Development of a high-order parallel solver for direct and large eddy simulations of turbulent flows

Turbulence is inherent in fluid dynamics, in that laminar flows are rather the exception than the rule, hence the longstanding interest in the subject, both within the academic community and the industrial R&D laboratories. Since 1883, much progress has been made, and statistics applied to turbulence have provided understanding of the scaling laws which are peculiar to several model flows, whereas experiments have given insight on the structure of real-world flows, but, soon enough, numerical approaches to the matter have become the most promising ones, since they lay the ground for the solution of high Reynolds number unsteady Navier-Stokes equations by means of computer systems. Nevertheless, despite the exponential rise in computational capability over the last few decades, the more computer technology advances, the higher the Reynolds number sought for test-cases of industrial interest: there is a natural tendency to perform simulations as large as possible, a habit that leaves no room for wasting resources. Indeed, as the scale separation grows with Re, the reduction of wall clock times for a high-fidelity solution of desired accuracy becomes increasingly important. To achieve this task, a CFD solver should rely on the use of appropriate physical models, consistent numerical methods to discretize the equations, accurate non-dissipative numerical schemes, efficient algorithms to solve the numerics, and fast routines implementing those algorithms. Two archetypal approaches to CFD are direct and large-eddy simulation (DNS and LES respectively), which profoundly differ in several aspects but are both “eddy-resolving” methods, meant to resolve the structures of the flow-field with the highest possible accuracy and putting in as little spurious dissipation as possible. These two requirements of accurate resolution of scales, and energy conservation, should be addressed by any numerical method, since they are essential to many real-world fluid flows of industrial interest. As a consequence, high order numerical schemes, and compact schemes among them, have received much consideration, since they address both goals, at the cost of a lower ease of application of the boundary condition, and a higher computational cost. The latter problem is tackled with parallel computing, which also allows to take advantage of the currently available computer power at the best possible extent. The research activity conducted by the present author has concerned the development, from scratch, of a three-dimensional, unsteady, incompressible Navier-Stokes parallel solver, which uses an advanced algorithm for the process-wise solution of the linear systems arising from the application of high order compact finite difference schemes, and hinges upon a three-dimensional decomposition of the cartesian computational space. The code is written in modern Fortran 2003 — plus a few features which are unique to the 2008 standard — and is parallelized through the use of MPI 3.1 standard’s advanced routines, as implemented by the OpenMPI library project. The coding was carried out with the objective of creating an original CFD high-order parallel solver which is maintainable and extendable, of course within a well-defined range of possibilities. With this main priority being outlined, particular attention was paid to several key concepts: modularity and readability of the source code and, in turn, its reusability; ease of implementation of virtually any new explicit or implicit finite difference scheme; modern programming style and avoidance of deprecated old legacy Fortran constructs and features, so that the world wide web is a reliable and active means to the quick solution of coding problems arising from the implementation of new modules in the code; last but not least, thorough comments, especially in critical sections of the code, explaining motives and possible expected weak links. Design, production, and documentation of a program from scratch is almost never complete. This is certainly true for the present effort. The method and the code are verified against the full three-dimensional Lid-Driven Cavity and Taylor-Green Vortex flows. The latter test is used also for the assessment of scalability and parallel efficiency

Light Steel-frame Walls: Thermal Insulation Performances and Thermal Bridges

Abstract This paper deals with the evaluation of thermal insulation performance of metal framed lightweight walls. This technology, more and more popular also in Italy, offers interesting advantages, but available commercial documentation lacks in reliable information about the real thermal insulation performance of the whole building envelope taking into account all the details and related thermal bridges. In other countries the available knowledge has been completed after long time and the recent growth of insulation performances requires something more than a simple Italian translation. In this paper the main envelope solutions are identified. The thermal transmittance has been calculated using a specialized freeware FEM application (THERM [1]) and the results checked with a commercial HAM application (WUFI [2]). The existing simplified methods have been extended in order to take into account also the most recent solutions proposed and realized, for a simple assessment of the real (corrected) avera ge thermal transmittance, far from singular points. Finally the main thermal bridges have been analyzed, optimized and used to calculate the average thermal transmittance of a standard facade module comparing it with the non-corrected U-value

Reflecting on the architecture curriculum through a survey on career switching

Due to the deteriorating investment environment, many real-estate companies in China have started transferring their business out of the construction industry. This leads to the shrinkage of the design market and also architects’ salary. A great number of architects have switched career to maintain the same living quality as before. Meanwhile, architectural education in China is not able to integrate itself with emerging science and technologies, losing possibilities to explore new employment channels for its graduates. There is a huge gap between qualities needed in the current or future labour market and the architectural education in schools. An online survey was conducted to investigate the current state of architects’ career shifting, trying to expose the problem mentioned above. In the second part of this paper, education missions from 50 universities are analysed and detailed education curriculums from three top universities are scrutinised. At the end, the education boundary is suggested to be reconstructed from three aspects: integrating the emerging technologies; reducing unnecessary content; and training in self-learning skills

The role of Life Cycle Assessment (LCA) and energy efficiency optimization during the early stage of building design

The environmental impact of buildings could not be minimized only by optimizing the operational energy since the reduction of operational energy frequently consumes more embodied energy due to the increase of materials and systems used for energy efficiency. Meanwhile, although LCA has been widely used to evaluate the environmental footprint, few studies explored its role in the early building design stage during which majority of the prominent decisions actually already have been made. This paper tries to offer a roadmap by incorporating LCA with energy optimization during the early design phase, to make LCA a more useful guidance tool for improving the design sustainability rather than a method only for the final verification. The workflow of integrating these two approaches is proposed. Several mainstream LCA software are compared and simplified LCA approaches are introduced for the implementation. In the same time, limitations related to this integrative work are also pointed out. For instance, the nature of design is a sequential processing work which fights against the demand of simulation software

EVALUATION OF MEASUREMENT UNCERTAINTIES IN THE ASSESSMENT OF THE NOISE IMPACT OF SHIPS

Measurement operations are all inevitably affected by uncertainty, that is defined as the "degree of uncertainty" with which the measurement process obtains the result. It produces a range of values in which the true value of the measurand is present with a certain probability. In the specific case of the evaluation of the acoustic emissions associated with ships, this degree of uncertainty is referable to several causes, better understandable if the measurement procedures indi cated by the reference standards are described (for example ASA (Acoustical Society of America) S12.64-2009/PART 1), adopted for all types of ship (with no limitation in size) that transits at a speed not exceeding 50 kn in deep water. The standard offers three degrees of measurement (A, B or C), which differ in terms of uncertainty, complexity and repeatability. In general, information is given on the characteristics of the instru ments, signal processing and positioning of hydrophones. The standard is valid only in deep water and this represents its main limit: in the case, for example, of very large ships it is difficult to reach the great depths with the instruments. From the analysis of the prescriptions, it clearly follows that noise measurements in water are intrin sically affected by measurement errors that can be reported to the following three macro-types: 1. Error due to the degree of precision of the measurement chain 2. Error due to relative positioning between source and receivers 3. Error due to the characteristics of the measurement environment The 28th International Congress on Sound and Vibration (ICSV28), 24-28 July 2022 2 In the present work, all these possible sources of error have been evaluated on the basis of numerical simulation models whose results have been validated by experimental tests at sea, to arrive at the defi nition of a procedure for estimating the overall error inherent in the measurement and thus defining procedures for the control of the same

L’espace politique virtuel avant et après la chute de Moubarak : une critique des réseaux sociaux digitaux en Egypte

En intégrant les théories critiques des médias avec une approche sociologico-ethnographique, cet article revient sur les dynamiques de la sphère virtuelle de l’activisme politique égyptien, avant et après la chute de Moubarak. La thèse que l’on souhaite démontrer à travers cette analyse se base en apparence sur un paradoxe : d’une part, les réseaux digitaux des activistes ne constituent pas un espace égalitaire et horizontal, mais sont plutôt caractérisés par des hiérarchies de visibilité et de pouvoir qui tendent à reproduire celles existantes dans la société. D’autre part, c’est précisément ce « manque de démocratie » qui facilite l’instrumentalisation politique des nouveaux médias par des groupes d’activistes, dans le cadre de la contestation contre le régime au pouvoir. L’organisation des réseaux du Net permet de créer un « environnement social » capable de filtrer les contenus qui circulent sur la Toile, de les placer dans un contexte et de leur donner de la visibilité. Cela permet également de produire des narratives révolutionnaires cohérentes et capables d’induire de nouvelles formes d’engagement politique. La deuxième partie de l’article est consacrée à l’évolution de la sphère publique en réseau après la chute de Moubarak. Après 2012, internet ne semble plus être un « médium tactique » aussi efficace qu’auparavant. Les changements relatifs au contexte politique, aux dynamiques propres à la Toile et aux pratiques qui la caractérisent sont autant d’éléments ayant contribué à affaiblir la capacité d’usage des nouveaux médias comme instruments au service de la politique de la dissension.Integrating critical media theory with a sociological-ethnographic approach, the article examines the dynamics of the political virtual sphere in Egypt before and after the fall of Mubarak. The thesis that the author aims to demonstrate is based on an apparent paradox. On the one hand, the activists’ digital networks are not an egalitarian and horizontal space, as they would be portrayed according to the myth of the « intrinsically democratic » internet. On the contrary, they are characterized by hierarchies of visibility and power that tend to reproduce offline inequalities. On the other hand, it is this very « lack of democracy » within the networks that facilitates the political use of new media to express dissent against the regime. The organization of the networks enables the shaping of a « social environment » capable of filtering and contextualizing the content circulating on the web. Ultimately, it enables groups to produce coherent revolutionary narratives that pave the way for new forms of political engagement. A second part of the article is dedicated to analysing the evolution of the networked public sphere after Mubarak’s fall. After 2012, the internet has in part lost its efficacy as a « tactical medium ». The changes in the political context, as well as the changing dynamics internal to the virtual sphere, contribute to weakening the possibility to use new media as tools in the context of the politics of dissent

Introduction: The hybrid system of Egypt and “cultural chaos”

In the last few years the media landscape in the Arab world has undergone profound changes. The revolts of 2011 accelerated some transformations, and on other occasions changed their course. Some of the processes are of global importance, such as the spread of digital technologies and of social networks, the growing integration between old and new media, the emergence of a social and political sphere based on greater connectivity, and the synergy between street movements and the internet. Oth..

Introduction : Le système hybride égyptien et le « chaos culturel »

Le paysage médiatique arabe a subi ces dernières années de profondes transformations. Les révoltes de 2011 ont parfois contribué à accélérer ou à modifier ce processus. Certaines de ces transformations ont lieu à l’échelle mondiale, telles que la diffusion accrue des technologies digitales et des social network, l’intégration croissante entre les anciens et les nouveaux médias, l’affirmation d’une sphère sociale et politique basée sur une connectivité plus importante, et enfin, la synergie en..

Introduction : Le système hybride égyptien et le « chaos culturel »

Le paysage médiatique arabe a subi ces dernières années de profondes transformations. Les révoltes de 2011 ont parfois contribué à accélérer ou à modifier ce processus. Certaines de ces transformations ont lieu à l’échelle mondiale, telles que la diffusion accrue des technologies digitales et des social network, l’intégration croissante entre les anciens et les nouveaux médias, l’affirmation d’une sphère sociale et politique basée sur une connectivité plus importante, et enfin, la synergie en..

Inherent electronic trap states in TiO2 nanocrystals: effect of saturation and sintering

We report a quantum mechanical investigation on the nature of electronic trap states in realistic models of individual and sintered anatase TiO2 nanocrystals (NCs) of ca. 3 nm diameter. We find unoccupied electronic states of lowest energy to be localized within the central part of the NCs, and to originate from under-coordinated surface Ti atoms lying mainly at the edges between the (100) and (101) facets. These localized states are found at about 0.3–0.4 eV below the fully delocalized conduction band states, in good agreement with both electrochemical and spectro-electrochemical results. The overall DensityOf-States (DOS) below the conduction band (CB) can be accurately fitted to an exponential distribution of states, in agreement with capacitance data. Water molecules adsorbed on the NC surface raise the energy and reduce the number of localized states, thus modifying the DOS. As a possible origin of additional trap states, we further investigated the oriented attachment of two TiO2 NCs at various possible interfaces. For the considered models, we found only minor differences between the DOS of two interacting NCs and those of the individual constituent NCs. Our results point at the presence of inherent trap states even in perfectly stoichiometric and crystalline TiO2 NCs due to the unavoidable presence of under-coordinated surface Ti(IV) ions at the (100) facets