4,880 research outputs found

    Scaling and Dissipation in the GOY Shell Model

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    This is a paper about multi-fractal scaling and dissipation in a shell model of turbulence, called the GOY model. This set of equations describes a one dimensional cascade of energy towards higher wave vectors. When the model is chaotic, the high-wave-vector velocity is a product of roughly independent multipliers, one for each logarithmic momentum shell. The appropriate tool for studying the multifractal properties of this model is shown to be the energy current on each shell rather than the velocity on each shell. Using this quantity, one can obtain better measurements of the deviations from Kolmogorov scaling (in the GOY dynamics) than were available up to now. These deviations are seen to depend upon the details of inertial-range structure of the model and hence are {\em not} universal. However, once the conserved quantities of the model are fixed to have the same scaling structure as energy and helicity, these deviations seem to depend only weakly upon the scale parameter of the model. We analyze the connection between multifractality in the velocity distribution and multifractality in the dissipation. Our arguments suggest that the connection is universal for models of this character, but the model has a different behavior from that of real turbulence. We also predict the scaling behavior of time correlations of shell-velocities, of the dissipation,Comment: Revised Versio

    Solidification of liquid metal drops during impact

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    Hot liquid metal drops impacting onto a cold substrate solidify during their subsequent spreading. Here we experimentally study the influence of solidification on the outcome of an impact event. Liquid tin drops are impacted onto sapphire substrates of varying temperature. The impact is visualised both from the side and from below, which provides a unique view on the solidification process. During spreading an intriguing pattern of radial ligaments rapidly solidifies from the centre of the drop. This pattern determines the late-time morphology of the splat. A quantitative analysis of the drop spreading and ligament formation is supported by scaling arguments. Finally, a phase diagram for drop bouncing, deposition and splashing as a function of substrate temperature and impact velocity is provided

    Wake-Driven Dynamics of Finite-Sized Buoyant Spheres in Turbulence

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    Particles suspended in turbulent flows are affected by the turbulence and at the same time act back on the flow. The resulting coupling can give rise to rich variability in their dynamics. Here we report experimental results from an investigation of finite-sized buoyant spheres in turbulence. We find that even a marginal reduction in the particle's density from that of the fluid can result in strong modification of its dynamics. In contrast to classical spatial filtering arguments and predictions of particle models, we find that the particle acceleration variance increases with size. We trace this reversed trend back to the growing contribution from wake-induced forces, unaccounted for in current particle models in turbulence. Our findings highlight the need for improved multi-physics based models that account for particle wake effects for a faithful representation of buoyant-sphere dynamics in turbulence.Comment: 5 pages, 4 figures, http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.12450

    Transport properties of dense dissipitive hard-sphere fluids for arbitrary energy loss models

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    The revised Enskog approximation for a fluid of hard spheres which lose energy upon collision is discussed for the case that the energy is lost from the normal component of the velocity at collision but is otherwise arbitrary. Granular fluids with a velocity-dependent coefficient of restitution are an important special case covered by this model. A normal solution to the Enskog equation is developed using the Chapman-Enskog expansion. The lowest order solution describes the general homogeneous cooling state and a generating function formalism is introduced for the determination of the distribution function. The first order solution, evaluated in the lowest Sonine approximation, provides estimates for the transport coefficients for the Navier-Stokes hydrodynamic description. All calculations are performed in an arbitrary number of dimensions.Comment: 27 pages + 1 figur

    Cavitation and bubble collapse in hot asymmetric nuclear matter

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    The dynamics of embryonic bubbles in overheated, viscous and non-Markovian nuclear matter is studied. It is shown that the memory and the Fermi surface distortions significantly affect the hinderance of bubble collapse and determine a characteristic oscillations of the bubble radius. These oscillations occur due to the additional elastic force induced by the memory integral.Comment: Revtex file (10 pages) and 3 figure

    Detailed design of a lattice composite fuselage structure by a mixed optimization method

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    In this paper, a procedure for designing a lattice fuselage barrel has been developed and it comprises three stages: first, topology optimization of an aircraft fuselage barrel has been performed with respect to weight and structural performance to obtain the conceptual design. The interpretation of the optimal result is given to demonstrate the development of this new lattice airframe concept for the fuselage barrel. Subsequently, parametric optimization of the lattice aircraft fuselage barrel has been carried out using Genetic Algorithms on metamodels generated with Genetic Programming from a 101-point optimal Latin hypercube design of experiments. The optimal design has been achieved in terms of weight savings subject to stability, global stiffness and strain requirements and then was verified by the fine mesh finite element simulation of the lattice fuselage barrel. Finally, a practical design of the composite skin complying with the aircraft industry lay-up rules has been presented. It is concluded that the mixed optimization method, combining topology optimization with the global metamodel-based approach, has allowed to solve the problem with sufficient accuracy as well as provided the designers with a wealth of information on the structural behaviour of the novel anisogrid composite fuselage design

    The Kappa in J/Psi -> Kpplus-piminus-Kminus-piplus

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    BES II data for J/Psi->K*(890)Kpi reveal a strong kappa peak in the Kpi S-wave near threshold. Both magnitude and phase are determined in slices of Kpi mass by interferences with strong Ko(1430), K1(1270) and K1(1400) signals. The phase variation with mass agrees within errors with LASS data for Kpi elastic scattering. A combined fit is presented to both BES and LASS data. The fit uses a Breit-Wigner amplitude with an s-dependent width containing an Adler zero. The kappa pole is at 760+-20(stat)+-40(syst) - i(420+-45+-60syst) MeV. The S-wave I=0 scattering length a_0 = 0.23+-0.04 (in units of m(pi)) is close to the prediction 0.19+-0.02 of Chiral Perturbation Theory.Comment: 20 pages, 5 figure
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