Simulation of 3D Model, Shape, and Appearance Aging by Physical, Chemical, Biological, Environmental, and Weathering Effects

Physical, chemical, biological, environmental, and weathering effects produce a range of 3D model, shape, and appearance changes. Time introduces an assortment of aging, weathering, and decay processes such as dust, mold, patina, and fractures. These time-varying imperfections provide the viewer with important visual cues for realism and age. Existing approaches that create realistic aging effects still require an excessive amount of time and effort by extremely skilled artists to tediously hand fashion blemishes or simulate simple procedural rules. Most techniques do not scale well to large virtual environments. These limitations have prevented widespread utilization of many aging and weathering algorithms. We introduce a novel method for geometrically and visually simulating these processes in order to create visually realistic scenes. This work proposes the ``mu-ton system, a framework for scattering numerous mu-ton particles throughout an environment to mutate and age the world. We take a point based representation to discretize both the decay effects and the underlying geometry. The mu-ton particles simulate interactions between multiple phenomena. This mutation process changes both the physical properties of the external surface layer and the internal volume substrate. The mutation may add or subtract imperfections into the environment as objects age. First we review related work in aging and weathering, and illustrate the limitations of the current data-driven and physically based approaches. We provide a taxonomy of aging processes. We then describe the structure for our ``mu-ton framework, and we provide the user a short tutorial how to setup different effects. The first application of the ``mu-ton system focuses on inorganic aging and decay. We demonstrate changing material properties on a variety of objects, and simulate their transformation. We show the application of our system aging a simple city alley on different materials. The second application of the ``mu-ton system focuses organic aging. We provide details on simulating a variety of growth processes. We then evaluate and analyze the ``mu-ton framework and compare our results with ``gamma-ton tracing. Finally, we outline the contributions this thesis provides to computer-based aging and weathering simulation

Real-time rendering and simulation of trees and snow

Tree models created by an industry used package are exported and the structure extracted in order to procedurally regenerate the geometric mesh, addressing the limitations of the application's standard output. The structure, once extracted, is used to fully generate a high quality skeleton for the tree, individually representing each section in every branch to give the greatest achievable level of freedom of deformation and animation. Around the generated skeleton, a new geometric mesh is wrapped using a single, continuous surface resulting in the removal of intersection based render artefacts. Surface smoothing and enhanced detail is added to the model dynamically using the GPU enhanced tessellation engine. A real-time snow accumulation system is developed to generate snow cover on a dynamic, animated scene. Occlusion techniques are used to project snow accumulating faces and map exposed areas to applied accumulation maps in the form of dynamic textures. Accumulation maps are xed to applied surfaces, allowing moving objects to maintain accumulated snow cover. Mesh generation is performed dynamically during the rendering pass using surface o�setting and tessellation to enhance required detail

Environmental Objects for Authoring Procedural Scenes

International audienceWe propose a novel approach for authoring large scenes with automatic enhancement of objects to create geometric decoration details such as snow cover, icicles, fallen leaves, grass tufts or even trash. We introduce environmental objects that extend an input object geometry with a set of procedural effects that defines how the object reacts to the environment, and by a set of scalar fields that defines the influence of the object over of the environment. The user controls the scene by modifying environmental variables, such as temperature or humidity fields. The scene definition is hierarchical: objects can be grouped and their behaviours can be set at each level of the hierarchy. Our per object definition allows us to optimize and accelerate the effects computation, which also enables us to generate large scenes with many geometric details at a very high level of detail. In our implementation, a complex urban scene of 10 000 m², represented with details of less than 1 cm, can be locally modified and entirely regenerated in a few seconds

A study of remote sensing as applied to regional and small watersheds. Volume 1: Summary report

The accuracy of remotely sensed measurements to provide inputs to hydrologic models of watersheds is studied. A series of sensitivity analyses on continuous simulation models of three watersheds determined: (1)Optimal values and permissible tolerances of inputs to achieve accurate simulation of streamflow from the watersheds; (2) Which model inputs can be quantified from remote sensing, directly, indirectly or by inference; and (3) How accurate remotely sensed measurements (from spacecraft or aircraft) must be to provide a basis for quantifying model inputs within permissible tolerances

ClimateNeRF: Physically-based Neural Rendering for Extreme Climate Synthesis

Physical simulations produce excellent predictions of weather effects. Neural radiance fields produce SOTA scene models. We describe a novel NeRF-editing procedure that can fuse physical simulations with NeRF models of scenes, producing realistic movies of physical phenomena inthose scenes. Our application -- Climate NeRF -- allows people to visualize what climate change outcomes will do to them. ClimateNeRF allows us to render realistic weather effects, including smog, snow, and flood. Results can be controlled with physically meaningful variables like water level. Qualitative and quantitative studies show that our simulated results are significantly more realistic than those from state-of-the-art 2D image editing and 3D NeRF stylization.Comment: project page: https://climatenerf.github.io

Climate change scenarios for the California region

To investigate possible future climate changes in California, a set of climate change model simulations was selected and evaluated. From the IPCC Fourth Assessment, simulations of twenty-first century climates under a B1 (low emissions) and an A2 (a medium-high emissions) emissions scenarios were evaluated, along with occasional comparisons to the A1fi (high emissions) scenario. The climate models whose simulations were the focus of the present study were from the Parallel Climate Model (PCM1) from NCAR and DOE, and the NOAA Geophysical Fluid Dynamics Laboratory CM2.1 model (GFDL). These emission scenarios and attendant climate simulations are not “predictions,” but rather are a purposely diverse set of examples from among the many plausible climate sequences that might affect California in the next century. Temperatures over California warm significantly during the twenty-first century in each simulation, with end-of-century temperature increases from approximately +1.5°C under the lower emissions B1 scenario in the less responsive PCM1 to +4.5°C in the higher emissions A2 scenario within the more responsive GFDL model. Three of the simulations (all except the B1 scenario in PCM1) exhibit more warming in summer than in winter. In all of the simulations, most precipitation continues to occur in winter. Relatively small (less than ~10%) changes in overall precipitation are projected. The California landscape is complex and requires that model information be parsed out onto finer scales than GCMs presently offer. When downscaled to its mountainous terrain, warming has a profound influence on California snow accumulations, with snow losses that increase with warming. Consequently, snow losses are most severe in projections by the more responsive model in response to the highest emissions

Towards a predictive multi-phase model for alpine mass movements and process cascades

Alpine mass movements can generate process cascades involving different materials including rock, ice, snow, and water. Numerical modelling is an essential tool for the quantification of natural hazards. Yet, state-of-the-art operational models are based on parameter back-calculation and thus reach their limits when facing unprecedented or complex events. Here, we advance our predictive capabilities for mass movements and process cascades on the basis of a three-dimensional numerical model, coupling fundamental conservation laws to finite strain elastoplasticity. In this framework, model parameters have a true physical meaning and can be evaluated from material testing, thus conferring to the model a strong predictive nature. Through its hybrid Eulerian–Lagrangian character, our approach naturally reproduces fractures and collisions, erosion/deposition phenomena, and multi-phase interactions, which finally grant accurate simulations of complex dynamics. Four benchmark simulations demonstrate the physical detail of the model and its applicability to real-world full-scale events, including various materials and ranging through five orders of magnitude in volume. In the future, our model can support risk-management strategies through predictions of the impact of potentially catastrophic cascading mass movements at vulnerable sites

Impact of climate and land cover changes on snow cover in a small Pyrenean catchment

International audienceThe seasonal snow in the Pyrenees Mountains is an essential source of runoff for hydropower production and crop irrigation in Spain and France. The Pyrenees are expected to undergo strong environmental perturbations over the 21st century because of climate change (rising temperatures) and the abandonment of agro-pastoral areas (reforestation). Both changes are happening at similar timescales and are expected to have an impact on snow cover. The effect of climate change on snow in the Pyrenees is well understood , but the effect of land cover changes is much less documented. Here, we analyze the response of snow cover to a combination of climate and land cover change scenarios in a small Pyrenean catchment (Bassiès, 14.5 km 2 , elevation range 940–2651 m a.s.l.) using a distributed snowpack evolution model. Climate scenarios were constructed from the output of regional climate model projections, whereas land cover scenarios were generated based on past observed changes and an inductive pattern-based model. The model was validated over a snow season using in situ snow depth measurements and high-resolution snow cover maps derived from SPOT (Satellite Pour l'Observation de la Terre – Earth Observation Satellite) satellite images. Model projections indicate that both climate and land cover changes reduce the mean snow depth. However, the impact on the snow cover duration is moderated in reforested areas by the shading effect of trees on the snow surface radiation balance. Most of the significant changes are expected to occur in the transition zone between 1500 m a.s.l. and 2000 m a.s.l. where (i) the projected increase in air temperatures decreases the snow fraction of the precipitation and (ii) the land cover changes are concentrated. However, the consequences on the runoff are limited because most of the meltwater originates from high-elevation areas of the catchment, which are less affected by climate change and reforestation

Numerical modelling of the snow flow characteristics surrounding Sanae IV Research Station, Antarctica

Thesis (PhD)--University of Stellenbosch, 2004.ENGLISH ABSTRACT:This work is concerned with the numerical simulation of the aeolian snow transportation process (drifting or wind blown snow) and especially the snow deposition and erosion phenomenon (snow drift). The research work is interested in modelling the atmospheric boundary layer wind flow and its associated snow drifting processes around threedimensional obstacles by means of computational fluid dynamics (CFD). A modelling method is required to predict and evaluate the snow drifting phenomenon surrounding the SANAE IV research station in Antarctica. This station is of an elevated design to ensure that wind blown snow may travel around the structure relatively undisturbed and without deposition near the structure. This design is partly successful but localised drifts are formed especially leeward of the interconnecting structures that join the main building sections together. The theoretical and numerical description to describe the turbulent transport of the two-phase mixture of air and snow particles is investigated. This theory is subsequently employed to describe the snow deposition and erosion process and two models are developed to determine the deposition flux onto the snow surface. These models presented and discussed are a threshold based approach and a conservative based approach. The first model is dependent on a threshold shear velocity to determine the onset of either erosion or deposition. The second model determines the deposition or erosion flux based on the conservation of the snow mass transport in the near surface control volume. A numerical scheme that evaluates the snow deposition flux at the surface and forces a temporal surface adaptation during the simulation is established and implemented in a commercial CFD software code by means of user subroutines. Various test cases for which observed snow drift data are available are numerically modelled to validate the snow drift schemes presented in this work. These tests include the wind driven snow accumulation around a three-dimensional cube, around two adjacent three-dimensional cubes and near a typical porous snow fence. The results indicate that both methods can predict realistic snow drifts for a variety of wind flow conditions but also show that the conservative approach is superior to the threshold based approach in describing the snow drift process around obstacles. This model allows drifts to form not only in areas of low flow velocities but also under high shear conditions. The theoretical investigation and the development and validation of the conservatively based snow drift scheme shows that drift formation depends strongly on the near surface flow divergence and secondary flow structures. To resolve the snow drift formation under a variety of flow conditions a three-dimensional field solution is required to determine velocity and snow concentration gradients and include the effects of near surface convective and turbulent entrainment. The model is applied to numerically simulate and predict snow drifting around the SANAE IV base for a moderate as well as a high wind speed event. The predicted snow drift around the base agrees favourably with the observed drifts at the station. Further numerical simulations are carried out to evaluate the effects a few design modifications may have on the snow deposition. These results suggest that a simple baffle plate installation near the bottom of the interconnecting link structures may minimise the snow accumulation leeward of that area. This study shows that to achieve realistic numerical snow drift predictions around, on or near obstacles, a conservative based snow drift scheme should be considered using some form of temporal terrain adaptation strategy. Only then does one include a sufficient level of important flow effects such as deposition along near surface boundaries of strong flow divergence which plays as an important role as vertical settling and entrainment in determining deposition rates.AFRIKAANSE OPSOMMING:Hierdie studie behels die numeriese simulasie van windgedrewe sneeubeweging asook die daarmee gepaardgaande sneeu neerslag en erosie eienskappe. Die navorsing het verder belang in die berekening van die atmosferiese grenslaag vloei en die simulasie van sneeu neerslag naby drie-dimensionele strukture deur gebruik te maak van berekeningsvloeimeganika (BVM). ‘n Berekeningsmetodiek is nodig om die eienskappe van die sneeu neerslag rondom die SANAE IV navorsingsstasie in Antarktika te voorspel en te evalueer. Die bogrondse struktuur is spesifiek so ontwerp om te verseker dat wind gedrewe sneeu hoofsaaklik onversteurd verby die struktuur kan beweeg sonder neerslag teenaan die struktuur. Die ontwerp is grotendeels suksesvol alhoewel sneeu neerslag wel lokaal plaasvind, wind af vanaf die aansluitings strukture tussen die hoof geboue. Die teoretiese en numeriese beskrywing van die twee-fase lug- en sneeumengsel beweging word ondersoek en gebruik om die sneeu neerslag en erosie einskappe te beskryf. Twee modelle wat hierdie verskynsel beskryf word beskryf en bespreek naamlik ‘n drumpel gebaseerde benadering en ‘n konserwatief gebaseerde benadering. Die eerste model is afhanklik van ‘n drumpel skuifsnelheid om die aanvang van of erosie of neerslag te bereken. Die tweede model bereken die neerslag eerder gebaseer op die behoud van die sneeu massa vloei in die kontrole volume naby aan die oppervlak. ‘n Numeriese metode is ontwikkel en geimplementeer in ‘n kommersiële BVM sagteware pakket deur van gebruikerssubroetines gebruik te maak. Die ontwikkelde kode evalueer die sneeu neerslag vloed by die oppervlak en forseer ‘n tydafhanklike oppervlak aanpassing gedurende die simulasie. Die sneeu neerslag metode wat beskryf word in hierdie studie word ge-evalueer teen verskeie toetsgevalle waarvoor daar waargenome sneeu neerslag resultate beskikbaar is. Hierdie toetse sluit in die wind gedrewe sneeu neerslag rondom ‘n drie-dimensionele kubus, rondom twee naby geleë kubusse en naby ‘n tipiese poruese sneeu heining. Die resultate dui aan dat beide die metodes realistiese sneeu neerslag voorspel vir verskeie wind toestande. Die studie wys ook dat die konserwatief gebaseerde benadering vir die beskrywing van die sneeu neerslag proses meer akkuraat is as die drumpel gebaseerde benadering aangesien die neerslagvoorspel kan word nie net alleenlik in gebiede met lae vloeisnelhede nie, maar ook in gebiede waar hoë skuifsnelhede teenwoordig is. Die teoretiese ondersoek, ontwikkeling en toepassing van die konserwatief gebaseerde model dui daarop dat die neerslag afhanklik is van die divergensie van die vloeiveld asook van die sekondêre vloei patrone naby die oppervlak. Ten einde die sneeu neerslag vir verskeie toestande op te los is dit nodig om snelheids- en sneeukonsentrasie gradiënte te kan bereken in ‘n drie-dimensionele vloei veld om sodoende die invloed van naby-oppervlak konveksie en turbulente verspreiding in ag te neem. Die metode word toegepas deur die sneeu neerslag rondom die SANAE IV navorsingsstasie te voorspel vir ‘n gematigde asook ‘n hoë wind snelheid toestand. Die sneeu neerslag voorspelling stem gunstig ooreen met die waargenome neerslag by die struktuur. Verdere numeriese simulasies is uitgevoer om die invloed van ontwerpsverandering op die neerslag te evalueer. Uit hierdie resultate blyk dit dat ‘n eenvoudige plaat struktuur onder die aansluitingsstrukture die sneeu neerslag wind af mag verminder. Hierdie navorsingsstudie dui daarop dat ‘n tydafhanklike terrein aanpassing strategie saam met die konserwatiewe neerslag model noodsaaklik is ten einde realistiese resultate te behaal vir die sneeu opbou rondom of naby strukture. Sodoende word genoegsame vlakke van belangrike vloei verskynsels, soos die invloed van vloei divergensie, in ag geneem wat net so ‘n belangrik rol in neerslag speel soos vertikale afsetting