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1.
The baroclinic primitive equation model used for short and medium range forecasting admits high frequency as well as desirable
Rossby modes. These high frequency oscillations are excited by initial imbalances between the observed mass and wind fields.
In this paper we determine and describe the normal modes of the linearized version of the general circulation model of Laboratoire
de Meteorologie Dynamique, Paris. These normal modes are then used to initialize the model through Machenhauer’s nonlinear
correction scheme. The adiabatic nonlinear normal mode initialization technique is shown to be superior to dynamic initialization
in terms of elimination of high-frequency oscillations in the forecast. Normal modes of a particular model depend on the finite
difference scheme chosen to approximate the governing system of model equations. The results presented correspond to enstrophy-conserving
finite difference scheme. 相似文献
2.
3.
A number of sensitivity experiments have been conducted to investigate the influence of using synthetic data on cyclone forecasts
by a global spectral model. Some well known vortices have been used and the generated wind and pressure profiles are compared.
It is found that the Rankine vortex and Holland’s vortex show the best representation of cyclonic circulation. Hence these
two vortices are used in the sensitivity studies to simulate two cyclones, one of May 1979 and the other of August 1979. For
this purpose the FGGE level-III b data set, produced at ECM WF, UK is used. Synthetic temperature and humidity data are also
introduced to make the cyclones more realistic.
With the use of Holland’s vortex the system is found to move faster than with the Rankine vortex. Also, the tracks of the
cyclones simulated with Rankine vortex are found to be on the left side of the observed track while that of Holland’s vortex
is on the right side of the observed track. However, substantial filling up of the systems are noticed with introduction of
diabatic initialization of the mass and velocity fields and the forecasts of both the vortices behave differently. It is suggested
that proper selection of synthetic vortex, initialization scheme and resolution of the model are very important for better
forecast of cyclones. 相似文献
4.
传统的非连续变形分析法（DDA）法采用简单的线性位移模式计算效率高,描述大块体的高阶多项式位移模式在一定程度保留了该特点,并提高了计算精度。近年来流行的耦合有限元、自然单元的DDA法实质上是引入相应的插值形函数构成块体位移函数,计算相对低效,但具有计算更精细、更容易施加边界条件等优点。为结合传统DDA法与DDA耦合法各自的优点,建立了一种同时利用传统DDA法线性位移模式与耦合型DDA法非线性位移模式的混合法。该方法非线性模式主要针对大块体,采用了自然单元插值,缘于其具有一定无网格特征,且效率比有限元高。建立了混合模式下的整体矩阵并推导出接触等因素刚度子矩阵和荷载子向量的具体表达式。该方法建模更加方便合理,计算精度、效率介于线性模式的传统DDA法和非线性位移模式的耦合法之间。通过基本算例验证了混合法的有效性,并给出了节理围岩-隧道衬砌整体分析模型的计算结果,体现了新方法的优越性。 相似文献
5.
The yield vertex non-coaxial model is different from classical elastoplastic models, in that there is an additional plastic strain rate tangential to yield surfaces, as well as the plastic strain rate normal to yield surfaces, when orientations of principal stress change. This feature raises concerns on its finite element implementations. In nonlinear finite element numerical iterations, a large tangential plastic strain rate is likely to make the trial total strain rate direct inside a yield surface, which entails convergence difficulty. Some modifications are introduced on the non-coaxial model itself to make numerical convergence easier in the work published in Yang and Yu (2010) [20]. This paper is an extension of the previous work. Instead of modifying the non-coaxial model itself, this paper concerns the use of finite element explicit procedure, which is suitable for highly discontinuous problems. The simulations of shallow foundation load-settlement responses indicate that the finite element explicit procedure, assisted with a robust and explicit automatic substepping integration scheme of the non-coaxial model, does not encounter numerical difficulty. In addition, the overall trends of implicit and explicit simulations are similar. 相似文献
6.
In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional
spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day
of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields
(analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization
(a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall
forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution
physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian
summer monsoon region are achieved using this version of the regional model with physical initialization.
A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for
the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa
level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble
approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological
Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon
region. 相似文献
7.
基于整体经验模态分解和支持向量回归的北京市 PM 2．5预测 总被引：5，自引：0，他引：5
为了更好地掌握大气中PM2.5浓度的变化规律,利用EEMD-SVR混合模型对该地区的PM2.5浓度值进行了短期预测。首先,通过采用整体经验模态分解(EEMD)方法分析北京市PM2.5,把原始时间序列分解成多个固有模态函数和趋势项;然后,对各阶固有模态函数进行周期性分析,揭示了北京市PM2.5的周期性变化特点;最后,对经过EEMD分解后的各阶固有模态函数和趋势项用支持向量机回归(SVR)方法进行预测。结果表明,EEMD-SVR混合模型比单一的SVR模型预测精度更高。 相似文献
8.
绿片岩三轴流变力学特性的研究(II):模型分析 总被引：29，自引：6，他引：29
首先,基于在岩石全自动流变伺服仪上得到的绿片岩三轴流变试验曲线,采用五元件线性粘弹性模型对表现为粘弹性流变特性的曲线进行了辨识,获得了绿片岩的粘弹性流变参数;然后,提出了一个新的非线性粘性元件,并将其与塑性体并联起来,得到一个新的非线性粘塑性体(NVPB),该体能充分反映岩石的加速流变特性:同时,将NVPB模型与五元件粘弹性模型串联起来,建立了一个新的岩石七元件非线性粘弹塑性流变模型。采用绿片岩加速流变全过程曲线,对提出的岩石七元件非线性粘弹塑性流变模型进行了辨识,得到了岩石七元件非线性粘弹塑性流变模型的材料参数。流变模型与试验结果的比较,显示了所建模型的正确性与合理性。 相似文献
9.
龙滩水电站泥板岩剪切流变力学特性研究 总被引：20，自引：2，他引：18
利用岩石剪切流变仪,对龙滩水电站泥板岩进行了剪切流变试验,分析了泥板岩剪切位移随时间的变化规律,探讨了不同应力状态下剪切流变速率的变化趋势,讨论了岩石剪切强度随时间的变化规律。将非线性流变元件(NRC模型)与西原模型串联起来,建立了新的能够描述加速流变特性的岩石非线性流变模型。采用泥板岩剪切流变试验曲线,对建立的黏弹塑性剪切流变模型进行了辨识,获得了岩石黏弹塑性剪切流变模型的材料参数,流变模型与试验结果的比较显示所建模型的正确性与合理性。 相似文献
10.
A primitive equation spectral model has been successfully integrated for five days starting with the initial data of 26 February
1982. The geopotential heights and wind strengths are well predicted up to day 3. The 24-hour accumulated precipitation of
the model reasonably agrees only up to two days, with the observed rainfall under the influence of western disturbance that
prevailed over Afghanistan, Pakistan and north India till 3 March 1982. For one day global integration of the model, the CPU
time requirement in Cyber 170/730 is about one hour. 相似文献
11.
计算地球流体力学的回顾、进展及展望 总被引：1，自引：0，他引：1
简要回顾了计算地球流体力学的发展历史,概括介绍了计算地球流体力学的研究进展及最新发展方向。针对线性发展方程的计算稳定性问题,介绍了判定线性发展方程初值问题的稳定性判别条件：CLF条件。对分析线性偏微分方程差分格式计算稳定性判据的Fourier方法、启发性稳定性分析方法,也做了简要的介绍。同时,重点介绍了判定线性发展方程初边值问题计算稳定性的GKS理论。在非线性发展方程的计算稳定性方面,重点介绍的主要内容包括：非线性发展方程的计算紊乱现象和计算不稳定的原因;克服非线性发展方程计算不稳定的方法;瞬时平方守恒型差分格式的构造;隐式和显式完全平方守恒格式的设计;强迫耗散非线性发展方程的计算稳定性问题。在计算地球流体力学的近期进展方面,重点介绍了非线性发展方程的计算稳定性与初值的关系,强迫耗散非线性发展方程显式准完全平方守恒格式的构造。对计算地球流体力学需要进一步研究的问题,也做了简要介绍。这些研究工作的介绍,无疑对推动计算地球流体力学的研究和大气海洋模式的研制具有一定的指导意义。 相似文献
12.
S S Singh 《Journal of Earth System Science》1985,94(2):159-184
A five-level primitive equation model in a (x, y, p, t) coordinate system has been developed. A fairly sophisticated scheme of physical processes has been incorporated in the model. The model physics include air-sea interaction, cumulus parametrization, large scale condensation, dry convective adjustment, horizontal and vertical diffusion and simulated radiation. The initial balance between mass and motion fields has been obtained through a dynamic initialization scheme. The model has been integrated upto 48 hr using input data of a case of monsoon depression. The results of initialization and forecast have been presented and discussed. Wind, temperature and vertical velocity fields have been found to retain the observed map features; after the initialization, however, the surface pressure has been considerably modified. The model produced a reasonably good forecast up to 24 hr as far as the flow fields, rainfall region, structure of the depression and the movement of cyclonic circulation were concerned and beyond that damped rapidly. The rainfall rates were underestimated. Some of the shortcomings of the model are also discussed. 相似文献
13.
The roles of vortex initialization and model spin-up in tropical cyclone (TC) prediction using Advanced Research Weather Research and Forecasting (ARW) Model are studied through a case study of NARGIS (2008) cyclone over Bay of Bengal. ARW model is designed to have three two-way interactive nested domains, and a suite of 36 numerical experiments are performed with three values of maximum wind (MW), four of radius of maximum wind (RMW), and three of α and one experiment without vortex initialization. The results indicate that vortex initialization is important toward realistic representation of initial structure and location of cyclone vortex. Model spin-up during the first 18–24 h of model integration lead to faster intensification than of the real atmosphere, thus a weaker initial vortex evolved more realistically. Three experiments from vortex initialization produced MW and RMW nearer to the observations, but none of these produced a good prediction due to unrealistic intensification during model spin-up. A weaker vortex with intensity less than 50 % than observations produced the best forecast in terms of intensity, track, and landfall. The results suggest that slightly larger (~30 %) RMW than observations with α as ?0.5 (for 81 km model resolution) that produces weaker vortex is to be implemented in the design of bogus vortex. This study assesses the merits of TC bogus scheme in ARW model, illustrates the need for vortex initialization, and analyzes the spin-up problem in cold-start model simulations of TC prediction. 相似文献
14.
Hybrid time integration and coupled solution methods for nonlinear finite element analysis of partially saturated deformable porous media at small strain 
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下载免费PDF全文 The goal of the paper is to determine the most efficient, yet accurate and stable, finite element nonlinear solution method for analysis of partially saturated deformable porous media at small strain. This involves a comparison between fully implicit, semi‐implicit, and explicit time integration schemes, with monolithically coupled and staggered‐coupled nonlinear solution methods and the hybrid combination thereof. The pore air pressure pa is assumed atmospheric, that is, pa=0 at reference pressure. The solid skeleton is assumed to be pressure‐sensitive nonlinear isotropic elastic. Coupled partially saturated ‘consolidation’ in the presence of surface infiltration and traction is simulated for a simple one‐dimensional uniaxial strain example and a more complicated plane strain slope example with gravity loading. Three mixed plane strain quadrilateral elements are considered: (i) Q4P4; (ii) stabilized Q4P4S; and (iii) Q9P4; “Q” refers to the number of solid skeleton displacement nodes, and “P” refers to the number of pore fluid pressure nodes. The verification of the implementation against an analytical solution for partially saturated pore water flow (no solid skeleton deformation) and comparison between the three time integration schemes (fully implicit, semi‐implicit, and explicit) are presented. It is observed that one of the staggered‐coupled semi‐implicit schemes (SIS(b)), combined with the fully implicit monolithically coupled scheme to resolve sharp transients, is the most efficient computationally. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
基于多尺度的老采空区上方建筑物变形分析及预报 总被引：2，自引：0，他引：2
老采空区上方地表变形是一个具有复杂性、突然性和长期性等显著特点的非线性过程。在老采空区上方建设生活或服务设施时,必须对老采空区上方地基稳定性和残余变形情况进行评价和预测。基于多尺度经验模态分解（EMD）,提出了老采空区上方地表建筑物稳定性分析及预测新方法。通过实例研究,证实采用多尺度经验模态分解可获得老采空区上方地表建筑物的动态变形细部信号。对各分解尺度进行分析能更准确有效地评价原始数据所反映的建筑物变形特征和进行变形机制研究。同时,实例计算也证实,采用考虑多尺度特征的预测模型可获得比传统方法更优的变形预报精度,为更科学地评价老采空区建筑物稳定性提供理论依据。 相似文献
16.
基于ANN与GIS技术的区域岩溶塌陷稳定性预测———以桂林西城区为例 总被引：6，自引：0，他引：6
岩溶地面塌陷是岩溶区常见的一种地质灾害, 塌陷区域预测是进行国土规划、资源开发与灾害防治的必要工作.由于岩溶塌陷的影响因素众多且相互作用, 发展过程复杂, 加之各评价因子的数值获取困难, 致使长期以来塌陷区域定量预测成为一个难以解决的课题.现行的区域预测模型不能描述塌陷形成模式的非线性特征, 也难以克服评价因子权重确定过程中人为经验因素的影响.神经网络技术的自学习、自适应与高度非线性映射特点显示了其在塌陷区域预测领域中应用的前景.根据研究区内地面塌陷空间聚集分布的特征, 提出了不同因子组合条件下塌陷发生可能性的定量化方法, 结合选定的评价因子类别确定了神经网络预测模型的结构, 利用312个塌陷点样本中的292个进行网络训练, 余下的20个样本的校验结果表明该模型具有较高的可信度.运用GIS技术将研究区进行评价单元划分, 并获取各评价因子的取值, 输入到训练好的网络中进行预测.将各单元的输出值进行归并处理后得到研究区岩溶塌陷的稳定级分区图. 相似文献
17.
人工神经网络技术在水文地质学中的应用潜力初探 总被引：2，自引：0，他引：2
在许多水文地质问题中,多因素且非线性的影响常使传统的集中参数随机模型或分布参数确定性数值模型的方法难以对其作出符合实际的评价与预测。本文从几个典型的水文地质问题入手,利用人工神经网络技术的高度自组织、自适应与自学习能力和分类计算能力,对这些问题的解决进行了系统的ＢＰ网分析。结果表明,人工神经网络的应用可有效减少人为的主观臆断性,其训练识别的结果更符合实际,效果令人满意,因此具有十分广阔的应用前景。 相似文献
18.
软土固结过程中展现出明显的非线性压缩和渗透特性,同时竖井的淤堵效应常导致井阻在固结过程中随深度和时间不断演化,但目前能考虑井阻随时空演化的竖井地基非线性固结解析解还很鲜见。通过引入孔隙比与有效应力及孔隙比与渗透系数间的半对数模型描述了土体的非线性固结特性,建立了能同时考虑井阻随时空变化和涂抹影响的竖井地基非线性固结模型,并采用分离变量法获得了固结模型的解析解。将特定参数下固结解的计算结果与实测数据、已有的竖井地基固结解答进行了对比分析以验证其可靠性。最后,对竖井地基的非线性固结性状开展了大量计算分析。结果表明：竖井渗透系数随深度线性衰减越明显则地基固结速率越慢;外荷载一定时,随着软土压缩指数cc与渗透率指数ck之比的增大,竖井地基固结速度减慢;在cc /ck值不变的情况下,外荷载增加,地基固结速率加快。在涂抹区的3种径向渗透系数变化模式中,抛物线变化模式下的地基固结速度最快,线性变化模式下的地基固结速度次之,恒定模式下的地基固结速度最慢,且这种性状并不因为考虑井阻变化或土体非线性固结特性而发生改变。 相似文献
19.
将无厚度接触摩擦单元,引入观音岩混合坝接头的堆石体与混凝土挡墙之间的接触面力学行为进行模拟。采用Ducan双曲线E-B模型模拟堆石体及心墙的本构关系,考虑堆石坝的实际填筑施工过程和水库蓄水过程,对接头处的结构形式进行了接触面坡度变化和水平面上转角变化的敏感性分析,以揭示竣工期和运行期不同接头结构形式接触面上的法向应力、接触状态和可能发生水力劈裂的范围,推荐最优的接头结构方案。大坝连接坝段的三维非线性仿真分析结果表明,心墙接触面上的法向正应力均为压应力,接触面坡度越陡,接触面法向压应力越小;混凝土挡墙向上游转动的转角越大,法向压应力越大。综合来看,插入式方案4的接头部位的综合防渗性能最好,因此推荐该方案为混合坝接头的结构设计方案。 相似文献
20.
阐述了Hoek建议的非线性关系原理,以此提出了求取岩体抗剪强度的算法：考虑了岩体抗剪破坏时总体或平均水平,通过计算出不同正应力 下对应的剪应力 ,线性回归确定一定应力范围内线性化后的 、 值,解决了Hoek-Brown准则拟合算法不能求解一定正应力 条件下岩土的抗剪强度的问题。在对中缅油气管道（国内段）澜沧江跨域工程边坡岩体应用以及进一步对比研究,结果表明：采用文中算法给出的第1种确定正应力 的方法所得的 、 值与Hoek-Brown准则拟合算法所得的结果相差不大,究其原因是两种算法考虑的因素不太一样,导致围压 或正应力 大小有所差别;在实际工程正应力 较低的情况下,应采用文中算法给出的第2种确定正应力 的方法来获取的 、 值,这样所得的结果才与实际情况比较接近,克服了Hoek-Brown准则拟合算法对围压 依赖的问题。 相似文献