Showing 4 results for Khoshravan
Volume 0, Issue 2 (8-2011)
Abstract
We measured the impacts of coastal modification on beach erosion and beach retreat conditions, selecting the Miankaleh Region as an example of a complex high-pressure free zone with high levels of engineering and tourism activity. Nine sampling transects, stretching from the shoreline to a 10 meter depth, were defined and 36 sediment samples were collected from the sea bed at depths of 1, 3, 5, and 10 m. After conducting laboratory tests, data were analyzed in terms of sediment dynamic parameters such as grain size, sediment size distribution, mean, median, skewness, kurtosis, standard deviation, and mineral composition. Beach structure and morphodynamic conditions were assessed in the Miankaleh region, by means of satellite image interpretation and field surveys. Results show that from 1978 until the present the average rate of beach retreat rapidly increased due to sea level rise and coastal constructions that have resulted in a progressive increase in sea level height in this region. Erosion vulnerability hazards have also increased in the eastern part of the study area and deposition processes have developed in the western Amirabad region.
Farid Vakil-Tahami, Mohammad Reza Khoshravan, Arash Moahammad Alizadeh Fard,
Volume 16, Issue 9 (11-2016)
Abstract
The main objective of this research is to employ Imperialist Competitive Algorithm (ICA) to determine the optimum condition for an FG cylindrical shell with outer piezoelectric layer. Design parameters in this problem are thickness and volume fraction of the material. The shell is subjected to outer radial moving load and internal pressurized fluid. To formulate the problem, First Order Shear Deformation theory and Maxwell’s equation have been combined to develop governing equations and by solving these equations using analytical-numerical methods, the dynamic deformation has been obtained. Then, by adopting displacement-strain and stress-strain relationships, distribution of the dynamic stresses within the shell has been calculated. Due to the moving of the external load, the use of dynamic analysis is necessary so that the dynamic and transient response is significant comparing with the static one. To validate the dynamic analysis, the results are compared with those provided in the literature based on other solution methods or experimental measurements. Finally, a computer code has been developed to link the dynamic solution method with the optimization algorithm based on ICA to obtain the optimum values of the design parameters. The major advantage of this method is using control points along the thickness to define volume fraction rather than using predefined functions which usually impose unnecessary restriction. The volume fraction between these control points is obtained by Hermite interpolation method. The results show the efficiency of the method and its major strength which is the flexibility and higher convergence rate to determine the optimum configuration.
F. Vakili-Tahami , M. Khoshravan , T. H. Smit, A. Rasoulian,
Volume 20, Issue 5 (May 2020)
Abstract
The intervertebral discs are of the most important body tissues that provides the required flexibility for the spine during daily activities. Due to the lamellar structure of the Annulus Fibrosus, that surrounds the central part of Nucleus Pulposus, it may show anisotropic behavior in carrying the applied loads. Therefore, this aspect was investigated using the experimental data that were obtained by confined compression relaxation tests on samples in three different directions: Axial, radial and circumferential. To obtain the experimental values of the permeability and aggregate modulus as material parameters, test data in three directions were fit to the constitutive equations that were based on the biphasic relaxation model. The results for the permeability and aggregate modulus in three directions show that the material parameters are almost independent of direction and therefore, it is concluded that AF can be treated as an isotropic material under the compressive loads.
F. Vakili-Tahami, M.r. Khoshravan, T. H.smit, A. Rasoulian,
Volume 20, Issue 10 (October 2020)
Abstract
One of the most important and active body tissues during daily life is the intervertebral disc that not only sustains the applied loads to the spine but also it provides the required flexibility for doing different activities. This tissue as an important factor to carry applied loads to the body is always subjected to possible damages. Hence, due to the improvements in medical sciences in treatment or replacing these damaged tissues, investigating the mechanical behavior of the intervertebral disc and assessing the damage level is a major concern for the researchers. For this purpose, different tests should be carried out but to simulate the behavior of the disc more accurately, it is necessary to ensure that the test conditions are as close as possible to the real ones in the body. Hence, the aim of this research is to develop a set of creep constitutive equations that are based on the experimental investigation of the effect of temperature on the creep behavior of the intervertebral disc. To do this, compressive creep tests were carried out on the goat intervertebral disc tissue and the permeability and aggregate modulus were obtained based on fitting the biphasic constitutive equations with the experimental data. Statistical analyses of the experimental data reveal the significant effect of the temperature on the values of both material parameters and the creep behavior of the intervertebral disc, so that with increasing temperature permeability increases and aggregate modulus decreases or vice versa.
