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

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

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

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%

Aerosol-Cloud-Radiation Interactions in Regimes of Liquid Water Clouds

Despite large efforts and decades of research, the scientific understanding of how aerosols impact climate by modulating microphysical cloud properties is still low and associated radiative forcing estimates (RFaci ) vary with a wide spread. But since anthropogenically forced aerosol-cloud interactions (ACI) are considered to oppose parts of the global warming, it is crucial to know their contribution to the total radiative forcing in order to improve climate predictions. To obtain a better understanding and quantification of ACI and the associated radiative effect it as been suggested to use concurrent measurements and observationally constrained model simulations. In this dissertation a joint satellite-reanalysis approach is introduced, bridging the gap between climate models and satellite observations in a bottom-up approach. This methodology involves an observationally constrained aerosol model, refined and concurrent multi-component satellite retrievals, a state-of-the-art aerosol activation parameteriza- tion as well as radiative transfer model. This methodology is shown here to be useful for a quantitative as well as qualitative analysis of ACI and for estimating RFaci . As a result, a 10-year long climatology of cloud condensation nuclei (CCN) (particles from which cloud droplets form) is produced and evaluated. It is the first of its kind providing 3-D CCN concentrations of global coverage for various supersaturations and aerosol species and offering the opportunity to be used for evaluation in models and ACI studies. Further, the distribution and variability of the resulting cloud droplet numbers and their susceptibility to changes in aerosols is explored and compared to previous estimates. In this context, an analysis by cloud regime has been proven useful. Last but not least, the computation and analysis of the present-day regime-based RFaci represents the final conclusion of the bottom-up methodology. Overall, this thesis provides a comprehensive assessment of interactions and uncertainties related to aerosols, clouds and radiation in regimes of liquid water clouds and helps to improve the level of scientific understanding

Compendium of meteorology scientific issues of 1950 still outstanding

The Compendium of Meteorology was published in 1951 by the American Meteorological Society. A review was made of the Compendium of Meteorology to identify the studies and future needs which the authors expressed in their papers. The needs as seen by the authors are organized into sections and papers following the format of the Compendium of Meteorology. In some cases the needs they identified are as valid today as they were in 1951. In other cases one will easily be able to identify examples where significant progress has been made. It is left to the individual scientists and scientific program managers to assess whether significant progress has been made over the past thirty-five years on these outstanding scientific issues

Visual Simulation of Multiple Fluids in Computer Graphics: A State-of-the-Art Report

Realistic animation of various interactions between multiple fluids, possibly undergoing phase change, is a challenging task in computer graphics. The visual scope of multi-phase multi-fluid phenomena covers complex tangled surface structures and rich color variations, which can greatly enhance visual effect in graphics applications. Describing such phenomena requires more complex models to handle challenges involving the calculation of interactions, dynamics and spatial distribution of multiple phases, which are often involved and hard to obtain real-time performance. Recently, a diverse set of algorithms have been introduced to implement the complex multi-fluid phenomena based on the governing physical laws and novel discretization methods to accelerate the overall computation while ensuring numerical stability. By sorting through the target phenomena of recent research in the broad subject of multiple fluids, this state-of-the-art report summarizes recent advances on multi-fluid simulation in computer graphics

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

There is a growing demand for new technologies and ight procedures that will enable aircraft operators to burn less fuel and reduce the impacts of aviation on the environment. Conventional approaches to trajectory optimisation do not include aircraft systems in the optimisation set-up. However, the fuel penalty due to aircraft systems operation is signi cant. Thus, applying optimised trajectories which do not account for systems o -takes in real aircraft Flight Management System (FMS) will likely fail to achieve a true optimum. This is more important in real scenarios where the ambient conditions in uence the systems operation signi cantly. This research proposed an ice protection methodology which enables the development of a decision making process within the FMS dependent on weather conditions; thus transforming the conventional anti-icing method into a more intelligent system. A case of a medium size transport aircraft ight from London - Amsterdam under various levels of possible icing was studied. The results show that fuel burn due to anti-icing operation can increase up to 3.7% between climb and cruise altitudes. Up to 5.5% of this penalty can be saved using icing optimised trajectories. A 45% reduction in awakenings due to noise was achieved with 3% fuel penalty. The novelty of the study was extended using 3D optimisation to further improve ight operations. It was found that the simulation successfully changed the lateral position of the aircraft to minimise the time spent and distance covered in icing conditions. The work here presents a feasible methodology for future intelligent ice protection system (IPS) development, which incorporates intelligent operation

Molecular simulations reveal that heterogeneous ice nucleation occurs at higher temperatures in water under capillary tension

Homogeneous ice nucleation rates occur at higher temperatures when water is under tension, otherwise referred to as negative pressure. If also true for heterogeneous ice nucleation rates, then this phenomenon can result in higher heterogeneous freezing temperatures in water capillary bridges, pores, and other geometries where water is subjected to negative Laplace pressure. Using a molecular model of water freezing on a hydrophilic substrate, it is found that heterogeneous ice nucleation rates exhibit a similar temperature increase at negative pressures as homogeneous ice nucleation. For pressures ranging from from 1 atm to &minus;1000 atm, the simulations reveal that the temperature corresponding to the heterogeneous nucleation rate coefficient jhet (m&minus;2 s&minus;1) increases linearly as a function of negative pressure, with a slope that can be approximately predicted by the water density anomaly and the latent heat of fusion at atmospheric pressure. Simulations of water in capillary bridges confirm that negative Laplace pressure within the water corresponds to an increase in heterogeneous freezing temperature. The freezing temperature in the water capillary bridges increases linearly with inverse capillary height (1/h). Varying the height and width of the capillary bridge reveals the role of geometric factors in heterogeneous ice nucleation. When substrate surfaces are separated by less than approximately h = 20 Angstroms the nucleation rate is enhanced and when the width of the capillary bridge is less than approximately 30 Angstroms the nucleation rate is suppressed. Ice nucleation does not occur in the region within 10 Angstroms of the air-water interface and shows a preference for nucleation in the region just beyond 10 Angstroms. These results help unify multiple lines of experimental evidence for enhanced nucleation rates due to reduced pressure, either resulting from surface geometry (Laplace pressure) or mechanical agitation of water droplets. This concept is relevant to the phenomenon of contact nucleation and could potentially play a role in a number of different heterogeneous nucleation or secondary ice mechanisms.</p