Numerical analysis of multiphase flows through the lattice boltzmann method

Questa tesi analizza il comportamento dei flussi multifase, nei quali ad esempio c’è la contemporanea presenza di diverse fasi fluide o di fase solida e fluida. Più specificatamente, in questo lavoro, i fluidi considerati sono fasi diverse della stessa sostanza, come ad esempio liquido e vapore. Una precisa definizione delle interazioni tra le molecole è di difficile formulazione. Ci sono molteplici fattori che sono sorgente di complessità nei flussi multifase, non solo l’interazione tra bolle/gocce/particelle immerse in un fluido, ma anche problemi fisici, come la transizione tra diversi regimi di flusso liguido-gas, o la presenza di interfacce perturbate, così come la simultanea presenza di fenomeni che si manifestano a diverse scale caratteristiche. Questa complessità rappresenta un limite piuttosto stringente all’utilizzo di metodi analitici sviluppati al fine di risolvere in forma chiusa questo tipo di problemi. Per le applicazioni più interessanti, riferiti a moderati numeri di Reynolds, manca una soluzione matematica chiusa. Dopo aver evidenziato il grande vantaggio dell’analisi numerica di flussi multifase, è utile introdurre alcune applicazioni ingegneristiche. Alcuni esempi di flussi multifase sono spray (ad esempio nei Motori a Combustione Interna), oppure flussi nei tubi, letti fluidi, colonne di distillazione, etc. In aggiunta, ci sono diversi fenomeni “naturali” che coinvolgono flussi multifase come nuvole e pioggia, impatto di gocce liquide, onde, fiumi e cascate. Ancora, come anticipato in precedenza, le scale coinvolte nei flussi multifase coprono un ampio intervallo, partendo dai micrometri (spray) fino a raggiungere scale macroscopiche (kilometri). Questo enorme intervallo non permette la definizione di un modello universale per risolvere tutte queste applicazioni. Partendo dalla semplicità dell’implementazione e maneggevolezza del metodo un sempre maggior numero di utilizzatori è stato incoraggiato ad utilizzare il Metodo Lattice Boltzmann al fine di ricostruire le equazioni fluidodinamiche. La grande diffusione è stata raggiunta soprattutto per modelli monofase. Ad ogni modo, diversi modelli sono stati definiti per questo approccio innovativo al fine di modellare le interazioni tra le diverse fasi. Il grande vantaggio nell’utilizzo di modelli multifase accoppiati con il Metodo Lattice Boltzmann è la possibilità di risolvere le equazioni di stato in ogni punto della griglia, con evidenti vantaggi intermini di accuratezza. Quindi, lo scopo di questa tesi è di analizzare ed evidenziare quali sono le potenzialità di un innovativo modello multifase per LBM. Il modello proposto, basato sulla modellazione dell’energia libera, permette di raggiungere elevati livelli del rapporto tra le densità in relazione alle formulazioni tradizionalmente adottate. I risultati ottenuti in termini di break up primario e secondario, così come di coalescenza tra due gocce saranno approfonditamente analizzate. Nella parte finale del lavoro alcuni risultati per la formulazione tri-dimensionale saranno mostrati.This thesis deals with multiphase flows, i.e. systems in which different fluid phases, or fluid and solid phases, are simultaneously present. More specifically, in this work, the fluids are different phases of the same substance, such as a liquid and its vapor. A precise definition of interparticles’ interactions is difficult to formulate as, often, whether a certain situation should be considered as a multiphase flow problem depends more on the point of view of the investigator than on its intrinsic nature. There are a lot of factors which are source of complexity in the multiphase flow phenomena; not only the interaction between bubble/droplets/particles immersed in a fluid, but also physical problems, like the transition between different liquid-gas flow regimes, or the presence of a perturbed interface, as well the simultaneous presence of phenomena occurring at different scales. This complexity represents a tough limit in the use of fully analytical methods designed in order to solve this kind of problems. For the most interesting applications, referred to moderate Reynolds numbers, a closed analytical solution is missing. After having pointed out the great advantage of multiphase flow numerical analysis, introducing some interesting engineering applications is useful. The multiphase problems, in fact, some examples are sprays (e.g. in Internal Combustion Engine -ICE-), or pipelines, fluidized bed, distillation columns, etc. Moreover there are many “Natural” phenomena which involve multiphase flows like clouds and rain, liquid droplets impingement, waves, rivers and water-falls. Again, as pointed out above, the scales involved in multiphase flows cover a complete range, starting from micro-meters (sprays) until reaching kilo-meters. This wide range does not allow defining a universal model capable to solve all these applications. Due to the simplicity of implementation and managing a lot of users have been encouraged in using the Lattice Boltzmann Method –LBM in order to recast fluid-dynamic equations. The great diffusion has been reached concerning single-phase approach. However, many techniques have been defined for this innovative approach in order to model interactions between phases. The main advantage in using multiphase models coupled with the LBM is the possibility to solve the Equation of State -EOS- in every grid-point, with apparent advantages in terms of accuracy. Thus, the aim of this work is to analyze and point out which are the capabilities for an innovative multiphase LBM approach. The proposed model, based on free energy modelling, allows to reach higher value for density ratio in comparison with standard formulations. The results obtained in terms of primary and secondary break-up, as well as coalescence between two droplets will be deeply described. In the final part of the work some results of the three-dimensional fully parallelized code will be shown

Prediction of bending wave transmission across coupled plates affected by spatial filtering and non-diffuse vibration fields

This thesis concerns models based on Statistical Energy Analysis (SEA) to predict bending wave vibration in heavyweight buildings from structure-borne sound sources such as machinery. These sources tend to inject most power in the low- and mid-frequency ranges where the walls and floors have low mode counts and low modal overlap for which calculated Coupling Loss Factors (CLFs) from semi-infinite plate theory can be in error. For machinery it is necessary to predict vibration on walls/floors that are remote from the source room. In this situation, propagation across successive structural junctions causes spatial filtering of the wave field and the assumption of a diffuse field in each plate subsystem breaks down. The predictive approach described in the European Standard EN12354 uses SEA path analysis which assumes that transmission is dominated by first-order paths. However the feasibility of extending the concept of path analysis to walls and floors of rooms that are distant from the source room(i.e. not adjacent) is unknown. These issues are addressed in the thesis. The feasibility of SEA path analysis was assessed by quantifying the total contribution to receiver subsystem energy from paths containing specified numbers of CLFs. For receiving subsystems which are attached directly to the source subsystem, the EN12354 approach was found to underestimate the energy levels. For rooms remote from the source room, path analysis was found to significantly underestimate the vibration of the walls/floors which form the receiver room. Alternative approaches to improve predictions in large heavyweight buildings were assessed through comparison with Monte-Carlo Finite Element Method (MCFEM) models which were validated on a small heavyweight building. Matrix SEA was used with CLFs calculated for L-, T- and X-junctions using analytical models for rectangular plates to try and incorporate modal features. For isolated junctions, there was good agreement with MCFEM but in large buildings. However, it was unable to predict the peaks and troughs in the vibration response to one-third octave band accuracy although it can estimate the envelope response for plates that are directly connected to the source plate. In general, matrix SEA using finite plate theory CLFs does not improve the prediction in one-third octave bands when the statistical mode count is less than unity. Ray tracing was therefore investigated which showed that the angular distribution of power incident on the plate edges differed significantly from a diffuse field. Computationally efficient ray tracing was then developed for inclusion in Advanced SEA (ASEA) models to account for indirect coupling between plate subsystems. ASEA gave significant improvements over matrix SEA when there were large numbers of structural junctions between the source and receiving plates

Bowdoin Orient v.120, no.14-25 (1991-1991)

https://digitalcommons.bowdoin.edu/bowdoinorient-1990s/1002/thumbnail.jp

2004-2005, University of Memphis bulletin

University of Memphis bulletin containing the undergraduate catalog for 2004-2005.https://digitalcommons.memphis.edu/speccoll-ua-pub-bulletins/1445/thumbnail.jp

2005-2006, University of Memphis bulletin

University of Memphis bulletin containing the undergraduate catalog for 2005-2006.https://digitalcommons.memphis.edu/speccoll-ua-pub-bulletins/1446/thumbnail.jp

Undergraduate catalog 2008-10, original

The Undergraduate Catalog for the University of Missouri Columbia has been organized to enhance readability. The initial sections are related to University-wide programs, policies and procedures. The second section provides the listing of academic offerings, organized by the academic units (also may be called colleges or schools) that offer the courses and/or the degrees (major, minor or certificate) that students seek to earn. In addition to the Table of Contents, the Faculty listing and Index at the back of the catalog are invaluable for locating a person or topic quickly. An electronic version is also on the MU web site. Graduate and professional programs (Law, Medicine and Veterinary Medicine) have separate catalogs. -- Page 11.Origina

Undergraduate catalog 2008-10, revised

The Undergraduate Catalog for the University of Missouri Columbia has been organized to enhance readability. The initial sections are related to University-wide programs, policies and procedures. The second section provides the listing of academic offerings, organized by the academic units (also may be called colleges or schools) that offer the courses and/or the degrees (major, minor or certificate) that students seek to earn. In addition to the Table of Contents, the Faculty listing and Index at the back of the catalog are invaluable for locating a person or topic quickly. An electronic version is also on the MU web site. Graduate and professional programs (Law, Medicine and Veterinary Medicine) have separate catalogs. -- Page 11.Revised May 2009."Version B.

The Long-term Role of Hydropower in Ecuador’s Power System: Assessing Climate Change and Cost Uncertainties

Hydropower is the leading source of renewable electricity generation worldwide. Traditionally, hydropower has been perceived as a cheap, reliable and a low greenhouse gas emitting energy source. However, evidence suggests that, given hydropower’s dependency on the hydrological cycle, it could be particularly vulnerable to the effects of climate change. In addition, hydropower infrastructure has shown to be prone to significant cost overruns and delays, due to the inherent complexities that accompany its deployment. Previous research has quantified these issues but little investigation has taken place to assess them in an integrated manner. The interest of this research is to assess how assumptions about climate change, policy and costs can induce shifts in generation portfolio optima, particularly of power systems that are based or plan to be based on hydropower in the long-term. For this purpose, a series of hydrological, hydropower and energy system models have been developed in order to take these factors into account, and search generation alternatives regarding technical characteristics (i.e. power system operation, energy system configuration, demand), economic specificities (i.e. technology costs, resource prices, cost risk) and geospatial factors (i.e. water resource distribution, precipitation, climate change). The proposed method is illustrated with a case study for the Republic of Ecuador until 2050, a South American country that relies heavily on hydropower and plans to continue harnessing its potential in the future. Findings have identified that hydropower will remain an important least-cost and low emitting electricity source in Ecuador’s future, however its share in the electricity generation matrix could vary greatly. Furthermore, portfolio analysis has revealed the trade-off between generation portfolio cost and risk. Suggesting that shifting away from run-ofriver hydropower, gas and oil-fired generation towards a system with larger shares of hydropower with reservoir, solar PV and geothermal energy can help hedge the power system against the uncertainties of climate change, fossil fuel price volatility and electricity infrastructure cost overruns. Failing to diversify the power system could create a lock-in to natural gas. This research adds to the literature seeking to provide insights for new hydropower developments particularly concentrated in emerging economies of South East Asia, South America and Africa