水平层状岩体边坡动力响应中的结构面效应研究     

周剑  张路青  王学良 《工程地质学报》2011,19(3):352-358

根据应力波传播原理分析了水平层状岩体边坡中应力波传播特征,建立了应力波在该类边坡中传播的模型.利用离散元软件UDEC分析了不同频率垂向压缩应力波作用下边坡动力响应规律中的结构面效应.结果表明:边坡中的水平层面对坡顶的动力响应有明显影响.低频应力波作用下,水平层状岩体边坡坡顶的垂向峰值速度较均质坡体相同部位的峰值速度的增...  相似文献   

Model tree approach for prediction of pile groups scour due to waves   总被引：1，自引：0，他引：1  

A. Etemad-Shahidi  N. Ghaemi 《Ocean Engineering》2011,38(13):1522-1527

Scour around piles could endanger the stability of the structures placed on them. Hence, an accurate estimation of the scour depth around piles is very important in coastal and marine engineering. Due to the complex interaction between the wave, seabed and pile group; prediction of the scour depth is not an easy task and the available empirical formulas have limited accuracy. Recently, soft computing methods such as Artificial Neural Networks (ANNs) and Support Vector Machines (SVMs) have been used for the prediction of the scour depth. However, these methods do not give enough insight about the process and are not as easy to use as the empirical equations. In this study, new formulas are given that are easy to use, accurate and physically sound. Available empirical equations for estimating the pile group scour depth such as those of Sumer et al. (1992) and Bayram and Larson (2000), are less accurate compared to the given equations. These equations are as accurate as other soft computing methods such as ANN and SVM. Moreover, in this study, safety factors are given for different levels of acceptable risks, which can be so useful for engineers.  相似文献   

Numerical simulation of nearshore circulation on field topography under random wave environment     

Junwoo Choi  Sung Bum Yoon 《Coastal Engineering》2011

In order to investigate surf zone hydrodynamics through two-dimensional numerical simulations of nearshore circulation under random wave environment, a nearshore circulation model, SHORECIRC, and a random wave model, SWAN, were combined and utilized. Using this combined model, a numerical simulation of the October 2, 1997 SandyDuck field experiment was performed. For this simulation, field topography and an input offshore spectrum were constructed using observed data sets synchronized with the experiment. The wave-breaking model in SWAN was modified by using breaker parameters varied according to bottom slope. The simulation results were compared with the experimental data, which revealed a well-developed longshore current, as well as with results using other combinations which were SHORECIRC and its original monochromatic wave-driver, and SHORECIRC and the default of SWAN. The results from the novel combined model agreed well with the experimental data. The results of the present simulation also indicate that alongshore field topography influences shear fluctuation of longshore currents.  相似文献   

Seismic random noise attenuation and signal-preserving by multiple directional time-frequency peak filtering     

《Comptes Rendus Geoscience》2015,347(1):2-12

Time-frequency peak filtering (TFPF) is an effective method for seismic random noise attenuation. The linearity of the signal has a significant influence on the accuracy of the TFPF method. The higher the linearity of the signal to be filtered is, the better the denoising result is. With this in mind, and taking the lateral coherence of reflected events into account, we do TFPF along the reflected events to improve the degree of linearity and enhance the continuity of these events. The key factor to realize this idea is to find the traces of the reflected events. However, the traces of the events are too hard to obtain in the complicated field seismic data. In this paper, we propose a Multiple Directional TFPF (MD–TFPF), in which the filtering is performed in certain direction components of the seismic data. These components are obtained by a directional filter bank. In each direction component, we do TFPF along these decomposed reflected events (the local direction of the events) instead of the channel direction. The final result is achieved by adding up the filtering results of all decomposition directions of seismic data. In this way, filtering along the reflected events is implemented without accurately finding the directions. The effectiveness of the proposed method is tested on synthetic and field seismic data. The experimental results demonstrate that MD–TFPF can more effectively eliminate random noise and enhance the continuity of the reflected events with better preservation than the conventional TFPF, curvelet denoising method and F–X deconvolution method.  相似文献   

Sources of polycyclic aromatic hydrocarbons (PAHs) to northwestern Saskatchewan lakes east of the Athabasca oil sands     

《Organic Geochemistry》2015

The past several decades have witnessed a significant expansion of mining activities in the Athabasca oil sands region, raising concerns about their impact on the surrounding boreal forest ecosystem. To better understand the extent to which distal sites are impacted by oil sands-derived airborne contaminants, we examine sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments and dated sediment cores from Saskatchewan lakes situated ∼100–220 km east–northeast of the main area of bitumen mining activities. The concentrations and fluxes of both parent and alkylated PAHs are low and show considerable variability over the past 70–100 years. Small yet discernible increases in PAH concentrations and fluxes occurred over the past 30 years, a trend which coincides with the rapid growth in bitumen production. However, several lines of evidence point to wildfires as the principal source of PAHs to these lakes: (1) the significant co-variations in most cores between retene (1-methyl-7-isopropyl phenanthrene) and other groups of parent and alkylated PAHs, (2) the similarity in compound specific δ¹³C signatures of the parent PAHs phenanthrene and pyrene in recently deposited surficial sediments and those corresponding to time intervals considerably pre-dating the large scale development of the oil sands and (3) the discernible up-core increases in the proportion of refractory carbon (i.e., char) in Rock-Eval 6 data. The collective evidence points to softwood combustion from boreal forest fires as the principal source of retene in sediments and the general increase in forest fire activity in this region over the past several decades as the source of refractory carbon. Mining activities associated with the Athabasca oil sands are thus not considered a major source of PAHs to these lakes.  相似文献   

Comparing future patterns of energy system change in 2 °C scenarios with historically observed rates of change     

《Global Environmental Change》2015

This paper systematically compares modeled rates of change provided by global integrated assessment models aiming for the 2 °C objective to historically observed rates of change. Such a comparison can provide insights into the difficulty of achieving such stringent climate stabilization scenarios. The analysis focuses specifically on the rates of change for technology expansion and diffusion, emissions and energy supply investments. The associated indicators vary in terms of system focus (technology-specific or energy system wide), temporal scale (timescale or lifetime), spatial scale (regional or global) and normalization (accounting for entire system growth or not). Although none of the indicators provide conclusive insights as to the achievability of scenarios, this study finds that indicators that look into absolute change remain within the range of historical growth frontiers for the next decade, but increase to unprecedented levels before mid-century. Indicators that take into account or normalize for overall system growth find future change to be broadly within historical ranges. This is particularly the case for monetary-based normalization metrics like GDP compared to energy-based normalization metrics like primary energy. By applying a diverse set of indicators alternative, complementary insights into how scenarios compare with historical observations are acquired but they do not provide further insights on the possibility of achieving rates of change that are beyond current day practice.  相似文献   

Legacies of 19th century land use shape contemporary forest cover     

《Global Environmental Change》2015

Historic land use can exert strong land-use legacies, i.e., long-lasting effects on ecosystems, but the importance of land-use legacies, alongside other factors, for subsequent forest-cover change is unclear. If past land use affects rates of forest disturbance and afforestation then this may constrain land use planning and land management options, and legacies of current land management may constrain future land use. Our goal was to assess if and how much land-use legacies affect contemporary forest disturbance, and the abundance of different forest types in the Carpathian region in Eastern Europe (265,000 km², encompassing parts of Poland, Slovakia, Ukraine, Romania, Hungary, and Czech Republic). We modeled contemporary forest disturbance (based on satellite image analysis from 1985 to 2010) as a function of historic land use (based on digitized topographic maps from 1860 and 1960). Contemporary forest disturbance was strongly related to historic land use even when controlling for environmental, accessibility and socio-political variation. Across the Carpathian region, the odds of forest disturbance were about 50% higher in areas that were not forested in 1860 (new forests) compared to areas that were forested then (old forests). The forest disturbance in new forests was particularly high in Poland (88% higher odds), Slovakia (69%) and Romania (67%) and persisted across the entire range of environmental, accessibility and socio-political variation. Reasons for the observed legacy effects may include extensive plantations outside forest ranges, predominantly spruce, poplar, and black locust, which are prone to natural disturbances. Furthermore, as plantations reach harvestable age of about 70 years for pulp and 120 year for saw-timber production, these are likely to be clear-cut, producing the observed legacy effects. Across the Carpathians, forest types shifted towards less coniferous cover in 2010 compared to the 1860s and 1960s likely due to extensive historic conifer harvest, and to recent natural disturbance events and clear-cuts of forest plantations. Our results underscore the importance of land-use legacies, and show that past land uses can greatly affect subsequent forest disturbance for centuries. Given rapid land use changes worldwide, it is important to understand how past legacies affect current management and what the impact of current land management decisions may be for future land use.  相似文献   

Normalized algorithm for mapping and dating forest disturbances and regrowth for the United States     

Liming He  Jing M. Chen  Shaoliang Zhang  Gustavo Gomez  Yude Pan  Kevin McCullough  Richard Birdsey  Jeffrey G. Masek 《International Journal of Applied Earth Observation and Geoinformation》2011

Forest disturbances such as harvesting, wildfire and insect infestation are critical ecosystem processes affecting the carbon cycle. Because carbon dynamics are related to time since disturbance, forest stand age that can be used as a surrogate for major clear-cut/fire disturbance information has recently been recognized as an important input to forest carbon cycle models for improving prediction accuracy. In this study, forest disturbances in the USA for the period of ∼1990–2000 were mapped using 400+ pairs of re-sampled Landsat TM/ETM scenes in 500m resolution, which were provided by the Landsat Ecosystem Disturbance Adaptive Processing System project. The detected disturbances were then separated into two five-year age groups, facilitated by Forest Inventory and Analysis (FIA) data, which was used to calculate the area of forest regeneration for each county in the USA.  相似文献   

3D modeling of light interception in heterogeneous forest canopies using ground-based LiDAR data     

Dimitry Van der Zande  Jan Stuckens  Willem W. Verstraeten  Simone Mereu  Bart Muys  Pol Coppin 《International Journal of Applied Earth Observation and Geoinformation》2011

  相似文献   

A spatial stochastic algorithm to reconstruct artificial drainage networks from incomplete network delineations     

J.S. Bailly  F. Levavasseur  P. Lagacherie 《International Journal of Applied Earth Observation and Geoinformation》2011

  相似文献