Reverse Skew-T - A Cloudmaking Tool for CG

We present 'Reverse Skew-T', a tool that allows users to direct a physically inspired simulation of layered clouds. To achieve this, we extend existing models for cloud simulation and provide a graphical user interface for providing important simulation parameters to our system

Realistic natural atmospheric phenomena and weather effects for interactive virtual environments.

Clouds and the weather are important aspects of any natural outdoor scene, but existing dynamic techniques within computer graphics only offer the simplest of cloud representations. The problem that this work looks to address is how to provide a means of simulating clouds and weather features such as precipitation, that are suitable for virtual environments. Techniques for cloud simulation are available within the area of meteorology, but numerical weather prediction systems are computationally expensive, give more numerical accuracy than we require for graphics and are restricted to the laws of physics. Within computer graphics, we often need to direct and adjust physical features or to bend reality to meet artistic goals, which is a key difference between the subjects of computer graphics and physical science. Pure physicallybased simulations, however, evolve their solutions according to pre-set rules and are notoriously difficult to control. The challenge then is for the solution to be computationally lightweight and able to be directed in some measure while at the same time producing believable results. This work presents a lightweight physically-based cloud simulation scheme that simulates the dynamic properties of cloud formation and weather effects. The system simulates water vapour, cloud water, cloud ice, rain, snow and hail. The water model incorporates control parameters and the cloud model uses an arbitrary vertical temperature profile, with a tool described to allow the user to define this. The result of this work is that clouds can now be simulated in near real-time complete with precipitation. The temperature profile and tool then provide a means of directing the resulting formation

Procedural Cloudscapes

International audienceWe present a phenomenological approach for modeling and animating cloudscapes. We propose a compact procedural model for representing the different types of cloud over a range of altitudes. We define primitive-based field functions that allow the user to control and author the cloud cover over large distances easily. Our approach allows us to animate cloudscapes by morphing: instead of simulating the evolution of clouds using a physically-based simulation, we compute the movement of clouds using key-frame interpolation and tackle the morphing problem as an Optimal Transport problem. The trajectories of the cloud cover primitives are generated by solving an Anisotropic Shortest Path problem with a cost function that takes into account the elevation of the terrain and the parameters of the wind field

Impact, runoff and drying of wind-driven rain on a window glass surface: numerical modelling based on experimental validation

This paper presents a combination of two models to study both the impingement and the contact and surface phenomena of rainwater on a glass window surface: a Computational Fluid Dynamics (CFD) model for the calculation of the distribution of the wind-driven rain (WDR) across the building facade and a semi-empirical droplet-behaviour model. The CFD model comprises the calculation of the wind-flow pattern, the raindrop trajectories and the specific catch ratio as a measure of the WDR falling onto different parts of the facade. The droplet-behaviour model uses the output of the CFD model to simulate the behaviour of individual raindrops on the window glass surface, including runoff, coalescence and drying. The models are applied for a small window glass surface of a two-storey building. It is shown that by far not all WDR that impinges on a glass surface runs off, due to evaporation of drops adhered to the surface. The reduction of runoff by evaporation is 26% for a typical cumuliform rain event and 4% for a typical stratiform rain event. These models can be used to provide the knowledge about WDR impact, runoff and evaporation that is needed for the performance assessment of selfcleaning glass or the study of the leaching of nanoparticles from building facades

Numerical investigation of atmospheric icing on wind turbine blades

The research work presented in this thesis aims to predict ice accretion effect on a wind turbine blade section at 80% of blade span. All simulations are obtained using FENSAP ICE, a widely used solver for aircraft in-flight icing simulations. Using low and high liquid water concentrations existed in clouds at lower altitudes, different icing events are simulated. Ice accretion predictions are computed using single-shot and multi-shot approaches. Blade surface roughness is investigated, as well as the relationships between ice mass, liquid water content, median volume diameter and temperature are predicted. To study the effect of blade design / curvature parameters on the ice formation process, ice accretion loads are predicted for all NREL airfoil families used for horizontal axis wind turbines. The effect of low and high LWC conditions on blade thickness is presented. Effects of atmospheric temperature, LWC, MVD and flow angle of attack on resulted ice shape are investigated. The degradation in aerodynamic characteristics due to ice formation is investigated at different icing conditions. The new numerical data presented in this thesis provide useful insights on ice accretion rates for wind turbines operating in cold and harsh environments

3D Weather – Towards a Real-time 3D Simulation of Localised Weather presented at EVA 2011

Weather forecasts are nearly always portrayed from either a satellite view perspective, a numerical or symbol based representation. None of these methods actually portray weather visually from the point of view of the observer, that is, they do not represent our experience of weather. This problem presents a challenge to displaying weather using real-time 3D computer graphics. 3D Weather is a proposed method to solve this problem, to create more believable representations of the weather using real weather data. By employing computer graphic techniques and computer game concepts the project intends to create a localized display of weather using mapping and weather data. Started in 2010, the project has been exploring existing techniques, scoping out the needs of stakeholders (such as the Met Office), and creating a prototype to explore the issues. The paper concludes that the quest for realism with computer graphics can be a double-edged sword. It can lead to expectations of accuracy in the data its meant to represent, which can be desired, but in the case of the weather forecast the representation is not necessary what the weather will be, its what the weather might be. The continuing project will explore the balance of issues when representing the weather for past events as well as for forecasts

Development of a tool to study aircraft trajectory optimisation in the presence of icing conditions

With the increasing demand of air travel, the impact on the environment due to aviation has shown a significant increase in recent times. As a result, there is a growing demand for new technologies and flight procedures that will enable aircraft operators to burn less fuel and reduce the adverse effect of aviation on the environment. Conventional approaches to trajectory optimisation do not take the effect of aircraft systems into account. Neglecting these effects may be inadequate, especially when one considers real aircraft operations in real weather scenarios. This research has developed a tool capable of simulating aircraft ice protection performance for trajectory optimisation, which enables the development of a decision making process dependent on weather within the flight management system, thus transforming the conventional ice protection system to a more intelligent system. Presently, thermal ice protection methods are the leading ice protection technology on most of the medium and large transport aircraft. An enhanced aircraft anti-icing model was developed based on Messinger mass and energy balance method for thermal anti-icing. The tool developed in this work can calculate the total water catch and evaluate power requirement due to icing under a wide range of meteorological conditions. The model was successfully integrated with a trajectory optimisation framework for independent assessment of fuel penalty due to icing and investigation of pollutant emissions reduction through aircraft trajectory optimisation. A case of typical departure from London Airport Heathrow was optimised for fuel burn and time. The preliminary results show that when operating in known icing condition, including icing parameters in the optimisation loop could give as much as 2.1% fuel savings

Preventing Atmospheric Icing in Aviation: Passive Repulsion of Super Cooled Water Droplets through Hydrophobic Nanocomposites

The aviation industry already consists of a complex system of strict regulations related to operation and maintenance, where severe weather conditions further challenge flight operations. Recent research has shown that most aircraft accidents are caused by icing externally, where severe icing conditions lead to the critical degradation of the aerodynamic effectiveness – increasing the stall speed. If only a thin film of ice accumulates on the airframe, it will rapidly increase the risk for a fatal accident to occur. The following thesis addresses critical icing conditions that might substantially affect the aerodynamic performance and propose an accessible method of a hydrophobic coating to mitigate the risk of ice accretion on planes. The results show that the most exposed phase within in-flight icing occurs at cruising altitude, with glaze ice accretions. A risk assessment of components suggests that the wing part has the most significant effect on aerodynamic sustainability. A further CFD analysis of the wing section of an Airbus A320neo, at cruising altitude, was simulated and compared with and without glaze ice conditions. The ice formation led to a mass of 2.3 kg after 100 seconds, while measurements determined that the drag capacity was increased significantly. The lifting capacity was virtually unaffected. Furthermore, a feasibility study has been conducted with the underlying goal of identifying the most promising of anti-icing coatings for aircraft. To date, there are no coat-ings capable of independently functioning as a passive anti-icing system. However, findings reveal two promising methods that were further carried out for testing. The preparation of a highly hydrophobic and ice phobic coating based on Zinc Stearate (ZnSt) and a curable Polydimethylsiloxane (PDMS) was carried out. Indicatively, the coating showed high water repellent and ice repellent properties by measuring the ice adhesion, which reduced the interaction between the aluminum surface and freezing water droplets by over 50%

Measured and calculated structures of a multi-layer altocumulus cloud

Spring 1998.Bibliography: leaves 130-132