Steady and unsteady Poisson and Stokes equations are solved using mesh dependent Finite Element M... more Steady and unsteady Poisson and Stokes equations are solved using mesh dependent Finite Element Method and meshless Radial Basis Function Collocation Method to compare the performances of these two numerical techniques across several criteria. The accuracy of Radial Basis Function Collocation Method with multiquadrics is enhanced by implementing a shape parameter optimization algorithm. For the time-dependent problems, time discretization is conducted using Backward Euler Method. The performances are assessed over the accuracy, runtime, condition number, and ease of implementation criteria. Three kinds of errors were calculated; least square error, root mean square error and maximum relative error. To calculate the least square error while using meshless Radial Basis Function Collocation Method, a novel technique is implemented. Imaginary numerical solution surfaces are created and then the volume between those imaginary surfaces and the analytic solution surfaces is calculated, ena...
The stream function-vorticity formulation of the equations governing the two dimensional, incompr... more The stream function-vorticity formulation of the equations governing the two dimensional, incompressible flow past an impulsively started ellipse are integrated numerically. The periodic coordinate of the flow variables is expanded in truncated Fourier series while the remaining spatial coordinate is discretized using finite difference schemes. The Fourier series expansions lead to analytic formulation of the spatial dependence of the stream function coefficients and to an integral relation used for the wall vorticity determination. The vorticity transport equation yields the time derivative formulation of the vorticity coefficient used in the time stepping procedure. Fast algorithms are used to perform the convolutions arising from the convective terms. Second order accuracy is achieved for time discretization and third order accuracy for the spatial discretization. An asymmetric flow condition past an ellipse at an angle of attack reveals the patterns involved in the Kutta condition establishment and clarifies the correlation existing between the flow patterns in the vicinity of the cylinder and the extrema of the lift coefficient. Moderate Reynolds number simulations reveal the patterns of time dependent complex flow configurations existing in the vicinity of the ellipse surface
ABSTRACT Municipal waste landfills represent a viable and quite commonly used method for domestic... more ABSTRACT Municipal waste landfills represent a viable and quite commonly used method for domestic waste disposal even though the method has been used for centuries. Municipal waste landfills, at the same time, pose potentially adverse environmental impacts that need to be considered during the site selection process, landfill design, operational and post closure phases. An Environmental Impact Assessment (EIA) study represents an effective tool built into the legislative process of many countries and institutions that can be used to identify potential adverse effects on human health, environment impacts and ecologic risks. The decision makers are able to review all the necessary data on potential impacts prior to project approval. In this manner appropriate remedial measures can be identified and implemented prior to the project start-up.
Advances in Groundwater Pollution Control and Remediation, 1996
Deep well injection operations represent one of the available methods of waste disposal. Approxim... more Deep well injection operations represent one of the available methods of waste disposal. Approximately 14 million tons of liquid wastes in United States were injected into the subsurface in 1988 [Hanson, 1989]; the majority of the hazardous waste injection wells were located along the Gulf Coast and near the Great Lakes. The location of these wells often coincided with areas where oil and gas related explorations had been performed; the exploration efforts provided abundant data on the subsurface formations which were found to be environmentally safe for injection of wastes. The largest user of hazardous waste injection wells in the United States was noted to be the chemical industry [U.S.EPA, 1985]. Deep well injection programs are used in several countries including Canada and Greece. The environmental regulations for hazardous wastes which are presently being drafted in Turkey envision the use of deep well injection programs.
Flow leakage through abandoned wells and improperly plugged boreholes drilled between hydrogeolog... more Flow leakage through abandoned wells and improperly plugged boreholes drilled between hydrogeologically separated water‐bearing zones represent potential pathways of contamination. The present study provides an analytical evaluation of the transient flow rate through these artificial conduits and the resulting hydraulic head distributions when (1) artificial gradients are created by an injection well operating in one of the aquifers or (2) natural hydraulic head differences are present between two confined aquifers. The analysis is conducted by solving the groundwater flow equations in the confined aquifers that are coupled by the flow through the well or borehole. A case study was investigated involving contamination leakage through abandoned wells and improperly plugged boreholes caused by the operation of deep waste injection wells.
Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer ... more Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer hydraulic properties. Numerous researches have been conducted to predict the effects of aquifer heterogeneity on the groundwater levels during pumping tests. The objectives of the present work were as follows: (1) to predict drawdown conditions and to estimate aquifer properties during pumping tests undertaken in radially symmetric heterogeneous aquifers, and (2) to identify a method for assessing the transmissivity field along the radial coordinate in radially symmetric and fully heterogeneous transmissivity fields. The first objective was achieved by expanding an existing analytical drawdown formulation that was valid for a radially symmetric confined aquifer with two concentric zones around the pumping well to an N concentric zone confined aquifer having a constant transmissivity value within each zone. The formulation was evaluated for aquifers with three and four concentric zones to...
Abstract A new analysis technique has been proposed for interpreting transient step-drawdown test... more Abstract A new analysis technique has been proposed for interpreting transient step-drawdown test data. The pro-posed method is based on taking the derivative of the drawdown with respect to time for the entire pumping test period to eliminate the time-independent well-loss ...
Recent interest in ground‐water contamination problems has led to a renewed interest in the devel... more Recent interest in ground‐water contamination problems has led to a renewed interest in the development of accurate procedures for the analysis of in situ permeability tests. The present study involves the derivation of analytical procedures for slug tests and constant head tests performed in wells with casings open at the bottom and installed flush with the upper confining boundary of a finite‐depth, anisotropic, homogeneous aquifer; the analysis takes into account the effects of a finite‐thickness skin located at the casing bottom. The Laplace transform is used on the governing ground‐water flow equations to derive the transform of time‐dependent water levels measured in the casing. The expression is numerically inverted back into the real time domain to obtain (1) a set of dimensionless type curves for analyzing slug test data, and (2) a relation between the inflow rate, the head maintained in the well, the hydraulic conductivity, and a shape factor expression for the analysis of...
ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heter... more ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heterogeneous solute dispersive characteristics and/or media hydraulic properties. A radial basis function collocation method (RBFCM)-based numerical method was developed in order to investigate the ability of RBFCM to accurately portray solute transport phenomena under heterogeneous conditions. Simulations were performed for 1-D and 2-D transport scenarios in which scale-dependent dispersivity fields were taken into consideration and compared with available analytical solutions. Different radial basis functions (RBFs) were employed for assessing the sensitivity of the present method on the selected RBFs. The simulation results were also compared with the results of MT3DMS which is a modular three-dimensional transport model with alternative solution schemes including the method of characteristics, the implicit central finite difference and the third order total variation diminishing finite volume. The proposed model was also used to simulate a real case condition where solute transport through a two-layer soil medium had been investigated experimentally. The results showed that RBFCM represented a powerful tool for predicting the solute transport occurrence under heterogeneous conditions with high accuracy.
ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heter... more ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heterogeneous solute dispersive characteristics and/or media hydraulic properties. A radial basis function collocation method (RBFCM)-based numerical method was developed in order to investigate the ability of RBFCM to accurately portray solute transport phenomena under heterogeneous conditions. Simulations were performed for 1-D and 2-D transport scenarios in which scale-dependent dispersivity fields were taken into consideration and compared with available analytical solutions. Different radial basis functions (RBFs) were employed for assessing the sensitivity of the present method on the selected RBFs. The simulation results were also compared with the results of MT3DMS which is a modular three-dimensional transport model with alternative solution schemes including the method of characteristics, the implicit central finite difference and the third order total variation diminishing finite volume. The proposed model was also used to simulate a real case condition where solute transport through a two-layer soil medium had been investigated experimentally. The results showed that RBFCM represented a powerful tool for predicting the solute transport occurrence under heterogeneous conditions with high accuracy.
Steady and unsteady Poisson and Stokes equations are solved using mesh dependent Finite Element M... more Steady and unsteady Poisson and Stokes equations are solved using mesh dependent Finite Element Method and meshless Radial Basis Function Collocation Method to compare the performances of these two numerical techniques across several criteria. The accuracy of Radial Basis Function Collocation Method with multiquadrics is enhanced by implementing a shape parameter optimization algorithm. For the time-dependent problems, time discretization is conducted using Backward Euler Method. The performances are assessed over the accuracy, runtime, condition number, and ease of implementation criteria. Three kinds of errors were calculated; least square error, root mean square error and maximum relative error. To calculate the least square error while using meshless Radial Basis Function Collocation Method, a novel technique is implemented. Imaginary numerical solution surfaces are created and then the volume between those imaginary surfaces and the analytic solution surfaces is calculated, ena...
The stream function-vorticity formulation of the equations governing the two dimensional, incompr... more The stream function-vorticity formulation of the equations governing the two dimensional, incompressible flow past an impulsively started ellipse are integrated numerically. The periodic coordinate of the flow variables is expanded in truncated Fourier series while the remaining spatial coordinate is discretized using finite difference schemes. The Fourier series expansions lead to analytic formulation of the spatial dependence of the stream function coefficients and to an integral relation used for the wall vorticity determination. The vorticity transport equation yields the time derivative formulation of the vorticity coefficient used in the time stepping procedure. Fast algorithms are used to perform the convolutions arising from the convective terms. Second order accuracy is achieved for time discretization and third order accuracy for the spatial discretization. An asymmetric flow condition past an ellipse at an angle of attack reveals the patterns involved in the Kutta condition establishment and clarifies the correlation existing between the flow patterns in the vicinity of the cylinder and the extrema of the lift coefficient. Moderate Reynolds number simulations reveal the patterns of time dependent complex flow configurations existing in the vicinity of the ellipse surface
ABSTRACT Municipal waste landfills represent a viable and quite commonly used method for domestic... more ABSTRACT Municipal waste landfills represent a viable and quite commonly used method for domestic waste disposal even though the method has been used for centuries. Municipal waste landfills, at the same time, pose potentially adverse environmental impacts that need to be considered during the site selection process, landfill design, operational and post closure phases. An Environmental Impact Assessment (EIA) study represents an effective tool built into the legislative process of many countries and institutions that can be used to identify potential adverse effects on human health, environment impacts and ecologic risks. The decision makers are able to review all the necessary data on potential impacts prior to project approval. In this manner appropriate remedial measures can be identified and implemented prior to the project start-up.
Advances in Groundwater Pollution Control and Remediation, 1996
Deep well injection operations represent one of the available methods of waste disposal. Approxim... more Deep well injection operations represent one of the available methods of waste disposal. Approximately 14 million tons of liquid wastes in United States were injected into the subsurface in 1988 [Hanson, 1989]; the majority of the hazardous waste injection wells were located along the Gulf Coast and near the Great Lakes. The location of these wells often coincided with areas where oil and gas related explorations had been performed; the exploration efforts provided abundant data on the subsurface formations which were found to be environmentally safe for injection of wastes. The largest user of hazardous waste injection wells in the United States was noted to be the chemical industry [U.S.EPA, 1985]. Deep well injection programs are used in several countries including Canada and Greece. The environmental regulations for hazardous wastes which are presently being drafted in Turkey envision the use of deep well injection programs.
Flow leakage through abandoned wells and improperly plugged boreholes drilled between hydrogeolog... more Flow leakage through abandoned wells and improperly plugged boreholes drilled between hydrogeologically separated water‐bearing zones represent potential pathways of contamination. The present study provides an analytical evaluation of the transient flow rate through these artificial conduits and the resulting hydraulic head distributions when (1) artificial gradients are created by an injection well operating in one of the aquifers or (2) natural hydraulic head differences are present between two confined aquifers. The analysis is conducted by solving the groundwater flow equations in the confined aquifers that are coupled by the flow through the well or borehole. A case study was investigated involving contamination leakage through abandoned wells and improperly plugged boreholes caused by the operation of deep waste injection wells.
Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer ... more Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer hydraulic properties. Numerous researches have been conducted to predict the effects of aquifer heterogeneity on the groundwater levels during pumping tests. The objectives of the present work were as follows: (1) to predict drawdown conditions and to estimate aquifer properties during pumping tests undertaken in radially symmetric heterogeneous aquifers, and (2) to identify a method for assessing the transmissivity field along the radial coordinate in radially symmetric and fully heterogeneous transmissivity fields. The first objective was achieved by expanding an existing analytical drawdown formulation that was valid for a radially symmetric confined aquifer with two concentric zones around the pumping well to an N concentric zone confined aquifer having a constant transmissivity value within each zone. The formulation was evaluated for aquifers with three and four concentric zones to...
Abstract A new analysis technique has been proposed for interpreting transient step-drawdown test... more Abstract A new analysis technique has been proposed for interpreting transient step-drawdown test data. The pro-posed method is based on taking the derivative of the drawdown with respect to time for the entire pumping test period to eliminate the time-independent well-loss ...
Recent interest in ground‐water contamination problems has led to a renewed interest in the devel... more Recent interest in ground‐water contamination problems has led to a renewed interest in the development of accurate procedures for the analysis of in situ permeability tests. The present study involves the derivation of analytical procedures for slug tests and constant head tests performed in wells with casings open at the bottom and installed flush with the upper confining boundary of a finite‐depth, anisotropic, homogeneous aquifer; the analysis takes into account the effects of a finite‐thickness skin located at the casing bottom. The Laplace transform is used on the governing ground‐water flow equations to derive the transform of time‐dependent water levels measured in the casing. The expression is numerically inverted back into the real time domain to obtain (1) a set of dimensionless type curves for analyzing slug test data, and (2) a relation between the inflow rate, the head maintained in the well, the hydraulic conductivity, and a shape factor expression for the analysis of...
ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heter... more ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heterogeneous solute dispersive characteristics and/or media hydraulic properties. A radial basis function collocation method (RBFCM)-based numerical method was developed in order to investigate the ability of RBFCM to accurately portray solute transport phenomena under heterogeneous conditions. Simulations were performed for 1-D and 2-D transport scenarios in which scale-dependent dispersivity fields were taken into consideration and compared with available analytical solutions. Different radial basis functions (RBFs) were employed for assessing the sensitivity of the present method on the selected RBFs. The simulation results were also compared with the results of MT3DMS which is a modular three-dimensional transport model with alternative solution schemes including the method of characteristics, the implicit central finite difference and the third order total variation diminishing finite volume. The proposed model was also used to simulate a real case condition where solute transport through a two-layer soil medium had been investigated experimentally. The results showed that RBFCM represented a powerful tool for predicting the solute transport occurrence under heterogeneous conditions with high accuracy.
ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heter... more ABSTRACT Groundwater solute transport phenomena typically occur in water-bearing zones with heterogeneous solute dispersive characteristics and/or media hydraulic properties. A radial basis function collocation method (RBFCM)-based numerical method was developed in order to investigate the ability of RBFCM to accurately portray solute transport phenomena under heterogeneous conditions. Simulations were performed for 1-D and 2-D transport scenarios in which scale-dependent dispersivity fields were taken into consideration and compared with available analytical solutions. Different radial basis functions (RBFs) were employed for assessing the sensitivity of the present method on the selected RBFs. The simulation results were also compared with the results of MT3DMS which is a modular three-dimensional transport model with alternative solution schemes including the method of characteristics, the implicit central finite difference and the third order total variation diminishing finite volume. The proposed model was also used to simulate a real case condition where solute transport through a two-layer soil medium had been investigated experimentally. The results showed that RBFCM represented a powerful tool for predicting the solute transport occurrence under heterogeneous conditions with high accuracy.
Uploads
Papers by Cem Avci