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Numerical Aspects (numerical + aspect)
Selected AbstractsCreep of Single Crystals , Modelling and Numerical AspectsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Ivaylo Vladimirov A number of constitutive models, utilizing both microstructural and/or phenomenological considerations, have been developed for the simulation of the creep behaviour of nickel-base single crystal superalloys at elevated temperatures. In this work, emphasis is placed on the rate-dependent single crystal plasticity model [1]. A strategy for the identification of the material parameters of the model to fit the results from experiments has been implemented. The parameter fitting methodology rests upon a two-membered evolution strategy. In addition, a proposal is made for the extension of the Cailletaud model [1] by means of an evolution equation for a damage variable which enables the modelling of the tertiary creep stage. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Poroelastodynamic Boundary Element Method in Time Domain: Numerical AspectsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Martin Schanz Based on Biot's theory the governing equations for a poroelastic continuum are given as a coupled set of partial differential equations (PDEs) for the unknowns solid displacements and pore pressure. Using the Convolution Quadrature Method (CQM) proposed by Lubich a boundary time stepping procedure is established based only on the fundamental solutions in Laplace domain. To improve the numerical behavior of the CQM-based Boundary Element Method (BEM) dimensionless variables are introduced and different choices studied. This will be performed as a numerical study at the example of a poroelastic column. Summarizing the results, the normalization to time and spatial variable as well as on Young's modulus yields the best numerical behavior. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical aspects of a real-time sub-structuring technique in structural dynamicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2007R. Sajeeb Abstract A time domain coupling technique, involving combined computational and experimental modelling, for vibration analysis of structures built-up of linear/non-linear substructures is developed. The study permits, in principle, one or more of the substructures to be modelled experimentally with measurements being made only on the interfacial degrees of freedom. The numerical and experimental substructures are allowed to communicate in real time within the present framework. The proposed strategy involves a two-stage scheme: the first is iterative in nature and is implemented at the initial stages of the solution in a non-real-time format; the second is non-iterative, employs an extrapolation scheme and proceeds in real time. Issues on time delays during communications between different substructures are discussed. An explicit integration procedure is shown to lead to solutions with high accuracy while retaining path sensitivity to initial conditions. The stability of the integration scheme is also discussed and a method for numerically dissipating the temporal growth of high-frequency errors is presented. For systems with non-linear substructures, the integration procedure is based on a multi-step transversal linearization method; and, to account for time delays, we employ a multi-step extrapolation scheme based on the reproducing kernel particle method. Numerical illustrations on a few low-dimensional vibrating structures are presented and these examples are fashioned after problems of seismic qualification testing of engineering structures using real-time substructure testing techniques. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical aspects of improvement of the unsteady pipe flow equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2007Romuald Szymkiewicz Abstract The paper presents an analysis of some recently proposed improvements of the water hammer equations, which concern the friction term in the momentum equation. A comparison of the experimental data and numerical results shows that the required damping and smoothing of the pressure wave cannot be obtained by modification of the friction factor only. In order to evaluate the significance of the introduced improvements into the momentum equation, the accuracy of the numerical solution has been analysed using the modified equation approach. The analysis shows why the physical dissipation process observed in the water hammer phenomenon cannot be reproduced with the commonly used source term in Darcy,Weisbach form, representing friction force in the momentum equation. Therefore, regardless of the proposed form of the friction factor for unsteady flow, the model of water hammer improved in such a way keeps its hyperbolic character. Consequently, it cannot ensure the expected effects of damping and smoothing of the calculation head oscillations. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical aspects of an algorithm for the Eulerian simulation of two-phase flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10-11 2003Paulo J. Oliveira Abstract It is often the case that the numerical simulation of two phase flows leads to a number of difficulties associated with the solution algorithms utilized. Those difficulties manifest themselves as an impossibility to converge the iterative solution process, typical of the finite-volume pressure-correction methods, and are particularly persistent in cases with phase segregation (complete, or almost complete, separation of one phase from the other) and with fine meshes. A number of effective measures to overcome such problems are here proposed and tested, encompassing: (1) modification of the momentum equations formulation in a way that avoids singularity as volume fractions (,) tend to zero; (2) bounding of the volume fractions during the iterative algorithm in a way that enforces the physical limits, ,0 and 1; (3) symmetric treatment of some terms in the equations, and consistent formulation of cell-face fluxes in order to prevent numerical-induced oscillations. Copyright © 2003 John Wiley & Sons, Ltd. [source] Analysis of a time discretization for an implicit variational inequality modelling dynamic contact problems with frictionMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 7 2001Jean-Marc Ricaud Abstract Some dynamic contact problems with friction can be formulated as an implicit variational inequality. A time discretization of such an inequality is given here, thus giving rise to a so-called incremental solution. The convergence of the incremental solution is established, and then the limit is shown to be the unique solution of the variational inequality. This paper contains therefore not only some new results concerning the numerical aspect of some models of contact and friction but also a constructive existence result. Copyright © 2001 John Wiley & Sons, Ltd. [source] Inversion of earthquake focal mechanisms to obtain the seismotectonic stress IV,a new method free of choice among nodal planesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2002Jacques Angelier Summary A new method is presented, to obtain the stress state that best accounts for a set of double couple focal mechanisms of earthquakes. This method is based on the slip shear stress component (SSSC) criterion. The sum of the SSSC values is maximized as a function of four unknowns that describe the reduced stress tensor, including the orientations of the principal stress axes and the ratio between the principal stress differences. This new method combines two advantages. First, no choice between the nodal planes of each focal mechanism is needed, because of the intrinsic properties of the SSSC. Secondly, the runtime is negligible regardless of the size of the data set, because the inverse problem is solved by analytical means so that the numerical aspects are reduced to a minimum. For these reasons, the SSSC-based inversion is easily included in a variety of processes for separating or refining the data. A typical set of focal mechanisms of earthquakes in Taiwan is processed to illustrate the application and potential of the new method. [source] Smoothed nodal forces for improved dynamic crack propagation modeling in XFEMINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010Thomas Menouillard Abstract Improvements in numerical aspects of dynamic crack propagation procedures by the extended finite element method are described and studied. Using only the discontinuous enrichment function in XFEM gives a binary description of the crack tip element: it is either cut or not. We describe a correction force to modify the forces to smoothly release the tip element while the crack tip travels through the element. This avoids creating spurious stress waves and improves the accuracy of the stress intensity factors during propagation by decreasing the oscillations. Copyright © 2010 John Wiley & Sons, Ltd. [source] Numerical issues in the virtual fields methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2004Michel Grédiac Abstract This paper deals with the direct identification of parameters governing anisotropic elastic constitutive equations. These parameters are identified from heterogeneous strain fields with the virtual fields method. This method is based on a relevant use of the principle of virtual work. Different numerical aspects of the implementation of the method are discussed in the paper, mainly in terms of stability of the identified parameters when noisy data are processed. It is shown that the sensitivity of the method to noisy data is compatible with a practical use during experiments. Copyright © 2004 John Wiley & Sons, Ltd. [source] Discussions on driven cavity flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2009Article first published online: 9 SEP 200, Ercan Erturk Abstract The widely studied benchmark problem, two-dimensional-driven cavity flow problem is discussed in detail in terms of physical and mathematical and also numerical aspects. A very brief literature survey on studies on the driven cavity flow is given. On the basis of several numerical and experimental studies, the fact of the matter is that physically the flow in a driven cavity is not two-dimensional above moderate Reynolds numbers. However, there exist numerical solutions for two-dimensional-driven cavity flow at high Reynolds numbers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of stirred tanks with two-zone modelsAICHE JOURNAL, Issue 10 2009Ville Alopaeus Abstract Stirred tank turbulence and fluid flow characteristics are analyzed based on a two-zone model. Instead of using the zonal model for stirred tank performance prediction as often proposed in the literature, the zoning is used here as a tool for mixing analysis. A systematic zoning approach is proposed, where the tank is divided into two nested regions. By gradually increasing the inner zone volume, continuous curves can be obtained for turbulent energy dissipation distribution and pumping numbers between the zones as functions of the zone sizes. It is shown here that these curves can be used as a powerful tool for visualizing stirred tank performance. They can be used, e.g., in impeller performance comparisons and analysis of mixing characteristics with changing rheology, or to examine various numerical aspects related to stirred tank CFD modeling. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||