考虑最优运行点的超速风电机组调频控制策略

风电机组凭借超速控制预留备用容量,可以同时实现惯性响应和一次调频2个控制目标.传统的控制策略往往对机组的备用容量利用不足,尚未发挥出超速风电机组的最大调频优势.为此,在深入研究超速风电机组频率控制的基础上,分别分析惯性响应和一次调频与稳态运行点的关系,提出了考虑最优运行点的超速风电机组调频控制策略.该控制策略通过调频能量模型求解出不同风速下的最优运行点,充分利用风电机组的备用容量参与频率调整,以实现频率跌落速度、深度和稳态偏差之间的优化协调.在DIgSILENT中搭建系统仿真模型进行验证,结果表明所提控制策略能够改善不同风速下系统动态频率响应特性,同时可保证风电机组自身运行的稳定性.     

高水头船闸一字闸门水动力特性数值模拟

针对某山区高水头船闸30 m淹没水深下一字闸门的水动力特性进行研究,借助FLUENT软件提供的Realizable k-ε紊流模型对门体启闭过程非恒定流场进行动态模拟,通过建立由二维平面混合网格纵向拉伸成的三维棱柱体网格,结合2.5D重构和弹性光顺动网格法,在降低网格数量、提高计算效率的同时,实现一字闸门启闭全过程三维流场模拟。引入VOF法对自由水面迭代求解,得到一字闸门启闭过程门前后水位差及动水阻力矩变化规律,将计算结果与模型试验进行比较,两者吻合较好。模拟计算发现:门底间隙对闸门运行整个阶段动水阻力矩均有影响,动水阻力矩峰值随门底间隙增大而变小。     

Self‐regulation during e‐learning: using behavioural evidence from navigation log files

The current paper examined the relationship between perceived characteristics of the learning environment in an e‐module in relation to test performance among a group of e‐learners. Using structural equation modelling, the relationship between these variables is further explored in terms of the proposed double mediation as outlined by Ning and Downing. These authors initially proposed that motivation and self‐regulation strategies are mediators between the perception of the learning environment and performance. In our replication and extension study, we substituted self‐reported self‐regulation with behavioural indicators of self‐regulation using navigation log files and focused on test‐taking rather than general motivation. We proposed that navigational patterns captured using log files can also help deduce self‐regulation in e‐modules and provide information in the absence of self‐reports. Path analyses provide partial support for our navigational hypotheses and the model. Implications of our results for the use of e‐module data and conclusions based on navigation are discussed.     

基于单轴速率转台的角速度传感器标定方法

针对传统的标定方法标定成本高且对北向基准的要求严格等问题,提出了一种用单轴速率转台作为标定设备的光纤陀螺捷联航姿系统标定方法。对光纤陀螺组合的误差进行建模,将光纤陀螺捷联航姿系统安装于单轴速率转台上,使光纤陀螺捷联航姿系统的3个陀螺轴向分别朝下进行标定实验,由此标定出3只光纤陀螺的零偏、标度因数和安装失准角共12个误差参数。通过对标定精度进行分析,验证了该方法的可行性,其标定成本低且不需要北向基准,具有一定的工程应用价值。     

实用的MEMS惯性器件外场标定方法

在实际工程应用中,当不具备高精度实验室标定设备时,研究简易可行的MEMS惯性器件外场标定算法非常有必要。在分析MEMS惯性器件误差模型的基础上,提出一种基于椭球模值约束算法的外场标定方法,通过设计合理的实验编排方案和有效的求解算法来实现对误差模型参数的估计。对比实验结果表明:所提出的标定方法简易可行,其误差系数在合理的误差范围内,从而证明了该外场标定方法的有效性。     

晃动基座下捷联惯导的抗干扰自对准算法

针对捷联惯导(SINS) 晃动基座下, SINS 难以快速实现自对准的问题, 提出SINS 的抗干扰自对准算法. 该算法通过将初始对准问题转化为Wahba 求解问题来消除角运动干扰的影响; 利用惯性坐标系重力矢量和晃动干扰加速度的频率特点, 通过设计低通滤波器对比力在惯性坐标下的投影进行滤波来消除线振动干扰的影响. 仿真结果表明, 该算法不需要进行粗对准, 能够在角运动干扰和线振动干扰同时存在的情况下快速实现自对准.

     

用于高速旋转载体的惯性导航系统设计

针对高速旋转载体的实际应用情况,采用了无陀螺捷联惯性导航技术方案,快速精确测量载体的姿态、速度和位置信息。无陀螺捷联惯导系统采用加速度计来解算载体相对惯性系的角速度,从而代替角速度陀螺仪,提高了系统的高过载的适应能力。首先推导了一种基于六加速度计配置方式力学编排方程,分析了加速度计精度、杆臂长度以及时间等因素对角速度误差产生影响,最后仿真分析了加速度计精度对惯导系统的定位精度的影响,为系统设计提供理论依据。     

A comparative study of two wayfinding aids for simulated driving tasks – single-scale and dual-scale GPS aids

Global Positioning System (GPS) is currently the most frequently used wayfinding aid for driving. Yet, GPS is designed to act as a driving guide rather than to help users gain spatial knowledge. Accordingly, GPS might be less usable in situations where such knowledge is required or highly desirable. In this study, we experimentally study the influence of GPS display scales (single-scale vs. dual-scale) using simulated driving tasks in a virtual environment. The single-scale GPS is similar to the regular GPS view. The dual-scale GPS aid is a dual-scale navigation tool that provides two levels of detail, including both detailed and contextual information. The results demonstrate that the dual-scale GPS was more efficient in leading the participants to the destination during the simulated driving and was more useful for the participants to establish spatial awareness and a cognitive map; the dual-scale GPS participants also reported higher subjective evaluations. The proposed dual-scale GPS design and experimental results show some indications for designing new wayfinding aids aimed at increasing wayfinding performance while simultaneously helping users construct a cognitive map.     

基于Walker星座的导航卫星自主导航的GDOP最小值分析

卫星自主定轨时选择测量卫星的几何构型对于定轨精度有着重要的影响.目前地面接收机与导航卫星的几何构型对定位精度的影响主要由GDOP（几何衰减因子）来衡量,GDOP值的下限限制了在一定的测量精度下用户定位的精度范围.通过构建Walker构型的导航星座将地面接收机GDOP取最小值时的边界确定,推广应用到自主导航环境下,利用均匀采样和遗传算法分别独立得到GDOP的最小值,同时用仿真数据验证了这个值的正确性.     

采用JFM7201的北斗基带数字接收通道设计

北斗卫星导航定位系统是我国自行研制的,它采用直接序列扩频技术,只有当扩频码完全同步之后才能解调出信息码。因此,对于扩频码的捕获和跟踪就成为一个非常重要的环节,基带信号处理就可实现这样的功能。JFM7201芯片是一款基带信号处理芯片,与相关的处理器配合,可以实现信号的捕获、跟踪、解调以及输出位置、速度和时间的相关信息,是北斗接收机一种比较好的实现方式。