基于低成本单频u-blox接收机的GPS/BDS定向性能分析

针对高精度GNSS定向应用场景,通过实验对比对低成本单频u-blox接收机的数据质量和解算精度。结果表明,u-blox接收机GPS、BDS观测值的信噪比略低于测量型接收机;伪距精度分别为0.91 m、0.56 m,相位精度分别为1.35 cm、1.20 cm。在静态观测环境下,u-blox的定向精度可以达到航向0.2°/m和俯仰0.4°/m;动态环境下解算结果稍差,但也可以达到航向0.3°/m和俯仰0.6°/m,略低于高成本测量型接收机单频数据的实时动态定向精度。     

Discrete time-delay control of an autonomous underwater vehicle: Theory and experimental results

A discrete time-delay control (DTDC) law for a general six degrees of freedom unsymmetric autonomous underwater vehicle (AUV) is presented. Hydrodynamic parameters like added mass coefficients and drag coefficients, which are generally uncertain, are not required by the controller. This control law cancels the uncertainties in the AUV dynamics by direct estimation of the uncertainties using time-delay estimation technique. The discrete-time version of the time-delay control does not require the derivative of the system state to be measured or estimated, which is required by the continuous-time version of the controller. This particularly provides an advantage over continuous-time controller in terms of computational effort or availability of sensors for measuring state derivatives, i.e., linear and angular accelerations. Implementation issues for practical realization of the controller are discussed. Experiments on a test-bed AUV were conducted in depth, pitch, and yaw degrees of freedom. Results show that the proposed control law performs well in the presence of uncertainties.     

船体可靠性评估

为了研究不同结构船体的寿命和使用时可靠度的关系,提出了一种基于试验的可靠度估计方法.针对不同结构船体寿命服从Weibull分布,在无失效数据情形下、置信度至少为γ和寿命为t时,根据船体寿命试验数据,给出了可靠度的单侧置信下限.该方法是在Weibull分布形状参数下限已知的情况下,能将所有的无失效寿命数据进行累加,大大提高了可靠性分析的精度.最后,对钢结构、钛合金结构、铝合金结构的船体,在寿命为t月、置信度至少为γ时,计算了3种结构船体的可靠度单侧置信下限.结果表明该方法易于计算,便于工程应用.     

Wavelet analysis and nonparametric test for climate change in Tarim River Basin of Xinjiang during 1959–2006

Using wavelet analysis, regression analysis and the Mann-Kendall test, this paper analyzed time-series (1959–2006) weather data from 23 meteorological stations in an attempt to characterize the climate change in the Tarim River Basin of Xinjiang Uygur Autonomous Region, China. Major findings are as follows: 1) In the 48-year study period, average annual temperature, annual precipitation and average annual relative humidity all presented nonlinear trends. 2) At the 16-year time scale, all three climate indices unanimously showed a rather flat before 1964 and a detectable pickup thereafter. At the 8-year time scale, an S-shaped nonlinear and uprising trend was revealed with slight fluctuations in the entire process for all three indices. Incidentally, they all showed similar pattern of a slight increase before 1980 and a noticeable up-swing afterwards. The 4-year time scale provided a highly fluctuating pattern of periodical oscillations and spiral increases. 3) Average annual relative humidity presented a negative correlation with average annual temperature and a positive correlation with annual precipitation at each time scale, which revealed a close dynamic relationship among them at the confidence level of 0.001. 4) The Mann-Kendall test at the 0.05 confidence level demonstrated that the climate warming trend, as represented by the rising average annual temperature, was remarkable, but the climate wetting trend, as indicated by the rising annual precipitation and average annual relative humidity, was not obvious.     

达州市气候变化的特征分析

基于达县测站1961-2007年的地面常规观测资料,主要采用小波分析,结合趋势分析、功率谱分析等方法分析了达州市47年来近地表气温、降水随时间的变化特征.结果表明,达州市近50年来冬季(年平均)地表气温变暖幅度约为0.9℃(0.4℃),增温速率接近0.18℃/10a(0.08℃/10a),低于全球的升温幅度.利用小波分析方法研究冬季气温的周期性发现,达州市的冬季气温存在着明显的8年和50年以上的特征时间尺度和周期性振荡.通过对降水的趋势分析发现,夏季降水的增加幅度比年均显著.小波分析方法结果显示达州市的夏季降水同样存在50年以上的特征时间尺度,但在小尺度上20世纪70年代末前后存在不同的变化特征.     

一种新的聚焦点不同的近景影像融合方法

近景摄影测量是实现地面目标高精度三维建模的主要方法之一。实际摄影测量过程中,普通数字摄像机在拍摄与镜头距离不同的多个目标时,无法同时聚焦到所有目标而使近景影像各处都清晰。本文以不同聚焦点近景影像的融合为研究内容,以图像一层小波分解的高频系数能量为影像清晰度衡量指标。通过计算小波影像能量,将整幅影像划分为清晰区域、模糊区域及二者的交界区域。对于清晰区域和模糊区域,将清晰区域的像元值直接应用于融合影像,而对于二者的交界区域,将curvelet变换所得初始融合影像的像元值应用于对应位置处的融合影像,从而得到融合影像。最后,用两组实例数据对融合方法进行了验证,并采用信息熵、均方根误差和峰值信噪比三种客观评价准则,对所得融合影像进行定量分析。     

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浅谈计算机技术在煤矿储量估算中的应用

介绍了在煤矿储量估算中应用Microsoft Excel制作各种表格及计算,同时应用MAPGIS软件直接绘制储量估算图,提高图件的精度及节省绘制图件的时间。     

郯庐断裂带苏皖段重力变化的多尺度分解与构造活动分析

基于多期绝对重力与相对重力联测资料,获取不同时空尺度的郯庐断裂带苏皖段及周边地区重力场动态变化,采用小波多尺度分解方法计算不同深度的重力变化,结合区域地质构造,从深度层次的横向变化与时间尺度的纵向变化2个方面进行分析。结果表明,研究区重力变化主要由中、上地壳密度变化或断裂构造活动引起。沿郯庐断裂带苏皖段走向断裂活动分布不均,受周边深大断裂带交切作用的影响表现出明显的分段活动特征。淮阴-响水口断裂、滁河断裂等深大活动断裂带构造活动对局部重力变化具有一定的控制作用,沿断裂带走向分布有明显的重力变化梯度带;郯庐断裂带郯城-泗县段、大别山构造带霍山-六安及江苏溧阳-镇江地区在小波细节动态变化中存在重力变化梯度带异常区,但强度不高,考虑到多条深大断裂交切于此,后期需要重点关注。