Hydraulic Potential Research Articles

Valuation of hydraulic fracturing potentials of organic-rich shales from the Anambra basin using rock mechanical properties from wireline logs

This study was carried out to determine the rock mechanical properties relevant for hydrocarbon exploration and production by hydraulic fracturing of organic rich shale formations in Anambra basin. Shale samples and wireline logs were analysed to determine the petrophysical, elastic, strength and in-situ properties necessary for the design of a hydraulic fracturing programme for the exploitation of the shales. The results obtained indicated shale failure in shear and barreling under triaxial test conditions. The average effective porosity of 0.06 and permeability of the order of 10-1 to 101 millidarcies showed the imperative for induced fracturing to assure fluid flow. Average Young’s modulus and Poisson’s ratio of about 2.06 and 0.20 respectively imply that the rocks are favourable for the formation and propagation of fractures during hydraulic fracking. The minimum horizontal stress, which determines the direction of formation and growth of artificially induced hydraulic fractures varies from wellto-well, averaging between 6802.62 to 32790.58 psi. The order of variation of the in-situ stresses is maximum horizontal stress>vertical stress>minimum horizontal stress which implies a reverse fault fracture regime. The study predicts that the sweet spots for the exploration and development of the shale-gas are those sections of the shale formations that exhibit high Young’s modulus, low Poisson’s ratio, and high brittleness. The in-situ stresses required for artificially induced fractures which provide pore space for shale gas accumulation and expulsion are adequate. The shales possess suitable mechanical properties to fracture during hydraulic fracturing. Application of these results will enhance the potentials of the onshore Anambra basin as a reliable component in increasing Nigeria’s gas reserves, for the improvement of the nation’s economy and energy security.
 Key Words: Hydraulic Fracturing, Organic-rich Shales, Rock Mechanical Properties, Petrophysical Properties, Anambra Basin

ОСОБЕННОСТИ ВОДОЭНЕРГЕТИЧЕСКИХ РЕЖИМОВ ГЭС ПРИ СИМБИОЗЕ С ГЕЛИОУСТАНОВКАМИ

The results of the analysis of the problems associated with the development of the world solar energy are presented. It is noted that at the present stage of the electric power industry, the potential of renewable energy sources (RES) is still poorly realized. The specific issues of water-energy modes of operation of hydroelectric power plants (HPPs), operating in symbiosis with solar photovoltaic installations (SPEU) have been identified, the schedule of which should be the same. It is shown that the operation of hydroelectric power plants and SPEU in the joint electric load schedule makes it possible to obtain a constructive and economic effect due to the fuel saving of power plants of various types, including thermal ones. The maximum capacity of the HPP-SPEU power complex is optimized by the installed capacity of the HPP while observing the full duplication of the SPEU capacity by other power plants of the energy system. It is shown on the example of the Lagdo hydroelectric complex in the northern Cameroon that under the conditions of developing countries with a large solar and hydraulic potential (Cameroon, Zimbabwe, Uganda, etc.), as well as for the southern regions of Russia, SPEU can produce up to 75% of the annual electricity generation during the low-water period of the year at its joint work in the energy complex with the hydroelectric power plant. This makes it possible to facilitate the redistribution of the river fl ow during the entire low-water period without attracting additional useful storage capacity of the reservoir. The developed methodology for optimizing the water-energy regulation regime can also be applied during the operation of the HPP of the HPP-SPEU energy complex along the watercourse, i.e. with daily flow regulation.

Прогнозирование возможности продолжения эксплуатации самотечных сетей водоотведения с отложениями в лотковой части труб

In this work, the formula for forecasting the continued operation of gravity drainage networks with deposits in pipe water troughs is deduced and refined. In the authors' opinion, such a forecast should be based on the hydraulic principle for assessing the efficiency of a network operation, as the most accurate. To this end, the concept associated with the efficiency of gravity drainage networks was introduced, and a criterion for its assessment was proposed. In the study, the characteristics of hydraulic potential for concrete pipes with a diameter of 400 mm were calculated as an example. An empirical formula was proposed for determining the efficiency factor of the gravity drainage network, and its deviation range was shown. It was concluded that the expert prognosis of continued operation of gravity drainage networks should be based on the efficiency factor of the network, calculated using the obtained formula. It is recommended that a method for calculating an efficiency factor describing gravity drainage networks and special tables for the hydraulic calculation of pipes having a sediment layer of different thicknesses be elaborated. The data presented in the article allow servicing of gravity drainage network to be improved by forecasting its continued operation using the efficiency factor К_ef.

Optimization of pump selection for running as turbine and performance analysis within the regulation schemes

Increasing Renewable energies efficiency and harnessing the available potentials are among the goals that have been addressed in sustainable development. Helping to promote the utilization of these valuable and reliable sources can provide a basis for their worldwide expansion. Pump as turbine (PAT) is a suitable device to generate clean energy from hydraulic potentials. One of the main challenges of using a PAT is the lack of control tools on the flow, which affects mainly the off-design performance of the machine. In this paper, the criteria of pump selection for running in turbine mode were modified under variable head and discharge conditions by improving existing performance indicators and introducing availability. The effect of operating schemes was studied on optimal pump specifications with the effectiveness criterion consisting of capability, availability and adaptability. The performance of power plant components was investigated in regulating the flow and reducing the potential. Using a case study in Iran, dual regulation is the most effective scheme with an effectiveness of 0.4037, but mechanical scheme had the most capability with 0.4230. The results showed that compared to using average values of head and discharge for pump selection, optimization could increase the effectiveness up to 20%.

Comparison of root water uptake models in simulating CO<sub>2</sub> and H<sub>2</sub>O fluxes and growth of wheat

Abstract. Stomatal regulation and whole plant hydraulic signaling affect water fluxes and stress in plants. Land surface models and crop models use a coupled photosynthesis–stomatal conductance modeling approach. Those models estimate the effect of soil water stress on stomatal conductance directly from soil water content or soil hydraulic potential without explicit representation of hydraulic signals between the soil and stomata. In order to explicitly represent stomatal regulation by soil water status as a function of the hydraulic signal and its relation to the whole plant hydraulic conductance, we coupled the crop model LINTULCC2 and the root growth model SLIMROOT with Couvreur's root water uptake model (RWU) and the HILLFLOW soil water balance model. Since plant hydraulic conductance depends on the plant development, this model coupling represents a two-way coupling between growth and plant hydraulics. To evaluate the advantage of considering plant hydraulic conductance and hydraulic signaling, we compared the performance of this newly coupled model with another commonly used approach that relates root water uptake and plant stress directly to the root zone water hydraulic potential (HILLFLOW with Feddes' RWU model). Simulations were compared with gas flux measurements and crop growth data from a wheat crop grown under three water supply regimes (sheltered, rainfed, and irrigated) and two soil types (stony and silty) in western Germany in 2016. The two models showed a relatively similar performance in the simulation of dry matter, leaf area index (LAI), root growth, RWU, gross assimilation rate, and soil water content. The Feddes model predicts more stress and less growth in the silty soil than in the stony soil, which is opposite to the observed growth. The Couvreur model better represents the difference in growth between the two soils and the different treatments. The newly coupled model (HILLFLOW–Couvreur's RWU–SLIMROOT–LINTULCC2) was also able to simulate the dynamics and magnitude of whole plant hydraulic conductance over the growing season. This demonstrates the importance of two-way feedbacks between growth and root water uptake for predicting the crop response to different soil water conditions in different soils. Our results suggest that a better representation of the effects of soil characteristics on root growth is needed for reliable estimations of root hydraulic conductance and gas fluxes, particularly in heterogeneous fields. The newly coupled soil–plant model marks a promising approach but requires further testing for other scenarios regarding crops, soil, and climate.

Sarooj mortar: From a traditional building material to an engineered pozzolan -mechanical and thermal properties study

Developing new energy efficient building materials to reduce the carbon footprint is now the core of sustainability in construction and an essential factor of life cycle assessment (LCA). The extensive and increasing usage of conventional concrete, mortar, plasters and various cement-based materials is only one of the many factors contributing towards urban thermal discomfort caused by urban heat island phenomena and the poor thermal insulation of ordinary cement mortar. Not only this, the wide use of concrete and mortar in construction increases the consumption of their primary components mainly -Portland cement-requiring a large consumption of energy and causing a significant rise in CO2 emissions.Embedding natural and artificial cementitious/pozzolana materials in today's cement-based building materials has become a common practice. Cementitious and Pozzolanic materials are known to provide an added value to mortar/concrete not only in terms of mechanical and durability properties but also in energy efficiency and enhancing sustainability. Sarooj is a local term describing an artificial cementitious and pozzolana material obtained by traditional calcining of the raw clayey soil. Although its usage is nowadays very limited, Sarooj has been used in Oman and other neighboring countries for centuries, in various buildings and defense structures. The main objective of this research is to transform the traditionally produced Sarooj into an engineered binding material and hence investigating its physico-mechanical and thermal properties. The raw soil used to produce the traditional Sarooj was employed to engineer a modern “Sarooj” under controlled energy processing (grinding and calcination) conditions. The raw clay minded from specific location was ground first to a fine powdered material and then subjected to full characterization. The physical and chemical characterization indicated that the raw soil is suitable for producing a cementitious/pozzolanic calcined clay. The thermogravimetric and differential thermal analysis of the clay used reveal that only a moderate temperature of around 800 °C is required for its calcination which preserves energy and reduces CO2 emissions compared to 1600 °C to produce clinker cement. The strength development showed a slow early-age reactivity but an appreciable enhancement in long-term which demonstrates a remarkable latent hydraulic potential of the clay used. It was also found that adding an optimum amount of the calcined clay enhances the thermal properties. The annual energy performance of a typical housing in the hot climate of Muscat, Oman, was evaluated using DesignBuilder software, a whole-building simulation tool. The simulation results showed insignificant savings in annual energy consumption when the developed mixes are used as plastering materials. The clay alkali-activated with NaOH has, however, showed great potential to enhance the mortar's long-term strength. Using locally engineered cementitious material in a partial replacement of Portland cement can further enhance durability and sustainability by reducing the manufacturing energy of the produced building material such as mortars and plasters.

Anisotropy of unsaturated hydraulic properties of compacted mineral capping systems seven years after construction

The mechanical compaction of soil material of mineral landfill systems affects the continuity and connectivity of the complex soil pore network. A horizontally-oriented layering is intended to generate a slope-induced lateral water flow out of mineral capping systems that is sufficient to minimise the statutory required vertical percolation through the underlying waste body and the potential leachate.In this case, soil compaction affects both the porosity and water retention as capacity values and the hydraulic conductivity as intensity parameter. The idea of this study was to combine information on both soil properties in an extended anisotropy factor based on the soil water diffusivity. The analysis is focused on the direction-dependent soil hydraulic properties of a mechanically compacted landfill capping system.In particular, the volume fractions were related to the fractional capillary potential for each of the characteristic pore size classes. Three different soil profiles of top, middle, and bottom slopes of the mineral capping system of the Rastorf landfill in Northern Germany were sampled seven years after construction. Undisturbed soil cores of 100 cm3 and 438 cm3 were extracted in vertical (ver) and horizontal directions (hor) in depths of 20, 50, and 80 cm representing the main layers. The soil water retention and unsaturated hydraulic conductivity, K, functions were determined by suctions plates, permeameter, and the evaporation method. In the coarse pores range (pressure head values of h ≥ −300 hPa), the standard anisotropy ratio, AR, (K(Se)hor/K(Se)ver) as a function of effective saturation, Se, in the sealing liner in 80 cm depth was larger than 1, indicating higher horizontal than vertical K(Se) values. Thus, AR-values above 1 in the range close to water saturation especially in 80 cm depth suggest the tendency of lateral water flow out of mineral capping system due to a sufficient hydraulic potential and thus its reasonable functionality, even seven years after construction.The anisotropy factor was extended in two steps; for AR* and AR**, the pore size class-related matric flux potential, ϕ, and the soil water diffusivity, D(θ), were proposed to combine intensity parameters with capacity-based volume fractions of pore size classes and the fractional capillary potential. The ϕ- and D(θ)-weighted anisotropy ratios, AR* and AR**, indicate that anisotropy increases with the volume fraction of macropores (r2AR* of 0.69−0.77; r2AR** of 0.71−0.80) and wide coarse pores (r2AR* of 0.57−0.78; r2AR** of 0.79−0.89) in both directions. The results suggest that by combining both the intensity and the capacity parameters of the soil hydraulic properties in an extended anisotropy ratio improves the information on compacted mineral capping systems.

Aerogeophysical characterization of an active subglacial lake system in the David Glacier catchment, Antarctica

Abstract. In the 2016–2017 austral summer, the University of Texas Institute for Geophysics (UTIG) and the Korea Polar Research Institute (KOPRI) collaborated to perform a helicopter-based radar and laser altimeter survey of lower David Glacier with the goals of characterizing the subglacial water distribution that supports a system of active subglacial lakes and informing the site selection for a potential subglacial access drilling project. This survey overlaps with and expands upon an earlier survey of the Drygalski Ice Tongue and the David Glacier grounding zone from 2011 and 2012 to create a 5 km resolution survey extending 200 km upstream from the grounding zone. The surveyed region covers two active subglacial lakes and includes reflights of ICESat ground tracks that extend the surface elevation record in the region. This is one of the most extensive aerogeophysical surveys of an active lake system and provides higher-resolution boundary conditions and basal characterizations that will enable process studies of these features. This paper introduces a new helicopter-mounted ice-penetrating radar and laser altimetry system, notes a discrepancy between the original surface-elevation-derived lake outlines and locations of possible water collection based on basal geometry and hydraulic potential, and presents radar-based observations of basal conditions that are inconsistent with large collections of ponded water despite laser altimetry showing that the hypothesized active lakes are at a highstand.

Production of electricity employing sewerage lines using a micro cross flow turbine

In the design of cross flow turbines, efficiency is a significant parameter. The crossflow turbine for developing nations is the most cost-efficient electricity generation source and often used in isolated power systems. This research work analyzes the potential of electricity production using a micro-cross flow turbine from sewage lines. To measure the hydraulic potential of the sewage’s wastewater, flow rate at the connection point was investigated by experimentation on site and the efficiency of the micro cross flow turbine was evaluated. The experimental results show that the hydraulic potential of the selected point for electricity production is enough throughout the year. It also shows that the micro-cross flow turbine can be used effectively to produce electricity from the sewage at the link points. The highest efficient 2 mm head was observed with a maximum flow rate of 0.112 m3/s. Depending on the flow rate, the turbine velocity was 103-263 rpm. The maximum power of shaft was 284.58 W and the highest power generated was 196.24 W. The maximum overall efficiency was 68.2%. This article discusses the design, efficiency, operation and cost of low-head micro crossflow turbines.
 Keywords: Electricity Generation, Hydraulic Potential, Micro Cross Flow Turbine, Sewage

Computational analysis of vortex rope in a hydroturbine of Tucuruí dam

There is a relevant hydraulic potential in Amazon rivers, from which it is generated most of the energy available for the largest part of Brazil. One of the most important hydropower plants in the Amazon is Tucurui dam, which can produce 8370 MW through Francis turbines. This kind of turbine often presents hydrodynamic issues due to the vortex rope formation, which can induce vibrations and reduce assembly operating life. The present work concentrates in a computational study to determine the frequency pressure fluctuations in a hydraulic generation unit of the Tucurui hydroelectric power plant. A numerical technique is applied for modeling the turbulent flow throughout the generation unit in a transient regime using finite volume method. For the analysis of velocity and pressure fields on the hydrogenerator, a 3D fully turbulent transient modeling for characterizing the pressure fluctuations at the runner outlet is performed. The structure of vortex rope formed is investigated in order to evaluate the hydrodynamic phenomena resulting from the turbine operating condition. Low-frequency pressure pulsations are caused by the movement of the vortex rope at the runner outlet. Additionally, vortex shedding dynamics is heavily influenced by the turbine operating conditions, demonstrating the importance of such investigation. For 63% distributor opening, the structure of the vortex rope reaches a big size in the suction duct, increasing the possibility of vibration. For 89% distributor opening, the turbine operates under overload condition, and the vortex rope becomes unstable. Comparisons with field data show the efficiency and validity of the numerical modeling, demonstrating good agreement.

On the assimilation of environmental tracer observations for model-based decision support

Abstract. It has been advocated that history matching numerical models to a diverse range of observation data types, particularly including environmental tracer concentrations and their interpretations and derivatives (e.g., mean age), constitutes an effective and appropriate means to improve model forecast reliability. This study presents two regional-scale modeling case studies that directly and rigorously assess the value of discrete tritium concentration observations and tritium-derived mean residence time (MRT) estimates in two decision-support contexts; “value” is measured herein as both the improvement (or otherwise) in the reliability of forecasts through uncertainty variance reduction and bias minimization as a result of assimilating tritium or tritium-derived MRT observations. The first case study (Heretaunga Plains, New Zealand) utilizes a suite of steady-state and transient flow models and an advection-only particle-tracking model to evaluate the worth of tritium-derived MRT estimates relative to hydraulic potential, spring discharge and river–aquifer exchange flux observations. The worth of MRT observations is quantified in terms of the change in the uncertainty surrounding ecologically sensitive spring discharge forecasts via first-order second-moment (FOSM) analyses. The second case study (Hauraki Plains, New Zealand) employs paired simple–complex transient flow and transport models to evaluate the potential for assimilation-induced bias in simulated surface-water nitrate discharge to an ecologically sensitive estuary system; formal data assimilation of tritium observations is undertaken using an iterative ensemble smoother. The results of these case studies indicate that, for the decision-relevant forecasts considered, tritium observations are of variable benefit and may induce damaging bias in forecasts; these biases are a result of an imperfect model's inability to properly and directly assimilate the rich information content of the tritium observations. The findings of this study challenge the advocacy of the increasing use of tracers, and of diverse data types more generally, whenever environmental model data assimilation is undertaken with imperfect models. This study also highlights the need for improved imperfect-model data assimilation strategies. While these strategies will likely require increased model complexity (including advanced discretization, processes and parameterization) to allow for appropriate assimilation of rich and diverse data types that operate across a range of spatial and temporal scales commensurate with a forecast of management interest, it is critical that increased model complexity does not preclude the application of formal data assimilation and uncertainty quantification techniques due to model instability and excessive run times.

Water transport and tracer mixing in volcanic ash soils at a tropical hillslope: A wet layered sloping sponge

AbstractAndosol soils formed in volcanic ash provide key hydrological services in montane environments. To unravel the subsurface water transport and tracer mixing in these soils we conducted a detailed characterization of soil properties and analyzed a 3‐year data set of sub‐hourly hydrometric and weekly stable isotope data collected at three locations along a steep hillslope. A weakly developed (52–61 cm depth), highly organic andic (Ah) horizon overlaying a mineral (C) horizon was identified, both showing relatively similar properties and subsurface flow dynamics along the hillslope. Soil moisture observations in the Ah horizon showed a fast responding (few hours) “rooted” layer to a depth of 15 cm, overlying a “perched” layer that remained near saturated year‐round. The formation of the latter results from the high organic matter (33–42%) and clay (29–31%) content of the Ah horizon and an abrupt hydraulic conductivity reduction in this layer with respect to the rooted layer above. Isotopic signatures revealed that water resides within this soil horizon for short periods, both at the rooted (2 weeks) and perched (4 weeks) layer. A fast soil moisture reaction during rainfall events was also observed in the C horizon, with response times similar to those in the rooted layer. These results indicate that despite the perched layer, which helps sustain the water storage of the soil, a fast vertical mobilization of water through the entire soil profile occurs during rainfall events. The latter being the result of the fast transmissivity of hydraulic potentials through the porous matrix of the Andosols, as evidenced by the exponential shape of the water retention curves of the subsequent horizons. These findings demonstrate that the hydrological behavior of volcanic ash soils resembles that of a “layered sponge,” in which vertical flow paths dominate.

Potential energy exploitation in collective irrigation systems using pumps as turbines: A case study in Calabria (Southern Italy)

The development of efficient energy, water and environment systems is considered a fundamental key to satisfy the principles of cleaner production, energy security and circular economy. The present study aims at investigating the possible energy exploitation of the untapped hydraulic potential in collective irrigation systems by adopting pumps as turbines. These machines are not extensively used to produce electricity due to the lack of information in reverse operation mode and the low efficiency outside the best efficiency point. This study proposes new correlation rules to obtain more accurate performance of the pumps as turbines and introduces a novel methodology to select the proper hydraulic machines and define the optimal hydropower configuration. The proposed procedure based on a multi-variable optimisation has been applied to the whole collective irrigation networks of Calabria (Southern Italy). Specifically, the energy production, greenhouse gas emissions and investment costs of 114 potential small hydropower plants have been estimated. The results show that the adoption of pumps as turbines in small-scale hydropower plants is a viable, clean and cheap solution for an extensive use in collective irrigation systems. These machines lead to a noticeable decrease in the electro-mechanical costs (−74%) with only a slight reduction (−19%) in the total electric power compared to specific-site designed turbines. Furthermore, the proposed hydropower systems guarantee a significant fall in greenhouse gas emissions (larger than 8800 tons/year) with respect to the conventional Italian electric production. The generated electricity could be used to satisfy a larger share of electric demand coming from collective irrigation agencies and/or agricultural farms with significant improvements in their economic and environmental impact. Overall, the proposed methodology may represent a valid design tool for an extensive exploitation of hydropower sources in rural water systems, in an effort to enhance cleaner energy productions and integrated systems of energy, water and environment.

Avaliação dos impactos ambientais gerados na implantação das pequenas centrais hidrelétricas Canhadão e Tigre no Sudoeste do Paraná, pelo método RIAM

O impacto ambiental está relacionado à alteração realizada no meio ambiente, seja ela negativa ou positiva, portanto, ao estudá-los avalia-se as consequências de ações, para que possa ser preservada a qualidade do ambiente em todas as fases de desenvolvimento do empreendimento. O presente artigo tem como objetivo analisar os impactos ambientais ocasionados pela implantação das Pequenas Centrais Hidrelétricas (PCHs) Canhadão e Tigre através do método da matriz de avaliação de impacto rápido - RIAM. Para realizar tal análise, tendo o intuito de tornar o processo o menos subjetivo possível, procurou-se o auxílio de geotecnologias, levantamento de campo e documentos relacionados com as PCHs. Os resultados dessas matrizes permitiram identificar que os impactos negativos significativos foram: a alteração da vazão a jusante em função do período de enchimento do reservatório e / ou desvio permanente do rio, a inundação da vegetação com perda do patrimônio vegetal, o desmatamento do canteiro de obras, locais que são prejudiciais à produção florestal, assoreamento do reservatório, processos de erosão, degradação das áreas utilizadas para a exploração de material de construção e obras de construção temporárias. Os impactos positivos significativos foram: a melhoria da rede rodoviária local e, no contexto atual, as PCHs, são apresentadas como uma das formas mais sustentáveis de produzir energia elétrica, utilizando o potencial hidráulico da região estudada.

Ecohydrological Behaviour of Mountain Beech Forest: Quantification of Stomatal Conductance Using Sap Flow Measurements

In forested regions, transpiration as a main component of evaporation fluxes is important for evaporation partitioning. Physiological behaviours among various vegetation species are quite different. Thus, an accurate estimation of the transpiration rate from a certain tree species needs specific parameterization of stomatal response to multiple environmental conditions. In this study, we chose a 300-m2 beech forest plot located in Vydra basin, the Czech Republic, to investigate the transpiration of beech (Fagus sylvatica) from the middle of the vegetative period to the beginning of the deciduous period, covering 100 days. The sap flow equipment was installed in six trees with varying ages among 32 trees in the plot, and the measurements were used to infer the stomatal conductance. The diurnal pattern of stomatal conductance and the response of stomatal conductance under the multiple environmental conditions were analysed. The results show that the stomatal conductance inferred from sap flow reached the highest at midday but, on some days, there was a significant drop at midday, which might be attributed to the limits of the hydraulic potential of leaves (trees). The response of stomatal conductance showed no pattern with solar radiation and soil moisture, but it did show a clear correlation with the vapour deficit, in particular when explaining the midday drop. The relation to temperature was rather scattered as the measured period was in the moderate climate. The findings highlighted that the parametrization of stress functions based on the typical deciduous forest does not perfectly represent the measured stomatal response of beech. Therefore, measurements of sap flow can assist in better understanding transpiration in newly formed beech stands after bark beetle outbreaks in Central Europe.

Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System

AbstractSubglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water flow, hat is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from single‐conduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3–7 days, while tremor produced by single‐conduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.

Study of External Characteristics of Hydraulic Electromagnetic Regenerative Shock Absorber

According to the composition and the principle of the liquid-electric energy-sensing damper, the corresponding hydraulic regenerative model is designed. In this paper, an advanced type of shock absorber combined with the mechanical and electromagnetic hydraulic structure has been proposed that recycles the energy dissipated by shock absorber in the driving process. In addition, the damping characteristics of the conventional mechanical vehicle and the advanced hydraulic regenerative mechanical vehicle have been analyzed by using AMESim simulation. The regenerative suspension is reformed from the traditional hydraulic and pneumatic suspension. The suspension absorbs kinetic energy converts it into hydraulic potential and pneumatic power to be stored in the accumulator. The kinetic energy is then converted into electricity instead of heat by using the hydraulic suspension and Power-Generating Shock Absorber (PGSA). The AMESim simulation results have efficiently verified the displacement characteristics curves and flow rate of hydraulic fluid in the body. Finally the conversion of energy produced by advanced hydraulic regenerative mechanical vehicle transferred into electrical energy. The designed hydraulic shock absorber allows a significant fuel saving of 1.5% to 4% depending on the vehicle and driving conditions.

Do karst woody plants control xylem tension to avoid substantial xylem cavitation in the wet season?

BackgroundPlants have been hypothesized to maintain strong control over xylem tension by closing stomata and to operate at a water potential above or near the critical potential at which cavitation commences. An alternative hypothesis holds that cavitation temporarily relieves water stress and stomatal closure is insufficient to prevent short term “run-away” cavitation.MethodsThe objectives of this study were to investigate the leaf conductivity loss at noon (Loss) of 13 woody species differing in leaf phenology at two sites on karst topography in the wet season in southwestern China; the hydraulic architecture of woody species has rarely been reported previously. Loss was predicted from minimum field leaf water potentials (Ψmin) and laboratory-generated vulnerability curves. We also measured the maximum quantum efficiency of photosystem II using chlorophyll a fluorescence (Fv/Fm) and other associated leaf traits.ResultsLoss in the field varied substantially, from 1.39% in evergreen Itea chinensis to 90.07% in deciduous Sapium sebiferum. However, the Loss did not significantly decrease the efficiency of photosystem II. The water potential at which a 50% loss in leaf conductivity occurred (Ψ50) was not correlated to Ψmin. The co-occurring evergreen and deciduous species differed significantly in some stem hydraulic and associated leaf traits. Deciduous species had higher hydraulic conductance, photosynthetic rate, stomatal conductance, lower cavitation-resistance and minimum water potential than co-occurring evergreen species.ConclusionsThere was no sign that karst woody species in southwestern China could control xylem tension above the threshold to avoid substantial xylem cavitation in the wet season. There was no association between Loss and Fv/Fm among the studied species. This “isohydric” regulation behaviour, as well as abundant rainfall in the wet season, may explain why large variations of Loss existed across karst woody species in southwestern China.

Multiscale modeling of unsaturated granular materials based on thermodynamic principles

The effect of water on the hydromechanical behavior of unsaturated granular materials has been studied with a micromechanical model based on thermodynamic principles. A general framework based on the theory of thermodynamics with internal variables for constructing thermodynamically consistent multiscale constitutive relations for unsaturated granular materials has been developed. Within this framework, the microscopic total Helmholtz free energy has been separated between a mechanical and a hydraulic part, each of which is a function of either the elastic displacement or the capillary bridge volume and the distance between particles at the microscale. The inter-particle dissipation of energy, assumed to be frictional in origin, is a function of the incremental plastic displacements at the microscale. Both the microscale Helmholtz free energy and the dissipative energy have been volumetrically averaged to obtain the homogenized energy functions at the macroscale. In accordance with the suggested multiscale thermomechanical framework, a micromechanical model has been constructed to describe the behavior of partially saturated granular soils. This model has considered the deformation of soil skeleton by applying a Coulomb-type criterion at the inter-particle contacts. The hydraulic potential is made to be dependent on the size of the particles and is derived through use of the expression for the water retention curve by assuming that liquid bridges are isotropically distributed within the specimen. The performance of the suggested model has been demonstrated through numerical simulations of the behavior of sand under various degrees of saturation and a wide range of mechanical loadings.

Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets

Subglacial hydrology modulates how ice sheets flow, respond to climate, and deliver meltwater, sediment and nutrients to proglacial and marine environments. Here, we investigate the development of subglacial lakes and drainage networks beneath the Fennoscandian and Barents Sea ice sheets over the Late Weichselian. Utilizing an established coupled climate/ice flow model, we calculate high-resolution, spatio-temporal changes in subglacial hydraulic potential from ice sheet build-up (∼37 ka BP) to complete deglaciation (∼10 ka BP). Our analysis predicts up to 3500 potential subglacial lakes, the largest of which was 658 km2, and over 70% of which had surface areas <10 km2, comparable with subglacial lake-size distributions beneath the Antarctic Ice Sheet. Asynchronous evolution of the Fennoscandian Ice Sheet into the flatter relief of northeast Europe affected patterns of subglacial drainage, with up to 100 km3 more water impounded within subglacial lakes during ice build-up compared to retreat. Furthermore, we observe frequent fill/drain cycles within clusters of subglacial lakes at the onset zones and margins of ice streams that would have affected their dynamics. Our results resonate with mapping of large subglacial channel networks indicative of high-discharge meltwater drainage through the Gulf of Bothnia and central Barents Sea. By tracking the migration of meltwater drainage outlets during deglaciation, we constrain locations most susceptible to focussed discharge, including the western continental shelf-break where subglacial sediment delivery led to the development of major trough-mouth fans. Maps of hydraulic potential minima that persist throughout the Late Weichselian reveal potential sites for preserved subglacial lake sediments, thereby defining useful targets for further field-investigation.