2D Hydrodynamics of a Plate: From Creeping Flow to Transient Vortex Regimes

Based on the numerical and experimental visualization methods, the flow patterns around a uniformly moving plate located at an arbitrary angle of attack are studied. The study is based on the fundamental equations of continuity, momentum and stratifying substance transport for the cases of strong and weak stratified fluids, as well as potential and actually homogeneous ones. The visualization technique and computation codes were compiled bearing in mind conditions of internal waves, vortices, upstream, and downstream wakes registration, as well as the resolution of ligaments in the form of thin interfaces in schlieren flow images. The analysis was carried out in a unified mathematical formulation for a wide range of plate motion parameters, including slow diffusion-induced flows and fast transient vortex flows. The patterns of formation and subsequent evolution of the basic structural components, such as upstream disturbances, downstream wake, internal waves, vortices, and ligaments, are described both at start of motion and subsequent uniform movement of the plate. Calculations of forces acting on the obstacle in the flow were carried out to study effects of variations in fluid properties, flow conditions and plate parameters on the dynamic characteristics of the obstacle. The numerical and experimental results on the flow patterns around a plate are in a good agreement with each other for different flow regimes.

Implementation of computation codes in geostructural surveys to evaluate rock mass stability aimed at the protection of cultural heritage

<p>Instability of rock masses is a frequent problem in Italy, which territory is naturally predisposed to a variety of geological hazards. Therefore, issues related to the study of rock masses have always been of primary importance, since their consequences directly affect human lives and the urbanized areas, causing severe losses to society. In order to identify the areas most susceptible to gravity-related phenomena in such settings, the traditional approaches are often not sufficient, and need to be integrated by new tools and techniques aimed at properly and quantitatively describe the structural arrangement of rock masses. These include the use of close range remote sensing techniques. It is now many years that various attempts have been made to standardize processes to extract volumetric shapes from digital data, in order to individuate geometrical features in point clouds and, eventually, to identify discontinuities on rock outcrops. <br>We present an attempt to develop and experimentally implement an application of computation codes and software control via command line, to carry out geomechanical investigations on rock masses, starting from 3D surveys. The final goal is to provide reliable results on the likely instability processes in surface and underground settings, as a contribution to the mitigation of the related risks. For this aim, a novel approach is proposed: in order to combine user observation made in situ and on digital results of scanning, our attention was focused on developing non-automatic methods, which could allow, giving a tolerance angle for both dip and dip direction, the extraction of discontinuities on well-structured datasets representing point clouds. This approach could be considered a fully supervised type of classification, because the user can specify the query by placing a numerical input representing an interval of tolerance in degrees; then, it has as output a cluster of planar surfaces belonging to the given interval for each set. The code, organized in a basic software called GEODS (alpha version), which runs on Windows operating systems, also utilizes the results to represent the rocky surfaces on charts and stereographic projections, and is able to calculate standard deviation and mean values of the classified clusters. It is useful to identify the density of each identified discontinuity and to evaluate potential kinematics as well, based on geometric relationships, through analyses carried by a skilled user. This approach was tested at the Cocceio cave, in Campania, southern Italy: this site has historical importance since the Roman age. Reused during World War II, it is now part of a redevelopment project of the Phlegraean Fields, an area renowned for its natural beauty, which includes numerous archaeological sites. At the cave, with this new method, we were able to recognize an additional set, with minor frequency than the other sets, and which was not identified during previous studies. <br>As a final result, it is thus expected to contribute in an innovative way to the implementation of alternative and accurate methods in structural analysis and the geomechanical characterization of rock masses.</p>

RESIDUAL HEAT ESTIMATION OF NUCLEAR FUEL IN ENERGY WELL REACTOR

Energy Well (EW) is a concept of a small modular reactor, designed as a source of energy for places with low infrastructure. Its design combines TRISO fuel particles, graphite moderator and molten salt coolant. One of key features is that the active core is small and therefore easy to transport. Residual heat estimation of EW fuel assembly is conducted using two different computation codes, SCALE and SERPENT. The obtained residual heat power is then used as an input in TRACE model of the EW to obtain the development of residual temperature in the coolant in the core inlet and outlet and also maximum temperature on the outer side of a fuel slab. The resulting temperatures are below the operational temperature.

Strong Scaling Analysis of a Parallel, Unstructured, Implicit Solver and the Influence of the Operating System Interference

PHASTA falls under the category of high-performance scientific computation codes designed for solving partial differential equations (PDEs). Its a massively parallel unstructured, implicit solver with particular emphasis on fluid dynamics (CFD) applications. More specifically, PHASTA is a parallel, hierarchic, adaptive, stabilized, transient analysis code that effectively employs advanced anisotropic adaptive algorithms and numerical models of flow physics. In this paper, we first describe the parallelization of PHASTA's core algorithms for an implicit solve, where one of our key assumptions is that on a properly balanced supercomputer with appropriate attributes, PHASTA should continue to strongly scale on high core counts until the computational workload per core becomes insufficient and inter-processor communications start to dominate. We then present and analyze PHASTA's parallel performance across a variety of current near petascale systems, including IBM BG/L, IBM BG/P, Cray XT3, and custom Opteron based supercluster; this selection of systems with inherently different attributes covers a majority of potential candidates for upcoming petascale systems. On one hand, we achieve near perfect (linear) strong scaling out to 32,768 cores of IBM BG/L; showing that a system with desirable attributes will allow implicit solvers to strongly scale on high core counts (including petascale systems). On the contrary, we find that the relative tipping point for strong scaling fundamentally differs among current supercomputer systems. To understand the loss of scaling observed on a particular system (Opteron based supercluster) we analyze the performance and demonstrate that such a loss can be associated to an unbalance in a system attribute; specifically compute-node operating system (OS). In particular, PHASTA scales well to high core counts (up to 32,768 cores) during an implicit solve on systems with compute nodes using lightweight kernels (for example, IBM BG/L); however, we show that on a system where the compute node OS is more heavy weight (e.g., one with background processes) a loss in strong scaling is observed relatively at much fewer number of cores (4,096 cores).