Analysis of the flow in grooved pumps with specified pressure boundary conditions

In this study the numerical method is employed to examine the flow in pumps with spiral grooves. A methodology suitable for the use of unstructured grids is developed. In order to have the greatest feasibility, the governing equations are formulated in such a manner that the grids are allowed to rotate with the rotor. Different from common practices, pressures are specified on the inlet and the outlet boundaries. Therefore, special treatments are required to calculate the mass flow rate and the inlet and outlet velocities. The methodology developed here is assessed via comparison with existing measurements and good agreement is obtained. Examination of pump parameters reveals that in order to obtain maximum flow rate, both the spiral angle and the groove height need to be carefully determined. The force balance over the entire flow channel shows that for a fixed pressure rise across the pump, the pressure difference between side walls is proportional to tangent of the spiral angle and the groove width, but inversely proportional to the groove height and the rotor length. These relationships can roughly be seen in the calculated results.     

MaterialVis: Material visualization tool using direct volume and surface rendering techniques

Visualization of the materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called MaterialVis. Unlike the existing tools, MaterialVis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. MaterialVis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, MaterialVis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography.     

Robust and accurate viscous discretization via upwind scheme – I: Basic principle

In this paper, we introduce a general principle for constructing robust and accurate viscous discretization, which is applicable to various discretization methods, including finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. The principle is based on a hyperbolic model for the viscous term. It is to discretize the hyperbolic system by an advection scheme, and then derive a viscous discretization from the result. A distinguished feature of the proposed principle is that it automatically introduces a damping term into the resulting viscous scheme, which is essential for effective high-frequency error damping and, in some cases, for consistency also. In this paper, we demonstrate the general principle for the diffusion equation on uniform grids in one dimension and unstructured grids in two dimensions, for node/cell-centered finite-volume, residual-distribution, discontinuous-Galerkin, and spectral-volume methods. Numerical results are presented to verify the accuracy of the derived diffusion schemes and to illustrate the importance of the damping term for highly-skewed typical viscous grids.     

TRANSPORE : A GENERIC HEAT AND MASS TRANSFER COMPUTATIONAL MODEL FOR UNDERSTANDING AND VISUALISING THE DRYING OF POROUS MEDIA

ABSTRACT

In this work a sophisticated numerical model is presented that describes the drying of porous media. This model, which is known as TransPore, has evolved over the years through the direct inputs of both authors. Nowadays, TransPore can be used to analyse the drying of media that are of completely arbitrary shape and size, under a variety of drying conditions. The engine of the computational model uses a number of state-of-the-art numerical methods that ensure the simulation results describe the particular drying process accurately, whilst guaranteeing the most efficient and effective usage of computer resources. For example, the numerical discretisation method is based on a completely conservative hybrid finite element control volume technique that uses a finite element mesh for its background gradient interpolation. Furthermore, flux limiting is used to reduce numerical dispersion in the drying kinetics and the generated non-linear system is resolved using the full Newton method for the outer iteration coupled together with a preconditioned conjugate gradient technique for the inner iteration. A graphical interface has been linked to the model to enable online visualisation of the drying process. The mathematical model allows both homogeneous and heterogeneous porous media to be simulated. The resultant software is an extremely powerful and effective tool for investigating existing dryer designs and for proposing new and innovative drying schedules that provide optimal drying quality in minimal drying time.     

An optimized GPU implementation of a 2D free surface simulation model on unstructured meshes

This work is related with the implementation of a finite volume method to solve the 2D Shallow Water Equations on Graphic Processing Units (GPU). The strategy is fully oriented to work efficiently with unstructured meshes which are widely used in many fields of Engineering. Due to the design of the GPU cards, structured meshes are better suited to work with than unstructured meshes. In order to overcome this situation, some strategies are proposed and analyzed in terms of computational gain, by means of introducing certain ordering on the unstructured meshes. The necessity of performing the simulations using unstructured instead of structured meshes is also justified by means of some test cases with analytical solution.     

Development of discrete ordinates code supporting unstructured tetrahedral mesh and applied in neutronics analysis for the Korea Helium Cooled Ceramic Reflector Test Blanket Module

The discrete ordinates code under development by KAERI uses an unstructured tetrahedral mesh, and thus it can be applied to solve the radiation transport in a complicated geometry. In addition, the geometry modeling process has become much easier because computational tetrahedral meshes are generated based on the CAD file by Gmsh.As our first phase of applying the code to a TBM neutronics analysis, the neutron flux distribution in the Korea HCCR TBM is compared with that of MCNPX, and visualized in a three-dimensional system domain. Visualization of the fluxes and associated reaction rates in the whole system with a single run is one of the merits of a deterministic method and is very useful for checking hot spots.     

On robust stabilization regions of unstructured uncertainties

Relations on the robust stabilization regions of four main forms of unstructured uncertainties are investigated. The robust stabilization regions represented by three other perturbations are derived from coprime factor perturbation and additive perturbation, respectively. Furthermore, it is shown that the normalized coprime factor H^∞ robust controller can also be explained in additive and multiplicative perturbations.     

An effective architecture for Decision Support Systems

Decision Support Systems (DSS) are, by nature, general- purpose systems, because they must support a variety of managers who have different decision styles and different problems. However, it seems that no effective general-purpose DSS have yet come into existence, although the components of DSS such as data base technology, modeling techniques, inexpensive graphic display etc., have progressed to the point where we should now be able to build effective DSS.This shortcoming seems to result from the following fact: Research on decision support has focused on data enlargement and model refinement, however, little attention has been paid to DSS architecture which integrates these components of DSS. It has not been well appreciated that DSS architecture itself facilitates learning about unstructured-problem solving and enables system evolution.In this paper, we propose a DSS architecture based on the study of unstructured-problem solving and considerations of the needs of managers as non-computer specialists. We illustrate this with a system realized using this architecture.     

An optimized strategy for update path selection in unstructured P2P networks

With the growth of P2P file sharing systems, people are no longer satisfied with the sharing of the read-only and static files, and thus the systems with mutually writable and dynamic files have emerged, resulting in the replica inconsistency problem. To maintain the replica consistency, too many update messages need to be redundantly propagated due to the lack of the sharing of globally updated path information in the existing strategies. To address this problem, we propose an optimized strategy for update path selection, which makes the nodes share the update path information by using clone, variation and crossover operations for the update paths. We also present a repeated update strategy to cope with the churn problem so as to maintain replica consistency as far as possible even if some nodes temporarily leave the network. The simulation results show that our strategy can significantly reduce the number of the redundant update messages without lowering the message coverage, thus improving the availability of the unstructured P2P networks.