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991.
A numerical study of mechanical behavior of a cement paste under mechanical loading and chemical leaching 下载免费PDF全文
Based on relevant experimental data of a petroleum cement paste under mechanical loading and chemical leaching, an elastic‐plastic model is first proposed by taking into account plastic shearing and pore collapse. The degradation of mechanical properties induced by the chemical leaching is characterized by a chemical damage variable which is defined as the increase of porosity. Both elastic and plastic properties of the cement paste are affected by the chemical damage. The proposed model is calibrated from and applied to describe mechanical responses in triaxial compression tests respectively on sound and fully leached samples. In the second part, a phenomenological chemical model is defined to establish the relationship between porosity change and calcium dissolution process. The dissolution kinetics is governed by a diffusion law taking into account the variation of diffusion coefficient with calcium concentration. The chemical model is coupled with the mechanical model, and both are applied to describe mechanical response of cement paste samples subjected to progressive chemical leaching and compressive stresses. Comparisons between experimental data and numerical results are presented. 相似文献
992.
Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya 下载免费PDF全文
Vincent Omondi Odongo Christiaan van der Tol Pieter R. van Oel Frank M. Meins Robert Becht Japheth Onyando Zhongbo Su 《水文研究》2015,29(15):3276-3293
Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 106 m3 year?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
993.
Towards more systematic perceptual model development: a case study using 3 Luxembourgish catchments 下载免费PDF全文
Sebastian Wrede Fabrizio Fenicia Núria Martínez‐Carreras Jérôme Juilleret Christophe Hissler Andreas Krein Hubert H. G. Savenije Stefan Uhlenbrook Dmitri Kavetski Laurent Pfister 《水文研究》2015,29(12):2731-2750
The synthesis of experimental understanding of catchment behaviour and its translation into qualitative perceptual models is an important objective of hydrological sciences. We explore this challenge by examining the cumulative understanding of the hydrology of three experimental catchments and how it evolves through the application of different investigation techniques. The case study considers the Huewelerbach, Weierbach and Wollefsbach headwater catchments of the Attert basin in Luxembourg. Subsurface investigations including bore holes and pits, analysis of soil samples and Electrical Resistivity Tomography measurements are presented and discussed. Streamflow and tracer data are used to gain further insights into the streamflow dynamics of the catchments, using end‐member mixing analysis and hydrograph separation based on dissolved silica and electrical conductivity. We show that the streamflow generating processes in all three catchments are controlled primarily by the subsolum and underlying bedrock. In the Huewelerbach, the permeable sandstone formation supports a stable groundwater component with little seasonality, which reaches the stream through a series of sources at the contact zone with the impermeable marls formation. In the Weierbach, the schist formation is relatively impermeable and supports a ‘fill and spill’‐type of flow mechanism; during wet conditions, it produces a delayed response dominated by pre‐event water. In the Wollefsbach, the impermeable marls formation is responsible for a saturation‐excess runoff generating process, producing a fast and highly seasonal response dominated by event water. The distinct streamflow generating processes of the three catchments are represented qualitatively using perceptual models. The perceptual models are in turn translated into quantitative conceptual models, which simulate the hydrological processes using networks of connected reservoirs and transfer functions. More generally, the paper illustrates the evolution of perceptual models based on experimental fieldwork data, the translation of perceptual models into conceptual models and the value of different types of data for processes understanding and model representation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
994.
Assessing the effects of catchment‐scale urban green infrastructure retrofits on hydrograph characteristics 下载免费PDF全文
Run‐off from impervious surfaces has pervasive and serious consequences for urban streams, but the detrimental effects of urban stormwater can be lessened by disconnecting impervious surfaces and redirecting run‐off to decentralized green infrastructure. This study used a before–after‐control‐impact design, in which streets served as subcatchments, to quantify hydrologic effectiveness of street‐scale investments in green infrastructure, such as street‐connected bioretention cells, rain gardens and rain barrels. On the two residential treatment streets, voluntary participation resulted in 32.2% and 13.5% of parcels having green infrastructure installed over a 2‐year period. Storm sewer discharge was measured before and after green infrastructure implementation, and peak discharge, total run‐off volume and hydrograph lags were analysed. On the street with smaller lots and lower participation, green infrastructure installation succeeded in reducing peak discharge by up to 33% and total storm run‐off by up to 40%. On the street with larger lots and higher participation, there was no significant reduction in peak or total stormflows, but on this street, contemporaneous street repairs may have offset improvements. On the street with smaller lots, lag times increased following the first phase of green infrastructure construction, in which streetside bioretention cells were built with underdrains. In the second phase, lag times did not change further, because bioretention cells were built without underdrains and water was removed from the system, rather than just delayed. We conclude that voluntary green infrastructure retrofits that include treatment of street run‐off can be effective for substantially reducing stormwater but that small differences in design and construction can be important for determining the level of the benefit. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
995.
996.
Assessing regression‐based statistical approaches for downscaling precipitation over North America 下载免费PDF全文
This paper assesses linear regression‐based methods in downscaling daily precipitation from the general circulation model (GCM) scale to a regional climate model (RCM) scale (45‐ and 15‐km grids) and down to a station scale across North America. Traditional downscaling experiments (linking reanalysis/dynamical model predictors to station precipitation) as well as nontraditional experiments such as predicting dynamic model precipitation from larger‐scale dynamic model predictors or downscaling dynamic model precipitation from predictors at the same scale are conducted. The latter experiments were performed to address predictability limit and scale issues. The results showed that the downscaling of daily precipitation occurrence was rarely successful at all scales, although results did constantly improve with the increased resolution of climate models. The explained variances for downscaled precipitation amounts at the station scales were low, and they became progressively better when using predictors from a higher‐resolution climate model, thus showing a clear advantage in using predictors from RCMs driven by reanalysis at its boundaries, instead of directly using reanalysis data. The low percentage of explained variances resulted in considerable underestimation of daily precipitation mean and standard deviation. Although downscaling GCM precipitation from GCM predictors (or RCM precipitation from RCM predictors) cannot really be considered downscaling, as there is no change in scale, the exercise yields interesting information as to the limit in predictive ability at the station scale. This was especially clear at the GCM scale, where the inability of downscaling GCM precipitation from GCM predictors demonstrates that GCM precipitation‐generating processes are largely at the subgrid scale (especially so for convective events), thus indicating that downscaling precipitation at the station scale from GCM scale is unlikely to be successful. Although results became better at the RCM scale, the results indicate that, overall, regression‐based approaches did not perform well in downscaling precipitation over North America. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
997.
Analysis of the interannual variability of annual daily extreme water levels in the St Lawrence River and Lake Ontario from 1918 to 2010 下载免费PDF全文
We compared the interannual variability of annual daily maximum and minimum extreme water levels in Lake Ontario and the St Lawrence River (Sorel station) from 1918 to 2010, using several statistical tests. The interannual variability of annual daily maximum extreme water levels in Lake Ontario is characterized by a positive long‐term trend showing two shifts in mean (1929–1930 and 1942–1943) and a single shift in variance (in 1958–1959). In contrast, for the St Lawrence River, this interannual variability is characterized by a negative long‐term trend with a single shift in mean, which occurred in 1955–1956. As for annual daily minimum extreme water levels, their interannual variability shows no significant long‐term change in trend. However, for Lake Ontario, the interannual variability of these water levels shows two shifts in mean, which are synchronous with those for maximum water levels, and a single shift in variance, which occurred in 1965–1966. These changes in trend and stationarity (mean and variance) are thought to be due to factors both climatic (the Great Drought of the 1930s) and human (digging of the Seaway and construction of several dams and locks during the 1950s). Despite this change in means and variance, the four series are clearly described by the generalized extreme value distribution. Finally, annual daily maximum and minimum extreme water levels in the St Lawrence and Lake Ontario are negatively correlated with Atlantic multidecadal oscillation over the period from 1918 to 2010. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
998.
Assessing the effectiveness of imperviousness on stormwater runoff in micro urban catchments by model simulation 下载免费PDF全文
Imperviousness, considered as a critical indicator of the hydrologic impacts of urbanization, has gained increasing attention both in the research field and in practice. However, the effectiveness of imperviousness on rainfall–runoff dynamics has not been fully determined in a fine spatiotemporal scale. In this study, 69 drainage subareas <1 ha of a typical residential catchment in Beijing were selected to evaluate the hydrologic impacts of imperviousness, under a typical storm event with a 3‐year return period. Two metrics, total impervious area (TIA) and effective impervious area (EIA), were identified to represent the impervious characteristics of the selected subareas. Three runoff variables, total runoff depth (TR), peak runoff depth (PR), and lag time (LT), were simulated by using a validated hydrologic model. Regression analyses were developed to explore the quantitative associations between imperviousness and runoff variables. Then, three scenarios were established to test the applicability of the results in considering the different infiltration conditions. Our results showed that runoff variables are significantly related to imperviousness. However, the hydrologic performances of TIA and EIA were scale dependent. Specifically, with finer spatial scale and the condition heavy rainfall, TIA rather than EIA was found to contribute more to TR and PR. EIA tended to have a greater impact on LT and showed a negative relationship. Moreover, the relative significance of TIA and EIA was maintained under the different infiltration conditions. These findings may provide potential implications for landscape and drainage design in urban areas, which help to mitigate the runoff risk. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
999.
This paper endows the recently‐proposed granular element method (GEM) with the ability to perform 3D discrete element calculations. By using non‐uniform rational B‐Splines to accurately represent complex grain geometries, we proposed an alternative approach to clustering‐based and polyhedra‐based discrete element methods whereby the need for complicated and ad hoc approaches to construct 3D grain geometries is entirely bypassed. We demonstrate the ability of GEM in capturing arbitrary‐shaped 3D grains with great ease, flexibility, and without excessive geometric information. Furthermore, the applicability of GEM is enhanced by its tight integration with existing non‐uniform rational B‐Splines modeling tools and ability to provide a seamless transition from binary images of real grain shapes (e.g., from 3D X‐ray CT) to modeling and discrete mechanics computations.Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
1000.
A multidirectional semi‐analytical method for analysis of laterally loaded pile groups in multi‐layered elastic strata 下载免费PDF全文
A semi‐analytical method for calculating the response of single piles and pile groups subjected to lateral loading is developed in this paper. Displacements anywhere in the soil domain are tied to the displacements of the piles through decay functions. The principle of virtual work and the calculus of variations are used to derive the governing differential equations that describe the response of the piles and soil. The eigenvalue method and the finite difference technique are used to solve the system of coupled differential equations for the piles and soil, respectively. The proposed method takes into account the soil surface displacement along and perpendicular to the loading direction and produces displacement fields that are very close to those produced by the finite element method but at lower computational effort. Compared with the previous method that considered only the soil displacement along the loading direction, accounting for the multi‐directional soil displacement field produces responses for the piles and soil that are closer to those approximated by the finite element method. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献