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1.
This paper investigates the dynamic response of an axially loaded Timoshenko beam coupled with a multilayered transversely isotropic (TI) half-space subjected to a moving load. An axial force induced by the thermal expansion is taken into account in the Timoshenko beam. The half-space considers the alternate distribution of an arbitrary number of TI elastic and poroelastic layers to model foundation soils with different properties and moisture conditions. To solve the governing equations, Fourier transform is adopted. The stratified foundation is formulated by extending an “adapted stiffness matrix method” to a more general scenario with an arbitrary number of layers. The beam is then coupled with the foundation to derive solutions to the system in the frequency-wavenumber domain. The final results in the time-spatial domain are recovered by the inverse Fourier transform. After confirming the accuracy of the method in this study, the influences of the pore water existence, the transverse isotropy of different parameters, and the axial force are investigated. It can be observed that the effect of pore water existence on the maximum beam deflection can reach 22% in this study. The transverse isotropy of the elastic and shear moduli influences the critical speed of the beam deflection by altering the phase velocity of the first wave propagation mode of the beam-foundation system. The vertical permeability coefficient is more important than the horizontal one in determining the excess pore pressure. The rise of the beam temperature (axial force) decreases the critical speed and magnifies the vibrations. 相似文献
2.
总磷是长江流域水环境污染的首要超标因子,岷江作为长江上游流量最大的支流,总磷污染严重,对长江总磷污染贡献较大。为了解岷江流域总磷污染,采用排污系数法,计算得到2016年岷江流域污染源总磷入河量为1 154 t,以农村生活污染负荷占比最高(51.3%),其次为城镇生活源(28.7%)、农业非点源(8.24%)、工业源(9.57%)、畜禽养殖源(1.21%),城市径流源(0.99%)最低;在空间上岷江流域总磷污染负荷呈中游(64.2%)>下游(32.6%)>上游(3.1%)的特点,与岷江干流总磷浓度变化趋势相符,其中成都市总磷污染负荷最高(51.2%),与区域人口密度高、生产和生活活动密集有关。结合资料收集和现场调查,岷江流域总磷污染成因主要包括农村生活污染治理缺口较大、城镇生活污染处理基础设施建设不足、工业企业密布、部分支流总磷污染严重、水污染治理导向不全面。针对岷江总磷污染负荷分布特征及成因,提出“上游保护优质水体、中游治理重污染水体、下游恢复不达标水体”的分区污染防治对策,统筹流域监管体制机制,强化岷江流域水环境保护和治理。 相似文献
3.
Bipin K. Gupta 《Geomechanics and Geoengineering》2020,15(1):10-28
ABSTRACTShort stubby piles like monopiles and large diameter drilled shafts undergo rigid body translation and rotation when subjected to a lateral force and/or a moment at the head. A method of analysis for these piles embedded in multi-layered elastic soil is developed using the variational principles of mechanics. Using this analysis, the soil resistance against pile movement can be rigorously related to the soil elastic constants, and the pile head displacement and rotation can be quickly calculated. The equilibrium equations for pile and soil displacements are obtained using the principle of virtual work and solved using an iterative algorithm. Pile responses obtained from the analysis match well with those obtained from three-dimensional finite element analyses in which the same inputs of loads, geometry, and material properties are given. Based on the new analysis, fitted equations for soil resistance parameters are developed, which can be used to directly calculate the pile head displacement and rotation without the use of the iterative algorithm. Numerical examples are provided that demonstrate how the method can be used to analyse practical problems. 相似文献
4.
Cristián Frêne Juan J. Armesto Freddy Véliz Fernando D. Alfaro Kathleen C. Weathers 《水文研究》2021,35(5):e14175
The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history. 相似文献
5.
Pile foundations that support transmission towers or offshore structures are dominantly subjected to cyclic lateral load induced by wind and waves. For a successful design, it is crucial to investigate the effect of cyclic lateral loads on the pile behavior that is loaded laterally. Although the p–y curve method is generally utilized to design the cyclic laterally loaded pile foundations, the effect of cyclic lateral loads on the pile has not been properly implemented with the p–y curve. This reflects a lack of consideration of the overall stiffness change in soil–pile interaction. To address this, a series of model pile tests were conducted in this study on a preinstalled aluminum flexible pile under various sandy soil conditions. The test results were used to investigate the effect of cyclic lateral loads on the p–y behavior. The cyclic p–y curve, which properly takes into account this effect, was developed as a hyperbolic function. Pseudo-static analysis was also conducted with the proposed cyclic p–y curve, which showed that it was able to properly simulate cyclic laterally loaded pile behavior in sandy soil. 相似文献
6.
A regime shift in sediment export from a coastal watershed during a record wet winter,California: Implications for landscape response to hydroclimatic extremes 下载免费PDF全文
Amy E. East Andrew W. Stevens Andrew C. Ritchie Patrick L. Barnard Pamela Campbell‐Swarzenski Brian D. Collins Christopher H. Conaway 《地球表面变化过程与地形》2018,43(12):2562-2577
Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles. Published 2018. This article is a U.S. Government work and is in the public domain in the USA. 相似文献
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Peng Yue Fan Gao Boyi Shangguan Zheren Yan 《International journal of geographical information science》2020,34(11):2243-2274
ABSTRACT High performance computing is required for fast geoprocessing of geospatial big data. Using spatial domains to represent computational intensity (CIT) and domain decomposition for parallelism are prominent strategies when designing parallel geoprocessing applications. Traditional domain decomposition is limited in evaluating the computational intensity, which often results in load imbalance and poor parallel performance. From the data science perspective, machine learning from Artificial Intelligence (AI) shows promise for better CIT evaluation. This paper proposes a machine learning approach for predicting computational intensity, followed by an optimized domain decomposition, which divides the spatial domain into balanced subdivisions based on the predicted CIT to achieve better parallel performance. The approach provides a reference framework on how various machine learning methods including feature selection and model training can be used in predicting computational intensity and optimizing parallel geoprocessing against different cases. Some comparative experiments between the approach and traditional methods were performed using the two cases, DEM generation from point clouds and spatial intersection on vector data. The results not only demonstrate the advantage of the approach, but also provide hints on how traditional GIS computation can be improved by the AI machine learning. 相似文献
10.
桑沟湾沉积碳库年汇入速率的长期变化及其区域性差异 总被引:1,自引:1,他引:0
对取自桑沟湾北西南三根柱样近200 a碳来源及埋藏通量的解析,分析了湾内不同站位各形态碳的差异性,进而对全湾碳埋藏进行了估算。湾内环流、贝藻养殖等造成湾内不同区域碳埋藏的差异;桑沟湾总碳(TC)平均量1.79%,有机碳(TOC)平均量0.54%,无机碳(TIC)平均量1.25%,TOC含量相对较小,为海陆混合来源,以陆源有机碳(Ct)为主,大规模人工养殖后,海源有机碳(Ca)有明显增加的趋势。桑沟湾碳埋藏通量平均为228.9 g/(m2·a),以无机碳为主要埋藏形式(约占70%),高的沉积速率及生物残骸沉降使桑沟湾养殖区碳的来源及埋藏区别于其他陆架海域。 相似文献