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Spurious Modes (spurious + mode)

Distribution by Scientific Domains
Engineering100%

Selected Abstracts

Reduced modified quadratures for quadratic membrane finite elements

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2004
Craig S. Long
Abstract Reduced integration is frequently used in evaluating the element stiffness matrix of quadratically interpolated finite elements. Typical examples are the serendipity (Q8) and Lagrangian (Q9) membrane finite elements, for which a reduced 2 × 2 Gauss,Legendre integration rule is frequently used, as opposed to full 3 × 3 Gauss,Legendre integration. This ,softens' these element, thereby increasing accuracy, albeit at the introduction of spurious zero energy modes on the element level. This is in general not considered problematic for the ,hourglass' mode common to Q8 and Q9 elements, since this spurious mode is non-communicable. The remaining two zero energy modes occurring in the Q9 element are indeed communicable. However, in topology optimization for instance, conditions may arise where the non-communicable spurious mode associated with the elements becomes activated. To effectively suppress these modes altogether in elements employing quadratic interpolation fields, two modified quadratures are employed herein. For the Q8 and Q9 membrane elements, the respective rules are a five and an eight point rule. As compared to fully integrated elements, the new rules enhance element accuracy due to the introduction of soft, higher-order deformation modes. A number of standard test problems reveal that element accuracy remains comparable to that of the under-integrated counterparts. Copyright © 2004 John Wiley & Sons, Ltd. [source]

A uniform nodal strain tetrahedron with isochoric stabilization

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2009
M. W. Gee
Abstract A stabilized node-based uniform strain tetrahedral element is presented and analyzed for finite deformation elasticity. The element is based on linear interpolation of a classical displacement-based tetrahedral element formulation but applies nodal averaging of the deformation gradient to improve mechanical behavior, especially in the regime of near-incompressibility where classical linear tetrahedral elements perform very poorly. This uniform strain approach adopted here exhibits spurious modes as has been previously reported in the literature. We present a new type of stabilization exploiting the circumstance that the instability in the formulation is related to the isochoric strain energy contribution only and we therefore present a stabilization based on an isochoric,volumetric splitting of the stress tensor. We demonstrate that by stabilizing the isochoric energy contributions only, reintroduction of volumetric locking through the stabilization can be avoided. The isochoric,volumetric splitting can be applied for all types of materials with only minor restrictions and leads to a formulation that demonstrates impressive performance in examples provided. Copyright © 2008 John Wiley & Sons, Ltd. [source]

High-order accurate numerical solutions of incompressible flows with the artificial compressibility method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004
John A. Ekaterinaris
Abstract A high-order accurate, finite-difference method for the numerical solution of incompressible flows is presented. This method is based on the artificial compressibility formulation of the incompressible Navier,Stokes equations. Fourth- or sixth-order accurate discretizations of the metric terms and the convective fluxes are obtained using compact, centred schemes. The viscous terms are also discretized using fourth-order accurate, centred finite differences. Implicit time marching is performed for both steady-state and time-accurate numerical solutions. High-order, spectral-type, low-pass, compact filters are used to regularize the numerical solution and remove spurious modes arising from unresolved scales, non-linearities, and inaccuracies in the application of boundary conditions. The accuracy and efficiency of the proposed method is demonstrated for test problems. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Design of multilayer triangular substrate integrated waveguide filter in LTCC

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2009
Wei Shen
Abstract This article proposes a four-pole quasi-elliptic function triangular substrate integrated waveguide bandpass filter, which was fabricated using multilayer low-temperature cofired ceramic technology. In our design, neural network inverse model is adopted to fast capture the sizes of TSIW cavities, with the coupling matrix transformation implemented to achieve cross coupling on the basis of multilayer TSIW. A slot on the top metal layer is introduced so as to suppress the two higher spurious modes. The filter has 65% size reduction in comparison with its planar counterpart, with good agreement obtained between the simulated and measured S-parameters. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2582,2585, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24680 [source]