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Study of groundwater recharge processes is vital for quantification of total natural recharge to the aquifers. One of the
recharge processes demonstrated earlier by tracer experiments in the unsaturated zone is that of piston flow movement of soil
moisture. Based on this recharge process, environmental tritium, chloride and injected tritium studies have been carried out
extensively in various geological environs of India. The purpose of this paper is to evaluate the validity of the piston flow
concept in different geological environs viz. consolidated fractured and weathered granites, semi-consolidated sandstones
and unconsolidated alluvial tracts, and quantify the contribution from this process as well as that from the preferential
flow mechanism using different tracers. Analysis of tracer data demonstrates that the preferential flow recharge process contributes
very significantly (an average of 75% of total recharge) in the case of fractured granites and is important (an average of
33% of total recharge) for semi-consolidated sandstones, whereas the preferential flow recharge component is minimal in unconsolidated
alluvial tracts (piston flow model is applicable). These findings necessitate re-evaluation of the total natural recharge
potential of the above mentioned geological environs in view of the significant preferential flow recharge that is evidenced
and estimated.
Electronic Publication 相似文献
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The theoretical model of Molin [6] is extended to the case of rectangular moonpools with one or two recesses, as can be found in some drillships. Obtained natural frequencies and modal shapes of the piston and first sloshing modes are compared with experimental results available in literature, with good agreement. An approximation easy to implement is proposed for the natural frequency of the piston mode. Further illustrative results are presented when some geometrical parameters of the moonpool are being varied. 相似文献
4.
Analysis of dynamic effects relevant for the wear damage in hydraulic machines for wave energy conversion 总被引:1,自引:0,他引:1
The present paper deals with a mathematical model of a heaving-buoy Wave Energy Converter (WEC) equipped with high-pressure hydraulic power take-off machinery for energy conversion. This model is based on linear hydrodynamic theory, and a hybrid frequency-time domain model is used to study the dynamics of the heaving-body exposed to an irregular incident wave. For the power take-off system, end-stop devices are provided to protect the hydraulic machinery when the buoy is exposed to severe sea states. The model also takes into account the lubricated friction force and pressure drops of orifice flow through the valves in the hydraulic system. All the forces mentioned in the hydraulic power take-off machinery have non-linear features. A complete non-linear state space model for the WEC system is presented in this study.The WEC system was numerically simulated for different cylinder lengths under a fixed volume. The effect of fluid compressibility in the cylinder has been investigated in the mathematical model. High frequency oscillations (HFOs) caused by the compressibility of the fluid are displayed in the time series and in corresponding power spectra, and variation is shown for different cylinder sizes. Piston ring and cylinder bore wear damage is estimated by using Archard’s equation on the basis of the simulation results. A comparison of these results with a performance of an identical WEC system which neglects fluid compressibility has been done in this work. It shows that although the spectral power is small, HFO can make a large contribution to both the ring and cylinder bore wear. For the purpose of wear prediction, oscillations at or below the wave frequency and HFO may be equally important. 相似文献
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The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments. 相似文献
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Jens Mingram Jörg F. W. Negendank Achim Brauer Dieter Berger Andreas Hendrich Michael Köhler Hartmut Usinger 《Journal of Paleolimnology》2007,37(4):517-528
We present a unique, versatile piston corer for recovering continuous lake and bog sediment sequences with superior accuracy
and quality. The main components of the system and their function are described, with special focus on measures for obtaining
long, continuous lake sediment sections up to a current maximum length of 95 m. Examples of lake sediment profiles obtained
with this system from different climatic zones are presented. 相似文献
7.
Timothy G. Fisher 《Journal of Paleolimnology》2004,31(3):377-382
A monopod and piston coring apparatus for coring water-saturated sediment is described. The lightweight apparatus can be used from either an ice platform or the ground surface and can be transported by aircraft. Using a piston, core recovery is increased to better than 90%, and depending upon the monopod height, 7 m-long cores can be obtained. Tips for coring in freezing temperatures are also given. 相似文献
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Synthesis of PGE sulfide standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) 总被引:1,自引:0,他引:1
Cora C. Wohlgemuth-Ueberwasser Chris Ballhaus Jasper Berndt Vaida Stotter née Paliulionyte Thomas Meisel 《Contributions to Mineralogy and Petrology》2007,154(5):607-617
Sulfide compositions with known Re, Os, Ir, Ru, Rh, Pt, and Pd contents are synthesized to be used as standards for noble
metal analysis in solid solution in sulfides. Major elements were added as metals and elemental S. The noble metals, i.e.
35 and 60 ppm each, were added as solutions by micro syringe. Following synthesis at 1 atm the sulfides were sintered at 1.5
to 2 GPa to obtain pellets with theoretical density. Aliquots of the pellets were analysed by isotope dilution ICP-MS for
bulk Re and platinum-group elements (PGE). The spatial noble metal distribution was investigated with an ArF excimer laser
coupled to a single collector ICP mass spectrometer. Sample homogeneity is shown to depend on the metal/S spectrum and the
major element composition of the sulfide, as well as on more subtle factors like oxygen partial pressure during synthesis,
run temperature, and degree of partial melting. The most homogeneous sulfide composition is a (Fe,Ni)1 − x
S monosulfide with 5 wt % Ni and 1-sigma variations in 34S-normalized noble metal count rates of <3.6%. Nearly as homogeneous is a pure Fe1 − x
S monosulfide with 1-sigma variations in 34S-normalized noble metal count rates of <5.8 %. A Cu-bearing Fe1 − x
S monosulfide with 2 wt % Cu was found to be considerably more heterogeneous, suggesting that Cu in solid solution in monosulfides
promotes noble metal heterogeneity. The sulfide composition least suitable for the synthesis of noble metal sulfide standards
is NiS. 相似文献
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