潮滩是全球固碳能力最高的生态系统之一,是缓解全球变暖的有效蓝色碳汇。针对潮滩碳汇功能,现有研究多关注生物作用下的碳输入过程,关于地貌演变,特别是潮沟曲流摆动引起的沉积物碳输出过程研究较少,因此无法准确评估潮滩碳汇功能的动...潮滩是全球固碳能力最高的生态系统之一,是缓解全球变暖的有效蓝色碳汇。针对潮滩碳汇功能,现有研究多关注生物作用下的碳输入过程,关于地貌演变,特别是潮沟曲流摆动引起的沉积物碳输出过程研究较少,因此无法准确评估潮滩碳汇功能的动态变化。研究结合野外观测、遥感反演与室内实验,探究了潮沟曲流摆动对潮滩沉积物碳输出过程的影响,从曲流摆动速率与有机碳空间分布特征两方面开展分析。研究结果表明:潮沟曲流摆动速率的空间差异可达数个量级,由粉砂滩的10^(-3) m/s锐减至互花米草盐沼滩的10^(-6) m/s;粉砂淤泥滩潮沟摆动速率存在显著的季节性差异,冬季摆动速率约为夏季的两倍;潮滩土壤有机碳含量呈海向递减趋势:互花米草盐沼滩(4.62 g/kg)>粉砂淤泥滩(2.61 g/kg)>粉砂滩(1.51 g/kg);综合考虑曲流摆动速率与土壤有机碳含量,发现粉砂滩沉积物碳输出速率显著高于互花米草盐沼滩,可达49.4 g C m^(-2) a^(-1),与该区域的碳埋藏速率相当。研究证实了潮沟曲流摆动对潮滩沉积物碳输出过程的重要性,为提升潮滩碳汇功能预测水平提供了重要的理论依据与数据支撑。展开更多
针对滩涂履带车在受潮汐影响的滩涂环境中进行长时间勘测作业的需求,提出柯西贝塞尔快速搜索随机树星(Cauchy Bessel Rapidly-exploring Random Tree Star,CB-RRT^(*))算法进行路径规划。为规划出安全路径,基于全局地图和潮汐数据,并通...针对滩涂履带车在受潮汐影响的滩涂环境中进行长时间勘测作业的需求,提出柯西贝塞尔快速搜索随机树星(Cauchy Bessel Rapidly-exploring Random Tree Star,CB-RRT^(*))算法进行路径规划。为规划出安全路径,基于全局地图和潮汐数据,并通过滩涂履带车到分界区的距离构建出滩涂预测模型;为提高滩涂履带车移动到目标点需进行多次路径规划的速度,对初始路径的关键树节点使用柯西概率密度函数进行采样缩小采样范围来提高节点的利用率,进而提高算法的收敛性;在重选父节点过程中考虑最大转角约束设定相应系数,并使用连续二次贝塞尔曲线进行拼接的方式来生成路径,达到提高路径平滑度的目的和解决平滑后路径与原路径偏差过大造成的安全性问题。仿真实验结果表明,CB-RRT^(*)算法在静态滩涂环境和动态滩涂环境中,能大大提高算法的收敛性和路径的平滑性,且保证路径长度最优,研究内容可以保证滩涂履带车在各种滩涂环境中进行长时间安全作业。展开更多
By large eddy simulation （LES）, turbulent databases of channel flows at different Reynolds numbers were established. Then, the probability distribution functions of the streamwise and wall-normal velocity fluctuatio...By large eddy simulation （LES）, turbulent databases of channel flows at different Reynolds numbers were established. Then, the probability distribution functions of the streamwise and wall-normal velocity fluctuations were obtained and compared with the corresponding normal distributions. By hypothesis test, the deviation from the normal distribution was analyzed quantitatively. The skewness and flatness factors were also calculated. And the variations of these two factors in the viscous sublayer, buffer layer and log-law layer were discussed. Still illustrated were the relations between the probability distribution functions and the burst events-sweep of high-speed fluids and ejection of low-speed fluidsIin the viscous sub-layer, buffer layer and loglaw layer. Finally the variations of the probability distribution functions with Reynolds number were examined.展开更多
The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer was finely measured in a wind tunnel. The concept of coarse_grained velocity structure functions, which ...The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer was finely measured in a wind tunnel. The concept of coarse_grained velocity structure functions, which describes the relative motions of straining and compressing for multi_scale eddy structures in turbulent flows, was put forward based on the theory of locally multi_scale average. Based on the consistency between coarse_grained velocity structure function and Harr wavelet transformation,detecting method was presented, by which the coherent structures and their intermittency was identified by multi_scale flatness factor calculated by locally average structure function. Phase_averaged evolution course for multi_scale coherent eddy structures in wall turbulence were extracted by this conditional sampling to educe scheme. The dynamics course of multi_scale coherent eddy structures and their effects on statistics of turbulent flows were studied.展开更多
A new method——the third power B-spline function method is developed to analyse the stability and the buckle of rolled strip under residual stress.The large deflection theory of thin plate is used to calculate the bu...A new method——the third power B-spline function method is developed to analyse the stability and the buckle of rolled strip under residual stress.The large deflection theory of thin plate is used to calculate the buckle of rolled strip and criterion of critical buckle is given.The computed results tally with those of experiment well,which provides theoretical basis and method for developing the mathematical model of flatness control.展开更多
文摘潮滩是全球固碳能力最高的生态系统之一,是缓解全球变暖的有效蓝色碳汇。针对潮滩碳汇功能,现有研究多关注生物作用下的碳输入过程,关于地貌演变,特别是潮沟曲流摆动引起的沉积物碳输出过程研究较少,因此无法准确评估潮滩碳汇功能的动态变化。研究结合野外观测、遥感反演与室内实验,探究了潮沟曲流摆动对潮滩沉积物碳输出过程的影响,从曲流摆动速率与有机碳空间分布特征两方面开展分析。研究结果表明:潮沟曲流摆动速率的空间差异可达数个量级,由粉砂滩的10^(-3) m/s锐减至互花米草盐沼滩的10^(-6) m/s;粉砂淤泥滩潮沟摆动速率存在显著的季节性差异,冬季摆动速率约为夏季的两倍;潮滩土壤有机碳含量呈海向递减趋势:互花米草盐沼滩(4.62 g/kg)>粉砂淤泥滩(2.61 g/kg)>粉砂滩(1.51 g/kg);综合考虑曲流摆动速率与土壤有机碳含量,发现粉砂滩沉积物碳输出速率显著高于互花米草盐沼滩,可达49.4 g C m^(-2) a^(-1),与该区域的碳埋藏速率相当。研究证实了潮沟曲流摆动对潮滩沉积物碳输出过程的重要性,为提升潮滩碳汇功能预测水平提供了重要的理论依据与数据支撑。
文摘针对滩涂履带车在受潮汐影响的滩涂环境中进行长时间勘测作业的需求,提出柯西贝塞尔快速搜索随机树星(Cauchy Bessel Rapidly-exploring Random Tree Star,CB-RRT^(*))算法进行路径规划。为规划出安全路径,基于全局地图和潮汐数据,并通过滩涂履带车到分界区的距离构建出滩涂预测模型;为提高滩涂履带车移动到目标点需进行多次路径规划的速度,对初始路径的关键树节点使用柯西概率密度函数进行采样缩小采样范围来提高节点的利用率,进而提高算法的收敛性;在重选父节点过程中考虑最大转角约束设定相应系数,并使用连续二次贝塞尔曲线进行拼接的方式来生成路径,达到提高路径平滑度的目的和解决平滑后路径与原路径偏差过大造成的安全性问题。仿真实验结果表明,CB-RRT^(*)算法在静态滩涂环境和动态滩涂环境中,能大大提高算法的收敛性和路径的平滑性,且保证路径长度最优,研究内容可以保证滩涂履带车在各种滩涂环境中进行长时间安全作业。
文摘By large eddy simulation （LES）, turbulent databases of channel flows at different Reynolds numbers were established. Then, the probability distribution functions of the streamwise and wall-normal velocity fluctuations were obtained and compared with the corresponding normal distributions. By hypothesis test, the deviation from the normal distribution was analyzed quantitatively. The skewness and flatness factors were also calculated. And the variations of these two factors in the viscous sublayer, buffer layer and log-law layer were discussed. Still illustrated were the relations between the probability distribution functions and the burst events-sweep of high-speed fluids and ejection of low-speed fluidsIin the viscous sub-layer, buffer layer and loglaw layer. Finally the variations of the probability distribution functions with Reynolds number were examined.
文摘The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer was finely measured in a wind tunnel. The concept of coarse_grained velocity structure functions, which describes the relative motions of straining and compressing for multi_scale eddy structures in turbulent flows, was put forward based on the theory of locally multi_scale average. Based on the consistency between coarse_grained velocity structure function and Harr wavelet transformation,detecting method was presented, by which the coherent structures and their intermittency was identified by multi_scale flatness factor calculated by locally average structure function. Phase_averaged evolution course for multi_scale coherent eddy structures in wall turbulence were extracted by this conditional sampling to educe scheme. The dynamics course of multi_scale coherent eddy structures and their effects on statistics of turbulent flows were studied.
文摘A new method——the third power B-spline function method is developed to analyse the stability and the buckle of rolled strip under residual stress.The large deflection theory of thin plate is used to calculate the buckle of rolled strip and criterion of critical buckle is given.The computed results tally with those of experiment well,which provides theoretical basis and method for developing the mathematical model of flatness control.
