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Rotation Velocity (rotation + velocity)
Selected AbstractsDynamics of particles suspended in a yield stress fluid flowing in a pipeAICHE JOURNAL, Issue 5 2008Othmane Merkak Abstract This study seeks to understand the basic mechanisms governing the dynamics of a solid particle in a Poiseuille flow field of a viscoplastic fluid. An experimental set-up to create flows with a prescribed flow rate and enable the particles to be visualized in three dimensions was designed and validated. The absence of slip at the interfaces between flows and particles was characterized. The Reynolds numbers are low, gravity effects negligible and plastic effects significant. The ratio of pipe diameter to particle diameter is 8. The dynamics of a particle in a velocity field depends strongly on its position in the sheared wall zone or in the moving rigid zone. The effect of rigid and sheared zones on particle behavior was examined. Changes in particle translation and rotation velocities were quantified. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Optimal setpoint chasing in dynamic positioning of deep-water drilling and intervention vesselsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 13 2001Asgeir J. Sørensen Abstract Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal-plane about desired position and heading co-ordinates defined by the operator. A three degrees-of-freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi-submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust-induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work-over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co-ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi-submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd. [source] The velocity function of gas-rich galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010M. A. Zwaan ABSTRACT We measure the distribution function of rotational velocities ,(Vc) of late-type galaxies from the HIPASS galaxy catalogue. Previous measurements of the late-type velocity function are indirect, derived by converting the galaxy luminosity function using the relation between galaxy luminosity and rotation velocity (the Tully,Fisher relation). The advantage of H i Parkes All Sky Survey is that space densities and velocity widths are both derived from the same survey data. We find good agreement with earlier inferred measurements of ,(Vc), but we are able to define the space density of objects with Vc as low as 30 km s,1. The measured velocity function is ,flat' (power-law slope ,,,1.0) below Vc, 100 km s,1. We compare our results with predictions based on , cold dark matter simulations and find good agreement for rotational velocities in excess of 100 km s,1, but at lower velocities current models over-predict the space density of objects. At Vc= 30 km s,1, this discrepancy is approximately a factor of 20. [source] Dynamical response to supernova-induced gas removal in spiral galaxies with dark matter haloMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Hiroko Koyama ABSTRACT We investigate the dynamical response, in terms of disc size and rotation velocity, to mass loss by supernovae in the evolution of spiral galaxies. A thin baryonic disc having the Kuzmin density profile embedded in a spherical dark matter halo having a density profile proposed by Navarro, Frenk & White is considered. For the purpose of comparison, we also consider the homogeneous and r,1 profiles for dark matter in a truncated spherical halo. Assuming for simplicity that the dark matter distribution is not affected by mass-loss from discs and the change of baryonic disc matter distribution is homologous, we evaluate the effects of dynamical response in the resulting discs. We found that the dynamical response only for an adiabatic approximation of mass-loss can simultaneously account for the rotation velocity and disc size as observed particularly in dwarf spiral galaxies, thus reproducing the Tully,Fisher relation and the size versus magnitude relation over the full range of magnitude. Furthermore, we found that the mean specific angular momentum in discs after the mass-loss becomes larger than that before the mass-loss, suggesting that the mass-loss would most likely occur from the central disc region where the specific angular momentum is low. [source] An asteroseismic study of the , Cephei star , Ophiuchi: constraints on global stellar parameters and core overshootingMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. Briquet ABSTRACT We present a seismic study of the , Cephei star , Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split ,= 1 triplet and three components of a rotationally split ,= 2 quintuplet for which the m values were well identified by spectroscopy. We identify the radial mode as fundamental, the triplet as p1 and the quintuplet as g1. Our non-local thermodynamic equilibrium abundance analysis results in a metallicity and CNO abundances in full agreement with the most recent updated solar values. With X,[0.71, 0.7211] and Z,[0.009, 0.015], and using the Asplund et al. mixture but with a Ne abundance about 0.3 dex larger, the matching of the three independent modes enables us to deduce constrained ranges for the mass (M= 8.2 ± 0.3 M,) and central hydrogen abundance (Xc= 0.38 ± 0.02) of , Oph and to prove the occurrence of core overshooting (,ov= 0.44 ± 0.07). We also derive an equatorial rotation velocity of 29 ± 7 km s,1. Moreover, we show that the observed non-equidistance of the ,= 1 triplet can be reproduced by the second-order effects of rotation. Finally, we show that the observed rotational splitting of two modes cannot rule out a rigid rotation model. [source] The Tully,Fisher relation and its implications for the halo density profile and self-interacting dark matterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000H. J. Mo We show that the Tully,Fisher relation observed for spiral galaxies can be explained in the current scenario of galaxy formation without invoking subtle assumptions, provided that galactic-sized dark haloes have low concentrations which do not change significantly with halo circular velocity. This conclusion does not depend significantly on whether haloes have cuspy or flat profiles in the inner region. In such a system, both the disc and the halo may contribute significantly to the maximum rotation of the disc, and the gravitational interaction between the disc and halo components leads to a tight relation between the disc mass and maximum rotation velocity. The model can therefore be tested by studying the Tully,Fisher zero points for galaxies with different disc mass-to-light ratios. With model parameters (such as the ratio between disc and halo mass, the specific angular momentum of disc material, disc formation time) chosen in plausible ranges, the model can well accommodate the zero-point, slope and scatter of the observed Tully,Fisher relation, as well as the observed large range of disc surface densities and sizes. In particular, the model predicts that low surface brightness disc galaxies obey a Tully,Fisher relation very similar to that of normal discs, if the disc mass-to-light ratio is properly taken into account. About half of the gravitational force at maximum rotation comes from the disc component for normal discs, while the disc contribution is lower for galaxies with a lower surface density. The halo profile required by the Tully,Fisher relation is as concentrated as that required by the observed rotation curves of faint discs, but less concentrated than that given by current simulations of cold dark matter (CDM) models. We discuss the implication of such profiles for structure formation in the Universe and for the properties of dark matter. Our results cannot be explained by some of the recent proposals for resolving the conflict between conventional CDM models and the observed rotation-curve shapes of faint galaxies. If dark matter self-interaction (either scattering or annihilation) is responsible for the shallow profile, the observed Tully,Fisher relation requires the interaction cross-section ,X to satisfy ,,X|v|,/mX,10,16 cm3 s,1 GeV,1, where mX is the mass of a dark matter particle. [source] Study on Lead Dioxide Modified Electrode and Its Application in Detection of PhenolsCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Ai Shi-Yun Abstract The conditions for the preparation of PbO2 modified Pt rotation disc electrode in solutions containing HC104 and Pb(II) were studied, and the morphology and composition of the obtained PbO2 film were characterized by SEM and XRD techniques, respectively. The results show that the modification process of PbO is dependent on the rotation velocity of the electrode and the concentrations of HCIO4 and Pb(II). And it was observed that the obtained PbO2 film was rutile ,-PDO2 structure. At a certain positive potential, HO· and HO2· radicals can be generated on the surface of the modified PbO2/Pt electrode and then oxidize phenols. According to the change of the responding anodic current, the determination of phenols was realizable and good results were obtained. [source] | ||||||||||