Prediction of weather parameters on a very short time scale by an Auto Regressive process for aviation flight planning

Forecasting weather parameters such as temperature and pressure with a reasonable degree of accuracy three hours ahead of the scheduled departure of an aircraft helps economic and efficient planning of aircraft operations. However, these two parameters exhibit a high degree of persistency and have nonstationary mean and variance at sub-periods (i.e. at 0000, 0300, 0600,…, 2100UTC). Hence these series have been standardised (to have mean 0 and variance 1) and thereafter seasonal differenced (lag 8) to achieve almost near stationarity. An attempt has been made to fit the standardised and seasonal differenced series of Chennai (a coastal station) and Trichy (an inland station) airport into an Auto Regressive (AR) process. The model coefficients have been estimated based on adaptive filter algorithm which uses the method of convergence by the steepest descent. The models were tested with an independent data set and diagnostic checks were made on the residual error series. An independent estimation of fractal dimension has also been made in this study to conform the number parameters used in the AR processes. The models contemplated in this study are parsimonious and can be used to forecast surface temperature and pressure.     

生态区评价研究的兴起与发展--以美国森林生态系统管理评价(FEMAT)研究为例

生态区评价是近年来出现在美国的一种新型区域生态系统管理方法的理论与实践科学研究,起始于美国总统森林会议(1993)后成立的森林生态系统管理评价组(FEMAT),目标是实现地区生态系统的科学管理.本文评介了生态区评价首项案例--美国西北太平洋沿岸区原始森林及其他各类森林经营管理方案的生态、经济、社会影响综合评价的科学与方法实践意义.指出FEMAT的生态区评价:1)迈出了生态区评价历史上坚实的第一步,实现了区域土地利用规划与生态系统管理方案从以行政疆域为准划分向以生态区域为准划定边界的转变;2)方案优化过程充分考虑区域生态、经济、社会的历史、现状与未来趋势等各方面,将科学、政策、管理融为一体,使之易于在实践中贯彻;3)促进了不同政府机构和利益团体间为实现资源开发与生态保育双重目标而共同协作.     

自适应非线性有限元的多重网格法求解及应用

描述了非线性自适应有限元的多重网格法求解过程。 通过算例说明了方法的有效性以及自适应多重网格有限元用于开挖施工过程模拟分析的优越性。     

A virtual globe-based time-critical adaptive visualization method for 3D city models

3D city models, which are important items of content on the virtual globe, are characterized by complicated structures and large amounts of data. These factors make the visualization of 3D city models highly dependent upon the performance of computer hardware. Thus, achieving the efficient rendering of 3D city models using different hardware performance levels represents one of the key problems currently facing researchers. This paper proposes a time-critical adaptive visualization method that first estimates the possible rendering time for each model according to the data structure of the model in addition to the CPU/GPU performance of the computer. It then dynamically adjusts the rendering level for each model based on the results of an estimation of the rendering time to ensure that the final scene can be completed within a given time. To verify the effectiveness and flexibility of this method, it is applied using different computers. The results show that the adaptive visualization method presented in this paper not only can adapt to computers with different levels of performances but also demonstrates an obvious improvement in the time estimation precision, visual effects, and optimization speed relative to existing adaptive visualization methods.     

自适应网格技术在数值模式中的应用研究 I.一维问题

利用变分原理的自适应网格技术被应用到三个有解析解的问题上,它能根据问题 的求解、在解的大梯度区自动加密网格,从而非常成功地算出了激波。通过分析发现自适应 网格技术在提高精度、减少运行时间方面显示了优良的性能。     

基于鲁棒自适应策略的燃气轮机系统控制器设计

太阳能、风能和潮汐能等可再生能源的发电系统,具有间歇性发电的特性.因此,具有快速响应、发电效率高的燃气轮机发电系统,能够在可再生能源发电间歇出现时充当替代系统,不仅稳固电网的负荷能力,还有助于推动可再生能源的发展.由于燃气轮机是一个模型包含未知的复杂非线性系统,目前针对转速环节主要采取传统PID控制技术.然而,实际运行中系统工况发生变化时,控制器参数不能随着这些变化做出相应的调整,使得控制效果欠佳,执行器故障的出现也可能导致系统无法正常工作.因而,本文针对单轴燃气轮机的孤岛发电模式,结合燃气轮机系统特性,基于反步法的设计思路,引入不依赖于系统模型的鲁棒自适应控制策略,并加入容错控制和Nussbaum函数构造转速控制器.在控制器设计过程中融合动态面方法,解决高阶系统中反步法引起的计算爆炸问题.最后,通过仿真,验证了控制器的可靠性.     

黑河中游荒漠绿洲农业适应气候变化技术研究

以我国第二大内陆河流域——黑河流域的中游荒漠绿洲为例,基于长期定位试验成果,研究了绿洲农业适应气候变化的技术及其潜力。结果表明,在田间水平上,垄沟灌溉种植、主栽作物与伴生植物混播种植、优化水肥管理、建立枣粮复合系统是绿洲农业适应气候变化的有效技术;在绿洲水平上,调整农业种植结构、加大农田林网规格和减少农田林网的灌溉次数、降低防风固沙体系中高耗水树种——杨树的比例等技术是应对气候变化的重要途径。综合评价结果表明,在黑河中游绿洲,通过推广上述技术,在不降低绿洲农业产值和不影响绿洲生态系统稳定性的前提下,初步估算每年可节水2.96×108m3,抵消了气温上升大约1℃所带来的蒸散发消耗量。     

自适应网格技术在MM5中的应用研究

结合一次暴雨过程，将自适应网格技术应用于中尺度模式MM5中进行数值试验，同时对比自适应网格方案和固定网格方案的优劣，对模拟结果作了诊断分析。结果表明：对于此次降水过程，自适应网格模拟的效果取决于一些参数的选择。     

基于小波变换系数自适应阈值法在语音去噪中的应用

在软阈值去噪算法基础上，根据小波变换后信号与噪音具有的奇异性，提出无偏风险自适应阈值估计算法，并应用于语音信号的去噪处理，实验结果表明该算法的最小均方误差低于其他的去噪算法。