Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Citation - Scopus: 4Betonarme Çerçeve Yapıların Olasılıklı Sismik Analizi(Gazi Üniversitesi, 2006) Korkmaz, Armağan; Aktaş, EnginBetonarme çerçeve yapıların sismik davranışlarının belirlenmesinde, analizlere olasılıklı ifadelerin dahil edilmesi, sismik davranışın daha gerçekçi tanımlanmasına yardımıcı olacaktır. Çalışmada betonarme çerçeve yapıların olasılıklı sismik analizlerinin gerçekleştirilmesi amaçlanmış, bu amaçla örnek betonarme çerçeve yapılar ele alınmıştır. Bu betonarme çerçeve yapılar için öteleme analizleri DRAIN 2D programı ile yapılmıştır. Öteleme analizlerinin ardından zaman tanım alanında dinamik analizler gerçekleştirilmiştir. Öteleme analizleri, zaman tanım alanında dinamik analiz sonuçları ile karşılaştırılmıştır. Bu karşılaştırmanın ardından kırılganlık analizleri yapılmıştır. Betonarme çerçeve yapıların olasılıklı sismik davranışını ortaya koymak amacı ile kırılganlık analizleri ile kırılganlık eğrileri elde edilmiştir. Çalışmanın ana amacı, öteleme analizleri ile zaman tanım alanında dinamik analizlerin karşılaştırılması sonucu, daha gerçekçi bir sismik davranış tanımlama ihtiyacının olduğunu göstermek ve kırılganlık analizleri ile, sismik davranışın olasılıklı olarak daha gerçekçi bir şekilde ifadesini sağlayabilmektir.Article Citation - WoS: 15Citation - Scopus: 17Genetic Algorithm-Based Discharge Estimation at Sites Receiving Lateral Inflows(American Society of Civil Engineers (ASCE), 2009) Tayfur, Gökmen; Barbetta, Silvia; Moramarco, TommasoThe genetic algorithm (GA) technique is applied to obtain optimal parameter values of the standard rating curve model (RCM) for predicting, in real time, event-based flow discharge hydrographs at sites receiving significant lateral inflows. The standard RCM uses the information of discharge and effective cross-sectional flow area at an upstream station and effective cross-sectional flow area wave travel time later at a downstream station to predict the flow rate at this last site. The GA technique obtains the optimal parameter values of the model, here defined as the GA-RCM model, by minimizing the mean absolute error objective function. The GA-RCM model was tested to predict hydrographs at three different stations, located on the Upper Tiber River in central Italy. The wave travel times characterizing the three selected river branches are, on the average, 4, 8, and 12h. For each river reach, seven events were employed, four for the model parameters' calibration and three for model testing. The GA approach, employing 100 chromosomes in the initial gene pool, 75% crossover rate, 5% mutation rate, and 10,000 iterations, made the GA-RCM model successfully simulate the hydrographs observed at each downstream section closely capturing the trend, time to peak, and peak rates with, on the average, less than 5% error. The model performance was also tested against the standard RCM model, which uses, on the contrary to the GA-RCM model, different values for the model parameters and wave travel time for each event, thus, making the application of the standard RCM for real time discharge monitoring inhibited. The comparative results revealed that the RCM model improved its performance by using the GA technique in estimating parameters. The sensitivity analysis results revealed that at most two events would be sufficient for the GA-RCM model to obtain the optimal values of the model parameters. A lower peak hydrograph can also be employed in the calibration to predict a higher peak hydrograph. Similarly, a shorter travel time hydrograph can be used in GA to obtain optimal model parameters that can be used to simulate floods characterized by longer travel time. For its characteristics, the GA-RCM model is suitable for the monitoring of discharge in real time, at river sites where only water levels are observed.Article Citation - WoS: 37Citation - Scopus: 49Predicting Suspended Sediment Loads and Missing Data for Gediz River, Turkey(American Society of Civil Engineers (ASCE), 2009) Ülke, Aslı; Tayfur, Gökmen; Özkul, SevinçPrediction of suspended sediment load (SSL) is important for water resources quantity and quality studies. The SSL of a stream is generally determined by direct measurement of the suspended sediment concentration or by employing sediment rating curve method. Although direct measurement is the most reliable method, it is very expensive, time consuming, and, in many instances, problematic for inaccessible sections, especially during floods. On the other hand, measuring precipitation and flow discharge is relatively easier and hence, there are more rain and flow gauging stations than SSL gauging stations in Turkey. Furthermore, due to its cost, measurements of SSL are carried out in longer periods compared to precipitation and flow measurements. Although daily precipitation and flow measurements are available for most of the Turkish river basins, at best semimonthly measurements are available for SSL. As such, it is essential to predict SSL from precipitation and flow data and to fill the gap for the missing data records. This study employed artificial intelligence methods of artificial neural networks (ANN) and neurofuzzy inference system, the sediment rating curve method, multilinear regression, and multinonlinear regression methods for this purpose. The comparative analysis of the results showed that the artificial intelligence methods have superiority over the other methods for predicting semimonthly suspended sediment loads. The ANN using conjugate gradient optimization method showed the best performance among the proposed models. It also satisfactorily generated daily SSL data for the missing period record of Gediz River, Turkey.Article Citation - WoS: 5Citation - Scopus: 5Kinematic Wave Theory for Transient Bed Sediment Waves in Alluvial Rivers(American Society of Civil Engineers (ASCE), 2008) Singh, Vijay P.; Tayfur, GökmenTransient bed sediment waves in alluvial rivers have been described using a multitude of hydraulic formulations. These formulations are based on some form of the St. Venant equations and conservation of mass of sediment in suspension and in bed. Depending on the assumptions employed, a hierarchy of formulations is expressed. These formulations in the literature employ uncoupled, semicoupled, or fully coupled transport models treating the sediment waves as either hyperbolic (dynamic wave) or parabolic (diffusion wave). It is, however, hypothesized that the movement of bed sediment waves in alluvial rivers can be described as a kinematic wave. Kinematic wave theory employs a functional relation between sediment transport rate and concentration and a relation between flow velocity and depth. This study summarizes the hierarchy of the formulations while emphasizing the kinematic wave theory for describing transient bed sediment waves. The applicability of the theory is shown for laboratory flume data and hypothetical cases.Article Citation - WoS: 10Citation - Scopus: 14Numerical Model for Sediment Transport Over Nonplanar, Nonhomogeneous Surfaces(American Society of Civil Engineers (ASCE), 2004) Tayfur, Gökmen; Singh, Vijay P.Sediment transport on surfaces with spatially variable microtopography, roughness, and infiltration was investigated using the diffusion wave equation. An implicit finite-difference scheme together with multivariate Newton's method was employed to solve the equation numerically. The simulation results showed that microtopography and roughness were the dominant factors causing significant spatial variations in sediment concentration. If the spatially varying microtopography was replaced by an average constant slope, the result was an overestimation of the sediment load. On the other hand, when the spatially varying roughness was replaced by the average roughness and the spatially varying infiltration rate by the average infiltration rate, the sediment discharge was not significantly affected. The sedimentograph reached an equilibrium much sooner when a constant infiltration rate was substituted for the time-varying infiltration rate.Article Citation - WoS: 5Citation - Scopus: 8Forecasting Interregional Commodity Flows Using Artificial Neural Networks: an Evaluation(Taylor and Francis Ltd., 2004) Çelik, Hüseyin MuratPrevious studies have concluded that the use of artificial neural networks (ANNs) is a promising new technique for modelling freight distribution, supporting, the findings of other studies in the area of spatial interaction modelling. However, the forecasting performance of ANNs is still under investigation. This study tests the predictive performance of the ANN Model with respect to a Box-Cox spatial interaction model. It is concluded that the Box-Cox model outperforms ANN in forecasting interregional commodity flows even if ANN had proven calibration superiority in comparison to conventional gravity type models.Article Citation - WoS: 36Citation - Scopus: 43Applicability of Sediment Transport Capacity Models for Nonsteady State Erosion From Steep Slopes(American Society of Civil Engineers (ASCE), 2002) Tayfur, GökmenThe physics-based sediment transport equations are derived from the assumption that the sediment transport rate can be determined by a dominant variable such as flow discharge, flow velocity, slope, shear stress, stream power, and unit stream power. In modeling of sheet erosion/sediment transport, many models that determine the transport capacity by one of these dominant variables have been developed. The developed models mostly simulate steady-state sheet erosion. Few models that are based on the shear-stress approach attempt to simulate nonsteady state sheet erosion. This study qualitatively investigates the applicability of the transport capacity models that are based on one of the commonly employed dominant variables-unit stream power, stream power, and shear stress-to simulate nonsteady state sediment loads from steep slopes under different rainfall intensities. The test of the calibrated models with observed data sets shows that the unit stream power model gives better simulation of sediment loads from mild slopes. The stream power and the shear stress models, on the other hand, simulate sediment loads from steep slopes more satisfactorily. The exponent (ki) in the sediment transport capacity formula is found to be 1.2, 1.9, and 1.6 for the stream power model, the shear stress model, and the unit stream power model, respectively.Article Citation - WoS: 33Citation - Scopus: 38Modeling Two-Dimensional Erosion Process Over Infiltrating Surfaces(American Society of Civil Engineers (ASCE), 2001) Tayfur, GökmenThe physics-based modeling of the rainfall-runoff induced erosion process is accomplished. The existing one-dimensional erosion process equations are extended to two dimensions and kinematic wave approximation is used. The model assumes that suspended sediment does not affect flow dynamics. The model considers the effect of flow depth plus loose soil depth on soil detachment. Sensitivity analysis results indicate that the effects of the soil erodibility coefficient (η) and exponent (k1) on sediment discharges are quite pronounced. On steep slopes, the effect of flow depth plus loose soil depth on sediment discharge is insignificant.Article Citation - WoS: 23Citation - Scopus: 26Body Waves in Fractured Porous Media Saturated by Two Immiscible Newtonian Fluids(Springer Verlag, 1996) Tuncay, Kağan; Çorapçıoplu, M. YavuzA study of body waves in fractured porous media saturated by two fluids is presented. We show the existence of four compressional and one rotational waves. The first and third compressional waves are analogous to the fast and slow compressional waves in Biot's theory. The second compressional wave arises because of fractures, whereas the fourth compressional wave is associated with the pressure difference between the fluid phases in the porous blocks. The effects of fractures on the phase velocity and attenuation coefficient of body waves are numerically investigated for a fractured sandstone saturated by air and water phases. All compressional waves except the first compressional wave are diffusive-type waves, i.e., highly attenuated and do not exist at low frequencies.Article Citation - WoS: 54Citation - Scopus: 61Wave Propagation in Fractured Porous Media(Springer Verlag, 1996) Tuncay, Kağan; Çorapçıoplu, M. YavuzA theory of wave propagation in fractured porous media is presented based on the double-porosity concept. The macroscopic constitutive relations and mass and momentum balance equations are obtained by volume averaging the microscale balance and constitutive equations and assuming small deformations. In microscale, the grains are assumed to be linearly elastic and the fluids are Newtonian. Momentum transfer terms are expressed in terms of intrinsic and relative permeabilities assuming the validity of Darcy's law in fractured porous media. The macroscopic constitutive relations of elastic porous media saturated by one or two fluids and saturated fractured porous media can be obtained from the constitutive relations developed in the paper. In the simplest case, the final set of governing equations reduce to Biot's equations containing the same parameters as of Biot and Willis