二维矢量边界推进非结构网格生成方法

提出二维矢量边界推进生成非结构三角形网格方法并证明其可行性.根据流场边界尺度布置边界节点并运用矢量边界推进方法生成背景网格,运用符号面积函数和概率筛选方法布置初始点阵,提出Spring-Laplace方法优化节点位置,同时利用边交换技术优化网格结构.该方法可包含任意点源、线源和内嵌边界,可自由进行局部自适应加密或稀疏,实现任意平面域内与尺度要求一致的高效光滑三角网格剖分.     

近壁面气泡的运动规律研究

基于势流假设,建立气泡与壁面耦合数值模型,运用边界积分法求解,并开发三维计算程序,计算值与实验值符合很好.从气泡与壁面相互作用的基本现象入手,基于开发的程序系统地研究了刚性壁面附近气泡的动力学特性,其中包括水平壁面及倾斜壁面,研究壁面的Bjerknes效应与各特征参数之间的关系,并将各种工况的计算结果与基于Kelvin-impulse理论的Blake准则进行对比分析讨论,得出偏射流方向及壁面压力与气泡的特征参数有密切的关系,同时给出了Blake准则的适用范围.旨在为相关的近壁面气泡动态特性研究提供参考. 关键词： 气泡 壁面 边界积分 Bjerknes效应     

Segregation of H, C and B to Σ = 5 (0 1 3) α-Fe grain boundary: A theoretical study

The ASED-MO theory is used to study the effects of H and the HC and HB pairs in the electronic structure of a Fe grain boundary (GB). The results obtained for H in a GB model are consistent with its behavior as a chemical embrittler. The total energies calculated for FeH, FeC and FeB clusters indicate that all interstitials segregate to the GB. C has the lowest energy, followed by B, and could compete with other impurities for the site location on the GB.The results obtained for FeCH and FeBH are consistent with the observed behavior of C and B as cohesion enhancers. A strong repulsive interaction between C and H and B and H atoms is developed if they occupy the nearest interstitial site on the GB. When C or B are present, the total energies are similar to that obtained for the FeH cluster. This indicates that H is displaced from the capped trigonal prism (CTP). Also, we do not detect any CH or BH interaction.Density of states (DOS) and crystal orbital overlap population (COOP) curves are used to shed more light on the interstitial-Fe GB interaction. The existence of strong metal-metalloid bonds is shown, which are primarily due to Fe 3d, 4s and C (or B) 2s, 2p interactions.     

Prediction of binary interaction coefficients in grain boundary segregation

A simple semiempirical method is proposed for prediction of the values of the binary interaction coefficients in grain boundary segregation (Fowler interaction). The method is based on the volume solid solubility, the maximum possible concentration of the solute at the grain boundary, and an additional parameter that represents an activity exponent of both the solute and the host metal. Values of the interaction coefficients for numerous solutes in α‐iron are predicted. The comparison with available literature data shows reasonable agreement.     

A plasma-fluid model for EHD flow in DBD actuators and experimental validation

A numerical method to simulate plasma induced electrohydrodynamic flow is proposed in this study. The numerical model consists of three components. Firstly, a potential module to simulate temporal potential and electric field generated in the ionized fluid. Secondly, a plasma module to simulate plasma development and charge particle densities. Finally, a fluid module to simulate the flow affected by the body forces induced by the movement of the charged particles. Fluid flow is modeled using modified predictor-corrector strategy as proposed in the marker and cell method. The velocity field was corrected to achieve incompressible flow by calculating pressure correction factors, considered in all cells. Numerical convergence and time sensitivity analysis were carried to confirm grid independence and determine an efficient time step for simulations. Numerical computations are validated by comparing with experimental results of discharge currents and current densities. They were found to be in very good agreement thus providing an extensive validation. Furthermore, quiescent flow over a dielectric barrier discharge actuator is simulated in the this study, using the proposed plasma-fluid model, to model flow evolution and resolve temporal flow features for detailed analysis. The streamline and vorticity plots were analyzed and compared with experimental results, and flow results were found to be in-line with the experiments.     

Time reversal for obstacle location in elastodynamics from acoustic recording

The Note is concerned with a feasibility study of time reversal in a non-homogeneous elastic medium, from data recorded in an acoustic medium. Our aim here is to determine the presence and some physical properties of elastic “inclusions” (unknown, not observable solid objects, characterized by their elastic properties) from partial observations of acoustic waves scattered by these inclusions. A finite element numerical method, based on a variational acousto-elastodynamics formulation, is derived and used to solve the forward, and then, the time-reversed problem. A criterion, derived from the reverse time migration framework, is introduced, to help construct images of the inclusions to be determined. Numerical illustrations on configurations that mimic the breast cancer configuration are proposed, and show that one can differentiate between two inclusions, even with different properties.     

Hjelmslev quadrilateral central configurations

A Hjelmslev quadrilateral is a quadrilateral with two right angles at opposite vertices. Using mutual distances as coordinates, we show that any four-body central configuration forming a Hjelmslev quadrilateral must be a right kite configuration.     

Influence of saddle-splay deformation on lyotropic chromonic liquid crystals confined between two coaxial cylinders

ABSTRACT

A striking feature of lyotropic chromonic liquid crystals confined in cylinder model exhibit double-twist director configurations. Evidence suggests that saddle-splay deformation is among the most important factors for the distortions of director. Previous researches limit the director to distort at a fixed plane (r-? plane) by using specific boundary conditions such as degenerate planar anchoring condition. In this work, we consider lyotropic chromonic liquid crystals confined between two coaxial cylinders with free-surface boundary conditions and Rapini-Papoular-type anchoring conditions. By using finite-difference iterative method to solve the numerical solution of Euler equation, we find that saddle-splay deformation leads to double-twist director configurations under free-surface boundary conditions, which consist of the result under degenerate planar anchoring conditions. Furthermore, at Rapini-Papoular-type anchoring conditions, saddle-splay deformation has a great influence on the director in the radial direction (r direction) and the director distorts in three-dimensional space. Remarkably, our method provides a more accurate theory basis for the measured values of saddle-splay elastic constant K_24。