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    Estimation of global solar radiation using ANN over Turkey
    (PERGAMON-ELSEVIER SCIENCE LTD, 2012) Ozgoren, Muammer; Bilgili, Mehmet; Sahin, Besir
    The main objective of the present study is to develop an artificial neural network (ANN) model based on multi-nonlinear regression (MNLR) method for estimating the monthly mean daily sum global solar radiation at any place of Turkey. For this purpose, the meteorological data of 31 stations spread over Turkey along the years 2000-2006 were used as training (27 stations) and testing (4 stations) data. Firstly, all independent variables (latitude, longitude, altitude, month, monthly minimum atmospheric temperature, maximum atmospheric temperature, mean atmospheric temperature, soil temperature, relative humidity, wind speed, rainfall, atmospheric pressure, vapor pressure, cloudiness and sunshine duration) were added to the Enter regression model. Then, the Stepwise MNLR method was applied to determine the most suitable independent (input) variables. With the use of these input variables, the results obtained by the ANN model were compared with the actual data, and error values were found within acceptable limits. The mean absolute percentage error (MAPE) was found to be 5.34% and correlation coefficient (R) value was obtained to be about 0.9936 for the testing data set. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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    FLOW STRUCTURE FROM A HORIZONTAL CYLINDER COINCIDENT WITH A FREE SURFACE IN SHALLOW WATER FLOW
    (VINCA INST NUCLEAR SCI, 2012) Kahraman, Ali; Ozgoren, Muammer; Sahin, Besir
    Vortex formation from a horizontal cylinder coincident with a free surface of a shallow water flow having a depth of 25.4 mm was experimentally investigated using the particle image velocimetry technique. Instantaneous and time-averaged flow patterns in the wake region of the cylinder were examined for three different cylinder diameter values under the fully developed turbulent boundary layer condition. Reynolds numbers were in the range of 1124 <= Re <= 3374 and Froude numbers were in the range of 0.41 <= Fr <= 0.71 based on the cylinder diameter. It was found that a jet-like flow giving rise to increasing the flow entrainment between the core and wake regions depending on the cylinder diameter was formed between the lower surface of the cylinder and bottom surface of the channel. Vorticity intensity, Reynolds stress correlations, and the primary recirculating bubble lengths were grown to higher values with increasing the cylinder diameter. On the other hand, in the case of the lowest level of the jet-like flow emanating from the beneath of the smallest cylinder, the variation of flow characteristics were attenuated significantly in a shorter distance. The variation of the reattachment location of the separated flow to the free-surface is a strong function of the cylinder diameter and the Froude number.
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    Large eddy simulation of flow around two side-by-side spheres
    (KOREAN SOC MECHANICAL ENGINEERS, 2013) Hassanzadeh, Rahim; Sahin, Besir; Ozgoren, Muammer
    Large eddy simulation, using a dynamic Smagorinsky sub-grid scale, is used for the prediction of flow structures around two identical spheres fixed side-by-side at a subcritical flow regime with the Reynolds number equal to 5,000. The QUICK discretization method is applied to discretize the convection terms of the Navier-Stokes equation by means of the finite volume approach. This work focuses mainly on the wake structures downstream of the two interactive spheres located at three various dimensionless separation distances between spheres such as G/D = 1.50, 2.00, and 3.00. The obtained results revealed that the interaction between wakes affects the flow structures downstream of spheres. The rate of this interaction is strongly altered as a function of separation distance. On the other hand, some flow data such as mean drag and mean lift coefficients are affected due to the wake interactions. Finally, examination of the Reynolds stress variation along the different lateral axis, L/D, revealed that the nozzle effect does not play a significant role on the turbulence characteristics beyond the G/D = 3.00.
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    Numerical investigation of flow structures around a sphere
    (TAYLOR & FRANCIS LTD, 2011) Hassanzadeh, Rahim; Sahin, Besir; Ozgoren, Muammer
    A numerical investigation of flow around a sphere is performed and compared with previous studies. Here, a second-order accurate, finite volume method is used in order to predict the instantaneous and time-averaged flow characteristics using large eddy simulation (LES) on the multi-block grid system. Namely, the objectives of this article are: (i) the presentation of flow structures in the wake region downstream of the sphere with a wide variety of flow properties such as the distribution of velocity vectors, patterns of streamlines, Reynolds stress correlations, root mean square of velocity components and other time-averaged flow data in order to reveal the vortical flow structures in detail and (ii) to demonstrate the abilities of computational methods in simulation of vortical flow data. Finally, it has been concluded that there are good agreements between the experimental results and numerical predictions.