scholarly journals Sunda Shelf Seas: flushing rates and residence times

2015 ◽  
Vol 12 (3) ◽  
pp. 863-895 ◽  
Author(s):  
B. Mayer ◽  
T. Stacke ◽  
I. Stottmeister ◽  
T. Pohlmann
Keyword(s):  
Numerical Models ◽  
Environmental Water ◽  
Hydrodynamical Model ◽  
Strong Impact ◽  
Residence Times ◽  
Sunda Shelf ◽  
Flushing Rate ◽  
Shelf Seas ◽  
Java Sea ◽  
Flushing Rates

Abstract. The region of the Sunda Shelf has an average depth of approx. 48 m and is subject to many physical and biogeochemical processes with a strong impact from human activities. For the investigation of marine environmental water properties and quality, it is helpful to have an idea about exchange rates of water masses in the different parts of this region. Four numerical models, the global hydrodynamical model MPI-OM, the global hydrological model MPI-HM, the regional hydrodynamical model HAMSOM and a Lagrangian tracer model have been utilized to estimate the flushing rates and residence times in different seas on the Sunda Shelf. Using decadal averaged monthly transports, the commonly used flushing rate formula gives rates for the different months of approximately 40 to 70 days for the entire Sunda Shelf. For most parts of it (Malacca Strait, southern South China Sea, Java Sea), the results are similar, while for the Gulf of Thailand, the flushing rates amount to 80 to 170 days. The tracer model provides quite different but very detailed 3-D pictures with residence times of below 30 days to more than two years, depending on the location within the region, on the starting layer and on the season.

Pu Residence Times in Freshwaters and Accumulation in Shield Lake Sediments

1988 ◽  
Vol 45 (3) ◽  
pp. 407-415 ◽  
Author(s):  
R. J. Cornett ◽  
L. Chant
Keyword(s):  
Great Lakes ◽  
Lake Sediments ◽  
Laurentian Great Lakes ◽  
Residence Times ◽  
Input Output ◽  
Oligotrophic Lakes ◽  
Flushing Rate ◽  
Flushing Rates ◽  
Shield Lakes

Activity balances for 239,240Pu in seven oligotrophic lakes were constructed from measurements of 239,240Pu inputs and measurements of 239,240Pu accumulated in the lake sediments. 239,240Pu eroded from the catchment was a significant input to lakes with rapid hydrologic flushing rates. From 28 to 100% of the 239,240Pu input to the lakes accumulated in the lake sediments. The fraction of 239,240Pu inputs accumulated in the lake sediments was inversely correlated with the hydrologic flushing rate of the lake. 239,240Pu concentrations in the sediments were simulated using a single reservoir input–output model. Partial residence times for 239,240Pu transfer from the water to the sediments ranged from 0.09 to 2.7 yr and were shorter in lakes with more rapid flushing. Partial residence times of 239,240Pu in these small shield lakes were very similar to the residence times of 239,240Pu in the Laurentian Great Lakes and to those of 137Cs and 210Pb in other small oligotrophic lakes.

scholarly journals PROPAGATION OF WIND WAVES ON TIDES

1988 ◽  
Vol 1 (21) ◽  
pp. 36 ◽  
Author(s):  
Hendrick L. Tolman
Keyword(s):  
Wave Propagation ◽  
Wind Wave ◽  
Numerical Models ◽  
Wind Waves ◽  
Absolute Frequency ◽  
Shelf Seas ◽  
Shelf Sea

Effects of instationary depths and currents in tides on shelf seas on wind wave propagation are investigated using two numerical models in two academical situations representing shelf sea conditions. It is shown that changes in absolute frequency, which are induced by the instationarity of depth and current, are significant in contrast to what is usually assumed. If these changes are neglected large and unpredictable errors may occur in calculated changes of wavenumber and amplitude.

Renewed thinking on groundwater age

2021 ◽  
Author(s):  
Grant Ferguson ◽  
Mark Cuthbert ◽  
Kevin Befus ◽  
Tom Gleeson ◽  
Chandler Noyes ◽  
...  
Keyword(s):  
Environmental Flows ◽  
Numerical Models ◽  
Groundwater Age ◽  
Holistic Approach ◽  
Water Levels ◽  
Residence Times ◽  
Groundwater Sustainability ◽  
Long Time ◽  
Mean Residence Times ◽  
Recharge Rates

<p>Groundwater age and mean residence times have been invoked as measures of groundwater sustainability, with the idea that old or "fossil" groundwater is non-renewable. This idea appears to come from the link between groundwater age and background recharge rates, which are also of questionable use in assessing the sustainability of groundwater withdrawals. The use of groundwater age to assess renewability is further complicated by its relationship with flow system geometry. Young groundwaters near recharge areas are not inherently more renewable than older groundwaters down gradient. Similarly, there is no reason to preferentially use groundwater from smaller aquifers, which will have smaller mean residence times than larger aquifers for the same recharge rate. In some cases, groundwater ages may provide some information where groundwater recharge rates were much higher in the past and systems are no longer being recharged. However, there are few examples where the relationship between depletion and changes in recharge over long time periods has been rigorously explored. Groundwater age measurements can provide insights into the functioning of groundwater flow systems and calibration targets for numerical models and we advocate for their continued use, but they are not a metric of sustainable development. Simple metrics to assess groundwater sustainability remain elusive and a more holistic approach is warranted to maintain water levels and environmental flows.</p>

The importance of phase morphology for rheology of ferropericlase-bridgmanite mixtures

2021 ◽  
Author(s):  
Marcel Thielmann ◽  
Gregor Golabek ◽  
Hauke Marquardt
Keyword(s):  
Lower Mantle ◽  
Mantle Convection ◽  
Effective Viscosity ◽  
Large Scale ◽  
Numerical Models ◽  
Phase Morphology ◽  
Strong Impact ◽  
Analytical Approximations ◽  
The Impact ◽  
Strong Control

<p>The rheology of the Earth’s lower mantle is poorly constrained due to a lack of knowledge of the rheological behaviour of its constituent minerals. In addition, the lower mantle does not consist of only a single, but of multiple mineral phases with differing deformation behaviour. The rheology of Earth’s lower mantle is thus not only controlled by the rheology of its individual constituents (bridgmanite and ferropericlase), but also by their interplay during deformation. This is particularly important when the viscosity contrast between the different minerals is large. Experimental studies have shown that ferropericlase may be significantly weaker than bridgmanite and may thus exert a strong control on lower mantle rheology.</p><p>Here, we thus explore the impact of phase morphology on the rheology of a ferropericlase-bridgmanite mixture using numerical models. We find that elongated ferropericlase structures within the bridgmanite matrix significantly lower the effective viscosity, even in cases where no interconnected network of weak ferropericlase layers has been formed. In addition to the weakening, elongated ferropericlase layers result in a strong viscous anisotropy. Both of these effects may have a strong impact on lower mantle dynamics, which makes is necessary to develop upscaling methods to include them in large-scale mantle convection models. We develop a numerical-statistial approach to link the statistical properties of a ferropericlase-bridgmanite mixture to its effective viscosity tensor. With this approach, both effects are captured by analytical approximations that have been derived to describe the evolution of the effective viscosity (and its anisotropy) of a two-phase medium with aligned elliptical inclusions, thus allowing to include these microscale processes in large-scale mantle convection models.</p>

Assessment of Scale Resolved CFD Methods for the Investigation of Lean Burn Spray Flames

2016 ◽  
Author(s):  
A. Andreini ◽  
D. Bertini ◽  
L. Mazzei ◽  
S. Puggelli
Keyword(s):  
Steady State ◽  
Numerical Models ◽  
Combustion Model ◽  
Experimental Investigations ◽  
Strong Impact ◽  
Lean Burn ◽  
Two Phase ◽  
Spray Flames ◽  
Flamelet Generated Manifold ◽  
Reactive Processes

Incoming standards on NOx emissions are motivating many aero-engines manufacturers to adopt the lean burn combustion concept. However, several technological issues have to be faced in this transition, among which limited availability of air for cooling purpose and thermoacoustics phenomena that should be managed to safely implement this burning mode. In this scenario, standard numerical design tools are not often capable of characterizing such devices. Thus, considering also the difficulties of experimental investigations in a highly pressurized and reactive environment, unsteady scale resolved CFD methods are required to correctly understand the combustor performances. In the last years Large Eddy (LES) and hybrid RANS-LES models such as Scale Adaptive Simulations (SAS) have undergone considerable developments. Such approaches have been already applied for gaseous flames, leading to a strong enhancement in phenomena prediction with respect to standard steady-state simulations. However, huge research efforts are still required when spray flames are considered, since all the numerical models chosen to describe spray dynamics and the related reactive processes can have a strong impact on the accuracy of the whole simulation. In this work a set of scale resolved simulations have been carried out on the DLR Generic Single Sector Combustor spray flame for which measurements both in non-reactive and reactive test conditions are available. Exploiting a two-phase Eulerian-Lagrangian approach combined with a Flamelet Generated Manifold (FGM) combustion model, LES simulations have been performed in order to assess the potential improvements with respect to steady state solutions. Additional comparisons have also been accomplished with SAS calculations based on Eddy Dissipation combustion model (EDM). The comparison with experimental results shows that the chosen unsteady strategies lead to a more physical description of reactive processes with respect to RANS simulations. FGM model showed some limitations in reproducing the partially-premixed nature of the flame, whereas SAS-EDM proved to be a robust modelling strategy within an industrial perspective. A new set of spray boundary conditions for liquid injection is also proposed whose realiability is proved through a detailed comparison against experimental data.

Advantages of vertically adaptive coordinates in numerical models of stratified shelf seas

2015 ◽  
Vol 92 ◽  
pp. 56-68 ◽  
Author(s):  
Ulf Gräwe ◽  
Peter Holtermann ◽  
Knut Klingbeil ◽  
Hans Burchard
Keyword(s):  
Numerical Models ◽  
Shelf Seas

Mixing in seasonally stratified shelf seas: a shifting paradigm

2005 ◽  
Vol 363 (1837) ◽  
pp. 2837-2854 ◽  
Author(s):  
Tom P Rippeth
Keyword(s):  
Continental Shelf ◽  
Numerical Models ◽  
Vertical Mixing ◽  
Internal Tide ◽  
Shear Instability ◽  
Small Contribution ◽  
Shelf Seas ◽  
Shelf Sea ◽  
Ocean Carbon ◽  
Energy Dissipated

Although continental shelf seas make up a relatively small fraction ( ca 7%) of the world ocean's surface, they are thought to contribute significantly (20–50% of the total) to the open-ocean carbon dioxide storage through processes collectively known as the shelf sea pump. The global significance of these processes is determined by the vertical mixing, which drives the net CO 2 drawdown (which can occur only in stratified water). In this paper, we focus on identifying the processes that are responsible for mixing across the thermocline in seasonally stratified shelf seas. We present evidence that shear instability and internal wave breaking are largely responsible for thermocline mixing, a clear development from the first-order paradigm for the water column structure in continental shelf seas. The levels of dissipation observed are quantitatively consistent with the observed dissipation rates of the internal tide and near-inertial oscillations. It is perhaps because these processes make such a small contribution to the total energy dissipated in shelf seas that they are not well represented in current state-of-the-art numerical models of continental shelf seas. The results thus present a clear challenge to oceanographic models.

scholarly journals Debris-Influenced Sliding Laws and Basal Debris Balance

1986 ◽  
Vol 32 (111) ◽  
pp. 224-231 ◽  
Author(s):  
E.M. Shoemaker
Keyword(s):  
Pressure Fluctuation ◽  
Effective Pressure ◽  
Sliding Velocity ◽  
Channel Diameter ◽  
Flushing Rate ◽  
Erosion Rates ◽  
Abrasion Rate ◽  
Flushing Rates ◽  
Definition Of ◽  
Drag Term

AbstractIn order to determine the effect of basal debris drag as a component in a sliding law, it is necessary to know the basal debris concentration. Does, for example, this debris concentration exhibit uniformity, in an average sense, across a valley? What effect does a localized region of high quarryability have on basal debris concentration down-stream? The analysis presented here suggests that, for the case of sparse debris, debris concentration tends to be uniform over the entire bed. Consequently, the debris-drag term in a sliding law will also tend to be uniform.In order to reach the above conclusions, it is necessary to consider debris balance, the balance of the quarrying, abrasion, and debris-flushing rates. This entails proposing and testing quarrying and flushing laws, since these laws have not been previously proposed. It is concluded that the quarrying, flushing, and erosion rates depend weakly on the sliding velocity. Furthermore, the abrasion rate is negligible compared to the quarrying rate. (This conclusion depends partially on the definition of abrasion.) The quarrying rate also depends on other factors such as the effective pressure_pressure-fluctuation mechanism; the cross-valley dependency of this mechanism is investigated. The flushing rate is found to depend on the ratio, N-channel area/bed area, and on average N-channel diameter.

Extreme Wave Impacts on Monopiles: Re-Analysis of Experimental Data by a Coupled CFD Solver

2017 ◽  
Author(s):  
Amin Ghadirian ◽  
Henrik Bredmose ◽  
Signe Schløer ◽  
Martin Dixen
Keyword(s):  
Time Series ◽  
Numerical Models ◽  
Bending Moment ◽  
Exceedance Probability ◽  
Strong Impact ◽  
Back Side ◽  
Sea Bed ◽  
Secondary Load ◽  
Pressure Time ◽  
Good Agreement

Two different numerical models, OceanWave3D and a coupled solver, OceanWave3D-OpenFOAM (Waves2Foam), are used to reproduce extreme events in one sea state. The events are chosen as, the measured event that generates the largest peak moment (exceedance probability of 0.05%) and one event with a slightly smaller peak moment (exceedance probability of 0.3%). Time series of free surface elevation, depth integrated forces, bending moment at the sea bed and pressure time series at 5 different heights on the cylinder are compared for two events between the measurements and the numerical models. The numerical pressure field on the monopile at impact is analyzed and stagnation pressures at the back side of the cylinder, in addition to the main impact pressure at the front side are observed. There is a good agreement between the OceanWave3D results and the measurements in the reproduction of the first selected event. However, for the larger selected event, OceanWave3D results in the peaks of time series are smaller than the measurements. This illustrates the sensitivity of the strong impact loads to the state of wave breaking. For small values of the inline force, the OpeanFOAM results provided good agreement with the measurements. The secondary load cycles are observed in the measured force and bending moment time series and the reproduced times series using OpenFOAM.

scholarly journals What controls the large-scale magnetic fields of M dwarfs?

2013 ◽  
Vol 9 (S302) ◽  
pp. 166-169
Author(s):  
T. Gastine ◽  
J. Morin ◽  
L. Duarte ◽  
A. Reiners ◽  
U. Christensen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Numerical Models ◽  
Strong Impact ◽  
M Dwarfs ◽  
Relative Contribution ◽  
Broad Variety ◽  
Field Geometry ◽  
M Stars

AbstractObservations of active M dwarfs show a broad variety of large-scale magnetic fields encompassing dipole-dominated and multipolar geometries. We detail the analogy between some anelastic dynamo simulations and spectropolarimetric observations of 23 M stars. In numerical models, the relative contribution of inertia and Coriolis force –estimated by the so-called local Rossby number– is known to have a strong impact on the magnetic field geometry. We discuss the relevance of this parameter in setting the large-scale magnetic field of M dwarfs.

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