Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Conference Object A Boundary Element Method for Axisymmetric Elastodynamic Analysis(John Wiley and Sons Inc., 1996) Özkan, Gonca; Mengi, YalçınA new numerical method is proposed for the boundary element analysis of axisymmetric bodies. The method is based on complex Fourier series expansion of boundary quantities in circumferential direction, which reduced the boundary element equation to an integral equation in (r-z) plane involving the Fourier coefficients of boundary quantities, where r and z are the coordinates of the r theta z cylindrical coordinate system. The kernels appearing in these integral equations can be computed effectively by discrete Fourier transform formulas together with the fast Fourier transform (FFT) algorithm, and the integral equations (r-z) plane can be solved by Gaussian quadrature, which establishes the Fourier coefficients associated with boundary quantities. The Fourier transform solution can then be inverted into r theta z space by using again discrete Fourier transform formulas together with FFT algorithm. In this paper, we present the formulation of the proposed method which is outlined above. A comparison is given between the existent methods in literature and our method, which shows that the use of FFT algorithm for the integrations in circumferential direction provides considerable saving in computer time.Article Citation - WoS: 2Citation - Scopus: 3Numerical Model for Biaxial Earthquake Response of Reinforced Concrete(John Wiley and Sons Inc., 2007) Dönmez, Cemalettin; Sözen, Mete A.A numerical constitutive model is developed to simulate the biaxial nonlinear flexural response of slender reinforced concrete members subjected to earthquake excitation. The model is tested using data from two types of experiments with reinforced concrete elements: (1) elements subjected to varying pseudo-static biaxial lateral loads and (2) elements that responded biaxially to simulated earthquake motions. The goal for the model was not only to help determine the absolute maxima for earthquake response but also to enable calculation of the entire waveform, including the ranges of low- and moderate-amplitude response. The comparisons of measured and calculated results and sensitivity of the proposed model to variations in the input parameters are discussed. The output was found to be insensitive to the changes in input parameters related to concrete and sensitive to input parameters related to reinforcing steel. The results of the calculations were tested using experimental data.Article Citation - WoS: 16Citation - Scopus: 18Kinematic Wave Model of Bed Profiles in Alluvial Channels(John Wiley and Sons Inc., 2006) Tayfur, Gökmen; Singh, Vijay P.A mathematical model, based on the kinematic wave (KW) theory, is developed for describing the evolution and movement of bed profiles in alluvial channels. The model employs a functional relation between sediment transport rate and concentration, a relation between flow velocity and depth and Velikanov's formula relating suspended sediment concentration to flow variables. Laboratory flume and field data are used to test the model. Transient bed profiles in alluvial channels are also simulated for several hypothetical cases involving different water flow and sediment concentration characteristics. The model-simulated bed profiles are found to be in good agreement with what is observed in the laboratory, and they seem theoretically reasonable for hypothetical cases. The model results reveal that the mean particle velocity and maximum concentration (maximum bed form elevation) strongly affect transient bed profiles.Article Citation - WoS: 46Citation - Scopus: 49Predicting and Forecasting Flow Discharge at Sites Receiving Significant Lateral Inflow(John Wiley and Sons Inc., 2007) Tayfur, Gökmen; Moramarco, Tommaso; Singh, Vijay P.Two models, one linear and one non-linear, were employed for the prediction of flow discharge hydrographs at sites receiving significant lateral inflow. The linear model is based on a rating curve and permits a quick estimation of flow at a downstream site. The non-linear model is based on a multilayer feed-forward back propagation (FFBP) artificial neural network (ANN) and uses flow-stage data measured at the upstream and downstream stations. ANN predicted the real-time storm hydrographs satisfactorily and better than did the linear model. The results of sensitivity analysis indicated that when the lateral inflow contribution to the channel reach was insignificant, ANN, using only the flow-stage data at the upstream station, satisfactorily predicted the hydrograph at the downstream station. The prediction error of ANN increases exponentially with the difference between the peak discharge used in training and that used in testing. ANN was also employed for flood forecasting and was compared with the modified Muskingum model (MMM). For a 4-h lead time, MMM forecasts the floods reliably but could not be applied to reaches for lead times greater than the wave travel time. Although ANN and MMM had comparable performances for an 8-h lead time, ANN is capable of forecasting floods with lead times longer than the wave travel time.Article Citation - WoS: 17Citation - Scopus: 19Kinematic Wave Model for Transient Bed Profiles in Alluvial Channels Under Nonequilibrium Conditions(John Wiley and Sons Inc., 2007) Tayfur, Gökmen; Singh, Vijay P.Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear-stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.Article Citation - WoS: 12Citation - Scopus: 12Oil Mound Spreading and Migration With Ambient Groundwater Flow in Coarse Porous Media(John Wiley and Sons Inc., 1996) Çorapçıoplu, M. Yavuz; Tuncay, Kağan; Ceylan, B. KağanWhen a light, immiscible oil leaks above an unconfined aquifer, it spreads and forms a floating mound on the table. The oil mound migrates in the direction of ambient ground flow. In this study we present a governing equation for the migrating mound thickness by averaging the oil phase mass balance equation. Analytical and numerical solutions to an advective- dispersive type equation are presented to estimate the temporal and spatial distribution of the migrating oil mound thickness for two problems of practical importance: formation, spreading, and migration of an oil mound on the table and spreading and migration of an established layer of oil with ambient ground flow. The model results compare favorably with test data obtained by laboratory flume experiments. Although the model has some simplifying assumptions such as the absence of capillary pressure gradients, sharp saturation changes across the phase interfaces, and single mobile phase (i.e., oil flow only), it can be useful as a screening or site assessment tool because of its relative simplicity.Article Citation - WoS: 75Citation - Scopus: 82Body Waves in Poroelastic Media Saturated by Two Immiscible Fluids(John Wiley and Sons Inc., 1996) Tuncay, Kağan; Çorapçıoğlu, M. YavuzA study of body waves in elastic porous media saturated by two immiscible Newtonian fluids is presented. We analytically show the existence of three compressional waves and one rotational wave in an infinite porous medium. The first and second compressional waves are analogous to the fast and slow compressional waves in Biot's theory. The third compressional wave is associated with the pressure difference between the fluid phases and dependent on the slope of capillary pressure-saturation relation. Effect of a second fluid phase on the fast and slow waves is numerically investigated for Massillon sandstone saturated by air and water phases. A peak in the attenuation of the first and second compressional waves is observed at high water saturations. Both the first and second compressional waves exhibit a drop in the phase velocity in the presence of air. The results are compared with the experimental data available in the literature. Although the phase velocity of the first compressional and rotational waves are well predicted by the theory, there is a discrepancy between the experimental and theoretical values of attenuation coefficients. The causes of discrepancy are explained based on experimental observations of other researchers.