海洋工程试验池中风场模拟

在考虑海洋工程装备在极端海况和运行海况下的载荷与受力,风载荷也是一个不可忽视的因素.目前物理模型试验仍是研究海洋工程结构物载荷与运动性能的重要手段,而深海结构物在水平漂移运动较大,如何在较大范围内得到满足试验要求的风场,是提高试验能力的重要问题.应用数值计算方法对大范围的风场模拟进行了分析,并进行了相应的物理实验,在此基础上对海洋工程试验的风场模拟提出了若干建议.     

Very short-term behaviour of the flare star EV Lac

Sinusoidal variations in Johnson'sB-band of the flare star EV Lac have been confirmed at its quiet state luminosity. The cycle lengths are more than one hour and less than two hours with amplitudes varying from 0 _. ^m 105 to 0 _. ^m 306. These registered cycles have agreed with cycles detected by Mavridis and Varvoglis (1990) and Mavridis (1990). In the same time, the cycles have confirmed the light variation detection in Johnson'sV-band in the same flare star by Pettersen (1980) with a cyclic period equals about 4 _. ^d 378 and an amplitude of about 0 _. ^m 07. Our net results confirm, to some extent, the presence of active region(s) as an origin of stellar flare phenomenon of UV Ceti type flare stars. We can cautiously say that the solar and stellar flare phenomenon have a similar origin.     

Settlement of inhomogeneous consolidating soils—II: The symmetrically loaded mass

We continue our study of the consolidation of inhomogeneous clay soils with an analysis of the response of a soil mass, whose shear modulus increases linearly with depth, to axially symmetric pressure on its surface. This extends the work reported in Part I on the corresponding one-dimensional problem of a clay column, and generalizes researches of Gibson and coworkers on the elastic model of the soil (i.e., the initial response). Because of great mathematical complexity when Poisson's ratio is allowed to assume arbitrary values, we have confined ourselves (as did Gibson in several of his papers) to variations of the modulus from a zero surface value, this being in reasonable accord with published test results on London clay. The deflection of points within this region, the deflection relative to the central one (that is, the shape of the deformed loading area), as well as the absolute deflection of surface points exterior to the load.     

The Quaternary development of tributary channels to the Nile River at Kom Ombo area,Eastern Desert of Egypt,and their implication for groundwater resources

The dry wadis ‘ephemeral channel’ constituting the main tributaries to the Nile River in Kom Ombo are structurally and tectonically controlled and exhibit complex drainage pattern. This complicated drainage pattern is inherited from the morpho‐tectonic evolution of the ancestral Nile River (‘Protonile’), which drained the Eastern Desert during the Middle Pleistocene. A digital elevation model derived from Shuttle Radar Topography Mission data is used to delineate the contemporary drainage networks and their catchments. Satellite images acquired during a flash flood event were used to validate the delineated watershed divides and flow pathways, particularly where the courses of dry wadis are interlocked. Currently, the westward flow of Wadi Abu‐Suberah is derived from a small area in the Eastern Desert, as the palaeo‐upper reaches of this wadi were captured due to tectonic movements along NW/SE and N/S faults by wadis in the Kharit and Elewa areas. The influence of these tectonic movements on groundwater distribution is also shown where the deep Nubian aquifer discharges its water into the Quaternary aquifer through fault planes. The northward flowing ‘Protonile’ main course has tectonically shifted from the Gallaba plain in the Western Desert, eastward to the current Nile River course. This shift has produced several cut‐off segments of the palaeo‐tributary drainage that was originally flowing westward towards the old ‘Protonile’ main course in the Gallaba plain. However, these segments have reversed their surface run‐off flow directions eastward towards the current Nile course; they could include potential groundwater resources, as their alluvium may be still recharged by the Nile River. Copyright © 2010 John Wiley & Sons, Ltd.     

Fluid geochemistry of natural manifestations from the Southern Poroto–Rungwe hydrothermal system (Tanzania): Preliminary conceptual model

The South Poroto–Rungwe geothermal field, in the northern part of the Malawi rift, Tanzania divides in two main areas. The relatively high altitude northern area around the main Ngozi, Rungwe, Tukuyu and Kyejo volcanoes, is characterised by cold and gas-rich springs. In contrast, hot springs occur in the southern and low-altitude area between the Kyela and Livingstone faults. The isotopic signature of the almost stagnant, cold springs of the Northern district is clearly influenced by H₂O–CO_2(g) exchange as evidenced from negative oxygen-shifts in the order of few deltas permil. In contrast, the isotopic signature of waters discharged from the hot springs of the Southern district is markedly less affected by the H₂O–CO_2(g) interaction. This evidence is interpreted as an effect of the large, permanent outflow of these springs, which supports the hypothesis of a regional-scale recharge of the major thermal springs. Measurements of carbon isotope variations of the dissolved inorganic carbon of waters and CO_2(g) from the Northern and Southern springs support a model of CO_2(g)-driven reactivity all over the investigated area. Our combined chemical and isotopic results show that the composition of hot springs is consistent with a mixing between (i) cold surface fresh (SFW) and (ii) Deep Hot Mineralised (DHMW) Water, indicating that the deep-originated fluids also supply most of the aqueous species dissolved in the surface waters used as local potable water. Based on geothermometric approaches, the temperature of the deep hydrothermal system has been estimated to be higher than 110 °C up to 185 °C, in agreement with the geological and thermal setting of the Malawi rift basin. Geochemical data point to (i) a major upflow zone of geothermal fluids mixed with shallow meteoric waters in the Southern part of the province, and (ii) gas absorption phenomena in the small, perched aquifers of the Northern volcanic highlands.     

TEM study of the geoelectrical structure and groundwater salinity of the Nahal Hever sinkhole site, Dead Sea shore, Israel

Since the 1990s a large number of sinkholes have appeared in the Dead Sea (DS) coastal area. Sinkhole development was triggered by the lowering of the DS level. In the literature the relationship between the sinkholes and the DS level is explained by intrusion of relatively fresh water into the aquifer thereby dramatically accelerating the salt dissolution with creation of subsurface caverns, which in turn cause sinkholes. The main goal of our project was detection and localization of relatively fresh groundwater. During our study we used the transient electromagnetic method (TEM) to measure the electrical resistivity of the subsurface. As a test site we selected Nahal Hever South which is typical for the DS coast. Our results show that resistivity of the shallow subsurface reflects its vertical and lateral structure, e.g., its main hydrogeological elements explain the inter-relations between geology, hydrogeology, and sinkholes. The TEM method has allowed detailed differentiation of layers (clay, salt, etc.) in the subsurface based on their bulk resistivity. The 10 m-thick salt layer composed of idiomorphic crystals of halite deposited during the earlier Holocene period was extrapolated from borehole HS-2 through the study area. It was found that in Nahal Hever the typical value of the bulk resistivity of clay saturated with the DS brine varies between 0.2 and 0.3 Ωm, whereas saturated gravel and sandy sediments are characterized by resistivity between 0.4 and 0.6 Ωm. The high water salinity of the aquifer (enveloping the salt layer) expressed in terms of resistivity is also an important characterization of the sinkhole development mechanism. The electrical resistivity of the aquifer in the vicinity of the salt unit and its western border did not exceed 1 Ωm (in most cases aquifer resistivity was 0.2-0.6 Ωm) proving that, in accordance with existing criteria, the pores of the alluvial sediments are filled with highly mineralized DS brine. However, we suggest that the criterion of the aquifer resistivity responsible for the salt dissolution should be decreased from 1 Ωm to 0.6 Ωm corresponding to the chloride concentration of approximately 100 g/l (the chloride saturation condition reaches 224 g/l in the northern DS basin and 280 g/l in the southern one).Based on TEM results we can reliably conclude that in 2005, when most of sinkholes had appeared at the surface, salt was located within a very low resistivity environment inside sediments saturated with DS brine. Intrusion of relatively fresh groundwater into the aquifer through the 600 × 600 m²area affected by sinkholes has not been observed.     

Uncertainty of climate change impact on crop characteristics: a case study of Moghan plain in Iran

Theoretical and Applied Climatology - Crop yield is one of the most critical factors in the food security chain. Climate plays a crucial role in crop water productivity in rainfed and irrigated...     

Probabilistic assessment of seismic hazard of dam sites in Jordan

A Probabilistic method is used to evaluate the seismic hazard of nineteen embankment dam sites in Jordan. A line source model developed by McGuire (1978) is used in this study. An updated earthquake catalogue covering the period from 1 A.D. to 1991 A.D. is used for this purpose. This catalogue includes all earthquakes that occurred in Jordan and adjacent areas, more specifically between latitudes 27.0°–35.5° N and longitudes 32.0°–39.0° E.Nine distinct seismic sources of potential seismic activities are identified. The seismic hazard parameters are determined using the method suggested by Kijko and Sellevoll (1989).The Peak Ground Acceleration (PGA) is selected as a measure of ground motion severity. Esteva (1974) attenuation relationship is used in evaluating PGA values at each dam site. Analysis is carried out for 50%, 90%, and 95% probability that is not being exceeded in a life time of 50, 100, and 200 years.Results of analysis indicate that PGA values are higher for dam sites closer to the Dead Sea Fault. This fault is believed to be responsible for most earthquake activities in Jordan and vicinity. The highest PGA value is found to be for Al-Karama dam site.     

Magmatic and metamorphic evolution of the Shotur Kuh metamorphic complex (Central Iran)

Metamorphic basement rocks, that are exposed beneath the very low-grade to unmetamorphosed Upper Jurassic-Eocene formations north of the Torud fault zone within the Great Kavir Block, were investigated to elucidate the origin of their protoliths and the pressure and temperature conditions of metamorphism. The basement, previously assumed as a pre-Cambrian metamorphic complex, is mostly formed by amphibolite-facies orthogneisses (tonalite, granodiorite, and granite) with amphibolites and small amounts of metasediment-micaschists. Major- and trace-element geochemistry in combination with U–Pb age dating of zircon showed that the protoliths formed during Late Neoproterozoic continental arc magmatism that has also been identified in other tectonic blocks of Central Iran. In addition to quartz, feldspar(s), micas in orthogneisses, and amphibole + plagioclase in amphibolite, all rocks may contain garnet that shows prograde zoning. Kyanite was found only in some Al-rich amphibolite together with gedrite. The PT conditions of the rocks, based on conventional geothermobarometry and the pseudosection method, show a medium-pressure amphibolite-facies metamorphism. Ar–Ar age dating of muscovite reveals that this metamorphism occurred in the Middle Jurassic (166 Ma) and related to the closure of the Neotethyan basin.     

Rare earth elements in metarhyolite dyke constraints on processes in a dynamic hydrothermal system,Um Ghannam,South Eastern Desert,Egypt

The Um Ghannam area lies within the core of Hafafit Complex, South Eastern Desert. This area is occupied mainly by granitic gneiss (orthogneiss). However, the granitic gneiss is extruded by swarm metarhyolite dykes and quartz veins. The studied metarhyolite dyke is classified into two distinctive zones. However, the intense degree of hydrothermal alteration can partition this dyke into weakly and extremely altered zones. According to the extraordinary diversity in color, this dyke is distinguished into gray to dark gray (weakly altered) and greenish (extremely altered) metarhyolite. Petrographical, mineralogical, and geochemical characteristics of the two distinctive zones are detected in a representative sample. Petrographically, the weakly altered zone is mainly represented by chloritization of primary biotite, garnet, and epidote, and argillitization of primary plagioclase. Although the extremely altered zone contains intensely altered remnants of the original rock, the extremely altered zone is distinguished by intense oxidation products (carbonate minerals and quartz, with significant amounts of secondary Cr-muscovite and hematite). The mineralogical studies are imposed on the millimeter and the micrometer scale in this important hydrogeothermal system. Except for Ca and Mg, most of the major elements are depleted at the extremely altered zone. However, the extremely altered zone is enriched in trace elements (Cr, Mn, Co, and Ni). The major elements of the extremely altered zone reflect the significant alterations (desilication, muscovitization, and carbonatization). These alteration processes have taken place in the hydrogeothermal system in the extremely altered zone. The geothermal fluid is responsible for these hydrothermal alterations. High fO₂ and high temperature are characteristic features of this fluid. Then, the high-field-strength elements such as Zr, Ti, and P are depleted as a significant hydrothermal alteration. Also, nuclear elements with the anion of (CO₃)^2? can travel as molecular complexes (carbonates), as long as the chemical and structural conditions are suitable for the movement of these elements from the metarhyolite dyke to redeposit and accumulate in another geologic formation. The rare earth elements La and Ce, as well as Yb and Lu, are partially mobilized during intensity alterations. The rare earth elements (REEs) are depleted in abundance with enrichment of CO₂ from the weakly altered zone to the extremely altered zone. The REE budget is decreased from the weakly altered zone to the extremely altered zone as 121.17 to (27.38???16.52), respectively. The significant depletion of ∑REEs is controlled by dissolution of monazite. Monazite breakdown and even apatite formation can be caused by alkaline fluid. This fluid is related to event and thermal stage. However, the negative anomaly of Eu can be noticed in all studied samples. Then, Eu anomaly may be formed from plagioclase fractionation. The weakly altered metarhyolite zone and orthogneiss have lower HREE/LREE (0.07–0.11), respectively, relative to the extremely altered metarhyolite zone (0.17???0.2). Even all studied samples at two significant zones are characterized by the enrichment of ∑LREEs relative to ∑HREEs.