scholarly journals MEDIUM-TERM MORPHODYNAMIC MODELING OF MIXED MUD AND SAND IN THE

2011 ◽  
Vol 1 (32) ◽  
pp. 65
Author(s):  
Markus Witting ◽  
Christof Wehmeyer ◽  
Hanz Dieter Niemeyer
Keyword(s):  
Grain Size ◽  
Field Measurements ◽  
Model Parameters ◽  
Shear Stresses ◽  
Transport Parameters ◽  
Medium Term ◽  
Mud Transport ◽  
Spm Concentration ◽  
Morphodynamic Modeling ◽  
Qualitative Measurements

A morphodynamic model for the Jadebusen basin based on the current DELFT3D model is established. With morphological information such as qualitative measurements of SPM-concentration (Suspended Particular Matter) and bottom change estimates as well as detailed surveys of a sand pit refilling process the model parameters for cohesive transport (Partheniades 1965) are calibrated. Within a period of 8 month, which is condensed to a representative period of 28 days for the modeling, almost 45% of the initial pit volume was refilled with mud. Despite the lack of specific field measurements a setup of mud transport parameters can be defined, which allows further investigations of sand pit locations in the Jadebusen basin. On major outcome is that critical erosion shear stresses for mud should be spatially varied in order to account for the different consolidation states of the mud fraction. Furthermore the paper addresses the problem of the initial grain size distribution for graded sediment transport. Wadden flat types are characterized based on aerial observations which build the underlying information for a relocation model run.

scholarly journals MORPHODYNAMIC MODELING OF THE MEDIUM-TERM MIGRATION OF A TIDAL CHANNEL USING PROCESS-BASED MODEL

2011 ◽  
Vol 1 (32) ◽  
pp. 70
Author(s):  
Diem Nguyen ◽  
Talal Etri ◽  
Karl-Heinz Runte ◽  
Roberto Mayerle
Keyword(s):  
Field Measurements ◽  
Tidal Channel ◽  
Medium Term ◽  
Calibration And Validation ◽  
Sediment Fraction ◽  
Morphodynamic Modeling ◽  
Set Up ◽  
Temporal Coverage ◽  
Selection Of ◽  
Process Based Models

This paper investigates the predictive capability of a morphodynamic model in capturing the development of a tidal channel on the German North Sea coast which experienced migration in the last few years. A depth-averaged version of a process-based model, Delft3D, is used. A description of the set-up, calibration and validation of the process-based models is presented. Field measurements with a dense spatial and temporal coverage were used for the development of the models. Results from the hydrodynamic and sediment transport simulations were in agreement with observations. The morphodynamic model simulations were speeded up with a morphological acceleration factor in conjunction with a representative period. Results of model calibration and validation covering periods of several years proved the capability of the model to reproduce the migration of the tidal channel. According to the standards usually adopted for checking the accuracy of morphodynamic models, the performance of the model presented here was quite good. The model ability in predicting the migration in the medium-term was found to be dependent primarily on the accuracy of the starting bathymetry, characteristics of the substrata and of the mud sediment fraction as well as on the selection of the representative period. A reduction in the rate of migration of the tidal channel is predicted from 2008 till 2010.

Improved infrared temperature mapping of elastohydrodynamic contacts

2009 ◽  
Vol 223 (8) ◽  
pp. 1165-1177 ◽  
Author(s):  
T Reddyhoff ◽  
H A Spikes ◽  
A V Olver
Keyword(s):  
Effective Means ◽  
Field Measurements ◽  
Operating Conditions ◽  
Mapping Technique ◽  
Shear Stresses ◽  
Measured Temperature ◽  
Ir Camera ◽  
Full Field ◽  
Group I ◽  
Increased Sensitivity

An effective means of studying lubricant rheology within elastohydrodynamic contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. In the current work, the experimental approach initially developed by Sanborn and Winer and then by Spikes et al., has been advanced to include a high specification infrared (IR) camera and microscope. Besides the instantaneous capture of full field measurements, this has the advantage of increased sensitivity and higher spatial resolution than previous systems used. The increased sensitivity enables a much larger range of testable operating conditions: namely lower loads, speeds, and reduced sliding. In addition, the range of test lubricants can be extended beyond high shearing traction fluids. These new possibilities have been used to investigate and compare the rheological properties of a range of lubricants: namely a group I and group II mineral oil, a polyalphaolephin (group IV), the traction fluid Santotrac 50, and 5P4E, a five-ring polyphenyl-ether. As expected, contact temperatures increased with lubricant refinement, for the mineral base oils tested. Using moving heat source theory, the measured temperature distributions were converted into maps showing rate of heat input into each surface, from which shear stresses were calculated. The technique could therefore be validated by integrating these shear stress maps, and comparing them with traction values obtained by direct measurement. Generally there was good agreement between the two approaches, with the only significant differences occurring for 5P4E, where the traction that was deduced from the temperature over-predicted the traction by roughly 15 per cent. Of the lubricants tested, Santotrac 50 showed the highest average traction over the contact; however, 5P4E showed the highest maximum traction. This observation is only possible using the IR mapping technique, and is obscured when measuring the traction directly. Both techniques showed the effect of shear heating causing a reduction in traction.

Field evidence of resuspension in a mine tailings pond

2001 ◽  
Vol 38 (4) ◽  
pp. 796-808 ◽  
Author(s):  
Celestina Adu-Wusu ◽  
Ernest K Yanful ◽  
Mohammed H Mian
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Critical Shear Stress ◽  
Field Measurements ◽  
Shear Stresses ◽  
Wind Speeds ◽  
Tailings Pond ◽  
Field Evidence ◽  
Water Cover ◽  
Solubility Of Oxygen

Flooding of tailings under shallow water covers is an effective method of decommissioning potentially acid generating mine tailings. The low diffusivity and solubility of oxygen in water are attractive features of this technology. However, wind-induced waves can resuspend flooded tailings and expose them to greater contact with dissolved oxygen, thereby increasing the potential for oxidation and acid generation. Field measurements of wind activity and waves under different water cover depths and associated resuspension for a mine tailings pond in Ontario are presented and discussed. The results show that wind speeds greater than 8 m/s above water covers that are shallower than 1 m create waves of height greater than 10 cm and bottom shear stresses greater than 0.2 Pa. Under these conditions the critical shear stress of the mine tailings was exceeded, resulting in erosion and subsequent resuspension.Key words: mine tailings, water cover, wind-induced waves, resuspension, wind speed, shear stress.

scholarly journals Implications of sea-ice biogeochemistry for oceanic production and emissions of dimethyl sulfide in the Arctic

2017 ◽  
Vol 14 (12) ◽  
pp. 3129-3155 ◽  
Author(s):  
Hakase Hayashida ◽  
Nadja Steiner ◽  
Adam Monahan ◽  
Virginie Galindo ◽  
Martine Lizotte ◽  
...  
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Dimethyl Sulfide ◽  
Phytoplankton Bloom ◽  
Model Simulation ◽  
Field Measurements ◽  
Sulfur Cycle ◽  
The Arctic ◽  
Model Parameters ◽  
Ocean Ecosystem

Abstract. Sea ice represents an additional oceanic source of the climatically active gas dimethyl sulfide (DMS) for the Arctic atmosphere. To what extent this source contributes to the dynamics of summertime Arctic clouds is, however, not known due to scarcity of field measurements. In this study, we developed a coupled sea ice–ocean ecosystem–sulfur cycle model to investigate the potential impact of bottom-ice DMS and its precursor dimethylsulfoniopropionate (DMSP) on the oceanic production and emissions of DMS in the Arctic. The results of the 1-D model simulation were compared with field data collected during May and June of 2010 in Resolute Passage. Our results reproduced the accumulation of DMS and DMSP in the bottom ice during the development of an ice algal bloom. The release of these sulfur species took place predominantly during the earlier phase of the melt period, resulting in an increase of DMS and DMSP in the underlying water column prior to the onset of an under-ice phytoplankton bloom. Production and removal rates of processes considered in the model are analyzed to identify the processes dominating the budgets of DMS and DMSP both in the bottom ice and the underlying water column. When openings in the ice were taken into account, the simulated sea–air DMS flux during the melt period was dominated by episodic spikes of up to 8.1 µmol m−2 d−1. Further model simulations were conducted to assess the effects of the incorporation of sea-ice biogeochemistry on DMS production and emissions, as well as the sensitivity of our results to changes of uncertain model parameters of the sea-ice sulfur cycle. The results highlight the importance of taking into account both the sea-ice sulfur cycle and ecosystem in the flux estimates of oceanic DMS near the ice margins and identify key uncertainties in processes and rates that should be better constrained by new observations.

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

<p>The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.</p>

scholarly journals Using the LIST model to Estimate the Effects of Contact Tracing on COVID-19 Endemic Equilibria in England and its Regions

2020 ◽  
Author(s):  
Rosalyn J. Moran ◽  
Alexander J. Billig ◽  
Maell Cullen ◽  
Adeel Razi ◽  
Jean Daunizeau ◽  
...  
Keyword(s):  
Endemic Equilibrium ◽  
Contact Tracing ◽  
Model Parameters ◽  
Infection Rates ◽  
Stable States ◽  
Medium Term ◽  
The Stability ◽  
Lower Death Rate ◽  
The Impact ◽  
List Model

AbstractGovernments across Europe are preparing for the emergence from lockdown, in phases, to prevent a resurgence in cases of COVID-19. Along with social distancing (SD) measures, contact tracing – find, track, trace and isolate (FTTI) policies are also being implemented. Here, we investigate FTTI policies in terms of their impact on the endemic equilibrium. We used a generative model – the dynamic causal ‘Location’, ‘Infection’, ‘Symptom’ and ‘Testing’ (LIST) model to identify testing, tracing, and quarantine requirements. We optimised LIST model parameters based on time series of daily reported cases and deaths of COVID-19 in England— and based upon reported cases in the nine regions of England and in all 150 upper tier local authorities. Using these optimised parameters, we forecasted infection rates and the impact of FTTI for each area—national, regional, and local. Predicting data from early June 2020, we find that under conditions of medium-term immunity, a ‘40%’ FTTI policy (or greater), could reach a distinct endemic equilibrium that produces a significantly lower death rate and a decrease in ICU occupancy. Considering regions of England in isolation, some regions could substantially reduce death rates with 20% efficacy. We characterise the accompanying endemic equilibria in terms of dynamical stability, observing bifurcation patterns whereby relatively small increases in FTTI efficacy result in stable states with reduced overall morbidity and mortality. These analyses suggest that FTTI will not only save lives, even if only partially effective, and could underwrite the stability of any endemic steady-state we manage to attain.

scholarly journals SEIR Modeling of the Italian Epidemic of SARS-CoV-2 Using Computational Swarm Intelligence

2020 ◽  
Vol 17 (10) ◽  
pp. 3535 ◽  
Author(s):  
Alberto Godio ◽  
Francesca Pace ◽  
Andrea Vergnano
Keyword(s):  
Particle Swarm Optimization ◽  
Stochastic Approach ◽  
Model Parameters ◽  
Medium Term ◽  
Swarm Optimization ◽  
Community Mobility ◽  
Italian Regions ◽  
The World ◽  
Model Equations ◽  
Official Data

We applied a generalized SEIR epidemiological model to the recent SARS-CoV-2 outbreak in the world, with a focus on Italy and its Lombardy, Piedmont, and Veneto regions. We focused on the application of a stochastic approach in fitting the model parameters using a Particle Swarm Optimization (PSO) solver, to improve the reliability of predictions in the medium term (30 days). We analyzed the official data and the predicted evolution of the epidemic in the Italian regions, and we compared the results with the data and predictions of Spain and South Korea. We linked the model equations to the changes in people’s mobility, with reference to Google’s COVID-19 Community Mobility Reports. We discussed the effectiveness of policies taken by different regions and countries and how they have an impact on past and future infection scenarios.

Microvascular exchange and interstitial volume regulation in the rat: model validation

1988 ◽  
Vol 254 (2) ◽  
pp. H384-H399 ◽  
Author(s):  
J. L. Bert ◽  
B. D. Bowen ◽  
R. K. Reed
Keyword(s):  
Experimental Data ◽  
Osmotic Pressure ◽  
Plasma Proteins ◽  
Venous Pressure ◽  
Colloid Osmotic Pressure ◽  
Model Parameters ◽  
Transport Parameters ◽  
Interstitial Fluid Volume ◽  
Protein Tracers ◽  
Fitting Procedures

A dynamic mathematical model is formulated and used to describe the distribution and transport of fluid and plasma proteins between the circulation, interstitial space of skin and muscle, and the lymphatics in the rat. Two descriptions of transcapillary exchange are investigated: a homoporous "Starling model" and a heteroporous "plasma leak model." Parameters used in the two hypothetical transport mechanisms are determined based on statistical fitting procedures between simulation predictions and selected experimental data. These data consist of interstitial fluid volume and colloid osmotic pressure measurements as a function of venous pressure for muscle and interstitial colloid osmotic pressure vs. venous pressure for skin. The values determined for the transport parameters compare well with data in the literature. The fully determined model is used to simulate steady-state conditions of hypoproteinemia, overhydration, and dehydration, as well as the dynamic response to changes in venous pressure and intravascularly administered protein tracers. Comparisons between the simulation predictions and experimental data for these various perturbations are made. The plasma leak model appears to provide a better description of microvascular exchange.

scholarly journals Radiative Transfer Model parametrization for simulating the reflectance of meadow vegetation

2014 ◽  
Vol 18 (2) ◽  
pp. 5-9 ◽  
Author(s):  
Anna M. Jarocińska
Keyword(s):  
Radiative Transfer ◽  
Field Measurements ◽  
Radiative Transfer Model ◽  
Model Parameters ◽  
Transfer Model ◽  
Biophysical Parameters ◽  
Input Parameters ◽  
Vegetation Characteristics ◽  
Field Reflectance ◽  
Lower Water Content

Abstract Natural vegetation is complex and its reflectance is not easy to model. The aim of this study was to adjust the Radiative Transfer Model parameters for modelling the reflectance of heterogeneous meadows and evaluate its accuracy dependent on the vegetation characteristics. PROSAIL input parameters and reference spectra were collected during field measurements. Two different datasets were created: in the first, the input parameters were modelled using only field measurements; in the second, three input parameters were adjusted to minimize the differences between modelled and measured spectra. Reflectance was modelled using two datasets and then verified based on field reflectance using the RMSE. The average RMSE for the first dataset was equal to 0.1058, the second was 0.0362. The accuracy of the simulated spectra was analysed dependent on the value of the biophysical parameters. Better results were obtained for meadows with higher biomass value, greater LAI and lower water content.

Modeling the Densification of FeSi Sintered Magnetic Alloys

2012 ◽  
Vol 727-728 ◽  
pp. 175-180 ◽  
Author(s):  
José Adilson de Castro ◽  
Gilberto V. Concilio ◽  
Daniel Rodrigues ◽  
Livia S. Santomauro ◽  
Marcos Flavio de Campos
Keyword(s):  
Experimental Data ◽  
Grain Size ◽  
Sintering Temperature ◽  
Process Parameter ◽  
Model Parameters ◽  
Important Process ◽  
Sintering Process ◽  
Heating Rates ◽  
Magnetic Alloys ◽  
Sintered Alloys

An important process parameter in FeSi sintered alloys is the sintering temperature. If the sintering temperature can be reduced, the sintering process could be performed in less expensive furnaces. A densification model is here applied to experimental data. The model considers both grain size and density. After the model is applied to experimental data, the acquired model parameters allow the simulation of densification for other situations of temperature and heating rates. The model can be helpful to find suitable sintering temperatures in these alloys.

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