The dynamic behaviors of diblock copolymer/nanorod mixtures under equilibrium and nonequilibrium conditions

Cylindrical diblock copolymer/anisotropic nanorod composites under equilibrium and nonquilibrium conditions, have been modeled and simulated using dissipative particle dynamics. The aim of our present study is to understand how the anisotropic NRs affect the equilibrium self-assembled structure of diblock copolymers (DBCPs) melts and how the shear flow induces the dynamic behaviors of DBCPs/NRs composites, especially the orientation and distribution of NRs in diblock matrix. We consider two different shear directions categorized with respect to the flow velocity parallel or perpendicular to the orientation of initial structures, which are defined as z-axis shear flow and x-axis shear flow, respectively. Our results show the shear flow not only aligns the orientation of DBCPs template and the dispersed NRs toward the flow direction, but also regulates the orientational and positional order of NRs. The final self-assembly behaviors of DBCPs/NRs nanocomposites is determined by the interplay between shear-induced polymer thinning and NRs dispersion. This work provides us a viable strategy for creating polymer nanocomposites with tunable and enhanced processing properties.     

Dynamics analysis of distributed parameter system subjected to a moving oscillator with random mass, velocity and acceleration

The problem of calculating the response of a distributed parameter system excited by a moving oscillator with random mass, velocity and acceleration is investigated. The system response is a stochastic process although its characteristics are assumed to be deterministic. In this paper, the distributed parameter system is assumed as a beam with Bernoulli–Euler type analytical behaviour. By adopting the Galerkin's method, a set of approximate governing equations of motion possessing time-dependent uncertain coefficients and forcing function is obtained. The statistical characteristics of the deflection of the beam are computed by using an improved perturbation approach with respect to mean value. The method, useful to gathering the stochastic structural effects due to the oscillator–beam interaction, is simple and leads to results very close to Monte Carlo simulation for a wide interval of variation of the uncertainties.     

Tricubic interpolation in three dimensions

The purpose of this paper is to give a local tricubic interpolation scheme in three dimensions that is both C¹ and isotropic. The algorithm is based on a specific 64 × 64 matrix that gives the relationship between the derivatives at the corners of the elements and the coefficients of the tricubic interpolant for this element. In contrast with global interpolation where the interpolated function usually depends on the whole data set, our tricubic local interpolation only uses data in a neighbourhood of an element. We show that the resulting interpolated function and its three first derivatives are continuous if one uses cubic interpolants. The implementation of the interpolator can be downloaded as a static and dynamic library for most platforms. The major difference between this work and current local interpolation schemes is that we do not separate the problem into three one‐dimensional problems. This allows for a much easier and accurate computation of higher derivatives of the extrapolated field. Applications to the computation of Lagrangian coherent structures in ocean data are briefly discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Prediction of thermodynamic properties for fluid nitrogen with molecular dynamics simulations

Molecular dynamics simulation results in the isochoric isothermal ensemble are reported for a two-center Lennard Jones model of fluid nitrogen characterized by the fixed molecular elongationL = 1 = 0.3292, New values of and were determined by fitting the vapor pressure and the saturated liquid density of the model to experimental data at 94,67 K. The required vapor liquid equilibrium data of the model were taken from a study using the NpT + test particle method. The resulting values are k = 36.32013 K (36.673 K) and = 0.32973 nm (0.33073 nm), with values in parentheses being those obtained previously from a Weeks Chandler Andersen-type perturbation theory. Then pressures and internal energies were calculated by molecular simulations for 110 state points in the temperature range from 72 to 330 K and for densities up to 35 mol · L¹. Comparison of the predictions based on the new parameters with the empirical equation of state of Jacobsen et al. shows good to excellent agreement except in the near-critical region. Moreover. for almost all state points the new parameters yield an improvement over old ones from perturbation theory.     

Influence of a reduced mobility of triple points on grain growth in two dimensions

A vertex dynamics model is applied to the two-dimensional simulation of grain growth including a limited mobility of triple points. It is shown that a recent experiment on a triple node is well reproduced by the proposed model. This model is then applied to the grain growth of polycrystals to investigate the possible consequences of a reduced mobility of triple nodes. It is shown how this effect can be detected through a careful examination of the grain growth kinetics and grain size distribution function.     

Computational analysis of a three-dimensional high-velocity oxygen fuel (HVOF) thermal spray torch

An analysis of a high-velocity oxygen fuel thermal spray torch is presented using computational fluid dynamics (CFD). Three-dimensional CFD results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco diamond jet rotating wire torch, but wire feed is not simulated. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Argon is injected through the center of the nozzle. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled assuming instantaneous chemistry. A standard, two-equation, k-ε turbulence model is employed for the turbulent flow field. An implicit, iterative, finite volume numerical technique is used to solve the coupled conservation of mass, momentum, and energy equations for the gas in a sequential manner. Computed flow fields inside and outside the aircap are presented and discussed.     

三稳态压电能量采集器的动态特性与实验

为了探究三稳态压电振动能量采集器的动力学特性,以磁-机-压电耦合型三稳态压电振动能量采集器(tristable piezoelectric vibration energy harvester,简称TPVEH)为研究对象,利用磁荷法、力平衡和基尔霍夫定律分别建立了采集器末端磁铁与外部磁铁之间的非线性磁力模型和系统集总参数动力学模型。仿真分析了磁铁间距、激励加速度幅值和频率等参数对采集器动力学特性和采集电压的影响。研制了三稳态压电振动能量采集器原理样机,搭建了实验测试平台,实验验证了仿真结果的正确性。研究结果表明,随着激励加速度幅值增大,能量采集器依次经历单稳态、双稳态和三稳态3种运动状态,且三稳态运动时的工作频带和输出性能(位移、速度和采集电压)比双稳态和单稳态时要高。     

Verification of a CFD model for indoor airflow and heat transfer

The SST k–ω based model is applied to calculate air-flow velocities and temperatures in a model office room. Calculations are compared with experiments and with the results of the standard k–ε, the RNG k–ε model and the laminar model. It is concluded that (a) all the three tested turbulent models predict satisfactorily the main qualitative features of the flow and the layered type of temperature fields and (b) computations with the SST k–ω based model show the best agreement with measurements. The use of this model is proposed combined with a suitable grid.     

Treatment 1: Notes from an Informal Discussion on Interinstitutional Design Research and Image Production

Since 2003, Benjamin Bratton and Hernan Diaz-Alonso have conducted a series of parallel theory seminars and design studios at SCI-Arc (Southern California Institute of Architecture). These collaborations have addressed questions of collectivity at varying scales: personal (between two individuals, each with separate professional practices), institutional (between two disciplinary positions, one analytical and the other creative) and cultural (between what is inside and outside the architectural imaginary). The work featured in the article represents another primary mandate of their interinstitutional project: the transdisciplinary implications of design as a general form of practice as opposed to the historical definitions of ‘architecture’ or the architect. Copyright © 2006 John Wiley & Sons, Ltd.     

CFD在列车管充压特性研究中的应用

采用计算流体动力学(CFD)软件Star-cd对列车管的充压过程作了数值模拟,得出了充压过程的各特性参数;并分析了列车管长度对充压时间的影响,结果表明：充压时间随列车管长度的增加而增加,且增加率在不断变大。对列车管充气研究有一定的参考和应用价值。