排序方式： 共有11条查询结果，搜索用时 15 毫秒
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地下水水位时间序列中的混沌特征 总被引：20，自引：0，他引：20
利用相空间重构技术、G -P算法以及Wolf提出的从单变量中提取Lyapunov指数的方法 ,分别计算了太原盆地 4组地下水水位时间序列的关联维数和Lyapunov指数。结果揭示在自然状态下 ,太原盆地某些孔隙潜水和孔隙承压水水位变化存在明显的混沌特征。这不仅为以后建立水位预测模型提供了理论依据 ,并且也为运用分形理论研究地质参数的时空变异性以及含水层结构的自相似性提供了进一步的支持。 相似文献
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本文以欧阳首承教授“不损伤信息”的落区和落点结构分析方法，对四川省广汉地区的间断、持续性雷暴天气进行了具体地分析和预测。结果表明，该方法不仅可揭示天气的转折性变化，并使用10分钟一次数据的自记非规则信息，也已经能预测仅有半小时的局地雷暴天气。这不仅对民用、军用飞行有实际意义，也显示了充分利用自动气象站信息资源的必要性，并应改进目前自动气象站的记录读取方式。 相似文献
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Vasile Mioc Ernesto Pérez-Chavela Magda Stavinschi 《Celestial Mechanics and Dynamical Astronomy》2003,86(1):81-106
The two-body problem associated to an anisotropic Schwarzschild-type field is being tackled. Both the motion equations and the energy integral are regularized via McGehee-type transformations. The regular vector field exhibits nice symmetries that form a commutative group endowed with an idempotent structure. The physically fictitious flows on the collision and infinity manifolds, as well as the local flows in the neighbourhood of these manifolds, are fully described. Homothetic, spiral, and oscillatory orbits are pointed out. Some features of the global flow are depicted for all possible levels of energy. For the negative-energy case, few things have been done. The positive-energy global flow does not have zero-velocity curves; every orbit is of the type ejection – escape or capture – collision. In the zero-energy case, the collision and infinity manifolds have a very similar structure. The existence of eight trajectories that connect the equilibria on these manifolds is proved. The projectability of the zero-energy global flow completes the full understanding of the problem in this case. 相似文献
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利用一维时间序列确定吸引子维数中存在的若干问题 总被引：8，自引：0，他引：8
从一些控制方程已知的微分动力系统出发，利用它们不同分量、不同时间间隔的解序列重构相空间和原本相空间两种方式所得分维结果进行了比较，发现了一些有意义的事实，并探讨了用一维时间序列重构相空间确定吸引子维数的理论，揭示出其中存在的本质问题。最后指出，只有完全搞清动力系统的单分量序列采用怎样的延滞时间τ和怎样的采样间隔Ｈ延拓后才能保证重构相空间和原本相空间的度量性质不变时，我们才能获得真实、可靠、有用的结果。 相似文献
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预测滑坡地下水位的动态演变过程对滑坡稳定性分析具有重要意义, 三峡库区库岸滑坡地下水位时间序列受多种因素影响, 呈现出高度非线性非平稳的特征.为对其进行预测, 提出一种基于相空间重构的小波分析-粒子群优化支持向量机(wavelet analysis-support vector machine, 简称WA-PSVM)模型.该模型引入小波变换法对地下水位序列进行时频分解, 将非平稳的地下水位序列转变为多个不同分辨率尺度下的较平稳的地下水位子序列; 然后重构各子序列的相空间, 再利用PSVM(全称support vector machine)模型对地下水位各子序列进行预测, 最后将各子序列预测值相加得到最终预测结果.以三峡库区三舟溪滑坡前缘STK-1水文孔日平均地下水位序列为例, 首先分析滑坡前缘地下水位变化的影响因素, 再将WA-PSVM模型应用于地下水位预测, 并与单独PSVM模型和小波分析-BP网络模型(wavelet analysis-back propagation, 简称WA-BP)作对比.结果表明: 滑坡前缘地下水位受降雨和库水位影响较大, 利用WA-PSVM模型对STK-1水文孔地下水位进行预测的均方根误差为0.073m、拟合优度为0.966, WA-PSVM模型预测精度高于单独PSVM模型和WA-BP模型.WA-PSVM模型解决了地下水位序列非线性非平稳的问题, 在不考虑影响因素的情况下能获得满意的预测效果, 具有较高的建模效率和较强的实用性. 相似文献
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Comparison of local and global approximators in multivariate chaotic forecasting of daily streamflow
Hakan Tongal 《水文科学杂志》2020,65(7):1129-1144
ABSTRACTAlthough it is conceptually assumed that global models are relatively ineffective in modelling the highly unstable structure of chaotic hydrologic dynamics, there is not a detailed study of comparing the performances of local and global models in a hydrological context, especially with new emerging machine learning models. In this study, the performance of a local model (k-nearest neighbour, k-nn) and, as global models, several recent machine learning models – artificial neural network (ANN), least square-support vector regression (LS-SVR), random forest (RF), M5 model tree (M5), multivariate adaptive regression splines (MARS) – was analysed in multivariate chaotic forecasting of streamflow. The models were developed for Australia’s largest river, the River Murray. The results indicate that the k-nn model was more successful than the global models in capturing the streamflow dynamics. Furthermore, coupled with the multivariate phase-space, it was shown that the global models can be successfully used for obtaining reliable uncertainty estimates for streamflow. 相似文献
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???BP???????????????????????????????????????????????????????G??P??????????????????????????????????????D??h?????????????????m????????????????????????????????????????????????????BP????????????????????????????????????????????е??????????????????????????????????????????????????????????????????????t????????????? 相似文献
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《水文科学杂志》2013,58(4)
Abstract Abstract This work applies a fuzzy decision method to compare the performance of the grey model with that of the phase-space model, in forecasting rainfall one to three hours ahead. Four indices and two statistical tests are used to evaluate objectively the performance of the forecasting models. However, a trade-off must be made in choosing a suitable model because various indices may lead to different judgements. Therefore, a fuzzy decision model was applied to solve this problem and to make the optimum decision. The results of fuzzy decision making demonstrate that the grey model outperforms the phase-space model for forecasting one hour ahead, but the phase-space model performs better for forecasting two or three hours ahead. 相似文献