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1.
针对传统设计洪水频率分析采用单变量方法且不考虑变量间相关关系的问题,以江西省柘林水库坝址洪水为研究对象,采用Frank Copula函数构建洪峰与5d洪量的二元联合分布,并引入联合重现期的概念。结果表明,柘林水库坝址洪水主要受洪峰和洪量控制,峰量间存在良好的相关性;两变量方法推求的峰量联合设计值均大于单变量方法,各特征量的重现期均高于设计标准。可见Copula函数拟合度较高,计算所得频率设计值更符合洪水事件的内在规律以及工程实际要求,且同时可得不同情况下的峰量设计值组合,在水文领域具有广阔的应用前景。  相似文献   

2.
多变量水文联合分布方法及Copula函数的应用研究   总被引:1,自引:0,他引:1  
简介了水文事件中的多变量联合分布计算方法,系统总结了Copula函数的原理、性质、水文计算中常用的函数类型、参数估计方法及拟合检验方法,探讨了Copula函数在水文方面的应用前景.  相似文献   

3.
以清江流域(渔峡口以上)为例,采用分布式水文模型HEC-HMS研究了模型参数自动率定功能,并选取参数优化的目标函数,以探讨目标函数的选取对模型模拟结果的影响,并分析其原因.结果表明,峰值加权均方根误差目标函数的模拟效果最佳,为选取其他洪水模拟参数优化目标函数提供了理论依据.  相似文献   

4.
伽玛函数作为水文频率及洪水计算中应用广泛的函数,计算方法众多,适用范围和计算精度各不相同。为探索适合水文计算的高精度伽玛函数计算方法,采用斯特林级数及其衍生的近似式等不同伽玛函数渐进展开公式进行计算分析,比较各种方法的适用范围及计算精度。结果表明,分段多项式法截断误差最小,成果精度最高;其次为Ramanujan渐近展开式和stirling前四项式。推荐的高精度伽玛函数计算方法可提高水文成果的精度,为各类涉水工程规划、设计中确定工程规模和管理决策提供快速精准的成果。  相似文献   

5.
设计洪水分析是抽水蓄能电站工程设计的关键内容之一,以垣曲抽水蓄能电站为例,根据我国现行设计洪水理论,利用相关水文资料,结合历史调查洪水成果,分别采用水文比拟法、瞬时单位线法、推理公式法、经验公式法计算该电站坝址设计洪水,综合比较最终选择水文比拟法作为设计洪水结果,并利用地区综合法进行合理性检验。结果表明,垣曲抽水蓄能电站设计洪水符合区域暴雨洪水特性,研究结果可为山西省小流域设计洪水分析提供重要参考价值。  相似文献   

6.
针对城市化影响洪水形成的下垫面条件且对洪水形成影响较大,以昆明市为例,通过对两个水文站日暴雨、区间洪水样本系列均值、方差检验及对城市化影响洪水作用机理分析,揭示了城市化对水文变量影响显著、水文系列一致性被破坏、洪水特征量增大等,提出了加强扣完善水环境整治、合理控制雨洪径流及河道的行洪问题,以供借鉴.  相似文献   

7.
水库设计洪水分析是水电站规划设计中一个重要环节。以革什扎河两河口水电站为例,根据设计洪水理论与实际资料,分析了该流域水文特性,计算了历史调查洪水资料的洪峰流量,并分别采用推理公式法和水文比拟法计算坝址设计洪水和洪峰模数。综合比较两种方法选用结果表明,革什扎河流域从上游到下游洪峰模数递减,符合暴雨洪水特性规律。  相似文献   

8.
特小流域洪水计算,由于缺乏水文资料和实际观察资料,往往难以确定,需采用多种方法、综合分析、合理选定.本文推荐的特小流域设计洪水计算方法,对解决这一问题有一定的参考价值.  相似文献   

9.
以黄河万家寨水库为例,采用Copula函数构建洪峰和洪量的联合分布模型,随机抽样模拟洪峰和洪量系列并转化为洪水过程线,同时考虑泥沙淤积和泄流能力不确定性影响,在给定汛限水位和调洪规则下调洪演算模拟洪水.结果表明,水文因素的随机性、库容与水位关系的不确定性是万家寨水库防洪风险的主要影响因素,泄流能力不确定性对水库泄洪影响不明显,并获得了各汛限水位方案下水库的防洪风险率,为万家寨水库前汛期汛限水位选择提供了参考依据.  相似文献   

10.
采用变域变分原理,对以流函数描述的无粘流体流动的亚音速平面叶栅反设计问题进行了理论分析和有限元计算。由于变域变分能将未知形状的几何变量及控制方程结合在一个变分泛函中,使得数学描述简洁、紧凑,且几何变量及控制方程的求解能耦合地进行。采用变分有限元方法计算结果表明,该计算原理具有较高的精度,能获得较为满意的叶栅反设计的结果。  相似文献   

11.
Two uniqueness theorems of linear thermoelasticity with one relaxation time corresponding to natural initial boundary value problems described in terms of two different pairs of thermoelastic variables: displacement-heat flux and stress-temperature are proved.  相似文献   

12.
In addition to the probability density function (pdf) derived with maximum entropy principle (MEP), several kinds of mixture probability functions have already been applied to estimate wind energy potential in scientific literature, such as the bimodal Weibull function (WW) and truncated Normal Weibull function (NW). In this paper, two other mixture functions are proposed for the first time to wind energy field, i.e. the mixture Gamma–Weibull function (GW) and mixture truncated normal function (NN). These five functions will be reviewed and compared together with conventional Weibull function. Wind speed data measured from 2006 to 2008 at three wind farms experiencing different climatic environments in Taiwan are selected as sample data to test their performance. Judgment criteria include four kinds of statistical errors, i.e. the max error in Kolmogorov–Smirnov test, root mean square error, Chi-square error and relative error of wind potential energy. The results show that all the mixture functions and the maximum entropy function describe wind characterizations better than the conventional Weibull function if wind regime presents two humps on it, irrespective of wind speed and power density. For wind speed distributions, the proposed GW pdf describes best according to the Kolmogorov–Smirnov test followed by the NW and WW pdfs, while the NN pdf performs worst. As for wind power density, the MEP and GW pdfs perform best followed by the WW and NW pdfs. The GW pdf could be a useful alternative to the conventional Weibull function in estimating wind energy potential.  相似文献   

13.
误差平方和目标函数在参数率定过程中遇到的问题   总被引:1,自引:0,他引:1  
目标函数是参数估计最重要的信息来源,针对目前大多以误差平方和目标函数为参数率定方法,通过对误差平方和目标函数的结构及单参数、多参数模型进行实例计算分析,分别发现该方法遇到不同样本所对应的参数局部优值不同、不同样本组合的参数信息不合理、甚至会提供错误参数估计信息等问题,提出了选取合适目标函数的建议,为提高参数率定的精度和效果提供依据。  相似文献   

14.
《热应力杂志》2012,35(12):1551-1581
Abstract

Stress analysis is carried out for a bimaterial infinite plane with an interfacial cavity. Uniform heat flux applies to the normal to the interface. Four combinations of boundary conditions are considered, that is, isothermal and adiabatic boundary conditions for heat flux analysis, and external force and displacement boundary conditions for stress analyses. The infinite plane consists of two bonded dissimilar materials of a half plane with a single notch. To achieve analytical solutions, a rational mapping function and a complex variable method are used. By changing the mapping function, other geometries for the notch can be analyzed. Complex stress functions for isothermal and external boundary conditions can be only achieved for stress calculation. The stress intensities of debonding are investigated for various debonding lengths for some elliptical holes, and for the debonding extensions. Complex stress functions for isothermal and displacement boundary conditions can be expressed by an infinite series and stress components et al. cannot be calculated. However, a solution of interfacial rigid inclusion can be solved. Complex stress functions for the adiabatic boundary are achieved by the integral forms for external force and displacement boundary conditions, and the integral cannot be carried out, and therefore, stress components cannot be achieved.  相似文献   

15.
Probability density function (PDF) methods offer compelling advantages for modeling chemically reacting turbulent flows. In particular, they provide an elegant and effective resolution to the closure problems that arise from averaging or filtering the highly nonlinear chemical source terms, and terms that correspond to other one-point physical processes (e.g., radiative emission) in the instantaneous governing equations. This review is limited to transported PDF methods, where one models and solves an equation that governs the evolution of the one-point, one-time PDF for a set of variables that determines the local thermochemical and/or hydrodynamic state of a reacting system. Progress over the previous 20–25 years (roughly since Pope's seminal paper [24]) is covered, with emphasis on developments over the past decade. For clarity and concreteness, two current mainstream approaches are adopted as baselines: composition PDF and velocity–composition PDF methods for low-Mach-number reacting ideal-gas mixtures, with standard closure models for key physical processes (e.g., mixing models), and consistent hybrid Lagrangian particle/Eulerian mesh numerical solution algorithms. Alternative formulations, other flow regimes, additional physics, advanced models, and alternative solution algorithms are introduced and discussed with respect to these baselines. Important developments that are discussed include velocity–composition–frequency PDF's, PDF-based methods as subfilter-scale models for large-eddy simulation (filtered density function methods), PDF-based modeling of thermal radiation heat transfer and turbulence–radiation interactions, PDF-based models for soot and liquid fuel sprays, and Eulerian field methods for solving modeled PDF transport equations. Examples of applications to canonical systems, laboratory-scale flames, and practical combustion devices are provided to emphasize key points. An attempt has been made throughout to strike a balance between rigor and accessibility, between breadth and depth of coverage, and between fundamental physics and practical relevance. It is hoped that this review will contribute to broadening the accessibility of PDF methods and to dispelling misconceptions about PDF methods. Although PDF methods have been applied primarily to reacting ideal-gas mixtures using single-turbulence-scale models, multiple-physics, multiple-scale information is readily incorporated. And while most applications to date have been to laboratory-scale nonpremixed flames, PDF methods can be, and have been, applied to high-Damköhler-number systems as well as to low-to-moderate-Damköhler-number systems, to premixed systems as well as to nonpremixed and partially premixed systems, and to practical combustion devices as well as to laboratory-scale flames. It is anticipated that PDF-based methods will be adopted even more broadly through the 21st century to address important combustion-related energy and environmental issues.  相似文献   

16.
胡建军  常黎  丁坦  左艳  余群 《水电能源科学》2016,34(11):142-147
抽水蓄能电站的可逆式机组具有强非线性与工况复杂性特点,采用理论或试验的方法均难以得到其动态特性的精确表达。在建立可逆式机组不确定参数模型的基础上,通过构造控制系统输出函数和上界函数,研究了基于滑模结构的鲁棒控制策略。理论推导与仿真试验表明,所研究的控制策略具有对运行工况变化适应性强和应用方便的特点,是解决可逆式机组复杂非线性控制问题的一种有效方法。  相似文献   

17.
本文介绍了传统PID控制、带非均匀隶属函数的模糊控制、带智能权函数的模糊控制三种控制方法。并针对柴油机燃油压力的阶跃升高控制、压力抗干扰控制和压力跟随控制,在Simulink仿真软件平台上分别对上述三种方法进行了控制仿真。结果表明,带智能权函数的模糊控制方法在控制系统稳定性、控制系统响应时间上都具有较明显的优越性。  相似文献   

18.
基于雷达实测风向数据,采用统计学方法,通过拟合曲线和回归分析中拟合优度的对比,证明可用Lorentz分布函数来描述风向角变化量的分布。研究结果表明:相对于用Gauss函数描述自然风角度变化量的概率密度,用Lorentz分布来描述风向角变化量概率密度分布与Logistic分布的拟合优度基本相同,更符合风向角变化量的分布规律,并且得出风向角变化量的Lorentz概率密度函数;Lorentz分布概率密度函数中的特征角度是决定函数形状的参数,而特征角度是与采样时间间隔相对应的,进而得出特征角度与采样时间间隔的函数关系式。  相似文献   

19.
In this paper, the genetic algorithm (GA) is originally applied to compute the Weibull parameters for wind characterization analysis, in which an objective function required in GA for searching optimization solution has been first defined as well. Wind data analyzed are observed at a wind farm in the Taiwan Strait from 2006 to 2008. To accurately describe wind speed distribution three kinds of probability density functions are compared, i.e. the Weibull, logistic and lognormal functions. Statistical parameters including the max error in the Kolmogorov-Smirnov test, root mean square error, Chi-square error and relative error of wind power density are considered as judgment criterions. The results show that GA is a useful method, there is about 33% time saving when compared with conventional iteration method. Weibull function describes best the wind distribution, regardless of time periods. Accordingly, wind power density, availability factor and electrical energy output from an ideal turbine are assessed using the Weibull parameters; utilization rate of wind energy for the currently used turbine is discussed. Further the wind energy compensates very well with solar energy; when solar radiation is down in winter and spring, the wind power becomes greater; energy ratios for each month are calculated lastly.  相似文献   

20.
Focusing towards ternary metal hydrides has recently been regarded as a new avenue for research in pressure-dependent high-temperature superconductors, thanks highly to a fairly large number of permutations of alloying metals, even metalloids, with hydrogen. Herein, new phases of Mg ? B ? H ternary hydrides are predicted from the first-principles evolutionary techniques, as a result of which the corresponding phonon and electronic calculations for the three candidate phases are performed successively to confirm their dynamic stability and the possibility to become conductors. The metallic MgBH9 undergoes a superconducting phase with a maximum Tc of 64 K at 110 GPa, with its spectral function predominantly active around optical modes. The significant increase in cumulative electron-phonon coupling constant is associated with a relatively low cutoff frequency according to the bandwidth function. As for the non-metallic candidate, hydrogen-vacancy diffusion kinetics of the MgB2H8 phase are determined by means of total energy calculations. Stable pathways at varying pressure are reported, suggesting that elevated pressure lowers the activation energy which is presumably due to an optimal level of average nearest H ? H(B) inter-fragment distances.  相似文献   

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