Improvements in medium range weather forecasting system of India

Medium range weather forecasts are being generated in real time using Global Data Assimilation Forecasting System (GDAFS) at NCMRWF since 1994. The system has been continuously upgraded in terms of data usage, assimilation and forecasting system. Recently this system was upgraded to a horizontal resolution of T574 (about 22 km) with 64 levels in vertical. The assimilation scheme of this upgraded system is based on the latest Grid Statistical Interpolation (GSI) scheme and it has the provision to use most of available meteorological and oceanographic satellite datasets besides conventional meteorological observations. The new system has an improved procedure for relocating tropical cyclone to its observed position with the correct intensity. All these modifications have resulted in improvement of skill of medium range forecasts by about 1 day.     

Assimilation of IRS-P4 (MSMR) meteorological data in the NCMRWF global data assimilation system

Oceansat-1 was successfully launched by India in 1999, with two payloads, namely Multi-frequency Scanning Microwave Radiometer (MSMR) and Ocean Color Monitor (OCM) to study the biological and physical parameters of the ocean. The MSMR sensor is configured as an eight-channel radiometer using four frequencies with dual polarization. The MSMR data at 75 km resolution from the Oceansat-I have been assimilated in the National Centre for Medium Range Weather Forecasting (NCMRWF) data assimilation forecast system. The operational analysis and forecast system at NCMRWF is based on a T80L18 global spectral model and Spectral Statistical Interpolation (SSI) scheme for data analysis. The impact of the MSMR data is seen globally, however it is significant over the oceanic region where conventional data are rare. The dry-nature of the control analyses have been removed by utilizing the MSMR data. Therefore, the total precipitable water data from MSMR has been identified as a very crucial parameter in this study. The impact of surface wind speed from MSMR is to increase easterlies over the tropical Indian Ocean. Shifting of the positions of westerly troughs and ridges in the south Indian Ocean has contributed to reduction of temperature to around 30‡S.     

Impact of 3D Var GSI-ENKF hybrid data assimilation system

The hybrid two-way coupled 3DEnsVar assimilation system was tested with the NCMRWF global data assimilation forecasting system. At present, this system consists of T574L64 deterministic model and the grid-point statistical interpolation analysis scheme. In this experiment, the analysis system is modified with a two-way coupling with an 80 member Ensemble Kalman Filter of T254L64 resolution and runs are carried out in parallel to the operational system for the Indian summer monsoon season (June–September) for the year 2015 to study its impact. Both the assimilation systems are based on NCEP GFS system. It is found that hybrid assimilation marginally improved the quality of the forecasts of all variables over the deterministic 3D Var system, in terms of statistical skill scores and also in terms of circulation features. The impact of the hybrid system in prediction of extreme rainfall and cyclone track is discussed.     

考虑土-结构相互作用的结构控制H2/H∞混合凸优化方案

在地震信号和建筑结构系统的防数分析基础上，使用了混合控制优化指标J作为优化目标，并给出其物理含义。考虑土－结构相互作用的影响，针对H2控制方案和H∞控制方案的优缺点，通过LMI凸优化方法求解混合控制器，给出了在给定γ值的前提下极小化指标J的H2／H∞混合控制方案，并给出了仿真算例。     

基于Hoek-Brown强度准则的应变软化模型在隧道工程中的应用

基于Hoek-Brown强度准则及量化GSI围岩评级系统,分析岩体强度弱化行为,总结出确定岩体峰值及峰后强度参数的方法,提出应变软化模型的简化计算方法,并以FLAC3D数值模拟软件为工具,采用收敛-约束法对深埋大断面隧道支护结构及围岩稳定性进行分析,计算出支护结构安全系数。通过分析得出：随着围岩应力释放,岩体软化参数随之减小,岩体强度弱化行为突出;高地质强度GSI指标（GSI=75）的岩体虽然强度弱化程度较大,但围岩的变形量仍然较小,而低GSI指标（GSI=25）的岩体表现出了理想弹塑性行为;提出的简化Hoek-Brown应变软化模型适合应用于隧道中岩质相近区段围岩的研究;采用收敛-约束法对隧道支护结构的稳定性进行分析,可为隧道工程的初期支护优化设计及安全性评价提供参考。     

Rock mass characterization for the underground cavern design of Khiritharn pumped storage scheme

A general approach to rock engineering designing aspects adopted at the Khiritharn Pumped Storage Scheme is described. The scheme involves excavation of three large caverns and tunnels in jointed sandstone within a suture zone in Southeast Thailand. Geological condition and engineering properties of the sandstone were investigated. Strength and modulus properties of the intact rock were determined from laboratory tests and properties of rock mass were empirically estimated for the design analysis in the de.nite study stage on the basis of three rock mass classi.cation systems namely the Rock Mass Rating (RMR), Geological Strength Index (GSI) and a Japanese system (EPDC). While the GSI gives strength and modulus of deformation values slightly higher than the RMR classi.cation, the EPDC gives a lower value of modulus of deformation but comparable rock mass strength value for the level of con.ning pressures at the depth of the cavern excavation. The results of stress analysis and loosening wedge analysis for the cavern excavations suggest favorable excavation condition.     

Back analysis of an excavated slope failure in highly fractured rock mass: the case study of Kargar slope failure (Iran)

This paper examines the failure of Kargar cut slope located at the south part of Esfahan subway using analytical and numerical back analysis methods. The excavated trench has 27 m depth with near vertical walls due to the space limitation around it. The geology of the area comprises weathered and heavily jointed shale and sandstone overlaid by alluvium deposits. Despite the slope being supported by shotcrete and fully grouted rock bolts, a catastrophic failure occurred at the east wall. Due to the uncertainty about the causes of failure initiation, back analyses have been performed via both the limit equilibrium and numerical method for considering various probable mechanisms. In the back analysis with limit equilibrium method, the rock mass is assumed as an equivalent continuum and Hoek–Brown failure criterion and geological strength index (GSI) are applied to calculate the shear strength parameters. The results show that GSI value was 33 in the failed mass. In the numerical back analysis, the distinct element method is applied to study the contribution of rock joints to the failure and progressive rock mass strength degradation until failure. The results show that threshold values of joint cohesion and friction were 0.2 MPa and 30°, respectively. Also the modeled slip surface being step-shaped agrees with the observed one.     

Hoek-Brown准则参数在边坡工程中的敏感性分析

Hoek-Brown屈服准则是估计完整岩石或节理岩体剪切强度的半经验准则,已成为岩体强度预测及稳定性分析领域应用最广泛的准则之一。选取常见的3类岩石材料作为分析代表,通过有限差分法及敏感性分析方法研究了Hoek-Brown准则中各参数对岩质边坡安全系数的灵敏度。研究表明,地质强度指标GSI对岩质边坡稳定性影响最为显著,而反映岩石的软硬程度材料常数mi、岩体扰动系数D和岩石单轴抗压强度?ci影响显著性要小于地质强度指标。最后,对GSI对岩体的摩擦角? 和凝聚力c的影响规律进行了分析。结果表明,对于同一GSI,mi从小到大变化时,? 的变化幅度在减小,GSI值在55附近时,不同mi所对应的凝聚力趋于同一个值。     

Population structure and reproductive characteristics of the gulf pipefish,Syngnathus scovelli, in Mobile Bay, Alabama

The gulf pipefish,Syngnathus scovelli, is the dominant syngnathid found in coastal regions of the Gulf of Mexico and is the only species in this region known to occur in both freshwater and saltwater habitats. Relatively little is known about the population and reproductive cycles ofS. scovelli, particularly for those found in low salinity environments. The focus of the current study was to collect population structure and reproductive data forS. scovelli from a low salinity habitat, Meaher Park, located at the mouth of Mobile Bay, Alabama. Sampling was conducted twice a month from January 2003 to January 2004. Environmental parameters, as well as population and reproductive parameters, were collected. Water temperature was the primary abiotic factor associated with both the appearance ofS. scovelli and their breeding cycle. Based on gonadosomatic (GSI) and brood pouch somatic indices (BPSI), females and males were reproductively active throughout the summer. Peaks in male GSI and BPSI were consistent with the subsequent appearance of a large number of juveniles in early fall. These event coincided with the higher temperatures seen during late summer and early fall. Sex ratios (male : female 1 : 1.64) and operational sex ratios (1 : 4.09) indicated that this was a female biased population. Although there was no difference in the average size of males and females in this population, the largest individuals collected were female. The female-biased sex ratio supports previous genetic analyses suggesting thatS. scovelli exhibits true sex-role reversal and that operational sex ratios are a reliable indicator of the intensity of mating competition and sex roles.     

考虑桩-土作用的高速列车-桥梁地震响应分析

基于空间梁单元有限元法,建立了两种高速铁路多跨简支梁桥的全桥空间分析模型,一种是包括桩基的列车-桥梁模型,给出成层土的动力阻抗,采用改进的Penzien模型模拟桩-土作用;一种是不考虑桩-土作用的墩底固结的列车-桥梁模型;分析了两种模型的自振特性,计算了两种模型在不同车速、墩高、地震强度、不同地震波等工况下的地震反应。计算结果表明,桥梁横向位移、加速度主要受到低频成分的影响,这部分频率与其底部地震波相互反馈,改变了地基运动的频谱组成,使接近于桥梁结构自振频率的分量获得加强,考虑桩-土作用后,横向位移/加速度增加较大;桥梁竖向振动频率受桩-土作用影响较小,随墩高和车速的增加梁体竖向位移增加不大,梁体竖向加速度受高频成分的影响较大,这些高频主要由车辆荷载和轨道不平顺引起。     

First SHRIMP U–Pb zircon dating of granulites from the Kontum massif (Vietnam) and tectonothermal implications

The Kontum massif in Central Vietnam represents the largest continuous exposure of crystalline basement of the Indochina craton. The central Kontum massif is chiefly made of orthopyroxene granulites (enderbite, charnockite) and associated rocks of the Kannack complex. Mineral assemblages and geothermobarometric studies have shown that the Kannack complex has severely metamorphosed under granulite facies corresponding to P–T conditions of 800–850°C and 8±1 kbars. Twenty-three SHRIMP II U–Pb analyses of eighteen zircon grains separated from a granulite sample of the Kannack complex yield ca 254 Ma, and one analysis gives ca 1400 Ma concordant age for a zoned zircon core. This result shows that granulites of the Kannack complex in the Kontum massif have formed from a high-grade granulite facies tectonothermal event of Indosinian age (Triassic). The cooling history and subsequent exhumation of the Kannack complex during Indosinian times ranged from ∼850°C at ca 254 Ma to ∼300°C at 242 Ma, with an average cooling rate of ∼45°C/Ma.     

土-结构-流体动力相互作用的实时耦联动力试验

针对振动台试验中无限地基难以模拟和数值分析中流-固耦合作用难以计算两个难题,将最近发展的实时耦联动力试验方法引入土-结构-流体动力相互作用问题的研究。以一个渡槽结构为例,其中渡槽-水体作为物理子结构,采用振动台进行物理试验,而无限地基作为数值子结构,采用集总参数模型进行数值模拟。两个子结构之间实时交换数据,联合评估整个耦合体系的动力响应。试验结果和有限元数值模拟结果吻合良好,表明该试验方法具有较高精度。对不同特性地基土进行的试验对比分析结果表明：对于软土地基,考虑土-结构相互作用(SSI)的结构反应幅值明显减小,周期延长;随着地基土变硬,SSI效应逐渐变弱,结构反应最终收敛至刚性地基解。     

Dynamic soil-structure interaction: A three-dimensional numerical approach and its application to the Lotung case study

This paper presents a three-dimensional non-linear finite element (FE) approach to analyse the dynamic soil-structure interaction (SSI) phenomena observed at the Lotung Large-Scale Seismic Test (LSST) site. The numerical study is carried out in the time domain by a commercial FE code, taking into account the non-linear behaviour of soil and the multi-directional nature of real seismic events. The soil response is simulated by an isotropic hardening elasto-plastic hysteretic model (HSsmall) implemented in the material model library of the code. This model allows to describe the non-linear cyclic response ranging from small to large strain amplitudes and to account for the variation of the initial stiffness with depth.In the paper, the FE numerical approach is first validated through a series of parametric analyses simulating simplified cases (i.e. linear visco-elastic structures founded on a homogeneous linear visco-elastic soil deposit) for which analytical solutions exist. Then, it is adopted to back-analyse the behaviour of the 1/4-scale nuclear power plant containment structure constructed at the Lotung LSST site which was shook by several earthquakes of different intensities and frequency contents. The FE results are thus compared to the recorded in-situ free-field and structural motions, highlighting the satisfactory performance of the numerical model in replicating the observed response. The overall outcome of this research proves that nowadays complex dynamic SSI phenomena can be tackled by direct approach, overpassing the strong simplifications of the well-established substructure approaches.     

Interpolation with Splines in Tension: A Green''s Function Approach

Interpolation and gridding of data are procedures in the physical sciences and are accomplished typically using an averaging or finite difference scheme on an equidistant grid. Cubic splines are popular because of their smooth appearances; however, these functions can have undesirable oscillations between data points. Adding tension to the spline overcomes this deficiency. Here, we derive a technique for interpolation and gridding in one, two, and three dimensions using Green's functions for splines in tension and examine some of the properties of these functions. For moderate amounts of data, the Green's function technique is superior to conventional finite-difference methods because (1) both data values and directional gradients can be used to constrain the model surface, (2) noise can be suppressed easily by seeking a least-squares fit rather than exact interpolation, and (3) the model can be evaluated at arbitrary locations rather than only on a rectangular grid. We also show that the inclusion of tension greatly improves the stability of the method relative to gridding without tension. Moreover, the one-dimensional situation can be extended easily to handle parametric curve fitting in the plane and in space. Finally, we demonstrate the new method on both synthetic and real data and discuss the merits and drawbacks of the Green's function technique.     

A finite element procedure for calculation of strain from interpolated displacements

Second-order universal kriging is proposed as an accurate model for interpolating displacements measured in the field to nodal points of a superimposed finite element mesh. These interpolated displacements are used in a modified finite element procedure to calculate strain. This model is compared to a local trend model to judge superiority. Interpolation models are tested by randomly sampling displacements obtained in a finite element analysis, then applying interpolation in attempts to reconstruct the original results.     

Interpolation with Splines in Tension: A Green's Function Approach

Interpolation and gridding of data are procedures in the physical sciences and are accomplished typically using an averaging or finite difference scheme on an equidistant grid. Cubic splines are popular because of their smooth appearances; however, these functions can have undesirable oscillations between data points. Adding tension to the spline overcomes this deficiency. Here, we derive a technique for interpolation and gridding in one, two, and three dimensions using Green's functions for splines in tension and examine some of the properties of these functions. For moderate amounts of data, the Green's function technique is superior to conventional finite-difference methods because (1) both data values and directional gradients can be used to constrain the model surface, (2) noise can be suppressed easily by seeking a least-squares fit rather than exact interpolation, and (3) the model can be evaluated at arbitrary locations rather than only on a rectangular grid. We also show that the inclusion of tension greatly improves the stability of the method relative to gridding without tension. Moreover, the one-dimensional situation can be extended easily to handle parametric curve fitting in the plane and in space. Finally, we demonstrate the new method on both synthetic and real data and discuss the merits and drawbacks of the Green's function technique.     

基于GSI值量化和修正方法的岩体力学参数确定

为了准确确定岩体力学参数,通过综合分析多种地质强度指标(GSI)量化方法,提出了一种改进的GSI值量化和修正方法。首先,利用测线法估算结构面平均间距(d)和岩体块度指数(RBI)的改进型岩体块度率(RBR),根据岩体三维结构面网络,获得岩体体积节理数(Jv)和岩体结构等级(SR),然后采用上述参数和结构表面条件(SCR)及结构表面特性参数(Jc)进行了GSI值的定量化处理。为了克服GSI体系的缺点,考虑结构面产状和地下水对岩体力学性质的影响,提出了GSI值的修正方法和公式。以某铅锌矿体的矿岩体为例,根据改进的GSI值量化和修正方法及Hoek-Brown强度准则来确定矿岩体力学参数,通过与原位变形试验的对比分析,验证了该方法的精确性和可行性。该方法为从室内岩石力学试验合理地获取节理岩体力学参数提供了理论及实现的依据。     

Three dimensional Finite Element modeling of seismic soil–structure interaction in soft soil

Earthquakes in regions underlain by soft clay have amply demonstrated the detrimental effects of soil–structure interaction (SSI) in such settings. This paper describes a new three dimensional Finite Element model utilizing linear elastic single degree of freedom (SDOF) structure and a nonlinear elasto-plastic constitutive model for soil behavior in order to capture the nonlinear foundation–soil coupled response under seismic loadings. Results from an experimental SSI centrifuge test were used to verify the reliability of the numerical model followed by parametric studies to evaluate performance of linear elastic structures underlain by soft saturated clay. The results of parametric study demonstrate that rigid slender (tall) structures are highly susceptible to the SSI effects including alteration of natural frequency, foundation rocking and excessive base shear demand. Structure–foundation stiffness and aspect ratios were found to be crucial parameters controlling coupled foundation–structure performance in flexible-base structures. Furthermore, frequency content of input motion, site response and structure must be taken into account to avoid occurrence of resonance problem.     

广义自相似性原理与模型

为了理解各式各样的具有广义自相似性特征的尺度不变性系统, 提出了1个称之为GSI (generalized scale invariance) 的理论体系.它阐述了大小尺度可以相互关联而不需要引入任何1个特有(具体) 尺度的最普通情形.在二维线性GSI理论的基础上, 形成了2个重要的各向异性尺度不变性量化模型: SIG (scale invariant generator) 模型和S-A (spectrum-area) 模型.SIG模型通过在频率域中估计GSI理论中代表旋转和层化程度的尺度不变性生成元的参数来量化各向异性尺度不变性.而S-A模型通过从二维频率域中能谱密度大于P元素集的面积与P之间关系的非参数模型对各向异性尺度不变性进行量化.如果研究的对象是1个混合模式(多个不同尺度的过程或作用叠加而形成的), S-A模型不仅可以对异性尺度不变性进行量化, 还可以对该混合模式进行分解.系统阐述了GSI理论、SIG模型和S-A模型, 并将SIG模型和S-A模型结合提出了既能对混合模式进行分解又能对分解后模式的各向异性尺度不变性进行量化的模型.