平面棱柱铰内考虑摩擦效应的接触分析

研究了多体系统中平面棱柱铰内的摩擦接触分析。在忽略铰内的碰撞效应的前提下,根据接触力系与约束反力的等效关系,以及各个角点接触力自身满足的互补关系,得到了接触力系关于摩擦力的线性互补方程。结合库仑摩擦定律,确定了铰内角点处的接触反力以及摩擦合力;另外,由接触力曲线可以得到铰内的接触形式,以及各个接触形式发生改变的时刻。通过ADAMS算例验证,这些接触形式转换的时刻就是铰内发生碰撞的时刻,为高效率地研究铰内碰撞提供了可能。     

Dynamically adapted grids for interacting discontinuous solutions

Further development of the dynamic adaptation method for gas dynamics problems that describe multiple interactions of shock waves, rarefaction waves, and contact discontinuities is considered. Using the Woodward-Colella problem and a nonuniformly accelerating piston as examples, the efficiency of the proposed method is demonstrated for the gas dynamics problems with shock wave and contact discontinuity tracking. The grid points are distributed under the control of the diffusion approximation. The choice of the diffusion coefficient for obtaining both quasi-uniform and strongly nonuniform grids for each subdomain of the solution is validated. The interaction between discontinuities is resolved using the Riemann problem for an arbitrary discontinuity. Application of the dynamic adaptation method to the Woodward-Colella problem made it possible to obtain a solution on a grid consisting of 420 cells that is almost identical to the solution obtained using the WENO5m method on a grid consisting of 12 800 cells. In the problem for a nonuniformly accelerating piston, a proper choice of the diffusion coefficient in the transformation functions makes it possible to generate strongly nonuniform grids, which are used to simulate the interaction of a series of shock waves using shock wave and contact discontinuity tracking.     

用变长度“T”形法测量单根纤维热导率

为了解决"T"形法中的接触热阻问题,本文在不改变纤维与热线之间的接触节点的前提下,通过测量同一根纤维不同长度对应的表观热阻,同时得到了纤维热导率以及节点的接触热阻.用变长度"T"形法测量得到 Pt 丝以及两根沥青基碳纤维的热导率分别为 73,480 和 500 W m-1 K-1.     

Direct analytical solution of a modified form of the meshing equations in two dimensions for non-conjugate gear contact

The current technological state-of-the-art utilises modified gear profiles, which are in part non-conjugate and therefore cannot be analysed using standard conjugate contact theory. Existing non-conjugate mathematical models require the solution of a system of implicit equations, typically with significant computational effort and need for careful monitoring of solution stability, convergence and selection of initial values. This paper derives a modified form for the fundamental gear meshing equations, which are reduced analytically to a single scalar equation, resulting in improved solution speed and stability. The solution is verified in benchmark tests using real gear geometries.     

Mixed finite element analysis of semi-coercive unilateral contact problems with given friction

A unilateral contact 2D-problem is considered provided one of two elastic bodies can shift in a given direction as a rigid body. Using Lagrange multipliers for both normal and tangential constraints on the contact interface, we introduce a saddle point problem and prove its unique solvability. We discretize the problem by a standard finite element method and prove a convergence of approximations. We propose a numerical realization on the basis of an auxiliary “ bolted” problem and the algorithm of Uzawa.     

一类具有一般非线性接触率和隔离率的染病年龄结构SIRS传染病模型研究

首先,建立了一类具有一般非线性接触率及隔离函数的染病年龄结构SIRS传染病模型.然后综合运用Bellman-Grownall引理、不动点定理及解的延拓方法讨论模型全局非负解的存在性及惟一性.     

Sizing Polydisperse Dispersions by Focused Beam Reflectance and Small Angle Static Light Scattering

In this work, two different methods for particle characterization, namely focused beam reflectance and small angle static light scattering, are quantitatively compared. The results are presented in the form of moment ratios of the particle size distribution, i.e., the number weighted diameter, D_1/0, and the volume weighted diameter, D_4/3, for a broad range of particle size distributions ranging from 20 to 400 μm. Various aqueous dispersions including narrow, broad, and bimodal particle size distributions of spherical shaped ceramic beads were used in the comparison. It was found that the moment ratios obtained by focused beam reflectance measurements and small angle static light scattering correlate well, in the case of spherical particles. Furthermore, it was found that the D_1/0 values obtained by focused beam reflectance measurements are more sensitive to the presence of a small fraction of fine particles in a bimodal distribution than those obtained by small angle static light scattering.     

动态接触角的初步分析

应用经典的Moffatt解,通过引入接触线特征参数λ给出接触线上的粘性剪切应力,导出动态接触角和接触线移动速度的关系,尝试解释文献中两种不同测量方法所得静态接触角不一致的现象,理论所揭示的动态接触角和接触线移动速度的关系曲线和以往文献中的曲线形式基本一致,通过和Hoffman试验数据的比较发现,λ与流体性质无关,是表征固壁性质的特征参数,并初步探讨了λ的数理意义。     

A new high-pressure vapour–liquid equilibrium apparatus

A new variable volume static type high-pressure VLE apparatus has been designed, constructed, and tested on a number of systems. The apparatus has an operating temperature range from 250 K to 393 K and pressure range from absolute vacuum up to 120 bar. The stainless steel equilibrium cell has sapphire viewing windows and a novel liquid sampling technique utilizing gas chromatographic sampling valves which permit phase sampling without disturbance to the equilibrium condition. The apparatus was tested by measuring VLE isotherms for some binary systems, viz., carbon dioxide + toluene at 283.25 K, 311.15 K, 353.15 K and 391.45 K; carbon dioxide + methanol at 263.15 K, 273.15 K, 313.15 K, 363.15 K and 373.15 K; and propane + 1-propanol at 323.15 K, 378.15 K and 393.15 K. Satisfactory modeling was obtained of the measured VLE data and thermodynamic consistency tests showed the data to be not inconsistent.