Multiple steady states in exchange flows across faults and the dissolution of

2015 ◽  
Vol 769 ◽  
pp. 229-241 ◽  
Author(s):  
Andrew W. Woods ◽  
Marc Hesse ◽  
Rachel Berkowitz ◽  
Kyung Won Chang
Keyword(s):  
Initial Conditions ◽  
Storage Systems ◽  
Exchange Flow ◽  
Cross Contamination ◽  
Volume Flux ◽  
Geological Storage ◽  
Deep Aquifer ◽  
Exchange Flows ◽  
Equilibrium Exchange ◽  
Different Levels

We develop a model of the steady exchange flows which may develop between two aquifers at different levels in the geological strata and across which there is an unstable density stratification, as a result of their connection through a series of fractures. We show that in general there are multiple steady exchange flows which can develop, depending on the initial conditions, and which may involve a net upwards or downwards volume flux. We also show that there is a family of equilibrium exchange flows with zero net volume flux, each characterised by a different interlayer flux of buoyancy. We present experiments which confirm our simplified model of the exchange flow. Such exchange flows may supply unsaturated water from a deep aquifer to drive dissolution of a structurally trapped pool of geologically stored $\text{CO}_{2}$, once the water in the aquifer containing the trapped pool of $\text{CO}_{2}$ has become saturated in $\text{CO}_{2}$, and hence relatively dense. Such exchange flows may also lead to cross-contamination of aquifer fluids, which may be of relevance in assessing risks of geological storage systems.

Barotropically induced interfacial waves in two-layer exchange flows over a sill

2007 ◽  
Vol 592 ◽  
pp. 135-154 ◽  
Author(s):  
M. ELETTA NEGRETTI ◽  
DAVID Z. ZHU ◽  
GERHARD H. JIRKA
Keyword(s):  
Flow Rate ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Exchange Flow ◽  
Total Water ◽  
Interfacial Waves ◽  
Interfacial Wave ◽  
Exchange Flows ◽  
Wave Characteristics ◽  
Rate Oscillations

Two-layer exchange flows are observed in the channels/straits connecting two water bodies of different densities. This study examines the nature of the barotropic forcing and its effect on the interfacial waves in two-layer exchange flows over a smooth/break underwater sill. Experiments were conducted with different initial conditions, distinguishing the case of hydrostatic disequilibrium and the case of a global pressure-balanced state. The experiments demonstrate that the baroclinic exchange flow is dominated by the barotropic-forcing-induced oscillations. A simplified barotropic model is developed to predict the period of the barotropic oscillation with an excellent agreement with experimental measurements. Detailed velocity and flow-rate measurements also indicate the importance of the barotropic forcing in exchange flows. The effect of the superimposed barotropic forcing on the interfacial wave characteristics is also investigated. Large two-dimensional surge-like structures are observed during the experiments, whose generation is shown to be related to the flow-rate oscillations. The length scales of these structures is comparable with the total water depth and is shown to increase with increasing Reynolds numbers.

Unsteady convective exchange flows in cavities

1998 ◽  
Vol 368 ◽  
pp. 127-153 ◽  
Author(s):  
J. J. STURMAN ◽  
G. N. IVEY
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Boundary Layer Thickness ◽  
Buoyancy Flux ◽  
Exchange Flow ◽  
Flushing Time ◽  
Exchange Flows ◽  
Buoyancy Forcing ◽  
Convective Exchange ◽  
Approach To Steady State

Horizontal exchange flows driven by spatial variation of buoyancy fluxes through the water surface are found in a variety of geophysical situations. In all examples of such flows the timescale characterizing the variability of the buoyancy fluxes is important and it can vary greatly in magnitude. In this laboratory study we focus on the effects of this unsteadiness of the buoyancy forcing and its influence on the resulting flushing and circulation processes in a cavity. The experiments described all start with destabilizing forcing of the flows, but the buoyancy fluxes are switched to stabilizing forcing at three different times spanning the major timescales characterizing the resulting cavity-scale flows. For destabilizing forcing, these timescales are the flushing time of the region of forcing, and the filling-box timescale, the time for the cavity-scale flow to reach steady state. When the forcing is stabilizing, the major timescale is the time for the fluid in the exchange flow to pass once through the forcing boundary layer. This too is a measure of the time to reach steady state, but it is generally distinct from the filling-box time. When a switch is made from destabilizing to stabilizing buoyancy flux, inertia is important and affects the approach to steady state of the subsequent flow. Velocities of the discharges from the end regions, whether forced in destabilizing or stabilizing ways, scaled as u∼(Bl)1/3 (where B is the forcing buoyancy flux and l is the length of the forcing region) in accordance with Phillips' (1966) results. Discharges with destabilizing and stabilizing forcing were, respectively, Q−∼(Bl)1/3H and Q+∼(Bl)1/3δ (where H is the depth below or above the forcing plate and δ is the boundary layer thickness). Thus Q−/Q+>O(1) provided H>O(δ), as was certainly the case in the experiments reported, demonstrating the overall importance of the flushing processes occurring during periods of cooling or destabilizing forcing.

scholarly journals Analysis of Different Energy Storage Technologies for Microgrids Energy Management

2020 ◽  
Vol 173 ◽  
pp. 03004
Author(s):  
Darío Benavides ◽  
Paúl Arévalo ◽  
Luis G. Gonzalez ◽  
José A. Aguado
Keyword(s):  
Energy Storage ◽  
Energy Management ◽  
Storage Systems ◽  
Storage System ◽  
Lithium Ion ◽  
Operating Conditions ◽  
Energy Storage Systems ◽  
Efficiency Performance ◽  
Storage Technologies ◽  
Different Levels

The importance of energy storage systems is increasing in microgrids energy management. In this study, an analysis is carried out for different types of energy storage technologies commonly used in the energy storage systems of a microgrid, such as: lead acid batteries, lithium ion batteries, redox vanadium flux batteries and supercapacitors. In this work, it is analyzed the process of charging and discharging (slow and fast) in these systems, the calculation of energy efficiency, performance and energy supplied under different load levels, in its normal operating conditions and installed power capacity is developed. The results allow us to choose the optimal conditions of charge and discharge at different levels of reference power, analyzing the strengths and weaknesses of the characteristics of each storage system within a microgrid.

scholarly journals Formation sites of Population III star formation: The effects of different levels of rotation and turbulence on the fragmentation behaviour of primordial gas

2020 ◽  
Vol 494 (2) ◽  
pp. 1871-1893 ◽  
Author(s):  
Katharina M J Wollenberg ◽  
Simon C O Glover ◽  
Paul C Clark ◽  
Ralf S Klessen
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Turbulent Energy ◽  
Star Forming ◽  
Wide Range ◽  
Population Iii Stars ◽  
The Individual ◽  
The Masses ◽  
Different Levels ◽  
Population Iii

ABSTRACT We use the moving-mesh code arepo to investigate the effects of different levels of rotation and turbulence on the fragmentation of primordial gas and the formation of Population III stars. We consider nine different combinations of turbulence and rotation and carry out five different realizations of each setup, yielding one of the largest sets of simulations of Population III star formation ever performed. We find that fragmentation in Population III star-forming systems is a highly chaotic process and show that the outcomes of individual realizations of the same initial conditions often vary significantly. However, some general trends are apparent. Increasing the turbulent energy promotes fragmentation, while increasing the rotational energy inhibits fragmentation. Within the ∼1000 yr period that we simulate, runs including turbulence yield flat protostellar mass functions while purely rotational runs show a more top-heavy distribution. The masses of the individual protostars are distributed over a wide range from a few $10^{-3} \, {\rm M_{\odot }}$ to several tens of M⊙. The total mass growth rate of the stellar systems remains high throughout the simulations and depends only weakly on the degree of rotation and turbulence. Mergers between protostars are common, but predictions of the merger fraction are highly sensitive to the criterion used to decide whether two protostars should merge. Previous studies of Population III star formation have often considered only one realization per set of initial conditions. However, our results demonstrate that robust trends can only be reliably identified by considering averages over a larger sample of runs.

scholarly journals Tidal modulation of two-layer hydraulic exchange flows

Ocean Science ◽  
2007 ◽  
Vol 3 (2) ◽  
pp. 179-188 ◽  
Author(s):  
L. M. Frankcombe ◽  
A. McC. Hogg
Keyword(s):  
Time Dependent ◽  
Water Model ◽  
Exchange Flow ◽  
Shallow Water Model ◽  
Tidal Amplitude ◽  
Layer System ◽  
Tidal Period ◽  
Exchange Flows ◽  
The Relationship ◽  
Exchange Flux

Abstract. Time-dependent, two layer hydraulic exchange flow is studied using an idealised shallow water model. It is found that barotropic time-dependent perturbations, representing tidal forcing, increase the baroclinic exchange flux above the steady hydraulic limit, with flux increasing monotonically with tidal amplitude (measured either by height or flux amplitude over a tidal period). Exchange flux also depends on the non-dimensional tidal period, γ, which was introduced by by Helfrich (1995). When tidal amplitude is characterised by the barotropic flux amplitude, exchange flux is a monotonic function of γ as predicted by Helfrich (1995). However, the relationship between the (imposed) free surface amplitude and flux amplitude is complicated by reflections within the channel and by the baroclinic response of the two layer system, leading to a non-monotonic relationship between the height amplitude and γ.

Frictional two-layer exchange flow

2003 ◽  
Vol 474 ◽  
pp. 339-354 ◽  
Author(s):  
LILLIAN J. ZAREMBA ◽  
G. A. LAWRENCE ◽  
R. PIETERS
Keyword(s):  
Numerical Model ◽  
Analytical Solution ◽  
Viscous Flow ◽  
Constant Width ◽  
Flow Regimes ◽  
Exchange Flow ◽  
Hydraulic Control ◽  
Laboratory Measurements ◽  
Constant Depth ◽  
Exchange Flows

A numerical model is developed to study the effects of friction on the steady exchange flow that evolves when a barrier is removed from a constriction separating two reservoirs of slightly different densities. The model has excellent agreement with an analytical solution and laboratory measurements of exchange flows through channels of constant width and depth. The model reveals three viscous flow regimes for a convergent–divergent contraction of constant depth, and three additional viscous flow regimes when an offset sill is introduced. Each regime is characterized by a different set of internal hydraulic control locations. Examination of the predicted interface profiles reveals that it is not possible to distinguish between different flow regimes on the basis of these profiles alone.

scholarly journals Estuarine Exchange Flow Is Related to Mixing through the Salinity Variance Budget

2018 ◽  
Vol 48 (6) ◽  
pp. 1375-1384 ◽  
Author(s):  
Parker MacCready ◽  
W. Rockwell Geyer ◽  
Hans Burchard
Keyword(s):  
Steady State ◽  
3D Model ◽  
Exchange Flow ◽  
Volume Flux ◽  
Estuarine Exchange ◽  
The Relationship ◽  
Total Exchange

AbstractThe relationship between net mixing and the estuarine exchange flow may be quantified using a salinity variance budget. Here “mixing” is defined as the rate of destruction of volume-integrated salinity variance, and the exchange flow is quantified using the total exchange flow. These concepts are explored using an idealized 3D model estuary. It is shown that in steady state (e.g., averaging over the spring–neap cycle) the volume-integrated mixing is approximately given by Mixing ≅ SinSoutQr, where Sin and Sout are the representative salinities of in- and outflowing layers at the mouth and Qr is the river volume flux. This relationship provides an extension of the familiar Knudsen relation, in which the exchange flow is diagnosed based on knowledge of these same three quantities, quantitatively linking mixing to the exchange flow.

Maximal two-layer exchange over a sill and through the combination of a sill and contraction with barotropic flow

1986 ◽  
Vol 164 ◽  
pp. 53-76 ◽  
Author(s):  
D. M. Farmer ◽  
L. Armi
Keyword(s):  
Surface Layer ◽  
Reverse Flow ◽  
Single Layer ◽  
The Other ◽  
Exchange Flow ◽  
Strait Of Gibraltar ◽  
Exchange Flows ◽  
Barotropic Flow ◽  
Flow Through ◽  
Layer Flow

The analysis of two-layer exchange flow through contractions with a barotropic component treated by Armi & Farmer (1986) is extended to include exchange flows over sills and through a combination of a sill and contraction. It is shown that exchange over a sill is fundamentally different from exchange through a contraction. Control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer. This asymmetry in the control results in asymmetrical flows. The interface depth above the crest is not one half the total depth, as assumed in other studies by analogy with flow through contractions, but is somewhat deeper; the maximal exchange rate is less than for flow through a contraction of equal depth. When both a sill and a contraction are present, the contraction influences control at the sill crest only if it lies between the sill and the source of denser water. The response to barotropic flow is also asymmetrical: the transition to single-layer flow occurs at much lower speeds for a barotropic component in one direction than the other.Results of the analysis are applied to exchange flow through the Strait of Gibraltar, which includes both a sill and a contraction. It is shown that maximal exchange conditions apply throughout part of the tidal cycle, and observations illustrate several of the analytical predictions for barotropic flows, including the formation of fronts, single-layer flow, submaximal exchange and reverse flow.

Two-layer hydraulic exchange flow through the Burlington Ship Canal

2010 ◽  
Vol 37 (12) ◽  
pp. 1631-1640
Author(s):  
A. Jalili ◽  
S. S. Li
Keyword(s):  
Field Data ◽  
Lower Layer ◽  
Lake Ontario ◽  
Exchange Flow ◽  
Volume Flux ◽  
Oscillation Modes ◽  
Harbour Water ◽  
Flow Through ◽  
Multiple Frequencies ◽  
Time Average

The exchange flow through the Burlington Ship Canal connecting Hamilton Harbour with Lake Ontario is investigated, using a two-layer internal hydraulics model. The summer exchange features an upper layer of polluted Harbour Water flowing from the harbour into the lake, whereas a lower layer of fresh Lake Ontario Water flowing from the lake into the harbour. We predict this exchange, taking into account the effects of both friction and barotropic forcing of multiple frequencies. Predictions of density interface and volume flux compare well with experimental and field data. The interface varies non-linearly with distance along the canal, with and without barotropic forcing. Our results indicate that the exchange flow is highly frictional. The barotropic forcing comprises oscillation modes of different frequency; these individual forcing modes cause the interface and layer velocities to fluctuate significantly in time, but their influence on the time average flows through the canal is minimal.

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