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

2/2005


Contents:



From the History of Science in Gdansk
  • A.Januszajtis, At the Threshold of Maturity


Abstracts:

  • A.Ambroziak, Numerical Modeling of Elasto-Viscoplastic Chaboche Constitutive Equations Using MSC.Marc

    The aim of the present paper is to propose a special kind of finite element procedure for dynamic and static analysis of civil engineering structures (e.g. trusses, beams, shells and spatial structures) including elasto-viscoplastic models. The Chaboche model with damage has been chosen from the wide range of available elasto-viscoplastic constitutive models for numerical calculations. The main advantage of the presented approach is the possibility of interference in subroutines and adjusting them to a particular problem (e.g. altering the form of constitutive equations). A user-defined UVSCPL subroutine has been proposed to introduce the elasto-viscoplastic model into the MSC.Marc system.

  • A.Ambroziak, Analysis of Non-Linear Elastic Material Properties of PVC-Coated Panama Fabric

    The aim of the present paper is to propose a method of laboratory tests to determine non-linear elastic properties of coated Panama fabric. The material parameters are specified on the basis of uniaxial tensile tests in the warp and weft directions. Techniques based on the least squares' methods are used in the determination process. Reduction concepts of the strength parameters are proposed in order to take into account rheological effects in the fabric. Numerical applications to MSC.Marc, a commercial program, are presented. A user-defined HOOKLW subroutine is used to introduce the non-linear elastic properties of the PVC-coated fabric into the MSC.Marc system.

  • M.Magdon-Maksymowicz and A.Z.Maksymowicz, Simulating the Spread of the BSE Disease: a Cellular Automata Approach

    The rules of evolution applied in the cellular automata approach may correspond to the propagation of the mad cow disease. In a computer simulation of the BSE disease's spread both inherited and infectious mechanisms are accounted for. The initial population of items is randomly distributed on a two-dimensional square lattice, Nx × Ny = 1000 × 1000, with a fraction of 1 percent the items already infected. Alternatively, faulty prions may spontaneously develop during the simulation with a very small frequency. Our results indicate a critical probability, pc, of BSE transmission, so that for p below the threshold the population recovers. For p > pc the disease is launched in the population with a dynamic equilibrium between the healthy and infected fractions of the population. The threshold is very sensitive to spatial clustering of the population and the detailed rules for the disease's onset, evolution and propagation.

  • J.Swirydczuk, Unsteady Performance of an HP Turbine Stage Optimised for Steady Flow Conditions

    The article is focused on the examination of the unsteady performance of an HP turbine stage the blades of which were previously optimised for steady flow conditions. For the purpose of this examination, two pairs of initial and optimised stages of comparable output parameters were selected. The results have revealed that the modification of the blade profile in the optimisation process made the rotor blades more vulnerable to unsteady flow fluctuations, which eventually cancelled a considerable part of the stage efficiency gained from the steady flow optimisation.

  • J.Gluch, Application of Artificial Neural Networks (ANN) as Multiple Degradation Classifiers in Thermal and Flow Diagnostics

    Application of a neural network of the classifier type for diagnostic purposes is presented. The described ANN solves the task of recognizing causes of degradation of power units' thermal cycle components. Verification of the applied ANN responses is based on the presented research in the numerical simulation of selected power installations. The obtained results stand for a diagnosis worked out under condition of power cycle proper measurements. Considerably good obtained results prove that the ANN technique can be applied as an automatic detector of operational faults. Thus an ANN can serve as a support tool for operational decisions. The present work also offers a way of reducing training time.

  • P.Lampart and R.Puzyrewski, Numerical Analysis of Adaptive Control in LP Turbines

    A new design idea of adaptive control in LP steam turbines under conditions of (1) extraction of steam to the extraction point and (2) seasonal changes of pressure in the condenser is discussed. Nozzle blades of a stage located directly downstream of the extraction point or of the exit stage located upstream of the exit diffuser have adjustable trailing edges that can adapt the geometry of the blading system to the changing flow conditions. The idea has been validated numerically on a group of two exit stages of a 60MW extraction/condensation turbine. A series of flow calculations have been performed using a FlowER code for solving the flow of compressible viscous gas in a 3D turbomachinery environment. As a result, characteristics of the design, including the mass flow rate, flow angles in characteristic sections, enthalpy losses and turbine power, have been obtained in a range of given pressure drops and nozzle blade stagger angles. Based on these characteristics, the adequate position of the nozzle blade has been found to adapt the stage (stage group) geometry to the changing flow conditions. The advantages of adaptive control in the form of increased turbine efficiency and power have also been estimated.

  • A.Frackowiak and M.Cialkowski, Explicit Estimation of an Integral in a Domain by the Multiple Reciprocity Method with the Use of Inverse Operations

    The paper presents two methods of solving the Poisson equation. One is based on the multiple reciprocity method. An analytical form of the basic solution obtained by means of inverse operation technique enabled assessing the method's error. The other is based on source function expansion into a series according to polyharmonic functions. Further polyharmonic functions have been obtained through inverse operations (with the Δ -1 operator) applied to polyharmonic functions. Numerical results have confirmed perfect efficiency of both methods.

  • J.Wang, Y.Ou and K.Wu, Numerical Analysis of Internal Flow Phenomena in a Multi-Blade Centrifugal Fan

    A three-dimensional, steady, incompressible, turbulent flow field inside a multi-blade centrifugal fan used in an air-conditioner has been analyzed numerically. Reynolds-averaged Navier-Stokes equations with the standard kturbulence model have been discretized by the finite volume method. The calculation results have shown complex three-dimensional characteristics of the flow, especially in the blade passages near the shroud side. The results have revealed a boundary layer separating the flow from the leading edge on the blade suction surface, the flow's reversal from the high pressure region inside the volute to the low pressure region near the impeller inlet, the flow's recirculation near the shroud side, a jet-wake pattern at the rotor exit, pressure fluctuation on the blade surface, etc. Some of the numerical results agree well with previous experiment.