libcloudph++ 0.2: single-moment bulk, double-moment bulk, and particle-based warm-rain microphysics library in C++

This paper introduces a library of algorithms for representing cloud microphysics in numerical models. The library is written in C++, hence the name libcloudph++. In the current release, the library covers three warm-rain schemes: the single- and double-moment bulk schemes, and the particle-based scheme with Monte-Carlo coalescence. The three schemes are intended for modelling frameworks of different dimensionality and complexity ranging from parcel models to multi-dimensional cloud-resolving (e.g. large-eddy) simulations. A two-dimensional prescribed-flow framework is used in example simulations presented in the paper with the aim of highlighting the library features. The libcloudph++ and all its mandatory dependencies are free and open-source software. The Boost.units library is used for zero-overhead dimensional analysis of the code at compile time. The particle-based scheme is implemented using the Thrust library that allows to leverage the power of graphics processing units (GPU), retaining the possibility to compile the unchanged code for execution on single or multiple standard processors (CPUs). The paper includes complete description of the programming interface (API) of the library and a performance analysis including comparison of GPU and CPU setups.Comment: The library description has been updated to the new library API (i.e. v0.1 -> v0.2 update). The key difference is that the model state variables are now mixing ratios as opposed to densities. The particle-based scheme was supplemented with the "particle recycling" process. Numerous editorial corrections were mad

A novel approach for modeling bubbling gas–solid fluidized beds

A phenomenological discrete bubble model is proposed to help in the design and dynamic diagnosis of bubbling fluidized beds. An activation region mechanism is presented for bubble formation, making it possible to model large beds in a timely manner. The bubbles are modeled as spherical-cap discrete elements that rise through the emulsion phase that is considered as a continuum. The model accounts for the simultaneous interaction of neighboring bubbles by including the trailing effects due to the wake acceleration force. The coalescence process is not irreversible and therefore, the coalescing bubble pair is free to interact with other rising bubbles originating the splitting phenomena. To validate the model, the simulated dynamics are compared with both experimental and literature data. Time, frequency, and state space analysis are complementarily used with a multiresolution approach based on the empirical method of decomposition to explore the different dynamic scales appearing in both the simulated time series and those obtained from experimental runs. It is concluded that the bubble dynamics interactions play the main role as the driver of the resulting bed dynamics, matching the main features of measured bubble dynamics. Exploding bubble phenomena have been identified by establishing a direct relation between the bubble generation, interaction and eruption, and the measured signalsProjects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660)Publicad

HPC-enabling technologies for high-fidelity combustion simulations

With the increase in computational power in the last decade and the forthcoming Exascale supercomputers, a new horizon in computational modelling and simulation is envisioned in combustion science. Considering the multiscale and multiphysics characteristics of turbulent reacting flows, combustion simulations are considered as one of the most computationally demanding applications running on cutting-edge supercomputers. Exascale computing opens new frontiers for the simulation of combustion systems as more realistic conditions can be achieved with high-fidelity methods. However, an efficient use of these computing architectures requires methodologies that can exploit all levels of parallelism. The efficient utilization of the next generation of supercomputers needs to be considered from a global perspective, that is, involving physical modelling and numerical methods with methodologies based on High-Performance Computing (HPC) and hardware architectures. This review introduces recent developments in numerical methods for large-eddy simulations (LES) and direct-numerical simulations (DNS) to simulate combustion systems, with focus on the computational performance and algorithmic capabilities. Due to the broad scope, a first section is devoted to describe the fundamentals of turbulent combustion, which is followed by a general description of state-of-the-art computational strategies for solving these problems. These applications require advanced HPC approaches to exploit modern supercomputers, which is addressed in the third section. The increasing complexity of new computing architectures, with tightly coupled CPUs and GPUs, as well as high levels of parallelism, requires new parallel models and algorithms exposing the required level of concurrency. Advances in terms of dynamic load balancing, vectorization, GPU acceleration and mesh adaptation have permitted to achieve highly-efficient combustion simulations with data-driven methods in HPC environments. Therefore, dedicated sections covering the use of high-order methods for reacting flows, integration of detailed chemistry and two-phase flows are addressed. Final remarks and directions of future work are given at the end. }The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the CoEC project, grant agreement No. 952181 and the CoE RAISE project grant agreement no. 951733.Peer ReviewedPostprint (published version

Multiscale molecular dynamics/hydrodynamics implementation of two dimensional “Mercedes Benz” water model

A multiscale Molecular Dynamics/Hydrodynamics implementation of the 2D Mercedes Benz (MB or BN2D) [1] water model is developed and investigated. The concept and the governing equations of multiscale coupling together with the results of the two-way coupling implementation are reported. The sensitivity of the multiscale model for obtaining macroscopic and microscopic parameters of the system, such as macroscopic density and velocity fluctuations, radial distribution and velocity autocorrelation functions of MB particles, is evaluated. Critical issues for extending the current model to large systems are discussed

Parallel Lagrangian particle transport : application to respiratory system airways

This thesis is focused on particle transport in the context of high computing performance (HPC) in its widest range, from the numerical modeling to the physics involved, including its parallelization and post-process. The main goal is to obtain a general framework that enables understanding all the requirements and characteristics of particle transport using the Lagrangian frame of reference. Although the idea is to provide a suitable model for any engineering application that involves particle transport simulation, this thesis uses the respiratory system framework. This means that all the simulations are focused on this topic, including the benchmarks for testing, verifying and optimizing the results. Other applications, such as combustion, ocean residuals, or automotive, have also been simulated by other researchers using the same numerical model proposed here. However, they have not been included here in the interest of allowing the project to advance in a specific direction, and facilitate the structure and comprehension of this work. Human airways and respiratory system simulations are of special interest for medical purposes. Indeed, human airways can be significantly different in every individual. This complicates the study of drug delivery efficiency, deposition of polluted particles, etc., using classic in-vivo or in-vitro techniques. In other words, flow and deposition results may vary depending on the geometry of the patient and simulations allow customized studies using specific geometries. With the help of the new computational techniques, in the near future it may be possible to optimize nasal drugs delivery, surgery or other medical studies for each individual patient though a more personalized medicine. In summary, this thesis prioritizes numerical modeling, wide usability, performance, parallelization, and the study of the physics that affects particle transport. In addition, the simulation of the respiratory system should carry out interesting biological and medical results. However, the interpretation of these results will be only done from a pure numerical point of view.Aquesta tesi se centra en el transport de partícules dins el context de la computació d'alt rendiment (HPC), en el seu ventall més ampli; des del model numèric fins a la física involucrada, incloent-hi la part de paral·lelització del codi i de post-procés. L'objectiu principal és obtenir un esquema general que permeti entendre tant els requeriments com les característiques del transport de partícules fent servir el marc de referència Lagrangià. Encara que la idea sigui definir un model capaç¸ de simular qualsevol aplicació en el camp de l'enginyeria que involucri el transport de partícules, aquesta tesi utilitza el sistema respiratori com a temàtica de referència. Això significa que totes les simulacions estan emmarcades en aquest camp d'estudi, incloent-hi els tests de referència, verificacions i optimitzacions de resultats. L'estudi d'altres aplicacions, com ara la combustió, els residus oceànics, l'automoció o l'aeronàutica també han estat dutes a terme per altres investigadors utilitzant el mateix model numèric proposat aquí. Tot i així, aquests resultats no han estat inclosos en aquesta tesi per simplificar-la i avançar en una sola direcció; facilitant així l'estructura i millor comprensió d'aquest treball. Pel que fa al sistema respiratori humà i les seves simulacions, tenen especial interès per a propòsits mèdics. Particularment, la geometria dels conductes respiratoris pot variar de manera considerable en cada persona. Això complica l'estudi en aspectes com el subministrament de medicaments o la deposició de partícules contaminants, per exemple, utilitzant les tècniques clàssiques de laboratori (in-vivo o in-vitro). En altres paraules, tant el flux com la deposició poden canviar en funció de la geometria del pacient i aquí és on les simulacions permeten estudis adaptats a geometries concretes. Gràcies a les noves tècniques de computació, en un futur proper és probable que puguem optimitzar el subministrament de medicaments per via nasal, la cirurgia o altres estudis mèdics per a cada pacient mitjançant una medicina més personalitzada. En resum, aquesta tesi prioritza el model numèric, l'amplitud d'usos, el rendiment, la paral·lelització i l'estudi de la física que afecta directament a les partícules. A més, el fet de basar les nostres simulacions en el sistema respiratori dota aquesta tesi d'un interès biològic i mèdic pel que fa als resultats

On the propagation and multiple reflections of a blast wave travelling through a dusty gas in a closed box

This paper concerns the propagation of shock waves in an enclosure filled with dusty gas. The main motivation for this problem is to probe the effect on such dynamics of solid particles dispersed in the fluid medium. This subject, which has attracted so much attention over recent years given its important implications in the study of the structural stability of systems exposed to high-energy internal detonations, is approached here in the framework of a hybrid numerical two-way coupled Eulerian-Lagrangian methodology. In particular, insights are sought by considering a relatively simple archetypal setting corresponding to a shock wave originating from a small spherical region initialized on the basis of available analytic solutions. The response of the system is explored numerically with respect to several parameters, including the blast intensity (via the related value of the initial shock Mach number), the solid mass fraction (mass load), and the particle size (Stokes number). Results are presented in terms of pressure-load diagrams. Beyond practical applications, it is shown that a kaleidoscope of fascinating patterns is produced by the “triadic” relationships among multiple shock reflections events and particle-fluid and particle-wall interaction dynamics. These would be of great interest to researchers and scientists interested in fundamental problems relating to the general theory of pattern formation in complex nonlinear multiphase systems