A Three-Dimensional Prediction Method for Thermal Diffusion

A three-dimensional,first order turbulence closure,thermal diffusion model is described inthis paper.The governing equations consist of an equation of continuity,three components of momentum,conservation equations for salt,temperature and subgridscale energy,and an equation of state.In the mod-el,according to the hypothesis of Kolmogorov and Prandtl,the viscosity coefficient of turbulent flow ofhomogeneous fluid is related to the local turbulent energy,and the horizontal and vertical exchangecoefficients of mass,heat and momentum are computed with the introduction of subgridscale turbulenceenergy.The governing equations are solved by finite difference techniques.This model is applied to theJiaozhou bay to predict thermal pollution by the Huangdao power plant.An instantaneous tidal currentfield is computed,then the distribution of temperature increment is predicted,and finally the effect of windstress on thermal discharge is discussed.     

白云石有序度与流变特征的研究进展

白云石CaMg(CO3)2常见于白云岩、灰岩及大理岩中,其稳定的温压范围很广,是研究俯冲隧道变形、全球碳循环和地幔交代作用的重要矿物。白云石的有序度可能与重结晶过程相关,温度是影响白云石有序度的关键因素,压力对白云石有序度的影响较弱。在1~3 GPa 下白云石完全无序的转变温度为1150~1200℃,Fe、Mn、Cd 离子含量的增高可显著降低白云石结构无序化的转变温度。天然变形的白云石常发育由底面c 滑移控制的晶格优选定向。根据白云石的流变律,在天然 应变速率下（10-15~10-12 s-1）,>400℃细粒白云石以扩散蠕变为主;而粗粒白云石以位错蠕变为主,只有在高温下（>600~700℃） 扩散蠕变才成为主控变形机制。分解反应或者动态重结晶可导致白云石流变强度的显著下降,应变集中。白云石c滑移的临界剪应力随温度升高而增大的现象可能与白云石有序度的变化有关,而围压、水逸度和成分对白云石流变的影响尚不清楚,定量研究白云石的有序度与流变学性质的相关性将为追踪碳酸盐岩和大理岩的成岩和变形历史提供新的信息。     

时间域航空电磁扩散特征和成像深度研究

为了研究时间域航空电磁系统扩散特征,基于连续性边界条件将电磁场向下延拓得到地下介质中各点处的频率域响应,通过傅里叶变换将其变换到时间域.计算阶跃波形发射时垂直磁偶极子和水平磁偶极子在均匀半空间介质和两层介质中产生的电磁场,通过电流密度矢量图和随时间变化的电流密度等值线展示电磁场在地下介质中的扩散过程.电磁场在地下的扩散受电阻率结构的影响.在良导地区电磁场扩散慢、衰减快,而在高阻地区电磁场扩散快、衰减慢.垂直磁偶极子在地下产生的感应电流形成一个电流环随时间向下、向外扩散.水平磁偶极子在地下产生的感应电流形成两个互相叠加的电流环.时间域电磁场扩散代表着真正物理意义上的电磁扩散,因为它展示了地下电磁场空间分布随时间的变化和场强的衰减.基于对感应电流环的研究,我们探究了扩散深度和时间域航空电磁数据成像深度的关系.时间域电磁场扩散规律的研究不仅加深了对电磁扩散特征的理解,更有助于提高航空电磁数据解释水平.     

The influence of climate and microclimate (aspect) on soil creep efficiency: Cinder cone morphology and evolution along the eastern Mediterranean Golan Heights

Although hillslope evolution has been subject to much investigation for more than a century, the effect of climate on the morphology of soil‐mantled hillslopes remains poorly constrained. In this study, we perform numerical simulations of volcanic cinder cones in the Golan Heights (eastern Mediterranean) to estimate soil transport efficiency across a significant north–south gradient in mean annual precipitation (1100 to 500 mm). We use the initial cinder cone morphology (constrained by stratigraphy), the modern hillslope form (surveyed with sub‐meter accuracy) and the eruption age (based on ⁴⁰Ar–³⁹Ar chronology) to predict the best‐fit value of the soil transport coefficient (‘diffusivity’) based on a nonlinear transport model. Our results indicate that the best‐fit diffusivity (K ) varies from 1 to 6 m² ka^?1 among the five cinder cones in our field area. Diffusivity (K ) values vary systematically with precipitation and hillslope aspect; specifically, K is higher on south‐facing (drier) hillslopes and decreases with mean annual precipitation. We interpret this climate dependency to reflect vegetation‐driven variations in apparent soil cohesion, which increases with root network density, and attenuation of rain splash and overland flow erosion, which increases with vegetative ground cover. To assess how vegetative root mass and ground cover vary with precipitation and aspect, we quantified the spatial distribution of NDVI (normalized difference vegetation index) from ASTER satellite images and observed spatial variations that correlate with our calibrated values of K . Analysis of previously studied cinder cones in the USA can be used to extend our framework to arid domains. This endeavor suggests a humped relationship between K and precipitation with maximum diffusivity at mean annual precipitation of 400–600 mm. Copyright © 2017 John Wiley & Sons, Ltd.     

Flood routing based on diffusion wave equation using mixing cell method

A one-dimensional non-linear diffusion wave equation is derived from the Saint Venant equations with neglect of the inertia terms. This non-linear equation has no general analytical solution. Numerical schemes are therefore employed to discretize the space and time axes and convert the differential equation to difference form. In this study, the mixing cell method is used to convert the diffusion wave equation to difference form, in which the difference term can be eliminated by selecting an optimal space step size Δx when time step size Δt is given. When the time step size Δt→0, the space step size Δx=Q/(2S₀BC]_k) where Q is discharge, S₀ is bed slope, B is channel width and C_k is kinematic wave celerity, which is the same as the characteristic length proposed by Kalinin and Milyukov. The results of application to two cases show that the mixing cell and linear channel flow routing methods produce hydrographs that are in agreement with the observed flood hydrographs. © 1997 John Wiley & Sons, Ltd.     

运移参数对GCL中污染物运移的影响研究

分析了运移参数的变化对GCL中污染物运移的影响。从衬垫底部浓度比、对流和扩散通量、污染物累积运移量等方面,对污染物在GCL中的运移进行了计算。结果表明,减小渗透系数和扩散系数可以有效减缓衬垫底部浓度比的增加速度。渗透系数对对流通量的大小、扩散通量的变化速度的影响较大;扩散系数主要影响最大扩散通量。当渗透系数较大时,可以忽略扩散累积运移量,用对流累积运移量代替总累积运移量引起的误差很小。当渗透系数较小时,忽略扩散运移量可能产生较大的误差,尤其是在扩散系数也较大的情况下误差更加明显。      

蒸发条件下路基对气候变化的响应模型及影响因素分析

以受大气影响下的公路路基为研究对象,建立了蒸发条件下路基对气候变化的响应模型,该模型考虑了温度-水-应力的耦合作用,采用非饱和土实际蒸发量作为边界条件。采用该模型对大气蒸发条件下南宁某公路路基的蒸发过程进行了模拟分析,结果表明,用实际蒸发量作为边界条件的热-水-应力模型可以较好地模拟大气在蒸发条件下路基的响应过程。在蒸发过程中,水蒸气的扩散对路基的蒸发量和含水率的影响较大。通过用正弦波描述昼夜蒸发强度的变化,研究了天气的周期变化对蒸发过程的影响,可以看出,天气周期变化对表层影响很大,但影响的深度有限。天气周期变化影响下的表层含水率并不是单调减小,而是随着蒸发强度的变化有一个干湿过程。     

近海海面油类漂流扩散的研究和预测实践

根据珠江口气象站风速与潮汐站潮位资料，对1955－1998年12次El Nino过程的珠江口季风强度与海平面变化特点进行合成分析，结果表明，El Nino发生前一年冬季，珠江口冬季平均风速较常年值大0．4m/s,El Nino发生当年，月平均风速也普遍大于常年，而月平均海平面则普遍较常年偏低，其中10与11月份负距平为6cm左右。东亚地区的季风异常对珠江口海平面异常有着重大的影响。