三角形菱柱表面积法在材料断面分形维数测算中的应用

分形维数是材料断面特征的定量表征参数之一,同时也是判断材料断裂机理的依据,在材料力学中具有非常重要的意义。为了准确和有效地测算材料断面分形维数,引入三角形菱柱表面积法（TPSAM）,并根据其原理编写程序,在Matlab 7.1运行环境条件下实现了该算法,最后采用实例对该算法作了测算。结果表明,该程序简单明了,便于操作;所求算的表面分形维数介于2~3之间,准确度高,可推广使用。

密封唇部微观纹理方向对油封密封性能的影响

基于旋转轴密封的泵送机理,综合考虑密封唇表面三角形纹理方向的影响,建立了油封密封区域的数值计算模型,模型耦合了关于温度求解的能量守恒方程.通过迭代求解数值方程,得到唇表面三角形纹理不同方向(以三角形的重心为旋转中心,分别向右旋转0°,45°,90°,135°,180°,225°,270°,315°)时油封的泵汲率、油膜厚度、摩擦扭矩、唇口密封压力、唇口平均温度、唇口最高温度等密封性能参数,结果表明:所研究的三角形纹理的8个方向,泵汲率随方向的变化最显著,变化差值为0.7836 mL/h,而其余密封性能参数变化值相比较小,表面纹理设计时应优先考虑三角形纹理方向对泵汲率的影响;综合考虑各项密封性能参数,三角形纹理方向为135°时油封的泵汲率、摩擦扭矩、唇口平均温度、唇口最高温度均较优,在8组不同纹理方向油封中密封性能最优.

Meniscus behaviors and capillary pressures in capillary channels having various cross-sectional geometries

A numerical study has been conducted to simulate the liquid/gas interface(meniscus) behaviors and capillary pressures in various capillary channels using the volume of fluid(VOF) method. Calculations are performed for four channels whose cross-sectional shapes are circle, regular hexagon, square and equilateral triangle and for four solid/liquid contact angles of 30°, 60°, 120° and 150°. No calculation is needed for the contact angle of 90° because the liquid/gas interface in this case can be thought to be a plane surface. In the calculations, the liquid/gas interface in each channel is assumed to have a flat surface at the initial time, it changes towards its due shape thereafter, which is induced by the combined action of the surface tension and contact angle. After experiencing a period of damped oscillation, it stabilizes at a certain geometry. The interface dynamics and capillary pressures are compared among different channels under three categories including the equal inscribed circle radius, equal area, and equal circumscribed circle radius. The capillary pressure in the circular channel obtained from the simulation agrees well with that given by the Young–Laplace equation, supporting the reliability of the numerical model. The channels with equal inscribed circle radius yield the closest capillary pressures, while those with equal circumscribed circle radius give the most scattered capillary pressures,with those with equal area living in between. A correlation is developed to calculate the equivalent radius of a polygonal channel, which can be used to compute the capillary pressure in such a channel by combination with the Young–Laplace equation.

Curvatures estimation on triangular mesh

Curvatures are important geometric attributes of surfaces. There are many applications that require as a first step the accurate estimation of curvatures at arbitrary vertices on a triangulated surface. Chen and Schmitt (1992) and Taubin (1995) presented two simple methods to estimate principal curvatures. They used circular arcs to approximate the normal curvature. We find this may cause large error in some cases. In this paper, we describe a more accurate method to estimate the normal curvature, and present a novel algorithm to estimate principal curvatures by simplifying the Chen and Schmitt’s method. Some comparison results are also shown in this paper.

Curvature detail representation of triangular surfaces

Curvature tells much about details of surfaces and is studied widely by researchers in the computer graphics com- munity. In this paper, we first explain the mean-curvature view of Dirichlet energy of triangular surfaces and introduce a curvature representation of details, and then present surfaces editing applications based on their curvature representation. We apply our method to surfaces with complex boundaries and rich details. Results show the validity and robustness of our method and dem- onstrate curvature map can be a helpful surfaces detail representation.

An experimental investigation of tribological performance of triangular textures in water lubrication regime

Surface texturing has been considered as an effective approach to improve the tribological performances.Based on the consideration of enhancing the tribological performance,the experiments are carried out to investigate tribological performance of triangular textures in water lubrication.The textures are generated by the Nd:YAG laser marking system,with an area density of 20%and a depth of 7 m and are distributed uniformly on the surface of the SiC rings.Compared with the circular textures,the triangular textures have obvious tribological anisotropy.The triangular textures in clockwise direction show the best friction reduction effect among the three textures.The friction reduction mechanisms of the triangular textures in clockwise direction are also analyzed and discussed.

A fast mapping method to evaluate immersed boundary hydrodynamic forces

Immersed boundary method is a crucial method to deal with particle suspension flow.Particle shapes involved in such flow are usually simple geometry,such as sphere and ellipsoid,which can be conveniently represented by the triangular surface grid.When the number of particles and resolution of the surface grid increase,calculating the hydrodynamic force on the particle surface through integration can be time-consuming.Hence,the present paper establishes a fast mapping method to evaluate immersed boundary hydrodynamic force.Firstly,the particle surface grid is generated by an initial triangular element grid.Subsequently,the initial surface grid is refined by bisection refinement to the desired resolution.The final step is to find the triangular element index on the particle triangular surface grid,which contains the projective point.Test cases show that the present mapping algorithm has good accuracy and efficiency for calculating hydrodynamic forces of particles.