Tropical cyclone rainbands can trigger meteotsunamis

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shi, L., Olabarrieta, M., Nolan, D. S., & Warner, J. C. Tropical cyclone rainbands can trigger meteotsunamis. Nature Communications, 11(1), (2020): 678, doi:10.1038/s41467-020-14423-9.Tropical cyclones are one of the most destructive natural hazards and much of the damage and casualties they cause are flood-related. Accurate characterization and prediction of total water levels during extreme storms is necessary to minimize coastal impacts. While meteotsunamis are known to influence water levels and to produce severe consequences, their impacts during tropical cyclones are underappreciated. This study demonstrates that meteotsunami waves commonly occur during tropical cyclones, and that they can contribute significantly to total water levels. We use an idealized coupled ocean–atmosphere–wave numerical model to analyze tropical cyclone-induced meteotsunami generation and propagation mechanisms. We show that the most extreme meteotsunami events are triggered by inherent features of the structure of tropical cyclones: inner and outer spiral rainbands. While outer distant spiral rainbands produce single-peak meteotsunami waves, inner spiral rainbands trigger longer lasting wave trains on the front side of the tropical cyclones.We thank all the developers of COAWST, ROMS, WRF, and SWAN models. D.N. was supported by NSF grant AGS-1654831. We would like to thank Dr. K. Bagamian for her editorial and writing suggestions. We would like to thank Dr. A. Aretxabaleta for the internal US Geological Survey internal revision and suggestions

Numerical Simulation of Cyclone Efficiency and Pressure Drop

The Department of Environment Malaysia (DOE) has been regulating particulate emission since the 1978. More stringent environmental regulations have resulted in considerable research into ways of reducing harmful and gloomy particulate emissions. Cyclones are probably the most commonly used means of separating dust from gases, controlling pollution, collecting particulate product or recovering catalyst particles from fluidised reactors. Their popularity is due to low maintenance and investment costs. Cyclone design maybe simple but models use to predict the cyclone efficiency and pressure drop are not always accurate. The objective of this study is to carry out simulation via a commercial spreadsheet, MS EXCEL and CFD code FLUENT 6.1, on cyclone design, efficiency, and pressure drop for particulate emission control. In this study, CFD code FLUENT and four cyclone collection models earlier developed by other researchers are used for prediction of cyclone efficiency. This study focuses on various operating conditions of cyclone and the simulation result is then verified via experimental data published in the literature. The model with the best prediction on experimental data is then used to evaluate the effects of cyclone configuration, dimension, and variable on its collection efficiency. The cyclone pressure drop calculations are performed using CFD and empirical models adopted from the literature. These four empirical models and CFD are compared with presented experimental data available in the literature.All the modelling and simulation of cyclone efficiency and pressure drop are proved to be satisfactory when compared with the presented experimental data. The CFD simulations and Li and Wang model predict excellently the cyclone cut-off size for all operating conditions with a deviation of 3 and 6% from the experimental data respectively. The CFD simulations also predict excellently the cyclone pressure drop under different temperature and inlet velocity with a maximum deviation of 3% from the experimental data. Specifically, results obtained from the computer modelling exercise have demonstrated that CFD and Li and Wang model is a best method of modelling cyclones collection efficiency and pressure drop. The result or finding obtained from the research work can be used to develop a cyclone with greater separation efficiency, which is capable of removing up to 99% of PM5. This cyclone can then be used for particulate pollutant control from industrial factory to the atmosphere

Optimisation and modelling of the spiral jet mill

D Eng ThesisThe spiral jet mill is a widely applied and robust apparatus for reduction of mean particle size to less than 10 microns. Despite the spiral jet mill being a well established technology, there are no proven scale up methodologies and many commercial mill designs are not optimised for energy efficiency. Within this thesis a novel analytical derivation is presented for spiral jet mill cut size as a function of micronisation settings, gas thermodynamic properties and empirically derived constants for the material and mill. The derivation is corroborated by experimental evidence for a number of products owned by GlaxoSmithKline (GSK) and previously reported data in the academic literature. This equation provides an insight into the interaction between aerodynamic particle classification and fine grinding for the spiral jet mill, and brings great advancement to the level of understanding in the academic literature on the control of particle size with a spiral jet mill. The constants within the equation can be determined empirically for a given material and mill, leading to a better prediction across a design space than standard empirical models. A scale up methodology is proposed for a high value material by using a small scale mill to determine the material specific constants of the high value material and a cheaper surrogate material to determine mill specific parameters at increased scale. In addition to a novel analytical derivation, this thesis presents the first ever Computational Fluid Dynamics (CFD) based optimisation of a combined spiral jet mill and cyclone. Some combined spiral jet mill and cyclone designs have poor cyclonic separation yields, and this thesis presents the CFD and experimental investigation which led to an optimised mill and cyclone that significantly improved yield while maintaining similarity of particle size

Sensitivity of Simulated Hurricane Eyewall Replacement Cycles to Horizontal Turbulent Mixing

Eyewall replacement cycles (ERCs) are naturally occurring phenomena in some intense tropical cyclones. The exact mechanisms of ERCs are currently not known and successful numerical simulations of ERCs are also rare. The objectives of this thesis are to 1) validate the current ERC theories for a set of numerical simulations which resolved ERC processes, 2) investigate the role of boundary layer turbulence in ERCs, and 3) propose a mechanism for ERCs. Using the Advanced Research and Weather Forecasting (WRF-ARW) model, Hurricane Danielle (2010) was simulated. The ERCs that occurred in simulated Danielle are sensitive to parameterized horizontal turbulent mixing. Five theories on the initiating mechanisms of eyewall replace cycles are discussed with respect to each of our simulations and based on the results, a new idea of how the eyewall replacement process formed in our simulations is proposed. Two sensitivity experiments are performed to test the validity of this mechanism