洞塞式消能工的数值模拟

针对有压洞内洞塞式消能工附近局部流动,分析研究了水流紊动特点,应用三维RNG k-ε紊流模型,利用物理模型试验资料对其计算结果进行了验证,利用模型对洞塞式消能工引起的水头损失进行计算分析,分析结果表明,当洞塞段相对长度从很小开始增加时,水头损失系数呈现先急剧降低而后明显增加,最后缓慢线性增加的趋势;在有压洞半径一定的情况下,洞塞段过流半径的变化比洞塞段过流长度的变化对水头损失系数影响更为明显,可为洞塞式消能工的设计提供相关参考依据。     

Feed-forward-based software sensor for outlet turbidity of coagulation process considering plug flow condition

Physical online sensors are widely used in wastewater treatment plants. The high costs of acquisition and maintenance as well as the delayed response due to long hydraulic retention times, applications of some physical online sensors are limited. Consequently, studies on developing software sensors have been drawn much attentions these years. Aiming to predict treatment results after water is coagulated, and this paper focuses on developing a software sensor of outlet turbidity for coagulation process. Solution to address the potential non-plug flow conditions in sedimentation tanks is discussed. Model validation results show that the proposed software sensor has 86% of accuracy within the main working range. This paper expresses a novel concept that what the proposed software sensor predicted has been not formed in the coagulation process. Since the software sensor enables to know the treatment results without waiting for long hydraulic retention time of sedimentation tank, it not only shortens the response time of manual dosing control but also serves as a feedback parameter to define optimal dosage for coagulant dosing control systems.     

Structure of melt flow channels in the mantle

Structural events during the formation of the mantle peridotite section in the Voikar-Syn’ya massif of the Polar Urals are considered. The structural units of the mantle section were formed during several deformation stages. Dunite bodies in restitic peridotites were formed in the course of deformation that completed the formation of large-scale folds of high-temperature plastic flow of mantle material. The final stage of deformation accompanied by migration of melt through harzburgite occurred in the shallow mantle in the setting of suprasubduction spreading related to the ascent of a mantle diapir. The rate of plastic deformation was relatively low. As a result, the intracrystal translation gliding of dislocations in olivine was the main mechanism in both harzburgite and dunite. The paths of focused melt flow are marked by dunite veins and associated pyroxenite and chromitite. It is suggested that stress concentration in fold hinges and their abrupt relaxation with formation of orthogonal network of weakened zones with high permeability was one of the possible mechanisms of the formation of melt conduits. The dispersed melt ascending from a great depth spontaneously migrated toward these zones. The distribution and structure of chromitite bodies reflect multistage formation of dunite, nonstationary dynamics of melt flow through restite, and abrupt variations of local stress fields in the areas adjacent to melt conduits.     

The orientation of helical flow in curved channels

The planform patterns of meandering submarine channels and subaerial fluvial bends show many similarities that have given rise to strong analogies concerning the fluid dynamics of these channel types. Existing models of helical motion in open‐channel bends depict flow that is characterized by surface flow towards the outer bank, and basal flow towards the inner bank. This paper investigates and compares, through an analytical model and physical experiment, flows within fluvial meanders, and submarine channel bends that contain density‐driven gravity currents. The results indicate that the sense of helical motion can be reversed in submarine bends that contain density currents when compared with fluvial bends, and that the orientation of the helical flow is dependent on the vertical distribution of downstream velocity. Specifically, the sense of helical motion is reversed in bends when the maximum downstream velocity is near the bed, resulting in near‐bed flow towards the outer bank. These findings suggest that the dynamics of sediment transport and deposition in curved channels with such velocity profiles will be fundamentally different to those currently assumed from sinuous open‐channels.     

Block-supported cataclastic flow within the upper crust

Recent work from portions of the Sevier fold-thrust belt that have deformed primarily within the elastico-frictional regime, demonstrates that cataclastic flow can be subdivided into two types: matrix- and block supported. The two types may operate simultaneously within the same deforming material. However, their activity can vary spatially, temporally and across scales. Although block-supported cataclastic flow is a critical process in upper crustal deformation, it continues to be largely ignored and/or misunderstood, primarily because established concepts and definitions for cataclastic flow are chiefly based on matrix-supported cataclastic flow. Here, block-supported cataclastic flow is examined to better understand cataclastic flow in general and to explore its relationship with matrix-supported cataclastic flow.     

宽窄相间河道水流紊动特性试验研究

为了探索宽窄相间河道的水流紊动特性,以西南地区宝兴河上游宽窄相间河段为研究对象,基于室内概化模型试验,采用多普勒声学流速仪(ADV)测量了室内模型典型断面上的三维瞬时流速,分析典型断面上的纵向时均流速、紊动强度、雷诺切应力和紊动能的分布规律。试验结果显示:宽窄相间水槽中,扩散段边壁的紊动强度大于中心区域的紊动强度,最大值位于0.2倍水深处;扩散段两侧坡脚处紊动能最大;侧壁区的平面和立面雷诺切应力最大值出现在扩散段内,中心区域最大雷诺切应力位于两槽间的中间断面处;扩散段内水流紊乱,两侧出现旋涡和涡脱,易造成侧壁侵蚀加强,引起河道拓宽。深入分析了宽窄相间河道水流的紊动特性,可为山区河流治理和自然灾害防治提供参考。     

宽窄相间河道水流紊动特性试验研究

为了探索宽窄相间河道的水流紊动特性，以西南地区宝兴河上游宽窄相间河段为研究对象，基于室内概化模型试验，采用多普勒声学流速仪（ADV）测量了室内模型典型断面上的三维瞬时流速，分析典型断面上的纵向时均流速、紊动强度、雷诺切应力和紊动能的分布规律。试验结果显示：宽窄相间水槽中，扩散段边壁的紊动强度大于中心区域的紊动强度，最大值位于0.2倍水深处；扩散段两侧坡脚处紊动能最大；侧壁区的平面和立面雷诺切应力最大值出现在扩散段内，中心区域最大雷诺切应力位于两槽间的中间断面处；扩散段内水流紊乱，两侧出现旋涡和涡脱，易造成侧壁侵蚀加强，引起河道拓宽。深入分析了宽窄相间河道水流的紊动特性，可为山区河流治理和自然灾害防治提供参考。     

潼关金矿区矿渣型泥石流熵权评价

在简述信息熵概念的基础上,对陕西潼关金矿区8条泥石流沟堆积的采矿废石量、沟谷纵坡降比等9个定量、定性调查指标进行了统计,求出各指标熵Hj、熵权Wj以及沟谷指标可能的概率值fij后,计算得出了潼关金矿区矿渣型泥石流潜势度信息熵的综合评价值;探讨了熵权评价与主观赋权评价的结果差异的原因及建议.     

江心洲头部冲淤动力临界特性

不同流量级下,分汊河段进口主流摆动导致江心洲头部的平面冲淤分布呈现出复杂变化特征。为探究江心洲头部冲淤与来流过程之间的响应关系,借助长江中下游多个分汊河段内水沙、地形资料,对江心洲头部水动力特征实施了数值模拟,并对不同流量级下的河床变形强度进行综合比较。研究表明:江心洲头部低滩的冲淤动力随着流量涨落呈现出明显的临界特性,冲淤过程中存在大、小两个临界流量Q₁与Q₂,在介于两个临界流量之间的流量级持续作用下,洲头低滩发生冲刷;流量大于Q₁或小于Q₂时,洲头低滩表现为淤积。由于不同流量级造成的冲淤效果不同,因而水文过程中各级流量的持续时间,是影响洲头低滩年内、年际变形的主要因素。     

基于重力流相的深水水道分类方案研究*

深水水道是深水环境下的油气储集的重要场所。当前,深水水道的沉积构型及级次划分已有诸多报道,但对于单一水道分类研究较少。现有主流分类方案主要依据水道侵蚀能力,然而受地震分辨率及露头完整度影响,在实际应用中存在较大局限性。基于全球26个野外露头和西非尼日尔三角洲Akpo油田X油藏的钻井岩心资料,对不同重力流相类型进行流态学解释,将水道内部岩相简化为高密度浊流相(HTL)、低密度浊流相(LTL)以及碎屑流相(CL);在此基础上,根据不同重力流相在水道内部占比,划分出9种单一水道类型: 高密度浊流单一充填水道(HTL>70%)、低密度浊流单一充填水道(LTL>75%)、碎屑流单一充填水道(CL>60%)、块状砂质混合充填水道(HTL=40%~70%、LTL=40%~20%、CL<30%)、含砾砂质混合充填水道(HTL=40%~70%、LTL<30%、CL=15%~50%)、层状砂质混合充填水道(HTL=5%~60%、LTL=40%~75%、CL<20%)、夹碎屑砂质混合充填水道(HTL<40%、LTL=40%~75%、CL=20%~40%)、等相混合充填水道(HTL=20%~40%、LTL=20%~40%、CL=20%~40%)、含砂砾质混合充填水道(HTL<50%、LTL<60%、CL=40%~60%)。根据野外露头及划分方案在深水油田实际应用,综合分析认为不同类型水道在垂向分布具有一定规律,即碎屑流相充填的水道往往发育在水道体系底部,高密度浊流相充填的水道类型靠近水道中下部,而低密度浊流相充填的水道主要位于水道体系中上部。方案根据不同重力流相充填的百分比,对不同水道类型进行了明确定义,具有更好的适用性与可操控性,同时对于深水水道储集层预测及储集层质量评价具有重要的实际意义。     

Primary fractionation and secondary alteration within an Archean ultramafic lava flow

Fifteen samples across a 4 m thick komatiite flow from the Val d'Or region in the southeast portion of the Abitibi greenstone belt have been analysed for major oxides and trace elements including the rare earth elements (REE). The flow has been subjected to low grade regional metamorphism: virtually all primary mineralogy (olivine and clinopyroxene) has been obliterated although primary textures are well preserved. Compositional differences between the upper, spinifex textured portion and the underlying massive portion of the flow are largely consistent with the primary fractionation of approximately 30% olivine with a composition close to Fo92. Variations in incompatible element ratios across the flow and in enrichments between the spinifex and massive units suggest that Si, Ce and possibly Lu have been lost to, and Ca, Sr and possibly Y have been gained from, the surroundings. Remobilization of other elements (e.g. Zr, Hf, and alkali metals and most of the REE) appears to have been confined within the flow. AI, Ti, V and Sc appear to have been immobile during alteration of the flow. For the flow as a whole values for many element ratios (e.g. Al/Zr, Al/Sc, Sc/Yb, Zr/Hf, K/Rb) are very similar to chondritic values. If the flow represents a 40% melt approximately, and if the residue was essentially dunitic then the source abundance for most elements was close to chondritic; exceptions are the REE (1.5 to 2×chondrite), Ti (enriched relative to chondrites), and V (depleted relative to chondrites).     

Postcollisional flow of aqueous fluid within ultrahigh-pressure eclogite in the Dabie orogen

A combined study of chronometric dating and oxygen isotope analysis for minerals from vein and host eclogite as well as regional country-rock gneiss in the Dabie orogen provides a direct constraint on timing of fluid flow in this orogen formed by continental collision. Oxygen isotope ratios of vein minerals are significantly lower than those of the host eclogite, but comparable with those of the regional gneiss. This suggests the veining fluid came from the regional gneiss (i.e. exhumed slab itself) rather than the host eclogite. While zircon U–Pb and phengite Ar–Ar dating yields ages of 214 to 222 Ma for the eclogite and gneiss, the vein gives a quartz–muscovite Rb–Sr isochron age of 181 Ma and a muscovite K–Ar age of 179 Ma. Thus the veining postdates the Triassic ultrahigh pressure metamorphic event, witnessing postcollisional fluid flow after the orogenic cycle of continental collision.     

Finite element analyses of soil plug response

Open-ended pipe piles are often used in offshore foundations. The response of the soil plug inside a pipe pile is poorly understood, and only limited work has been performed to quantify the response under the different loading conditions relevant to offshore platforms. This paper describes numerical analyses that have been carried out in order to assess the end-bearing capacity of the soil plug under loading conditions which range from undrained to fully drained. The soil plug has been modelled as either elastic, elastic–perfectly-plastic or elastoplastic. The soil–pile interface, an important aspect of the problem, has been examined critically. Comparison with experimental data from model test at laboratory scale indicates that the load–deformation behaviour of the soil plug is modelled well using an elastoplastic model for the soil plug, and an elastic–perfectly-plastic joint element to model the soil–pile interface. The finite element analyses show that, under typical loading conditions, adequate end bearing may be mobilized by the soil plug, largely by high effective stresses in the bottom 3–5 diameters of the soil plug.     

Fluid flow and alkali transport within a metamorphic terrane, western North Carolina

This paper presents preliminary results from study of a metasedimentary terrane near the Great Smoky Mountains of North Carolina. Grade of metamorphism ranges from garnet to staurolite-kyanite zone. The stratigraphic section is dominated by metasandstone but contains thick pelitic horizons over the central portion (Anakeesta Formation) of the studied interval. Metasandstone beds contain numerous isolated calcite concretions; these react to form leucocratic calc-silicate rock at variable grade of metamorphism. Metasandstones themselves are unreactive. Study of calc-silicate reaction permits the following statements regarding fluid flow and alkali transport within the studied terrane.Within unreacted concretions, the typical mineral assemblage is quartz-oligoclase-muscovite-biotite-calcite. Reaction between micas and calcite proceeded through several stages, forming as prograde minerals andesine/bytownite, clinozoisite, zoisite, garnet, hornblende, and chlorite. Reaction occurred in the presence of a fluid phase containing a H₂O/CO₂ ratio of 9 and resulted in massive expulsion of Na₂O, K₂O and CO₂. Since postulated reactions would have produced, on average, a fluid phase whose H₂O/CO₂ ratio is only one, flow of water-rich fluid through the concretions accompanied reaction. Rough estimate suggests a volumetric ratio of external fluid to rock of at least 1.1.The metamorphic grade at which concretions undergo reaction is controlled by stratigraphic position of the host metasandstone relative to metashale. Within the Anakeesta Formation and overlying strata, extensive reaction occurs near the pelitic staurolite and kyanite isograds. Within massive metasandstones of the underlying strata, reaction is delayed to the middle staurolite-kyanite zone, 5 km upgrade. Some reaction occurs within the upper garnet zone, but this is restricted to certain thin metasandstone beds interlayered with metashale. Study of dehydration reactions within metashale demonstrates that calc-silicate reaction was coupled to production of H₂O-rich fluids within pelitic strata.Transport of H₂O-rich fluids beyond outcrop scale was by advection. Diffusion was limited to outcrop distance. On most outcrops, all isolated concretions show the same degree of reaction. But at larger scale separate metasandstone packets bounded by metashale show differing degrees of reaction. Also, all rocks underwent some degree of penetrative deformation during time of reaction. The suggestion is made that advective flow was in fact channelized into fractures within metasandstone, and that diffusion between fractures promoted reaction within outcrop-size volumes of rock. Overall direction of fluid transport was in part upsection and in part channelized within metasandstone strata. Downsection flow was limited.For the most part alkalis liberated by calc-silicate reaction appear to have left the terrane. Metasandstones do not appear to constitute a sink for alkalis, and no sink of any sort was found for sodium. Potassium metasomatism of pelitic rock did occur and is marked by conversion of chlorite to biotite. But such K deposition is limited to sections within which metashale and calc-silicate rock are within outcrop distance. No sink is evident for most liberated potassium. It is within conjecture that the liberated elements caused alkali metasomatism elsewhere within the metamorphic belt, but such an event has yet to be demonstrated.     

Sensitivity of incipient particle motion to fluid flow penetration depth within a packed bed

A discrete element method is applied to a three‐dimensional analysis related to sediment entrainment on a micro‐scale. Sediment entrainment is the process by which a fluid medium accelerates particles from rest and advects them upward until they are either transported as bedload or suspended by the flow. Modelling of the entrainment process is a critically important aspect for studies of erosion, pollutant resuspension and transport, and formation of bedforms in environmental flows. Previous discrete element method studies of sediment entrainment have assumed the flow within the particle bed to be negligible and have only allowed for the motion of the topmost particles. At the same time, micro‐scale experimental studies indicate that there is a small slip of the fluid flow at the top of the bed, indicating the presence of non‐vanishing fluid velocity within the topmost bed layers. The current study demonstrates that the onset of particle incipient motion, which immediately precedes particle entrainment, is highly sensitive to this small fluid flow within the topmost bed layers. Using an exponential decay profile for the inner‐bed fluid flow, the discrete element method calculations are repeated with different fluid penetration depths within the bed for several small particle Reynolds numbers. For cases with slip velocity corresponding to that observed in previous experiments with natural sediment, the predicted particle velocity is found to be a few percent of the fluid velocity at the top of the viscous wall layer, which is a reasonable range of velocities for observation of incipient particle motion. This method for prescribing the fluid flow within the particle bed allows for the current discrete element method to be extended in future studies to the analysis of sediment entrainment under the influence of events such as turbulent bursting. Additionally, predictions for the slip velocities and fluid flow profile within the bed suggest the need for further experimental studies to provide the data necessary for additional improvement of the discrete element method models.     

Groundwater flow into underground openings in fractured crystalline rocks: an interpretation based on long channels

Rethinking an old tracer experiment in fractured crystalline rock suggests a concept of groundwater flow in sparse networks of long channels that is supported by results from an innovative lattice network model. The model, HyperConv, can vary the mean length of ‘strings’ of connected bonds, and the gaps between them, using two independent probability functions. It is found that networks of long channels are able to percolate at lower values of (bond) density than networks of short channels. A general relationship between mean channel length, mean gap length and probability of percolation has been developed which incorporates the well-established result for ‘classical’ lattice network models as a special case. Using parameters appropriate to a 4-m diameter drift located 360 m below surface at Stripa Mine Underground Research Laboratory in Sweden, HyperConv is able to reproduce values of apparent positive skin, as observed in the so-called Macropermeability Experiment, but only when mean channel length exceeds 10 m. This implies that such channel systems must cross many fracture intersections without bifurcating. A general relationship in terms of flow dimension is suggested. Some initial investigations using HyperConv show that the commonly observed feature, ‘compartmentalization’, only occurs when channel density is just above the percolation threshold. Such compartments have been observed at Kamaishi Experimental Mine (Japan) implying a sparse flow network. It is suggested that compartments and skin are observable in the field, indicate sparse channel systems, and could form part of site characterization for deep nuclear waste repositories.     

Analytical solution of electrohydrodynamic flow and transport in rectangular channels: inclusion of double layer effects

Upscaling electroosmosis in porous media is a challenge due to the complexity and scale-dependent nonlinearities of this coupled phenomenon. “Pore-network modeling” for upscaling electroosmosis from pore scale to Darcy scale can be considered as a promising approach. However, this method requires analytical solutions for flow and transport at pore scale. This study concentrates on the development of analytical solutions of flow and transport in a single rectangular channel under combined effects of electrohydrodynamic forces. These relations will be used in future works for pore-network modeling. The analytical solutions are valid for all regimes of overlapping electrical double layers and have the potential to be extended to nonlinear Boltzmann distribution. The innovative aspects of this study are (a) contribution of overlapping of electrical double layers to the Stokes flow as well as Nernst–Planck transport has been carefully included in the analytical solutions. (b) All important transport mechanisms including advection, diffusion, and electromigration have been included in the analytical solutions. (c) Fully algebraic relations developed in this study can be easily employed to upscale electroosmosis to Darcy scale using pore-network modeling.     

Reaction-induced grain boundary cracking and anisotropic fluid flow during prograde devolatilization reactions within subduction zones

Devolatilization reactions during prograde metamorphism are a key control on the fluid distribution within subduction zones. Garnets in Mn-rich quartz schist within the Sanbagawa metamorphic belt of Japan are characterized by skeletal structures containing abundant quartz inclusions. Each quartz inclusion was angular-shaped, and showed random crystallographic orientations, suggesting that these quartz inclusions were trapped via grain boundary cracking during garnet growth. Such skeletal garnet within the quartz schist formed related to decarbonation reactions with a positive total volume change (?V _t > 0), whereas the euhedral garnet within the pelitic schists formed as a result of dehydration reaction with negative ?V _t values. Coupled hydrological–chemical–mechanical processes during metamorphic devolatilization reactions were investigated by a distinct element method (DEM) numerical simulation on a foliated rock that contained reactive minerals and non-reactive matrix minerals. Negative ?V _t reactions cause a decrease in fluid pressure and do not produce fractures within the matrix. In contrast, a fluid pressure increase by positive ?V _t reactions results in hydrofracturing of the matrix. This fracturing preferentially occurs along grain boundaries and causes episodic fluid pulses associated with the development of the fracture network. The precipitation of garnet within grain boundary fractures could explain the formation of the skeletal garnet. Our DEM model also suggests a strong influence of reaction-induced fracturing on anisotropic fluid flow, meaning that dominant fluid flow directions could easily change in response to changes in stress configuration and the magnitude of differential stress during prograde metamorphism within a subduction zone.     

Geochemical indicators of interbasin groundwater flow within the southern Rio Grande Valley, southwestern USA

Increased groundwater withdrawals for the growing population in the Rio Grande Valley and likely alteration of recharge to local aquifers with climate change necessitates an understanding of the groundwater connection between the Jornada del Muerto Basin and the adjoining and more heavily used aquifer in the Mesilla Basin. Separating the Jornada and Mesilla aquifers is a buried bedrock high from Tertiary intrusions. This bedrock high or divide restricts and/or retards interbasin flow from the Jornada aquifer into the Mesilla aquifer. The potentiometric surface of the southern Jornada aquifer near part of the bedrock high indicates a flow direction away from the divide because of a previously identified damming effect, but a groundwater outlet from the southern Jornada aquifer is necessary to balance inputs from the overall Jornada aquifer. Differences in geochemical constituents (major ions, δD, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr) indicate a deeper connection between the two aquifers through the Tertiary intrusions where Jornada water is geochemically altered because of a geothermal influence. Jornada groundwater likely is migrating through the bedrock high in deeper pathways formed by faults of the Jornada Fault Zone, in addition to Jornada water that overtops the bedrock high as previously identified as the only connection between the two aquifers. Increased groundwater withdrawals and lowering of the potentiometric surface of the Jornada aquifer may alter this contribution ratio with less overtopping of the bedrock high and a continued deeper flowpath contribution that could potentially increase salinity values in the Mesilla Basin near the divide.