A semi‐analytical approach for modelling heat transfer during salt‐cavern leaching process

The use of gas‐storage caverns in salt formations is a growing industry that continues to gain momentum because it allows gas to be injected and withdrawn at high rates compared with other underground gas‐storage systems such as porous rock systems. In order to predict cavern production performances, cavern thermodynamics behaviour must be studied by higher accuracy approaches. This behaviour is extremely related to the temperature distribution in the surrounding formations. During the leaching process, the thermal equilibrium of the rock salt surrounding the cavern is extensively disrupted. The purpose of this paper is to study the heat transfer problem during the leaching process and to develop a thermal model that can be easily used in field applications. The results of this work will be the input data for the prediction of the gas temperature and pressure during cavern gas‐storage operation phase. Moreover, the developed model can find its use in the design of salt caverns since it can be coupled with geometrical modelling of salt dissolution codes. Copyright © 2008 John Wiley & Sons, Ltd.     

A review of major progresses in mesoscale dynamic research in China since 1999

Mesoscale research conducted by Chinese meteorologists during the past four years is reviewed.Advances in theoretical studies include (a) mesoscale quasi-balanced and semi-balanced dynamics, derived through scale analysis and the perturbation method which are suitable for describing mesoscale vortices;(b) subcritical instability and vortex-sheet instability; (c) frontal adjustment mechanism and the effect of topography on frontgenesis; and (d) slantwise vorticity development theories, the slantwise vortex equation,and moist potential vorticity (MPV) anomalies with precipitation-related heat and mass sinks and MPV impermeability theorem. From the MPV conservation viewpoint, the transformation mechanism between different scale weather systems is analyzed. Based on the data analysis, a new dew-point front near the periphery of the West Pacific subtropical high is identified. In the light of MPV theory and Q-vector theory, some events associated with torrential rain systems and severe storms are analyzed and diagnosed.Progress in mesoscale numerical simulation has been made in the development of meso-α, meso-β vortices,meso-γ-scale downbursts and precipitation produced by deep convective systems with MM5 and other mesoscale models.     

Gravitational torque on the inner core and decadal polar motion

A decadal polar motion with an amplitude of approximately 25 milliarcsecs (mas) is observed over the last century, a motion known as the Markowitz wobble. The origin of this motion remains unknown. In this paper, we investigate the possibility that a time-dependent axial misalignment between the density structures of the inner core and mantle can explain this signal. The longitudinal displacement of the inner core density structure leads to a change in the global moment of inertia of the Earth. In addition, as a result of the density misalignment, a gravitational equatorial torque leads to a tilt of the oblate geometric figure of the inner core, causing a further change in the global moment of inertia. To conserve angular momentum, an adjustment of the rotation vector must occur, leading to a polar motion. We develop theoretical expressions for the change in the moment of inertia and the gravitational torque in terms of the angle of longitudinal misalignment and the density structure of the mantle. A model to compute the polar motion in response to time-dependent axial inner core rotations is also presented. We show that the polar motion produced by this mechanism can be polarized about a longitudinal axis and is expected to have decadal periodicities, two general characteristics of the Markowitz wobble. The amplitude of the polar motion depends primarily on the Y ¹₂ spherical harmonic component of mantle density, on the longitudinal misalignment between the inner core and mantle, and on the bulk viscosity of the inner core. We establish constraints on the first two of these quantities from considerations of the axial component of this gravitational torque and from observed changes in length of day. These constraints suggest that the maximum polar motion from this mechanism is smaller than 1 mas, and too small to explain the Markowitz wobble.     

南极海冰导温系数与孔隙率关系初探

利用南极中山站附近固定冰不同季节的温度垂直廓线,冰芯盐度、密度数据,基于Cox等发展的冰内孔隙率计算方法,获得冰内孔隙率的垂直廓线。再通过建立分布参数系统最优控制模型,优化辨识在无热源条件下冰内温度垂直廓线对应的海冰导温系数。通过比较7种冰导温系数同孔隙率的关系,选择出海冰导温系数和孔隙率的最优关系式。用该关系式对同一地点不同年份的海冰进行温度垂直廓线计算,比较辨识的导温系数同孔隙率的关系相对于前人理想海冰模型中的导热系数、比热等公式计算对应条件的海冰垂直温度廓线的优势。两种计算结果说明,辨识得到的关系所引起的偏差在趋势和量级上同理想模式计算的结果相同,但辨识得到的关系更简洁,且更具有物理背景。     

基于生命周期理论的煤矿区 土地利用演化模拟

准确、可靠地模拟和预测煤矿区土地利用结构的变化,是矿区制定土地利用规划、土地复垦措施的重要依据。考虑到元胞自动机模型(CA)在土地利用结构变化模拟和预测方面的优越性能,将CA模型引入了矿区土地利用结构变化的模拟和预测。但矿区在不同的发展阶段,土地利用类型之间的转换具有不同方式,使得土地利用结构的演化存在阶段性的特点。因而利用CA模型对矿区的土地利用变化进行模拟和预测,就要求在不同阶段使用不同的转换规则,而传统CA模型难以满足这样的要求。本文基于矿区生命周期理论,改进了传统CA模型,通过控制变量的引入,实现了元胞转换规则的动态获取和应用。为了验证模型的有效性,以潞安矿区为研究区域,常村矿为研究对象,利用改进的模型对常村矿的土地利用空间结构进行了成熟期和衰退期的预测。通过和传统CA模型预测结果的比较,表明该模型的预测结果和矿区的不同阶段的土地利用演化特点比较吻合。因此该模型能够提高矿区土地利用结构演变模拟和预测的精度,是有效可行的方法。     

Evaluation of a gravel transport sensor for bed load measurements in natural flows

A recent acoustic instrument （Gravel Transport Sensor, GTS） was tested for predicting sediment transport rate （bed load rate） in gravel bed streams. The GTS operation is based on the particle collision theory of submerged obstacles in fluids. When particles collide with the GTS cylinder their momentum is recorded in the form of ping rates. The GTS is attractive for further consideration here because of its potential to provide continuous unattended local bed load measurements, especially in areas found in streams that access may be difficult under extreme conditions. Laboratory experiments coupled with numerical simulations for the same flow conditions were performed in order to determine the conditions under which particles of different size will hit the GTS cylinder and be able to register a ping rate. The GTS was able to detect the number of particles with diameter in the range of 15.9 to 25.4 mm, with reasonable accuracy, if the applied Shields effective stress τ＊e = τ＊ - τ＊cr was in the range of 0.006 to 0.015. A drawback of the tested prototype GTS, however, was that it exerted increased resistance on the incoming particles. The added drag effects increased the overall resistance that was exerted by the flow on particles and thus increased the likelihood that particles will rest in the ambient region of the cylinder instead of hitting it. Numerical simulation of the flow around the GTS cylinder revealed that changing the prototype geometry from cylindrical to ellipsoid or rhomboid will increase the likelihood of the particles hitting the instrument under the same flow conditions failed by the original tested GTS cylinder.     

Volcanic hazard zonation of the Nevado de Toluca volcano,México

The Nevado de Toluca is a quiescent volcano located 20 km southwest of the City of Toluca and 70 km west of Mexico City. It has been quiescent since its last eruptive activity, dated at ∼ 3.3 ka BP. During the Pleistocene and Holocene, it experienced several eruptive phases, including five dome collapses with the emplacement of block-and-ash flows and four Plinian eruptions, including the 10.5 ka BP Plinian eruption that deposited more than 10 cm of sand-sized pumice in the area occupied today by Mexico City. A detailed geological map coupled with computer simulations (FLOW3D, TITAN2D, LAHARZ and HAZMAP softwares) were used to produce the volcanic hazard assessment. Based on the final hazard zonation the northern and eastern sectors of Nevado de Toluca would be affected by a greater number of phenomena in case of reappraisal activity. Block-and-ash flows will affect deep ravines up to a distance of 15 km and associated ash clouds could blanket the Toluca basin, whereas ash falls from Plinian events will have catastrophic effects for populated areas within a radius of 70 km, including the Mexico City Metropolitan area, inhabited by more than 20 million people. Independently of the activity of the volcano, lahars occur every year, affecting small villages settled down flow from main ravines.