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

Volume 16, Number 1-2, 2012


Contents:



Abstracts:

  • M.Kujawa, Torsion of Restrained Thin-walled Bars of Open Constant Bisymmetric Cross-section

    Elastic and geometric stiffness matrices were derived using Castigliano’s first theorem, for the case of torsion of restrained thin-walled bars of open constant bisymmetric cross-section. Functions which describe the angles of torsion were adopted from the solutions of the differential equation for restrained torsion. The exact solutions were simplified by expanding them in a power series. Numerical examples were taken from Kujawa M 2009 Static and Sensitivity Analysis of Grids ... 97, GUT Publishing House, and Szymczak C 1978 Engineering Transaction 26 323. Convergence of the solutions was analyzed using the matrices derived for torsion angles, warping, bimoments and critical forces.

  • M.Kujawa, Distorsional Analysis of I-section Beam

    An elastic stiffness matrix was derived in the case of distortion of a restrained thin-walled I-section beam using the minimum total stationary elastic energy condition (Przemieniecki J S 1968 Theory of Matrix Structural Analysis, McGraw-Hill, NY). The function describing the angle of distortion was adopted form the solution of differential equation in the case of restrained distortion. The example presented in the paper helps to assess the correctness of the proposed solution. The proposed elastic stiffness matrix is applicable for solving distortion problems of bar structures composed of thin-walled members.

  • I.Lubowiecka, Orthotropic Membrane as a Mechanical Model of Surgical Implant in Abdominal Hernia Repair

    Even though the incisional hernia repair surgery is a well known procedure, mechanical properties of the tissue-implant system are unknown, so the implantation of the repairing mesh is quite intuitive, and recurrences of the condition continue to occur.

    The main objective of the study is to define a model of repaired hernia that can be used for surgery planning and assessment of the repair durability. The load applied to the structure corresponds to this widely accepted model as the one that can cause hernia recurrence. In the proposed solution, the reaction forces calculated when the extreme abdominal pressure acts on the model are considered as the crucial factors in the repair planning and the connection strength evaluation. These reactions representing the tissue-implant junction forces cannot exceed the limit value experimentally obtained for the synthetic mesh and porcine tissue connection described in literature.

    The achieved finite element simulations results are compared with the experiments and the proposed solution shows good accuracy.

  • M.Luniewski, P.Kotula, J.Pozorski, Large-Eddy Simulations of Particle-laden Turbulent Jets

    The work presents an application of Large-Eddy Simulation (LES) for turbulent two-phase flows with dispersed particles. For the simulations of the continuous phase (fluid), an academic, finite volume LES solver was applied and customised. For comparison purposes, also a spectral solver was considered. The LES of fluid was used together with a Lagrangian module for the dispersed phase in the point-particle approximation, including the two-way momentum coupling between the phases. The particle solver has been further developed for parallel computations. The simulations of turbulent, particle-laden round jets were performed. The results for fluid and particle statistics were compared with available reference data.

  • M.Szydlowski, J.Machalinska-Murawska, Numerical Simulation of Transient Flow in Storm Sewers Using Standard and Improved McCormack Scheme

    This paper describes the results of the first part of the research project which aims at developing a hydraulic model for simulation of unsteady flows in storm sewers ranging from gravity flows to surcharged flows resulting with water outflow on the ground surface and propagation of inundation in the flooded area. The paper focuses on the development and assessment of a second-order explicit numerical scheme for unsteady flows in sewers, but only in a single pipe at this moment, without any special elements such as manholes or drop shafts and with no water overflowing problem. The problem of water flow in sewer system pipes is associated with some specific phenomena occurring in conduits during storm events. If the pipes start to be fully filled with water, there is a transition from free surface to pressurized flow. Then, the vice versa effect can be observed. Such transitions are also possible in sewers when the discharge is controlled by control devices, such as gates for example. Moreover, the rapidly varied flow with some hydraulic local effects such as hydraulic jumps or bores can appear during extreme rain episodes. The appropriate modeling techniques have to be applied to solve these problems. The ‘Preissmann slot’ concept is implemented to simulate the pressurized flow. The original and improved McCormack scheme is used for transcritical flow simulation. The calculated results obtained for some benchmark tests are compared with numerical solutions and laboratory measurements published in the technical literature.

  • A.L.Kozub, Study of Icosahedral Clusters in Close-packed Simple Liquids

    The local structure of liquid copper was determined using Steinhardt order parameters, with particular attention paid to icosahedral clusters. The positions of atoms were obtained from three sets of molecular dynamics simulations, with the forces obtained from: the Sutton-Chen (SC) potential, the Naval Research Laboratory total energy tight-binding (NRL-TB) method and the divide-and-conquer learn-on-the-fly (DCLOTF) method, respectively. A broad range of local geometries appeared, which is a typical result for close-packed liquids. Among them a number of icosahedral clusters were detected. The highest density of icosahedral clusters was obtained at the temperature of 1000K for the NRL-TB and DCLOTF simulations and 1200K for the SC simulations. I propose various means of analysing the icosahedral clusters formed in liquid copper. The average number of the clusters, their lifetime and correlations between them at various temperatures were studied as a function of the approach used to generate the trajectories. Finally, I studied the formation and decay of icosahedral clusters.

  • M.Bialoskorski, J.Rybicki, Nanomechanical Properties of Metallic fcc Nanorods from Molecular Simulations with the Sutton-Chen Force Field

    Basic elastic constants (Young′s modulus, Poisson′s ratio, shear modulus) were determined for several monocrystalline, metallic (Ni, Cu, Pt, Au) nanorods using molecular dynamics with the Sutton-Chen force field. Stress-strain curves were also calculated and discussed.

  • A.Pieta, M.Dwornik, Parallel Implementation of Ray Tracing Procedure in Anisotropic Medium

    This article describes a parallel implementation of a ray tracing algorithm in a heterogeneous anisotropic geological medium. The shortest path method, which was used for calculations, can give ray path and travel time of seismic wave propagation even for a random and discontinuous velocity field. The high precision required in such calculations was obtained by employing a dense computational grid. This led to a significant increase in the computational effort of the algorithm. The procedure was parallelized using domain decomposition. The results show that the parallel performance of the ray tracing procedure strongly depends on the assumed geological method and differs between media with and without anisotropy of seismic wave propagation.

  • H.Krawczyk, J.Proficz, T.Ziolkowski, A Parallel Genetic Algorithm for Creating Virtual Portraits of Historical Figures

    In this paper we present a genetic algorithm (GA) for creating hypothetical virtual portraits of historical figures and other individuals whose facial appearance is unknown. Our algorithm uses existing portraits of random people from a specific historical period and social background to evolve a set of face images potentially resembling the person whose image is to be found. We then use portraits of the person’s relatives to judge which of the evolved images are most likely to resemble his/her actual appearance. Unlike typical GAs, our algorithm uses a new supervised form of fitness function which itself is affected by the evolution process. Additional description of requested facial features can be provided to further influence the final solution (i.e. the virtual portrait). We present an example of a virtual portrait created by our algorithm. Finally, the performance of a parallel implementation developed for the KASKADA platform is presented and evaluated.

  • Personalia: On the 55th Birthday of Sergei Pavlovich Kruchinin