Showing 10 results for Khodarahmi
Volume 5, Issue 3 (9-2019)
Abstract
In this survey, 154 bee species of Apoidea superfamily, from the western part of the Isfahan province, Iran were recorded, of which 29 species are new for the fauna of Iran. Among the identified specimens, there were 35 species of Andrenidae, 11 of Apidae, 20 of Colletidae, 50 of Halictidae, 36 of Megachilidae and 2 of Melittidae. All specimens are deposited in the Museum of Iranian Pollinating Insects of Yasouj University, Yasouj, Iran.
Ali Alavi Nia, Mogtaba Zolfaghari, Hossein Khodarahmi, Mahmood Nili, Amir Hossin Ghorbankhani,
Volume 13, Issue 15 (Third Special Issue 2014)
Abstract
In this paper, the behavior of concrete subjected to eroding penetration of projectiles is studied. Based on qualitative similarities of eroding penetration at metallic and concrete targets, plastic flow of the particles around the projectile tip in a concrete target is illustrated. Based on visco-plastic behavior of concrete, changes on the plastic field of the target at Walker-Anderson model is made in order to analyze eroding penetration into concrete. Since there is not any analytical model and standard tests for eroding long rod (9≤L/d≤11 and 11gr<m<9gr) penetration into the concrete, 52 high velocity penetration tests were designed and carried out. Furthermore, with solving the final equations of the Forrestal model, penetration depth of eroding projectiles is calculated. Comparison between the results of the improved Walker-Anderson model and the Forrestal model showed that although the Forrestal model is a comprehensive model in rigid penetration, using it for assessment of eroding penetration into concrete is completely wrong. Besides, the improved Walker-Anderson model can analyze this phenomenon satisfactorily.
Alireza Naddaf Oskouei, Hossein Khodarahmi, Mojtaba Pakian Booshehri,
Volume 15, Issue 2 (4-2015)
Abstract
One of the most important devices for absorbing energy of the impact is circular tubes which absorb energy in different modes of plastic deformation. But one of the most important modes of deformation is dynamic progressive buckling caused by the axial collapse. This mode has the most energy absorption. In this study, the behavior of thin walled tubes (with caps) which have a fossa near the end edges of the tube has been investigated in numerical and experimental way. This is the contrary to the previous researches on energy absorption which used the quasi-static form. To carry out experimental tests, a drop hammer machine has been used. In the numerical part, capabilities of Abaqus have been employed. The results show that caps improve energy absorption thus more energy is absorbed in less length crushing, and the up and down fossa of the tube causes the maximum collapse force occurred with a delay. Also these absorbers have a linear behavior in absorbing energy with respect to the crushing length and the average collapse force has not been changed by increasing the hammer weight. An experiment was done to assess the collisions with the same kinetic energy to study strain rates in four collisions. It was seen that a reduction of 16.9 percent in strain rate increases 2.6 percent of the crushing length.
Alireza Naddaf Oskouei, Hossein Khodarahmi, Moslem Sohrabi,
Volume 15, Issue 7 (9-2015)
Abstract
A numerical and experimental study of the collapse and energy absorption behavior of thin-walled end capped conical shells under dynamic loading is presented in this paper. Among the structural components, the truncated conical shells whose energy absorption characteristics are better than others are used. In order to carry out the designed tests, a drop hammer machine has been used. Also in numerical part, Abaqus software capabilities have been applied. In this article, the effect of the velocity and mass of the hammer on the collapse behavior of these samples has been investigated. Moreover, by placing the cone reversely, the force effect on the collapse behavior evaluated and analyzed. Also, the multiple sets of cones as energy absorbing system are analyzed numerically. For the samples, mode of collapse of diamond with quadrilateral pattern was obtained and a very good agreement with experimental results was recorded. The results shows that the change of wall thickness has the most influence on the collapse behavior of these shells. So that with a 20% reduction of shell thickness, maximum force had 34.5% and the average force collapse 39.3% reduction.
Volume 16, Issue 4 (winter 2016 2016)
Abstract
Banks as economic firms try to provide banking services in low cost. The efficiency of banking system and its convergence among the Iranian banks is a top priority for planners and decision-makers. In this research, the data of 9 Iranian banks (6 commercial and 3 specialized) during 2001-2012 period are utilized according to intermediate approach and Stochastic Frontier Analysis (SFA) within a translog cost function and Model I of Battese and Colli (1992). The results show that average efficiency for commercial and specialized banks has been 78.95% and 87.58%, respectively, which imply that the average efficiency of specialized banks is more than that of commercial banks. In addition, the convergence process has been studied as a result of economic growth models. The speed of efficiency convergence has been estimated by -571% in absolute model, and -576% in conditional model, respectively. The average efficiency growth is decreasing and the efficiency adjustment speed is convergent.
Majid Khansari, Hossein Khodarahmi, Abas Vaziri,
Volume 17, Issue 8 (10-2017)
Abstract
One of the recent techniques which has attracted attention from researchers is the use of Nano particles to reinforce composites. While the technique does not make any changes in the weight of the structure, it improves its mechanical and physical properties. One form of Nano particles includes Carbonic Nano Tubes (CNT). Since its discovery, CNT has found wide application in industryIn this article, the response of aluminum hybrid panels and composites made from epoxy-Kevlar and aluminum hybrid panels and Nano-composites made from epoxy-Kevlar to ballistic impact was studied. Four groups of the panels were constructed using 0, 0.5, 1 and 1.5 percent of carbon nanotubes (CNT)s. The hybrid samples constructed and tried out in this experiment has been done using manual layer-making and heated press.The thickness of the panels constructed from two aluminum plates and ten Kevlar 29 plates was consistent. The ballistic impact test using gas gun was implementated by conical bullet 7.6 gr shooting in two avrege velocities (220 m/s and 275 m/s). input and output velocity with each sample was assessed using a laser speedometer. The amount of energy absorption and special energy absorption of passing of the rocket was determined as the criteria for the comparison of the efficiency of ballistic of different panels. The results indicated that among the four samples examined, the panel made up of 1 percent CNTs had the most amount of energy absorption and ballistic resistance.
M. Ziya-Shamami , H. Babaei , T. Mirzababaie Mostofi , H. Khodarahmi,
Volume 20, Issue 9 (September 2020)
Abstract
In this paper, the large inelastic deformation and failure mechanism of single and multi-layered circular plates under repeated uniform impulsive loading were studied. The ballistic pendulum was used to conduct a series of experiments (67 experiments) on aluminum alloy plates with different structural configurations. Three different layering configurations including single, double, and triple-layered plates made of the same material were considered and tested for the range of charge masses from 1.5g to 12.5g up to five times for repeated loading. The experimental results indicated large plastic global deformation with thinning happening at the clamped boundary and also tearing for some experiments. The results also represented that the maximum permanent deflections of plates were increased by the increase of the charge mass and the number of blast loads. On the other hand, the progressive deflection of the plates at the center was decreased exponentially with increasing the number of blasts. Furthermore, in the numerical modeling section, the Group Method of Data Handling (GMDH) neural network was used to present a mathematical model based on dimensionless numbers to predict the maximum permanent deflection of single and multi-layered circular plates under repeated impulsive loading. In order to increase the prediction capability of the proposed neural network for this process, the experimental data were divided into two training and prediction sets. Good agreement between the proposed model and the corresponding experimental results is obtained and all and 77% of data points are within the <10% error range for single and multi-layered plates, respectively.
Mojtaba Ghamarizadeh, Hossein Khodarahmi, علی Mirzababaie Mostofi,
Volume 21, Issue 10 (October 2021)
Abstract
Sandwich panels which can be used as an explosion shield are important structures for absorbing explosion energy. Crushing and plastic deformation of the core with the plastic bending of the faces are the main factors in absorbing the explosion energy in this sandwich panel. Structural components undergo permanent deformation after explosion and energy absorption. In this paper, the energy absorption of the structure and the deformation of circular metal sandwich panels with tubular core under explosion load have been investigated analytically, numerically and experimentally. The tubes are arranged radially and symmetrically in the core constructions. The experiment have been performed by making sandwich panels under free blast load in order to evaluate and validate analytical and numerical results. The analytical solution is performed using the energy method by balancing the kinetic energy and the plastic work which is done by the different components of the sandwich panels. Numerical solution is performed in ABAQUS finite element software and the pressure function is generated by CONWEP method. The amount of energy absorbed by the structure and different parts of it is obtained. There is good agreement between the results in different ways.
Behrooz Khodaeipour, Hossein Khodarahmi, Milad Sadeghyazdi, Mojtaba Zia Shamami,
Volume 24, Issue 8 (August 2024)
Abstract
Multi-compartment structures are a sort of multi-layer armor widely used to protect naval equipment, due to their high resistance to underwater blasts, simple-tech/low-cost production, and repairability. The present article numerically investigates the contact UNDEX damages of conceptual-construction structures consisting of three metal layers and two mid-compartments. For this purpose, a set of experiments was designed and executed using AUTODYN. The numerical modeling process and outputs were validated with the results of an experimental test. The results showed that all the structures with the same mediums in compartments suffered rupture in their last layer. Structures with air-water mediums did not experience tearing in their last layer if had a St37 midplate. Benefiting from a St37 front plate led to a significant energy absorption increase of 62%. Also, all structures with water-air mediums had excellent resistance performances and presented a meaningful reduction of 49% in the last layer deflection providing a St37 midplate. Furthermore, the comparison of structural performances showed that the structure consisting of Al2024-T3, St37, and St37 layers respectively, and water-air mediums brings forward the most competitive altogether values for the minimum last layer's central deflection of 11.6 mm and maximum energy absorption per areal mass equal to 84.6 J.m2/kg.
Volume 26, Issue 3 (Fall 2022)
Abstract
One of the most important and significant issues in the present study is how to apply economic models in identifying and establishing liability rules. The function of models in analyzing the legal phenomena, including liability rules, is to understand the decision-making logic when encountering interdisciplinary issues so that decisions made by decision-making entities can be optimized in the liability system. The application of the liability rules to achieve the optimization goal by economics makes the nature of the issue raised in these models interdisciplinary. For example, the criterion for the efficiency of liability rules is to create optimal economic incentives to apply care and activity. In fact, the problem facing the presented economic model regarding the rules of liability is to establish the liability rules in cases of unilateral incidents in such a way that the decision variables such as care and activity level, optimality, and the goal contained in the objective function are realized. While emphasizing the role of modeling in identifying and establishing liability rules, the present study strives to first determine the unilateral incident cases and present the criterion for determining these cases and second to conduct analysis of the strict rules of liability and negligence in the cases of unilateral incidents based on the modeling approach. This issue has not been addressed in the research conducted so far. Accordingly, this study presents an example of the application of the modeling method, which indeed a problem with an interdisciplinary nature is presented.
