Civil Engineering / İnşaat Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/13

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Citation - WoS: 53
Citation - Scopus: 62
Effective Stress Principle for Saturated Fractured Porous Media
(Wiley-Blackwell, 1995) Tuncay, Kağan; Çorapçıoğlu, M. Yavuz
An effective stress principle for saturated fractured porous media is proposed based On the double-porosity representation. Both the solid grains and the fractured porous medium are assumed to be linearly elastic materials. The derivation employs volume averaging technique to obtain macroscopic scale expressions. Two parameters, the bulk modulus of the fractured medium and bulk modulus of the porous matrix, are introduced in the formulation. The final expression reduces to the one obtained by Blot and Willis [1957], Skempton [1960], Nur and Byeerle [1971], and Verruijt [1984] when the volume fraction of the fractures vanishes, that is, for a nonfractured porous medium.
Citation - WoS: 12
Citation - Scopus: 13
Modeling Deficit Irrigation in Alfalfa Production
(American Society of Civil Engineers (ASCE), 1995-11) Tayfur, Gökmen; Tanji, Kenneth K.; House, Brett; Robinson, Frank; Teuber, Larry; Kruse, Gordon
A conceptual agronomic model EPIC was extended to consider the effects of salinity in alfalfa production under optimal and water stress irrigation conditions. The extended model was calibrated and validated with observed lysimeter data. The model parameters that affected alfalfa yield and soil salinity the most were wilting point, field capacity, hydraulic conductivity, nitrate concentration, biomass energy ratio, seeding rate, average soil salinity EC e at which crop yield is reduced by 50% ( EC50 ), and initial soil gypsum concentration. The calibrated and validated model was then applied to an alfalfa deficit irrigation study. The four irrigation treatments included optimum check, minimum stress, short stress, and long stress, each of which produced differential alfalfa yields. The purpose of summer deficit irrigation was to ascertain how much agricultural water at what cost could be made available for urban water uses during water shortfalls. The results of model simulation were found to be satisfactory under all irrigation treatments though the model slightly overestimated the yields and underestimated the soil EC e at the end of short and long stress treatments. An economic component is included to determine the appropriate compensation for farmers undergoing a range of deficit irrigations.
Citation - WoS: 70
Citation - Scopus: 79
Body Waves in Poroelastic Media Saturated by Two Immiscible Fluids
(John Wiley and Sons Inc., 1996) Tuncay, Kağan; Çorapçıoğlu, M. Yavuz
A 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.
A Boundary Element Method for Axisymmetric Elastodynamic Analysis
(John Wiley and Sons Inc., 1996) Özkan, Gonca; Mengi, Yalçın
A 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.
Citation - WoS: 49
Citation - Scopus: 59
Wave Propagation in Fractured Porous Media
(Springer Verlag, 1996) Tuncay, Kağan; Çorapçıoplu, M. Yavuz
A 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
Citation - WoS: 5
Citation - Scopus: 9
Consolidation of Elastic Porous Media Saturated by Two Immiscible Fluids
(American Society of Civil Engineers (ASCE), 1996) Tuncay, Kağan; Çorapçıoğlu, M. Yavuz
A theory is presented to simulate the consolidation of elastic porous media saturated by two immiscible Newtonian fluids. The macroscopic equations, including mass and momentum balance equations and constitutive relations, are obtained by volume averaging the microscale equations. The theory is based on the small deformation assumption. In the microscale, the grains are assumed to be linearly elastic and the fluids are Newtonian. The bulk and shear moduli of the solid matrix are introduced to obtain the macroscopic constitutive equations. Momentum transfer terms are expressed in terms of intrinsic and relative permeabilities assuming the validity of Darcy's law. In one dimension, the governing equations reduce to two coupled diffusion equations in terms of the pore pressures of the fluid phases. An analytical solution is obtained for a column with a fixed impervious base and a free drainage surface. Results are presented for cases of practical interest, i.e., columns saturated by oil-water and air-water phases. Results indicate that the presence of a second fluid phase affects pore water pressure and total settlement.
Citation - Scopus: 41
Propagation of Waves in Porous Media
(Elsevier Ltd., 1996) Çorapçıoplu, M. Yavuz; Tuncay, Kağan
Wave propagation in porous media is of interest in various diversified areas of science and engineering. The theory of the phenomenon has been studied extensively in soil mechanics, seismology, acoustics, earthquake engineering, ocean engineering, geophysics, and many other disciplines. This review presents a general survey of the literature within the context of porous media mechanics. Following a review of the Biot's theory of wave propagation in linear, elastic, fluid saturated porous media which has been the basis of many analyses, we present various analytical and numerical solutions obtained by several researchers. Biot found that there are two dilatational waves and one rotational wave in a saturated porous medium. It has been noted that the second kind of dilatational wave is highly attenuated and is associated with a diffusion type process. The influence of coupling between two phases has a decreasing effect on the first kind wave and an increasing effect on the second wave. Procedures to predict the liquefaction of soils due to earthquakes have been reviewed in detail. Extension of Biot's theory to unsaturated soils has been discussed, and it was noted that, in general, equations developed for saturated media were employed for unsaturated media by replacing the density and compressibility terms with modified values for a water-air mixture. Various approaches to determine the permeability of porous media from attenuation of dilatational waves have been described in detail. Since the prediction of acoustic wave speeds and attenuations in marine sediments has been extensively studied in geophysics, these studies have been reviewed along with the studies on dissipation of water waves at ocean bottoms. The mixture theory which has been employed by various researchers in continuum mechanics is also discussed within the context of this review. Then, we present an alternative approach to obtain governing equations of wave propagation in porous media from macroscopic balance equations. Finally, we present an analysis of wave propagation in fractured porous media saturated by two immiscible fluids.
Citation - WoS: 12
Citation - Scopus: 12
Oil Mound Spreading and Migration With Ambient Groundwater Flow in Coarse Porous Media
(John Wiley and Sons Inc., 1996-05) Çorapçıoplu, M. Yavuz; Tuncay, Kağan; Ceylan, B. Kağan
When 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.
Citation - WoS: 22
Citation - Scopus: 26
Body Waves in Fractured Porous Media Saturated by Two Immiscible Newtonian Fluids
(Springer Verlag, 1996-06) Tuncay, Kağan; Çorapçıoplu, M. Yavuz
A 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.
Citation - WoS: 29
Citation - Scopus: 33
Areally-Averaged Overland Flow Equations at Hillslope Scale
(Taylor and Francis Ltd., 1998-06) Tayfur, Gökmen; Kavvas, M. Levent
Microscale-averaged inter-rill area sheet flow and rill flow equations (Tayfur and Kavvas, 1994) are averaged along the inter-rill area length and rill length to obtain local areally-averaged inter-rill area sheet flow and rill flow equations (local-scale areal averaging). In this averaging, the local areally-averaged flow depths are related to the microscale-averaged flow depths at the outlet sections (downstream ends) of a rill and an inter-rill area by the assumption that the flow in these sections has the profile of a sine function. The resulting local areally-averaged flow equations become time dependent only. To minimize computational efforts and economize on the number of model parameters, local areally-averaged flow equations are then averaged over a whole hillslope section (hillslope-scale areal averaging). The expectations of the terms containing more than one variable are obtained by the method of regular perturbation. Comparison of model results with observed data is satisfactory. The comparison of the model results with those of previously developed models which use point-scale and large-scale (transectionally) averaged technology indicates the superiority of this model over them. Microscale-averaged inter-rill area sheet flow and rill flow equations (Tayfur & Kavvas, 1994) are averaged along the inter-rill area length and rill length to obtain local areally-averaged inter-rill area sheet flow and rill flow equations (local-scale areal averaging). In this averaging, the local areally-averaged flow depths are related to the microscale-averaged flow depths at the outlet sections (downstream ends) of a rill and an inter-rill area by the assumption that the flow in these sections has the profile of a sine function. The resulting local areally-averaged flow equations become time dependent only. To minimize computational efforts and economize on the number of model parameters, local areally-averaged flow equations are then averaged over a whole hillslope section (hillslope-scale areal averaging). The expectations of the terms containing more than one variable are obtained by the method of regular perturbation. Comparison of model results with observed data is satisfactory. The comparison of the model results with those of previously developed models which use point-scale and large-scale (transectionally) averaged technology indicates the superiority of this model over them
Citation - WoS: 33
Citation - Scopus: 38
Modeling Two-Dimensional Erosion Process Over Infiltrating Surfaces
(American Society of Civil Engineers (ASCE), 2001-05) Tayfur, Gökmen
The 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.
Citation - WoS: 36
Citation - Scopus: 43
Applicability of Sediment Transport Capacity Models for Nonsteady State Erosion From Steep Slopes
(American Society of Civil Engineers (ASCE), 2002-05) Tayfur, Gökmen
The 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.
Citation - WoS: 1
Citation - Scopus: 6
Genetic Algorithm-Artificial Neural Network Model for the Prediction of Germanium Recovery From Zinc Plant Residues
(Taylor and Francis Ltd., 2002-09) Akkurt, Sedat; Özdemir, Serhan; Tayfur, Gökmen
A multi-layer, feed-forward, back-propagation learning algorithm was used as an artificial neural network (ANN) tool to predict the extraction of germanium from zinc plant residues by sulphuric acid leaching. A genetic algorithm (GA) was used for the selection of training and testing data and a GA-ANN model of the germanium leaching system was created on the basis of the training data. Testing of the model yielded good error levels (r2 = 0.95). The model was employed to predict the response of the system to different values of the factors that affect the recovery of germanium and the results facilitate selection of the experimental conditions in which the optimum recovery will be achieved.
Citation - WoS: 148
Citation - Scopus: 170
Artificial Neural Networks for Sheet Sediment Transport
(Taylor and Francis Ltd., 2002-12) Tayfur, Gökmen
Sheet sediment transport was modelled by artificial neural networks (ANNs). A three-layer feed-forward artificial neural network structure was constructed and a back-propagation algorithm was used for the training of ANNs. Event-based, runoff-driven experimental sediment data were used for the training and testing of the ANNs. In training, data on slope and rainfall intensity were fed into the network as inputs and data on sediment discharge were used as target outputs. The performance of the ANNs was tested against that of the most commonly used physically-based models, whose transport capacity was based on one of the dominant variables-flow velocity (V), shear stress (SS), stream power (SP), and unit stream power (USP). The comparison results revealed that the ANNs performed as well as the physically-based models for simulating nonsteady-state sediment loads from different slopes. The performances of the ANNs and the physically-based models were also quantitatively investigated to estimate mean sediment discharges from experimental runs. The investigation results indicated that better estimations were obtained for V over mild and steep slopes, under low rainfall intensity; for USP over mild and steep slopes, under high rainfall intensity; for SP and SS over very steep slopes, under high rainfall intensity; and for ANNs over steep and very steep slopes, under very high rainfall intensities.
Polimerlerin transport özelliklerinin gravimetrik yöntemle ölçülmesi
(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2003) Alsoy Altınkaya, Sacide; Tıhmınlıoğlu, Funda; Yürekli, Yılmaz
Bu çalışmanın amacı ülkemizde oldukça yaygın bulunan sektörlerden biri olan boya sektöründe kullanılan metilmetakrilat bütilakrilat kopolimerinin kopolimerinin içinde metilmetakrilat monomerinin difüzyon katsayıları ve çözünürlüğünün ölçülmesi ve bu verilerden pratik bir korelasyon elde edilmesidir. Çalışmanın bir diğer amacı da bu korelasyonun türetilecek bir matematik model içinde kullanılarak boyada kalan monomerin havaya geçiş hızının ve monomerin havadaki konsantrasyonunun hesaplanmasıdır.
Upscaling Surface Flow Equations Depending Upon Data Availability at Different Scales
(Springer Verlag, 2003) Tayfur, Gökmen
St. Venant equations, which are used to model sheet flows, are point-scale, depth-averaged equations, requiring data on model parameters at a very fine scale. When data are available at the scale of a hillslope transect, the point equations need to be upscaled to conserve the mass and momentum at that scale, Hillslope-scale upscaled model must be developed if data are available at that scale. The performance of the three models applied to simulate flows from non-rilled surfaces revealed that the hillslope-scale upscaled model performs as good as the point-scale model though it uses far less data. The transectionally-upscaled model slightly underestimates the observed data.
Citation - Scopus: 100
Phase Ii Benchmark Control Problem for Seismic Response of Cable-Stayed Bridges
(Pitagora Editrice, 2003-07) Caicedo, Juan Martin; Dyke, Shirley J.; Moon, Seokjun; Bergman, Lawrence A.; Turan, Gürsoy; Hague, Steven T.
This paper presents the problem definition for the second generation of benchmark structural control problems for cable-stayed bridges. The goal of this study is to provide a testbed for the development of strategies for the control of cable stayed-bridges. Based on detailed drawings of the Bill Emerson Memorial Bridge, a three-dimensional evaluation model has been developed to represent the complex behavior of the full-scale benchmark bridge. Phase II considers more complex structural behavior than phase I, including multi-support and transverse excitations. Evaluation criteria are presented for the design problem that are consistent with the goals of seismic response control of a cable-stayed bridge. Control constraints are also provided to ensure that the benchmark results are representative of a control implementation on the physical structure. Each participant in this benchmark bridge control study is given the task of denning, evaluating and reporting on their proposed control strategies. Participants should also evaluate the robust stability and performance of their resulting designs through simulation with an evaluation model which includes additional mass due to snow loads. The problem and a sample control design have been made available in the form of a set of MATLAB equations.
Citation - WoS: 130
Citation - Scopus: 183
Phase I Benchmark Control Problem for Seismic Response of Cable-Stayed Bridges
(American Society of Civil Engineers (ASCE), 2003-07) Dyke, Shirley J.; Caicedo, Juan Martin; Turan, Gürsoy; Bergman, Lawrence A.; Hague, Steven T.
This paper presents the problem definition for the first generation of benchmark structural control problems for cable-stayed bridges. The benchmark problem is based on the Bill Emerson Memorial Bridge that is currently under construction in Cape Girardeau, Missouri. Construction of the bridge is expected to be completed in 2003. The goal of this study is to provide a testbed for the development of strategies for the control of cable-stayed bridges. Based on detailed drawings, a three-dimensional evaluation model has been developed to represent the complex behavior of the full scale benchmark bridge. The linear evaluation model is developed using the equations of motion generated around the deformed equilibrium position. Evaluation criteria are selected that are consistent with the goals of seismic response control of a cable-stayed bridge. Control constraints ensure that the results are representative of a control implementation on the physical structure. Each participant in this benchmark study is given the task of defining (including devices, sensors, and algorithms), evaluating, and reporting on their proposed control strategies. These strategies may be either passive, active, semiactive, or a combination thereof. A simulation program is provided to facilitate direct comparison of the capabilities and efficiency of the various control strategies. The problem is available through the internet in the form of a set of MATLAB programs and includes a sample control design to guide participants through the benchmark problem.
Citation - WoS: 134
Citation - Scopus: 157
The Use of Ga-Anns in the Modelling of Compressive Strength of Cement Mortar
(Elsevier Ltd., 2003-07) Akkurt, Sedat; Özdemir, Serhan; Tayfur, Gökmen; Akyol, Burak
In this paper, results of a project aimed at modelling the compressive strength of cement mortar under standard curing conditions are reported. Plant data were collected for 6 months for the chemical and physical properties of the cement that were used in model construction and testing. The training and testing data were separated from the complete original data set by the use of genetic algorithms (GAs). A GA-artificial neural network (ANN) model based on the training data of the cement strength was created. Testing of the model was also done within low average error levels (2.24%). The model was subjected to sensitivity analysis to predict the response of the system to different values of the factors affecting the strength. The plots obtained after sensitivity analysis indicated that increasing the amount of C3S, SO3 and surface area led to increased strength within the limits of the model. C2S decreased the strength whereas C3A decreased or increased the strength depending on the SO3 level. Because of the limited data range used for training, the prediction results were good only within the same range. The utility of the model is in the potential ability to control processing parameters to yield the desired strength levels and in providing information regarding the most favourable experimental conditions to obtain maximum compressive strength.
Citation - WoS: 11
Citation - Scopus: 12
Experimental and Artificial Neural Network Modeling Study on Soot Formation in Premixed Hydrocarbon Flames
(Elsevier Ltd., 2003-08) İnal, Fikret; Tayfur, Gökmen; Melton, Tyler R.; Senkan, Selim M.
The formation of soot in premixed flames of methane, ethane, propane, and butane was studied at three different equivalence ratios. Soot particle sizes, number densities, and volume fractions were determined using classical light scattering measurement techniques. The experimental data revealed that the soot properties were sensitive to the fuel type and combustion parameter equivalence ratio. Increase in equivalence ratio increased the amount of soot formed for each fuel. In addition, methane flames showed larger particle diameters at higher distances above the burner surface and propane, ethane, and butane flames came after the methane flames, respectively. Three-layer, feed-forward type artificial neural networks having seven input neurons, one output neuron, and five hidden neurons for soot particle diameter predictions and seven hidden neurons for volume fraction predictions were used to model the soot properties. The network could not be trained and tested with sufficient accuracy to predict the number density due to a large data range and greater uncertainty in determination of this parameter. The number of complete data set used in the model was 156. There was a good agreement between the experimental and predicted values, and neural networks performed better when predicting output parameters (i.e. soot particle diameters and volume fractions) within the limits of the training data.

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