四步法三维编织减纱预制件表观模拟

对四步法三维编织减纱预制件表面外观进行了分析,结合实际工作需要,设计了三维编织减纱预制件的计算机表现模拟算法,并经过编程和测试实现了四步法三维编织减纱预制件的计算机表观模拟．

三维编织预制件表观模拟系统的开发

对四步法三维编织预制件表面外观进行了分类研究。在分析计算的基础上,提出了开发三维编织预制件表观模拟系统的思路和方法,并经过程序设计实现了该模拟系统。

基于变化光源方向多图像的植物叶片表观三维模拟

为了真实准确地模拟植物叶片表观颜色,提出一种基于多图像的叶片表观模拟方法。首先搭建基于线性光源的表观图像采集系统,用以获得400张视线角度固定、光源方向变化的叶片图像集合;采用拟合方法自动地从400张图像中获得整个叶片表面的表观特征参数,包括漫反射强度、高光反射强度和粗糙度;利用该拟合方法对线性光源移动条件下理想物体的各种反射特征的变化情况进行仿真计算,然后针对叶片图像中的每个像素寻找与仿真计算结果最接近的表观模型参数作为拟合结果。通过该拟合方法,可将叶片表面上各个位置的表观参数合成3张表观参数图像,采用基于点光源的实时光照方法测试最终的可视化模拟效果。从模拟结果中可以看出利用该文方法得到的结果能够真实地表现叶片自身的表观质感特性,相对于传统方法更加真实准确。

基于农学参数的玉米叶片表观建模与可视化方法

为提高农业题材三维数字媒体内容制作效率,提出基于SPAD(soil and plant analyzer development)和生育期农学参数的作物叶片表观建模与可视化方法,并以玉米为例进行实际验证。将玉米叶片分成叶肉、一级叶脉、二级叶脉3种结构,首先获取主要生育期下各结构表观材质(包括漫反射强度、透射强度、高光反射强度、粗糙度4种参数)及SPAD数据;之后构建各类表观材质参数与SPAD及生育期之间的定量化模型;再对玉米叶片纹理样式进行抽象,构建参数化的玉米纹理结构几何表达,并基于定量化模型为纹理结构分配表观参数;最后整合实时光照计算框架,对大田光环境下玉米表观进行可视化模拟。该文方法搭建了农业知识与三维可视化效果间的桥梁,使用户可以通过调整农学参数实现对作物叶片表观的快速、准确设计与制作,为农业题材的三维数字资源开发提供技术工具。

Constitutive analysis of AZ31 magnesium alloy plate

The plastic deformation simulation of AZ31 magnesium alloy at different elevated temperatures （from 473 to 723 K） was performed on Gleeble-1500 thermal mechanical simulator at the strain rates of 0.01, 0.1, 1, 5 and 10 s-t and the maximum deformation degree of 80%. The relationship between the flow stress and deformation temperature as well as strain rate was analyzed. The materials parameters and the apparent activation energy were calculated. The constitutive relationship was established with a Zener-Hollomon （Z） parameter. The results show that the flow stress increases with the increase of strain rate at a constant temperature, but it decreases with the increase of deformation temperature at a constant strain rate. The apparent activation energy is estimated to be 129-153 kJ/mol, which is close to that for self-diffusion of magnesium. The established constitutive relationship can reflect the change of flow stress during hot deformation.

CFD Simulation of Film Flow and Gas/Liquid Countercurrent Flow on Structured Packing

A mathematic model of two-phase flow and a physical model of two-dimensional (2D) vertical section for the plate-type structured packing Mellapak 250.Y were set up and verified. The models were used to study the influence of packing’s surface microstructure on the continuity of liquid film and the amount of liquid holdup. Simulation results show that the round corner shape and micro wavy structure are favorable in remaining the continuity of liquid film and increasing the amount of liquid holdup. The appropriate liquid flow rate was determined by investigating different liquid loadings to obtain an unbroken liquid film on the packing surface. The pressure difference between inlet and outlet for gas phase allowed gas and liquid to flow countercurrently in a 2D computational domain. The direction change of gas flow occurred near the phase interface area.

Numerical Simulation of the Response Features of Apparent Seismic Wave Velocity Ratio in a Horizontal Layered Medium

This paper deals with the response features of AR(apparent ratio of seismic wave velocities to the changes of TR(true ratio of wave velocities)in the horizontal layered model by mathematical modeling.The results show that:(1)the response features of AR are associated with the parameters of the structure and its dynamic changes,and the relative position between the hypocenters and the monitoring networks,showing complicated patterns strongly related to the concrete paths of propagation of seismic waves from the source to the receiver in the observatories of the network;(2)the depth of the seismic source would have important influence on the response features of AR,especially the capacity to carry the anomalous information in the condition of the earth media,being in the anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers;(3)the response features of AR are clearly related to the changes of TR(true ratio of wave velocities)instead of changes of wave velocities themselves,i.e.the response could be small as the changes in TR is small even in the case of large changes in the wave velocities.It is suggested that more attention must be paid to all these features in combination with detailed investigation of the velocity structure of the earth media in the study region and best fitting of precise hypocenter locations when one wants to obtain the reliable precursors from the changes in AR.