TASK Quarterly   Scientific Bulletin of the Centre of Informatics - Tricity Academic Supercomputer & networK   ISSN 1428-6394

1-2/2008


Contents:



Abstracts:

  • Z.Wan, W.Liu, Z.Tu, A.Nakayama, Conjugate Numerical Investigation of a Miniature Flat-Plate Evaporator of a Capillary Pumped Loop for Electronics Cooling

    A capillary pumped loop (CPL) is a two-phase thermal control device applied in cooling electronic devices. A two-dimensional conjugate numerical model of a miniature flat-plate capillary evaporator is presented in order to describe liquid and vapor flow, heat transfer and phase change in the porous wick structure, liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and the metallic wall. The entire evaporator is solved with the SIMPLE algorithm as a conjugate problem. The shape and location of the vapor-liquid interface inside the wick are calculated, and a side wall effect heat transfer limit is introduced to estimate the evaporator's heat transport capability. The influence of various wall materials on the evaporator's performance is discussed in detail. The results suggest that an evaporator with a combined wall is capable of dissipating high heat flux and stabilizing the temperature of electronic devices at a moderate temperature level.

  • F.Liu, J.Wang, K.Wu, Numerical Analysis of Controlling Separation in Axial Cascades by Excitation of Periodical Incoming Wake

    Numerical analysis has been performed of time-space structures in a large turning angle axial cascade subject to unsteady incoming wake excitation. The results have shown that intentional unsteady excitation could increase the cascade's time-averaged performance. As a result, the vortex structures corresponding to the external exciting frequency are strengthened and other disordered vortices are involved, so that the separation structures of the suction surface are translated from disorder to order. Two interaction regimes between incoming periodic wakes and separation structures are analyzed, indicating that turbulent kinetic energy can enhance momentum interchange and that wave-vortex resonance can promote rolled-up and plus-minus pairing of vortices. Based on these, responses of separation structures from two periodic incoming wake regimes are compared. The feasibility of far-field noise reduction in ducting fans by using periodic incoming wake is considered.

  • A.Ambroziak, P.Klosowski, Determining the Viscoplastic Parameters of Rubber-toughened Plastics

    This paper describes the material parameter determination procedure for the elastoviscoplastic Bodner-Partom model. A set of viscoplastic parameters is determined for rubbertoughened propylene-ethylene copolymer, and is used to numerical simulations of the material behaviour under different strain rate deformations. The evaluation of material parameters for Bodner-Partom constitutive equations is carried out using tensile tests.

  • W.Sobieski, Influence of Selected Eulerian Multiphase Model Parameters on the Simulation Results for a Spouted Bed Grain Dryer

    The results of a numerical simulation of a spouted bed grain dryer based on the Eulerian Multiphase Model are presented. The influence of various model parameters on the height of the fountain forming in the drying chamber was analyzed. The following computer model parameters were considered: air inlet velocity, grain size and density, and the lowering of bed surface resulting from drying shrinkage and grain pack. An analysis of the approach of turbulence modeling of similar systems is included. The number of computation dimensions and numerical grids is discussed. The presented studies are based on earlier experiments conducted at a dedicated experimental station. Their main objective was to determine the basic principles of modeling fluidized beds found in grain dryers and the computer model's sensitivity to changes in its basic parameters.

  • E.Zieniuk, A.Boltuc, A Non-element Method of Solving the Two-dimensional Navier-Lam'e Equation in Problems with Non-homogeneous Polygonal Subregions

    The paper introduces a parametric integral equation system (PIES) for solving 2D boundary problems defined on connected polygonal domains described by the Navier-Lam'e equation. Parametric linear functions were applied in the PIES to define analytically the polygonal subregions' interfaces. Only corner points and additional extreme points on the interface between the connected subregions are posed to practically define a polygonal domain. An important advantage of this approach is that the number of such points is independent of the area of identically shaped domains due to the elimination of traditional elements from modeling, the number of those elements being dependent on the domain's surface area. In order to test the reliability and effectiveness of the proposed method, test examples are included in which areas of displacements and stresses are analyzed in each subregion.

  • S.Kubacki, A.Boguslawski, Dirichlet/Dirichlet and Dirichlet/Dirichlet-Neumann/Neumann Non-overlapping Iterative Domain Decomposition Methods

    A new iterative non-overlapping domain decomposition method is proposed for solving the one- and two-dimensional Helmholtz equation on parallel computers. The spectral collocation method is applied to solve the Helmholtz equation in each subdomain based on the Chebyshev approximation, while the patching conditions are imposed at the interfaces between subdomains through a correction, being a linear function of the space coordinates. Convergence analysis is performed for two applications of the proposed method (DDLC and DDNNLC algorithms - the meaning of these abbreviations is explained below) based on the works of Zanolli and Funaro et al.

    Numerical tests have been performed and results obtained using the proposed method and other iterative algorithms have been compared. Parallel performance of the multi-domain algorithms has been analyzed by decomposing the two-dimensional domain into a number of subdomains in one spatial direction.

    For the one-dimensional problem, convergence of the iteration process was quickly obtained using the proposed method, setting a small value of the σ constant in the Helmholtz equation. Another application of the proposed method may be an alternative to other iterative schemes when solving the two-dimensional Helmholtz equation.

  • S.Fiori, Estimating Independent Components by Mapping onto an Orthogonal Manifold

    Algorithms for independent component analysis based on information-theoretic criteria optimization over differential manifolds have been devised over the last few years. The principles informing their design lead to various classes of learning rules, including the fixed-point and the geodesic-based ones. Such learning algorithms mainly differ by the way in which single learning steps are effected in the neural system's parameter space, i.e. by the action that a connection variable is moved by in the parameter space toward the optimal connection pattern. In the present paper, we introduce a new class of learning algorithms by recalling from the literature on differential geometry the concept of mapping onto manifolds, which provides a general way of acting upon a neural system's connection variable in order to optimize the learning criteria. The numerical behavior of the introduced learning algorithms is illustrated and compared with experiments carried out on mixtures of statistically-independent signals.

  • S.Gulkowski, J.M.Olchowik, I.Jozwik, P.P.Moskvin, Modelling of Thin Si Layers Growth on Partially Masked Si Substrate

    This paper presents a numerical simulation of epitaxial lateral overgrowth of silicon layers from the liquid phase of an Sn solvent. A two-dimensional diffusion equation has been solved and the concentration profiles of Si in a Si-Sn rich solution during the growth have been constructed. The epilayer thickness and width have been obtained from the concentration near the interface.