人-板耦合动力响应分析

针对大跨度空间结构楼板振动舒适度问题,建立相应的人-板耦合模型,通过理论分析及有限元计算,系统研究了人-板相互作用体系的动力特性.详细分析了板的约束条件、楼板装饰层以及人群荷载密度分布等各种因素对楼板自振特性的影响.以大跨度车站结构为背景,采用人-板耦合体系,进行人行荷载同步、队列、散步等不同方式作用下楼板竖向振动的研...     

基于等效单自由度体系的结构地震输入能量的研究

通过对多自由度体系结构在地震作用下的能量分析,考虑地震动因素和结构自身特性,提出一种框架结构地震总输入能量的简化求解方法.实例计算结果表明:基于等效单自由度体系来估计多自由度体系的地震总输入能,是一种计算简便且较为准确的方法.     

Optical signatures of dissolved organic matter in the watershed of a globally large river (Yangtze River,China)

Parallel factor analysis of fluorescence excitation emission matrices of surface water samples of a globally large river (Yangtze River, China) watershed identified three classes of fluorescent dissolved organic matter (FDOM) that had ex/em = 280/330 nm, 305/385 nm and 350/450 nm respectively, resembling “peak T”, “peak M” and “peak C” commonly identified in natural water, respectively. Peak T (a tyrosine/tryptophan-like FDOM) did not show correlations to peak M or C which were humic-like substances, while a positive correlation (r = 0.935, p < 0.001) was present between the natural log-transformed maximum fluorescence intensity (F_max) of peaks T and M indicating a tight link during their production and processing. F_max values (in Raman unit nm^?1) normalized to dissolved organic carbon (DOC) concentration were low, varying in ranges 15.93–85.95, 29.83–83.54 and 19.73–51.05 × 10^?5 nm^?1 (μmol/L)^?1 for peaks T, M and C, respectively, in line with the history of strong photobleaching of the water samples as indicated by fairly high absorption spectral slope ratios (0.75–1.53 with a mean 1.03). Intermediate fluorescence index (FI) (1.46–1.83 with a mean 1.61) and small specific absorption at 254 nm (0.64–1.93 with a mean 1.15 m^?1 mg^?1 L) of the water samples, indicated the presence of both aquatic microbial DOM (e.g. peak T) and soil DOM (e.g. peak C). Peak C could be substantially removed by UV-A (320–400 nm) irradiation, while peak M was slightly increased when a microbe-containing water was exposed to the same UV-A irradiation. Taken together, peak C was attributed to diffuse soil source while peak M was likely attributed to joint effects of microbial activities and solar irradiation on the chromophores in the sample.     

Regulating Environmental Factors of Nutrients Release from Wheat Straw Biochar for Sustainable Agriculture

One mechanism by which biochar application enhances soil nutrient availability is through direct nutrients release from biochar. However, factors controlling the release processes are poorly understood. In this study, the effects of pH, biochar to water ratio, temperature, ionic strength, and equilibration time on the release of PO, NO, NH, K⁺, Na⁺, Ca²⁺, and Mg²⁺ from biochar were evaluated in simulated experiments. The release of PO, K⁺, Ca²⁺, and Mg²⁺ was significantly affected by extraction pH, suggesting that their release from biochar was pH dependent or an H⁺‐consuming process. Correlation analysis indicated that PO and Ca²⁺, PO and Mg²⁺, and Ca²⁺ and Mg²⁺ were co‐solubilized with increasing soil acidity. To a lesser extent, the recovery of the nutrients was also affected by the ratio of biochar to water: more nutrients were soluble with more water supply. In contrast, the release of Na was not affected by pH while the concentration increased with decreasing biochar to water ratio. Meanwhile, other factors (temperature, ionic strength, and equilibration time) had less effect on nutrient release from biochar. Under the influence of pH, the patterns of NO and PO release from biochar were different: extractable NO concentration was not affected by the pH but more PO was released in strongly acidic conditions. Our data suggested that P was mainly retained in inorganic forms while N was in organic forms in biochar. We conclude that environmental factors have marked influences on nutrients release from biochar.     

Mass Balance Study on Phosphorus Removal in Constructed Wetland Microcosms Treating Polluted River Water

A number of studies have showed that the mass removal rates of phosphorus (P) in different constructed wetlands (CWs) varied significantly, and it is essential to quantify the contributions of major P removal processes in order to improve system design. The objective of this study was to investigate the effects of vegetation, hydraulic retention time (HRT), and water temperature on P removal from polluted river water and to quantify the contributions of different P removal pathways in surface CWs. Results showed that the average total P removal rates ranged between 2.69 and 20.84 mg/(m² day) in different seasons and were influenced significantly by vegetation, HRT, and water temperature. According to the mass balance approach, plant uptake removed 4.81–22.33% of P input, while media storage contributed 36.16–49.66%. Other P removal processes such as microbiota uptake removed around 0.26–4.13%. Media storage and plant uptake were identified as the main P removal processes in surface CWs treating polluted river water. This illustrated the importance of selecting media and plants in CWs for future practical application.     

Statistical interpretation of the daily variation of urban water consumption in Beijing,China

Abstract

The efficient planning and design of water networks, as well as the management and strategies of existing water supply systems, require accurate short-term water demand forecasts. In this study, a statistical model for the estimation of daily urban water consumption was developed. The model was applied to analyse and forecast the daily water consumption in the main district of Beijing, China, from 2006 to 2010. The model exhibited good performance with a coefficient of determination, R², greater than 0.9 in both the calibration and validation periods. The results indicate that: (a) the 7-day moving average temperature is an efficient variable that can be used to depict water-use variation in a year; (b) a daily maximum temperature of 31.1°C and the occurrence of precipitation are two thresholds of water-use behaviour; and (c) the current day’s water consumption has a strong correlation with the consumption of one, two and seven days ago.

Editor Z.W. Kundzewicz; Associate editor D. Yang

Citation Zhang, D.W., et al., 2013. Statistical interpretation of the daily variation of urban water consumption in Beijing, China. Hydrological Sciences Journal, 59 (1), 181–192.     

Effects of initial soil water content and saturated hydraulic conductivity variability on small watershed runoff simulation using LISEM

Abstract

Soil water content (θ) and saturated hydraulic conductivity (K_s) vary in space. The objective of this study was to examine the effects of initial soil water content (θ_i) and K_s variability on runoff simulations using the LImburg Soil Erosion Model (LISEM) in a small watershed in the Chinese Loess Plateau, based on model parameters derived from intensive measurements. The results showed that the total discharge (TD) and peak discharge (PD) were underestimated when the variability of θ_i and K_s was partially considered or completely ignored compared with those when the variability was fully considered. Time to peak (TP) was less affected by the spatial variability compared to TD and PD. Except for TP in some cases, significant differences were found in all hydrological variables (TD, PD and TP) between the cases in which spatial variability of θ_i or K_s was fully considered and those in which spatial variability was partially considered or completely ignored. Furthermore, runoff simulations were affected more strongly by K_s variability than by θ_i variability. The degree of spatial variability influences on runoff simulations was related to the rainfall pattern and θ_i. Greater rainfall depth and instantaneous rainfall intensity corresponded to a smaller influence of the spatial variability. Stronger effects of the θ_i variability on runoff simulation were found in wetter soils, while stronger effects of the K_s variability were found in drier soils. For accurate runoff simulation, the θ_i variability can be completely ignored in cases of a 1-h duration storm with a return period greater than 10 years, while K_s variability should be fully considered even in the case of a 1-h duration storm with a return period of 20 years.

Editor D. Koutsoyiannis; Associate editor A. Fiori     

Simulating and understanding effects of water level fluctuations on thermal regimes in Miyun Reservoir

ABSTRACT

Water temperature dynamics in a reservoir are affected by its bathymetry, climatic conditions and hydrological processes. Miyun Reservoir in China is a large and deep reservoir that experienced a large water level decline in 1999–2004 due to low rainfall and relatively high water supply to Beijing. To study changes of stratification characteristics in Miyun Reservoir from 1998 to 2011, the one-dimensional year-round lake model MINLAKE2010 was modified by adding a new selective withdraw module and a reservoir hydrological model. Simulation results under three scenarios demonstrated that the new MINLAKE2012 model accurately predicted daily water levels and temperature dynamics during the water level fluctuation period. The water level decline led to 7.6 and 3.8°C increases in the maximum and mean bottom temperatures and about 29 days reduction in the stratification days. These simulation results provide an insight into the thermal evolution of Miyun Reservoir during the planned future water filling process.

Editor D. Koutsoyiannis Associate editor M. Acreman