利用中尺度气象数值模式(Weather Research and Forecasting Model,WRF)模拟风场,结合兰州大学半干旱气候与环境观测站(Semi-Arid Climate and Environment Observatory of Lanzhou University,SACOL)湍流观测资料,分析了黄土高原复杂...利用中尺度气象数值模式(Weather Research and Forecasting Model,WRF)模拟风场,结合兰州大学半干旱气候与环境观测站(Semi-Arid Climate and Environment Observatory of Lanzhou University,SACOL)湍流观测资料,分析了黄土高原复杂地形上稳定边界层低空急流对近地层湍流活动的影响.黄土高原复杂地形上稳定边界层低空急流的形成与地形作用引发的局地环流有关.低空急流对近地层湍流活动有强烈影响,剪切作用使小尺度湍涡活动加剧,湍动能增大,同时非平稳运动被压制.低空急流发生时,观测数据有87.3%是弱稳定情形(梯度理查森数小于0.25);而无低空急流时,对应时段的观测表明65.4%属于强稳定层结(梯度理查森数大于0.3),非平稳运动造成湍流功率谱在低频端迅速增大.与无低空急流和弱低空急流情形相比,强低空急流发生时,近地层湍动能增大1倍,湍动能在垂直方向上的传递增大1个量级,且方向向下,约为-3×10-3 m3·s-3,湍流在上层产生并向下传递.展开更多
For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlin...For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlinear iteration.However,due to the complex underwater environment,the sound speed changes with time and space,and then the acoustic propagation path is actually a curve,which inevitably causes some errors to the traditional distance intersection positioning algorithm.To reduce the position error caused by the uncertain underwater sound speed,a new time of arrival(TOA)intersection underwater positioning algorithm of LBL system is proposed.Firstly,combined with the vertical layered model of the underwater sound speed,an implicit positioning model of TOA intersection is constructed through the constant gradient acoustic ray tracing.And then an optimization function based on the overall TOA residual square sum is advanced to solve the position parameters for the underwater target.Moreover,the particle swarm optimization(PSO)algorithm is replaced with the tra-ditional nonlinear least square method to optimize the implicit positioning model of TOA intersection.Compared with the traditional distance intersection positioning model,the TOA intersec-tion positioning model is more suitable for the engineering practice and the optimization algorithm is more effective.Simulation results show that the proposed methods in this paper can effectively improve the positioning accuracy for the underwater target.展开更多
文摘利用中尺度气象数值模式(Weather Research and Forecasting Model,WRF)模拟风场,结合兰州大学半干旱气候与环境观测站(Semi-Arid Climate and Environment Observatory of Lanzhou University,SACOL)湍流观测资料,分析了黄土高原复杂地形上稳定边界层低空急流对近地层湍流活动的影响.黄土高原复杂地形上稳定边界层低空急流的形成与地形作用引发的局地环流有关.低空急流对近地层湍流活动有强烈影响,剪切作用使小尺度湍涡活动加剧,湍动能增大,同时非平稳运动被压制.低空急流发生时,观测数据有87.3%是弱稳定情形(梯度理查森数小于0.25);而无低空急流时,对应时段的观测表明65.4%属于强稳定层结(梯度理查森数大于0.3),非平稳运动造成湍流功率谱在低频端迅速增大.与无低空急流和弱低空急流情形相比,强低空急流发生时,近地层湍动能增大1倍,湍动能在垂直方向上的传递增大1个量级,且方向向下,约为-3×10-3 m3·s-3,湍流在上层产生并向下传递.
基金supported by the National Natural Science Foundation of China(61903086,61903366,62001115)the Natural Science Foundation of Hunan Province(2019JJ50745,2020JJ4280,2021JJ40133)the Fundamentals and Basic of Applications Research Foundation of Guangdong Province(2019A1515110136).
文摘For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlinear iteration.However,due to the complex underwater environment,the sound speed changes with time and space,and then the acoustic propagation path is actually a curve,which inevitably causes some errors to the traditional distance intersection positioning algorithm.To reduce the position error caused by the uncertain underwater sound speed,a new time of arrival(TOA)intersection underwater positioning algorithm of LBL system is proposed.Firstly,combined with the vertical layered model of the underwater sound speed,an implicit positioning model of TOA intersection is constructed through the constant gradient acoustic ray tracing.And then an optimization function based on the overall TOA residual square sum is advanced to solve the position parameters for the underwater target.Moreover,the particle swarm optimization(PSO)algorithm is replaced with the tra-ditional nonlinear least square method to optimize the implicit positioning model of TOA intersection.Compared with the traditional distance intersection positioning model,the TOA intersec-tion positioning model is more suitable for the engineering practice and the optimization algorithm is more effective.Simulation results show that the proposed methods in this paper can effectively improve the positioning accuracy for the underwater target.
