Study on CaCO3/PMMA nanocomposite microspheres by soapless emulsion polymerization

A soapless emulsion polymerization method was applied to synthesize CaCO₃/PMMA spherical composite with different loading of CaCO₃. CaCO₃ nanoparticles were pretreated with oleic acid after the carbonation process of Ca(OH)₂ slurry by CO₂, in order to improve the compatibility between the CaCO₃ particles and MMA monomer in emulsion system. The results of photon correlation spectroscopy (PCS) showed the particles size of composites were bigger than the pure PMMA. And the size increased with the increase of the content of CaCO₃ nanoparticles. TEM images showed that the morphology of the composite microspheres was uniform and CaCO₃ nanoparticles can be well encapsulated in the polymeric microsphere, and were located at the edge of the spheres. The results of DTG and TG indicated that the CaCO₃ nanoparticles could improve the thermal stability of PMMA. Moreover, capsulation of CaCO₃ by PMMA can increase the acid-resistant of CaCO₃ nanofillers.     

Synthesis of stable hollow silica microspheres with mesoporous shell in nonionic W/O emulsion

Stable hollow silica microspheres were synthesized by a solgel method in nonionic W/O emulsion; the mesoporous shell wall of the spheres could have potential applications as controlled release capsules for drugs, dyes, cosmetics and inks, artificial cells, catalysts, and fillers.     

多体动力学的几何积分方法研究进展

动力系统的几何积分研究是近20年来工程计算领域非常活跃的方向.多体动力学方程(微分方程, 微分代数方程)是一类典型的动力系统,将其从Lagrange体系向Hamilton系统过渡,目的在于从欧氏几何过渡到辛几何形态, 将对偶变量引入到力学研究中,然后利用辛几何的数学框架对多体系统动力学方程进行数值计算,可以预知多体动力学系统的一些定性信息,并在数值离散时能保持这些定性性质特征,尤其在表示关键的物理意义时需要强调保持这些几何性质.简要介绍多体系统(无约束多刚体系统、完整约束多刚体系统和柔性多体系统)的Hamilton正则方程的建立和几何积分方法的构造,着重介绍了在多体动力学计算中非常有应用前景的高阶辛算法(合成辛算法、分裂合成辛算法和辛精细积分法)、多辛算法,以及广义Hamilton 系统与Lie 群积分方法等计算几何力学方法, 并对Lie群积分的投影方法、流形局部坐标法等方法进行了阐述.      

水电站压力钢管外压稳定问题的数值仿真研究

水电站压力钢管因失稳屈曲破坏过程的复杂性及影响失稳因素的多样性,导致对该问题的研究很难进行.目前该问题的传统计算方法存在一定的局限性,有时甚至计算结果相差较大.本文用神经网络模型结合模拟退火算法对该问题进行数值仿真求解,并通过测试样本验证了算法的可行性,为压力钢管外压稳定问题的分析方法开拓了一条新的研究思路.     

夹层梁低速冲击下的接触定律与结构响应

在考虑面板面内拉伸刚度等非线性因素的基础上,将夹层梁上面板视为弹塑性地基上的梁,由其平衡方程推导准静态压入接触定律. 进而研究了底面固定于刚性平面的夹层梁的低速冲击响应,验证了所推导的准静态压入接触定律在低速冲击下依然足够精确. 最后,用能量守恒模型,离散模型和连续模型分析了两端简支夹层梁的低速冲击响应以及接触持续时间.同时讨论了冲头与夹层梁质量比和初速度对结构响应以及分析模型适用性的影响. 理论分析结果与数值模拟结果比较表明:推导的接触定律是准确有效的. 给定初速度,质量比很小时,只有连续模型有效,而当质量比较大时3种模型均有效;给定质量,初速度较大时只有连续模型比较有效. 连续模型预测的接触持续时间与初速度无关.      

12-Tungstophosphoric acid niched in Zr-based metal-organic framework: a stable and efficient catalyst for Friedel-Crafts acylation

Heteropoly acids(HPA) are well known for their versatile solid acid catalysis in diverse chemical reactions, however they suffer from low surface area(10 m~2/g) and leaching into the reactions media, which reduce their prospects as industrial catalyst.Herein, a novel hybrid material HPW@Zr-BTC,composed of 12-tungstophoric acid(HPW) and Zr~(Ⅳ)-benzene tri-carboxylate(Zr-BTC) metal-organic framework(MOF), was prepared via one-pot solvothermal method. Excellent HPW loading up to 32.3 wt% was achieved, and HPW@Zr-BTC composite proved to be highly stable, besides the crystalline morphology of Zr-BTC was intact. The catalytic activity of the hybrid composite was explored via Friedel-Crafts acylation of anisole with benzoyl chloride.The 28.2 wt% HPW@Zr-BTC showed excellent catalytic performance, with 99.4% anisole conversion and 97.6% yield(pmethoxybenzophenone) under solvent free conditions. Excellent retention of catalytic activity was achieved after at least five consecutive runs due to non-observable HPW leaching. The promising activity and stability of the catalyst forecasted its potential industrial applications.     

空间拦截最优末端导引规律研究的新方法

给出了空间拦截控制的非线性微分方程，并在非线性控制系统引入了结构力学中的多重子结构法，从而求出了空间拦截非线性最优末端导引规律，同时给出了相应的数值仿真。     

An improved precise integration method for nonlinear dynamic system

In the present paper, based on the precise integration method established in linear dynamic system, an improved precise integration method is presented for nonlinear dynamic system. Firstly, the nonlinear dynamic system is converted into an augmented Lie type dynamic system. Then the precise integration method is improved for solving the above augmented equation and preserving its group structure in the meantime. Finally, two numerical examples are presented to demonstrate the validity and effectiveness of the proposed method.     

Accurate and straightforward symplectic approach for fracture analysis of fractional viscoelastic media

An accurate and straightforward symplectic method is presented for the fracture analysis of fractional two-dimensional(2D) viscoelastic media. The fractional Kelvin-Zener constitutive model is used to describe the time-dependent behavior of viscoelastic materials. Within the framework of symplectic elasticity, the governing equations in the Hamiltonian form for the frequency domain(s-domain) can be directly and rigorously calculated. In the s-domain, the analytical solutions of the displacement ...     

Research on data assimilation strategy of turbulent separated flow over airfoil

In order to increase the accuracy of turbulence field reconstruction, this paper combines experimental observation and numerical simulation to develop and establish a data assimilation framework, and apply it to the study of S809 low-speed and high-angle airfoil flow. The method is based on the ensemble transform Kalman filter(ETKF) algorithm, which improves the disturbance strategy of the ensemble members and enhances the richness of the initial members by screening high flow field sensitivity ...