Improving the applicability of discrete phase simulations by smoothening their exchange fields

Discrete phase (DP) models are widely used in simulating dilute particle flows. In these methods point-masses that are representing parcels of particles are traced through the computational domain by evaluating local force balances. Their influence on the continuous phase is expressed by momentum exchange fields, which are based on the loss or gain of the particles’ momentum.     

Stagnation slip flow and heat transfer over a nonlinear stretching sheet

Stagnation slip flow and heat transfer characteristics of a viscous fluid over a nonlinear stretching surface has been investigated. The governing partial differential equations are transformed to nonlinear ordinary differential equations using similarity transformations. The analytical solution of the nonlinear system is obtained in series form using the very efficient homotopy analysis method (HAM). Convergence of the series solution is shown explicitly. Important features of flow and heat transfer characteristics are plotted and discussed. Comparison is made with existing numerical results when the stagnation‐point and slip effects are excluded. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011     

The density theorem for discrete series representations restricted to lattices

This article considers the relation between the spanning properties of lattice orbits of discrete series representations and the associated lattice co-volume. The focus is on the density theorem, which provides a trichotomy characterizing the existence of cyclic vectors and separating vectors, and frames and Riesz sequences. We provide an elementary exposition of the density theorem, that is based solely on basic tools from harmonic analysis, representation theory, and frame theory, and put the results into context by means of examples.     

Research in mechanical model of bionic foot intruding into sands with different physical characteristics

In this study, a bionic foot with sand fixation and fluidization limitation functions was designed. Also a rectangular foot with the same sizes, named the common foot, was designed for comparison. Three kinds of quartz sands were selected to study how particle size, shape and compactness affected the intrusion performances of mechanical feet. The intrusion resistive forces and pressures of the bionic foot on these three kinds of quartz sands were all smaller compared with the common foot. Discrete element simulations showed particle disturbance areas were smaller and particle motion trends were more consistent under the bionic foot versus the common foot. The intrusion resistive forces of these two kinds of mechanical feet firstly increased and then decreased with the increasing particle sizes of quartz sands. Moreover, the intrusion resistive force on spherical particles was less than that of irregular particles for both the bionic foot and the common foot. The corresponding resistive forces of mechanical feet were characterized based on quartz sand compactness. The classic pressure-sinkage model was modified based on the intrusion tests, and the relationships between intrusion resistive force and mechanical foot depth were obtained.     

Double‐mode modeling of nonlinear flexural vibration analysis for a symmetric rectangular honeycomb sandwich thin panel by the homotopy analysis method

Nonlinear flexural vibration of a symmetric rectangular honeycomb sandwich thin panel with simply supported along all four edges is studied in this paper. The nonlinear governing equations of the symmetric rectangular honeycomb sandwich panel subjected to transverse excitations are simplified to a set of two ordinary differential equations by the Galerkin method. Based on the homotopy analysis method, the average equations of the primary resonance and harmonic resonance are obtained. The influence of structural parameters, the transverse exciting force amplitude, and transverse damping to the symmetric rectangular honeycomb sandwich panel are discussed by using the analytic approximation method. Compared with the results obtained by single‐mode modeling technique, the results obtained by double‐mode modeling technique change the softening and hardening nonlinear characteristics when Ω ≈ ω₁, ω₁/3, and ω₂/3.     

Advanced numerical analyses by the Non-Smooth Contact Dynamics method of an ancient masonry bell tower

Advanced numerical analyses were carried out in order to assess the nonlinear dynamical behaviour of the bell tower of Pomposa Abbey in Codigoro, in the province of Ferrara (Italy), by means of the Non-Smooth Contact Dynamics (NSCD) method. The main purpose of the work is to investigate the capacity of the main mechanical parameter used in the analyses, namely, the friction coefficient, to have effects on the mechanical response of ancient masonry structures undergoing seismic actions. Therefore, the tower was modelled following the discrete element method (DEM) and assembling the masonry texture as rigid bodies tied by frictional joints. Thus a discontinuous approach was used to assess the dynamic properties and the vulnerability of the masonry structure, through large deformations regulated by the Signorini's law, concerning the impenetrability between the rigid bodies; and by the Coulomb's law, regarding the dry-friction model. Afterward, different values were assigned to the friction coefficient of the models, and a variety of real seismic shocks have been applied in the nonlinear analyses. Finally, it is possible to see different failure mechanisms resulting for each friction value and types of dynamic actions used, as expected.     

Discrete time Markov chain model for age of information

Most of the existing models for Age of Information (AoI) are limited to cases where data generation is according to Poisson process and/or Exponential distribution processing times. Those that consider more general distributions have results only for the first moment of AoI. Discrete time systems for AoI are now receiving attention. In this paper the system is modelled as a discrete time Markov chain and matrix-geometric method is used to obtain the probability mass function of the AoI.     

Random packing of tetrahedral particles using the polyhedral discrete element method

The random packing of tetrahedral particles is studied by applying the discrete element method (DEM), which simulates the effects of friction, height ratio, and eccentricity. The model predictions are analyzed in terms of packing density and coordination number (CN). It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing density of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.     

Discrete element method for high-temperature spread in compacted powder systems

The discrete element method is applied to investigate high-temperature spread in compacted metallic particle systems formed by high-velocity compaction. Assuming that heat transfer only occurs at contact zone between particles, a discrete equation based on continuum mechanics is proposed to investigate the heat flux. Heat generated internally by friction between moving particles is determined by kinetic equations. For the proposed model, numerical results are obtained by a particle-flow-code-based program. Temperature profiles are determined at different locations and times. At a fixed location, the increase in temperature shows a logarithmic relationship with time. Investigation of three different systems indicates that the geometric distribution of the particulate material is one of the main influencing factors for the heat conduction process. Higher temperature is generated for denser packing, and vice versa. For smaller uniform particles, heat transfers more rapidly.     

一种新型脉冲进样装置的研究及其在火焰原子吸收光谱中的应用

本文设计了一种双脉冲微量进样装置。本装置与氢化物法相结合并应用于微量样品的分析。本装置不仅结构简单、操作方便,同时又具备各种单脉冲进样装置所不具备的优点。