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Showing 3 results for Rajabi

M. R. Kavianpour, E. Rajabi,
Volume 10, Issue 4 (December 2012)
Abstract

The objective of this work is to perform a direct numerical simulation of turbulent channel flow where all essential scales of

motion are resolved due to variable time-stepping algorithm in various time advancement method and different discritized form

of convection term. A pseudo spectral method (Fourier series in stream-wise and span-wise directions and Chebychev polynomial

expansion in normal direction) is employed for the spatial derivatives. The time advancement is carried out by different semiimplicit

and splitting schemes. Also Alternating and Linearized forms are added to four commonly used forms of the convective

term, referred to as divergence, Convection, skew-symmetric, and rotational. Spectral method based on the primitive variable

formulation is used in Cartesian coordinates with two periodic and one non-periodic boundary condition in three dimensional

directions &Omega=[0,4&pi]×[-1,1]×[0,2&pi]. The friction Reynolds number for channel flow is set to be Re&tau=175 and the computational

grids of 128×65×128 are used in the x, y and z directions, respectively. The comparison is made between turbulent quantities

such as the turbulent statistics, wall shear velocity, standard deviation of u and total normalized energy of instantaneous velocities

in different time-discretization methods and different forms of nonlinear term. The present results show that third-order timediscretizations

forward Euler for explicit terms and backward Euler for implicit terms can minimize the computational cost of

integration by maximizing the time step, while keeping the CFL number near a threshold in time-discretization schemes. Also, the

de-aliased results of turbulence statistics do indicate that different expressions of nonlinear terms have minor discrepancy in

pseudo spectral method. The results show that the most desirable approach is a combination of variable time stepping third order

backward difference algorithm and rotational form, which provides reduced cost and further accuracy improvements.


M. Effati, M. A. Rajabi, F. Samadzadegan, Sh. Shabani,
Volume 12, Issue 3 (Transaction A: Civil Engineering September 2014)
Abstract

Road transportation by way of automobiles is a very convenient means of transportation. Today, the most detrimental consequence of developing transportation systems in a country is traffic accident that places a huge financial burden on society. This paper investigates the role of information systems in transportation safety that leads to improved planning and operation of the transportation system through the application of new technologies. Current methods for identification of segments of roads with high potential of accident are based on statistical approaches. Since there are not accident records for newly built roads, these methods cannot be used for regional roads that are recently built. This paper presents a GIS based Neuro-Fuzzy modeling for identification of road hazardous zones. The results of proposed approach are compared with statistical methods. It is shown that this method is a cheaper but at the same time robust means of analyzing the level of hazard associated with each road segment under consideration, specially when data are uncertain and incomplete.
Dr M. Khodaparast, Dr A.m. Rajabi, Mr. M. Mohammadi,
Volume 13, Issue 2 (Transaction B: Geotechnical Engineering June 2015)
Abstract

The Dynamic Probe is an effective tool used in site investigation. It is more economic than the use of direct drilling, particularly in explorations with moderate depth. This paper presents an experimental study to investigate the capability of using dynamic probing to evaluate the shear strength and compaction percent of fine soil. A series of dynamic probe tests were carried out at 6 different sites in the Khozestan, Hormozgan and Qom provinces in the central and southern regions of Iran. The repeatability of the results is considered and new empirical equations relating the dynamic point resistance to undrained shear strength and compaction percent are proposed. For undrained shear strength evaluation of fine soils, i.e. clay and silty clay soils, a reliable site-specific correlation between qd and Cu can be developed when considering the correlation between log qd and log Cu. Also compaction present can be evaluated by qd. These equations can be developed to provide site-specific relationships based upon geotechnical data at each new location. Using this approach an estimation of the undrained shear strength Cu and compaction percent CP can be determined from dynamic probe tests with acceptable accuracy. The present paper also encourages the wider application of dynamic probing for site investigation in fine soils.

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