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31.
—The nonlinear behaviors of plane coupled motions for a given two-point tension mooring sys-tem,are discussed in the present paper.For a cylinder moored by two taut lines under the action ofgravity,buoyance and forces due to wave-current and mooring lines,a mathematical model of motionswith three degrees of freedom is established.The steady solution and stability are analyzed.By integratingthe equations of motions,history,phase map and Poincare map are obtained.The Liapunov exponentsare also computed.The numerical results show that:the horizontal movement will increase,and stabilitywill also increase as the steady force increases.The amplitude of responses will decrease as time-dependentforces decrease.Because of the geometric nonlinearity,there exist many windows bifurcating to pseudo-pe-riodic or multi-periodic solution.The bifurcating patterns may be different.The behaviors are very com-plex.Under wave excitation alone,the motions are nonsymmetrical but still symmetrical statistically. 相似文献
32.
岩性储集层的混沌识别技术研究 总被引：2，自引：0，他引：2
本文从动力学系统原理出发,论述了混沌理论中的李指数法,并从地震剖面上提取李指数,并应用李指数来区分和识别储集层的岩性变化特征和含油气性。计算和应用研究表明,李指数随着相空间维数的增加容易趋于稳定值,这就使它预测地震序列横向变化的可靠性增大,这正是李指数预测岩性和含油气性的一个优越性。成功地应用实例表明,混沌识别技术是岩性储集层的一种有效识别技术,并具有广阔的应用前景。 相似文献
33.
The present study was carried out as part of a complex survey of urban groundwater quality and quantity in Szeged, southeast Hungary. The concentrations of 12 inorganic contaminants in 28 shallow groundwater monitoring wells were determined over a 2-year period (2010–2012). The evaluation of concentrations indicates remarkable contamination all over the city. Discriminant analysis (DA) was used to evaluate the spatial changes of groundwater quality. The groundwater levels were measured over a 14-year period (2000–2013). The fractal properties of water level fluctuations time series characterizing the groundwater system and Tisza River were investigated using rescaled range (R/S) analysis. The resulting Hurst exponents clearly showed the persistency and thus long memory effects of both the groundwater and the river flow. Comparison of the results of DA with the results of R/S analysis thus implies that the geological conditions and the changing groundwater quantities are not related to groundwater quality.
EDITOR A. CastellarinASSOCIATE EDITOR A. Fiori 相似文献
34.
The persistence effect contribution of legacy nutrients is often cited as a reason for little or no improvement in water quality following extensive implementation of watershed nutrient mitigation actions, yet there is limited knowledge concerning factors influencing this response, often called the “persistence effect.” Here, we adopted detrended fluctuation analysis and Spearman analysis methods to assess the influence of land use on the watershed phosphorus (P) persistence effect, using monthly water quality records during 2010–2016 in 13 catchments within a drinking water reservoir watershed in eastern China. Detrended fluctuation analysis was used to calculate the Hurst exponent α to assess watershed legacy P characteristics (α ≈ 0.5, α > 0.5, and α < 0.5 indicate white noise, persistence, and anti‐persistence, respectively). Results showed weak to strong P persistence (0.60–0.81) in the time series of riverine P in the 13 catchments. The Hurst exponent α had negative relationships with agricultural land (R = ?.47, p = .11) and developed land (R = ?.67, p = .01) and a positive relationship with forest land cover (R = .48, p = .10). The persistence effect of riverine P was mainly determined by retention ability (biogeochemical legacy) and migration efficiency (hydrological legacy). A catchment with strong retention capacity (e.g., biomass uptake/storage and soil PO4 sorption) and low migration efficiency results in a stronger persistence effect for riverine P. In practice, source control is more effective in catchments with weak persistence, whereas sink control (e.g., riparian buffers and wetlands) is preferred in catchments with strong persistence effects. 相似文献
35.
??????????κ??????R/S????????????????????????????M??4.5????1970??2010??????M??1.0?????з???????????????????????????????????????????????????????е?H???H=0.79????????????е?H?(H=0.87)???????????????????????????ν??? 相似文献
36.
This study aims to reveal the multi-scaling behavior and quantify the irregularity of near-fault earthquake ground motions from a new perspective of multifractal theory. Based on multifractal detrended fluctuation analysis, the multifractal characteristic parameters of acceleration time series for typical near-fault ground motions are calculated, and their correlations with two period parameters (i.e., mean period Tm and characteristic period Tc) and box-counting fractal dimensions are analyzed. Numerical results of strong nonlinear dependence of generalized Hurst exponents h(q) upon the fluctuation orders q indicate that near-fault ground motions present the multifractal properties and long-range correlation obviously. Furthermore, the scaling exponent h(2) of near-fault records has a strong correlation with their periods Tm and Tc, and strongly negative correlation with their box dimension. Moreover, h(2) can be regarded as a measure of frequency content and irregularity degree of strong earthquake ground motions. Finally, it is pointed out that the long-range correlation of small and large fluctuation is the major source of multifractality of near-fault ground motions. 相似文献
37.
杨赤中推估法是一种对空间域复合变量通过连续的几何滤波过程来建立核函数的最小二乘推估法,建模过程简便且能基于少量已知数据点取得好的建模效果。针对地质勘查中离散、稀疏而不规则分布的地质特征点数据难以构建地质体三维模型的难点问题,提出了一种基于杨赤中推估法的三维地质空间插值与模型建立的自动化方法。该方法首先以地质特征点数据库为基础,选用负幂指数函数模型建立适合三维地质空间插值的杨赤中推估法估值数学模型;在此基础上,构建一套基于杨赤中推估法的三维地质空间插值计算和地质体隐式建模的自动化实现流程与程序;最后以实例矿化插值数据为基础,采用基于移动立方体算法的三维隐式建模方法,快速构建实例矿体三维模型。与人工交互圈定地质体边界和进行矿体推断的三维地质显式建模相比,这种方法能快速直观地分析地质特征并处理样品分析数据,方法可行且高效。 相似文献
38.
39.
本文汇总整理了2000-2014年中国发生的472起重特大煤矿事故,获得其空间分布状况;基于分形理论,利用网格法统计不同网格尺度下覆盖重特大煤矿事故的非空网格中的事故数量,计算煤矿事故的全国、三大自然地理区以及干湿分区的分维值,分析其空间分布分形特征;利用R/S方法研究15年来重特大煤矿事故发生的时间分形特征。研究表明,从全国范围来看,重特大煤矿事故具有较好的空间分形特性,但不同区域的重特大煤矿事故的分形特性却具有很大差别。15年来发生重特大事故数量及事故死亡人数逐年下降,由R/S分析得到的Hurst指数表明事故时间序列的分形特征客观存在,并且年发生事故数量及事故死亡人数量减少趋势。 相似文献
40.
R. F. S. Andrade O. Oliveira A. L. Cardoso L. S. Lucena F. E. A. Leite M. J. Porsani R. C. Maciel 《Computational Geosciences》2009,13(2):155-163
Self-affine properties have been observed in a large variety of rough profiles and time series from natural data sets. In
this work, seismograms used for oil prospecting, which contain information of distinct subsurface features collected by seismic
waves reflected or scattered at their interfaces, are taken into consideration. It is expected that any self-affine property,
measured by the Hurst exponent H, depends on the depth. For each seismic trace, H is evaluated locally within a moving window, which is chosen narrow enough to reveal space dependency but also wide enough
to display scale invariance. With the use of color code diagrams, it is possible to draw two-dimensional diagrams that show
the local dependence of H for the analyzed seismogram. The reliability of the method is tested by the investigation of seismograms that contain ground
roll components, as well as multiple reflections. The effect of different kinds of filter in the scaling properties is also
investigated. In this case, comparisons are drawn among the diagrams obtained from original seismograms and those subjected
to appropriate filter to eliminate spurious components.
Work supported by the Brazilian agencies CNPq, FINEP-CTPETRO and Petrobras. 相似文献