混凝土核心筒的水平双向循环加载试验研究

为了研究地震多维性对于混凝土核心筒抗震性能的影响,对大尺寸混凝土核心筒试件进行了水平双向加载下的拟静力试验.重点研究在双向加载下,核心筒的破坏形态与机理、承载能力、变形性能、刚度退化等方面的问题.结果表明,由于水平双向加载下简体一个方向的损伤影响到另一个方向的性能,因而对混凝土核心筒的抗震能力造成不利影响.因此,在实际工程中应合理地考虑这种影响,这对于确保混凝土核心筒的抗震安全具有重要意义.     

Geomorphological site classification for the Fujian province

Geomorphological classification of the Fujian province was done based on remote-sensing imaging, digital elevation maps, and slope gradient data acquired by ArcGIS 9.2. The engineering geological units in the Fujian province were divided into five types by the geomorphologic shape and genesis. The relationship among geomorphological type, engineering geological unit, and site category was determined using engineering geological data and site category data. Then, after making a preliminary site classification adjusted by drill hole data, the site was classified into four types: I₀, I₁, II, and III according to site classification standards of equivalent shear-wave velocity and overburden thickness. The results showed that the site categories in the Fujian province mainly consist of type II, which accounts for 85.26 % of the land area. The percentage of I₀ was the smallest, which accounts for only 2.44 % of the total area.     

Perfectly matched layer-absorbing boundary condition for finite-element time-domain modeling of elastic wave equations

The perfectly matched layer (PML) is a highly efficient absorbing boundary condition used for the numerical modeling of seismic wave equation. The article focuses on the application of this technique to finite-element time-domain numerical modeling of elastic wave equation. However, the finite-element time-domain scheme is based on the second-order wave equation in displacement formulation. Thus, the first-order PML in velocity-stress formulation cannot be directly applied to this scheme. In this article, we derive the finite-element matrix equations of second-order PML in displacement formulation, and accomplish the implementation of PML in finite-element time-domain modeling of elastic wave equation. The PML has an approximate zero reflection coefficients for bulk and surface waves in the finite-element modeling of P-SV and SH wave propagation in the 2D homogeneous elastic media. The numerical experiments using a two-layer model with irregular topography validate the efficiency of PML in the modeling of seismic wave propagation in geological models with complex structures and heterogeneous media.     

金沙江下游梯级水库运行后三峡水库高洪水期入库水沙特性

泥沙淤积问题直接影响着三峡水库的使用寿命及综合效益的发挥,研究其入库水沙特性对于解决水库泥沙淤积问题具有重要意义。根据水文站实测数据,分析了三峡水库入库水沙输移特性及来源组成变化,重点研究了金沙江下游梯级水库运行后的三峡水库高洪水期入库水沙特性。结果表明:2003—2021年,三峡水库入库泥沙集中于汛期的高洪水期,2013年以后该现象更为显著,泥沙来源也由金沙江为主转变为嘉陵江为主。寸滩站洪峰流量高于50000 m³/s的高洪水期三峡入库沙量显著大于30000～50000 m³/s区间的高洪水期,三峡水库泥沙调度关键在于上游发生编号洪水期间。三峡水库上游沱江或嘉陵江等支流发生流域性大洪水时,易引起高洪水期入库水沙出现“小水大沙”的特点。金沙江下游梯级水库运行后,三峡水库高洪水期入库泥沙大幅减少,中小洪水调度期间泥沙淤积量也大幅减小。研究结果可为三峡水库的泥沙精细化调度和长期高效使用提供基础数据支撑。     

基于“水文频率-水质”拟合曲线的河流水质变异与等级特征值分析方法

时空特征分析对全面掌握水质变异规律具有重要意义,但现有的水质时空特征分析方法仍存在水质变异次序不分、水质变幅极值不清、水质评价特征值不明等不足。为更加清晰地探析水质时空特征信息,以秦淮河为研究对象,参考工程水文学经验频率法,建立“水文频率-水质”拟合曲线用于探索流域内高/低活动区不同时间段和丰/枯水期不同河段水质变异特征,并与传统的箱线图法进行对比。结果表明:与箱线图相比,“水文频率-水质”拟合曲线可量化关键水质评判点与特征值信息,使水质时空变异过程更为清晰。在时间上“水文频率-水质”拟合曲线的最佳形式为线性曲线,水质浓度一般不会发生突变;在空间上“水文频率-水质”拟合曲线的最佳形式为指数曲线,水质浓度有较大可能发生突增。各时间段高活动区氮磷浓度大于低活动区,各水体断面丰水期氮磷浓度低于枯水期。该方法分析过程简单方便,结果直观有序,能将水质信息以统计规律自动反映出来,在水质采样点、采样时间和采样频率典型时可作为优选方法用于河流水质时空特征研究。     

Experimental study on strain field evolution around a simulated thrust fault

Earthquakes result from continuous geodynamic processes. A topic of significant interest for the scientific community is to elaborate on the phenomena governing the faulting and fracturing of crustal rocks. Therefore, in this study, uniaxial compressive shear failure experiments were conducted on Fangshan marble rock samples with a prefabricated slot to simulate thrust faulting. The center of each marble plate (105 mm × 80 mm × 5 mm) was engraved with a 30-mm long double-sided nonpenetrating slot (depth: 2 mm, width: 0.5 mm). The deformation and destruction processes of the rock surface were recorded using a high-speed camera. The digital image correlation method was used to calculate the displacement and strain distribution and variation at different loading stages. The accumulative and incremental displacement fields u and v , strain field e_x and e_y, and shear strain e_xy were analyzed. When the loading level reached its ultimate value, the strain field was concentrated around the prefabricated slot. The concentration reached a maximum at the ends of the prefabricated slot. The magnitude of shear strain reached 0.1. This experiment contributes to our understanding of the dynamic process of active faulting.     

Evaluation of the 15 July 2009 Fiordland,New Zealand Tsunami in the Source Region

We undertake detailed near-field numerical modelling of the tsunami generated by the 15 July 2009 earthquake (Mw 7.8) in Fiordland, New Zealand. High resolution bathymetry and topography data at Breaksea and Dusky Sounds, and Chalky and Preservation Inlets are derived mostly from digitised New Zealand nautical charts, Shuttle Radar Topographic Mission (SRTM) 3 arc-second data, and General Bathymetric Chart of the Ocean (GEBCO) 30 s data. A combination of continuous and campaign Global Positioning System (GPS), satellite radar (ALOS/PALSAR InSAR images) and seismology data are used to constrain the seafloor deformation for the initial tsunami condition. This source model, derived independently of DART observations, provides an excellent fit to observed tsunami elevations recorded by DART buoy 55015. The model results in the near field show maximum tsunami elevations in the range 0.5–2.0 m inside the sounds and inlets with maximum flow speeds of 3.0 m/s. Along the open coast, maximum tsunami elevations reach 2.0 m. The high flow speeds through the inlets may change the inlet stratifications and water mass inside the sounds. Media reports and field reconnaissance data show some tsunami evidence at Cormorant Cove, Duck and Goose Coves, and Passage Point.     

Computing the Sensitivity Kernels for 2.5-D Seismic Waveform Inversion in Heterogeneous,Anisotropic Media

2.5-D modeling and inversion techniques are much closer to reality than the simple and traditional 2-D seismic wave modeling and inversion. The sensitivity kernels required in full waveform seismic tomographic inversion are the Fréchet derivatives of the displacement vector with respect to the independent anisotropic model parameters of the subsurface. They give the sensitivity of the seismograms to changes in the model parameters. This paper applies two methods, called ‘the perturbation method’ and ‘the matrix method’, to derive the sensitivity kernels for 2.5-D seismic waveform inversion. We show that the two methods yield the same explicit expressions for the Fréchet derivatives using a constant-block model parameterization, and are available for both the line-source (2-D) and the point-source (2.5-D) cases. The method involves two Green’s function vectors and their gradients, as well as the derivatives of the elastic modulus tensor with respect to the independent model parameters. The two Green’s function vectors are the responses of the displacement vector to the two directed unit vectors located at the source and geophone positions, respectively; they can be generally obtained by numerical methods. The gradients of the Green’s function vectors may be approximated in the same manner as the differential computations in the forward modeling. The derivatives of the elastic modulus tensor with respect to the independent model parameters can be obtained analytically, dependent on the class of medium anisotropy. Explicit expressions are given for two special cases—isotropic and tilted transversely isotropic (TTI) media. Numerical examples are given for the latter case, which involves five independent elastic moduli (or Thomsen parameters) plus one angle defining the symmetry axis.     

Sensitivity of Typhoon Vamei (2001) Simulation to Planetary Boundary Layer Parameterization Using PSU/NCAR MM5

This paper investigates the sensitivity of the numerical simulations of a near equatorial Typhoon Vamei (2001) to various planetary boundary layer (PBL) parameterization schemes in the Pennsylvania State University (PSU)/National Centre for Atmospheric Research (NCAR) non-hydrostatic mesoscale model (MM5). The numerical simulations are conducted on two domains at 45 and 15 km grids nested in a one-way fashion. Four different PBL parameterization schemes including the Blackadar (BLK) scheme, the Burk–Thompson (BURKT) scheme, the NCEP Eta model scheme and the NCEP medium range forecast (MRF) model scheme are investigated. Results indicate that the intensity and propagation track of the simulated near equatorial typhoon system is not very sensitive to the different PBL treatments. The simulated minimum central pressures and the maximum surface wind speeds differ by only 5–6 hPa and 6–8 ms⁻¹, respectively. Larger variations between the simulations occur during the weakening phase of the typhoon system. While all schemes simulated the typhoon with reasonable accuracy, the ETA scheme produces the strongest storm intensity with the largest heat exchanges over the marine environment and the highest warm moisture air content in the PBL around the core of the storm.     

FerryBox - Application of continuous water quality observations along transects in the North Sea

In 2002, the Helmholtz-Zentrum Geesthacht, Germany, started to use FerryBox-automated monitoring systems on Ships of Opportunity to continuously record standard oceanographic, biological and chemical in situ data in the North Sea. The present study summarises the operational experience gathered since the beginning of this deployment and reflects on the potential and limits of FerryBox systems as a monitoring tool. One part relates to the instrumental performance, constancy of shipping services, and the availability and quality of the recorded in situ data. The other considers integration of the FerryBox observations in scientific applications and routine monitoring campaigns. Examples are presented that highlight the added value of the recorded data for the study of both long- and short-term variability in water mass stability, plankton communities and surface water productivity in the North Sea. Through the assessment of technical and scientific performance, it is evident that FerryBoxes have become a valuable tool in marine research that helps to fill gaps in coastal and open ocean operational observation networks.