Browsing by Publisher "Sharif University of Technology"
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Item Mechanism and modelling of shallow soil slope stability during high intensity and short duration rainfall(Sharif University of Technology, 2011) Egeli I.; Pulat H.F.Shallow landslides in nearly saturated uncohesive to slightly cohesive soils are triggered by high intensity, short duration rainfall which infiltrates into soil and changes intergranular friction and effective stresses. For this, the especially developed SoilWater Interaction Modelling System (SWIMS) was used with CL-ML type soils. For simplicity, rainfall intensity and duration were kept constant. Results showed that (1) All 35° slopes were failed by translational failure. For the other (15°,25°) slopes, no failures were observed; (2) For all slopes, FOS increased with increasing compaction degree and decreased with increasing slope angle; (3) Other parameters, such as soil density, porosity, saturation degree, water contents, and water permeability may also affect shear strength/slope stability, especially for low degrees of saturation (S<95%), compared to high degrees of saturation (S=,>95%). (4) A correlation of SWIMS tests observed that average wetting band depths ( hobser), with the calculated wetting band depths from the Lump Equation (hLE), were poor, as hobser values were much higher than hLE values. Differences increased for very low degrees of saturation (S), compared to S>95%. This meant that the Lump equation underestimated wetting band depths. Further, if the Lump equation is still considered valid, this would imply either water-permeability increases, porosity decreases or both occur towards full saturation; a process where the last possibility is the most probable occurrence. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.Item Lie group analysis of a non-Newtonian fluid flow over a porous surface(Sharif University of Technology, 2012) Akgül M.B.; Pakdemirli M.Two-dimensional, unsteady squeezed flow over a porous surface for a power-law non-Newtonian fluid is considered. Continuity, momentum and energy equations are written and cast into a non-dimensional form. Boundary conditions are selected in a general form. Lie Group theory is applied to the equations. Then, a partial differential system with three independent variables is converted into an ordinary differential system, via application of two successive symmetry generators. The ordinary differential equations are solved numerically. Effects of flow behavior index, Prandtl number, squeezing parameter, surface velocity parameter and suction/injection parameter on the flow are outlined in the figures. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.Item The use of neural networks for the prediction of the critical factor of safety of an artificial slope subjected to earthquake forces(Sharif University of Technology, 2012) Erzin Y.; Cetin T.This study deals with the development of Artificial Neural Network (ANN) and Multiple Regression (MR) models for estimating the critical factor of safety (Fs) value of a typical artificial slope subjected to earthquake forces. To achieve this, while the geometry of the slope and the properties of the man-made soil are kept constant, the natural subsoil properties, namely, cohesion, internal angle of friction, the bulk unit weight of the layer beneath the ground surface and the seismic coefficient, varied during slope stability analyses. Then, the Fs values of this slope were calculated using the simplified Bishop method, and the minimum (critical) Fs value for each case was determined and used in the development of the ANN and MR models. The results obtained from the models were compared with those obtained from the calculations. Moreover, several performance indices, such as determination coefficient, variance account for, mean absolute error and root mean square error, were calculated to check the prediction capacity of the models developed. The obtained indices make it clear that the ANN model has shown a higher prediction performance than the MR model. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.Item Effect of 3D isotropic resolutions of sequenced images on natural vibration properties of trabecular bone(Sharif University of Technology, 2013) Altintas G.; Ergut A.; Goktepe A.B.The voxel based finite element (FE) method used to obtain primary data for non-invasive imaging techniques has emerged as a major focus of interest in several disciplines such as medicine, mechanics and material engineering for solving micro and nano-scale problems. Owing to the fact that, voxel based FE models are directly affected by parameters of imaging techniques such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), the consequences of these effects on the natural vibration analysis of structures having complex geometry in micro scale, are investigated in this study. In this context, voxel based FE models are obtained using Micro-CT imaging data that has three different resolutions of vertebral trabecular bone tissue. Furthermore, resolutions of image data sets are artificially increased and equalized for evaluating voxel based FE models that are free from FE size effects. Natural vibration characteristics of voxel based FE models are investigated not only numerically but also including associated mode shapes. Unpredictable vibrational behavior for various voxel sizes, is, thus, revealed. Element size effects of voxel based FE models are considerably different from the effects on structural components with regular prismatic shapes. Obtained results show that, investigated parameters have a crucial influence on the natural vibration behavior of trabecular bone tissue which is selected as an example of complex geometries. Modal behaviors that are effective in micro local regions, but less in the whole body, where there are possibilities for working with approximate geometry without considering the micro structure have been observed. Moreover, the results are new from a theoretical point of view, and they also represent the importance of quality in imaging data, which, in practical applications must be taken into consideration. © 2013 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.Item Comparison and successive iteration of approximate solution of ordinary differential equations with initial conditions by the new modified Krasnoselskii iteration method(Sharif University of Technology, 2013) Bildik N.; Bakir Y.; Mutlu A.In this paper, we used the Picard successive iteration method and the new modified Krasnoselskii iteration method in order to solve different types of ordinary linear differential equations having initial conditions. By applying the new modified Krasnoselskii iteration method, not only do we obtain the approximate solutions for the problem, but also establish the corresponding iterative schemes. Finally, it is shown that the accuracy of the new iteration method (called the new modified Krasnoselskii iteration method) is substantially improved by employing variable steps which adjust themselves to the solution of the differential equation. © 2013 Sharif University of Technology. All rights reserved.Item Comparison of solutions of systems of delay differential equations using Taylor collocation method, Lambert W function and variational iteration method(Sharif University of Technology, 2015) Bildik N.; Deniz S.In this paper, solution of systems of delay differential equations, with initial conditions, using numerical methods, including the Taylor collocation method, the Lambert W function and the variational iteration method, is considered. We have endeavored to show the most appropriate method by comparing the solutions of this system of equations with different types of methods. All numerical computations have been performed on the computer algebraic system, Matlab. © 2015 Sharif University of Technology. All rights reserved.Item Investigations into factors influencing the CBR values of some Aegean sands(Sharif University of Technology, 2016) Erzin Y.; Türköz D.; Tuskan Y.; Yilmaz I.The California Bearing Ratio (CBR) value of the soils is very important for geotechnical engineering and earth structures. A CBR value is affected by the soil type and different soil properties. With this in view, in this paper, an attempt has been made for investigating the factors that affect the CBR values of some Aegean sands collected from nine different locations in Manisa (Turkey). The sand samples were tested for mineralogy, particle shape and size, and specific gravity. The CBR tests were then performed on these samples at different dry densities to examine the influence of dry density, relative density, water content, and particle shape and size on the CBR value. Multiple Regression Analysis (MRA) was performed to predict the CBR value of the sands by using the experimental results. Moreover, several performance indices, such as coefficient of correlation and variance account for mean absolute error and root mean square error, were calculated to check the prediction capacity of the proposed MR equation. The obtained indices make it clear that the equation derived from the samples used in this study applies well, with an acceptable accuracy, to the CBR estimation at the preliminary stage of site investigations. © 2016 Sharif University of Technology. All rights reserved.Item The use of neural networks for predicting the factor of safety of soil against liquefaction(Sharif University of Technology, 2019) Erzin Y.; Tuskan Y.In this paper, the Factor of Safety (FS) values of soilaga instliquefaction was investigated by means of Artificial Neural Network (ANN) and Multiple Regression (MR). To achieve this, two earthquake parameters, namely earthquake magnitude (Mw) and horizontal peak ground acceleration (a m a x ), and six soil properties, namely Standard Penetration Test Number (SPT-N), saturated unit weight (γsat), natural unit weight (γn), Fines Content (FC), the depth of Ground Water Level (GWL), and the depth of the soil (d), varied in the liquefaction analysis; then, the FS value was calculated by the simplified method for each case by using the Excel program developed and utilized in the simulation of the feed-forward ANN model with backpropagation algorithm and the MR model. The FS values predicted by both ANN and MR models were compared with those calculated by the simplified method. In addition, five different performance indices were used to evaluate the predictabilities of the models developed. These performance indices indicated that the ANN models were superior to the MR model in terms of predicting the FS value of the soil. © 2019 Sharif University of Technology. All rights reserved.Item Machinability of hardened AISI S1 cold work tool steel using cubic boron nitride(Sharif University of Technology, 2021) Şahinoglu A.; Rafighi M.Recently, hard turning has become an interesting method for manufacturers as an alternative to the grinding process due to its superior features such as good surface quality, good productivity, lower production costs, lower power consumption, and shorter processing time. Despite its considerable benefits, hard turning is a difficult process that needs advanced cutting inserts such as ceramics and cubic boron nitride. However, these cutting inserts are costly and should be used properly by choosing appropriate machining parameters. In the presented work, the hard turning process was employed to investigate the machinability of AISI S1 cold work tool steel using a cubic boron nitride insert. The relation between machining parameters, namely depth of cut, cutting speed, and feed rate, on the responses such as power consumption, surface roughness, and machining sound was found using a full factorial orthogonal array of response surface methodology. In addition, analysis of variance was used to identify the most important machining parameters that inuence output parameters. Based on the results, surface roughness was dominantly affected by feed rate, whereas sound and power consumption were inuenced by all machining parameters, especially cutting speed and feed rate. Good agreement between the experimental and predicted values was observed. © 2021 Sharif University of Technology.