Using MODFLOW code to approach transient hydraulic head with a sharp‐interface solution

Saltwater intrusion problems have been usually tackled through analytical models because of its simplicity, easy implementation and low computational cost. Most of these models are based on the sharp‐interface approximation and the Ghyben–Herzberg relation, which neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. This paper provides insight into the validity of a sharp‐interface approximation defined from a steady state solution when applied to transient seawater intrusion problems. The validation tests have been performed on a 3D unconfined synthetic aquifer, which include spatial and temporal distribution of recharge and pumping wells. Using a change of variable, the governing equation of the steady state sharp‐interface problem can be written with the same structure of the steady confined groundwater flow equation as a function of a single potential variable (?). We propose to approach also the transient problem solving a single potential equation (using also the ? variable) with the same structure of the confined groundwater flow equation. It will allow solving the problem by using the classical MODFLOW code. We have used the parameter estimation model PEST to calibrate the parameters of the transient sharp‐interface equation. We show how after the calibration process, the sharp‐interface approach may provide accurate enough results when applied to transient problems and improve the steady state results, thus avoiding the need of implementing a density‐dependent model and reducing the computational cost. This has been proved by comparing results with those obtained using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density‐dependent transport. The comparison was performed in terms of piezometric heads, seawater penetration, transition zone width and critical pumping rates. Copyright © 2014 John Wiley & Sons, Ltd.     

后发团盘星系自转轴方向的分布：统计样本

为研究后发团盘星系自转轴方向的分布,本文对后发团的两个星系表进行交叉证认,给出后发团中心2°.63×2°.63范围内,完整到m_p≤15.7等的138个盘星系的方位角表,其中包括94个S0星系.44个S和Irr星系。     

降尘对中国北方主要城市光伏电站发电量的影响

中国太阳能光伏发电在2010-2015年实现了飞速发展。降尘降低了光伏电池板表面玻璃的透光率,导致电池板的发电量下降。降尘对太阳能光伏发电影响的量化是预测光伏电站发电量的基础。以降尘相对较严重的北方（年均降雨量小于800mm）36个城市的光伏电站为研究对象,综合考虑温度、降尘、辐射等因素导致的光伏发电量损失,模拟了各城市光伏电站25年内的年均最大发电量。模拟结果显示：（1）36个城市平均年发电量为209.62±30.15kWh·5m^-2,其中,发电量最大的城市是拉萨,最小的为西安,前者约为后者的两倍;（2）年降雨量100~200mm地区年发电量最高,其次为≤100mm的地区,200~400mm和400~600mm的地区发电量几乎相等,600~800mm的地区发电量最小;（3）降尘与电池板最佳倾角的关系可以忽略;（4）降尘导致的光伏发电量损失最大值发生在降雨量为100~200mm区域（5.32%）,然后依次为≤100mm（5.21%）、200~400mm（4.46%）、400~600mm（3.29%）和600~800mm（2.09%）的区域。     

2011年春末夏初长江中下游地区旱涝急转成因初探

选用NCEP/NCAR、NOAA、国家气候中心(NCC)提供的各要素资料及NOAA-Hysplit模型,对2011年春末夏初发生在中国长江中下游地区旱涝急转的降水异常事件及其影响机制进行初步分析,并建立天气学概念模型.结果表明:(1)长江中下游地区,尤其是(27°N～～32°N,l10°E～120°E)区域在6月第1候...     

排放角度对波浪环境中圆管射流运动和稀释特性的影响

采用粒子图像测速和平面激光诱导荧光技术对波浪环境中倾斜射流的运动和稀释特性进行了实验研究,对比分析了排放角度对射流瞬时运动形态、时均速度场和时均浓度场的影响。实验结果表明排放角度的变化对波浪环境中射流的运动形态、速度分布和混合范围等均有显著影响。当射流顺波浪方向运动时,射流主体段速度剖面呈双峰分布,达到初始浓度20%、30%、40%和50%的混合范围随排放角度增加而先增大后减小;当射流逆波浪方向运动时,射流速度剖面双峰分布不明显,相应的混合范围随排放角度增加而减小。在波浪牵引和射流卷吸的共同作用下,逆向射流的稀释效果总体上优于与垂线方向相同夹角的顺向射流。     

大旋转角空间直角坐标转换改进模型研究

针对大旋转角三维坐标转换模型法方程系数阵病态的问题,提出中心化和自适应缩放相结合的改进模型。结合算例分析,验证了该模型能显著改善法方程系数矩阵病态性,转换参数结果稳定可靠,优于现有模型。     

Long term AVHRR observations of surface radiative flux from El Chichón crater lake (1996–2006)

It has been shown that due to the small surface of crater lakes, temperature surveillance is a problem using meteorological satellites. This is particularly true for El Chichón surface lake because it's about one tenth of an AVHRR pixel at nadir. In order to guarantee at least one unmixed pixel in AVHRR data, it is necessary to use only AVHRR data from NOAA satellite passes as close as possible to the nadir for the period 1996–2006, therefore AVHRR data of El Chichón's crater lake were only used it they were cloudless and had scan angles close to nadir. The analysis of the time series data shows that lake surface temperature had annual maximum values (> 35 °C) during 1996 and 1997 then surface temperature decay with a negative exponential trend reaching a steady state of about 30 °C in the last years (2004–2006). A seasonal temperature variation between the dry (December to May) and the wet (June to November) seasons is also observed. Differences between nocturnal and midday temperatures indicate the influence of lake energy emission (including reflectance) at midday under a strong short-wave solar radiation. Water surface radiative flux under these conditions reaches an average of 77.8 W m^− 2 and a maximum of 187.1 W m^− 2. Whereas nocturnal heat output from El Chichón crater lake has an average surface radiative flux of 20.4 W m^− 2 and a maximum of 74.3 W m^− 2.     

Experimental investigation of melt topology in partially molten quartzo-feldspathic aggregates under hydrostatic and non-hydrostatic stress

Continental collision results in deep burial of crustal rocks and their subsequent partial melting. Field relations of melt along zones of intense deformation suggest that partially molten rocks may play an important role in regional tectonics. However, subsequent deformation may erase the microstructures produced by the earlier deformation mechanisms, inhibiting our understanding of the rheology of partially molten crustal rocks. Thus, in this paper, we report the results of an experimental study of the distribution of 2–5 vol% melt in quartzo-feldspathic aggregates of various grain sizes: 2–5, 5–10, 10–16 and 26–31 μm. Three types of samples were examined, all with the composition of 60 wt% albite, 25 wt% potassium feldspar, 10 wt% quartz and 5 wt% biotite. The first group included mineral powders annealed at 1000 °C, 1.0 GPa, for c. 100 h. The second group included commercially hot-pressed mineral powders which yielded c. 25 vol% glass; cores of this material were also annealed at 1000 °C, 1.0 GPa, for c. 100 h. The third group included cores of hot-pressed material that were annealed at 1000 °C, 1.0 GPa, for c. 45 h, then deformed. All samples were quenched rapidly in order to examine the melt distribution. Wetting angles are very similar in both the hydrostatically annealed and the deformed samples. Analysis of melt pool orientations reveal that melt migrates away from grain boundaries normal to the maximum compressive stress direction in response to the applied non-hydrostatic stress. This response is easily seen in the coarser-grained samples in which melt pools elongated parallel to the maximum compressive stress direction formed during deformation. If these results extrapolate to naturally deformed rocks, it will be important to consider the orientation of the state of stress in a region during syn-magmatic deformation because of its effect on the melt distribution.     

Critical response of structures to multicomponent earthquake excitation

This paper aims to develop an improved understanding of the critical response of structures to multicomponent seismic motion characterized by three uncorrelated components that are defined along its principal axes: two horizontal and the vertical component. An explicit formula, convenient for code applications, has been derived to calculate the critical value of structural response to the two principal horizontal components acting along any incident angle with respect to the structural axes, and the vertical component of ground motion. The critical response is defined as the largest value of response for all possible incident angles. The ratio r_cr/r_srss between the critical value of response and the SRSS response—corresponding to the principal components of ground acceleration applied along the structure axes—is shown to depend on three dimensionless parameters: the spectrum intensity ratio γ between the two principal components of horizontal ground motion characterized by design spectra A(T_n) and γA(T_n); the correlation coefficient α of responses r_x and r_y due to design spectrum A(T_n) applied in the x‐ and y‐directions, respectively; and β = r_y/r_x. It is demonstrated that the ratio r_cr/r_srss is bounded by 1 and . Thus the largest value of the ratio is , 1.26, 1.13 and 1.08 for γ = 0, 0.5, 0.75 and 0.85, respectively. This implies that the critical response never exceeds times the result of the SRSS analysis, and this ratio is about 1.13 for typical values of γ, say 0.75. The correlation coefficient α depends on the structural properties but is always bounded between −1 and 1. For a fixed value of γ, the ratio r_cr/r_srss is largest if β = 1 and α = ±1. The parametric variations presented for one‐storey buildings indicate that this condition can be satisfied by axial forces in columns of symmetric‐plan buildings or can be approximated by lateral displacements in resisting elements of unsymmetrical‐plan buildings. Copyright © 2000 John Wiley & Sons, Ltd.     

Retrieval of Sea Surface Wind Speed by One-Dimensional Synthetic Aperture Microwave Radiometer

One-dimensional synthetic aperture microwave radiometers have higher spatial resolution and record measurements at multiple incidence angles. In this paper, we propose a multiple linear regression method to retrieve sea surface wind speed at an incidence angle between 0° ~65°. We assume that a one-dimensional synthetic aperture microwave radiometer operates at frequencies of 6.9, 10.65, 18.7, 23.8 and 36.5 GHz. Then, the microwave radiative transfer forward model is used to simulate the measured brightness temperatures. The sensitivity of the brightness temperatures at 0°~65° to the sea surface wind speed is calculated. Then, vertical polarization channels(VR), horizontal polarization channels(HR) and all channels(AR) are used to retrieve the sea surface wind speed via a multiple linear regression algorithm at 0° ~65°, and the relationship between the retrieval error and incidence angle is obtained. The results are as follows:(1) The sensitivity of the vertical polarization brightness temperature to the sea surface wind speed is smaller than that of the horizontal polarization.(2) The retrieval error increases with Gaussian noise. The retrieval error of VR first increases and then decreases with increasing incidence angle, the retrieval error of HR gradually decreases with increasing incidence angle, and the retrieval error of AR first decreases and then increases with increasing incidence angle.(3) The retrieval error of AR is the lowest and it is necessary to retrieve the sea surface wind speed at a larger incidence angle for AR.