scholarly journals Mathematical modelling of solute transport in a heterogeneous aquifer

2021 ◽  
Author(s):  
◽  
James Phillip Dommisse
Keyword(s):  
Numerical Model ◽  
Solute Transport ◽  
Test Data ◽  
Hydraulic Properties ◽  
Numerical Models ◽  
Tracer Test ◽  
Transport Processes ◽  
Model Parameters ◽  
Transport Modelling ◽  
Predictive Uncertainty

<p>This study provides a contribution to the understanding of parsimony and predictive uncertainty in the context of groundwater solute transport modelling. The study is unique because the modelling was undertaken using tracer test data from a heterogeneous artificial aquifer whose structure was known to a very high level of detail. The aquifer structure was based on a ‘real life’ Canterbury Plains alluvial aquifer (in New Zealand).  Parsimonious principles were applied by starting with a simple analytical model that assumed homogeneity then progressively adding heterogeneity using numerical models with varying degrees of parameterisation complexity. The results show that increased complexity did not necessarily make the model better at replicating the tracer test data. For example, the outputs from a numerical model that represented heterogeneity using a zone based approach based on the recorded distribution of all 2,907 blocks that comprised the artificial aquifer was little different to a simple numerical model that adopted a homogenous distribution and included a single value of dispersion. Parameterisation of numerical models using ‘pilot points’ provided the most complex representation of heterogeneity and resulted in the best replication of the tracer test data. However, increasing model complexity had its disadvantages such as decreasing parameterisation uniqueness.  The contribution to predictive uncertainty from model parameters and observations was assessed using a linear approach based on Bayes theorem. This approach has been applied to other groundwater modelling studies, but not to solute transport modelling within Canterbury Plains alluvial aquifers or to an artificial aquifer. A unique finding was the reduction in predictive uncertainty along the groundwater flow path. This finding correlated well with the numerical model outputs which showed closer fits to the observation data near the end of the aquifer compared to those near the top of the aquifer where the tracer was injected.  Physical solute transport processes were identified and described as part of the modelling. These included the increase in dispersivity with travel distance and the spatial distribution of the aquifer hydraulic properties. Analytical modelling was a useful tool in identifying physical processes, aquifer characteristics and the variation in aquifer hydraulic properties both spatially and with depth.  An important finding was the value of undertaking multiple modelling approaches. This is because each approach has its own advantages and disadvantageous and by comparing the results of different approaches, the true facts about the aquifer system are made clearer.</p>

scholarly journals Mathematical modelling of solute transport in a heterogeneous aquifer

2021 ◽  
Author(s):  
◽  
James Phillip Dommisse
Keyword(s):  
Numerical Model ◽  
Solute Transport ◽  
Test Data ◽  
Hydraulic Properties ◽  
Numerical Models ◽  
Tracer Test ◽  
Transport Processes ◽  
Model Parameters ◽  
Transport Modelling ◽  
Predictive Uncertainty

<p>This study provides a contribution to the understanding of parsimony and predictive uncertainty in the context of groundwater solute transport modelling. The study is unique because the modelling was undertaken using tracer test data from a heterogeneous artificial aquifer whose structure was known to a very high level of detail. The aquifer structure was based on a ‘real life’ Canterbury Plains alluvial aquifer (in New Zealand).  Parsimonious principles were applied by starting with a simple analytical model that assumed homogeneity then progressively adding heterogeneity using numerical models with varying degrees of parameterisation complexity. The results show that increased complexity did not necessarily make the model better at replicating the tracer test data. For example, the outputs from a numerical model that represented heterogeneity using a zone based approach based on the recorded distribution of all 2,907 blocks that comprised the artificial aquifer was little different to a simple numerical model that adopted a homogenous distribution and included a single value of dispersion. Parameterisation of numerical models using ‘pilot points’ provided the most complex representation of heterogeneity and resulted in the best replication of the tracer test data. However, increasing model complexity had its disadvantages such as decreasing parameterisation uniqueness.  The contribution to predictive uncertainty from model parameters and observations was assessed using a linear approach based on Bayes theorem. This approach has been applied to other groundwater modelling studies, but not to solute transport modelling within Canterbury Plains alluvial aquifers or to an artificial aquifer. A unique finding was the reduction in predictive uncertainty along the groundwater flow path. This finding correlated well with the numerical model outputs which showed closer fits to the observation data near the end of the aquifer compared to those near the top of the aquifer where the tracer was injected.  Physical solute transport processes were identified and described as part of the modelling. These included the increase in dispersivity with travel distance and the spatial distribution of the aquifer hydraulic properties. Analytical modelling was a useful tool in identifying physical processes, aquifer characteristics and the variation in aquifer hydraulic properties both spatially and with depth.  An important finding was the value of undertaking multiple modelling approaches. This is because each approach has its own advantages and disadvantageous and by comparing the results of different approaches, the true facts about the aquifer system are made clearer.</p>

scholarly journals Estimation of Coastal Currents Using a Soft Computing Method: A Case Study in Galway Bay, Ireland

2019 ◽  
Vol 7 (5) ◽  
pp. 157 ◽  
Author(s):  
Lei Ren ◽  
Jianming Miao ◽  
Yulong Li ◽  
Xiangxin Luo ◽  
Junxue Li ◽  
...  
Keyword(s):  
Numerical Model ◽  
Soft Computing ◽  
Initial Conditions ◽  
Numerical Models ◽  
Surface Velocity ◽  
Training Dataset ◽  
Model Parameters ◽  
Surface Currents ◽  
Coastal Currents ◽  
Computing Models

In order to obtain forward states of coastal currents, numerical models are a commonly used approach. However, the accurate definition of initial conditions, boundary conditions and other model parameters are challenging. In this paper, a novel application of a soft computing approach, random forests (RF), was adopted to estimate surface currents for three analysis points in Galway Bay, Ireland. Outputs from a numerical model and observations from a high frequency radar system were used as inputs to develop soft computing models. The input variable structure of soft computing models was examined in detail through sensitivity experiments. High correlation of surface currents between predictions from RF models and radar data indicated that the RF algorithm is a most promising means of generating satisfactory surface currents over a long prediction period. Furthermore, training dataset lengths were examined to investigate influences on prediction accuracy. The largest improvement for zonal and meridional surface velocity components over a 59-h forecasting period was 14% and 37% of root mean square error (RMSE) values separately. Results indicate that the combination of RF models with a numerical model can significantly improve forecasting accuracy for surface currents, especially for the meridional surface velocity component.

Changes of Peritoneal Transport Parameters with Time on Dialysis: Assessment with Sequential Peritoneal Equilibration Test

2017 ◽  
Vol 40 (11) ◽  
pp. 595-601 ◽  
Author(s):  
Jacek Waniewski ◽  
Stefan Antosiewicz ◽  
Daniel Baczynski ◽  
Jan Poleszczuk ◽  
Mauro Pietribiasi ◽  
...  
Keyword(s):  
Solute Transport ◽  
Fluid Transport ◽  
Transport Processes ◽  
Model Parameters ◽  
Hydraulic Permeability ◽  
Transport Parameters ◽  
Peritoneal Equilibration Test ◽  
Transport Barrier ◽  
Pore Model ◽  
Peritoneal Transport

Background Sequential peritoneal equilibration test (sPET) is based on the consecutive performance of the peritoneal equilibration test (PET, 4-hour, glucose 2.27%) and the mini-PET (1-hour, glucose 3.86%), and the estimation of peritoneal transport parameters with the 2-pore model. It enables the assessment of the functional transport barrier for fluid and small solutes. The objective of this study was to check whether the estimated model parameters can serve as better and earlier indicators of the changes in the peritoneal transport characteristics than directly measured transport indices that depend on several transport processes. Methods 17 patients were examined using sPET twice with the interval of about 8 months (230 ± 60 days). Results There was no difference between the observational parameters measured in the 2 examinations. The indices for solute transport, but not net UF, were well correlated between the examinations. Among the estimated parameters, a significant decrease between the 2 examinations was found only for hydraulic permeability LpS, and osmotic conductance for glucose, whereas the other parameters remained unchanged. These fluid transport parameters did not correlate with D/P for creatinine, although the decrease in LpS values between the examinations was observed mostly for patients with low D/P for creatinine. Conclusions We conclude that changes in fluid transport parameters, hydraulic permeability and osmotic conductance for glucose, as assessed by the pore model, may precede the changes in small solute transport. The systematic assessment of fluid transport status needs specific clinical and mathematical tools beside the standard PET tests.

scholarly journals A numerical model of the renal distal tubule

1999 ◽  
Vol 276 (6) ◽  
pp. F931-F951 ◽  
Author(s):  
Hangil Chang ◽  
Toshiro Fujita
Keyword(s):  
Numerical Model ◽  
Solute Transport ◽  
Basolateral Membrane ◽  
Kinetic Equations ◽  
Distal Tubule ◽  
K Channel ◽  
Na Channel ◽  
Model Parameters ◽  
Cl Channel ◽  
Water And Solute Transport

A numerical model of the rat distal tubule was developed to simulate water and solute transport in this nephron segment. This model incorporates the following: 1) Na-Cl cotransporter, K-Cl cotransporter, Na channel, K channel, and Cl channel in the luminal membrane; 2) Na-K-ATPase, K channel, and Cl channel in the basolateral membrane; and 3) conductances for Na, K, and Cl in the paracellular pathway. Transport rates were calculated using kinetic equations. Axial heterogeneity was represented by partitioning the model into two subsegments with different sets of model parameters. Model equations derived from the principles of mass conservation and electrical neutrality were solved numerically. Values of the model parameters were adjusted to minimize a penalty function that was devised to quantify the difference between model predictions and experimental results. The developed model could simulate the water and solute transport of the distal tubule in the normal state, as well as in conditions including thiazide or amiloride application and various levels of sodium load and tubular flow rate.

Sampling design for groundwater solute transport: Tests of methods and analysis of Cape Cod tracer test data

1991 ◽  
Vol 27 (5) ◽  
pp. 925-949 ◽  
Author(s):  
Debra S. Knopman ◽  
Clifford I. Voss ◽  
Stephen P. Garabedian
Keyword(s):  
Solute Transport ◽  
Test Data ◽  
Sampling Design ◽  
Tracer Test ◽  
Cape Cod

scholarly journals Inverse modelling for predicting both water and nitrate movement in a structured-clay soil (Red Ferrosol)

PeerJ ◽  
2019 ◽  
Vol 6 ◽  
pp. e6002 ◽  
Author(s):  
James M. Kirkham ◽  
Christopher J. Smith ◽  
Richard B. Doyle ◽  
Philip H. Brown
Keyword(s):  
Adsorption Isotherm ◽  
Solute Transport ◽  
Water Flow ◽  
Hydraulic Properties ◽  
Transport Processes ◽  
Inverse Modelling ◽  
Diffusion Experiment ◽  
Soil Hydraulic Properties ◽  
Soil Columns ◽  
Soil Hydraulic

Soil physical parameter calculation by inverse modelling provides an indirect way of estimating the unsaturated hydraulic properties of soils. However many measurements are needed to provide sufficient data to determine unknown parameters. The objective of this research was to assess the use of unsaturated water flow and solute transport experiments, in horizontal packed soil columns, to estimate the parameters that govern water flow and solute transport. The derived parameters are then used to predict water infiltration and solute migration in a repacked soil wedge. Horizontal columns packed with Red Ferrosol were used in a nitrate diffusion experiment to estimate either three or six parameters of the van Genuchten–Mualem equation while keeping residual and saturated water content, and saturated hydraulic conductivity fixed to independently measured values. These parameters were calculated using the inverse optimisation routines in Hydrus 1D. Nitrate concentrations measured along the horizontal soil columns were used to independently determine the Langmuir adsorption isotherm. The soil hydraulic properties described by the van Genuchten–Mualem equation, and the NO3–adsorption isotherm, were then used to predict water and NO3–distributions from a point-source in two 3D flow scenarios. The use of horizontal columns of repacked soil and inverse modelling to quantify the soil water retention curve was found to be a simple and effective method for determining soil hydraulic properties of Red Ferrosols. These generated parameters supported subsequent testing of interactive flow and reactive transport processes under dynamic flow conditions.

scholarly journals Numerical Modeling of Local Scour at the Junction of Open Channels in Flow3D Numerical Model

2016 ◽  
Vol 2 (9) ◽  
pp. 474-483 ◽  
Author(s):  
Behnam Shamohamadi ◽  
Ali Mehboudi
Keyword(s):  
Numerical Model ◽  
Numerical Modelling ◽  
Relative Error ◽  
Hydraulic Properties ◽  
Numerical Models ◽  
Local Scour ◽  
Physical Models ◽  
Maximum Relative Error ◽  
Flow Properties ◽  
Level Profile

At the junction of channels, the two corresponding flows of the main and submain channels are diverted from their main alignment and the form and the flow properties change at the junction. Changes in water level profile and depth of flow, velocity distribution, stagnation zone, constriction of public channel, energy loss and also formation of hydraulic jump are among the most important hydraulic variables in this location. For accurate recognition of hydraulic properties of flow and local scour at the junction of channels, physical models are made and constructed. Setting up a physical model requires many conditions and high costs which sometimes are not justifiable, hence appropriate numerical models could be proposed for such options. In this research using Flow3D numerical model, the numerical modelling of the flow has been performed in 3D form utilizing the available laboratory information which is calibrated and validated and accuracy of the numerical modelling, and the corresponding relative error are determined. The calibration and validation of the numerical model results demonstrate that the maximum relative error of the numerical model when simulating for maximum values of scour depth at the flow junction is equal to 8.2%. Also using the numerical model it was found that with passage of time in numerical model, from .....

scholarly journals Uncertain Parameter Numerical Model Updating According to Variable Modal Test Data in Application of Large Composite Fuselage Panel

2010 ◽  
Vol 17 (4-5) ◽  
pp. 445-459 ◽  
Author(s):  
Marcin Luczak ◽  
Antonio Vecchio ◽  
Bart Peeters ◽  
Ludo Gielen ◽  
Herman Van der Auweraer
Keyword(s):  
Numerical Model ◽  
Test Data ◽  
Composite Structures ◽  
Model Updating ◽  
Deterministic Model ◽  
Dynamic Properties ◽  
Dynamic Strain ◽  
Stochastic Methods ◽  
Model Parameters ◽  
Structural Dynamic

This paper presents a novel approach in the field of experimental and numerical investigation of mechanical properties of composite structures. It takes into account test data variability resulting from structural dynamic properties measurement and uses them to quantify uncertainties in model parameters updating. The main goal of the conducted research is to investigate the dynamic properties of fibre reinforced composite structures. Non-destructive experimental and numerical simulation methods are used hereto. In the experimental part, different test configurations were taken into account. The excitation was performed by means of random and harmonic, single and multi point stimuli while the response measurement was done through contact and non-contact acceleration, velocity and dynamic strain sensing. The test results are applied in two ways: for the structural identification of the object and for non-deterministic updating of the numerical model according to a range of experimental models obtained from test. The sources of the test data variabilities were related to the excitation and measurement technique applied for the investigated object. Non – deterministic model updating and verification & validation included uncertainties of its parameters by means of interval and stochastic methods. A number of variable test modal models were statistically assessed to investigate impact of variability source onto modal model parameters. The presented research was conducted in the context of the FP6 Marie Curie project UNVICO-2.

scholarly journals Aeolian Sediment Transport Integration in General Stratigraphic Forward Modeling

2011 ◽  
Vol 2011 ◽  
pp. 1-12
Author(s):  
T. Salles ◽  
C. Griffiths ◽  
C. Dyt
Keyword(s):  
Sediment Transport ◽  
Numerical Model ◽  
Transport Model ◽  
Numerical Models ◽  
Three Dimensional ◽  
Transport Processes ◽  
Aeolian Deposits ◽  
Geological Processes ◽  
Wide Range ◽  
Mixed Soils

A large number of numerical models have been developed to simulate the physical processes involved in saltation, and, recently to investigate the interaction between soil vegetation cover and aeolian transport. These models are generally constrained to saltation of monodisperse particles while natural saltation occurs over mixed soils. We present a three-dimensional numerical model of steady-state saltation that can simulate aeolian erosion, transport and deposition for unvegetated mixed soils. Our model simulates the motion of saltating particles using a cellular automata algorithm. A simple set of rules is used and takes into account an erosion formula, a transport model, a wind exposition function, and an avalanching process. The model is coupled to the stratigraphic forward model Sedsim that accounts for a larger number of geological processes. The numerical model predicts a wide range of typical dune shapes, which have qualitative correspondence to real systems. The model reproduces the internal structure and composition of the resulting aeolian deposits. It shows the complex formation of dune systems with cross-bedding strata development, bounding surfaces overlaid by fine sediment and inverse grading deposits. We aim to use it to simulate the complex interactions between different sediment transport processes and their resulting geological morphologies.

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