Experimental and numerical investigations of the behaviour of a heat exchanger pile

The geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid‐filled pipes cast in concrete and then to building environments. To improve the knowledge in the field of geothermal structures, the behaviour of a pile subjected to thermo‐mechanical loads is studied in situ. The aim is to study the increased loads on pile due to thermal effects. The maximum thermal increment applied to the pile is on the order of 21°C and the mechanical load reached 1300 kN. Coupled multi‐physical finite element modelling is carried out to simulate the observed experimental results. It is shown that the numerical model is able to reproduce the most significant thermo‐mechanical effects. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial Representation of Aquatic Vegetation by Macrofossils and Pollen in a Small and Shallow Lake

We have explored the contemporary spatial relationship between aquatic vegetation and surficial macrofossil and pollen remains in a small, shallow, English lake. A detailed point-based (n = 87) underwater vegetation survey was undertaken in the middle of the plant-growing season in July 2000. Then following plant die-back in November 2000, surface sediment samples (upper 1.5 cm) were collected from 30 of these plant survey points and analysed for plant macro-remains (all 30 samples), and pollen (4 evenly spaced samples). All data were stored as separate layers in a geographical information system and spatial relationships between the aquatic vegetation and plant remains were explored. In contrast to pollen types, plant macrofossils were not evenly dispersed across all parts of the lake and, with the exception of Chara oospores, higher concentrations of remains (particularly for Potamogeton) were found close to areas of source-plant dominance. The spatial pattern of macrophyte–macrofossil relationships revealed that vegetative remains (particularly leaf fragments) were probably deposited at source, whereas seeds were recovered close to the shore suggesting slightly wider dispersal. Overall, however, macro-remains best represented local ‘patch-scale’ vegetation within 20–30 m of the core site. The macro-remains effectively recorded the dominant plants in the lake with 63% of samples containing a combination of remains of Chara, Elodea, and Potamogeton. However, relationships between macrophytes and fossils were complex. Some species were significantly over-represented by macrofossils (e.g., Chara spp., Nitella flexilis agg., and Zannichellia palustris), while others were either under-represented (e.g., Potamogeton spp.), or not represented at all (e.g., Lemna trisulca). Pollen represented macrophyte diversity poorly, but some taxa were found (e.g., Myriophyllum spicatum, Ceratophyllum demersum) that were not recorded by macro-remains. We conclude that macrofossil analysis may be very usefully employed to determine the dominant taxa in past aquatic plant communities of shallow, productive lakes and that the addition of pollen analysis provides further information on former species richness.     

Seasonal dynamics of a large, shallow lake, laguna Chascomús: The role of light limitation and other physical variables

The most conspicuous waterbodies in the Pampa region of Argentina are the so-called “lagunas”. A typical Pampean laguna may be described as a relatively large (100+ha), permanent, shallow lake. Here, we report the dynamics of laguna Chascomús, sampled weekly, from April 2001 to June 2003. During the period, the lakes experienced three consecutive floods waves that affected the concentration of major ions and the optical signature of the dissolved organic matter. Despite these hydrological alterations, laguna Chascomús was permanently limited by light. Transparency was to a great extent controlled by the incident photosynthetic available radiation irradiance. We hypothesize that wind contributes to the permanent mixing of the lake, as well as to lessen the sedimentation losses of photoautotrophs.     

Nearshore sticky waters

Wind- and current-driven flotsam, oil spills, pollutants, and nutrients, approaching the nearshore will frequently appear to slow down/park just beyond the break zone, where waves break. Moreover, the portion of these tracers that beach will do so only after a long time. Explaining why these tracers park and at what rate they reach the shore has important implications on a variety of different nearshore environmental issues, including the determination of what subscale processes are essential in computer models for the simulation of pollutant transport in the nearshore. Using a simple model we provide an explanation for the underlying mechanism responsible for the parking of tracers, not subject to inertial effects, the role played by the bottom topography, and the non-uniform dispersion which leads, in some circumstances, to the eventual landing of all or a portion of the tracers. We refer to the parking phenomenon in this environment as nearshore sticky waters.     

Interpretation of gravity profiles across the northern Oaxaca terrane,its boundaries and the Tehuacán Valley,southern Mexico

A gravity study was conducted across the northern Oaxaca terrane and its bounding faults: the Caltepec and Oaxaca Faults to the west and east, respectively. These faults juxtapose the Oaxaca terrane against the Mixteca and Juarez terranes, respectively. The Oaxaca Fault also forms the eastern boundary of the Cenozoic Tehuacán depression. On the west, at depth, the Tehuacán valley is limited by the normal buried Tehuacán Fault. This gravity study reveals that the Oaxaca Fault system gives rise to a series of east tilted basamental blocks (Oaxaca Complex). The tectonic depression is filled with Phanerozoic rocks and has a deeper depocenter to the west. The gravity data also indicate that on the west, the Oaxaca Complex, the Caltepec and Santa Lucia faults continue northwestwards beneath Phanerozoic rocks. A major E–W to NE–SW discontinuity is inferred to exist between profiles 1 and 2.     

Hydrochemical and isotope characteristics of spring water discharging from Qiushe Loess Section in Lingtai,northwestern China and their implication to groundwater recharge

The loess plateau in northwestern China with an area of 640 000km~2, which has developed the loess deposits with a thickness up to 200m in typical areas, is regarded as a huge carbon stock like the karst area in southwestern China, and plays an important role in regional(even global) carbon cycle. But the spring discharging from loess is poorly known compared with karst spring so far. The objective of this study is to ascertain the characteristics and origin of spring at Qiushe Village, Lingtai County, Gansu Province by hydro-chemical and isotopic methods. The results show that the springs including LGQ, HMQ, YYQ and CZQ are the depression spring and belong to the same shallow aquifer with the well water JZJ. There are not distinct seasonal/diurnal-scale variations on the hydro-chemical characteristics of the spring water(LGQ, HMQ, YYQ, CZQ) and groundwater(JZJ). The hydro-chemical type of groundwater is Ca·Mg-HCO_3. The D and O isotope ratios indicate that the precipitation is the main recharge source of groundwater in study area. And the results of tritium(TU) and Cl concentration suggest that the recharge cycle of groundwater may be more than 60 yrs. Our study shows that the water cycle in loess plateau including rainfall, infiltration, recharge and discharge exerts a continuous impact on carbon stock in loess, which should be paid more attention to in future research on the quantitative reconstruction of paleoclimate.     

Numerical and experimental study on seakeeping performance of ship in finite water depth

Vessels operating in shallow waters require careful observation of the finite-depth effect. In present study, a Rankine source method that includes the shallow water effect and double body steady flow effect is developed in frequency domain. In order to verify present numerical methods, two experiments were carried out respectively to measure the wave loads and free motions for ship advancing with forward speed in head regular waves. Numerical results are systematically compared with experiments and other solutions using the double body basis flow approach, the Neumann-Kelvin approach with simplified m-terms, and linearized free surface boundary conditions with double-body m-terms. Furthermore, the influence of water depths on added mass and damping coefficients, wave excitation forces, motions and unsteady wave patterns are deeply investigated. It is found that finite-depth effect is important and unsteady wave pattern in shallow water is dependent on both of the Brard number τ and depth Froude number F_h.     

黄泛平原区（1∶25万济南幅）浅层孔隙水多年动态变化特征

分析济南幅黄泛平原区浅层孔隙水的补给来源、地下水流场形态变化、地下水排泄途径及水化学多年变化特征,并结合区内浅层地下水开采强度资料综合研究认为,引起济南幅黄泛平原区浅层孔隙水动力场变化的主要原因是地下水开采量的变化与天然补给源的减少。研究表明,局部水位下降甚至产生超采漏斗主要是由于地下水长期过量开采引起的,并对区域地下水流场形态影响较大,区内已形成地下水分水岭。