Planar and axially symmetric slow shearing granular flows: a comparative evaluation of assembly evolution incorporating wavelet transforms

We demonstrate the enhanced capacities of our analysis toolset for three-dimensional data. In particular, we provide supporting evidence for some of the conclusions reached in our previous studies of two-dimensional avalanching heaps. Segregation by self-diffusion is shown to take place in three-dimensional assemblies and self-diffusion velocities are shown to be of a comparable order of magnitude to those found in plane-strain situations. The effect on assembly evolution by discrete avalanching of the availability of a third dimension for translation is investigated. The discrete wavelet transform is again shown to be a useful component of the toolset in coupling process variables in the context of the discrete defining events associated with assembly evolution. In particular, we move towards the determination of time constants by correlating wavelet coefficients with a time shift.     

An Investigation of Error Sources in Computational Fluid Dynamics Modelling of a Co-current Spray Dryer

The paper is focused on identifying error sources in computational fluid dynamics(CFD) predictions of a spray drying process. Seven groups of drying and atomisation parameters were selected for analysis and 13 simulation trials were performed. The theoretical results were compared with experimental data and sensitivity of the simulation results to the analysed factors was determined. The following parameters affecting the accuracy of CFD spray modelling were found: gas turbulence model, particle dispersion, atomising air, initial parameters of atomisation and heat losses to the environment. A major difference in the errors committed during modelling of spray drying process for fine and coarse sprays was observed.     

Molecular dynamics studies of a model polymer-catalyst-carbon interface

Classical molecular dynamics simulations are performed to obtain insights into structural and dynamical behavior of water and O₂ transport through a model polymer membrane, and at the interface of such hydrated polymer with graphite-supported nanocatalyst platinum particles. Water clustering is observed near the membrane hydrophilic sites constituted by sulfonic groups, which due to their affinity with platinum, are located near the metallic surface. It is found that the diffusion of water through the model hydrated polymer membrane depends strongly on the level of membrane hydration due to contribution from various mechanisms whose relative weights change with the degree of hydration. Possible scenarios for O₂ diffusion are also analyzed.     

四元数与欧拉角刚体动力学数值积分算法及其比较

为推广四元数保辛积分在工程中的应用,对欧拉角表示的状态方程数值积分与四元数的保辛积分进行比较.重陀螺的数值仿真结果表明四元数保辛积分的数值结果明显优于欧拉角状态方程积分.与欧拉角状态方程积分相比,四元数保辛积分在刚体动力学的数值仿真中更具优势.     

基于祖冲之类方法的多体动力学方程保能量保约束积分

针对一类多体动力学问题导出的微分 代数方程,提出一种保能量、保约束的算法.该算法基于祖冲之类方法和欧拉中点保辛差分,利用祖冲之类方法保证在时间格点上精确满足约束方程,避免约束违约问题;并进一步证明该算法在时间格点上可以精确保能量.数值算例进一步验证该算法的可靠性.     

Al ionic radius influence on molecular dynamics simulations ofγ-Al2O3

Molecular dynamics (MD) simulations of-Al₂O₃, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties.     

黄腐酸结构、构象和聚集过程的分子模拟研究

自然界中广泛存在着的腐植物质(HS)有多种化学反应能力,诸如矿物质的风化、养分的生物有效利用和污染物的迁移等相关的生物地球化学反应能力。腐植物质的反应性取决于其官能团的化学特性与微观结构,同时又受到周围环境及介质组分的影响。为了更好地了解腐植物质在水、土壤中的结构、构象以及聚集过程,文中描述了以伯明翰东北部庙宇(TNB)的样本,按离子或非离子的黄腐酸分子结构建模研究的过程。该理论研究结果和黄腐酸的溶解度(偶极矩)、电子和振动光谱等一些实验研究的结果能很好的吻合。其中水分子的存在对静电有很大的稳定作用,并且随着离子化程度的增加,这种作用变得更强。在真空中,由于氢键和非键力相互作用增加,未离子化的聚集体比单体更稳定。因此,随着黄腐酸分子的离子化,聚集作用将不再发生。在溶液中,黄腐酸的浓度是聚集的关键因素。若当量浓度太低,含有两个黄腐酸的系统就不可能发生聚集,但是随着当量浓度的提高,系统中聚集体的数量也将上升,情况就发生改变。离子态是聚集的另一个关键因素。离子态的黄腐酸分子有着更高的负电荷,而这会增强能量势垒,阻碍由布朗运动引起的黄腐酸分子的相互接近。     

Controlling aliased dynamics in motion systems? An identification for sampled-data control approach

Sampled-data control systems occasionally exhibit aliased resonance phenomena within the control bandwidth. The aim of this paper is to investigate the aspect of these aliased dynamics with application to a high performance industrial nano-positioning machine. This necessitates a full sampled-data control design approach, since these aliased dynamics endanger both the at-sample performance and the intersample behaviour. The proposed framework comprises both system identification and sampled-data control. In particular, the sampled-data control objective necessitates models that encompass the intersample behaviour, i.e., ideally continuous time models. Application of the proposed approach on an industrial wafer stage system provides a thorough insight and new control design guidelines for controlling aliased dynamics.     

On constrained infinite-time nonlinear optimal control

In this work, we consider the infinite-time optimal control of input affine nonlinear systems subject to point-wise in time inequality constraints on both the process inputs and outputs. Fundamental to solving this constrained infinite-time nonlinear optimal control (CITNOC) problem is the ability to calculate the value function of it's unconstrained counterpart, the infinite-time nonlinear optimal control (ITNOC) problem. Unfortunately, the traditional ITNOC solution procedure of specifying an objective function and then solving for the optimal control policy and corresponding value function is computationally intractable in all but the simplest of examples. However, in many cases one can easily identify a stabilizing feedback for near operating point regulation. Building from this local policy, the proposed method is to construct a meaningful optimal control objective function as well as its corresponding value function. These functions are then used to analyze the closed-loop stability of the proposed policy. Upon return to the constrained case the constructed objective and value functions are again used to develop a self-consistent constrained finite-time scheme that will, for the first time, provide an exact solution to the CITNOC problem. The mechanics of the proposed method are then illustrated by an example from chemical reactor control.     

Broadband dielectric spectroscopy of nanostructured maleated polypropylene/polycarbonate blends prepared by in situ polymerization and compatibilization

The miscibility and molecular dynamics of nanostructured maleated polypropylene (mPP)/polycarbonate (PC) blends prepared by in situ polymerization of macrocyclic carbonates with polypropylene modified with 0.5 wt% of maleic anhydride-reactive groups were investigated over a wide range of frequencies (10⁻²-0.5 × 10⁷ Hz) at different constant temperatures using broadband dielectric spectroscopy and scanning transmission electron microscope (STEM). The molecular dynamics of the glass relaxation process of the blend (α-relaxation process) appeared at a lower temperature range compared with that of the pure PC. This shift in the molecular relaxation process is attributed to the partial miscibility of the two polymer components in the blends as previously confirmed by the morphology via STEM. Nanoscale morphologies with average domain diameters as small as 50 nm were obtained for the different blend compositions studied. The STEM photographs show that the graft mPP-g-PC prefers to locate at the interfaces as previously reported. The relaxation spectrum of pure PC and mPP/PC blends was resolved into α- and β-relaxation processes using the Havriliak-Negami equation and ionic conductivity. The dielectric relaxation parameters, such as relaxation peak broadness, maximum frequency, f_max, and dielectric strength, Δ? (for the α- and β-relaxation processes), were found to be blend composition dependent. The kinetics of the α-relaxation processes of the blends were well described by Vogel-Fulcher-Tammann (VFT) equation. The local process of PC was resolved into two relaxation processes β₁ and β₂, associated with the carbonyl groups' motion and the combined motions of carbonyl and phenylene groups, respectively. Only β₂ shifted to lower frequency in the blend while β₁ was relatively not affected by blending. The electric modulus of the blends was used to get a sufficient resolution of the different relaxation processes in the samples, i.e., α-, β-relaxation processes, ionic conductivity, and interfacial polarization. In addition, the blending method used was found to increase the d.c. conductivity without affecting the charge carrier transport mechanism, making it possible to develop novel polymer blends with tunable dielectric properties and morphology from existing polymers.