Showing 3 results for Saghafian
M. S. Saidi and M. Saghafian, ,
Volume 20, Issue 1 (7-2001)
Abstract
In this paper, the oscillating two-dimensional laminar flow about a cylinder and the oscillation of a cylinder in still water are studied. A finite volume method is applied to solve the Navier Stokes equations using SIMPLEC algorithm on a body fitted co-located O-type grid. In this study, the non-dimensional flow numbers, Keulegan-Carpenter and Stokes’ numbers are chosen over a range where different laminar flow regimes are normally three-dimensional. The results of this simulation and comparison with numerical and experimental works indicate the good capability of this two-dimensional model in showing the various regimes of flow patterns and vortex shedding. Considering the forces exerted on the cylinder, this study shows that in cases where the flow is of a
regular type, there is a good match between longitudinal force presented by this work and the one calculated through Morrison’s equation. But for irregular flows where the flow pattern changes in each cycle, there is less overlap and the accuracy of Morrison’s equation is reduced. Studying the time variation of the transversal force gives accurate information about the vortex shedding and its frequency in each cycle and mode changing. Since the flow mode changes continuously with time, the average of transversal and longitudinal forces on consecutive cycles is not a good representation of the force exerted on the cylinder. On the other hand, the model has satisfactorily reproduced the time variation of the tranversal and longitudinal forces of a pure mode, matching the experimental results.
Keywords: Oscillating flow, Laminar flow about a cylinder, Numerical solution
B. Saghafian, S. Rahimi Bandarabadi, H. Taheri Shahraeeni and J. Ghayoomian,
Volume 24, Issue 1 (7-2005)
Abstract
Rainfall is one of the most important climatic variables in the hydrology cycle. In flood estimation as well as environmental pollution studies in medium to large watersheds not only mus temporal pattern of rainfall t be known, but also the knowledge of its spatial distribution is required. Estimation of daily rainfall distribution without comparison and selection of
suitable methods may lead to errors in input parameters of rainfall – runoff models. Interpolation methods are among the techniques for estimating spatial distribution of rainfall. In this study, Thin Plate Smoothing Splines (TPSS), Weighted Moving Average (WMA) and Kriging are applied to estimate spatial daily rainfall in the southwest of Iran. Cross validation technique is used for comparison and evaluation of the methods. The results of analysis with two different station density showed that the TPSS method with power of 2 is the most accurate method in estimating daily rainfall. Zoning of the region also increased the interpolation accuracy. Generally speaking, division of the region based on cluster analysis improves accuracy compared with division by inter basin boundaries
D. Azadrooy, H. Saghafian,
Volume 36, Issue 3 (Journal of Advanced Materials-Fall 2017)
Abstract
The effect of stir casting process on the modification of the Fe-containing intermetallics formed in a cast in-situ composite based on Al-319 matrix alloy was studied in the present work. Microstructural observations using optical and scanning electron microscopes showed that the undesirable needle-like shape of the Fe-containing intermetallics (β) and also the coarse star-like α compounds were modified into the disc and spheroid shape particles with much less length to width ratio. The effect of parameters such as stirring temperature, cooling rate and Fe contents on the shape, size and distribution of intermetallic particles and eutectic Si blades were also studied. Results showed that the best condition to improve the shape, size and distribution of intermetallic particles can be achieved at a stirring speed of 1200 rpm for 5 minutes at the vicinity of β needles nucleation temperature followed by casting into a metallic mold. Based on the results obtained from the current work, it can be concluded that the harmful morphology of the β intermetallic needles can be properly modified by applying a shearing force during stirring the molten alloy in the semi-solid state.
