大型VOD（Video On Demand）系统需要设计用户许可控制、流调度等一系列算法，然而为研究此类算法而建立大型系统并不现实。本文提出VOD系统用户行为仿真平台，模拟大型VOD系统的用户行为并为各类算法提供仿真运行的平台。该平台描述了VOD系统用户行为的一般数学模型，刻划了典型用户进入系统行为分布、节目选择分布和VCR操作分布，设计了用户行为仿真平台结构，并完成了该平台。此平台提出的变强度用户流的概念，使对实际用户行为的仿真更加真实。实验表明，VOD系统用户行为仿真平台客观的反映了VOD系统的用户行为，同时还为其他算法研究和算法验证提供方便易用的基础。
Finite dement formulations are used to simulate the evolution of the elastoplastic response of functionally graded cemented carbides （FGCC） due to thermal loading. The geometry of specimens is an axisymmetric solid cylinder with a two-dimensional gradient. The elastoplastic constitutive relationship is developed by constraint factors. Numerical results show that compressive stresses occur in the surface zone and tensile stresses in the cobalt rich zone when the temperature drops from the initial stress-free temperature of 800 to 0℃. The maximum value of the surface compressive stress is 254 MPa and the maximum value of the tensile stress is 252 MPa in the cobalt rich zones. When the cobalt concentration difference in the specimens is equal to or greater than 0.3, there is pronounced plastic flow in cobalt rich zone. When the temperature heats up from 0 to 800 ℃, the total plastic strain reaches 0.001 4. Plastic flow has a significant effect on the reduction of thermal stress concentration.
