three metrics. The particle system had the lowest memory requirements. The 3D fractal tree had the least computational cost. The Lattice Boltzmann Model had the best visual representation. Over all, when rendering embers in a real-time environment, the 3D fractal tree is the best choice. However, if pre-rendering your images, then the Lattice Boltzmann Model is best.Computer Science Departmen

Interactive simulation of fire, burn and decomposition

This work presents an approach to effectively integrate into one unified modular fire simulation framework the major processes related to fire, namely: a burning process, chemical combustion, heat distribution, decomposition and deformation of burning solids, and rigid body simulation of the residue. Simulators for every stage are described, and the modular structure enables switching to different simulators if more accuracy or more interactivity is desired. A “Stable Fluids” based three gas system is used to model the combustion process, and the heat generated during the combustion is used to drive the flow of the hot air. Objects, if exposed to enough heat, ignite and start burning. The decomposition of the burning object is modeled as a level set method, driven by the pyrolysis process, where the burning object releases combustible gases. Secondary deformation effects, such as bending burning matches and crumpling burning paper, are modeled as a proxy based deformation. Physically based simulation, done at interactive rates, enables the user to ef- ficiently test different setups, as well as interact and change the conditions during the simulation. The graphics card is used to generate additional frames for real-time visualization. This work further proposes a method for controlling and directing high resolution simulations. An interactive coarse resolution simulation is provided to the user as a “preview” to control and achieve the desired simulation behavior. A higher resolution “final” simulation that creates all the fine scale behavior is matched to the preview simulation such that the preview and final simulations behave in a similar manner. In this dissertation, we highlighted a gap within the CG community for the simulation of fire. There has not previously been a physically based yet interactive simulation for fire. This dissertation describes a unified simulation framework for physically based simulation of fire and burning. Our results show that our implementation can model fire, objects catching fire, burning objects, decomposition of burning objects, and additional secondary deformations. The results are plausible even at interactive frame rates, and controllable

Haptic Interaction with 3D oriented point clouds on the GPU

Real-time point-based rendering and interaction with virtual objects is gaining popularity and importance as di�erent haptic devices and technologies increasingly provide the basis for realistic interaction. Haptic Interaction is being used for a wide range of applications such as medical training, remote robot operators, tactile displays and video games. Virtual object visualization and interaction using haptic devices is the main focus; this process involves several steps such as: Data Acquisition, Graphic Rendering, Haptic Interaction and Data Modi�cation. This work presents a framework for Haptic Interaction using the GPU as a hardware accelerator, and includes an approach for enabling the modi�cation of data during interaction. The results demonstrate the limits and capabilities of these techniques in the context of volume rendering for haptic applications. Also, the use of dynamic parallelism as a technique to scale the number of threads needed from the accelerator according to the interaction requirements is studied allowing the editing of data sets of up to one million points at interactive haptic frame rates

Modeling wildland fire radiance in synthetic remote sensing scenes

This thesis develops a framework for implementing radiometric modeling and visualization of wildland fire. The ability to accurately model physical and op- tical properties of wildfire and burn area in an infrared remote sensing system will assist efforts in phenomenology studies, algorithm development, and sensor evaluation. Synthetic scenes are also needed for a Wildland Fire Dynamic Data Driven Applications Systems (DDDAS) for model feedback and update. A fast approach is presented to predict 3D flame geometry based on real time measured heat flux, fuel loading, and wind speed. 3D flame geometry could realize more realistic radiometry simulation. A Coupled Atmosphere-Fire Model is used to de- rive the parameters of the motion field and simulate fire dynamics and evolution. Broad band target (fire, smoke, and burn scar) spectra are synthesized based on ground measurements and MODTRAN runs. Combining the temporal and spa- tial distribution of fire parameters, along with the target spectra, a physics based model is used to generate radiance scenes depicting what the target might look like as seen by the airborne sensor. Radiance scene rendering of the 3D flame includes 2D hot ground and burn scar cooling, 3D flame direct radiation, and 3D indirect reflected radiation. Fire Radiative Energy (FRE) is a parameter defined from infrared remote sensing data that is applied to determine the radiative energy released during a wildland fire. FRE derived with the Bi-spectral method and the MIR radiance method are applied to verify the fire radiance scene synthesized in this research. The results for the synthetic scenes agree well with published values derived from wildland fire images

Study of Titanium based Composite Coatings for Resistance against Molten Aluminium Soldering on H13 Tool Steel

The service life of industrial components is limited predominantly by chemical corrosion, mechanical failure or mechanical wear. In the aluminium high pressure die casting industry, liquid aluminium is extremely reactive with the constituents of H13 die steel and has a tendency to form intermetallic layers. This chemical interaction results in sticking of molten metal to the die surface which produces defective castings and also damages the die surface. The use of thermal spray coatings provides protection to the surfaces operating in severe environments. An HVOF thermally sprayed coating has the advantage of having excellent bond strength and very low porosity levels (< 1%). This research work is concerned with producing and evaluating the performance of titanium/alumina based composite coatings to improve the service life of tool steel (H13) used for dies in aluminium high pressure die casting and dummy blocks used in Al extrusion. In this research work, the powder feedstocks for making the composite coatings were produced by high energy mechanical milling of a mixture of Al and TiO₂ powders in two different molar ratios followed by a thermal reaction process. The feedstock powder was then thermally sprayed using a high velocity oxygen fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)/Al₂O₃ and TiAl/Al₂O₃ composite coatings. The performance of the coatings was assessed in terms of Al soldering, liquid metal corrosion resistance, thermal shock resistance and wear resistance. In an immersion test, the coated specimens were dipped into molten Al at a temperature of 700 ± 10 °C for different intervals of time. The performance of the coatings was tested in terms of liquid metal corrosion resistance and propensity to Al soldering. The dissolution behaviour of the coatings was evaluated by measuring weight loss after dipping the samples in to molten aluminium. The immersion test results showed that the coated samples have relatively few locations where aluminium soldering (reactive/chemical) occurred, however, an H13 steel surface showed more tendency for aluminium soldering. It was found that composite coatings changed the molten Al attack on H13 tool steel from a generalized to a localized one. No reaction between molten aluminium and a Ti(Al,O)/Al₂O₃ composite coating was identified. The TiAl/Al2O₃ composite coating was found to be attacked by molten aluminium as a result of a reaction between the coating and molten aluminium. The metallic phase TiAl in the composite coating is believed to be attacked by the molten Al. A Ti(Al,O)/Al₂O₃ composite coating was found to be a better protective coating than the TiAl/Al₂O₃ composite coating due its stability against molten aluminium attack. The thermal shock behaviour of the composite coatings was investigated by subjecting the coated coupons to a number of cycles, each cycle consisting of a holding time of 30 seconds in molten aluminium at 700 ± 10 °C followed by quenching into water. The surfaces of the coupons were examined for Al soldering and an evaluation of surface spallation. Any cracks found in the coatings were studied to explain their thermal shock behaviour. A Ti(Al,O)/Al₂O₃ composite coating on H13 tool steel produced from a fine feedstock has better thermal shock resistance than the Ti(Al,O)/Al₂O₃ TiAl/Al₂O₃ composite coatings produced from the agglomerated feedstocks. The study also describes and compares the tribological properties such as friction and sliding wear rate of the composite coatings both at room and high temperature (700.°C) under dry and lubricating conditions. The wear resistance of the coatings was investigated by a tribometer using a spherical ended alumina, flat ended high speed steel and spherical ended hardened steel pins as counter bodies. The experimental results show that the composite coatings look promising for high temperature applications due to their low wear rate at high temperature. However room temperature applications of the composite coatings can be improved under lubricated conditions. Successful trials of a Ti(Al,O)/Al₂O₃ composite coated dummy block revealed that the coating has potential as an industrial coating