Large eddy simulations of a circular orifice jet with and without a cross-sectional exit plate

The effect of a cross-sectional exit plane on the downstream mixing characteristics of a circular turbulent jet is in- vestigated using large eddy simulation （LES）. The turbulent jet is issued from an orifice-type nozzle at an exit Reynolds number of 5 ×104. Both instantaneous and statistical velocity fields of the jet are provided. Results show that the rates of the mean velocity decay and jet spread are both higher in the case with the exit plate than without it. The existence of the plate is found to increase the downstream entrainment rate by about 10% on average over the axial range of 8-30de （exit diameter）. Also, the presence of the plate enables the formation of vortex rings to occur further downstream by 0.5-1 .Ode. A physical insight into the near-field jet is provided to explain the importance of the boundary conditions in the evolution of a turbulent jet. In addition, a method of using the decay of the centreline velocity and the half-width of the jet to calculate the entrainment rate is proposed.     

基于被动力学的昆虫运动动力学建模与分析

在John Schmitt和Philip Holmes等人工作的基础上,基于被动力学建立了一个考虑阻尼效应的昆虫LLS(lateral leg-spring)爬行模型.通过在Matlab环境下对模型进行数值仿真,发现引入阻尼后的模型更加符合实际情况,并表现出较好的稳定性.证明在施加的控制作用十分有限的情况下,昆虫本身身体结构及其爬行姿态在维持运动的稳定性方面发挥着重要作用,事实上这样的控制策略具有重要的生物学意义,通过被动力学的机械反馈,生物体可以在有限的神经控制作用下保持稳定运动,从而在受到地面扰动时及时做出反馈,并提高能效性.同时,我们考虑了引入偏摆角扰动时系统的响应,发现相对于其他变量扰动,偏摆角可以有效地改变模型的前进方向,并具有较好的鲁棒性,提出了可能的方向控制策略.     

正常人血压与急性高原病易感性的相关性

目的:研究血压与急性高原病(AMS)的关系.方法:随机抽取新入伍士兵200名,乘飞机从海拔505米(平原)至3 658米(高原),以AMS问卷调查为基础诊断AMS.比较发生AMS组和未发生AMS组在平原地区的血压相关指标.用多重线性回归法分析AMS诊断评分值与血压各指标的相关性.结果:1)根据Lake Louise诊断标准AMS发生率为49％;根据国内诊断标准AMS发生率为13.5％,两者比较P＜0.05.2)分别根据Lake Louise诊断标准和国内诊断标准比较发生AMS组和未发生AMS组的脉压,P值分别为0.091和0.056;比较收缩压,P值分别为0.276和0.553;比较舒张压,P值分别为0.813和0.431.3)脉压和Lake Louise评分的关系用线性回归方程表示为y1=5.265 -0.060x3;脉压和国内评分的关系为y22=4.554 -0.057x3.结论:1)Lake Louise诊断标准与国内诊断标准存在差异.2)收缩压和舒张压与AMS易感性无关.3)脉压与AMS易感性呈负相关.