A detonation-driven shock tunnel is useful as a ground test facility for hypersonic flow research.The forward detonation driving mode is usually used to achieve high-enthalpy flows due to its strong driving capability...A detonation-driven shock tunnel is useful as a ground test facility for hypersonic flow research.The forward detonation driving mode is usually used to achieve high-enthalpy flows due to its strong driving capability.Unfortunately,the strong detonation wave front results in diaphragm fragments that disturb the test flow and scratch the nozzle or test models.In this study,a dual ignition system was developed to burst a metal diaphragm without fragmentation in the forward driving mode.A series of experiments were conducted to validate the proposed technique.The influences of the delay time setting on the test conditions were investigated in detail.Numerical simulations were also conducted to obtain a better understanding of the wave processes in the shock tube.The results showed that the dual ignition system solved the diaphragm issues in the forward driving mode.The test time was shortened due to the additional ignition close to the primary diaphragm;the smaller the delay time,the shorter the effective test time.However,a small amount of time loss is considered worthwhile because the severe diaphragm problems have been solved.展开更多
选取洞庭湖湿地三峡工程建成前后6期代表性遥感影像,采用支持向量机、最大似然和CART(classification and regression tree)算法分类,利用动态度和转移矩阵分析湿地格局演变,构建压力-状态-响应模型及健康评估体系。结果表明,CART算法...选取洞庭湖湿地三峡工程建成前后6期代表性遥感影像,采用支持向量机、最大似然和CART(classification and regression tree)算法分类,利用动态度和转移矩阵分析湿地格局演变,构建压力-状态-响应模型及健康评估体系。结果表明,CART算法具有良好的适用性;景观动态变化复杂,破碎化严重,异质性强。1995―2022年水域面积由680.59 km^(2)增至913.47 km^(2),但2001―2004年因水库蓄水及植被种植等经济活动影响面积骤减,湖区采砂使泥滩面积以每年8.8 km^(2)的速率减少,苔草和芦苇面积互为增减,林地面积2016年达到峰值后显著减少。健康指数从0.345增至0.661后降到0.335,呈“亚健康”―“很健康”―“亚健康”波动状态。生态健康受社会经济(权重0.262)与自然变化(权重0.205)双重胁迫,尤其近年气候极端变化对湿地健康影响高达0.281。综合考虑社会经济发展与自然环境平衡协调,需优化水资源调度并增加湿地保育投入。展开更多
基金supported by the National Natural Science Foundation of China (Nos. 11402275,11727901 and 11472280)
文摘A detonation-driven shock tunnel is useful as a ground test facility for hypersonic flow research.The forward detonation driving mode is usually used to achieve high-enthalpy flows due to its strong driving capability.Unfortunately,the strong detonation wave front results in diaphragm fragments that disturb the test flow and scratch the nozzle or test models.In this study,a dual ignition system was developed to burst a metal diaphragm without fragmentation in the forward driving mode.A series of experiments were conducted to validate the proposed technique.The influences of the delay time setting on the test conditions were investigated in detail.Numerical simulations were also conducted to obtain a better understanding of the wave processes in the shock tube.The results showed that the dual ignition system solved the diaphragm issues in the forward driving mode.The test time was shortened due to the additional ignition close to the primary diaphragm;the smaller the delay time,the shorter the effective test time.However,a small amount of time loss is considered worthwhile because the severe diaphragm problems have been solved.
