Initialization of lattice Boltzmann models with the help of the numerical Chapman-Enskog expansion

We extend the applicability of the numerical Chapman-Enskog expansion as a lifting operator for lattice Boltzmann models to map density and momentum to distribution functions. In earlier work [Vanderhoydonc et al. Multiscale Model. Simul. 10(3): 766-791, 2012] such an expansion was constructed in the context of lifting only the zeroth order velocity moment, namely the density. A lifting operator is necessary to convert information from the macroscopic to the mesoscopic scale. This operator is used for the initialization of lattice Boltzmann models. Given only density and momentum, the goal is to initialize the distribution functions of lattice Boltzmann models. For this initialization, the numerical Chapman-Enskog expansion is used in this paper.Comment: arXiv admin note: text overlap with arXiv:1108.491

High-resolution hydro-meteorological modeling of extreme weather events over complex orography areas: applications of WRF and WRF-Hydro model configurations

The main aim of this thesis is to investigate the complexity of modeling extreme hydrometeorological events in complex orography areas, starting from the atmospheric processes to terrestrial hydrology at different spatial and temporal scales. This work intends also to compare the classical stand alone meteorological approach with a fully coupled representation of the water cycle, and to explore possible improvements in terms of precipitation edictability of extreme flooding events in both of these configurations

A Lifting Relation from Macroscopic Variables to Mesoscopic Variables in Lattice Boltzmann Method: Derivation, Numerical Assessments and Coupling Computations Validation

In this paper, analytic relations between the macroscopic variables and the mesoscopic variables are derived for lattice Boltzmann methods (LBM). The analytic relations are achieved by two different methods for the exchange from velocity fields of finite-type methods to the single particle distribution functions of LBM. The numerical errors of reconstructing the single particle distribution functions and the non-equilibrium distribution function by macroscopic fields are investigated. Results show that their accuracy is better than the existing ones. The proposed reconstruction operator has been used to implement the coupling computations of LBM and macro-numerical methods of FVM. The lid-driven cavity flow is chosen to carry out the coupling computations based on the numerical strategies of domain decomposition methods (DDM). The numerical results show that the proposed lifting relations are accurate and robust

Plasticity without phenomenology: a first step

A novel, concurrent multiscale approach to meso/macroscale plasticity is demonstrated. It utilizes a carefully designed coupling of a partial differential equation (pde) based theory of dislocation mediated crystal plasticity with time-averaged inputs from microscopic Dislocation Dynamics (DD), adapting a state-of-the-art mathematical coarse-graining scheme. The stress-strain response of mesoscopic samples at realistic, slow, loading rates up to appreciable values of strain is obtained, with significant speed-up in compute time compared to conventional DD. Effects of crystal orientation, loading rate, and the ratio of the initial mobile to sessile dislocation density on the macroscopic response, for both load and displacement controlled simulations are demonstrated. These results are obtained without using any phenomenological constitutive assumption, except for thermal activation which is not a part of microscopic DD. The results also demonstrate the effect of the internal stresses on the collective behavior of dislocations, manifesting, in a set of examples, as a Stage I to Stage II hardening transition

Processes driving shallow convective development and their interactions with aerosols: aerosol transport and aerosol breezes

Includes bibliographical references.2022 Fall.In this two-part thesis we investigate the development of tropical shallow convective clouds (i.e. shallow cumulus and cumulus congestus) and their interactions with the aerosol environment using idealized large-eddy simulations (LES). Although much about shallow convection is well-understood, we specifically focus on three facets of shallow convection that remain understudied: (1) the factors governing the development of congestus extending above the 0ºC stable layer; (2) the detrainment of aerosol particles and water vapor from congestus clouds into the mid-troposphere; and (3) the impacts of strong horizontal gradients in aerosol concentration on mesoscale circulations. Part one of this study explores environmental controls on congestus development and the implications of that development on aerosol lofting and transport. Congestus is the middle mode of tropical convection, with cloud tops around or exceeding the 0ºC level (~5km AGL). While some congestus are terminal, meaning capped by the 0ºC stable layer, others are transient and may develop into deep convection. Although this distinction impacts the congestus-to-deep convection transition and the convective transport of water vapor and aerosols into the mid-troposphere, there is still much to be understood about the processes causing congestus to overshoot the 0℃ level and continue growing. We find that terminal and transient congestus updrafts are characterized by a similar overturning circulation between the updraft and subsiding shell. However, transient congestus have stronger updrafts, and importantly, the downward branch of their corresponding circulations is constrained by the 0ºC level. Our findings support previous results suggesting buoyancy as a control on congestus height, and we specifically demonstrate that congestus developing in more humid midlevel environments are more likely to be transient. We additionally determine that terminal congestus regenerate more aerosol via evaporation along their cloud edges, while transient congestus create stronger midlevel detrainment layers of aerosol and water vapor due to the trapping of the regenerated aerosol above the 0ºC level. Such midlevel detrainment layers are important for the formation of altocumulus clouds. Part two of this study introduces and explores the concept of an "aerosol breeze", a thermally-driven circulation resulting from mesoscale gradients in aerosol loadings. We call the resulting circulation an aerosol breeze so as to be analogous to well-documented circulations associated with heterogenous surfaces, like sea breezes. The aerosol-induced circulation sets up a gradient in convection and precipitation that is opposite in direction to that of the aerosol gradient. Clouds in the presence of an aerosol gradient precipitate sooner and more intensely than those in the same integrated aerosol loading distributed horizontally homogeneously. These results suggest unrepresented sub-grid scale heterogeneity in aerosol emissions may lead to biases in simulated cloudiness and precipitation. We also present two observational case studies of aerosol breezes that are similar to our model results in scale and cloud distribution. Further study of the aerosol breeze phenomena is warranted, especially in regions where strong aerosol gradients may be expected, such as along the edges of wildfire plumes or urbanized regions

Waves and vortices in the inverse cascade regime of stratified turbulence with or without rotation

We study the partition of energy between waves and vortices in stratified turbulence, with or without rotation, for a variety of parameters, focusing on the behavior of the waves and vortices in the inverse cascade of energy towards the large scales. To this end, we use direct numerical simulations in a cubic box at a Reynolds number Re=1000, with the ratio between the Brunt-V\"ais\"al\"a frequency N and the inertial frequency f varying from 1/4 to 20, together with a purely stratified run. The Froude number, measuring the strength of the stratification, varies within the range 0.02 < Fr < 0.32. We find that the inverse cascade is dominated by the slow quasi-geostrophic modes. Their energy spectra and fluxes exhibit characteristics of an inverse cascade, even though their energy is not conserved. Surprisingly, the slow vortices still dominate when the ratio N/f increases, also in the stratified case, although less and less so. However, when N/f increases, the inverse cascade of the slow modes becomes weaker and weaker, and it vanishes in the purely stratified case. We discuss how the disappearance of the inverse cascade of energy with increasing N/f can be interpreted in terms of the waves and vortices, and identify three major effects that can explain this transition based on inviscid invariants arguments

Robust aircraft trajectory planning under uncertain convective environments with optimal control and rapidly developing thunderstorms

Convective weather, and thunderstorm development in particular, represents a major source of disruption, delays and safety hazards in the Air Traffic Management system. Thunderstorms are challenging to forecast and evolve on relatively rapid timescales; therefore, aircraft trajectory planning tools need to consider the uncertainty in the forecasted evolution of these convective phenomena. In this work, we use data from a satellite-based product, Rapidly Developing Thunderstorms, to estimate a model of the uncertain evolution of thunderstorms. We then introduce a methodology based on numerical optimal control to generate avoidance trajectories under uncertain convective weather evolution. We design a randomized procedure to initialize the optimal control problem, explore the different resulting local optima, and identify the best trajectory. Finally, we demonstrate the proposed methodology on a realistic test scenario, employing actual forecast data and an aircraft performance model.This work is supported by the Spanish Government through Project entitled Analysis and optimisation of aircraft trajectories under the effects of meteorological uncertainty (TRA2014-58413-C2-2-R)12; this project has been funded under R&D&I actions of Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad (call 2014).Publicad

Impact of Rainfall Assimilation on High-Resolution Hydrometeorological Forecasts over Liguria, Italy

Abstract The autumn of 2014 was characterized by a number of severe weather episodes over Liguria (northern Italy) associated with floods and remarkable damage. This period is selected as a test bed to evaluate the performance of a rainfall assimilation scheme based on the nudging of humidity profiles and applied to a convection-permitting meteorological model at high resolution. The impact of the scheme is assessed in terms of quantitative precipitation forecast (QPF) applying an object-oriented verification methodology that evaluates the structure, amplitude, and location (SAL) of the precipitation field, but also in terms of hydrological discharge prediction. To attain this aim, the meteorological model is coupled with the operational hydrological forecasting chain of the Ligurian Hydrometeorological Functional Centre, and the whole system is implemented taking operational requirements into account. The impact of rainfall data assimilation is large during the assimilation period and still relevant in the following 3 h of the free forecasts, but hardly lasts more than 6 h. However, this can improve the hydrological predictions. Moreover, the impact of the assimilation is dependent on the environment characteristics, being more effective when nonequilibrium convection dominates, and thus an accurate prediction of the local triggering for the development of the precipitation system is required