CFD方法计算阻抗式调压室阻抗损失系数

运用CFD(计算流体力学)方法,计算了有长连接管的阻抗式调压室的阻抗损失系数.将计算结果与水力模型试验结果进行了比较,经比较发现,采用CFD方法计算得到的结果不管在变化规律还是数值上均可达到与模型试验结果相当的精度.     

Computational analysis of the performance of a venturi-shaped roof for natural ventilation: Venturi-effect versus wind-blocking effect

Computational Fluid Dynamics (CFD) is used to gain insight in the aerodynamic performance of a venturi-shaped roof (called VENTEC roof). The simulations are performed with the 3D steady Reynolds-averaged Navier–Stokes (RANS) equations and the Renormalisation Group k–ε model. A detailed analysis is conducted of the influence of the so-called venturi-effect and the wind-blocking effect on the aerodynamic performance of the VENTEC roof. The specific roof configuration is intended to create a negative pressure in the narrowest roof section (contraction) which can be used to partly or completely drive the natural ventilation of the building zones. The CFD simulations are based on a detailed grid-sensitivity analysis and on successful validation of the grid-independent results by comparison with experiments in an atmospheric boundary layer wind tunnel. The simulations show that the aerodynamic performance of the roof is governed by the balance between the so-called venturi-effect on the one hand and the wind-blocking effect on the other hand. The venturi-effect cannot act to its full extent because the flow is non-confined. The wind-blocking effect refers to the effect of the resistance exerted by the roof contraction on the air flow and the resulting tendency of the approaching wind to flow around and over the roof, rather than only being forced through the roof contraction. The results indicate that because of the wind-blocking effect, the highest contraction ratio does not provide the best aerodynamic performance and the largest negative pressure, which is a counter-intuitive result. The paper also provides a parametric analysis to optimise the roof contraction height and contraction ratio. The study in this paper illustrates the use of CFD to increase insight in building aerodynamics and to support sustainable building design.     

滚动轴承力学模型的研究及其进展

概述了滚动轴承力学模型研究的基础理论,分析了滚动轴承从静力学模型分析到动力学模型分析的原因和各阶段主要成果,总结了国内外轴承仿真技术的现状,最后讨论了滚动轴承力学模型研究的最新动向和发展趋势。     

用涡格子CFD方法研究反应堆堆芯元件流致振动的流体力学机理

将反应堆堆芯元件简化为圆柱排列,用涡格子CFD(计算流体力学)方法对其中基本并列双圆柱元素进行数值研究.利用这种方法直接计算出涡的对流和扩散,通过对流场中涡运动的物理机理的计算与描述,得到流体运动绕流双圆柱作用力的变化,揭示出堆芯元件的流致振动流体力学机理.     

三自由度并联机器人动力学及仿真

利用雅可比矩阵建立了一种三自由度并联机器人(3-RSR)动平台的外力、外力矩、惯性力、惯性力矩和重力到驱动关节的映射关系,在合理的假设基础上,运用牛顿欧拉动力学方程得到了动力学数学模型.并且基于虚拟样机技术,利用ADAMS软件对三自由度并联机器人进行动力学仿真.结果表明,用动力学模型计算的驱动力矩值和仿真结果一致,动力学模型精度较高,将其作为驱动力矩控制设计的基础是可行的.     

潜射导弹运载器水弹道动力学系统辨识

运用基于单纯形的模拟退火算法对某潜射导弹运载器水弹道动力学系统进行了辨识,并探索了未建模不确定性及待辨识参数矢量的维数对辨识精度的影响。结果表明：未建模不确定性对辩识精度的影响较大,而待 辨识参数矢量维数的影响较小;在克服未建模不确定性后,通过采用现代辨识技术可以获得系统的较完善模型。     

Evolution simulation of lightning discharge based on a magnetohydrodynamics method

In order to solve the load problem for aircraft lightning strikes,lightning channel evolution is simulated under the key physical parameters for aircraft lightning current component C.A numerical model of the discharge channel is established,based on magnetohydrodynamics (MHD) and performed by FLUENT software.With the aid of user-defined functions and a userdefined scalar,the Lorentz force,Joule heating and material parameters of an air thermal plasma are added.A three-dimensional lightning arc channel is simulated and the arc evolution in space is obtained.The results show that the temperature distribution of the lightning channel is symmetrical and that the hottest region occurs at the center of the lightning channel.The distributions of potential and current density are obtained,showing that the difference in electric potential or energy between two points tends to make the arc channel develop downwards.The arc channel comes into expansion on the anode surface due to stagnation of the thermal plasma and there exists impingement on the copper plate when the arc channel comes into contact with the anode plate.     

Comparison of joint angle,velocity and acceleration estimators for hydraulically actuated manipulators to a novel dynamical approach

Excavators are used for a wide range of applications like earthworks and material handling. Assistance systems are becoming more common to support the operator. For monitoring and control based assistance functions the angular position, velocity and acceleration of the joints from the working implement are required. Commercial systems often use inertial measurement units, consisting of triaxial accelerometers and gyroscopes, to accomplish an estimation of those states. A novel joint angle, velocity and acceleration estimation for hydraulic manipulators is proposed and compared to state of the art methods. A decentralized kinematic filter using no information about the underlying system and a centralized kinematic filter taking the system kinematics into account are implemented as state of the art approaches. Both filters only use inertial measurement units to obtain information about the current state of the system. The novel centralized dynamic filter uses the same information as the centralized kinematic filter and extends it by a dynamic model containing additional information about the angular acceleration due to pressure readings of the hydraulic cylinders. Kalman filtering is used to combine the derived system and measurement models with the sensor information. The methods are evaluated on a material handling excavator for single and coupled movements of the working implement. The novel centralized dynamic filter enables improvements for the angular acceleration estimation compared to the decentralized and centralized kinematic filter. Less noise of the acceleration estimation and a better tracking of the actual acceleration are shown.     

模拟堆芯散体结构地震响应的简化新方法

针对核反应堆堆芯散体结构在地震载荷作用下的复杂响应,提出一种高效的三维模拟方法。该方案采用Abaqus软件中刚体及连接器功能,将堆芯散体结构简化为弹簧和阻尼器链接的质点系统,通过合理的简化获得相关力学参数。同时开发出一套脚本程序以实现堆芯结构三维简化模型的参数化建模。数值算例表明,在保证模拟工程精度的前提下,该方法的计算效率比常规方法提高百倍以上。     

Molecular Formation upon Ionization of van der Waals Clusters and Implication to Astrochemistry

The presence and formation of a large variety of organic molecules in the interstellar medium is evident from both astronomical data of absorption and emission bands at different regions of the spectrum. Specifically, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium (ISM). The mechanism for their formation in ISM‘s low temperature environment is, as of yet, a mystery nonetheless. Understanding the mechanism of formation of complex molecules such as PAHs and nitrogen-based PAHs (PANH) in the ISM is a long-standing challenge which has been drawing a growing attention for the past several decades. In this review we wish to emphasize two things: Firstly, the essential role quantum chemistry can play in the study of astrochemical reactions. Secondly, we wish to demonstrate that said variety of possibilities for chemical reaction, starting upon ionization of van der Waals clusters. The potential for different chemical reactions to occur within a cluster environment arises from the fact that such processes can take place at low temperatures as the systems pose large amounts of energy upon ionization. Moreover, the spectator molecules in the cluster can provide a dissipation route for energy by detachment from the cluster, thus the system can stabilize efficiently even at low densities. The spectator molecules can also change the potential energy surface, by which it will pose a catalytic effect for certain reactions. We will demonstrate this by presenting Ab Initio Molecular Dynamic results on ionization of small acetylene clusters.