Yazar "Çiftçi, Emin" seçeneğine göre listele

Listeleniyor 1 - 4 / 4
  • Küçük Resim Yok
    Yayın
    Cessation time approach incorporating parametric and non-parametric machine-learning algorithms for recovery test data
    (Taylor & Francis Ltd, 2023) Şahin, A. Ufuk; Çiftçi, Emin
    In this study we propose a new method called the cessation time approach (CTA) for interpreting recovery tests in confined aquifers, which is based on the Theis solution. The CTA method involves selecting a residual drawdown measurement from the recovery phase and linking it to its dimensionless counterpart through simple algebraic steps. This approach is then incorporated with a regression model to estimate aquifer parameters. The performance of several parametric polynomial and non-parametric machine learning regression models was investigated using various datasets. Results show that CTA with third-order multivariable polynomials produced highly accurate parameter estimates with a normalized root mean squared error (NRMSE) within 0.5% for a field dataset. Among the machine learning algorithms tested, the radial basis function and Gaussian process regression achieved the highest accuracy with NRMSEs of 0.6%. We conclude that CTA can be a viable interpretation tool for recovery tests due to its accuracy and simplicity.
  • Küçük Resim Yok
    Yayın
    Interpretation of Step-Drawdown Tests with the Differential Evolution Approach
    (Asce-Amer Soc Civil Engineers, 2022) Çiftçi, Emin; Şahin, A. Ufuk
    A step-drawdown test is a common hydrogeological investigation tool employed for identifying the hydraulic characteristics of an aquifer as well as assessing the efficiency of the pumping conditions. Several graphical and optimization-based solution techniques have been devised for analyzing data sets obtained from step-drawdown tests to retrieve aquifer and well loss parameters. This study aimed to introduce the use of a differential evolution (DE) algorithm as an alternative and practical option for interpretation of step-drawdown tests conducted in confined aquifers. The proposed estimation procedure was tested for a large number of synthetically generated noise-free and noisy data sets for evaluating its estimation performance. The DE search method exhibited superior accuracy with considerably higher convergence speed when compared with other competitive and widely used population-based algorithms. Sensitivity analysis was performed to explore the capability of the method in estimating each investigated variable. The DE algorithm was implemented for analyzing a real field data set as well, and it was able to produce parameter estimation results consistent with those reported in previous studies. As demonstrated in this study, the DE search method can be an eligible algorithm for solving inverse problems in the field of hydrogeology, regarding its accuracy, high convergence speed, robustness, and simplicity in coding.
  • Küçük Resim Yok
    Yayın
    A new method for aquifer system identification and parameter estimation
    (Wiley, 2013) Avcı, Cem B; Şahin, A. Ufuk; Çiftçi, Emin
    The standard practice for assessing aquifer parameters is to match groundwater drawdown data obtained during pumping tests against theoretical well function curves specific to the aquifer system being tested. The shape of the curve derived from the logarithmic time derivative of the drawdown data is also very frequently used as a diagnostic tool to identify the aquifer system in which the pumping test is being conducted. The present study investigates the incremental area method (IAM) to serve as an alternative diagnostic tool for the aquifer system identification as well as a supplement to the aquifer parameter estimation procedure. The IAM based diagnostic curves for ideal confined, leaky, bounded and unconfined aquifers have been derived as part of this study, and individual features of the plots have been identified. These features were noted to be unique to each aquifer setting, which could be used for rapid evaluation of the aquifer system. The effectiveness of the IAM methodology was investigated by analyzing field data for various aquifer settings including leaky, unconfined, bounded and heterogeneous conditions. The results showed that the proposed approach is a viable method for use as a diagnostic tool to identify the aquifer system characteristics as well as to support the estimation of the hydraulic parameters obtained from standard curve matching procedures
  • Küçük Resim Yok
    Yayın
    Regression-Based Interpretation Method for Confined Aquifer Pumping Tests
    (Asce-Amer Soc Civil Engineers, 2023) Çiftçi, Emin; Şahin, A. Ufuk
    The constant-discharge pumping test is a widely used aquifer characterization tool for estimating hydrogeological parameters. Various graphical and numerical solution techniques have been devised for interpretation of pumping test results. This study proposes an alternative regression-based solution approach for analyzing pumping tests conducted in nonleaky, confined aquifers. A regression model was developed by making use of the similarity solution that describes the temporal drawdown behavior at a monitoring well within a pumping period. The field curve obtained from a pumping test (drawdown versus time data) and the theoretical type curve (dimensionless drawdown versus dimensionless time) exhibit identical behavior in logarithmic scale. Correspondingly, based on the equivalence of the area above these two curves, the proposed regression equation establishes a link between a selected drawdown value and its dimensionless counterpart. Once this drawdown value is associated with the corresponding dimensionless drawdown, the explored aquifer transmissivity and storativity can be retrieved easily with the similarity solution. The proposed fit equation enables users to retrieve hydrogeological parameters effortlessly by eradicating the difficulties encountered while implementing conventional graphical or optimization-based methods. The method was tested for a large number of hypothetical noise-free and noise-perturbed time drawdown data sets, each synthesized with different aquifer parameters within a wide range, and in all these attempts the proposed algorithm achieved providing highly accurate parameter estimates. In addition, two published test cases were employed to assess the estimation performance of the method in comparison with the existing techniques. The developed solution scheme was revealed to yield results in very good agreement with those reported in previous works. Considering the accuracy of the method and the ease of its implementation, the proposed approach can be a practical tool for analyzing constant-discharge tests performed in confined aquifers.