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Rigid Rotation (rigid + rotation)
Selected Abstracts2-D numerical simulation of differential viscoelastic fluids in a single-screw continuous mixer: Application of viscoelastic finite element methodsADVANCES IN POLYMER TECHNOLOGY, Issue 1 2003Robin K. Connelly Abstract Viscoelastic effects on mixing flows obtained with kneading paddles in a single-screw, continuous mixer were explored using 2-D finite element method numerical simulations. The single-mode Phan,Thien Tanner nonlinear, viscoelastic fluid model was used with parameters for a dough-like material. The viscoelastic limits of the simulations were found using elastic viscous stress splitting, 4 × 4 sub-elements for stress, streamline upwind, and streamline upwind Petrov,Galerkin (SUPG). Mesh refinement and comparison between methods was also done. The single-screw mixer was modeled by taking the kneading paddle as the point of reference, fixing the mesh in time. Rigid rotation and no slip boundary conditions at the walls were used with inertia taken into account. Results include velocity, pressure, and stress profiles. The addition of viscoelasticity caused the shear and normal stresses to vary greatly from the viscous results, with a resulting loss of symmetry in the velocity and pressure profiles in the flow region. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 22,41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10038 [source] Rigid rotation of the solar core?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001On the reliable extraction of low-, rotational p-mode splittings from full-disc observations of the Sun We present low-, rotational p-mode splittings from the analysis of 8 yr of observations made by the Birmingham Solar-Oscillations Network (BiSON) of the full solar disc. These data are presented in the light of a thorough investigation of the fitting techniques used to extract them. Particular attention is paid to both the origin and magnitude of bias present in these estimates. An extensive Monte Carlo strategy has been adopted to facilitate this study , in all, several thousand complete, artificial proxies of the 96-month data set have been generated to test the analysis of real ,full-disc' data. These simulations allow for an assessment of any complications in the analysis which might arise from variations in the properties of the p modes over the 11-yr solar activity cycle. The use of such an extended data set affords greater precision in the splittings, and by implication the rotation rate inferred from these data, and reduces bias inherent in the analysis, thereby giving a more accurate determination of the rotation. The grand, weighted sidereal average of the BiSON set is , a value consistent with that expected were the deep radiative interior to rotate at the same frequency, and in the same ,rigid' manner, as the more precisely and accurately studied outer part of the radiative zone. [source] A posteriori corrections to multireference limited configuration interaction based on a Brillouin,Wigner perturbative analysisINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2002I. Hubac Abstract A new a posteriori correction to the method of limited configuration interaction is described that attempts to restore a linear scaling with particle number. The corrections are based on an analysis of the limited configuration interaction method in terms of the Brillouin,Wigner perturbation theory using a Lippmann,Schwinger-like equation. The new correction procedure is general and, in this work, the application to the limited multireference configuration interaction approximation is considered in some detail. An illustrative application to the rigid rotation of the diimine molecule is presented and the results are compared with those obtained by employing Davidson-like corrections and the corresponding full configuration interaction energies. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Protostellar discs formed from rigidly rotating coresMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009S. Walch ABSTRACT We use three-dimensional smoothed particle hydrodynamic simulations to investigate the collapse of low-mass pre-stellar cores and the formation and early evolution of protostellar discs. The initial conditions are slightly supercritical Bonnor,Ebert spheres in rigid rotation. The core mass and initial radius are held fixed at MO= 6.1 M, and RO= 17 000 au, and the only parameter that we vary is the initial angular speed ,O. Protostellar discs forming from cores with ,O < 1.35 × 10,13 s,1 have radii between 100 and 300 au and are quite centrally concentrated; due to heating by gas infall on to the disc and accretion on to the central object, they are also quite warm, , and therefore stable against gravitational fragmentation. In contrast, more rapidly rotating cores form discs which are less concentrated and cooler, and have radii between 400 and 1000 au; as a consequence they are prone to gravitational fragmentation and the formation of multiple systems. We derive a criterion that predicts whether a rigidly rotating core having given MO, RO and ,O will produce a protostellar disc which fragments whilst material is still infalling from the core envelope. We then apply this criterion to core samples for which MO, RO and ,O have been estimated observationally. We conclude that the observed cores are stable against fragmentation at this stage, due to their low angular speeds and the heat delivered at the accretion shock where the infalling material hits the disc. [source] Tayler instability of toroidal magnetic fields in MHD Taylor-Couette flowsASTRONOMISCHE NACHRICHTEN, Issue 1 2010G. Rüdiger Abstract The nonaxisymmetric Tayler instability (TI) of toroidal magnetic fields due to axial electric currents is studied for conducting incompressible fluids between two infinitely long corotating cylinders. For given Reynolds number of rotation the magnetic Prandtl number Pm of the liquid conductor and the ratio of the cylinder's rotation rates are the free parameters. It is shown that for resting cylinders the critical Hartmann number for instability does not depend on Pm hence the TI also exists in the limit Pm , 0. By rigid rotation the instability is suppressed where for Pm = 1 the rotational quenching takes its maximum. Rotation laws with negative shear (i.e. d, /dR < 0) strongly destabilize the toroidal field if the rotation is not too fast. In galaxies with their quadrupolar magnetic field geometry this effect could have drastic implications. For sufficiently high Reynolds numbers of rotation, however, the TI completely disappears. For the considered magnetic constellation the superrotation laws support the rotational stabilization. The angular momentum transport of the instability is anticorrelated with the shear so that an eddy viscosity can be defined which proves to be positive. We have also shown the possibility of laboratory TI experiments with a wide-gap container filled with fluid metals like sodium or gallium. Even the effect of the rotational stabilization can be reproduced in the laboratory with electric currents of only a few kA (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Simple and efficient integration of rigid rotations suitable for constraint solversINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2010Tomasz Koziara Abstract Simple and efficient way of integrating rigid rotations is presented. The algorithm is stable, second-order accurate, and in its explicit version involves evaluation of only two exponential maps per time step. The semi-explicit version of the proposed scheme improves upon the long-term stability, while it retains the explicitness in the force evaluation. The algebraic structure of both schemes makes them suitable forthe analysis of constrained multi-body systems. The explicit algorithm is specifically aimed at the analysis involving small incremental rotations, where its modest computational cost becomes the major advantage. The semi-explicit scheme naturally broadens the scope of possible applications. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||