为提高人员室内疏散效率,实现疏散最优路径规划的高效化和智能化,该文开展了基于Dijkstra算法的室内疏散最优路径规划模型的研究。首先,基于计算机视觉技术和单目视觉方法,获取了建筑监控视频中的人群数量和人流速度信息。接着,基于IFC(industry foundation classes)标准提取建筑空间信息,构建了符合疏散需求的路径网络,并提出了设置预测边的摄像监控网络布局方法。然后,提出了计算剩余预测边的人流速度的方法,规定了导航路网中边权的计算方法。最后,利用Dijkstra算法得到各个节点到终点的用时最短的路径。利用自建行人数据库开展测试实验,实验结果表明,该模型可在每一个决策节点处动态显示当前最优路径方向。通过上述研究,验证了基于Dijkstra算法的室内疏散最优路径规划模型在提高疏散效率与安全性方面的可行性,为应对复杂室内疏散场景提供了理论基础和技术支持。
A thermodynamic consistent phase field model is developed to describe the sintering process with multiphase powders. In this model, the interface region is assumed to be a mixture of different phases with the same chemical potential, but with different compositions. The interface diffusion and boundary diffusion are also considered in the model. As an example, the model is applied to the sintering process with Fe-Cu powders. The free energy of each phase is described by the well-developed thermodynamic models, together with the published optimized parameters. The microstructure and solute distribution during the sintering process can both be obtained quantitively.
The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.
In order to quantitively model the real solidification process of industrial multicomponent alloys, a non-isothermal phase field model was studied for multicomponent alloy fully coupled with thermodynamic and diffusion mobility database, which can accurately predict the phase equilibrium, solute diffusion coefficients, specific heat capacity and latent heat release in the whole system. The results show that these parameters are not constants and their values depend on local concentration and temperature. Quantitative simulation of solidification in multicomponent alloys is almost impossible without such parameters available. In this model, the interfacial region is assumed to be a mixture of solid and liquid with the same chemical potentials, but with different composition. The anti-trapping current is also considered in the model. And this model was successfully applied to industrial A1-Cu-Mg alloy for the free equiaxed dendrite solidification process.
